Physicomechanical Characteristics of Polylactic Acid Films Containing Photo-assisted and Ultrasound-assisted Green Synthesized Silver Nanoparticles Using Nettle Extract

Physicomechanical Characteristics of Polylactic Acid Films Containing Photo-assisted and Ultrasound-assisted Green Synthesized Silver Nanoparticles Using Nettle Extract | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Article Physicomechanical Characteristics of Polylactic Acid Films Containing Photo-assisted and Ultrasound-assisted Green Synthesized Silver Nanoparticles Using Nettle Extract Farideh Peidaei mahmodabad, Hamed Ahari, Masoumeh Moslemi, Amirali Anvar This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-7890805/v1 This work is licensed under a CC BY 4.0 License Status: Under Revision Version 1 posted 16 You are reading this latest preprint version Abstract Nanoparticles improve protective characteristics of biodegradable packaging. The aim of this study was to investigate physicomechanical characteristics of polylactic acid film containing 1, 2 and 3% silver nanoparticles synthesized using photo-assisted and ultrasound-assisted methods and aqueous extract of nettle ( Urtica dioica ). Formation of silver nanoparticles was verified using UV-vis spectroscopy. Photochemical and sonochemical synthesized silver nanoparticles were monodisperse with particle sizes of 91.28 and 68.06 nm and polydispersity indices of 0.382 and 0.371, respectively. Solubility and water absorption decreased with silver nanoparticles, especially ultrasound-assisted synthesized ones, into polylactic acid films ( p < 0.05). Nanocomposites containing 2 and 3% of ultrasound-assisted synthesized silver nanoparticles showed the highest tensile strength and elongation at break. Fourier transform infrared spectroscopy verified the role of nettle extract as a decreasing, stabilizing and capping agent of silver nanoparticles. In fingerprint region of the spectra, presence of Ag-O bonding and synthesis of silver nanoparticles were verified. Silver nanoparticles improved the thermal stability of polylactic acid nanocomposite films. Therefore, use of silver nanoparticles is recommended to improve physicomechanical and thermal characteristics of polylactic acid films. Physical sciences/Chemistry Physical sciences/Materials science Physical sciences/Nanoscience and technology Biodegradable films Nettle extract Photo-induced synthesis Polylactic acid Silver nanoparticles Thermal stability Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Introduction In recent years, interests in biodegradable and renewable biopolymers have increased. Polylactic acid (PLA) is one of the biodegradable polymers with similar characteristics to synthetic polystyrene (PS) and polyethylene terephthalate (PET) with much less environmental effects, compared to PET. Technically, PLA is derived from renewable resources such as cornstarch. Necessary energy for the production of PLA is 20–50% less than that needed for petroleum-based polymers (Vink et al, 2006). However, PLA includes challenges such as brittleness, rigidity and low elasticity, limiting its uses. To solve these problems, nanoparticles are incorporated into PLA and improve the mechanical, thermal and antimicrobial characteristics of PLA-based films (Mulla et al., 2024; Malek et al., 2021 ). Nanoparticles are three-dimensional (3-D) materials with size ranges of 1–100 nm that include good antimicrobial characteristics (Tawakkal et al., 2014 ). Silver nanoparticles (AgNPs) are non-toxic and stable, which demonstrate antimicrobial, antioxidant and anticancer characteristics (Panja et al., 2021 ). The photochemical synthesis method (photo-induced synthesis) is a novel interesting method that does not need high temperatures and is carried out at room temperature (RT) and atmospheric pressure using common laboratory equipment. Photochemical reactions under UV-irradiation are addressed as green chemistry interactions and environmental friendly that accelerate the reaction time, produce nanoparticles with desirable characteristics and can be carried out without presence of reducing agents (Jara et al., 2021 ). Another method for the synthesis of AgNPs is sonochemical method and ultrasound-assisted synthesis (Ahmad et al., 2023 ; Gandlevskiy et al., 2025 ). Ultrasound waves improve synthesis of nanoparticles and create a homogeneous coating of nanoparticles on various substrates. Using ultrasound waves, it is possible to improve the performance of phase transfer catalysts and sometimes eliminate them (Xu et al., 2013 ). Green synthesis offers a superior alternative to traditional methods for producing nanoparticles. The plants in the green synthesis of nanoparticles are bio-safe, non-toxic, eco-friendly, cost-effective and highly stable and include a wide variety of metabolites involved in the reduction process (Sharifi-Rad et al., 2024 ; Chirumamilla et al., 2023 ; Parvathalu et al., 2023 ). Previous studies have shown that plant extracts such as Anthemis atropatana (Dehghanizade et al., 2018 ), Mentha aquatica aquatica (Nouri et al., 2020 ), Juniperus procera (Khan et al., 2022 ), Alhagi graecorum (Hawar et al., 2022 ), Myrsine africana (Sarwer et al., 2022 ), Morinda lucida (Labulo et al., 2022 ), flaxseeds (Alzubaidi et al., 2023 ), A. pseudocotula Boiss (Ajlouni et al., 2023 ), Perilla frutescens (Tavan et al., 2023 ), Argyreia nervosa (Parvathalu et al., 2023 ), Solanum khasianum (Chirumamilla et al., 2023 ), cinnamon (Ahmad et al., 2023 ), Kalanchoe fedtschenkoi (Mejía-Méndez et al., 2024 ) and Lallemantia royleana (Sharifi-Rad et al., 2024 ) decrease, stabilize and synthesize AgNPs. Nettle ( Urtica dioica L.) is a wild herbaceous perennial blooming plant and a multi-purpose crop, native to Europe, Asia, North Africa and North America. It is an edible plant, including nutritional and medicinal characteristics. Its leaves can be used to make curries and herbal and sour soups. The plant is used as a growth promoter in fish, as a vegetable and a botanical pesticide and in preparation of breads. Nettle treats prostatic hyperplasia, arthritis, rheumatism and allergic rhinitis. It is rich in fibers, minerals, vitamins and antioxidant compounds such as polyphenols and carotenoids. Nettle includes antiproliferative, anti-inflammatory, antioxidant, analgesic, anti-infectious, hypotensive and antiulcer characteristics and prevents cardiovascular diseases (CVD) (Bhusal et al., 2022 ). In this study, AgNPs were synthesized from nettle extracts using photo-assisted and ultrasound-assisted synthesis methods and incorporated into the PLA films. Then, physicomechanical characteristics of the nanocomposite films were investigated. Materials and Methods Materials The AgNO 3 , chloroform and all chemicals with analytical grades were purchased from Merck, Germany. Nettle aqueous extract preparation The aerial parts of nettle ( U. dioica ) were collected from((Scientific name): Urtica dioica L./ Family: Urticaceae./Name: Stinging Nettle./Source: Jihad-e-Daneshgahi Research Complex-Jihad University Research Institute of Medicinal Plants,Karaj./Date of collection :1401/12/05./Collector :Masoud Mohammadi./Herbarium No: UDI-1404-01./Notes: It is a herbaceous perennial with erect stems covered in stinging hairs that cause skin irritation upon contact. The leaves are opposite, toothed, and range from ovate to lanceolate in shape. Male and female flowers are found on the same stalk.).washed and then dried at 27°C for 3 D. To prepare the aqueous extract, 1 g of the nettle powder was mixed with 100 ml of distilled water (DW) and agitated for 1 h using shaker (IKA, Germany). The extract was filtered through Whatman filter papers no. 1 (Whatman, USA) and stored at refrigeration temperatures for further uses. Photo-assisted synthesis of silver nanoparticles The AgNO 3 (0.034 g, 1 mM) was dissolved in 10 ml of aqueous nettle extract and exposed to UV light (30 W) for 30 min under vigorous stirring (Cozzoli et al., 2004 ). Ultrasound-assisted synthesis of silver nanoparticles Briefly, 1 ml of the nettle aqueous extract was added to 9 ml of AgNO 3 (1 mM) and sonication (Hielscher UP400S, Germany) at 24 kHz and 400 W was carried out for 90 min at RT with an amplitude of 50%. Then, suspension containing nanoparticles was centrifuged () at 8000 rpm for 20 min. This was washed four times with DW to remove Ag + ions. The reddish-brown color change indicated synthesis of AgNPs. Precipitated nanoparticles were dried at 40°C under vacuum and stored at 4°C (Manjamadha and Muthukumar, 2016 ). Dynamic light scattering Particle size and polydispersity index (PDI) of the AgNPs were assessed using dynamic light scattering (DLS) analysis and particle size analyzer (Shimadzo, Japan). Polylactic acid film preparation The PLA granules (1 g) were added to 43 ml of chloroform and stirred for 8 h using magnetic stirrer. Then, nettle extract and AgNPs (1, 2 and 3%) were added to the mixture and stirred for 20 min and then homogenized at 12,000 rpm for 2 min. Prepared solution was poured into glass molds and incubated at RT for 4 h to evaporate the solvent. Then, films were removed from the molds and incubated at RT for 24 h. Films were punched into discs with a diameter of 13 mm. Then, seven treatments, including pure PLA films as controls and PLA composites with 1, 2 and 3% photochemical and sonochemical synthesized AgNPs, were produced (Cheng et al., 2021 ). Polylactic acid film characterization Thickness Film thickness was reported in µm (Farazma, Iran) with a resolution of 0.01 mm at various positions and then average values were calculated. Light transmission and opacity Films were cut and transferred into a glass cuvette and their light transmission was measured at 600 nm using UV-vis spectrophotometer (Hitachi, Japan). Opacity of the films was achieved using Eq. 1: Opacity = \(\:\frac{{\text{A}\text{b}\text{s}}_{600}}{\text{d}}\) (1) Where, Abs 600 was the absorbance and d was the film thickness (mm). Solubility Pieces of the film (600 mg) were incubated at 40°C for 24 h using desiccator with P 2 O 5 , transferred into a beaker filled with 100 ml of deionized water and then stirred at RT for 24 h. Mixture was filtered using filter papers. Solubility of the films was calculated using Eq. 2: Solubility (%) = \(\:\frac{\text{m}1-\text{m}2}{\text{m}1}\) (2) Where, m 1 was the initial dry weight of films (g) and m 2 was the final dry weight of films (g). Water absorption Films (22 × 2 cm) were cut and dried for 2 d using desiccator with P 2 O 5 . Samples were weighed with an accuracy of 0.0001 and transferred into a beaker containing 100 ml of deionized water. After 1 h of drying and weighing, water absorption of the films was calculated using Eq. 3 Water absorption (%) = \(\:\frac{\text{m}1}{\text{m}2}\) (3) Where, m 1 was the weight of absorbed moisture (g) and m 2 was the weight of dry films (g). Mechanical characteristics Tensile strength (TS) and elongation at break (EB) were assessed using texture analyzer (Zwick, Germany) with force of 200 N, gap of 40 mm and speed of 50 mm min − 1 (ASTM D412 standard). Fourier transform infrared spectroscopy Films were dried at 50°C for 48 h and analyzed using Fourier transform infrared spectroscopy (Shimadzo, Japan) from 20 scans at a wavelength range of 650–4000 cm − 1 . For each spectrum, 64 consecutive scans were used (Shaik et al., 2018 ). Thermal behaviors Nearly 2 mg of film samples were transferred into aluminum pans and the differential scanning calorimetry (DSC) was carried out at -100–200 o C with heating rate of 10 o C min − 1 and nitrogen flow rate of 20 ml min − 1 . An empty aluminum pan was used as reference (Khan et al., 2022 ). Statistical analysis Experiments were carried out in triplicate and results were expressed as mean ± SD (standard deviation). Statistical differences were reported using Duncan's multiple test and SPSS software v.26 (IBM, USA) at a significance level of p ≤ 0.05. Results and Discussion Dynamic light scattering analysis Based on Fig. 1 a, the photo-assisted synthesized AgNPs included single peak with a width of 24 nm and PDI of 0.382. Moreover, 45.5% of the nanoparticles included a size of 91.28 nm. The ultrasound-assisted synthesized AgNPs included single peak with width of 27 nm and PDI of 0.371. Nearly 80.1% of the nanoparticles included a size of 68.06 nm (Fig. 1 b). Polylactic acid nanocomposites characterization Thickness Addition of AgNPs did not significantly affect thickness of the PLA nanocomposites ( p > 0.05) (Fig. 2 ). Opacity Based on Fig. 3 , nanocomposites containing 3% AgNPs (photo-assisted and ultrasound-assisted synthetized) showed the highest opacity ( p < 0.05). In other words, these included lower transparency and light transmission. This phenomenon could be linked to the presence of AgNPs as minerals that could not be dissolved in the polymer matrix (Noshirvani et al., 2017 ) or light scattering through the heterogeneous network of films (Arfat et al., 2014 ). The pure PLA film (control) and nanocomposites containing 1 and 2% AgNPs did not show any significant differences ( p > 0.05). Results were similar to those of other researchers, who have reported increases in opacity of PLA and gelatin films by addition of zinc-oxide nanoparticles (Noshirvani et al., 2017 ; Arfat et al., 2014 ; Pantani et al., 2013 ). Solubility and water adsorption Incorporation of AgNPs to the PLA films significantly decreased solubility and water absorption of the films ( p < 0.05) (Fig. 4 ). Ultrasound-assisted synthesized nanoparticles showed lower solubility and water absorption, compared to those photo-assisted synthetized nanoparticles did ( p < 0.05). The highest and the lowest solubility and water absorption were observed in the control and T6 treatments, respectively ( p < 0.05). Placement of the nanoparticles between the PLA chains decreased free spaces between the chains for the absorption of water molecules. Furthermore, nanoparticles created tortuous paths in the biopolymer matrix, which decreased penetration of water molecules. In other studies, addition of zinc oxide (Nafchi et al., 2012 ) and zirconium oxide (Karimi Sani et al., 2021 ) nanoparticles have decreased moisture content of the nanocomposites, verifying findings of the present study. Mechanical characteristics Figure 5 . Tensile strength (a) and elongation at break (b) of the polylactic acid films. T1, Control (pure PLA); T2, polylactic acid and 1% photo-assisted synthetized silver nanoparticles; T3, polylactic acid and 2% photo-assisted synthetized silver nanoparticles; T4, polylactic acid and 3% photo-assisted synthetized silver nanoparticles; T5, polylactic acid and 1% ultrasound-assisted synthetized silver nanoparticles; T6, polylactic acid and 2% ultrasound-assisted synthetized silver nanoparticles; and T7, polylactic acid and 3% ultrasound-assisted synthetized silver nanoparticles. Different letters indicate significant differences ( p < 0.05) Increases in TS and EB of the PLA films by the addition of ultrasonically synthesized AgNPs could be attributed to the crosslinking between PLA, nanoparticles and phenolic compounds of the nettle extract. Moreover, high surface area of ​​the nanoparticles and electrostatic interactions between the PLA chains and AgNPs increased TS and improved mechanical characteristics of the nanocomposite films (Aghbolagh Sharifi and Pirsa, 2021 ; Wetzel et al., 2003 ). Nanoparticles effectively transferred stress from the matrix to the particles through shear mechanism, increasing TS of the nanocomposites (Brown and Ellyin, 2005 ). At higher concentrations of nanoparticles, agglomeration/ aggregation of the nanoparticles in the polymer matrix weakened mechanical characteristics (Wetzel et al., 2003 ). Similarly, addition of AgNPs to biodegradable starch-chitosan (Yoksan & Chirachanchai, 2010 ) and hydroxypropyl methylcellulose (De Moura et al., 2012 ) films have increased TS. Fourier transform infrared spectroscopy analysis Figure 6 shows the FTIR spectra of pure PLA films and PLA composites containing photo-induced and ultrasonically synthesized AgNPs. Stretching vibration of the C = O (carbonyl) bonds in the PLA structure was detected at 1732 cm − 1 (Alzubaidi et al., 2023 ; Ajlouni et al., 2023 ). The N-H bond in the amines indicated presence of proteins and enzymes in the nettle extract, which possibly acted as decreasing agents and stabilizers of AgNPs (Ahmad et al., 2023 ). Bending vibration of C-H bonds in CH 2 and CH 3 groups was shown at 11490 and 11380 cm − 1 , respectively (Roshanghias et al., 2022 ; Nasrin et al., 2017 ). Stretching vibration of C-O bonds in the structure of C-OH and C-O-C was shown at absorption peaks of 1132 and 1005 cm − 1 , respectively (Sadeghi and Gholamhoseinpoor, 2015 ; Ajlouni et al., 2023 ). This peak was detected due to the presence of phenols, alcohols, carboxylic acids, esters, ethers and/or biomolecules in the nettle extract (Alzubaidi et al., 2023 ; Tavan et al., 2023 ; Khan et al., 2022 ) as capping and stabilizing agents, responsible for the reduction of Ag + to AgNPs (Sarwer et al., 2022 ; Sarkar and Kotteeswaran, 2018 ). The peaks at 640 and 450 cm − 1 are also related to the deformation vibration of C-H bonds in the PLA structure (Jung et al., 2018), aromatic rings in the synthesis of AgNPs (Tavan et al., 2023 ), the presence of alkenes (Sarkar and Kotteeswaran, 2018 ) and C-N bond (Sarwer et al., 2022 ) in the extract structure. The FTIR analysis verified characterization of the molecular interactions of the nettle extract with the PLA matrix, Ag-O bonds in synthesis of AgNPs and presence of functional groups on the surface of AgNPs (Salmieri et al., 2014 ). Spectra of the pure PLA films and their nanocomposites did not differ significantly, indicating successful incorporation of nanoparticles into PLA films. Most of the peaks were present in AgNPs spectra with small shifts, verifying roles of the aqueous nettle extract as a decreasing stabilizing agent (Ajlouni et al., 2023 ). Interaction of metal ions with various functional groups caused slight shifts in the spectra of AgNPs (Alzubaidi et al., 2023 ). By addition of AgNPs (greater than 1%), several changes were observed at 500–560 cm − 1 in the fingerprint region (Fig. 7 ), which was linked to the stretching vibration of Ag-O bonds in the composite structure (Kakhki et al., 2019 ; Mohan Bhagyaraj et al., 2020). Increasing concentration of the nanoparticles increased the peak intensity as an indicator for the presence of AgNPs in the PLA structure. Peak intensity in the spectra of photo-assisted synthetized AgNPs was slightly higher than that in ultrasound-assisted synthetized AgNPs, which could indicate better performance of these nanoparticles in the composite. In addition, increasing proportion of AgNPs in the film structure decreased intensity of the peak located at 450 cm − 1 (associating to deformation vibration of the C-H bonds). It seemed that presence of AgNPs and their effects on chemical composition of the PLA matrix caused disturbed deformation vibration of the C-H bonds and their decreased peak intensity. Peak intensity of the photo-assisted synthetized AgNPs decreased more than that of ultrasound-assisted synthesis. Differential scanning calorimetry analysis The DSC thermograms and results of glass transition temperature (T g ), cold crystallization temperature (T c ), melting temperature (T m ), enthalpy of crystallization (∆H c ), enthalpy of melting (∆H m ) and Xc (∆H m - ∆H c / 93.7) are reported in Fig. 8 and Table 1 . Table 1 Differential scanning calorimetry analysis results Film T g ( o C) T c ( o C) T m1 ( o C) T m2 ( o C) ∆Hm (J/g) ∆Hc (J/g) X c Pure PLA 57.79 122.10 147.50 153.31 71.20 22.51 54.10 1% Ag (L) 59.42 120.24 149.17 154.98 77.15 20.26 60.72 2% Ag (L) 58.69 120.31 149.6 154.93 84.36 10.01 79.35 3% Ag (L) 57.75 17.70 146.25 154.47 91.44 67.06 26.01 1% Ag (U) 61.62 129.69 149.06 155.52 93.03 49.71 46.23 2% Ag (U) 60 120.01 147.65 15.71 112.30 75.25 39.54 3% Ag (U) 85.45 116.94 147.82 156.03 121.32 113.16 8.71 PLA, Polylactic acid; Ag (L), photo-assisted synthesized silver nanoparticles; Ag (U), ultrasound-assisted synthesized silver nanoparticles The T g and T c for pure PLA film were 57.79 and 122.10°C, respectively. Addition of 1% AgNPs to the composite slightly increased T g due to a higher T g of AgNPs, compared to the pure PLA, which verified reinforcing roles of nanoparticles in fabrication of nanocomposites at a wide temperature range. Nanoparticles acted as nucleating agents and included good compatibilities with the polymer matrix but at higher concentrations due to their agglomeration, acting as a plasticizer that did not increase T g (Girdthep et al., 2015 ). Similarly, T c decreased in a higher concentration of AgNPs [except for 2% Ag (L) treatment] due to the low crystallization rate of nanoparticles and incomplete crystallization of PLA. The higher T c and crystallinity rate in 2% photo-assisted synthesized AgNPs could indicate that nanoparticle dispersion in the composite was optimal. The T m of PLA was nearly 150°C (Malek et al., 2021 ). Regarding the higher T m of AgNPs compared to PLA, incorporation of nanoparticles into the PLA increased T m of the composite. Homogeneous distribution of nanoparticles in the polymer matrix and interaction of functional groups with PLA increased the T m and improved thermal characteristics of the polymer (Shankar et al., 2015 ). Increases in T m by the addition of nanoparticles was linked to two important mechanisms of (i) heterogeneous nucleation of nanoparticles and facilitated crystallization; and (ii) modification of the orientation of polymer chains by the nanoparticles, causing orderly chain arrangement and formation of larger crystals (Asadi and Pirsa, 2019 ). Two endothermic melting peaks in the DSC curve could be associated to the formation of two crystalline forms of β form, melting at a lower temperature; and α form, melting at a higher temperature with the most stable rate (Cuiffo et al., 2017 ). By adding nanoparticles, peak corresponding to the α-crystalline form was intensified, indicating increases in stability of the structure in presence of higher concentrations of AgNPs (Fig. 8 ). The ΔH m linked to the structural order (Nasreen et al., 2016 ) increased with the incorporation of nanoparticles into the PLA matrix. Improvement of thermal characteristics of nanocomposites has previously been reported using magnesium oxide (Swaroop and Shukla, 2019 ), zirconium oxide (Karimi Sani et al., 2021 ), zinc oxide (Pantani et al., 2013 ; Noshirvani et al., 2017 ), graphene (Girdthep et al., 2015 ) and titanium (Zolfi et al., 2014 ) nanoparticles. Conclusion In general, the major aim of the current study was to develop AgNPs using alternative, green cost-effective approach of photo-assisted and ultrasound-assisted syntheses by nettle extract incorporation into PLA films. This study showed that nettle was an appropriate plant as a decreasing capping agent in synthesis of AgNPs. The synthesized AgNPs were monodisperse and homogeneous nanoparticles, which decreased solubility and water absorption and improved mechanical and thermal characteristics of the PLA films. Ultrasound-assisted synthesized AgNPs were more efficient than photo-induced ones in improvement of physicomechanical characteristics of the PLA films. However, higher T c and crystallinity in photo-assisted synthetized nanoparticles in DSC analysis and increased peak intensity in FTIR analysis could reveal better performance of these samples in the composite, compared to ultrasound-assisted synthesis. Further studies are necessary to investigate toxicity of AgNPs. Declarations Research funding This research received no specific grant from any funding agency in the public, commercial, or not-for-profit sectors. Data Availability The datasets generated and/or analysed during the current study are not publicly available due [REASON WHY DATA ARE NOT PUBLIC] but are available from the corresponding author on reasonable request. Plant Material and Collection Authorization Statement (for Scientific Reports) The collection and use of Urtica dioica L. (Family: Urticaceae; Persian name: Gazaneh; English name: Stinging Nettle) complied with all relevant institutional, national, and international guidelines and legislation. Plant material was obtained from cultivated specimens grown under controlled greenhouse conditions at the Medicinal Plants Research Center, Academic Center for Education, Culture and Research (ACECR), Karaj, Iran. Authorization for the collection and use of the plant was granted by the Medicinal Plants Research Center, ACECR (Permit date: 24 February 2023). The plant material was collected by Mr. Masoud Mohammadi and authenticated by a qualified botanist. A voucher specimen (Herbarium No. UDI-1404-01) has been deposited in the institutional herbarium of the Medicinal Plants Research Center, ACECR, Karaj, Iran. Author Contribution F.P. wrote the main manuscript text / data collection(first Auther)H.A. project managment M.M.Data curation /softwareA.A. Resources/validation References Vink, E. T., Glassner, D. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-7890805","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":550038692,"identity":"6eee84aa-2d9f-4b6f-adba-634a4e87e807","order_by":0,"name":"Farideh Peidaei mahmodabad","email":"","orcid":"","institution":"Islamic Azad University","correspondingAuthor":false,"prefix":"","firstName":"Farideh","middleName":"Peidaei","lastName":"mahmodabad","suffix":""},{"id":550038694,"identity":"40ee7c20-b3ab-4412-bc7f-1c859eae847b","order_by":1,"name":"Hamed 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1","display":"","copyAsset":false,"role":"figure","size":88306,"visible":true,"origin":"","legend":"\u003cp\u003eDynamic light scattering\u003cstrong\u003e \u003c/strong\u003e\u0026nbsp;results of ultrasound-assisted (a) and photo-assisted (b) synthesized silver nanoparticles\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-7890805/v1/d6dab62678b608378efcf2db.png"},{"id":96914274,"identity":"656c0eff-4118-41a4-a351-945fbb03aa65","added_by":"auto","created_at":"2025-11-27 14:05:40","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":20210,"visible":true,"origin":"","legend":"\u003cp\u003eThickness of polylactic acid films. T1, Control (pure polylactic acid); T2, polylactic acid and 1% photo-assisted synthetized silver nanoparticles; T3, polylactic acid and 2% photo-assisted synthetized silver nanoparticles; T4, polylactic acid and 3% photo-assisted synthetized silver nanoparticles; T5, polylactic acid and 1% ultrasound-assisted synthetized silver nanoparticles; T6, polylactic acid and 2% ultrasound-assisted synthetized silver nanoparticless; and T7, polylactic acid and 3% ultrasound-assisted synthetized silver nanoparticles. Different letters indicate significant differences (\u003cem\u003ep\u003c/em\u003e \u0026lt; 0.05)\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-7890805/v1/40156b7459727674c724c169.png"},{"id":96756004,"identity":"9daca30a-5038-49ff-86c3-c8b6185cdd78","added_by":"auto","created_at":"2025-11-25 17:54:02","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":21215,"visible":true,"origin":"","legend":"\u003cp\u003eOpacity of polylactic acid films. T1, Control (pure polylactic acid); T2, polylactic acid and 1% photo-assisted synthetized silver nanoparticles; T3, polylactic acid and 2% photo-assisted synthetized silver nanoparticles; T4, polylactic acid and 3% photo-assisted synthetized silver nanoparticles; T5, polylactic acid and 1% ultrasound-assisted synthetized silver nanoparticles; T6, polylactic acid and 2% ultrasound-assisted synthetized silver nanoparticles; and T7, polylactic acid and 3% ultrasound-assisted synthetized silver nanoparticles. Different letters indicate significant differences (\u003cem\u003ep\u003c/em\u003e \u0026lt; 0.05)\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-7890805/v1/3b4c31d390661ad0526d7e9f.png"},{"id":96756003,"identity":"b6107fea-d148-4f3d-8062-5ccf496e0c9c","added_by":"auto","created_at":"2025-11-25 17:54:02","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":36921,"visible":true,"origin":"","legend":"\u003cp\u003eSolubility (a) and water absorption (b) of polylactic acid films. T1, Control (pure polylactic acid); T2, polylactic acid and 1% photo-assisted synthetized silver nanoparticles; T3, polylactic acid and 2% photo-assisted synthetized silver nanoparticles; T4, polylactic acid and 3% photo-assisted synthetized silver nanoparticles; T5, polylactic acid and 1% ultrasound-assisted synthetized silver nanoparticles; T6, polylactic acid and 2% ultrasound-assisted synthetized silver nanoparticles; and T7, polylactic acid and 3% ultrasound-assisted synthetized silver nanoparticles. Different letters indicate significant differences (\u003cem\u003ep \u003c/em\u003e\u0026lt; 0.05)\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-7890805/v1/dbb6b193fbc268e10ad90fba.png"},{"id":96914658,"identity":"48e1b024-99f4-4e22-bb25-551e449d2f97","added_by":"auto","created_at":"2025-11-27 14:06:13","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":40250,"visible":true,"origin":"","legend":"\u003cp\u003eTensile strength (a) and elongation at break (b) of the polylactic acid films. T1, Control (pure PLA); T2, polylactic acid and 1% photo-assisted synthetized silver nanoparticles; T3, polylactic acid and 2% photo-assisted synthetized silver nanoparticles; T4, polylactic acid and 3% photo-assisted synthetized silver nanoparticles; T5, polylactic acid and 1% ultrasound-assisted synthetized silver nanoparticles; T6, polylactic acid and 2% ultrasound-assisted synthetized silver nanoparticles; and T7, polylactic acid and 3% ultrasound-assisted synthetized silver nanoparticles. Different letters indicate significant differences (\u003cem\u003ep\u003c/em\u003e \u0026lt; 0.05)\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-7890805/v1/13e2a0ed6dfdb48a8980d2b0.png"},{"id":96914697,"identity":"1021d5fa-9fff-48c5-adc3-69bf48c12a46","added_by":"auto","created_at":"2025-11-27 14:06:14","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":354970,"visible":true,"origin":"","legend":"\u003cp\u003eFourier transform infrared spectroscopy spectra of pure polylactic acid and polylactic acid nanocomposites containing 1, 2 and 3% photo-assisted synthetized silver nanoparticles (L) and ultrasound-assisted synthetized silver nanoparticles (U)\u003c/p\u003e","description":"","filename":"6.png","url":"https://assets-eu.researchsquare.com/files/rs-7890805/v1/603eb427542df67be4ef682a.png"},{"id":96756007,"identity":"45d516a3-040a-4662-816e-a594e9d6c461","added_by":"auto","created_at":"2025-11-25 17:54:02","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":289863,"visible":true,"origin":"","legend":"\u003cp\u003eFTIR spectra of the finger region of pure polylactic acid and polylactic acid nanocomposites containing 1, 2 and 3% photo-assisted synthetized silver nanoparticles (L) and ultrasound-assisted synthetized silver nanoparticles (U)\u003c/p\u003e","description":"","filename":"7.png","url":"https://assets-eu.researchsquare.com/files/rs-7890805/v1/e30b9fa40f1dc9dd5cccb906.png"},{"id":96915544,"identity":"f65e5397-3ba4-49a3-beb5-beea6de4d4c6","added_by":"auto","created_at":"2025-11-27 14:07:22","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":388574,"visible":true,"origin":"","legend":"\u003cp\u003eDifferential scanning calorimetry\u003cstrong\u003e \u003c/strong\u003ethermograms of pure polylactic acid and polylactic acid nanocomposites containing 1, 2 and 3% photo-assisted synthetized silver nanoparticles (L) and ultrasound-assisted synthetized silver nanoparticles (U)\u003c/p\u003e","description":"","filename":"8.png","url":"https://assets-eu.researchsquare.com/files/rs-7890805/v1/73e988baafb35f7279a9dcac.png"},{"id":97136175,"identity":"a8289628-f0f2-485c-86e3-20dc8b0f7169","added_by":"auto","created_at":"2025-12-01 09:55:55","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1778364,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-7890805/v1/e0533212-923f-4aa2-9c1c-b4a093e9317d.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Physicomechanical Characteristics of Polylactic Acid Films Containing Photo-assisted and Ultrasound-assisted Green Synthesized Silver Nanoparticles Using Nettle Extract","fulltext":[{"header":"Introduction","content":"\u003cp\u003eIn recent years, interests in biodegradable and renewable biopolymers have increased. Polylactic acid (PLA) is one of the biodegradable polymers with similar characteristics to synthetic polystyrene (PS) and polyethylene terephthalate (PET) with much less environmental effects, compared to PET. Technically, PLA is derived from renewable resources such as cornstarch. Necessary energy for the production of PLA is 20\u0026ndash;50% less than that needed for petroleum-based polymers (Vink et al, 2006). However, PLA includes challenges such as brittleness, rigidity and low elasticity, limiting its uses. To solve these problems, nanoparticles are incorporated into PLA and improve the mechanical, thermal and antimicrobial characteristics of PLA-based films (Mulla et al., 2024; Malek et al., \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2021\u003c/span\u003e).\u003c/p\u003e\u003cp\u003eNanoparticles are three-dimensional (3-D) materials with size ranges of 1\u0026ndash;100 nm that include good antimicrobial characteristics (Tawakkal et al., \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e2014\u003c/span\u003e). Silver nanoparticles (AgNPs) are non-toxic and stable, which demonstrate antimicrobial, antioxidant and anticancer characteristics (Panja et al., \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). The photochemical synthesis method (photo-induced synthesis) is a novel interesting method that does not need high temperatures and is carried out at room temperature (RT) and atmospheric pressure using common laboratory equipment. Photochemical reactions under UV-irradiation are addressed as green chemistry interactions and environmental friendly that accelerate the reaction time, produce nanoparticles with desirable characteristics and can be carried out without presence of reducing agents (Jara et al., \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2021\u003c/span\u003e).\u003c/p\u003e\u003cp\u003eAnother method for the synthesis of AgNPs is sonochemical method and ultrasound-assisted synthesis (Ahmad et al., \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2023\u003c/span\u003e; Gandlevskiy et al., \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2025\u003c/span\u003e). Ultrasound waves improve synthesis of nanoparticles and create a homogeneous coating of nanoparticles on various substrates. Using ultrasound waves, it is possible to improve the performance of phase transfer catalysts and sometimes eliminate them (Xu et al., \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e2013\u003c/span\u003e). Green synthesis offers a superior alternative to traditional methods for producing nanoparticles. The plants in the green synthesis of nanoparticles are bio-safe, non-toxic, eco-friendly, cost-effective and highly stable and include a wide variety of metabolites involved in the reduction process (Sharifi-Rad et al., \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2024\u003c/span\u003e; Chirumamilla et al., \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2023\u003c/span\u003e; Parvathalu et al., \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2023\u003c/span\u003e).\u003c/p\u003e\u003cp\u003ePrevious studies have shown that plant extracts such as \u003cem\u003eAnthemis atropatana\u003c/em\u003e (Dehghanizade et al., \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2018\u003c/span\u003e), \u003cem\u003eMentha aquatica\u003c/em\u003e aquatica (Nouri et al., \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e2020\u003c/span\u003e), \u003cem\u003eJuniperus procera\u003c/em\u003e (Khan et al., \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2022\u003c/span\u003e), \u003cem\u003eAlhagi graecorum\u003c/em\u003e (Hawar et al., \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2022\u003c/span\u003e), \u003cem\u003eMyrsine africana\u003c/em\u003e (Sarwer et al., \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2022\u003c/span\u003e), \u003cem\u003eMorinda lucida\u003c/em\u003e (Labulo et al., \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2022\u003c/span\u003e), flaxseeds (Alzubaidi et al., \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e2023\u003c/span\u003e), \u003cem\u003eA. pseudocotula\u003c/em\u003e Boiss (Ajlouni et al., \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2023\u003c/span\u003e), \u003cem\u003ePerilla frutescens\u003c/em\u003e (Tavan et al., \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2023\u003c/span\u003e), \u003cem\u003eArgyreia nervosa\u003c/em\u003e (Parvathalu et al., \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2023\u003c/span\u003e), \u003cem\u003eSolanum khasianum\u003c/em\u003e (Chirumamilla et al., \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2023\u003c/span\u003e), cinnamon (Ahmad et al., \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2023\u003c/span\u003e), \u003cem\u003eKalanchoe fedtschenkoi\u003c/em\u003e (Mej\u0026iacute;a-M\u0026eacute;ndez et al., \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2024\u003c/span\u003e) and \u003cem\u003eLallemantia royleana\u003c/em\u003e (Sharifi-Rad et al., \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2024\u003c/span\u003e) decrease, stabilize and synthesize AgNPs.\u003c/p\u003e\u003cp\u003eNettle (\u003cem\u003eUrtica dioica\u003c/em\u003e L.) is a wild herbaceous perennial blooming plant and a multi-purpose crop, native to Europe, Asia, North Africa and North America. It is an edible plant, including nutritional and medicinal characteristics. Its leaves can be used to make curries and herbal and sour soups. The plant is used as a growth promoter in fish, as a vegetable and a botanical pesticide and in preparation of breads. Nettle treats prostatic hyperplasia, arthritis, rheumatism and allergic rhinitis. It is rich in fibers, minerals, vitamins and antioxidant compounds such as polyphenols and carotenoids. Nettle includes antiproliferative, anti-inflammatory, antioxidant, analgesic, anti-infectious, hypotensive and antiulcer characteristics and prevents cardiovascular diseases (CVD) (Bhusal et al., \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). In this study, AgNPs were synthesized from nettle extracts using photo-assisted and ultrasound-assisted synthesis methods and incorporated into the PLA films. Then, physicomechanical characteristics of the nanocomposite films were investigated.\u003c/p\u003e"},{"header":"Materials and Methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e\u003ch2\u003eMaterials\u003c/h2\u003e\u003cp\u003eThe AgNO\u003csub\u003e3\u003c/sub\u003e, chloroform and all chemicals with analytical grades were purchased from Merck, Germany.\u003c/p\u003e\u003c/div\u003e\n\u003ch3\u003eNettle aqueous extract preparation\u003c/h3\u003e\n\u003cp\u003eThe aerial parts of nettle (\u003cem\u003eU. dioica\u003c/em\u003e) were collected from((Scientific name): Urtica dioica L./ Family: Urticaceae./Name: Stinging Nettle./Source: Jihad-e-Daneshgahi Research Complex-Jihad University Research Institute of Medicinal Plants,Karaj./Date of collection :1401/12/05./Collector :Masoud Mohammadi./Herbarium No: UDI-1404-01./Notes: It is a herbaceous perennial with erect stems covered in stinging hairs that cause skin irritation upon contact. The leaves are opposite, toothed, and range from ovate to lanceolate in shape. Male and female flowers are found on the same stalk.).washed and then dried at 27\u0026deg;C for 3 D. To prepare the aqueous extract, 1 g of the nettle powder was mixed with 100 ml of distilled water (DW) and agitated for 1 h using shaker (IKA, Germany). The extract was filtered through Whatman filter papers no. 1 (Whatman, USA) and stored at refrigeration temperatures for further uses.\u003c/p\u003e\n\u003ch3\u003ePhoto-assisted synthesis of silver nanoparticles\u003c/h3\u003e\n\u003cp\u003eThe AgNO\u003csub\u003e3\u003c/sub\u003e (0.034 g, 1 mM) was dissolved in 10 ml of aqueous nettle extract and exposed to UV light (30 W) for 30 min under vigorous stirring (Cozzoli et al., \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e2004\u003c/span\u003e).\u003c/p\u003e\n\u003ch3\u003eUltrasound-assisted synthesis of silver nanoparticles\u003c/h3\u003e\n\u003cp\u003eBriefly, 1 ml of the nettle aqueous extract was added to 9 ml of AgNO\u003csub\u003e3\u003c/sub\u003e (1 mM) and sonication (Hielscher UP400S, Germany) at 24 kHz and 400 W was carried out for 90 min at RT with an amplitude of 50%. Then, suspension containing nanoparticles was centrifuged () at 8000 rpm for 20 min. This was washed four times with DW to remove Ag\u003csup\u003e+\u003c/sup\u003e ions. The reddish-brown color change indicated synthesis of AgNPs. Precipitated nanoparticles were dried at 40\u0026deg;C under vacuum and stored at 4\u0026deg;C (Manjamadha and Muthukumar, \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e2016\u003c/span\u003e).\u003c/p\u003e\n\u003ch3\u003eDynamic light scattering\u003c/h3\u003e\n\u003cp\u003eParticle size and polydispersity index (PDI) of the AgNPs were assessed using dynamic light scattering (DLS) analysis and particle size analyzer (Shimadzo, Japan).\u003c/p\u003e\u003cdiv id=\"Sec8\" class=\"Section2\"\u003e\u003ch2\u003ePolylactic acid film preparation\u003c/h2\u003e\u003cp\u003eThe PLA granules (1 g) were added to 43 ml of chloroform and stirred for 8 h using magnetic stirrer. Then, nettle extract and AgNPs (1, 2 and 3%) were added to the mixture and stirred for 20 min and then homogenized at 12,000 rpm for 2 min. Prepared solution was poured into glass molds and incubated at RT for 4 h to evaporate the solvent. Then, films were removed from the molds and incubated at RT for 24 h. Films were punched into discs with a diameter of 13 mm. Then, seven treatments, including pure PLA films as controls and PLA composites with 1, 2 and 3% photochemical and sonochemical synthesized AgNPs, were produced (Cheng et al., \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e2021\u003c/span\u003e).\u003c/p\u003e\u003c/div\u003e\n\u003ch3\u003ePolylactic acid film characterization\u003c/h3\u003e\n\u003cdiv id=\"Sec10\" class=\"Section2\"\u003e\u003ch2\u003eThickness\u003c/h2\u003e\u003cp\u003eFilm thickness was reported in \u0026micro;m (Farazma, Iran) with a resolution of 0.01 mm at various positions and then average values were calculated.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec11\" class=\"Section2\"\u003e\u003ch2\u003eLight transmission and opacity\u003c/h2\u003e\u003cp\u003eFilms were cut and transferred into a glass cuvette and their light transmission was measured at 600 nm using UV-vis spectrophotometer (Hitachi, Japan). Opacity of the films was achieved using Eq.\u0026nbsp;1:\u003c/p\u003e\u003cp\u003eOpacity = \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\frac{{\\text{A}\\text{b}\\text{s}}_{600}}{\\text{d}}\\)\u003c/span\u003e\u003c/span\u003e (1)\u003c/p\u003e\u003cp\u003eWhere, Abs\u003csub\u003e600\u003c/sub\u003e was the absorbance and d was the film thickness (mm).\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec12\" class=\"Section2\"\u003e\u003ch2\u003eSolubility\u003c/h2\u003e\u003cp\u003ePieces of the film (600 mg) were incubated at 40\u0026deg;C for 24 h using desiccator with P\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e, transferred into a beaker filled with 100 ml of deionized water and then stirred at RT for 24 h. Mixture was filtered using filter papers. Solubility of the films was calculated using Eq.\u0026nbsp;2:\u003c/p\u003e\u003cp\u003eSolubility (%) = \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\frac{\\text{m}1-\\text{m}2}{\\text{m}1}\\)\u003c/span\u003e\u003c/span\u003e (2)\u003c/p\u003e\u003cp\u003eWhere, m\u003csub\u003e1\u003c/sub\u003e was the initial dry weight of films (g) and m\u003csub\u003e2\u003c/sub\u003e was the final dry weight of films (g).\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec13\" class=\"Section2\"\u003e\u003ch2\u003eWater absorption\u003c/h2\u003e\u003cp\u003eFilms (22 \u0026times; 2 cm) were cut and dried for 2 d using desiccator with P\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e. Samples were weighed with an accuracy of 0.0001 and transferred into a beaker containing 100 ml of deionized water. After 1 h of drying and weighing, water absorption of the films was calculated using Eq.\u0026nbsp;3 Water absorption (%) = \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\frac{\\text{m}1}{\\text{m}2}\\)\u003c/span\u003e\u003c/span\u003e (3)\u003c/p\u003e\u003cp\u003eWhere, m\u003csub\u003e1\u003c/sub\u003e was the weight of absorbed moisture (g) and m\u003csub\u003e2\u003c/sub\u003e was the weight of dry films (g).\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec14\" class=\"Section2\"\u003e\u003ch2\u003eMechanical characteristics\u003c/h2\u003e\u003cp\u003eTensile strength (TS) and elongation at break (EB) were assessed using texture analyzer (Zwick, Germany) with force of 200 N, gap of 40 mm and speed of 50 mm min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (ASTM D412 standard).\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec15\" class=\"Section2\"\u003e\u003ch2\u003eFourier transform infrared spectroscopy\u003c/h2\u003e\u003cp\u003eFilms were dried at 50\u0026deg;C for 48 h and analyzed using Fourier transform infrared spectroscopy (Shimadzo, Japan) from 20 scans at a wavelength range of 650\u0026ndash;4000 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. For each spectrum, 64 consecutive scans were used (Shaik et al., \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e2018\u003c/span\u003e).\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec16\" class=\"Section2\"\u003e\u003ch2\u003eThermal behaviors\u003c/h2\u003e\u003cp\u003eNearly 2 mg of film samples were transferred into aluminum pans and the differential scanning calorimetry (DSC) was carried out at -100\u0026ndash;200 \u003csup\u003eo\u003c/sup\u003eC with heating rate of 10 \u003csup\u003eo\u003c/sup\u003eC min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and nitrogen flow rate of 20 ml min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. An empty aluminum pan was used as reference (Khan et al., \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2022\u003c/span\u003e).\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec17\" class=\"Section2\"\u003e\u003ch2\u003eStatistical analysis\u003c/h2\u003e\u003cp\u003eExperiments were carried out in triplicate and results were expressed as mean\u0026thinsp;\u0026plusmn;\u0026thinsp;SD (standard deviation). Statistical differences were reported using Duncan's multiple test and SPSS software v.26 (IBM, USA) at a significance level of \u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026le;\u0026thinsp;0.05.\u003c/p\u003e\u003c/div\u003e"},{"header":"Results and Discussion","content":"\u003cdiv id=\"Sec19\" class=\"Section2\"\u003e\u003ch2\u003eDynamic light scattering analysis\u003c/h2\u003e\u003cp\u003eBased on Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ea, the photo-assisted synthesized AgNPs included single peak with a width of 24 nm and PDI of 0.382. Moreover, 45.5% of the nanoparticles included a size of 91.28 nm. The ultrasound-assisted synthesized AgNPs included single peak with width of 27 nm and PDI of 0.371. Nearly 80.1% of the nanoparticles included a size of 68.06 nm (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eb).\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec20\" class=\"Section2\"\u003e\u003ch2\u003ePolylactic acid nanocomposites characterization\u003c/h2\u003e\u003cdiv id=\"Sec21\" class=\"Section3\"\u003e\u003ch2\u003eThickness\u003c/h2\u003e\u003cp\u003eAddition of AgNPs did not significantly affect thickness of the PLA nanocomposites (\u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026gt;\u0026thinsp;0.05) (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e).\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e\u003c/div\u003e\u003cdiv id=\"Sec22\" class=\"Section2\"\u003e\u003ch2\u003eOpacity\u003c/h2\u003e\u003cp\u003eBased on Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e, nanocomposites containing 3% AgNPs (photo-assisted and ultrasound-assisted synthetized) showed the highest opacity (\u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05). In other words, these included lower transparency and light transmission. This phenomenon could be linked to the presence of AgNPs as minerals that could not be dissolved in the polymer matrix (Noshirvani et al., \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e2017\u003c/span\u003e) or light scattering through the heterogeneous network of films (Arfat et al., \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e2014\u003c/span\u003e). The pure PLA film (control) and nanocomposites containing 1 and 2% AgNPs did not show any significant differences (\u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026gt;\u0026thinsp;0.05).\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eResults were similar to those of other researchers, who have reported increases in opacity of PLA and gelatin films by addition of zinc-oxide nanoparticles (Noshirvani et al., \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e2017\u003c/span\u003e; Arfat et al., \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e2014\u003c/span\u003e; Pantani et al., \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e2013\u003c/span\u003e).\u003c/p\u003e\u003cdiv id=\"Sec23\" class=\"Section3\"\u003e\u003ch2\u003eSolubility and water adsorption\u003c/h2\u003e\u003cp\u003eIncorporation of AgNPs to the PLA films significantly decreased solubility and water absorption of the films (\u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05) (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e). Ultrasound-assisted synthesized nanoparticles showed lower solubility and water absorption, compared to those photo-assisted synthetized nanoparticles did (\u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05). The highest and the lowest solubility and water absorption were observed in the control and T6 treatments, respectively (\u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05).\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003ePlacement of the nanoparticles between the PLA chains decreased free spaces between the chains for the absorption of water molecules. Furthermore, nanoparticles created tortuous paths in the biopolymer matrix, which decreased penetration of water molecules. In other studies, addition of zinc oxide (Nafchi et al., \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e2012\u003c/span\u003e) and zirconium oxide (Karimi Sani et al., \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e2021\u003c/span\u003e) nanoparticles have decreased moisture content of the nanocomposites, verifying findings of the present study.\u003c/p\u003e\u003c/div\u003e\u003c/div\u003e\u003cdiv id=\"Sec24\" class=\"Section2\"\u003e\u003ch2\u003eMechanical characteristics\u003c/h2\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eFigure \u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e. Tensile strength (a) and elongation at break (b) of the polylactic acid films. T1, Control (pure PLA); T2, polylactic acid and 1% photo-assisted synthetized silver nanoparticles; T3, polylactic acid and 2% photo-assisted synthetized silver nanoparticles; T4, polylactic acid and 3% photo-assisted synthetized silver nanoparticles; T5, polylactic acid and 1% ultrasound-assisted synthetized silver nanoparticles; T6, polylactic acid and 2% ultrasound-assisted synthetized silver nanoparticles; and T7, polylactic acid and 3% ultrasound-assisted synthetized silver nanoparticles. Different letters indicate significant differences (\u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05)\u003c/p\u003e\u003cp\u003eIncreases in TS and EB of the PLA films by the addition of ultrasonically synthesized AgNPs could be attributed to the crosslinking between PLA, nanoparticles and phenolic compounds of the nettle extract. Moreover, high surface area of ​​the nanoparticles and electrostatic interactions between the PLA chains and AgNPs increased TS and improved mechanical characteristics of the nanocomposite films (Aghbolagh Sharifi and Pirsa, \u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e2021\u003c/span\u003e; Wetzel et al., \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e2003\u003c/span\u003e). Nanoparticles effectively transferred stress from the matrix to the particles through shear mechanism, increasing TS of the nanocomposites (Brown and Ellyin, \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e2005\u003c/span\u003e). At higher concentrations of nanoparticles, agglomeration/ aggregation of the nanoparticles in the polymer matrix weakened mechanical characteristics (Wetzel et al., \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e2003\u003c/span\u003e). Similarly, addition of AgNPs to biodegradable starch-chitosan (Yoksan \u0026amp; Chirachanchai, \u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e2010\u003c/span\u003e) and hydroxypropyl methylcellulose (De Moura et al., \u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e2012\u003c/span\u003e) films have increased TS.\u003c/p\u003e\u003cdiv id=\"Sec25\" class=\"Section3\"\u003e\u003ch2\u003eFourier transform infrared spectroscopy analysis\u003c/h2\u003e\u003cp\u003eFigure \u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e shows the FTIR spectra of pure PLA films and PLA composites containing photo-induced and ultrasonically synthesized AgNPs. Stretching vibration of the C\u0026thinsp;=\u0026thinsp;O (carbonyl) bonds in the PLA structure was detected at 1732 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (Alzubaidi et al., \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e2023\u003c/span\u003e; Ajlouni et al., \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). The N-H bond in the amines indicated presence of proteins and enzymes in the nettle extract, which possibly acted as decreasing agents and stabilizers of AgNPs (Ahmad et al., \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). Bending vibration of C-H bonds in CH\u003csub\u003e2\u003c/sub\u003e and CH\u003csub\u003e3\u003c/sub\u003e groups was shown at 11490 and 11380 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, respectively (Roshanghias et al., \u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e2022\u003c/span\u003e; Nasrin et al., \u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e2017\u003c/span\u003e).\u003c/p\u003e\u003cp\u003eStretching vibration of C-O bonds in the structure of C-OH and C-O-C was shown at absorption peaks of 1132 and 1005 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, respectively (Sadeghi and Gholamhoseinpoor, \u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e2015\u003c/span\u003e; Ajlouni et al., \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). This peak was detected due to the presence of phenols, alcohols, carboxylic acids, esters, ethers and/or biomolecules in the nettle extract (Alzubaidi et al., \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e2023\u003c/span\u003e; Tavan et al., \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2023\u003c/span\u003e; Khan et al., \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2022\u003c/span\u003e) as capping and stabilizing agents, responsible for the reduction of Ag\u003csup\u003e+\u003c/sup\u003e to AgNPs (Sarwer et al., \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2022\u003c/span\u003e; Sarkar and Kotteeswaran, \u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). The peaks at 640 and 450 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e are also related to the deformation vibration of C-H bonds in the PLA structure (Jung et al., 2018), aromatic rings in the synthesis of AgNPs (Tavan et al., \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2023\u003c/span\u003e), the presence of alkenes (Sarkar and Kotteeswaran, \u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e2018\u003c/span\u003e) and C-N bond (Sarwer et al., \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2022\u003c/span\u003e) in the extract structure.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eThe FTIR analysis verified characterization of the molecular interactions of the nettle extract with the PLA matrix, Ag-O bonds in synthesis of AgNPs and presence of functional groups on the surface of AgNPs (Salmieri et al., \u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e2014\u003c/span\u003e). Spectra of the pure PLA films and their nanocomposites did not differ significantly, indicating successful incorporation of nanoparticles into PLA films. Most of the peaks were present in AgNPs spectra with small shifts, verifying roles of the aqueous nettle extract as a decreasing stabilizing agent (Ajlouni et al., \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). Interaction of metal ions with various functional groups caused slight shifts in the spectra of AgNPs (Alzubaidi et al., \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). By addition of AgNPs (greater than 1%), several changes were observed at 500\u0026ndash;560 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e in the fingerprint region (Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e), which was linked to the stretching vibration of Ag-O bonds in the composite structure (Kakhki et al., \u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Mohan Bhagyaraj et al., 2020).\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eIncreasing concentration of the nanoparticles increased the peak intensity as an indicator for the presence of AgNPs in the PLA structure. Peak intensity in the spectra of photo-assisted synthetized AgNPs was slightly higher than that in ultrasound-assisted synthetized AgNPs, which could indicate better performance of these nanoparticles in the composite. In addition, increasing proportion of AgNPs in the film structure decreased intensity of the peak located at 450 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (associating to deformation vibration of the C-H bonds). It seemed that presence of AgNPs and their effects on chemical composition of the PLA matrix caused disturbed deformation vibration of the C-H bonds and their decreased peak intensity. Peak intensity of the photo-assisted synthetized AgNPs decreased more than that of ultrasound-assisted synthesis.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec26\" class=\"Section3\"\u003e\u003ch2\u003eDifferential scanning calorimetry analysis\u003c/h2\u003e\u003cp\u003eThe DSC thermograms and results of glass transition temperature (T\u003csub\u003eg\u003c/sub\u003e), cold crystallization temperature (T\u003csub\u003ec\u003c/sub\u003e), melting temperature (T\u003csub\u003em\u003c/sub\u003e), enthalpy of crystallization (∆H\u003csub\u003ec\u003c/sub\u003e), enthalpy of melting (∆H\u003csub\u003em\u003c/sub\u003e) and Xc (∆H\u003csub\u003em\u003c/sub\u003e - ∆H\u003csub\u003ec\u003c/sub\u003e / 93.7) are reported in Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e and Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003eDifferential scanning calorimetry analysis results\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"8\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c8\" colnum=\"8\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u003cp\u003eFilm\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003eT\u003csub\u003eg\u003c/sub\u003e (\u003csup\u003eo\u003c/sup\u003eC)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003eT\u003csub\u003ec\u003c/sub\u003e (\u003csup\u003eo\u003c/sup\u003eC)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003eT\u003csub\u003em1\u003c/sub\u003e (\u003csup\u003eo\u003c/sup\u003eC)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c5\"\u003e\u003cp\u003eT\u003csub\u003em2\u003c/sub\u003e (\u003csup\u003eo\u003c/sup\u003eC)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c6\"\u003e\u003cp\u003e∆Hm (J/g)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c7\"\u003e\u003cp\u003e∆Hc (J/g)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c8\"\u003e\u003cp\u003eX\u003csub\u003ec\u003c/sub\u003e\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003ePure PLA\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e57.79\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e122.10\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e147.50\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e153.31\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e71.20\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e\u003cp\u003e22.51\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e\u003cp\u003e54.10\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e1% Ag (L)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e59.42\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e120.24\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e149.17\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e154.98\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e77.15\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e\u003cp\u003e20.26\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e\u003cp\u003e60.72\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e2% Ag (L)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e58.69\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e120.31\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e149.6\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e154.93\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e84.36\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e\u003cp\u003e10.01\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e\u003cp\u003e79.35\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e3% Ag (L)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e57.75\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e17.70\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e146.25\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e154.47\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e91.44\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e\u003cp\u003e67.06\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e\u003cp\u003e26.01\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e1% Ag (U)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e61.62\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e129.69\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e149.06\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e155.52\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e93.03\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e\u003cp\u003e49.71\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e\u003cp\u003e46.23\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e2% Ag (U)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e60\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e120.01\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e147.65\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e15.71\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e112.30\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e\u003cp\u003e75.25\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e\u003cp\u003e39.54\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e3% Ag (U)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e85.45\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e116.94\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e147.82\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e156.03\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e121.32\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e\u003cp\u003e113.16\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e\u003cp\u003e8.71\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003ePLA, Polylactic acid; Ag (L), photo-assisted synthesized silver nanoparticles; Ag (U), ultrasound-assisted synthesized silver nanoparticles\u003c/p\u003e\u003cp\u003eThe T\u003csub\u003eg\u003c/sub\u003e and T\u003csub\u003ec\u003c/sub\u003e for pure PLA film were 57.79 and 122.10\u0026deg;C, respectively. Addition of 1% AgNPs to the composite slightly increased T\u003csub\u003eg\u003c/sub\u003e due to a higher T\u003csub\u003eg\u003c/sub\u003e of AgNPs, compared to the pure PLA, which verified reinforcing roles of nanoparticles in fabrication of nanocomposites at a wide temperature range. Nanoparticles acted as nucleating agents and included good compatibilities with the polymer matrix but at higher concentrations due to their agglomeration, acting as a plasticizer that did not increase T\u003csub\u003eg\u003c/sub\u003e (Girdthep et al., \u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e2015\u003c/span\u003e). Similarly, T\u003csub\u003ec\u003c/sub\u003e decreased in a higher concentration of AgNPs [except for 2% Ag (L) treatment] due to the low crystallization rate of nanoparticles and incomplete crystallization of PLA. The higher T\u003csub\u003ec\u003c/sub\u003e and crystallinity rate in 2% photo-assisted synthesized AgNPs could indicate that nanoparticle dispersion in the composite was optimal.\u003c/p\u003e\u003cp\u003eThe T\u003csub\u003em\u003c/sub\u003e of PLA was nearly 150\u0026deg;C (Malek et al., \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). Regarding the higher T\u003csub\u003em\u003c/sub\u003e of AgNPs compared to PLA, incorporation of nanoparticles into the PLA increased T\u003csub\u003em\u003c/sub\u003e of the composite. Homogeneous distribution of nanoparticles in the polymer matrix and interaction of functional groups with PLA increased the T\u003csub\u003em\u003c/sub\u003e and improved thermal characteristics of the polymer (Shankar et al., \u003cspan citationid=\"CR53\" class=\"CitationRef\"\u003e2015\u003c/span\u003e). Increases in T\u003csub\u003em\u003c/sub\u003e by the addition of nanoparticles was linked to two important mechanisms of (i) heterogeneous nucleation of nanoparticles and facilitated crystallization; and (ii) modification of the orientation of polymer chains by the nanoparticles, causing orderly chain arrangement and formation of larger crystals (Asadi and Pirsa, \u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e2019\u003c/span\u003e).\u003c/p\u003e\u003cp\u003eTwo endothermic melting peaks in the DSC curve could be associated to the formation of two crystalline forms of β form, melting at a lower temperature; and α form, melting at a higher temperature with the most stable rate (Cuiffo et al., \u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). By adding nanoparticles, peak corresponding to the α-crystalline form was intensified, indicating increases in stability of the structure in presence of higher concentrations of AgNPs (Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e). The ΔH\u003csub\u003em\u003c/sub\u003e linked to the structural order (Nasreen et al., \u003cspan citationid=\"CR52\" class=\"CitationRef\"\u003e2016\u003c/span\u003e) increased with the incorporation of nanoparticles into the PLA matrix. Improvement of thermal characteristics of nanocomposites has previously been reported using magnesium oxide (Swaroop and Shukla, \u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e2019\u003c/span\u003e), zirconium oxide (Karimi Sani et al., \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e2021\u003c/span\u003e), zinc oxide (Pantani et al., \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e2013\u003c/span\u003e; Noshirvani et al., \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e2017\u003c/span\u003e), graphene (Girdthep et al., \u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e2015\u003c/span\u003e) and titanium (Zolfi et al., \u003cspan citationid=\"CR54\" class=\"CitationRef\"\u003e2014\u003c/span\u003e) nanoparticles.\u003c/p\u003e\u003c/div\u003e\u003c/div\u003e"},{"header":"Conclusion","content":"\u003cp\u003eIn general, the major aim of the current study was to develop AgNPs using alternative, green cost-effective approach of photo-assisted and ultrasound-assisted syntheses by nettle extract incorporation into PLA films. This study showed that nettle was an appropriate plant as a decreasing capping agent in synthesis of AgNPs. The synthesized AgNPs were monodisperse and homogeneous nanoparticles, which decreased solubility and water absorption and improved mechanical and thermal characteristics of the PLA films. Ultrasound-assisted synthesized AgNPs were more efficient than photo-induced ones in improvement of physicomechanical characteristics of the PLA films. However, higher T\u003csub\u003ec\u003c/sub\u003e and crystallinity in photo-assisted synthetized nanoparticles in DSC analysis and increased peak intensity in FTIR analysis could reveal better performance of these samples in the composite, compared to ultrasound-assisted synthesis. Further studies are necessary to investigate toxicity of AgNPs.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eResearch funding\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis research received no specific grant from any funding agency in the public, commercial, or not-for-profit sectors.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eData Availability\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe datasets generated and/or analysed during the current study are not publicly available due [REASON WHY DATA ARE NOT PUBLIC] but are available from the corresponding author on reasonable request.\u003c/p\u003e\n\u003cp\u003ePlant Material and Collection Authorization Statement (for Scientific Reports)\u003c/p\u003e\n\u003cp\u003eThe collection and use of Urtica dioica L. (Family: Urticaceae; Persian name: Gazaneh; English name: Stinging Nettle) complied with all relevant institutional, national, and international guidelines and legislation.\u003c/p\u003e\n\u003cp\u003ePlant material was obtained from cultivated specimens grown under controlled greenhouse conditions at the Medicinal Plants Research Center, Academic Center for Education, Culture and Research (ACECR), Karaj, Iran.\u003c/p\u003e\n\u003cp\u003eAuthorization for the collection and use of the plant was granted by the Medicinal Plants Research Center, ACECR (Permit date: 24 February 2023). The plant material was collected by Mr. Masoud Mohammadi and authenticated by a qualified botanist.\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;A voucher specimen (Herbarium No. UDI-1404-01) has been deposited in the institutional herbarium of the Medicinal Plants Research Center, ACECR, Karaj, Iran.\u003c/p\u003e\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eF.P. wrote the main manuscript text / data collection(first Auther)H.A. project managment M.M.Data curation /softwareA.A. Resources/validation\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eVink, E. T., Glassner, D. A., Kolstad, J. J., Wooley, R. J., \u0026amp; O\u0026rsquo;Connor, R. P. (2007). The eco-profiles for current and near-future NatureWorks polylactide (PLA) production. Industrial Biotechnology, 3(1), 58-81.\u003c/li\u003e\n\u003cli\u003eMalek N S A, Faizuwan M, Khusaimi Z, Bonnia N N, Rusop M, Asli N A. 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(2014). Development and characterization of the kefiran-whey protein isolate-TiO2 nanocomposite films. \u003cem\u003eInternational journal of biological macromolecules\u003c/em\u003e, \u003cem\u003e65\u003c/em\u003e, 340-345.\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"scientific-reports","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"scirep","sideBox":"Learn more about [Scientific Reports](http://www.nature.com/srep/)","snPcode":"","submissionUrl":"","title":"Scientific Reports","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Scientific Reports","inReviewEnabled":true,"inReviewRevisionsEnabled":true},"keywords":"Biodegradable films, Nettle extract, Photo-induced synthesis, Polylactic acid, Silver nanoparticles, Thermal stability","lastPublishedDoi":"10.21203/rs.3.rs-7890805/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-7890805/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eNanoparticles improve protective characteristics of biodegradable packaging. The aim of this study was to investigate physicomechanical characteristics of polylactic acid film containing 1, 2 and 3% silver nanoparticles synthesized using photo-assisted and ultrasound-assisted methods and aqueous extract of nettle (\u003cem\u003eUrtica dioica\u003c/em\u003e). Formation of silver nanoparticles was verified using UV-vis spectroscopy. Photochemical and sonochemical synthesized silver nanoparticles were monodisperse with particle sizes of 91.28 and 68.06 nm and polydispersity indices of 0.382 and 0.371, respectively. Solubility and water absorption decreased with silver nanoparticles, especially ultrasound-assisted synthesized ones, into polylactic acid films (\u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05). Nanocomposites containing 2 and 3% of ultrasound-assisted synthesized silver nanoparticles showed the highest tensile strength and elongation at break. Fourier transform infrared spectroscopy verified the role of nettle extract as a decreasing, stabilizing and capping agent of silver nanoparticles. In fingerprint region of the spectra, presence of Ag-O bonding and synthesis of silver nanoparticles were verified. Silver nanoparticles improved the thermal stability of polylactic acid nanocomposite films. Therefore, use of silver nanoparticles is recommended to improve physicomechanical and thermal characteristics of polylactic acid films.\u003c/p\u003e","manuscriptTitle":"Physicomechanical Characteristics of Polylactic Acid Films Containing Photo-assisted and Ultrasound-assisted Green Synthesized Silver Nanoparticles Using Nettle Extract","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-11-25 17:53:57","doi":"10.21203/rs.3.rs-7890805/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2026-03-04T12:02:34+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-02-18T09:37:35+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"1707848582410386493111853908480115799","date":"2026-02-11T12:24:18+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"105212852728345428595848389329305204844","date":"2026-02-09T05:01:50+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"274952916507051086986541539518432294079","date":"2026-02-08T13:37:14+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"156297248411611860649279750276254647875","date":"2026-01-10T08:34:54+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"177953590500422574689162316373855158957","date":"2025-12-13T06:25:44+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-12-08T06:48:41+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"89579322086961221154730200539231493852","date":"2025-12-08T06:38:50+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-11-20T14:25:59+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"328627906653303855967225177485565386631","date":"2025-11-15T04:11:26+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-11-14T15:22:41+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-11-14T15:21:09+00:00","index":"","fulltext":""},{"type":"editorInvited","content":"","date":"2025-11-13T13:02:59+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2025-11-11T18:28:05+00:00","index":"","fulltext":""},{"type":"submitted","content":"Scientific Reports","date":"2025-11-11T18:25:05+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"scientific-reports","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"scirep","sideBox":"Learn more about [Scientific Reports](http://www.nature.com/srep/)","snPcode":"","submissionUrl":"","title":"Scientific Reports","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Scientific Reports","inReviewEnabled":true,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"dc1348fd-b836-4602-96d3-76902da349d9","owner":[],"postedDate":"November 25th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"in-revision","subjectAreas":[{"id":58521415,"name":"Physical sciences/Chemistry"},{"id":58521416,"name":"Physical sciences/Materials science"},{"id":58521417,"name":"Physical sciences/Nanoscience and technology"}],"tags":[],"updatedAt":"2026-03-04T12:13:00+00:00","versionOfRecord":[],"versionCreatedAt":"2025-11-25 17:53:57","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-7890805","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-7890805","identity":"rs-7890805","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}