Synthesize, swelling and morphological properties of tea wased-based hydrogel as a slow-release NPK fertilizer applied to mini eggplant seeds growth

Synthesize, swelling and morphological properties of tea wased-based hydrogel as a slow-release NPK fertilizer applied to mini eggplant seeds growth | 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 Research Article Synthesize, swelling and morphological properties of tea wased-based hydrogel as a slow-release NPK fertilizer applied to mini eggplant seeds growth Wan Amirah Najwa Wan Anuar, Ros Azlinawati Ramli, Mei Lian Yuen, and 3 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-5394710/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Incorporating tea waste (TW) into hydrogel promotes sustainability and supports the principles of circular economy. Tea waste-grafted-polyacrylic acid containing NPK fertilizer (TW-g-PAA/NPK) was developed as potential slow-release fertilizer hydrogel (SRFH). Its properties were compared to those of synthesized PAA superabsorbent polymer (SAP) and TW-g-PAA superabsorbent polymer composite (SAPC). Chemical, morphological and elemental properties of SAP, SAPC and SRFH were analyzed using FTIR spectroscopy, SEM microscopy and SEM-EDX spectrometer. The grafting reactions were proven by the appearance of peaks at 1046 cm-1 in SAPC and SRFH spectra, indicating that -COH bonds of cellulose were broken to form -COC- bonds. SEM images showed that, TW fiber was grafted with PAA hydrogel and SRFH had the smallest pore sizes. Furthermore, EDX images proved the presence of nitrogen (N), phosphorus (P) and potassium (K) elements in SRFH. Swelling properties indicated that SRFH has the lowest WAC, resulting in slowest release rate. Re-swelling performance showed that SRFH and SAPC has no vital change in WAC even after five cycles of swelling. Germination and growth of mini eggplants seeds in black soil treated with SRFH showed faster germination and the best development. The developed TW-g-PAA/NPK provide an innovative approach as slow-release fertilizer and water retention in agriculture fields. Tea waste Grafting Acrylic acid Crosslinking Hydrogel Morphological Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11 Figure 12 Figure 13 1. Introduction Agriculture is an essential part of economy, but it uses much water, a scarce and precious resource. Adequate irrigation practices and water conservation measures affect plant growth, survival, and productivity. Hydrogel offered solutions to agriculture's water scarcity by increasing soil and water productivity without damaging the environment or natural resources. The inclusion of hydrophilic groups on the polymer chains, such as hydroxyl, carboxyl, and amide, contributes to enhance water absorbent qualities. Plant development primarily depends on fertilizer and water to enhance survival under drought conditions [ 1 ]. As the soil surrounding the root zone of plants dries out, the hydrogel gradually releases water and nutrients to support plant growth [ 2 ]. A superabsorbent polymer (SAP) is a hydrophilic polymeric material with the ability to absorb high amount of aqueous solutions within their structures. Moreover, SAP is essentially polyelectrolytes with three dimensional (3D) crosslinked structure, where the polymer chains are connected through crosslinking [ 1 ]. Commercial SAP hydrogels available on the global market are non-biodegradable, posing a potential risk of soil pollution and adverse effects on agricultural productivity [ 3 ]. Conventional SAP for agriculture applications presents several recognized environmental hazards, including non-biodegradability, subpar mechanical properties, and high production costs [ 4 ]. Commercial SAP is resistant to soil microorganisms due to the use of fully synthetic polymer such as polyacrylamide (PAAM) and polyacrylic acid (PAA). As a result, SAP will exhibit low biodegradability and persist in the soil, leading to environmental contamination as they accumulate in the soil [ 5 ]. Most of hydrogels are soft, weak, brittle, and prone to fracturing under high strains when compared to engineering materials. Numerous investigations on particle hydrogel have been conducted in the past decade to improve the properties. In the meantime, several efforts have focused on superabsorbent polymer composite (SAPC) [ 6 ]. Hydrogels can enhance their properties through copolymerization or the integration of natural fibers. For instance, combining acrylamide (AAm) with cashew gum through copolymerization resulted in a hydrogel exhibiting favorable mechanical characteristics [ 7 ]. SAPC is a hydrogel that contains natural fibers or inorganic materials and incorporated into SAP through a polymerization technique. Natural fibers are ecologically friendly materials that possess superior qualities compared to synthetic fibers [ 8 ]. Natural polymers, found abundantly in nature, offer a means to lower the production expenses of hydrogels while minimizing environmental pollution through the production of polymer-biomass waste. Natural fibers including kenaf, coco peat, sugarcane bagasse, banana peel, hemp, jute, cotton, sisal, flax, corn cob, ramie bast, rice straw and pineapple leaf are reinforced in polymer matrix to achieve target properties such as mechanical, thermal, biodegradability, lower cost and swelling properties. The interaction between synthetic polymers and natural fibers results in biodegradability, low production cost, non-toxicity, improved release rate and plant growth performance [ 9 ]. Tea waste (TW) or leftover tea is an outstanding reservoir of natural fibers suitable for grafting with hydrogels. Tea leaves are plentiful in lignin and holocellulose, which contain carboxyl, phenolic hydroxyl, hydroxyl, oxyl groups and oxygen/heteroatom groups [ 10 ]. TW is primarily a lignocellulosic fibers composed of lignin, hemicellulose, cellulose, polyphenols, tannins and proteins [ 11 ]. As the global demand for tea is rising, the amount of biomass waste generated has increased. Tea consumption was approximated at 6.3 million metrics ton in 2020 and is projected to escalate to 7.4 million tonnes by 2025 [ 12 ]. TW- based products have found applications across many fields, including wastewater treatment, pharmaceuticals, energy storing system and energy generation [ 13 ]. Therefore, the generation of TW post-consumption has escalated with increasing tea consumption. Debnath et al. have reviewed the potential and sustainable utilization of TW [ 14 ]. However, until now, there have been no studies reporting on the utilization of of TW in hydrogel production. The synthesis of hydrogel with fertilizer as slow-release fertilizer has emerged as a promising material to solve the drawbacks of conventional fertilizer by giving nutrients sustainably, reducing nutrients irrigation frequency, and minimizing fertilizer loss rate [ 15 ]. Slow-release fertilizer hydrogels integrate the characteristics of a superabsorbent hydrogel and a fertilizer, enhancing soil quality and improving fertilizer efficiency. Nowadays, the trend of combining fertilizers and superabsorbent hydrogels to regulate water and nutrients within a single system is on the rising trend [ 16 ]. SRFH that is produced from natural fibers and synthetic polymers can be categorized as organic–organic SRFH, also referred to as combined synthetic-natural SRFH [ 9 ]. This study focuses on grafting TW fibers onto PAA chains and incorporation of nutrient in situ to improve swelling, biodegradability and nutrient efficiency of SAP. To the best of my knowledge, this is the first research that reported the use of TW fibers to produce hydrogels. 2. Material and Method 2.1 Material Glacial acrylic acid (GAA) was purchased from BASF Petronas, Malaysia, sodium hydroxide (NaOH), 97%, ammonium persulfate (APS), 98%, and N'N -methylene- bis -acrylamide (MBA), 99%, were purchased from Merck, Malaysia. Tea powder brand BOH was purchased from Giant supermarket, NPK 15-15-15 brand Behn Meyer was purchased from local store. All chemicals were used as purchased and deionized water was used throughout this experiment. Tea powder was ground to 500 microns and washed with boiling water three times (normal procedure is two time, but three time is needed to simulate the used tea). After washed, the TW fibers were dried drying oven at 50°C until it reached a constant weight. Furthermore, 3.0 wt% of NaOH was dissolved in 15.0 wt% of deionized water. To prepare monomer mixture, added 25.0 wt% of GAA and 0.1 wt% of MBA to the NaOH solution and stirred for 30 minutes. The mixture of fertilizer with TW fibers were prepared by placing 1.3 wt% of NPK fertilizer into certain amount of deionized water and stirring for 30 minutes. After 30 minutes, 1.4 wt% of TW fibers was added to the mixture. To prepare APS solution, 0.2 wt% of APS powder was added to 2.7 wt% of deionized water. 2.2 Synthesis of Hydrogels The synthesis of TW- g -PAA/NPK SRFH was performed in a 500 mL jacketed glass reactor, connected with an overhead stirrer, paddle impeller, condenser, and circulating water bath, as shown in Fig. 1 . The monomer mixture was added into the reactor, followed by fertilizer mixture with TW fiber. The water bath was set to 70°C, and stirring speed was set to 145 rpm. The prepared APS solution was poured to the reactor once the reactor reached 60°C. The APS solution was added to the reactor when the reactor temperature reached 60°C. The mixtures was continuously stirred until it gelled up. A similar procedure was carried out to synthesize PAA SAP and TW- g -PAA SAPC. TW- g -PAA SAPC was synthesized in the absence of NPK fertilizer, whereas PAA SAP was synthesized in the absence of TW fiber and NPK fertilizer. The synthesized SAP, SAPC and SRFH were cut into small pieces before being dried in a drying oven at 60°C until a fixed weight achieved. Then, the dried SAP, SAPC and SRFH were grounded to 1.5 mm for characterization and testing. 2.3 Characterization of SAP, SAPC and SRFH FTIR spectroscopy (Perkin Elmer Spectrum 100) was employed to evaluate the grafting reactions of TW fibers on PAA hydrogel and identify related functional groups that present in SAP, SAPC, SRFH and washed TW fibers. The spectra were recorded at a resolution of 4 cm − 1 , ranging from 4000 to 500 cm − 1 by attenuated total reflectance (ATR) method for hydrogels and potassium bromide (KBR) method for TW fiber. SEM microscopy (Hitachi TM3030 Plus) equipped with EDX (energy dispersive X-ray) was employed to investigate surface morphology of dried SRFH and TW fiber. Furthermore, another SEM (Carl Zeiss model EVO 50) was used to examine the internal structures of swollen hydrogels samples. Both SEM were operated at 10 kV accelerating voltage. 2.4 Swelling ratio (SR), water absorbency capacity (WAC) and re-swelling capability The swelling ratio was used to analyze the absorption tendency and measure the time needed for the hydrogels to reach their equilibrium swelling states. 0.5 g of each dried hydrogels were soaked in 200 g of tap water respectively at room temperature. The swollen samples were passed through sieves to eliminate excess water before being weighed. Swelling ratio (SR) in g/g was calculated for every 1 hour until 5 hours using Eq. 1 [ 17 ]. SR = 𝑊t – 𝑊0 (1) 𝑊 0 Where, W t - weight of swollen sample in g W 0 - weight of dried sample in g Similar procedure was used to determine the WAC (g/g) and re-swelling capacity of hydrogels. However, WAC was evaluated based on the time required for hydrogel to reach equilibrium swelling state. Moreover, re-swelling capacity was evaluated by calculate the WAC after each cycle using Eq. 1. 2.5 Seeds growth performance Mini eggplant seeds were used to evaluate the performance of developed SRFH on the seed’s germination and growth under limited water conditions. Swollen SAP, SAPC and SRFH were mixed with black soil in ratio of 1:3 of each. Black soil without hydrogel was used as control. Mini eggplant seeds were sowed in seedling tray before transferred to pots. They were exposed to actual environmental conditions. An equal amount of water was irrigated for every 7 days. The germination and growth performance patterns of all mini eggplant were observed at different time intervals for 6 weeks. 3. Results and Discussions 3.1 Synthesis Reactions SRFH, SAPC and SAP were reacted at 70°C temperature and at 145 rpm stirring speed. However, the reaction time (time taken to react completely) of SRFH and SAPC is 20 mins and SAP is 9 mins. The difference in reaction time is due to incorporation of TW fiber into AA hydrogel. According to reaction kinetics, the reaction rate is proportional to concentration of reactants [ 18 ]. The absence of TW fiber in SAP allowed more concentrate AA monomer (reactant) to participate in the polymerization reaction, leading to a faster reaction rate and a shorter reaction time. Figure 2 shows the synthesized hydrogels of SAP (a), SAPC (b) and SRFH (c). The SAP exhibits a clear, colorless gel appearance, while SAPC and SRFH display a brown coloration characteristic of TW fiber. 3.1.2 Reaction Steps and 3D Netwok Formation Neutralization of AA by NaOH had increased hydrophilicity and osmotic pressure of the polymer, thereby enhancing its swelling rate [ 19 ]. Using APS as initiator, TW fiber was grafted onto PAA chains, followed by crosslinking of the grafted chains to form three-dimensional network (3D). Furthermore, NPK was incorporated into the network and pores to form TW- g -PAA/NPK. Free radical polymerization (FRP) of TW- g -PAA/NPK SRFH consists of initiation, propagation and termination steps. At initiation step, APS initiator dissociated to form two sulfate radicals (primary radicals) followed by association of AA monomer unit to the sulfates radical to form polymer radicals of sodium acrylate as shown in Fig. 3 . Sequential addition of AA monomer units to the polymer radicals formed growing polymer radicals then grafted with cellulose from TW fiber in propagation step. The propagation will continue until termination and cross-linking steps which is proposed to be by combination of grafted propagated chains. The crosslinking process occurred due to the bridging of the grafted chains by the crosslinker to form 3D network of SAPC and SRFH as shown in Fig. 4 . 3.2 Characterization of SAP, SAPC and SRFH Figure 5 shows the FTIR spectra of washed TW fiber (a), SAP (b), SAPC (c) and SRFH (d). According to Fig. 5 (a), the peak at 3417 cm − 1 corresponded to O–H stretching [ 20 ] and the peak 2921 cm − 1 corresponded to C − H stretching which mainly corresponded to aliphatic -CH 2 - group, 1521 cm − 1 , 1541 cm − 1 -stretching C = N, C = C of lignin, 1036 cm − 1 - the extension of C-O, 1652 cm − 1 – C = C aromatized ring stretch by vibrations [ 21 ]. The peak at 1740 cm − 1 was assigned o C = O functional group, due to the existence of acetyl ester group that linked to hemicellulose [ 22 ]. The peak ranging from 1110 cm − 1 to 1243 cm − 1 was indicative of the carbohydrate glycosidic bond and the glucose ring present in cellulose [ 23 ]. The band observed at 1036 cm − 1 was corresponded to C = O and C–H stretching within cellulose [ 24 ]. The peak at 1373 cm − 1 was corresponded to bending of C–H bending within cellulose [ 25 ]. In Fig. 5 (b), a distinctive broad absorption peak observed at 3444 cm − 1 in FTIR spectra, corresponded to C-H and O-H stretching vibrations present in the AA and MBA (Bora 2022). The peak represents the overlapping of C = O stretching vibration of carboxyl (COOH) groups and N-H bending vibration, occurring at 1635 cm − 1 [ 26 ]. The signal within the range of 1630–1639 cm − 1 was assigned to carbonyl stretching of carboxylic acid group [ 27 , 24 ]. Figure 5 (c) and (d) indicated the peaks that observed at 2940 cm − 1 to 2936 cm − 1 corresponded to the symmetric and asymmetric stretching of C-H bonds founded in AA within the hydrogel structures [ 28 ]. SAPC and SRFH had a new absorption band observed at 2540 cm − 1 corresponded to amide group stretch. The typical peaks of fibers had emerged in SAPC and SRFH in the region at 1550 cm − 1 to 1170 cm − 1 . The peaks observed at 1451 cm − 1 to 1450 cm − 1 corresponded to methylene -CH 2 vibration in carbonyl and 1248 cm − 1 to 1244 cm − 1 corresponding to carboxyl in ethers. This is the indication that the cellulose fiber chains have been grafted on the PAA chains of the polymeric network [ 20 ]. New peaks that appeared at 1715 cm − 1 and 1716 cm − 1 in SAPC and SRFH respectively were attributed to stretching vibration peak of C = O, suggesting successful grafting of fiber onto PAA hydrogel [ 29 , 30 ]. Moreover, the intense bands observed at 1550 cm − 1 to 1549 cm − 1 were assigned to symmetric and asymmetric stretching modes of carbonyl group in carboxylate group (COO) of the polyacrylate. Additionally, the peaks that observed at 1407 cm − 1 to 1405 cm − 1 were attributed to symmetric stretching of -COO groups [ 27 ]. As a strong peak of TW fiber at 1036 cm − 1 shifted to 1046 cm − 1 indicated that -COH bonds of cellulose was broken to form -COC- bonds due to grafting reaction with carboxylate group of PAA [ 31 , 21 ]. Moreover, the presence of new peaks at 811 cm − 1 to 810 cm − 1 corresponded to -CCC- bonds of crosslinking between PAA and MBA [ 32 ]. SEM was used to examine the morphology SAP, SAPC and SRFH. SEM images in Fig. 6 show the washed TW fibers, which demonstrates the vascular bundle, midrib, vein and mesophyll (spongy) tissue cells (a), vascular bundle of TW grafted onto SRFH in dried condition (b) and swollen SRFH showed the grafting points, open pores and close pores. The pores begin to close as part of water self-releasing process. This process can be divided into bulk release and surface release. Bulk release occurred when the polymeric chains were collapse consequently released water from hydrogel network. Furthermore, surface release occurred when water droplets form on hydrogels surface due to difference in diffusion and nucleation rates [ 33 ]. Figure 7 shows the SEM images of swollen SAPC (a) and, SRFH (b) which identify the mesophyll tissue of TW fiber grafted onto the PAA hydrogel was observed under 1000x magnification. It can clearly see that the pores were connected with the mesophyll tissues, which is proven that the grafting reactions had occurred. Figure 8 shows the hydrogels pores of SAP (a), (b), SAPC (c), (d) and, SRFH (e), (f). The pores size of SRFH is the smallest, followed by SAPC and SAP. These sizes are in line with WAC results in which the lowest WAC is SRFH followed by SAPC and SAP. The images demonstrate that pores are fully open (a), (c) and (e) when the hydrogels are at equilibrium state and the pores start to close (b), (c) and (f) when the hydrogels start to dehydrate. When the hydrogels are in dried state, no pores were observed as shown in Fig. 6 (b). EDX was employed to determine surface elements of TW-g-PAA/NPK SRFH. Figure 8 shows the EDX spectrum of the SRFH. The EDX analysis indicated that the SRFH sample contained nitrogen (N), phosphorus (P), and potassium (K) elements within its composition, suggesting a more effective loading of NPK fertilizer within the hydrogel composite network. Furthermore, intense peaks of carbon (C) and oxygen (O) were detected at 0.2 and 0.5 KeV, respectively, attributed to cellulose and acrylic chains which are the primary constituents of the hydrogels [ 34 ]. Other element detected was natrium (Na) due to sodium hydroxide (neutralization agent), silicon (Si) and titanium (Ti) due to fertilizer residue. 3.3 Swelling ratio (SR), water absorbency capacity (WAC) and re-swelling capability Figure 10 shows the SR of SAP, SAPC and SAPC for 5 hours. The graph demonstrated that the hydrogels absorbed water rapidly at the beginning and increased slowly after 1 hours. The SAP pattern began to flatten after 3 hours, however SAPC and SRFH took 4 hours to level off. This indicated that the hydrogel samples had reached their equilibrium swelling state [ 35 ]. SAP have slightly high affinity network than SAPC and SRFH. The high affinity enables the sample to attain its maximum swelling capacity more rapidly, owing to a high rate of diffusion. The particle sizes and compact structure of SAPC and SRFH make the rate of diffusion become slow. This feature is important for hydrogel to ensure slow release of nutrients and water to plants. Initial swelling is greater because the water penetrates and is absorbed by hydrophilic groups through the establishment of hydrogen bonds. The groups that exists on polymer chains included hydroxyl, carboxyl, amide, sulfonic and amino are responsible for inducing significant swelling in the material. Superabsorbent polymers are bound together by primary (covalent or ionic bonds) and secondary (hydrophilic interactions or hydrogen bonds) forces [ 36 ]. Swelling occurred due to osmotic pressure difference between hydrogels and external solutions. Afterward, the swelling gradually decelerates until it reaches an equilibrium swelling state [ 37 ]. Re-swelling performance indicates the samples’ ability to absorb water after a drought [ 40 ]. Reswelling capacity test of SAP, SRFH and SAPC samples were carried out for 5 cycles to determine WAC values that calculated using Eq. 1. Figure 12 demonstrates that SAPC and SRFH samples have high re-swelling capacity, without substanstial changes in WAC even after five cycles of swelling. In contrast, SAP samples had significant reduction in WAC starting from cycle 1 until cycle 5. The decrease in WAC may be due to the hydrogels’ exposed to water pressure, which lead to partial rupture of polymeric chains and collapsed of pores within hydrogel structures [ 41 ]. Meanwhile, remarkable re-swelling capability of SAPC and SRFH is a result of densely packed hydrogel network that is fortified by the crosslinking effect facilitated by the inclusion of fibers [ 40 ]. The decreasing pattern of WAC values after cycle 4 indicated to loss of gel content because of swelling-heating-swelling cycle [ 35 ]. 3.4 Seeds germination and growth Moisture availability is essential for the successful growth of plants, and insufficient soil moisture frequently poses a challenge, especially in dry and semi-arid regions [ 42 ]. Seeds germination and growth under limited water condition was studied. Figure 13 shows the digital images of seeds germination and growth of mini eggplants after cultivation of 6 weeks in seeding tray (From left to right: blank black soil, SAP, SAPC and SRFH), (a), and pots (From left to right: SAP, SAPC and SRFH), (b). It was observed that mini eggplant seeds with soil treated by SRFH started to germinate on 3rd day, SAPC on 4th day and SAP on 5th day. Unfortunately, seed sown in bare black soil didn’t germinate even after day 7. This might be due to the drought conditions faced by the seed in bare black soil, where all the water dried up from the soil before the seed could germinate. This obviously showed that the developed hydrogels can be effectively utilized in drought prone region. This can be explained by the function of hydrogels as water retaining which provided moisture to soil and water to seeds. The best growth trend of the seeds showed by the seedling with soil treated by SRFH, followed by SAPC and SAP. This is due to the presence of fertilizer in SRFH provided N, P, K to seedling which accelerated the growth. Besides that, the tea waste fiber presence in SAPC and SRFH also provided other nutrients to the seedlings. All the three seedlings well survived without wilting in 7 days without irrigation. The seedlings kept growth in stem high, leaf width and leaf length after 6 weeks of cultivation. This could be attributed to the timely release of fertilizer and water during the growth period. These results demonstrated that TW- g -PAA/NPK efficiently functions as a slow-release fertilizer. 4. Conclusions In summary, three hydrogels were successfully synthesized by grafting TW fibers onto the PAA chains, followed by crosslinking of the grafted chains to form 3D network. The formation of 3D network structures of TW- g -PAA was supported by FTIR and SEM studies. The appearance of peaks at 1046 cm − 1 in FTIR spectra indicated that -COH bond of cellulose was broken to form -COC- bond due to grafting reaction. SEM images showed that SRFH had the smallest pore sizes and compact structures. Moreover, EDX result showed that N, P and K elements had existed in TW- g -PAA/NPK SRFH. Swelling properties results showed that SRFH had the lowest WAC resulting in slowest release rate due to the compact structures and smallest pore sizes. Furthermore, SRFH had no significant change in WAC after 5 cycles of swelling and de-swelling. Moreover, the SRFH had proven to have a beneficial effect on the germination and growth of mini eggplant seeds. This can be concluded that TW- g -PAA/NPK SRFH is an effective approach for biomass waste management and has potential in sustainability and circular economy. Declarations CRediT authorship contribution statement Wan Amirah wan Anuar : Original draft writing, writing review and editing, characterization and analysis. Ros Azlinawati Ramli : Project and topic administration, writing review and editing, supervising, investigation and analysis. Yuen Mei Lian : Investigation, writing review and editing. Rodziah Nazlan : Characterizations and analysis. Tan Suat Hian : Investigation, writing review and editing; Rasidi Roslan : Characterizations and analysis. Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have influenced the work reported in this paper. Author Contribution Wan Amirah wan Anuar: Original draft writing, writing review and editing, characterization and analysis. Ros Azlinawati Ramli: Project and topic administration, writing review and editing, supervising, investigation and analysis. Yuen Mei Lian: Investigation, writing review and editing. Rodziah Nazlan: Characterizations and analysis. Tan Suat Hian: Investigation, writing review and editing; Rasidi Roslan: Characterizations and analysis. 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Adv Funct Mater 34(19):2313881 Rop K, Mbui D, Karuku GN, Michira I, Njomo N (2020) Characterization of water hyacinth cellulose-g-poly (ammonium acrylate-co-acrylic acid)/nano-hydroxyapatite polymer hydrogel composite for potential agricultural application. Results Chem 2:100020 Laftah W, Hashim S (2014) Synthesis, optimization, characterization, and potential agricultural application of polymer hydrogel composites based on cotton microfiber. Chem Pap 68(6):798–808 Prasad C, Park SY, Lee JS, Park JJ, Jang Y, Lee SW, Lee B-M, Nam Y-R, Rao AK, Choi HY (2023) Modeling and investigation of swelling kinetics of sodium carboxymethyl cellulose/starch/citric acid superabsorbent polymer. Int J Biol Macromol 253:127013 Abd El-Mohdy H, Abd El-Rehim H (2009) Radiation synthesis of kappa-carrageenan/acrylamide graft copolymers as superabsorbents and their possible applications. J Polym Res 16:63–72 Wu L, Liu M (2008) Preparation and properties of chitosan-coated NPK compound fertilizer with controlled-release and water-retention. Carbohydr Polym 72(2):240–247 Kabiri K, Mirzadeh H, Zohuriaan-Mehr MJ, Daliri M (2009) Chitosan‐modified nanoclay–poly (AMPS) nanocomposite hydrogels with improved gel strength. Polym Int 58(11):1252–1259 Lu K, Abouzeid R, Wu Q, Chen Q, Liu S (2024) Hydrogel Nanocomposite Based Slow-Release Urea Fertilizer: Formulation, Structure, and Release Behavior. Giant:100270 Xu T, Wang J, Zhao S, Chen D, Zhang H, Fang Y, Kong N, Zhou Z, Li W, Wang H (2023) Accelerating the prediction and discovery of peptide hydrogels with human-in-the-loop. Nat Commun 14(1):3880 KP AA, Saeed P, Manholi S, Sujith A (2024) Polyvinyl alcohol-soy protein isolate hydrogels: Controlled release of fertilizer and matrix nutrients for sustainable agriculture. J Clean Prod 451:141827 Additional Declarations No competing interests reported. Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. 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-5394710","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":376495878,"identity":"8e6583a4-d1e0-4686-8797-afe607ed4c3f","order_by":0,"name":"Wan Amirah Najwa Wan Anuar","email":"","orcid":"","institution":"Universiti Malaysia Pahang Al-Sultan Abdullah","correspondingAuthor":false,"prefix":"","firstName":"Wan","middleName":"Amirah Najwa Wan","lastName":"Anuar","suffix":""},{"id":376495882,"identity":"9637ba39-bb9c-42e8-b095-7b15d64e2368","order_by":1,"name":"Ros Azlinawati Ramli","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA+ElEQVRIiWNgGAWjYFAC5oYDEJr5AEzIgIAWRogWHma2BOK1gCkeBh64Svxa+PsPNh4uqDksb8/O803q5o46eQb25m0SjDmHcWqROHCw4fCMY4cNe5h5t0nnnjls2MBzrEyCcRtuLQwHGxsO87DdZoRoaTvA2CCRY4ZXi/xhRqCWf7fte5h5ngG11Nk3yL/Br8XgGFALb9vtRKAWNqAW5sQGCR78WgzPgLT0/U/uOcxmbA30S3IbT1qxReK2dJxa5M4fPvyZ51uabXv/4Ye3c3fU2fazH9544+M2a9zeRwGgOGIDMRIYmknQAgV1RGoZBaNgFIyCEQAA1rBVwyJcGxAAAAAASUVORK5CYII=","orcid":"","institution":"Universiti Malaysia Pahang Al-Sultan Abdullah","correspondingAuthor":true,"prefix":"","firstName":"Ros","middleName":"Azlinawati","lastName":"Ramli","suffix":""},{"id":376495884,"identity":"939b1831-8319-4698-b5be-c7086960c0fb","order_by":2,"name":"Mei Lian Yuen","email":"","orcid":"","institution":"Universiti Malaysia Pahang Al-Sultan Abdullah","correspondingAuthor":false,"prefix":"","firstName":"Mei","middleName":"Lian","lastName":"Yuen","suffix":""},{"id":376495886,"identity":"e30044a6-8699-4969-b558-2a9d6832aab9","order_by":3,"name":"Rodziah Nazlan","email":"","orcid":"","institution":"Universiti Malaysia Pahang Al-Sultan Abdullah","correspondingAuthor":false,"prefix":"","firstName":"Rodziah","middleName":"","lastName":"Nazlan","suffix":""},{"id":376495888,"identity":"c8365416-8055-4dd6-b609-bcc7614032e2","order_by":4,"name":"Suat Hian Tan","email":"","orcid":"","institution":"Universiti Malaysia Pahang Al-Sultan Abdullah","correspondingAuthor":false,"prefix":"","firstName":"Suat","middleName":"Hian","lastName":"Tan","suffix":""},{"id":376495891,"identity":"749e02b3-2d77-40cb-9383-320e249ad271","order_by":5,"name":"Rasidi Roslan","email":"","orcid":"","institution":"Universiti Malaysia Pahang Al-Sultan Abdullah","correspondingAuthor":false,"prefix":"","firstName":"Rasidi","middleName":"","lastName":"Roslan","suffix":""}],"badges":[],"createdAt":"2024-11-05 10:53:25","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-5394710/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-5394710/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":71002856,"identity":"392f49f4-c742-46b5-a286-216484597b71","added_by":"auto","created_at":"2024-12-10 06:00:59","extension":"jpg","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":126425,"visible":true,"origin":"","legend":"\u003cp\u003eSolution polymerization of TW-\u003cem\u003eg\u003c/em\u003e-P(AAc)/NPK SRFH.\u003c/p\u003e","description":"","filename":"Picture1.jpg","url":"https://assets-eu.researchsquare.com/files/rs-5394710/v1/b9d3e02a297c396f454c66f7.jpg"},{"id":71002857,"identity":"a6d68d74-6371-42fe-a75e-5d83d170280c","added_by":"auto","created_at":"2024-12-10 06:00:59","extension":"jpg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":107823,"visible":true,"origin":"","legend":"\u003cp\u003eSynthesized hydrogels of SAP (a), SAPC (b) and SRFH (c).\u003c/p\u003e","description":"","filename":"Picture2.jpg","url":"https://assets-eu.researchsquare.com/files/rs-5394710/v1/fbf628f118b8f2425d286e05.jpg"},{"id":71002860,"identity":"1b4d1fb3-cbe0-4cf2-b4f8-79f9c0deb793","added_by":"auto","created_at":"2024-12-10 06:00:59","extension":"jpg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":60473,"visible":true,"origin":"","legend":"\u003cp\u003eProposed mechanism of initiation steps of TW-\u003cem\u003eg\u003c/em\u003e-PAA.\u003c/p\u003e","description":"","filename":"Picture3.jpg","url":"https://assets-eu.researchsquare.com/files/rs-5394710/v1/90dceb4261e2ba3486cc6b62.jpg"},{"id":71002868,"identity":"aa31e6dd-7ec0-45dd-b70a-f2140e81e396","added_by":"auto","created_at":"2024-12-10 06:01:00","extension":"jpg","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":204414,"visible":true,"origin":"","legend":"\u003cp\u003eThe formation of 3D network structure of TW-\u003cem\u003eg\u003c/em\u003e-PAA.\u003c/p\u003e","description":"","filename":"Picture4.jpg","url":"https://assets-eu.researchsquare.com/files/rs-5394710/v1/157fef2cc2f9a7c0bcd0c2b9.jpg"},{"id":71002862,"identity":"3ab56297-a7f2-4587-a4c2-c984b1903e31","added_by":"auto","created_at":"2024-12-10 06:01:00","extension":"jpg","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":155101,"visible":true,"origin":"","legend":"\u003cp\u003eFTIR spectra of washed TW fiber (a), SAP (b), SAPC (c) and SRFH (d).\u003c/p\u003e\n\u003cp\u003eSEM was used to examine the morphology SAP, SAPC and SRFH. SEM images in Figure 6 show the washed TW fibers, which demonstrates the vascular bundle, midrib, vein and mesophyll (spongy) tissue cells (a), vascular bundle of TW grafted onto SRFH in dried condition (b) and swollen SRFH showed the grafting points, open pores and close pores. The pores begin to close as part of water self-releasing process. This process can be divided into bulk release and surface release. Bulk release occurred when the polymeric chains were collapse consequently released water from hydrogel network. Furthermore, surface release occurred when water droplets form on hydrogels surface due to difference in diffusion and nucleation rates [33].\u003c/p\u003e","description":"","filename":"Picture5.jpg","url":"https://assets-eu.researchsquare.com/files/rs-5394710/v1/ac7c69b0692b1c6713226af6.jpg"},{"id":71002865,"identity":"563201f6-4ee2-4db4-8a71-e79dd0161dbd","added_by":"auto","created_at":"2024-12-10 06:01:00","extension":"jpg","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":266430,"visible":true,"origin":"","legend":"\u003cp\u003eSEM images of washed TW fiber (a), vascular bundle of TW grafted onto SRFH (b) and swollen SRFH (c).\u003c/p\u003e","description":"","filename":"Picture6.jpg","url":"https://assets-eu.researchsquare.com/files/rs-5394710/v1/d702efa32adeed4a0978127d.jpg"},{"id":71005131,"identity":"ba5b4cb0-6e2e-4d09-97ef-c0711e419c70","added_by":"auto","created_at":"2024-12-10 06:17:00","extension":"jpg","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":190549,"visible":true,"origin":"","legend":"\u003cp\u003eSEM images of swollen SAPC (a) and SRFH (b) showing that pores was connected to mesophyll tissues.\u003c/p\u003e","description":"","filename":"Picture7.jpg","url":"https://assets-eu.researchsquare.com/files/rs-5394710/v1/df2296fc4db35f32293cef43.jpg"},{"id":71004287,"identity":"d4808da3-9087-4d77-a6fe-a600746ebf13","added_by":"auto","created_at":"2024-12-10 06:09:00","extension":"jpg","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":525370,"visible":true,"origin":"","legend":"\u003cp\u003eSEM images of SAP (a), (b), SAPC (c), (d) and, SRFH (e), (f) showed the pores size of SRFH is the smallest, followed by SAPC and SAP.\u003c/p\u003e","description":"","filename":"Picture8.jpg","url":"https://assets-eu.researchsquare.com/files/rs-5394710/v1/1551b7f32b99cad4f82c096f.jpg"},{"id":71004283,"identity":"e3249482-85d6-40e2-8763-b09bbabbb71a","added_by":"auto","created_at":"2024-12-10 06:08:59","extension":"jpg","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":121348,"visible":true,"origin":"","legend":"\u003cp\u003eEDX spectrum approved the appearance of N, P and K elements in TW-\u003cem\u003eg\u003c/em\u003e-PAA/NPK SRFH.\u003c/p\u003e","description":"","filename":"Picture9.jpg","url":"https://assets-eu.researchsquare.com/files/rs-5394710/v1/b10c1823c639728a85e2e7ba.jpg"},{"id":71002859,"identity":"aff0c2ea-b63c-4493-b797-4e70294813a6","added_by":"auto","created_at":"2024-12-10 06:00:59","extension":"jpg","order_by":10,"title":"Figure 10","display":"","copyAsset":false,"role":"figure","size":60636,"visible":true,"origin":"","legend":"\u003cp\u003eSwelling ratio of SAP, SAPC, and SRFH.\u003c/p\u003e","description":"","filename":"Picture10.jpg","url":"https://assets-eu.researchsquare.com/files/rs-5394710/v1/f6b532234e37e2d3beceb17e.jpg"},{"id":71002867,"identity":"29e98bfb-1138-4a7f-b090-c5bacd3129de","added_by":"auto","created_at":"2024-12-10 06:01:00","extension":"jpg","order_by":11,"title":"Figure 11","display":"","copyAsset":false,"role":"figure","size":231576,"visible":true,"origin":"","legend":"\u003cp\u003eDigital images of 0.5 g dried SAP, SAPC and SRFH samples before (a), (c), (d) and at equilibrium swelling state, (b), (d), (f).\u003c/p\u003e","description":"","filename":"Picture11.jpg","url":"https://assets-eu.researchsquare.com/files/rs-5394710/v1/7f136528e8c98b655c1f2a0e.jpg"},{"id":71004284,"identity":"c7adfbf6-11fd-4565-bbac-0dc7d10183b8","added_by":"auto","created_at":"2024-12-10 06:09:00","extension":"jpg","order_by":12,"title":"Figure 12","display":"","copyAsset":false,"role":"figure","size":270643,"visible":true,"origin":"","legend":"\u003cp\u003eReswelling capacity of SAP, SRFH and SRFH.\u003c/p\u003e","description":"","filename":"Picture12.jpg","url":"https://assets-eu.researchsquare.com/files/rs-5394710/v1/5328f916734d3624f8104cec.jpg"},{"id":71002869,"identity":"96ec2bbb-e303-4549-a864-c2ecd3fff3ed","added_by":"auto","created_at":"2024-12-10 06:01:00","extension":"jpg","order_by":13,"title":"Figure 13","display":"","copyAsset":false,"role":"figure","size":321708,"visible":true,"origin":"","legend":"\u003cp\u003eDigital images of seeds germination and growth of mini eggplants after cultivation of 6 weeks in seeding tray (From left to right: blank black soil, SAP, SAPC and SRFH), (a), and pots (From left to right: SAP, SAPC and SRFH), (b).\u003c/p\u003e","description":"","filename":"Picture13.jpg","url":"https://assets-eu.researchsquare.com/files/rs-5394710/v1/1558d66916463ee3691e2b9c.jpg"},{"id":71214188,"identity":"a60cd06a-39d1-40fd-8a0c-779d42d148c0","added_by":"auto","created_at":"2024-12-12 08:24:27","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":3162114,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-5394710/v1/857f23d7-10d8-424c-ac75-bbbabe6621c9.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Synthesize, swelling and morphological properties of tea wased-based hydrogel as a slow-release NPK fertilizer applied to mini eggplant seeds growth","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eAgriculture is an essential part of economy, but it uses much water, a scarce and precious resource. Adequate irrigation practices and water conservation measures affect plant growth, survival, and productivity. Hydrogel offered solutions to agriculture's water scarcity by increasing soil and water productivity without damaging the environment or natural resources. The inclusion of hydrophilic groups on the polymer chains, such as hydroxyl, carboxyl, and amide, contributes to enhance water absorbent qualities. Plant development primarily depends on fertilizer and water to enhance survival under drought conditions [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e]. As the soil surrounding the root zone of plants dries out, the hydrogel gradually releases water and nutrients to support plant growth [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eA superabsorbent polymer (SAP) is a hydrophilic polymeric material with the ability to absorb high amount of aqueous solutions within their structures. Moreover, SAP is essentially polyelectrolytes with three dimensional (3D) crosslinked structure, where the polymer chains are connected through crosslinking [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e]. Commercial SAP hydrogels available on the global market are non-biodegradable, posing a potential risk of soil pollution and adverse effects on agricultural productivity [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. Conventional SAP for agriculture applications presents several recognized environmental hazards, including non-biodegradability, subpar mechanical properties, and high production costs [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e]. Commercial SAP is resistant to soil microorganisms due to the use of fully synthetic polymer such as polyacrylamide (PAAM) and polyacrylic acid (PAA). As a result, SAP will exhibit low biodegradability and persist in the soil, leading to environmental contamination as they accumulate in the soil [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eMost of hydrogels are soft, weak, brittle, and prone to fracturing under high strains when compared to engineering materials. Numerous investigations on particle hydrogel have been conducted in the past decade to improve the properties. In the meantime, several efforts have focused on superabsorbent polymer composite (SAPC) [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e]. Hydrogels can enhance their properties through copolymerization or the integration of natural fibers. For instance, combining acrylamide (AAm) with cashew gum through copolymerization resulted in a hydrogel exhibiting favorable mechanical characteristics [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eSAPC is a hydrogel that contains natural fibers or inorganic materials and incorporated into SAP through a polymerization technique. Natural fibers are ecologically friendly materials that possess superior qualities compared to synthetic fibers [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]. Natural polymers, found abundantly in nature, offer a means to lower the production expenses of hydrogels while minimizing environmental pollution through the production of polymer-biomass waste. Natural fibers including kenaf, coco peat, sugarcane bagasse, banana peel, hemp, jute, cotton, sisal, flax, corn cob, ramie bast, rice straw and pineapple leaf are reinforced in polymer matrix to achieve target properties such as mechanical, thermal, biodegradability, lower cost and swelling properties. The interaction between synthetic polymers and natural fibers results in biodegradability, low production cost, non-toxicity, improved release rate and plant growth performance [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eTea waste (TW) or leftover tea is an outstanding reservoir of natural fibers suitable for grafting with hydrogels. Tea leaves are plentiful in lignin and holocellulose, which contain carboxyl, phenolic hydroxyl, hydroxyl, oxyl groups and oxygen/heteroatom groups [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e]. TW is primarily a lignocellulosic fibers composed of lignin, hemicellulose, cellulose, polyphenols, tannins and proteins [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e]. As the global demand for tea is rising, the amount of biomass waste generated has increased. Tea consumption was approximated at 6.3\u0026nbsp;million metrics ton in 2020 and is projected to escalate to 7.4\u0026nbsp;million tonnes by 2025 [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e]. TW- based products have found applications across many fields, including wastewater treatment, pharmaceuticals, energy storing system and energy generation [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e]. Therefore, the generation of TW post-consumption has escalated with increasing tea consumption. Debnath et al. have reviewed the potential and sustainable utilization of TW [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e]. However, until now, there have been no studies reporting on the utilization of of TW in hydrogel production.\u003c/p\u003e \u003cp\u003eThe synthesis of hydrogel with fertilizer as slow-release fertilizer has emerged as a promising material to solve the drawbacks of conventional fertilizer by giving nutrients sustainably, reducing nutrients irrigation frequency, and minimizing fertilizer loss rate [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e]. Slow-release fertilizer hydrogels integrate the characteristics of a superabsorbent hydrogel and a fertilizer, enhancing soil quality and improving fertilizer efficiency. Nowadays, the trend of combining fertilizers and superabsorbent hydrogels to regulate water and nutrients within a single system is on the rising trend [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e]. SRFH that is produced from natural fibers and synthetic polymers can be categorized as organic\u0026ndash;organic SRFH, also referred to as combined synthetic-natural SRFH [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eThis study focuses on grafting TW fibers onto PAA chains and incorporation of nutrient in situ to improve swelling, biodegradability and nutrient efficiency of SAP. To the best of my knowledge, this is the first research that reported the use of TW fibers to produce hydrogels.\u003c/p\u003e"},{"header":"2. Material and Method","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1 Material\u003c/h2\u003e \u003cp\u003eGlacial acrylic acid (GAA) was purchased from BASF Petronas, Malaysia, sodium hydroxide (NaOH), 97%, ammonium persulfate (APS), 98%, and \u003cem\u003eN'N\u003c/em\u003e-methylene-\u003cem\u003ebis\u003c/em\u003e-acrylamide (MBA), 99%, were purchased from Merck, Malaysia. Tea powder brand BOH was purchased from Giant supermarket, NPK 15-15-15 brand Behn Meyer was purchased from local store. All chemicals were used as purchased and deionized water was used throughout this experiment.\u003c/p\u003e \u003cp\u003eTea powder was ground to 500 microns and washed with boiling water three times (normal procedure is two time, but three time is needed to simulate the used tea). After washed, the TW fibers were dried drying oven at 50\u0026deg;C until it reached a constant weight. Furthermore, 3.0 wt% of NaOH was dissolved in 15.0 wt% of deionized water. To prepare monomer mixture, added 25.0 wt% of GAA and 0.1 wt% of MBA to the NaOH solution and stirred for 30 minutes. The mixture of fertilizer with TW fibers were prepared by placing 1.3 wt% of NPK fertilizer into certain amount of deionized water and stirring for 30 minutes. After 30 minutes, 1.4 wt% of TW fibers was added to the mixture. To prepare APS solution, 0.2 wt% of APS powder was added to 2.7 wt% of deionized water.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e2.2 Synthesis of Hydrogels\u003c/h2\u003e \u003cp\u003eThe synthesis of TW-\u003cem\u003eg\u003c/em\u003e-PAA/NPK SRFH was performed in a 500 mL jacketed glass reactor, connected with an overhead stirrer, paddle impeller, condenser, and circulating water bath, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. The monomer mixture was added into the reactor, followed by fertilizer mixture with TW fiber. The water bath was set to 70\u0026deg;C, and stirring speed was set to 145 rpm. The prepared APS solution was poured to the reactor once the reactor reached 60\u0026deg;C.\u003c/p\u003e \u003cp\u003eThe APS solution was added to the reactor when the reactor temperature reached 60\u0026deg;C. The mixtures was continuously stirred until it gelled up. A similar procedure was carried out to synthesize PAA SAP and TW-\u003cem\u003eg\u003c/em\u003e-PAA SAPC. TW-\u003cem\u003eg\u003c/em\u003e-PAA SAPC was synthesized in the absence of NPK fertilizer, whereas PAA SAP was synthesized in the absence of TW fiber and NPK fertilizer. The synthesized SAP, SAPC and SRFH were cut into small pieces before being dried in a drying oven at 60\u0026deg;C until a fixed weight achieved. Then, the dried SAP, SAPC and SRFH were grounded to 1.5 mm for characterization and testing.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003e2.3 Characterization of SAP, SAPC and SRFH\u003c/h2\u003e \u003cp\u003eFTIR spectroscopy (Perkin Elmer Spectrum 100) was employed to evaluate the grafting reactions of TW fibers on PAA hydrogel and identify related functional groups that present in SAP, SAPC, SRFH and washed TW fibers. The spectra were recorded at a resolution of 4 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e\u003csub\u003e,\u003c/sub\u003e ranging from 4000 to 500 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e by attenuated total reflectance (ATR) method for hydrogels and potassium bromide (KBR) method for TW fiber.\u003c/p\u003e \u003cp\u003eSEM microscopy (Hitachi TM3030 Plus) equipped with EDX (energy dispersive X-ray) was employed to investigate surface morphology of dried SRFH and TW fiber. Furthermore, another SEM (Carl Zeiss model EVO 50) was used to examine the internal structures of swollen hydrogels samples. Both SEM were operated at 10 kV accelerating voltage.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003e2.4 Swelling ratio (SR), water absorbency capacity (WAC) and re-swelling capability\u003c/h2\u003e \u003cp\u003eThe swelling ratio was used to analyze the absorption tendency and measure the time needed for the hydrogels to reach their equilibrium swelling states. 0.5 g of each dried hydrogels were soaked in 200 g of tap water respectively at room temperature. The swollen samples were passed through sieves to eliminate excess water before being weighed. Swelling ratio (SR) in g/g was calculated for every 1 hour until 5 hours using Eq.\u0026nbsp;1 [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eSR = \u003cspan type=\"Underline\" class=\"Underline\" name=\"Emphasis\"\u003e\u0026#119882;t \u0026ndash; \u0026#119882;0\u003c/span\u003e (1)\u003cdiv class=\"BlockQuote\"\u003e\u003cp\u003e\u0026#119882;\u003csub\u003e0\u003c/sub\u003e\u003c/p\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003eWhere,\u003cdiv class=\"BlockQuote\"\u003e\u003cp\u003eW\u003csub\u003et\u003c/sub\u003e - weight of swollen sample in g\u003c/p\u003e\u003cp\u003eW\u003csub\u003e0\u003c/sub\u003e - weight of dried sample in g\u003c/p\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eSimilar procedure was used to determine the WAC (g/g) and re-swelling capacity of hydrogels. However, WAC was evaluated based on the time required for hydrogel to reach equilibrium swelling state. Moreover, re-swelling capacity was evaluated by calculate the WAC after each cycle using Eq.\u0026nbsp;1.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003e2.5 Seeds growth performance\u003c/h2\u003e \u003cp\u003eMini eggplant seeds were used to evaluate the performance of developed SRFH on the seed\u0026rsquo;s germination and growth under limited water conditions. Swollen SAP, SAPC and SRFH were mixed with black soil in ratio of 1:3 of each. Black soil without hydrogel was used as control.\u003c/p\u003e \u003cp\u003eMini eggplant seeds were sowed in seedling tray before transferred to pots. They were exposed to actual environmental conditions. An equal amount of water was irrigated for every 7 days. The germination and growth performance patterns of all mini eggplant were observed at different time intervals for 6 weeks.\u003c/p\u003e \u003c/div\u003e"},{"header":"3. Results and Discussions","content":"\u003cdiv id=\"Sec9\" class=\"Section2\"\u003e \u003ch2\u003e3.1 Synthesis Reactions\u003c/h2\u003e \u003cp\u003eSRFH, SAPC and SAP were reacted at 70\u0026deg;C temperature and at 145 rpm stirring speed. However, the reaction time (time taken to react completely) of SRFH and SAPC is 20 mins and SAP is 9 mins. The difference in reaction time is due to incorporation of TW fiber into AA hydrogel. According to reaction kinetics, the reaction rate is proportional to concentration of reactants [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e]. The absence of TW fiber in SAP allowed more concentrate AA monomer (reactant) to participate in the polymerization reaction, leading to a faster reaction rate and a shorter reaction time. Figure\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e shows the synthesized hydrogels of SAP (a), SAPC (b) and SRFH (c). The SAP exhibits a clear, colorless gel appearance, while SAPC and SRFH display a brown coloration characteristic of TW fiber.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cdiv id=\"Sec10\" class=\"Section3\"\u003e \u003ch2\u003e3.1.2 Reaction Steps and 3D Netwok Formation\u003c/h2\u003e \u003cp\u003eNeutralization of AA by NaOH had increased hydrophilicity and osmotic pressure of the polymer, thereby enhancing its swelling rate [\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e]. Using APS as initiator, TW fiber was grafted onto PAA chains, followed by crosslinking of the grafted chains to form three-dimensional network (3D). Furthermore, NPK was incorporated into the network and pores to form TW-\u003cem\u003eg\u003c/em\u003e-PAA/NPK.\u003c/p\u003e \u003cp\u003eFree radical polymerization (FRP) of TW-\u003cem\u003eg\u003c/em\u003e-PAA/NPK SRFH consists of initiation, propagation and termination steps. At initiation step, APS initiator dissociated to form two sulfate radicals (primary radicals) followed by association of AA monomer unit to the sulfates radical to form polymer radicals of sodium acrylate as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e. Sequential addition of AA monomer units to the polymer radicals formed growing polymer radicals then grafted with cellulose from TW fiber in propagation step. The propagation will continue until termination and cross-linking steps which is proposed to be by combination of grafted propagated chains. The crosslinking process occurred due to the bridging of the grafted chains by the crosslinker to form 3D network of SAPC and SRFH as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003e3.2 Characterization of SAP, SAPC and SRFH\u003c/h2\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e shows the FTIR spectra of washed TW fiber (a), SAP (b), SAPC (c) and SRFH (d). According to Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e(a), the peak at 3417 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e corresponded to O\u0026ndash;H stretching [\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e] and the peak 2921 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e corresponded to C\u0026thinsp;\u0026minus;\u0026thinsp;H stretching which mainly corresponded to aliphatic -CH\u003csub\u003e2\u003c/sub\u003e- group, 1521 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, 1541 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e -stretching C\u0026thinsp;=\u0026thinsp;N, C\u0026thinsp;=\u0026thinsp;C of lignin, 1036 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e - the extension of C-O, 1652 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e \u0026ndash; C\u0026thinsp;=\u0026thinsp;C aromatized ring stretch by vibrations [\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eThe peak at 1740 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e was assigned o C\u0026thinsp;=\u0026thinsp;O functional group, due to the existence of acetyl ester group that linked to hemicellulose [\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e]. The peak ranging from 1110 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e to 1243 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e was indicative of the carbohydrate glycosidic bond and the glucose ring present in cellulose [\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e]. The band observed at 1036 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e was corresponded to C\u0026thinsp;=\u0026thinsp;O and C\u0026ndash;H stretching within cellulose [\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e]. The peak at 1373 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e was corresponded to bending of C\u0026ndash;H bending within cellulose [\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eIn Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e(b), a distinctive broad absorption peak observed at 3444 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e in FTIR spectra, corresponded to C-H and O-H stretching vibrations present in the AA and MBA (Bora 2022). The peak represents the overlapping of C\u0026thinsp;=\u0026thinsp;O stretching vibration of carboxyl (COOH) groups and N-H bending vibration, occurring at 1635 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e [\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e]. The signal within the range of 1630\u0026ndash;1639 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e was assigned to carbonyl stretching of carboxylic acid group [\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e, \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e(c) and (d) indicated the peaks that observed at 2940 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e to 2936 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e corresponded to the symmetric and asymmetric stretching of C-H bonds founded in AA within the hydrogel structures [\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e]. SAPC and SRFH had a new absorption band observed at 2540 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e corresponded to amide group stretch. The typical peaks of fibers had emerged in SAPC and SRFH in the region at 1550 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e to 1170 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. The peaks observed at 1451 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e to 1450 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e corresponded to methylene -CH\u003csub\u003e2\u003c/sub\u003e vibration in carbonyl and 1248 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e to 1244 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e corresponding to carboxyl in ethers. This is the indication that the cellulose fiber chains have been grafted on the PAA chains of the polymeric network [\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eNew peaks that appeared at 1715 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and 1716 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e in SAPC and SRFH respectively were attributed to stretching vibration peak of C\u0026thinsp;=\u0026thinsp;O, suggesting successful grafting of fiber onto PAA hydrogel [\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e, \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e]. Moreover, the intense bands observed at 1550 cm\u0026thinsp;\u0026minus;\u0026thinsp;1 to 1549 cm\u0026thinsp;\u0026minus;\u0026thinsp;1 were assigned to symmetric and asymmetric stretching modes of carbonyl group in carboxylate group (COO) of the polyacrylate. Additionally, the peaks that observed at 1407 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e to 1405 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e were attributed to symmetric stretching of -COO groups [\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e]. As a strong peak of TW fiber at 1036 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e shifted to 1046 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e indicated that -COH bonds of cellulose was broken to form -COC- bonds due to grafting reaction with carboxylate group of PAA [\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e, \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e]. Moreover, the presence of new peaks at 811 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e to 810 cm\u003csup\u003e\u0026minus;\u003c/sup\u003e1 corresponded to -CCC- bonds of crosslinking between PAA and MBA [\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e].\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eSEM was used to examine the morphology SAP, SAPC and SRFH. SEM images in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e show the washed TW fibers, which demonstrates the vascular bundle, midrib, vein and mesophyll (spongy) tissue cells (a), vascular bundle of TW grafted onto SRFH in dried condition (b) and swollen SRFH showed the grafting points, open pores and close pores. The pores begin to close as part of water self-releasing process. This process can be divided into bulk release and surface release. Bulk release occurred when the polymeric chains were collapse consequently released water from hydrogel network. Furthermore, surface release occurred when water droplets form on hydrogels surface due to difference in diffusion and nucleation rates [\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e].\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e shows the SEM images of swollen SAPC (a) and, SRFH (b) which identify the mesophyll tissue of TW fiber grafted onto the PAA hydrogel was observed under 1000x magnification. It can clearly see that the pores were connected with the mesophyll tissues, which is proven that the grafting reactions had occurred.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e shows the hydrogels pores of SAP (a), (b), SAPC (c), (d) and, SRFH (e), (f). The pores size of SRFH is the smallest, followed by SAPC and SAP. These sizes are in line with WAC results in which the lowest WAC is SRFH followed by SAPC and SAP. The images demonstrate that pores are fully open (a), (c) and (e) when the hydrogels are at equilibrium state and the pores start to close (b), (c) and (f) when the hydrogels start to dehydrate. When the hydrogels are in dried state, no pores were observed as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e (b).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eEDX was employed to determine surface elements of TW-g-PAA/NPK SRFH. Figure\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e shows the EDX spectrum of the SRFH. The EDX analysis indicated that the SRFH sample contained nitrogen (N), phosphorus (P), and potassium (K) elements within its composition, suggesting a more effective loading of NPK fertilizer within the hydrogel composite network. Furthermore, intense peaks of carbon (C) and oxygen (O) were detected at 0.2 and 0.5 KeV, respectively, attributed to cellulose and acrylic chains which are the primary constituents of the hydrogels [\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e]. Other element detected was natrium (Na) due to sodium hydroxide (neutralization agent), silicon (Si) and titanium (Ti) due to fertilizer residue.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec12\" class=\"Section2\"\u003e \u003ch2\u003e3.3 Swelling ratio (SR), water absorbency capacity (WAC) and re-swelling capability\u003c/h2\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003e shows the SR of SAP, SAPC and SAPC for 5 hours. The graph demonstrated that the hydrogels absorbed water rapidly at the beginning and increased slowly after 1 hours. The SAP pattern began to flatten after 3 hours, however SAPC and SRFH took 4 hours to level off. This indicated that the hydrogel samples had reached their equilibrium swelling state [\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e]. SAP have slightly high affinity network than SAPC and SRFH. The high affinity enables the sample to attain its maximum swelling capacity more rapidly, owing to a high rate of diffusion. The particle sizes and compact structure of SAPC and SRFH make the rate of diffusion become slow. This feature is important for hydrogel to ensure slow release of nutrients and water to plants.\u003c/p\u003e \u003cp\u003eInitial swelling is greater because the water penetrates and is absorbed by hydrophilic groups through the establishment of hydrogen bonds. The groups that exists on polymer chains included hydroxyl, carboxyl, amide, sulfonic and amino are responsible for inducing significant swelling in the material. Superabsorbent polymers are bound together by primary (covalent or ionic bonds) and secondary (hydrophilic interactions or hydrogen bonds) forces [\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e]. Swelling occurred due to osmotic pressure difference between hydrogels and external solutions. Afterward, the swelling gradually decelerates until it reaches an equilibrium swelling state [\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e].\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eRe-swelling performance indicates the samples\u0026rsquo; ability to absorb water after a drought [\u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e]. Reswelling capacity test of SAP, SRFH and SAPC samples were carried out for 5 cycles to determine WAC values that calculated using Eq.\u0026nbsp;1. Figure\u0026nbsp;\u003cspan refid=\"Fig12\" class=\"InternalRef\"\u003e12\u003c/span\u003e demonstrates that SAPC and SRFH samples have high re-swelling capacity, without substanstial changes in WAC even after five cycles of swelling. In contrast, SAP samples had significant reduction in WAC starting from cycle 1 until cycle 5. The decrease in WAC may be due to the hydrogels\u0026rsquo; exposed to water pressure, which lead to partial rupture of polymeric chains and collapsed of pores within hydrogel structures [\u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e]. Meanwhile, remarkable re-swelling capability of SAPC and SRFH is a result of densely packed hydrogel network that is fortified by the crosslinking effect facilitated by the inclusion of fibers [\u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e]. The decreasing pattern of WAC values after cycle 4 indicated to loss of gel content because of swelling-heating-swelling cycle [\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e].\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec13\" class=\"Section2\"\u003e \u003ch2\u003e3.4 Seeds germination and growth\u003c/h2\u003e \u003cp\u003eMoisture availability is essential for the successful growth of plants, and insufficient soil moisture frequently poses a challenge, especially in dry and semi-arid regions [\u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e]. Seeds germination and growth under limited water condition was studied. Figure\u0026nbsp;\u003cspan refid=\"Fig13\" class=\"InternalRef\"\u003e13\u003c/span\u003e shows the digital images of seeds germination and growth of mini eggplants after cultivation of 6 weeks in seeding tray (From left to right: blank black soil, SAP, SAPC and SRFH), (a), and pots (From left to right: SAP, SAPC and SRFH), (b). It was observed that mini eggplant seeds with soil treated by SRFH started to germinate on 3rd day, SAPC on 4th day and SAP on 5th day. Unfortunately, seed sown in bare black soil didn\u0026rsquo;t germinate even after day 7. This might be due to the drought conditions faced by the seed in bare black soil, where all the water dried up from the soil before the seed could germinate. This obviously showed that the developed hydrogels can be effectively utilized in drought prone region. This can be explained by the function of hydrogels as water retaining which provided moisture to soil and water to seeds.\u003c/p\u003e \u003cp\u003eThe best growth trend of the seeds showed by the seedling with soil treated by SRFH, followed by SAPC and SAP. This is due to the presence of fertilizer in SRFH provided N, P, K to seedling which accelerated the growth. Besides that, the tea waste fiber presence in SAPC and SRFH also provided other nutrients to the seedlings. All the three seedlings well survived without wilting in 7 days without irrigation. The seedlings kept growth in stem high, leaf width and leaf length after 6 weeks of cultivation. This could be attributed to the timely release of fertilizer and water during the growth period. These results demonstrated that TW-\u003cem\u003eg\u003c/em\u003e-PAA/NPK efficiently functions as a slow-release fertilizer.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e"},{"header":"4. Conclusions","content":"\u003cp\u003eIn summary, three hydrogels were successfully synthesized by grafting TW fibers onto the PAA chains, followed by crosslinking of the grafted chains to form 3D network. The formation of 3D network structures of TW-\u003cem\u003eg\u003c/em\u003e-PAA was supported by FTIR and SEM studies. The appearance of peaks at 1046 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003ein FTIR spectra indicated that -COH bond of cellulose was broken to form -COC- bond due to grafting reaction. SEM images showed that SRFH had the smallest pore sizes and compact structures. Moreover, EDX result showed that N, P and K elements had existed in TW-\u003cem\u003eg\u003c/em\u003e-PAA/NPK SRFH. Swelling properties results showed that SRFH had the lowest WAC resulting in slowest release rate due to the compact structures and smallest pore sizes. Furthermore, SRFH had no significant change in WAC after 5 cycles of swelling and de-swelling. Moreover, the SRFH had proven to have a beneficial effect on the germination and growth of mini eggplant seeds. This can be concluded that TW-\u003cem\u003eg\u003c/em\u003e-PAA/NPK SRFH is an effective approach for biomass waste management and has potential in sustainability and circular economy.\u003c/p\u003e "},{"header":"Declarations","content":"\u003cp\u003e \u003cb\u003eCRediT authorship contribution statement\u003c/b\u003e \u003c/p\u003e \u003cp\u003e \u003cb\u003eWan Amirah wan Anuar\u003c/b\u003e: Original draft writing, writing review and editing, characterization and analysis. \u003cb\u003eRos Azlinawati Ramli\u003c/b\u003e: Project and topic administration, writing review and editing, supervising, investigation and analysis. \u003cb\u003eYuen Mei Lian\u003c/b\u003e: Investigation, writing review and editing. \u003cb\u003eRodziah Nazlan\u003c/b\u003e: Characterizations and analysis. \u003cb\u003eTan Suat Hian\u003c/b\u003e: Investigation, writing review and editing; \u003cb\u003eRasidi Roslan\u003c/b\u003e: Characterizations and analysis.\u003c/p\u003e\u003cp\u003e \u003ch2\u003eDeclaration of Competing Interest\u003c/h2\u003e \u003cp\u003eThe authors declare that they have no known competing financial interests or personal relationships that could have influenced the work reported in this paper.\u003c/p\u003e \u003c/p\u003e\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eWan Amirah wan Anuar: Original draft writing, writing review and editing, characterization and analysis. Ros Azlinawati Ramli: Project and topic administration, writing review and editing, supervising, investigation and analysis. Yuen Mei Lian: Investigation, writing review and editing. Rodziah Nazlan: Characterizations and analysis. Tan Suat Hian: Investigation, writing review and editing; Rasidi Roslan: Characterizations and analysis.\u003c/p\u003e\u003ch2\u003eAcknowledgements\u003c/h2\u003e \u003cp\u003eThe authors would like to thank the Ministry of Higher Education Malaysia for providing financial support under Fundamental Research Grant Scheme (FRGS/1/2023/STG04/UMP/02/1) and Universiti Malaysia Pahang Al-Sultan Abdullah (RDU230137).\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eDas D, Prakash P, Rout PK, Bhaladhare S (2021) Synthesis and characterization of superabsorbent cellulose-based hydrogel for agriculture application. 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J Clean Prod 451:141827\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"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":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"Tea waste, Grafting, Acrylic acid, Crosslinking, Hydrogel, Morphological","lastPublishedDoi":"10.21203/rs.3.rs-5394710/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-5394710/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"Incorporating tea waste (TW) into hydrogel promotes sustainability and supports the principles of circular economy. Tea waste-grafted-polyacrylic acid containing NPK fertilizer (TW-g-PAA/NPK) was developed as potential slow-release fertilizer hydrogel (SRFH). Its properties were compared to those of synthesized PAA superabsorbent polymer (SAP) and TW-g-PAA superabsorbent polymer composite (SAPC). Chemical, morphological and elemental properties of SAP, SAPC and SRFH were analyzed using FTIR spectroscopy, SEM microscopy and SEM-EDX spectrometer. The grafting reactions were proven by the appearance of peaks at 1046 cm-1 in SAPC and SRFH spectra, indicating that -COH bonds of cellulose were broken to form -COC- bonds. SEM images showed that, TW fiber was grafted with PAA hydrogel and SRFH had the smallest pore sizes. Furthermore, EDX images proved the presence of nitrogen (N), phosphorus (P) and potassium (K) elements in SRFH. Swelling properties indicated that SRFH has the lowest WAC, resulting in slowest release rate. Re-swelling performance showed that SRFH and SAPC has no vital change in WAC even after five cycles of swelling. Germination and growth of mini eggplants seeds in black soil treated with SRFH showed faster germination and the best development. The developed TW-g-PAA/NPK provide an innovative approach as slow-release fertilizer and water retention in agriculture fields.","manuscriptTitle":"Synthesize, swelling and morphological properties of tea wased-based hydrogel as a slow-release NPK fertilizer applied to mini eggplant seeds growth","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-12-10 06:00:55","doi":"10.21203/rs.3.rs-5394710/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"8ca62dae-6d58-4afd-aba7-f9d8c5836cf7","owner":[],"postedDate":"December 10th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2024-12-23T11:38:19+00:00","versionOfRecord":[],"versionCreatedAt":"2024-12-10 06:00:55","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-5394710","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-5394710","identity":"rs-5394710","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}