Effect of heat treatment at mild temperatures on the composition and physico-chemical properties of Scots pine resin

Effect of heat treatment at mild temperatures on the composition and physico-chemical properties of Scots pine resin | 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 Effect of heat treatment at mild temperatures on the composition and physico-chemical properties of Scots pine resin Errj Sansonetti, Dace Cirule, Edgars Kuka, Ingeborga Andersone, and 3 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-3897681/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 03 May, 2024 Read the published version in European Journal of Wood and Wood Products → Version 1 posted 8 You are reading this latest preprint version Abstract A major function of resin in trees is to provide defense against external attacks by releasing the resin flow on the attacked or damaged area. Nonetheless, the leakage of the resin on the surface can have a negative aesthetic and economic impact on wood material. The aim of this study was to investigate how heat treatment affects the chemo-physical properties of the resin of Pinus sylvestris L. in order to hinder the exudation on wood surface during service. To reduce the fluidity of the resin, it is necessary to remove the volatile fraction of resin, and several studies have been carried out in this direction, providing useful information about this process. The results from thermal analyses (DSC, TGA) confirmed that heat treatment at mild temperatures, 80 °C, 90 °C and 100 °C, respectively, had a positive effect on increasing the glass transition temperature T g and showed a good correlation between the T g and the residual volatile content. FTIR spectroscopy, before and after heat treatment, did not show major changes in chemical structures, whilst UHPLC-DAD-MS analysis revealed significant differences for the ratios of compounds, which are the result of possible chemical reactions, such as dehydrogenation, oxidation and isomerization. glass transition heat treatment resin modification Scots pine thermal analysis Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 1 Introduction Wood has traditionally been used for structural and decorative purposes both outdoors and indoors. In recent years, interest in wood as a material experiences upspring mainly due to its contribution for reaching sustainability goals. However, there are inherent wood properties that limit its application in certain areas. Some of these properties are typical of wood per se, while others are genus- or species-specific, among which resin exudation is widespread in conifers, including pines (Cao et al. 2022). Scots pine ( Pinus sylvestris L.) is the most widely distributed pine species occurring discontinuously across Eurasia and ranging in altitude from sea level to 2600 m. However, the Scots pine stands, which are economically the most important, occupy boreal forests between 50°N and 65°N. (Auders and Spicer, 2012) In Latvia, Scots pine is the dominant tree species, occupying 32% of the forest area. In addition, the forest regeneration profile confirms that Scots pine will maintain its dominant role in the country’s wood processing sector, revealing the importance of expanding the use of wood for high quality and value products ( http://zalasmajas.lv ). Resin is a secondary metabolite that is a dynamic and complex mixture consisting mainly of terpenoids formed from the fundamental precursor isopentyl diphosphate via complex pathways of biosynthesis (Krokene, 2015; Trapp and Croteau, 2001). The composition of resins differs not only between genera and species but also between constitutive and induced resin, the latter being formed mainly as a response to external disturbance and for syntheses of which reserve carbohydrates are mobilized (Zulak and Bohlmann, 2010; Mengistu et al., 2013; Ferrenberg et al, 2014; Trapp and Croteau, 2001). Resins are located in special resin-storing structures that are intercellular spaces named resin ducts or canals. Resin ducts form a system which consists of complex networks of interconnected axial and radial canals, in which the resin secreted by epithelial cells is stored under pressure (Krokene, 2015). The exudation of resins is a defence strategy adapted by a number of tree genera (Neis et al., 2018). In trees, exudation pressure of resins varies depending on the species, tree properties and environmental conditions, reaching up to 1.2 MPa. (Rissanen et al., 2019). Resins and resin-storing structures are typical for trees of family Pinaceae. However, the resin systems differ between different genera (Wu and Zu, 1997; Rubini et al., 2022). The chemical composition and properties of resins are determined both genetically and environmentally (Liu et al., 2013; Smith, 2000; Verkasalo et al., 2022; Rodriguez et al., 2014). Consequently, considerable variations can exist among trees of the same species, depending on factors such as soil fertility, moisture availability and other key aspects of growth (Rubini et al., 2022; Lai et al., 2020; Knebel et al., 2008). In addition, the concentration of resin components varies within the season and depending on the wood location in a tree (Nerg et al., 1994; Neis et al., 2018; Willfor et al., 2003). Pines are known to have the most highly developed resin canal system among all conifers (Krokene, 2015). Comparing axial and radial resin ducts, the former serves as the largest resin reservoir in pines (Krokene, 2015). Chemically resin components can be divided into volatile and solid fractions with an average mass ratio of 30% and 70%, respectively (Cabaret et al., 2019a). The volatile fraction is a complex blend of terpenoids composed mainly of monoterpens and sesquiterpenes with α-pinene, β-pinene, limonene, camphene and Δ3-carene being the dominant components in pines (Lai et al., 2020; Wiyono et al., 2006). The solid fraction is mainly formed by diterpene based acids (approx. 90%) that forms the rosin (Gaillard et al. 2011). The rosin is composed of abietanes, pimaranes and labdanes types of molecules with acids of abietic and pimaric type dominating in most pine resins (Azemard et al., 2016; Kaitera et al., 2021; Odegaard et al., 2014). Although the resin plays a very important role in the tree’s defence strategy, the softening leading to increase in fluidity due to rise in temperature can cause resin leakage on the surface during the use phase of the wood products. This drawback hinders the wider application of resin containing wood for decorative purposes. Some decline in monoterpene content, which is the key factor influencing resin fluidity, is a part of natural transformation processes taking part in postharvested period (Eberhard et al., 2009). The flowability is also reduced by partial removal of resin’s volatile components together with the water vapour during the drying process of wood materials. Nevertheless, the rise in temperature can still induce resin exudation also from dried wood materials (Cao et al., 2022). Recently research on possibility of adjusting drying regimes to prevent the resin exudation from wood products by fixing them in wood has been carried out for maritime pine and unidentified mixture of resin (Cabaret et al., 2019b; Cabaret et al., 2019c; Cao et al., 2022). However, due to variation in the resin composition between pine species, the results cannot be directly applied for other species. In our previous study, we evaluated the effect of heat treatment in relatively broad interval of temperatures to assess the overall tendency of induced changes on naturally dried pine resin obtained in post harvested period (Sansonetti et al. 2023). The aim of the present study was to investigate the effect of heat treatment on the properties of Scots pine resin, in order to determine the optimal treatment temperatures that could be applied (localised heat treatment, surface treatment etc.) for reducing exudation risk in wood products. 2 Materials and methods 2.1 Resin harvesting and heat treatment Scots pine ( Pinus sylvestris L.) resin samples were harvested in a forest in Latvia during the summer period. Incisions were made at breast height on six pines, going from the bark, to the first layers of the xylem. The exuded resin was accurately removed and collected in plastic test tubes. Resin was washed with acetone, filtered to remove the solid impurities and dried at room temperature till constant mass. The purified resin samples were heat treated at 80°C, 90°C, and 100°C for 24 h in air atmosphere and then analysed. Each sample was labelled according to its treatment: Control (untreated resin), and R_80, R_90 and R_100 for each treatment temperature, respectively. 2.2 UV-Vis spectroscopy 20 ml of solution for each resin samples having a concentration of 0.1 g/L in pure ethanol 99% were prepared for UV-Vis measurements, to evaluate the concentration of abietanes in resin before and after the heat treatment. The spectrophotomer used was a UV-Vis PerkinElmer Lambda 650, and the absorption was measured in the range of wavelengths 400 − 200 nm. Three measurements were done for each sample. 2.3 UHPLC-DAD-MS Chemical Analysis The resin samples were diluted in water/acetonitrile (50:50 v/v) at a concentration of 2 mg/mL. For UHPLC-DAD-MS analysis, a Waters Acquity H-Class UPLC system with PDA and QDa detectors was used. The column was Waters Acquity BEH C18 UPLC column (50 mm, 2.1 mm, 1.7 µm) at 30°C. The mobile phase with flow rate 0.3 mL/min consisted of water with 0.2% formic acid and acetonitrile gradient: the method started with 75% acetonitrile maintained for 0.2 min, then increased to 85% at 1.5 min, maintained so till 2.0 min, then increased to 100% at 3.5 min. The initial composition was then returned and the column was stabilised till total run time of 7.0 min. The injection volume was 5 µL. The eluted resin components were detected with UV measurements at 244 nm. Single quadrupole MS detection was carried out in negative ESI (5 V cone voltage), and positive ESI (15 V cone voltage) in 100–500 Da range. The ionisation of the molecules in the samples was more consistent and intensive in the positive ionisation mode. Single ion recording (SIR) was used to increase the sensitivity for specific ions. 2.4 FTIR spectroscopy analysis The changes in chemical structures and composition were monitored with FTIR spectroscopy before and after heat treatment. The spectrometer was a Thermo Fisher Nicolet iS50 set at a resolution of 4 cm-1 and 32 scans. The FTIR data were collected using the attenuated total reflectance (ATR) technique with diamond crystal. Small amounts of resin were put on the crystal for each measurement. At least three spectra were measured for each sample. 2.5 Differential Scanning Calorimetry (DSC) A Mettler Toledo DSC 823e was used for the DSC. The tested samples weighed about 7 mg; aluminium crucibles were used for the tests. The samples were tested in a nitrogen atmosphere. Each sample was heated from 20°C to 105°C (10°C/min), cooled from 105°C to -100°C (10°C/min), and heated back to 120°C (10°C/min). Glass transition temperature was calculated from the second heating. 2.6 Thermogravimetric analysis (TGA) Residual volatile content (RVC) of resin samples was determined using a TA Instruments Discovery TGA thermogravimetric analyzer and autosampler. The mass of resin samples was around 10 ± 2 mg and the samples were placed on platinum scale pans and initially heated at 30°C for 5 min in a nitrogen atmosphere, before starting the ramp at a rate of 10°C/min from 30°C to 150°C, and then kept at 150°C for 30 min to ensure the removal of volatile content of resin. After the isothermal conditions at 150°C, the samples were heated up to 350°C at the same rate of 10°C/min to observe thermal degradation of resin. Three parallel analyzes were done for each resin sample. The RVC of resin was calculated from the mass loss during the heating ramp and the isothermal stages. 2.7 Principal component analysis FTIR spectra of resin were processed using PCA, which is a multivariate analysis technique used to transform multi-dimensional data into a new coordinate system of uncorrelated latent variables, which are called principal components. The PCA included calculation of covariance matrix from mean centered original data followed by calculation of eigenvalues and eigenvectors of the covariance matrix. The eigenvectors are the principal components (latent variables) of the new coordinate system. The eigenvalues were used to calculate the percent of the total variance explained by each principal component. MATLAB software was used for the data analysis. PCA was used to evaluate variances of the FTIR spectra of resin before and after heat treatment. 3 Results and discussion The UV spectra recorded for solutions with a similar resin concentration (Fig. 1 ) show an increase in the absorption up to 300 nm with increasing treatment temperature of the resin. The peaks at 251 and 244 nm can be assigned to neoabietic and abietic acid, respectively (Kersten et al., 2006). The increase in the relative content of abietanes in resin well demonstrates the removal of volatiles during mild heat treatment. The heat treatment at 100°C was the most effective among the studied temperatures showing the highest increase in abietanes, which are the main non-volatile components of resin. In the case of 80°C and 90°C, the absorption was almost the same, showing that no significant differences in removal of volatiles took place in this range of temperatures. More detailed information about the changes in resin can be obtained by performing thermal analyses. In Fig. 2 , DSC curves with corresponding 1st derivatives (Fig. 2 a) and T g (Fig. 2 b) are presented for the resin samples before and after the heat treatment. The temperatures of the inflection point of the DSC curves corresponding to the minimum of the 1st derivatives of the curves are the T g temperatures. It can be seen that the T g after the heat treatment significantly increases compared to the control sample, for which it was found to be about − 13°C. The process is temperature-dependent and a shift of approximately 14°C towards higher T g temperatures was observed rising the heat treatment temperature from 80°C to 100°C. These results agree with the findings of other similar studies indicating the significant effect of the heat treatment parameters (temperature and duration of treatment) on T g (Cabaret et al., 2019a; Sansonetti et al., 2023). Nonetheless, it must be highlighted that the increase of T g is not always positively correlated with the temperature of treatment. In our previous study, we observed that the T g of resin peaked, after which it again decreased by increasing the treatment temperature up to 150°C (Sansonetti et al., 2023). In case of the treatment at 80°C, considerable variation of the T g was observed among replicates, which was much greater than for the samples treated at other two temperatures. Such a high variation could arise from variability of the samples indicating less homogeneity of the material. The narrow range of standard deviation for samples treated at 90°C and 100°C shows a good repeatability of the experiment and a homogeneous composition of the resin after the treatment. The difference in the width of the 1st derivative curves also implies that the treatments at 90°C and 100°C impart resin much more homogeneity compared with the treatment at 80°C. According to Mondal et al. (2012), the increased ‘thermal stability’ of resin has been obtained thanks to the thermally induced reaction among resin components in combination with the evaporation of low molecular weight volatile compounds of resin. This is in agreement also with other similar studies on the properties of resin (Cao et al., 2023). The results of TGA confirmed that there is a correlation between the T g and the RVC after heat treatment. A similar conclusion has been formulated by Cabaret (2019a) regarding the softening temperature of resin treated at different temperatures, highlighting that a correlation between the turpentine content and the softening temperature had been found. In Table 1 , the mass loss during TGA is shown for each sample, corresponding to the RVC of resin before and after the heat treatment. Table 1 Mass loss of resin during TGA heating and isothermal stages for resin samples treated at different temperatures. Sample Mass loss 30–150°C (%) Mass loss 150°C 30 min (%) Total mass loss (%) Control 10.6 ± 1.2 4.1 ± 0.2 14.7 ± 1.0 R_80 2.3 ± 0.1 4.1 ± 1.4 6.4 ± 1.5 R_90 1.9 ± 0.1 3.6 ± 0.3 5.5 ± 0.4 R_100 1.1 ± 0.1 3.5 ± 0.3 4.6 ± 0.4 The TGA results also confirmed the better homogeneity of the resin samples heated at 90°C and 100°C compared to the samples treated at 80°C, for which a greater standard deviation was observed. The mass decrease of resin samples is visible in Fig. 3 a. During the isothermal stage at 150°C, the mass was not changing significantly, indicating that only the volatile fraction of the samples was removed, whilst in the last stage, passing from 150°C to 350°C, reactions of the thermal degradation occurred, leading to complete decomposition of the samples. The total mass loss in Table 1 can be assumed to be the RVC of resin after heat treatment. In Fig. 3 b, a good correlation can be observed between the T g and the RVC of resin, pointing to the importance of volatile fraction on the physico-chemical properties of resin. The FTIR spectra of resin samples in Fig. 4 do not show significant differences among the samples before and after the heat treatment, hence, based only on FTIR analysis, it is difficult to distinguish the changes occurring in the resin during the heat treatment. Typical absorption peaks of resin can be observed around 2900 cm -1 for C-H stretching vibration, the presence of carboxylic acids is explained by a strong stretching vibration of C = O of the carboxylic group at 1690 cm -1 and a smaller peak of stretching vibrations of C = C at 1600 cm -1 . CH 3 bending and rocking correspond to the peaks at 1368 cm -1 and 1450 cm -1 , respectively (Cabaret et al., 2019a). In other researches, some changes in the FTIR spectra have been reported, which demonstrated the chemical changes in resin. One of these changes has been observed for the absorption band in the region of 1100 − 970 cm -1 that corresponds to the C-OH vibrations, whose intensity decreased with increase of heat treatment temperature. However, in those studies the temperatures were much higher, namely up to 200°C (Cao et al., 2023; Cabaret, 2019a). In such experimental conditions, this band intensity could be affected due to oxidation, whilst this was not observed in our research. Another unusual result is for the O-H absorption band around 3400 cm-1, which is practically the same before and after heat treatment, in contradiction with other results (Cao et al., 2023; Amiralian et al., 2014), where O-H group stretching has been indicated as one of the typical IR bands revealing chemical changes in the resin. To analyze the FTIR spectra from another perspective, the data were processed using PCA. The results are shown in the score plot for the first two principal components, which explain 93.8% of variance of the analyzed spectra (Fig. 5 ). With the exception of two control samples outliers, the other observations are clustering together, confirming the similarity of the samples with weak differences in spectral data before and after the heat treatment. More detailed information regarding the chemical changes in the composition of resin can be provided by UHPLC-DAD-MS characterization of samples, whose chromatograms are shown in Fig. 6 . The peaks were integrated and the area of some peaks is given in Table 2 . Table 2 . Comparison of some of the peaks areas from UHPLC chromatograms for various resin components before and after the heat treatment. No. t R , min λ max , nm Ions in ESI+, Da Area, relative AU (average ± SD) Control R_80 R_90 R_100 1 0.40-0.65 - 299, 301, 315, 317 367 ± 29 1410 ± 289 1712 ± 178 1648 ± 83 4 0.79 243 301 249 ± 3 570 ± 102 944 ± 86 1198 ± 41 6 1.03 250 315 100 ± 1 76 ± 13 47 ± 10 22 ± 2 7 1.11 244 315 254 ± 1 225 ± 32 195 ± 33 179 ± 4 8 1.31 241 315 222 ± 5 95 ± 17 31 ± 5 <10 12 1.92 235 301 67 ± 1 58 ± 8 51 ± 6 51 ± 2 13 2.00 234 301 179 ± 2 18 ± 3 18 ± 4 10 ± 3 16 2.36 251 301 7833 ± 63 6510 ± 362 6047 ± 274 5312 ± 204 17, 18 2.41-2.46 270 303 10267 ± 43 8336 ± 210 8567 ± 211 8310 ± 349 The peaks 16, 17 and 18 correspond to the compounds having the highest concentration in the resin, and considering the natural abundance of the resin acids, the analytes having identical m/z of 303 could be identified as abietic and neoabietic acids, however some other isomer, which eventually was not well resolved at the used experimental conditions, could be eluted at the same time, giving place to overlay of the peaks 17 and 18. Both abietic and neoabietic acids, give essentially the same response at 244 nm, with little interference from levopimaric and palustric acids (Kersten, 2006), hence two of the detected abietanes can be identified as abietic and neoabietic acids. The main analyte eluted at peak 16 has a m/z of 301, hence it is a dehydrogenated resin acid isomer, which is naturally present in the resin (dehydroabietic acid). The peak areas of these three analytes decreased due to the heat treatment. This confirmed the reactivity of resin acids, which can give place to reactions of isomerization, dehydrogenation or oxidation. The area of the peak 4 increased with temperature of heat treatment, also in this case the m/z is 301, but differently from the peak 16, the concentration of the corresponding analyte increased, and its formation could be either a reaction of dehydrogenation of some of the resin acid or isomerization reaction. Another dehydrogenated compound was detected in the peak 1, having a m/z of 299, in this case the molecule has lost four hydrogen atoms (tetradehydrogenated resin acid), which increased its concentration after the heat treatment, similarly as the other analytes which were the firsts to be eluted, but could not be identified and separated. The oxidized forms detected in the chromatogram correspond to the peaks 1, 6, 7 and 8 (m/z 315), and their concentration was very low and tended to decrease, with the exception of the peak 1. One of the possible oxidized resin components could be 7-oxo-dehydroabietic acid (Pastorova et al., 1997). No reaction of decarboxylation was detected through the mass spectrometry. 4 Conclusion The pine ( Pinus sylvestris L.) resin was heated at mild temperatures. Significant changes in the physico-chemical properties were found after treatment of resin in a relatively narrow range of temperatures. The heat treatment had a positive effect on increasing the glass transition temperature T g of the resin and the residual volatile content of the resin had strong negative correlation with the T g values. The heat treatment in presence of air promoted oxidation, isomerization and dehydrogenation of resin acids, as revealed by UHPLC-DAD-MS analyses. These chemical transformations were not identified in the FTIR spectra. Further analysis of the morphological properties and chemical changes are necessary to better understand their influence on the physico-chemical changes after heat treatment. Declarations Author Contribution D.C. and E.K. wrote introduction. E.S wrote abstract, materials and methods section, results and discussion, conclusions and prepared figures and tables, K.M. and L.V contributed to the experimental section (methods). All authors reviewed the manuscript. Acknowledgements. 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Cite Share Download PDF Status: Published Journal Publication published 03 May, 2024 Read the published version in European Journal of Wood and Wood Products → Version 1 posted Editorial decision: Revision requested 22 Mar, 2024 Reviews received at journal 29 Feb, 2024 Reviewers agreed at journal 23 Feb, 2024 Reviewers agreed at journal 20 Feb, 2024 Reviewers invited by journal 08 Feb, 2024 Editor assigned by journal 08 Feb, 2024 Submission checks completed at journal 27 Jan, 2024 First submitted to journal 25 Jan, 2024 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. 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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-3897681","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":269605636,"identity":"3714e550-a757-4c68-b32a-924cb02d9238","order_by":0,"name":"Errj Sansonetti","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA8klEQVRIiWNgGAWjYJACAyS2hJwED2MDwwOitRxIkDAGa0kg2r4DCQyJM3iADHxa+KXPPihg+GOXJ9/ee/Dxxx8W6TN7DjcwJLbh1iLZl25gwNiWXGxw5lyyAdBhubN5G/FrMTjDxmDA2MCcuEEix0wCpGUeP8gvZ3BrsQdpYfhTnzh/Ro75D6CWdDlCWgx4QFrYDic23MgxA4VYgjTIYQkVuLVIgGxJbDueuOHMGWOJM2kShjN7DjYcwKeFv4eNzeDDn+rE+e09hh8qbOrkJc6kP3zwwQC3FiBgM0hAFzqAVwMDA/MDAgpGwSgYBaNgpAMAjwJOl/MhHrQAAAAASUVORK5CYII=","orcid":"","institution":"Latvian State Institute of Wood Chemistry","correspondingAuthor":true,"prefix":"","firstName":"Errj","middleName":"","lastName":"Sansonetti","suffix":""},{"id":269605637,"identity":"c91ad052-a3ab-4b5e-b0db-7c57e2090b1a","order_by":1,"name":"Dace Cirule","email":"","orcid":"","institution":"Latvian State Institute of Wood Chemistry","correspondingAuthor":false,"prefix":"","firstName":"Dace","middleName":"","lastName":"Cirule","suffix":""},{"id":269605638,"identity":"1ff4607e-e96d-4440-9bb3-6265eb4018f4","order_by":2,"name":"Edgars Kuka","email":"","orcid":"","institution":"Latvian State Institute of Wood Chemistry","correspondingAuthor":false,"prefix":"","firstName":"Edgars","middleName":"","lastName":"Kuka","suffix":""},{"id":269605639,"identity":"588508b1-75e5-44e4-92c8-dbebcdae4f9b","order_by":3,"name":"Ingeborga Andersone","email":"","orcid":"","institution":"Latvian State Institute of Wood Chemistry","correspondingAuthor":false,"prefix":"","firstName":"Ingeborga","middleName":"","lastName":"Andersone","suffix":""},{"id":269605640,"identity":"0bda02a8-56a2-45fb-87fd-94b35a738428","order_by":4,"name":"Bruno Andersons","email":"","orcid":"","institution":"Latvian State Institute of Wood Chemistry","correspondingAuthor":false,"prefix":"","firstName":"Bruno","middleName":"","lastName":"Andersons","suffix":""},{"id":269605641,"identity":"0f29588a-0a37-4565-86b8-91eacc6368be","order_by":5,"name":"Kristine Meile","email":"","orcid":"","institution":"Latvian State Institute of Wood Chemistry","correspondingAuthor":false,"prefix":"","firstName":"Kristine","middleName":"","lastName":"Meile","suffix":""},{"id":269605642,"identity":"2426607f-a6a9-46b4-bd7a-dc789731b0f0","order_by":6,"name":"Laima Vevere","email":"","orcid":"","institution":"Latvian State Institute of Wood Chemistry","correspondingAuthor":false,"prefix":"","firstName":"Laima","middleName":"","lastName":"Vevere","suffix":""}],"badges":[],"createdAt":"2024-01-25 15:44:22","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-3897681/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-3897681/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1007/s00107-024-02087-x","type":"published","date":"2024-05-03T19:57:48+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":50423701,"identity":"e54d1a0a-19b7-4aee-ba58-8af7466d8d5b","added_by":"auto","created_at":"2024-01-31 10:08:07","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":40154,"visible":true,"origin":"","legend":"\u003cp\u003eUV absorbance of resin solutions in ethanol before and after the heat treatment.\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-3897681/v1/17542c4153398fcfcf38ded1.png"},{"id":50423191,"identity":"246ca53e-f351-4ccf-85bd-383a54c9fa85","added_by":"auto","created_at":"2024-01-31 10:00:07","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":60208,"visible":true,"origin":"","legend":"\u003cp\u003eDSC curves and the corresponding derivatives in function of temperature for the heat treated resin samples (a) and glass transition temperature of resin before and after the heat treatment (b).\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-3897681/v1/c0f7ca9c562cd03ad1a9508a.png"},{"id":50422573,"identity":"6fdedd70-5f83-47ef-85dc-ed9d99a493d5","added_by":"auto","created_at":"2024-01-31 09:52:08","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":46065,"visible":true,"origin":"","legend":"\u003cp\u003eMass percent decrease of resin samples during TGA with the corresponding temperature stages (a) and the correlation between the glass transition temperature and the RVC of resin (b).\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-3897681/v1/6c64937446c08220849653bc.png"},{"id":50422568,"identity":"8770ed93-41b6-4fab-87b3-73f281a26f9f","added_by":"auto","created_at":"2024-01-31 09:52:07","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":40383,"visible":true,"origin":"","legend":"\u003cp\u003eComparison of FTIR spectra of resin before and after heat treatment. The spectra were normalized at 2927 cm\u003csup\u003e-1\u003c/sup\u003e.\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-3897681/v1/fe5584771cc4cb166706d97e.png"},{"id":50422569,"identity":"e99aecc8-9b9e-43ca-82db-bafcbc3d7e24","added_by":"auto","created_at":"2024-01-31 09:52:07","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":22648,"visible":true,"origin":"","legend":"\u003cp\u003eScore plot of the two first components of PCA for the FTIR data of resin before and after heat treatment.\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-3897681/v1/0a10ac181a0f2b9a793948ec.png"},{"id":50422572,"identity":"e049563f-17d0-4974-beb7-722ca891add9","added_by":"auto","created_at":"2024-01-31 09:52:08","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":80134,"visible":true,"origin":"","legend":"\u003cp\u003eComparison of chromatograms of resin samples before and after heat treatment, at 244 nm wavelength.\u003c/p\u003e","description":"","filename":"6.png","url":"https://assets-eu.researchsquare.com/files/rs-3897681/v1/9c6a93f3af71d83b4632ef56.png"},{"id":56042873,"identity":"de3d21cf-38b7-412d-8e75-7ecd188a120a","added_by":"auto","created_at":"2024-05-07 20:08:35","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":730417,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-3897681/v1/dabce1f4-7803-46ef-85b5-ba0edadcc0c2.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Effect of heat treatment at mild temperatures on the composition and physico-chemical properties of Scots pine resin","fulltext":[{"header":"1 Introduction","content":"\u003cp\u003e \u003cdiv class=\"BlockQuote\"\u003e \u003cp\u003eWood has traditionally been used for structural and decorative purposes both outdoors and indoors. In recent years, interest in wood as a material experiences upspring mainly due to its contribution for reaching sustainability goals. However, there are inherent wood properties that limit its application in certain areas. Some of these properties are typical of wood per se, while others are genus- or species-specific, among which resin exudation is widespread in conifers, including pines (Cao et al. 2022). Scots pine (\u003cem\u003ePinus sylvestris\u003c/em\u003e L.) is the most widely distributed pine species occurring discontinuously across Eurasia and ranging in altitude from sea level to 2600 m. However, the Scots pine stands, which are economically the most important, occupy boreal forests between 50\u0026deg;N and 65\u0026deg;N. (Auders and Spicer, 2012) In Latvia, Scots pine is the dominant tree species, occupying 32% of the forest area. In addition, the forest regeneration profile confirms that Scots pine will maintain its dominant role in the country\u0026rsquo;s wood processing sector, revealing the importance of expanding the use of wood for high quality and value products (\u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttp://zalasmajas.lv\u003c/span\u003e\u003cspan address=\"http://zalasmajas.lv\" targettype=\"URL\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eResin is a secondary metabolite that is a dynamic and complex mixture consisting mainly of terpenoids formed from the fundamental precursor isopentyl diphosphate via complex pathways of biosynthesis (Krokene, 2015; Trapp and Croteau, 2001). The composition of resins differs not only between genera and species but also between constitutive and induced resin, the latter being formed mainly as a response to external disturbance and for syntheses of which reserve carbohydrates are mobilized (Zulak and Bohlmann, 2010; Mengistu et al., 2013; Ferrenberg et al, 2014; Trapp and Croteau, 2001).\u003c/p\u003e \u003cp\u003eResins are located in special resin-storing structures that are intercellular spaces named resin ducts or canals. Resin ducts form a system which consists of complex networks of interconnected axial and radial canals, in which the resin secreted by epithelial cells is stored under pressure (Krokene, 2015). The exudation of resins is a defence strategy adapted by a number of tree genera (Neis et al., 2018). In trees, exudation pressure of resins varies depending on the species, tree properties and environmental conditions, reaching up to 1.2 MPa. (Rissanen et al., 2019). Resins and resin-storing structures are typical for trees of family Pinaceae. However, the resin systems differ between different genera (Wu and Zu, 1997; Rubini et al., 2022).\u003c/p\u003e \u003cp\u003eThe chemical composition and properties of resins are determined both genetically and environmentally (Liu et al., 2013; Smith, 2000; Verkasalo et al., 2022; Rodriguez et al., 2014). Consequently, considerable variations can exist among trees of the same species, depending on factors such as soil fertility, moisture availability and other key aspects of growth (Rubini et al., 2022; Lai et al., 2020; Knebel et al., 2008). In addition, the concentration of resin components varies within the season and depending on the wood location in a tree (Nerg et al., 1994; Neis et al., 2018; Willfor et al., 2003). Pines are known to have the most highly developed resin canal system among all conifers (Krokene, 2015). Comparing axial and radial resin ducts, the former serves as the largest resin reservoir in pines (Krokene, 2015).\u003c/p\u003e \u003cp\u003eChemically resin components can be divided into volatile and solid fractions with an average mass ratio of 30% and 70%, respectively (Cabaret et al., 2019a). The volatile fraction is a complex blend of terpenoids composed mainly of monoterpens and sesquiterpenes with α-pinene, β-pinene, limonene, camphene and Δ3-carene being the dominant components in pines (Lai et al., 2020; Wiyono et al., 2006). The solid fraction is mainly formed by diterpene based acids (approx. 90%) that forms the rosin (Gaillard et al. 2011). The rosin is composed of abietanes, pimaranes and labdanes types of molecules with acids of abietic and pimaric type dominating in most pine resins (Azemard et al., 2016; Kaitera et al., 2021; Odegaard et al., 2014).\u003c/p\u003e \u003cp\u003eAlthough the resin plays a very important role in the tree\u0026rsquo;s defence strategy, the softening leading to increase in fluidity due to rise in temperature can cause resin leakage on the surface during the use phase of the wood products. This drawback hinders the wider application of resin containing wood for decorative purposes. Some decline in monoterpene content, which is the key factor influencing resin fluidity, is a part of natural transformation processes taking part in postharvested period (Eberhard et al., 2009). The flowability is also reduced by partial removal of resin\u0026rsquo;s volatile components together with the water vapour during the drying process of wood materials. Nevertheless, the rise in temperature can still induce resin exudation also from dried wood materials (Cao et al., 2022).\u003c/p\u003e \u003cp\u003eRecently research on possibility of adjusting drying regimes to prevent the resin exudation from wood products by fixing them in wood has been carried out for maritime pine and unidentified mixture of resin (Cabaret et al., 2019b; Cabaret et al., 2019c; Cao et al., 2022). However, due to variation in the resin composition between pine species, the results cannot be directly applied for other species. In our previous study, we evaluated the effect of heat treatment in relatively broad interval of temperatures to assess the overall tendency of induced changes on naturally dried pine resin obtained in post harvested period (Sansonetti et al. 2023). The aim of the present study was to investigate the effect of heat treatment on the properties of Scots pine resin, in order to determine the optimal treatment temperatures that could be applied (localised heat treatment, surface treatment etc.) for reducing exudation risk in wood products.\u003c/p\u003e \u003c/div\u003e \u003c/p\u003e"},{"header":"2 Materials and methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1 Resin harvesting and heat treatment\u003c/h2\u003e \u003cp\u003e \u003cdiv class=\"BlockQuote\"\u003e \u003cp\u003eScots pine (\u003cem\u003ePinus sylvestris\u003c/em\u003e L.) resin samples were harvested in a forest in Latvia during the summer period. Incisions were made at breast height on six pines, going from the bark, to the first layers of the xylem. The exuded resin was accurately removed and collected in plastic test tubes. Resin was washed with acetone, filtered to remove the solid impurities and dried at room temperature till constant mass. The purified resin samples were heat treated at 80\u0026deg;C, 90\u0026deg;C, and 100\u0026deg;C for 24 h in air atmosphere and then analysed. Each sample was labelled according to its treatment: Control (untreated resin), and R_80, R_90 and R_100 for each treatment temperature, respectively.\u003c/p\u003e \u003c/div\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e2.2 UV-Vis spectroscopy\u003c/h2\u003e \u003cp\u003e \u003cdiv class=\"BlockQuote\"\u003e \u003cp\u003e20 ml of solution for each resin samples having a concentration of 0.1 g/L in pure ethanol 99% were prepared for UV-Vis measurements, to evaluate the concentration of abietanes in resin before and after the heat treatment. The spectrophotomer used was a UV-Vis PerkinElmer Lambda 650, and the absorption was measured in the range of wavelengths 400\u0026thinsp;\u0026minus;\u0026thinsp;200 nm. Three measurements were done for each sample.\u003c/p\u003e \u003c/div\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003e2.3 UHPLC-DAD-MS Chemical Analysis\u003c/h2\u003e \u003cp\u003e \u003cdiv class=\"BlockQuote\"\u003e \u003cp\u003eThe resin samples were diluted in water/acetonitrile (50:50 v/v) at a concentration of 2 mg/mL. For UHPLC-DAD-MS analysis, a Waters Acquity H-Class UPLC system with PDA and QDa detectors was used. The column was Waters Acquity BEH C18 UPLC column (50 mm, 2.1 mm, 1.7 \u0026micro;m) at 30\u0026deg;C. The mobile phase with flow rate 0.3 mL/min consisted of water with 0.2% formic acid and acetonitrile gradient: the method started with 75% acetonitrile maintained for 0.2 min, then increased to 85% at 1.5 min, maintained so till 2.0 min, then increased to 100% at 3.5 min. The initial composition was then returned and the column was stabilised till total run time of 7.0 min. The injection volume was 5 \u0026micro;L. The eluted resin components were detected with UV measurements at 244 nm. Single quadrupole MS detection was carried out in negative ESI (5 V cone voltage), and positive ESI (15 V cone voltage) in 100\u0026ndash;500 Da range. The ionisation of the molecules in the samples was more consistent and intensive in the positive ionisation mode. Single ion recording (SIR) was used to increase the sensitivity for specific ions.\u003c/p\u003e \u003c/div\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003e2.4 FTIR spectroscopy analysis\u003c/h2\u003e \u003cp\u003e \u003cdiv class=\"BlockQuote\"\u003e \u003cp\u003eThe changes in chemical structures and composition were monitored with FTIR spectroscopy before and after heat treatment. The spectrometer was a Thermo Fisher Nicolet iS50 set at a resolution of 4 cm-1 and 32 scans. The FTIR data were collected using the attenuated total reflectance (ATR) technique with diamond crystal. Small amounts of resin were put on the crystal for each measurement. At least three spectra were measured for each sample.\u003c/p\u003e \u003c/div\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003e2.5 Differential Scanning Calorimetry (DSC)\u003c/h2\u003e \u003cp\u003e \u003cdiv class=\"BlockQuote\"\u003e \u003cp\u003eA Mettler Toledo DSC 823e was used for the DSC. The tested samples weighed about 7 mg; aluminium crucibles were used for the tests. The samples were tested in a nitrogen atmosphere. Each sample was heated from 20\u0026deg;C to 105\u0026deg;C (10\u0026deg;C/min), cooled from 105\u0026deg;C to -100\u0026deg;C (10\u0026deg;C/min), and heated back to 120\u0026deg;C (10\u0026deg;C/min). Glass transition temperature was calculated from the second heating.\u003c/p\u003e \u003c/div\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003e2.6 Thermogravimetric analysis (TGA)\u003c/h2\u003e \u003cp\u003e \u003cdiv class=\"BlockQuote\"\u003e \u003cp\u003eResidual volatile content (RVC) of resin samples was determined using a TA Instruments Discovery TGA thermogravimetric analyzer and autosampler. The mass of resin samples was around 10\u0026thinsp;\u0026plusmn;\u0026thinsp;2 mg and the samples were placed on platinum scale pans and initially heated at 30\u0026deg;C for 5 min in a nitrogen atmosphere, before starting the ramp at a rate of 10\u0026deg;C/min from 30\u0026deg;C to 150\u0026deg;C, and then kept at 150\u0026deg;C for 30 min to ensure the removal of volatile content of resin. After the isothermal conditions at 150\u0026deg;C, the samples were heated up to 350\u0026deg;C at the same rate of 10\u0026deg;C/min to observe thermal degradation of resin. Three parallel analyzes were done for each resin sample. The RVC of resin was calculated from the mass loss during the heating ramp and the isothermal stages.\u003c/p\u003e \u003c/div\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec9\" class=\"Section2\"\u003e \u003ch2\u003e2.7 Principal component analysis\u003c/h2\u003e \u003cp\u003e \u003cdiv class=\"BlockQuote\"\u003e \u003cp\u003eFTIR spectra of resin were processed using PCA, which is a multivariate analysis technique used to transform multi-dimensional data into a new coordinate system of uncorrelated latent variables, which are called principal components. The PCA included calculation of covariance matrix from mean centered original data followed by calculation of eigenvalues and eigenvectors of the covariance matrix. The eigenvectors are the principal components (latent variables) of the new coordinate system. The eigenvalues were used to calculate the percent of the total variance explained by each principal component. MATLAB software was used for the data analysis. PCA was used to evaluate variances of the FTIR spectra of resin before and after heat treatment.\u003c/p\u003e \u003c/div\u003e \u003c/p\u003e \u003c/div\u003e"},{"header":"3 Results and discussion","content":"\u003cdiv class=\"BlockQuote\"\u003e\n \u003cp\u003eThe UV spectra recorded for solutions with a similar resin concentration (Fig. \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e) show an increase in the absorption up to 300 nm with increasing treatment temperature of the resin. The peaks at 251 and 244 nm can be assigned to neoabietic and abietic acid, respectively (Kersten et al., 2006). The increase in the relative content of abietanes in resin well demonstrates the removal of volatiles during mild heat treatment. The heat treatment at 100\u0026deg;C was the most effective among the studied temperatures showing the highest increase in abietanes, which are the main non-volatile components of resin. In the case of 80\u0026deg;C and 90\u0026deg;C, the absorption was almost the same, showing that no significant differences in removal of volatiles took place in this range of temperatures.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv class=\"BlockQuote\"\u003e\n \u003cp\u003eMore detailed information about the changes in resin can be obtained by performing thermal analyses. In Fig. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e, DSC curves with corresponding 1st derivatives (Fig. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003ea) and \u003cem\u003eT\u003c/em\u003e\u003csub\u003e\u003cem\u003eg\u003c/em\u003e\u003c/sub\u003e (Fig. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003eb) are presented for the resin samples before and after the heat treatment. The temperatures of the inflection point of the DSC curves corresponding to the minimum of the 1st derivatives of the curves are the \u003cem\u003eT\u003c/em\u003e\u003csub\u003e\u003cem\u003eg\u003c/em\u003e\u003c/sub\u003e temperatures. It can be seen that the \u003cem\u003eT\u003c/em\u003e\u003csub\u003e\u003cem\u003eg\u003c/em\u003e\u003c/sub\u003e after the heat treatment significantly increases compared to the control sample, for which it was found to be about \u0026minus;\u0026thinsp;13\u0026deg;C. The process is temperature-dependent and a shift of approximately 14\u0026deg;C towards higher \u003cem\u003eT\u003c/em\u003e\u003csub\u003e\u003cem\u003eg\u003c/em\u003e\u003c/sub\u003e temperatures was observed rising the heat treatment temperature from 80\u0026deg;C to 100\u0026deg;C. These results agree with the findings of other similar studies indicating the significant effect of the heat treatment parameters (temperature and duration of treatment) on \u003cem\u003eT\u003c/em\u003e\u003csub\u003e\u003cem\u003eg\u003c/em\u003e\u003c/sub\u003e (Cabaret et al., 2019a; Sansonetti et al., 2023). Nonetheless, it must be highlighted that the increase of \u003cem\u003eT\u003c/em\u003e\u003csub\u003e\u003cem\u003eg\u003c/em\u003e\u003c/sub\u003e is not always positively correlated with the temperature of treatment. In our previous study, we observed that the \u003cem\u003eT\u003c/em\u003e\u003csub\u003e\u003cem\u003eg\u003c/em\u003e\u003c/sub\u003e of resin peaked, after which it again decreased by increasing the treatment temperature up to 150\u0026deg;C (Sansonetti et al., 2023). In case of the treatment at 80\u0026deg;C, considerable variation of the \u003cem\u003eT\u003c/em\u003e\u003csub\u003e\u003cem\u003eg\u003c/em\u003e\u003c/sub\u003e was observed among replicates, which was much greater than for the samples treated at other two temperatures. Such a high variation could arise from variability of the samples indicating less homogeneity of the material. The narrow range of standard deviation for samples treated at 90\u0026deg;C and 100\u0026deg;C shows a good repeatability of the experiment and a homogeneous composition of the resin after the treatment. The difference in the width of the 1st derivative curves also implies that the treatments at 90\u0026deg;C and 100\u0026deg;C impart resin much more homogeneity compared with the treatment at 80\u0026deg;C. According to Mondal et al. (2012), the increased \u0026lsquo;thermal stability\u0026rsquo; of resin has been obtained thanks to the thermally induced reaction among resin components in combination with the evaporation of low molecular weight volatile compounds of resin. This is in agreement also with other similar studies on the properties of resin (Cao et al., 2023).\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv class=\"BlockQuote\"\u003e\n \u003cp\u003eThe results of TGA confirmed that there is a correlation between the \u003cem\u003eT\u003c/em\u003e\u003csub\u003e\u003cem\u003eg\u003c/em\u003e\u003c/sub\u003e and the RVC after heat treatment. A similar conclusion has been formulated by Cabaret (2019a) regarding the softening temperature of resin treated at different temperatures, highlighting that a correlation between the turpentine content and the softening temperature had been found. In Table\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e, the mass loss during TGA is shown for each sample, corresponding to the RVC of resin before and after the heat treatment.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv class=\"gridtable\"\u003e\u0026nbsp;\u003ctable id=\"Tab1\" border=\"1\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e\n \u003cdiv class=\"CaptionContent\"\u003e\n \u003cp\u003eMass loss of resin during TGA heating and isothermal stages for resin samples treated at different temperatures.\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003ccolgroup cols=\"4\"\u003e\u003c/colgroup\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eSample\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eMass loss\u003c/p\u003e\n \u003cp\u003e30\u0026ndash;150\u0026deg;C (%)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eMass loss\u003c/p\u003e\n \u003cp\u003e150\u0026deg;C 30 min (%)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eTotal\u003c/p\u003e\n \u003cp\u003emass loss (%)\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eControl\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e10.6\u0026thinsp;\u0026plusmn;\u0026thinsp;1.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e4.1\u0026thinsp;\u0026plusmn;\u0026thinsp;0.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e\u003cstrong\u003e14.7\u0026thinsp;\u0026plusmn;\u0026thinsp;1.0\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eR_80\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e2.3\u0026thinsp;\u0026plusmn;\u0026thinsp;0.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e4.1\u0026thinsp;\u0026plusmn;\u0026thinsp;1.4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e\u003cstrong\u003e6.4\u0026thinsp;\u0026plusmn;\u0026thinsp;1.5\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eR_90\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1.9\u0026thinsp;\u0026plusmn;\u0026thinsp;0.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e3.6\u0026thinsp;\u0026plusmn;\u0026thinsp;0.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e\u003cstrong\u003e5.5\u0026thinsp;\u0026plusmn;\u0026thinsp;0.4\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eR_100\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1.1\u0026thinsp;\u0026plusmn;\u0026thinsp;0.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e3.5\u0026thinsp;\u0026plusmn;\u0026thinsp;0.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e\u003cstrong\u003e4.6\u0026thinsp;\u0026plusmn;\u0026thinsp;0.4\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n\u003c/div\u003e\n\u003cdiv class=\"BlockQuote\"\u003e\n \u003cp\u003eThe TGA results also confirmed the better homogeneity of the resin samples heated at 90\u0026deg;C and 100\u0026deg;C compared to the samples treated at 80\u0026deg;C, for which a greater standard deviation was observed. The mass decrease of resin samples is visible in Fig. \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003ea. During the isothermal stage at 150\u0026deg;C, the mass was not changing significantly, indicating that only the volatile fraction of the samples was removed, whilst in the last stage, passing from 150\u0026deg;C to 350\u0026deg;C, reactions of the thermal degradation occurred, leading to complete decomposition of the samples. The total mass loss in Table \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e can be assumed to be the RVC of resin after heat treatment. In Fig. \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003eb, a good correlation can be observed between the \u003cem\u003eT\u003c/em\u003e\u003csub\u003e\u003cem\u003eg\u003c/em\u003e\u003c/sub\u003e and the RVC of resin, pointing to the importance of volatile fraction on the physico-chemical properties of resin.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv class=\"BlockQuote\"\u003e\n \u003cp\u003eThe FTIR spectra of resin samples in Fig. \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e do not show significant differences among the samples before and after the heat treatment, hence, based only on FTIR analysis, it is difficult to distinguish the changes occurring in the resin during the heat treatment. Typical absorption peaks of resin can be observed around 2900 cm\u003csup\u003e-1\u003c/sup\u003e for C-H stretching vibration, the presence of carboxylic acids is explained by a strong stretching vibration of C\u0026thinsp;=\u0026thinsp;O of the carboxylic group at 1690 cm\u003csup\u003e-1\u003c/sup\u003e and a smaller peak of stretching vibrations of C\u0026thinsp;=\u0026thinsp;C at 1600 cm\u003csup\u003e-1\u003c/sup\u003e. CH\u003csub\u003e3\u003c/sub\u003e bending and rocking correspond to the peaks at 1368 cm\u003csup\u003e-1\u003c/sup\u003e and 1450 cm\u003csup\u003e-1\u003c/sup\u003e, respectively (Cabaret et al., 2019a).\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv class=\"BlockQuote\"\u003e\n \u003cp\u003eIn other researches, some changes in the FTIR spectra have been reported, which demonstrated the chemical changes in resin. One of these changes has been observed for the absorption band in the region of 1100\u0026thinsp;\u0026minus;\u0026thinsp;970 cm\u003csup\u003e-1\u003c/sup\u003e that corresponds to the C-OH vibrations, whose intensity decreased with increase of heat treatment temperature. However, in those studies the temperatures were much higher, namely up to 200\u0026deg;C (Cao et al., 2023; Cabaret, 2019a). In such experimental conditions, this band intensity could be affected due to oxidation, whilst this was not observed in our research. Another unusual result is for the O-H absorption band around 3400 cm-1, which is practically the same before and after heat treatment, in contradiction with other results (Cao et al., 2023; Amiralian et al., 2014), where O-H group stretching has been indicated as one of the typical IR bands revealing chemical changes in the resin. To analyze the FTIR spectra from another perspective, the data were processed using PCA. The results are shown in the score plot for the first two principal components, which explain 93.8% of variance of the analyzed spectra (Fig. \u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003e). With the exception of two control samples outliers, the other observations are clustering together, confirming the similarity of the samples with weak differences in spectral data before and after the heat treatment.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv class=\"BlockQuote\"\u003e\n \u003cp\u003eMore detailed information regarding the chemical changes in the composition of resin can be provided by UHPLC-DAD-MS characterization of samples, whose chromatograms are shown in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003e. The peaks were integrated and the area of some peaks is given in Table\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e.\u003c/p\u003e\n\u003c/div\u003e\n\u003cp\u003e\u003cstrong\u003eTable 2\u003c/strong\u003e. Comparison of some of the peaks areas from UHPLC chromatograms for various resin components before and after the heat treatment.\u003c/p\u003e\n\u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\" width=\"519\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd width=\"7.514450867052023%\" rowspan=\"2\"\u003e\n \u003cp\u003e\u003cstrong\u003eNo.\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"10.982658959537572%\" rowspan=\"2\"\u003e\n \u003cp\u003e\u003cstrong\u003et\u003csub\u003eR\u003c/sub\u003e, min\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"10.211946050096339%\" rowspan=\"2\"\u003e\n \u003cp\u003e\u003cstrong\u003e\u0026lambda;\u003csub\u003emax\u003c/sub\u003e, nm\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"13.102119460500964%\" rowspan=\"2\"\u003e\n \u003cp\u003e\u003cstrong\u003eIons in ESI+, Da\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"58.188824662813104%\" colspan=\"4\"\u003e\n \u003cp\u003e\u003cstrong\u003eArea, relative AU (average \u0026plusmn; SD)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"25%\"\u003e\n \u003cp\u003e\u003cstrong\u003eControl\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"25%\"\u003e\n \u003cp\u003e\u003cstrong\u003eR_80\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"25%\"\u003e\n \u003cp\u003e\u003cstrong\u003eR_90\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"25%\"\u003e\n \u003cp\u003e\u003cstrong\u003eR_100\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"7.485604606525912%\"\u003e\n \u003cp\u003e\u003cstrong\u003e1\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"10.940499040307103%\"\u003e\n \u003cp\u003e0.40-0.65\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"10.17274472168906%\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"13.051823416506718%\"\u003e\n \u003cp\u003e299, 301, 315, 317\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"14.587332053742802%\"\u003e\n \u003cp\u003e367 \u0026plusmn; 29\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"14.587332053742802%\"\u003e\n \u003cp\u003e1410 \u0026plusmn; 289\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"14.587332053742802%\"\u003e\n \u003cp\u003e1712 \u0026plusmn; 178\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"14.587332053742802%\"\u003e\n \u003cp\u003e1648 \u0026plusmn; 83\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"7.485604606525912%\"\u003e\n \u003cp\u003e\u003cstrong\u003e4\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"10.940499040307103%\"\u003e\n \u003cp\u003e0.79\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"10.17274472168906%\"\u003e\n \u003cp\u003e243\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"13.051823416506718%\"\u003e\n \u003cp\u003e301\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"14.587332053742802%\"\u003e\n \u003cp\u003e249 \u0026plusmn; 3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"14.587332053742802%\"\u003e\n \u003cp\u003e570 \u0026plusmn; 102\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"14.587332053742802%\"\u003e\n \u003cp\u003e944 \u0026plusmn; 86\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"14.587332053742802%\"\u003e\n \u003cp\u003e1198 \u0026plusmn; 41\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"7.485604606525912%\"\u003e\n \u003cp\u003e\u003cstrong\u003e6\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"10.940499040307103%\"\u003e\n \u003cp\u003e1.03\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"10.17274472168906%\"\u003e\n \u003cp\u003e250\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"13.051823416506718%\"\u003e\n \u003cp\u003e315\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"14.587332053742802%\"\u003e\n \u003cp\u003e100 \u0026plusmn; 1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"14.587332053742802%\"\u003e\n \u003cp\u003e76 \u0026plusmn; 13\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"14.587332053742802%\"\u003e\n \u003cp\u003e47 \u0026plusmn; 10\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"14.587332053742802%\"\u003e\n \u003cp\u003e22 \u0026plusmn; 2\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"7.485604606525912%\"\u003e\n \u003cp\u003e\u003cstrong\u003e7\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"10.940499040307103%\"\u003e\n \u003cp\u003e1.11\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"10.17274472168906%\"\u003e\n \u003cp\u003e244\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"13.051823416506718%\"\u003e\n \u003cp\u003e315\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"14.587332053742802%\"\u003e\n \u003cp\u003e254 \u0026plusmn; 1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"14.587332053742802%\"\u003e\n \u003cp\u003e225 \u0026plusmn; 32\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"14.587332053742802%\"\u003e\n \u003cp\u003e195 \u0026plusmn; 33\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"14.587332053742802%\"\u003e\n \u003cp\u003e179 \u0026plusmn; 4\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"7.485604606525912%\"\u003e\n \u003cp\u003e\u003cstrong\u003e8\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"10.940499040307103%\"\u003e\n \u003cp\u003e1.31\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"10.17274472168906%\"\u003e\n \u003cp\u003e241\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"13.051823416506718%\"\u003e\n \u003cp\u003e315\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"14.587332053742802%\"\u003e\n \u003cp\u003e222 \u0026plusmn; 5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"14.587332053742802%\"\u003e\n \u003cp\u003e95 \u0026plusmn; 17\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"14.587332053742802%\"\u003e\n \u003cp\u003e31 \u0026plusmn; 5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"14.587332053742802%\"\u003e\n \u003cp\u003e\u0026lt;10\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"7.485604606525912%\"\u003e\n \u003cp\u003e\u003cstrong\u003e12\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"10.940499040307103%\"\u003e\n \u003cp\u003e1.92\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"10.17274472168906%\"\u003e\n \u003cp\u003e235\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"13.051823416506718%\"\u003e\n \u003cp\u003e301\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"14.587332053742802%\"\u003e\n \u003cp\u003e67 \u0026plusmn; 1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"14.587332053742802%\"\u003e\n \u003cp\u003e58 \u0026plusmn; 8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"14.587332053742802%\"\u003e\n \u003cp\u003e51 \u0026plusmn; 6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"14.587332053742802%\"\u003e\n \u003cp\u003e51 \u0026plusmn; 2\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"7.485604606525912%\"\u003e\n \u003cp\u003e\u003cstrong\u003e13\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"10.940499040307103%\"\u003e\n \u003cp\u003e2.00\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"10.17274472168906%\"\u003e\n \u003cp\u003e234\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"13.051823416506718%\"\u003e\n \u003cp\u003e301\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"14.587332053742802%\"\u003e\n \u003cp\u003e179 \u0026plusmn; 2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"14.587332053742802%\"\u003e\n \u003cp\u003e18 \u0026plusmn; 3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"14.587332053742802%\"\u003e\n \u003cp\u003e18 \u0026plusmn; 4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"14.587332053742802%\"\u003e\n \u003cp\u003e10 \u0026plusmn; 3\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"7.485604606525912%\"\u003e\n \u003cp\u003e\u003cstrong\u003e16\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"10.940499040307103%\"\u003e\n \u003cp\u003e2.36\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"10.17274472168906%\"\u003e\n \u003cp\u003e251\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"13.051823416506718%\"\u003e\n \u003cp\u003e301\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"14.587332053742802%\"\u003e\n \u003cp\u003e7833 \u0026plusmn; 63\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"14.587332053742802%\"\u003e\n \u003cp\u003e6510 \u0026plusmn; 362\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"14.587332053742802%\"\u003e\n \u003cp\u003e6047 \u0026plusmn; 274\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"14.587332053742802%\"\u003e\n \u003cp\u003e5312 \u0026plusmn; 204\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"7.485604606525912%\"\u003e\n \u003cp\u003e\u003cstrong\u003e17,\u003c/strong\u003e\u003c/p\u003e\n \u003cp\u003e\u003cstrong\u003e18\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"10.940499040307103%\"\u003e\n \u003cp\u003e2.41-2.46\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"10.17274472168906%\"\u003e\n \u003cp\u003e270\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"13.051823416506718%\"\u003e\n \u003cp\u003e303\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"14.587332053742802%\"\u003e\n \u003cp\u003e10267 \u0026plusmn; 43\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"14.587332053742802%\"\u003e\n \u003cp\u003e8336 \u0026plusmn; 210\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"14.587332053742802%\"\u003e\n \u003cp\u003e8567 \u0026plusmn; 211\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"14.587332053742802%\"\u003e\n \u003cp\u003e8310 \u0026plusmn; 349\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cdiv class=\"gridtable\"\u003e\n \u003cdiv align=\"left\" class=\"colspec\"\u003eThe peaks 16, 17 and 18 correspond to the compounds having the highest concentration in the resin, and considering the natural abundance of the resin acids, the analytes having identical m/z of 303 could be identified as abietic and neoabietic acids, however some other isomer, which eventually was not well resolved at the used experimental conditions, could be eluted at the same time, giving place to overlay of the peaks 17 and 18. Both abietic and neoabietic acids, give essentially the same response at 244 nm, with little interference from levopimaric and palustric acids (Kersten, 2006), hence two of the detected abietanes can be identified as abietic and neoabietic acids. The main analyte eluted at peak 16 has a m/z of 301, hence it is a dehydrogenated resin acid isomer, which is naturally present in the resin (dehydroabietic acid). The peak areas of these three analytes decreased due to the heat treatment. This confirmed the reactivity of resin acids, which can give place to reactions of isomerization, dehydrogenation or oxidation. The area of the peak 4 increased with temperature of heat treatment, also in this case the m/z is 301, but differently from the peak 16, the concentration of the corresponding analyte increased, and its formation could be either a reaction of dehydrogenation of some of the resin acid or isomerization reaction. Another dehydrogenated compound was detected in the peak 1, having a m/z of 299, in this case the molecule has lost four hydrogen atoms (tetradehydrogenated resin acid), which increased its concentration after the heat treatment, similarly as the other analytes which were the firsts to be eluted, but could not be identified and separated. The oxidized forms detected in the chromatogram correspond to the peaks 1, 6, 7 and 8 (m/z 315), and their concentration was very low and tended to decrease, with the exception of the peak 1. One of the possible oxidized resin components could be 7-oxo-dehydroabietic acid (Pastorova et al., 1997). No reaction of decarboxylation was detected through the mass spectrometry.\u003c/div\u003e\n\u003c/div\u003e"},{"header":"4 Conclusion","content":"\u003cp\u003e \u003cdiv class=\"BlockQuote\"\u003e \u003cp\u003eThe pine (\u003cem\u003ePinus sylvestris\u003c/em\u003e L.) resin was heated at mild temperatures. Significant changes in the physico-chemical properties were found after treatment of resin in a relatively narrow range of temperatures. The heat treatment had a positive effect on increasing the glass transition temperature \u003cem\u003eT\u003c/em\u003e\u003csub\u003e\u003cem\u003eg\u003c/em\u003e\u003c/sub\u003e of the resin and the residual volatile content of the resin had strong negative correlation with the \u003cem\u003eT\u003c/em\u003e\u003csub\u003e\u003cem\u003eg\u003c/em\u003e\u003c/sub\u003e values. The heat treatment in presence of air promoted oxidation, isomerization and dehydrogenation of resin acids, as revealed by UHPLC-DAD-MS analyses. These chemical transformations were not identified in the FTIR spectra. Further analysis of the morphological properties and chemical changes are necessary to better understand their influence on the physico-chemical changes after heat treatment.\u003c/p\u003e \u003c/div\u003e \u003c/p\u003e"},{"header":"Declarations","content":"\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eD.C. and E.K. wrote introduction. E.S wrote abstract, materials and methods section, results and discussion, conclusions and prepared figures and tables, K.M. and L.V contributed to the experimental section (methods). All authors reviewed the manuscript.\u003c/p\u003e\u003ch2\u003eAcknowledgements.\u003c/h2\u003e \u003cp\u003eThis research was funded by the Latvian State Institute of Wood Chemistry Bio-economy Grant \u0026ldquo;Limitation of pine resin exudation\u0026rdquo; project No. 06\u0026ndash;23.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eCao H, Huang S, Yi S, et al (2023) The effects of superheated steam heat-treatment on turpentine content and softening point of resin. Ind Crops Prod 192:116139. https://doi.org/10.1016/j.indcrop.2022.116139\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eAuders A.G., Spicer D.P. (2012) Encyclopedia of Conifers. 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Forests 13. https://doi.org/10.3390/f13050779\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eRodr\u0026iacute;guez-Garc\u0026iacute;a A, L\u0026oacute;pez R, Mart\u0026iacute;n JA, et al (2014) Resin yield in Pinus pinaster is related to tree dendrometry, stand density and tapping-induced systemic changes in xylem anatomy. For Ecol Manage 313:47\u0026ndash;54. https://doi.org/10.1016/j.foreco.2013.10.038\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLai M, Zhang L, Lei L, et al (2020) Inheritance of resin yield and main resin components in Pinus elliottii Engelm. at three locations in southern China. Ind Crops Prod 144:112065. https://doi.org/10.1016/j.indcrop.2019.112065\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eKnebel L, Robison DJ, Wentworth TR, Klepzig KD (2008) Resin flow responses to fertilization, wounding and fungal inoculation in loblolly pine (Pinus taeda) in North Carolina. Tree Physiol 28:847\u0026ndash;853. https://doi.org/10.1093/treephys/28.6.847\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eNerg A, Kainulainen P, Vuorinen M, et al (1994) Seasonal and geographical variation of terpenes, resin acids and total phenolics in nursery grown seedlings of Scots pine (Pinus sylvestris L.). New Phytol 128:703\u0026ndash;713. https://doi.org/10.1111/j.1469-8137.1994.tb04034.x\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWillf\u0026ouml;r S, Hemming J, Reunanen M, Holmbom B (2003) Phenolic and lipophilic extractives in Scots pine knots and stemwood. Holzforschung 57:359\u0026ndash;372. https://doi.org/10.1515/HF.2003.054\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eCabaret T, Harfouche N, Leroyer L, et al (2019) A study of the physico-chemical properties of dried maritime pine resin to better understand the exudation process. Holzforschung 73:1093\u0026ndash;1102. https://doi.org/10.1515/hf-2018-0264\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWiyono B, Tachibana S, Tinambunan D (2006) Chemical Compositions of Pine Resin, Rosin and Turpentine Oil from West Java. Indones J For Res 3:7\u0026ndash;17. https://doi.org/10.20886/ijfr.2006.3.1.7-17\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eGaillard Y, Mija A, Burr A, et al (2011) Green material composites from renewable resources: Polymorphic transitions and phase diagram of beeswax/rosin resin. Thermochim Acta 521:90\u0026ndash;97. https://doi.org/10.1016/j.tca.2011.04.010\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eAzemard C, Menager M, Vieillescazes C (2016) Analysis of diterpenic compounds by GC-MS/MS: contribution to the identification of main conifer resins. Anal Bioanal Chem 408:6599\u0026ndash;6612. https://doi.org/10.1007/s00216-016-9772-9\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eKaitera J, Piispanen J, Bergmann U (2021) Terpene and resin acid contents in Scots pine stem lesions colonized by the rust fungus Cronartium pini. For Pathol 51:1\u0026ndash;9. https://doi.org/10.1111/efp.12700\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eOdegaard N, Pool M, Bisulca C, et al (2014) Pine Pitch: new treatment protocols for a brittle and crumbly conservation problem. Objects Spec Gr Postprints 21:21\u0026ndash;41\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eEberhardt TL, Sheridan PM, Mahfouz JM (2009) Monoterpene persistence in the sapwood and heartwood of longleaf pine stumps: Assessment of differences in composition and stability under field conditions. Can J For Res 39:1357\u0026ndash;1365. https://doi.org/10.1139/X09-063\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eCabaret T, Gardere Y, Frances M, et al (2019) Measuring interactions between rosin and turpentine during the drying process for a better understanding of exudation in maritime pine wood used as outdoor siding. Ind Crops Prod 130:325\u0026ndash;331. https://doi.org/10.1016/j.indcrop.2018.12.080\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eCabaret T, Mariet F, Li K, et al (2019) High temperature drying effect against resin exudation for maritime pine wood used as outdoor siding. Eur J Wood Wood Prod 77:673\u0026ndash;680. https://doi.org/10.1007/s00107-019-01425-8\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSansonetti E, Cirule D, Kuka E, Meile K (2023) Analysis of Pine Resin Properties as a Way to Understand and Prevent Exudation from Wood Material. Adv Sci Technol 134 AST:21\u0026ndash;28. https://doi.org/10.4028/p-L0uODz\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eKersten PJ, Kopper BJ, Raffa KF, Illman BL (2006) Rapid analysis of abietanes in conifers. J Chem Ecol 32:2679\u0026ndash;2685. https://doi.org/10.1007/s10886-006-9191-z\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eMondal S, Memmott P, Wallis L, Martin D (2012) Physico-thermal properties of spinifex resin bio-polymer. Mater Chem Phys 133:692\u0026ndash;699. https://doi.org/10.1016/j.matchemphys.2012.01.058\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eAmiralian N, Annamalai PK, Fitzgerald C, et al (2014) Optimisation of resin extraction from an Australian arid grass \u0026ldquo;Triodia pungens\u0026rdquo; and its preliminary evaluation as an anti-termite timber coating. Ind Crops Prod 59:241\u0026ndash;247. https://doi.org/10.1016/j.indcrop.2014.04.045\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003ePastorova I, Van Der Berg KJ, Boon JJ, Verhoeven JW (1997) Analysis of oxidised diterpenoid acids using thermally assisted methylation with TMAH. J Anal Appl Pyrolysis 43:41\u0026ndash;57. https://doi.org/10.1016/S0165-2370(97)00058-2\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"european-journal-of-wood-and-wood-products","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"harw","sideBox":"Learn more about [European Journal of Wood and Wood Products](http://link.springer.com/journal/107)","snPcode":"107","submissionUrl":"https://submission.nature.com/new-submission/107/3","title":"European Journal of Wood and Wood Products","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"glass transition, heat treatment, resin modification, Scots pine, thermal analysis","lastPublishedDoi":"10.21203/rs.3.rs-3897681/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-3897681/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eA major function of resin in trees is to provide defense against external attacks by releasing the resin flow on the attacked or damaged area. Nonetheless, the leakage of the resin on the surface can have a negative aesthetic and economic impact on wood material. The aim of this study was to investigate how heat treatment affects the chemo-physical properties of the resin of \u003cem\u003ePinus sylvestris\u003c/em\u003e L. in order to hinder the exudation on wood surface during service. To reduce the fluidity of the resin, it is necessary to remove the volatile fraction of resin, and several studies have been carried out in this direction, providing useful information about this process. The results from thermal analyses (DSC, TGA) confirmed that heat treatment at mild temperatures, 80 °C, 90 °C and 100 °C, respectively, had a positive effect on increasing the glass transition temperature \u003cem\u003eT\u003c/em\u003e\u003csub\u003e\u003cem\u003eg\u003c/em\u003e\u003c/sub\u003e and showed a good correlation between the \u003cem\u003eT\u003c/em\u003e\u003csub\u003e\u003cem\u003eg\u003c/em\u003e\u003c/sub\u003e and the residual volatile content. FTIR spectroscopy, before and after heat treatment, did not show major changes in chemical structures, whilst UHPLC-DAD-MS analysis revealed significant differences for the ratios of compounds, which are the result of possible chemical reactions, such as dehydrogenation, oxidation and isomerization.\u003c/p\u003e","manuscriptTitle":"Effect of heat treatment at mild temperatures on the composition and physico-chemical properties of Scots pine resin","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-01-31 09:52:03","doi":"10.21203/rs.3.rs-3897681/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2024-03-22T09:57:52+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2024-03-01T04:39:42+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"35029a44-063e-436a-94cf-1c25434614ee","date":"2024-02-23T09:19:54+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"680f084d-5ba9-4802-bfa3-5d85cda2d91c","date":"2024-02-20T15:03:52+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2024-02-08T14:43:07+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2024-02-08T14:40:43+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2024-01-27T15:02:25+00:00","index":"","fulltext":""},{"type":"submitted","content":"European Journal of Wood and Wood Products","date":"2024-01-25T15:42:46+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"european-journal-of-wood-and-wood-products","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"harw","sideBox":"Learn more about [European Journal of Wood and Wood Products](http://link.springer.com/journal/107)","snPcode":"107","submissionUrl":"https://submission.nature.com/new-submission/107/3","title":"European Journal of Wood and Wood Products","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"e9c7f174-5758-4663-98a6-cc2e80bcf244","owner":[],"postedDate":"January 31st, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2024-05-07T20:01:59+00:00","versionOfRecord":{"articleIdentity":"rs-3897681","link":"https://doi.org/10.1007/s00107-024-02087-x","journal":{"identity":"european-journal-of-wood-and-wood-products","isVorOnly":false,"title":"European Journal of Wood and Wood Products"},"publishedOn":"2024-05-03 19:57:48","publishedOnDateReadable":"May 3rd, 2024"},"versionCreatedAt":"2024-01-31 09:52:03","video":"","vorDoi":"10.1007/s00107-024-02087-x","vorDoiUrl":"https://doi.org/10.1007/s00107-024-02087-x","workflowStages":[]},"version":"v1","identity":"rs-3897681","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-3897681","identity":"rs-3897681","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}