- Email: [email protected]
Synthesis and characterization of vegetable oil based polyurethanes with tunable thermomechanical performance
Industrial Crops & Products 140 (2019) 111711
Contents lists available at ScienceDirect
Industrial Crops & Products journal homepage: www.elsevier.com/locate/indcrop
Synthesis and characterization of vegetable oil based polyurethanes with tunable thermomechanical performance ⁎
Yingbin Shena,b,f, Jialiang Hec, Zhenxing Xied, Xing Zhoue, Changqing Fange, , Chaoqun Zhangf,
T ⁎
a
Department of Food Science and Engineering, School of Science and Engineering, Jinan University, Guangzhou 510632, Guangdong, China School of Life Sciences, Guangzhou University, Guangzhou 510006, Guangdong, China c School of Food and Bioengineering, Henan University of Science and Technology, Luoyang, Henan 471023, China d Basic School of Medicine, Henan University, Kaifeng 475004, China e Faculty of Printing, Packaging Engineering and Digital Media Technology, Xi’an University of Technology, Xi’an, 710048, China f College of Materials and Energy, South China Agricultural University, Guangzhou 510642, China b
A R T I C LE I N FO
A B S T R A C T
Keywords: Biomass transformation Vegetable oil Polyol Polyurethane Thermomechanical performance
The replacement of petroleum based polymers with the environmental-friendly counterparts derived from renewable resource has received much attention due to the growing concern toward the depletion of the world crude oil stock and environmental problem. In this study, a series of biobased polyurethanes were successfully prepared from polyols obtained by thiol-ene reaction of different plant oils (olive, rice bran, grape seed and linseed oils). Their properties were characterized by dynamic mechanical analysis (DMA), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and tensile test. Their thermomechanical and mechanical properties were compared and discussed to reveal the structure-property relationship. The results show that as the hydroxyl values of the polyols increase, Tgs and tensile strengths of the corresponding polyurethanes increase linearly while the thermal stability decrease. Furthermore, polyurethane from linseed oil had the highest Tg of 65.2 °C and tensile strength of 50.7 MPa. The resulting polyurethane films with tunable thermomechanical performance are promising to find application in coatings, leather, adhesive and so on.
1. Introduction Biobased polymers derived from renewable feedstocks receive more and more attention for their eco-friendly characters, including reducing the consumption of non-renewable sources like petroleum and lowering the greenhouse gas emission (Desroches et al., 2012). The most common used renewable sources are vegetable oils, polysaccharides, lignocellulose and proteins (Zhang et al., 2017). Among them, vegetable oils are one of the most promising candidates to substitute the petroleum derivatives as the monomers of polymers. They are mainly triglycerides of various kinds of fatty acids (Lligadas et al., 2010). Fatty acids are aliphatic carboxylic acids with long carbon chains containing from 8 to 18 carbon atoms and 0˜3 carbon-carbon double bonds, which are determined by the plant type and growth climate of the plants. Specially, some oils inherently possess hydroxyl (castor oil) or epoxy groups (vernonia oil). Multiple functional groups in their structures as mentioned above make them readily modify to the valuable monomers for biobased polymers. Thus, they have been developed into many kinds of polymers from alkyds (Thanamongkollit et al., 2012), vinyl
⁎
resins (Black and Rawlins, 2009) to epoxy resins (Stemmelen et al., 2011) and polyurethanes (Desroches et al., 2011). Of these polymers, polyurethanes (PUs) play the significant role in the modern society for its extensive applications in coatings (Noreen et al., 2016), adhesives (Li et al., 2013), fibers (Demir et al., 2002) and composites (Gupta et al., 2013). Their popularity is based on their excellent properties brought by the unique hydrogen bonding of carbamates, the characteristic bonds of PUs (Li et al., 2009). PUs are obtained by the polyaddition of polyisocyanates and polyols, so properties of PUs could be tuned by changing the type or the molar ratios of these two raw materials (Bhoyate et al., 2018; Blache et al., 2018). Polyisocyanates with rigid ring structure could increase the stiffness of the resulting PUs, thus PUs with diphenylmethane diisocyanate (MDI), toluene diisocyanate (TDI) and isophorone diisocyanate (IPDI) have higher Tgs and tensile strengths than with hexamethylene diisocyanate (HDI) (Javni et al., 2003). Besides, increasing the functional groups number of raw materials could enhance the crosslinking density of the final products, improving the mechanical properties (Lu and Larock, 2008). Finally, the molar ratio of NCO to OH is also the important factor
Corresponding authors. E-mail addresses: [email protected] (C. Fang), [email protected] (C. Zhang).
https://doi.org/10.1016/j.indcrop.2019.111711 Received 28 February 2019; Received in revised form 17 August 2019; Accepted 19 August 2019 0926-6690/ © 2019 Elsevier B.V. All rights reserved.
Industrial Crops & Products 140 (2019) 111711
Y. Shen, et al.
Scheme 1. The representative chemical structures and properties of vegetable oils and the corresponding polyols (Feng et al., 2017; Liang et al., 2018).
(Ionescu et al., 2016). In our previous study, novel biobased polyols were successfully prepared by thiol-ene reaction of soybean oil, and the reaction parameters were optimized for high conversion efficiency and yields (Feng et al., 2017). And the resulting polyurethanes possess the highest elongation at break of 471% and tensile strength of 15.7 MPa. However, to the best of our knowledge, properties of PUs based on these novel polyols from different vegetable oils have not been thoroughly investigated. In this paper, biobased polyurethanes from different vegetable oil based polyols were synthesized and characterized. Their properties were compared and discussed to establish the structure-property relationship. In detail, four biobased polyols from olive, rice bran, grape seed and linseed oil were prepared by thiol-ene reaction and reacted with IPDI to produce a series of bio-based polyurethanes. Their thermomechanical, thermal stability and mechanical properties were characterized by dynamic mechanical analysis (DMA), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and tensile test, respectively. The effect of polyol structure and functionalities on the performance of the resulting PUs was discussed.
to impact the performance of PUs (Chiou and Schoen, 2002). Higher NCO content enhances the rigidity of PUs for the increasing crosslinking density. As limited polyisocyanates are commercially available, polyols from vegetable oils become vital to the properties of biobased PUs. However, because not all vegetable oils inherently bear hydroxyl groups like castor oil, chemical modifications are necessary to transform these renewable sources to valuable polyols. So far, several routes have been successfully developed (Alagi et al., 2018; Kirpluks et al., 2018; Prociak et al., 2018). Dong et al. synthesized three polyols by oxirane ring opening of epoxidized soybean oil with methanol, phenol and cyclohexanol (Ji et al., 2015). The results show that these biobased polyols could partially substitute the petroleum counterparts in the systhesis of polyurethane rigid foams. Dumont et al. prepared ten kinds of polyols from North-American vegetable oils by ozonolysis followed by hydrogenation reaction (Dumont et al., 2013). They found these polyols to bear primary OH groups, which showed high reactivity to the isocyanates. Guo et al. converted the carbon-carbon double bonds of soybean oil to aldehydes through hydroformylation followed by hydrogenation to obtain polyols. The resultant polyurethanes can act as hard rubbers or rigid plastics according to the conversion of polyols. Veronese et al. increased the hydroxyl numbers of the resulting polyols by transesterification of the formiated soy polyol with polyfunctional alcohol (Veronese et al., 2011). The corresponding rigid polyurethane foam had the compression strength around 200 kPa due to the high hydroxyl value of polyols. Recently, an increasing interest has emerged in the application of thiol-ene reaction to transform the renewable vegetable oils into biobased polyols for its virtues of high yields, mild reaction conditions and easy purification (Alagi et al., 2016a, b; Desroches et al., 2011). For example, Ionescu et al. used this reaction to synthesize the high functional castor oil based polyols with hydroxyl value of 286 mg KOH/g
2. Materials and methods 2.1. Materials Linseed oil was purchased from Tianjin Guangfu Fine Chemical Research Institute. Rice bran and grape seed oil were purchased from Jinan Quanrun Rose Product Co., Ltd. Olive oil was purchased from Chengdu Kelong Chemical Reagents Factory. 2-Mercaptoethanol (> 98%) was obtained from Alfa Aesar (China) Chemicals Co., Ltd. 2Hydroxy-2,2-dimethylacetophenone (1173) was supplied by Ryoji Organic Chemical Co., Ltd. Isophorone diisocyanate (IPDI) was obtained from Guangdong Wengjiang Chemical Reagents Co., Ltd. 2
Industrial Crops & Products 140 (2019) 111711
Y. Shen, et al.
(Feng et al., 2017; Liang et al., 2018). The polyurethane films were prepared through the reaction between bio-based polyols and IPDI with molar ratio of 1:1.05. All the films demonstrate good transparency, showing the potential application in coatings (Fig. 1 (a)). The thermomechanical properties for all PU films were characterized by DMA. Thermal stability and mechanical properties of the films were characterized by TGA and tensile testing, respectively. Storage modulus (E´), loss modulus (E") and loss factor of the PU films as functions of temperature from -60 °C to 120 °C are shown in the Fig. 1 (b) and (c). Storage modulus of all the films first slightly declines with the increase of the testing temperature. Once it surpasses a certain temperature, a rapid decrease occurs in E´. At this stage, storage modulus increases with increasing OH number of the polyols from OOP, ROP, GSOP to LOP. Finally, E´curves of all the films demonstrate the rubbery plateau at high temperature. In the curves of loss factor, only one peak was observed, indicating the homogeneous property of PU films. As the hydroxyl values of the polyols increases from OOP, ROP, GSOP to LOP, the peaks of loss factor shift to high temperature and their peak values decline successively. Glass transition temperatures (Tg) were determined by the peak of loss factor curves and summarized in the Table 2. Crosslinking densities (νe) of all the films were calculated from the rubbery moduli according to the kinetic theory of rubber elasticity (Andjelkovic et al., 2005):
Dibutyltin dilaurate (DBTDL) was supplied by Tianjin Fuchen Chemical Reagents Factory. Methyl ethyl ketone was purchased from Tianjin Hongda Chemical Reagents Factory. All materials were used as received without further purification. 2.2. Synthesis of vegetable oil based polyols The thiol-ene reaction of olive, rice bran, grape seed and linseed oil with 2-mercaptoethanol was used to synthesis biobased polyols as previously reported (Feng et al., 2017; Liang et al., 2018). They are identified as OOP, ROP, GSOP and LOP, respectively. The representative chemical structures of vegetable oils and the resulting polyols are shown in Scheme 1. 2.3. Preparation of polyurethanes These novel polyols were mixed with IPDI (5% molar excess) in the presence of DBTDL. The mixtures were first reacted at 60 °C for 1 h with vigorous stirring, and then cast into silicone molds (length × width × thickness: 10 cm × 10 cm × 2 cm) and cured at 85 °C in an oven for 24 h. A small amount of methyl ethyl ketone was added in the mixture before treatment in the oven to remove the trapped air bubbles. The obtained PU films were cut into specific dimensions for thermomechanical and mechanical testing. The recipe composition for the polyurethanes is shown in Table 1.
E´ = 3νeRT´
where T´ is the absolute temperature of films in the rubbery plateau region at Tg +50 °C, and E´ is the corresponding storage modulus at T´. R represents the gas constant. With increasing OH number of the polyols, the crosslinking density of the films increases. Higher cross densities restrict the motion of polymer chain, leading to higher storage modulus and Tg as revealed by DMA (Zhang et al., 2015). DSC is also used to examine the glass transition temperature of all the films, which was determined from the midpoint temperature in the heat capacity change of the DSC scan as shown in Fig. 1(d). Tgs of polyurethanes from DSC and DMA both show the linear relationship with the hydroxyl values of the corresponding polyols as presented in the Fig. 2. With increasing hydroxyl value of polyols, the crosslinking density of PU films increases, leading to the increase of Tgs because of the restriction of molecular chains mobility. This is identical to the reports of Alisa Zlatanic(Zlatanic et al., 2004). The Tgs obtained from DMA are approx. 10–20 °C higher than those measured by DSC because of the different principles underlying these two characterization methods. TGA weight loss and weight loss derivative curves of the PU films are shown in the Fig. 3. According to the weight loss derivative curves, the degradation of the PU films is composed of three stages. The degradation between 200 °C and 330 °C is attributed to decomposition of labile urethane groups into primary amine, secondary amine, olefin and carbon dioxide (Hablot et al., 2008; Javni et al., 2000). As the OH numbers increase from OOP, ROP, GSOP to LOP, the thermal stability of the corresponding PU films decreases due to the increasing urethane contents. The degradation in the range 330˜430 °C was initiated by the chain scission of the vegetable oils. At this stage, all the curves demonstrate the similar trend because of the analogical structure of the triglyceride oils. The degradation of the PU films above 430 °C is corresponding to further thermo-oxidation of the PU films at high temperature. Moreover, temperature of 10% degradation (T10), 50% degradation (T50) and maximum decomposition rates (Tmax) are summarized in the Table 2. According to the T10, T50 and Tmax values, the thermal stability of the PU films decrease with the increase of OH number of the corresponding polyols. The mechanical properties of PU films from different vegetable oilbased polyols were measured by tensile testing. Fig. 4 shows the representative stress-strain curves of PU films which exhibit a broad range of mechanical properties, from soft and rubbery to hard and glassy. PU-
2.4. Characterization Dynamic mechanical analysis (DMA) of PU films (Rectangular specimens of 20 mm × 6 mm × 0.5 mm (length × width × thickness)) was performed with a film-tension mode of 1 Hz using a Netzsch DMA 242C dynamic mechanical analyzer. The samples were cooled and maintained isothermally at -60 °C for 5 min, followed by heating to 125 °C at a rate of 5 °C min−1. The glass transition temperatures (Tgs) of the samples were obtained from the peaks of tan δ curves. Differential scanning calorimetry (DSC) of PU films was measured using a PerkinElmer DSC 6000 thermal analyzer. The following heating programs were conducted on every sample: heating from room temperature to 90 °C at a rate of 20 °C min−1, cooling to -90 °C and holding for 5 min, heating to 90 °C at a rate of 20 °C min−1. 5 mg samples were used for the analysis. Tgs were obtained from the midpoint temperature in the heat capacity change of the second DSC scan. Thermogravimetric analysis (TGA) of the samples was performed on a Netzsch STA 449C thermal analyzer. The samples (approximately 10 mg) were heated from room temperature to 700 °C at a rate of 20 °C min−1 in nitrogen. The tensile properties of samples with size of 50 mm × 10 mm × 0.5 mm (length × width × thickness) were measured by a Shenzhen Suns UTM 5000 universal testing machine with a crosshead speed of 100 mm min−1. Average values of at least three replicates of each sample were taken. 3. Results and discussion Biobased polyols were synthesized by thiol-ene reaction of olive, rice bran, grape seed and linseed oil, and characterized previously Table 1 The recipe composition for the polyurethanes.
PU- OOP PU- ROP PU-GSOP PU-LOP
Polyols (g)
IPDI (g)
2-Hydroxy-2,2-dimethylacetophenone (g)
6 6 6 6
2.37 2.90 3.37 3.81
0.17 0.18 0.19 0.20
(1)
3
Industrial Crops & Products 140 (2019) 111711
Y. Shen, et al.
Fig. 1. (a) The appearance of PU films based on different vegetable oils. Storage modulus (b) and loss factor (c) as the function of temperature for the PU films based on different vegetable oils. (d) DSC curves for the PU films based on different vegetable oils. Table 2 Thermal properties of polyurethanes from different vegetable oil based polyols. DMA Tg (oC)
PU-OOP PU-ROP PU-GSOP PU-LOP
20.6 48.6 55.6 65.2
DSC Tg (oC)
8.7 34.7 42.7 56.9
νe (mol/m3)
208.4 438.7 526.7 674.3
TGA in nitrogen (oC) T10
T50
Tmax(1st/2nd)
293 297 307 299
363 355 359 353
337/417 325/341 321/343 317/345
Fig. 2. Dependence of glass transition temperature of polyurethanes on hydroxyl value of the corresponding polyols. (Hydroxyl values of olive, rice bran, grape seed and linseed oil based polyol are 190 mg KOH/g, 232 mg KOH/g, 270 mg KOH/g, 305 mg KOH/g, respectively).
GSOP and PU-LOP demonstrate the brittle behavior of hard plastic with low elongation at break, and high tensile strengths and Young’s modulus. In contrast, PU-ROP and PU-OOP show typical behavior of
Fig. 3. (a) TGA curves and (b) their derivative curves of polyurethanes from different vegetable oil based polyols.
4
Industrial Crops & Products 140 (2019) 111711
Y. Shen, et al.
et al., 2014). As presented in Fig. 5, tensile strength of the PU films increases linearly with increasing hydroxyl value of the corresponding polyols, while elongation at break displays the exponential reduction. Increasing hydroxyl numbers of the polyols results in an increase in crosslinking densities of the resulting PUs, leading to increase of tensile strength and Young’s modulus, and decrease of elongation at break. 4. Conclusions Four kinds of plant oils including olive, rice bran, grape seed and linseed oil were transformed into polyols by thiol-ene reaction and then reacted with IPDI to prepare bio-based polyurethanes. Tgs and tensile strengths of the resulting PUs increase linearly with the increase of hydroxyl values of the corresponding polyols, while elongation at break decreases exponentially because of the different crosslinking densities. Polyurethane from linseed oil had the highest Tg of 65.2 °C and tensile strength of 50.7 MPa. The thermal stability of the polyurethanes declines with the increase of hydroxyl values of polyols. All the films show excellent thermal stability up to 300 °C. This well-established structureproperty relationship could provide guidance for the design and the practical application of these novel bio-based PUs in the field of coatings, leather, adhesive and so on.
Fig. 4. Stress-strain curves of polyurethanes with different vegetable oil based polyols. Table 3 Mechanical properties of polyurethanes with different vegetable oil based polyols.
PU-OOP PU-ROP PU-GSOP PU-LOP
Tensile strength (MPa)
Elongation at break (%)
Young’s modulus (MPa)
Toughness (MPa)
4.7 ± 0.4 22.6 ± 0.3 37.1 ± 0.6 50.7 ± 2.6
331.5 ± 12.9 56.1 ± 4.3 18.5 ± 3.3 15.1 ± 2.4
1.4 ± 0.1 40.6 ± 3.6 203.9 ± 42.8 342.5 ± 36.2
7.66 10.79 4.94 5.37
Declaration of Competing Interest The authors declare no competing financial interest. Acknowledgements This work was sponsored by the Open Project of Jiangsu Key Laboratory for Biomass Energy and Materials (JSBEM201803), National Natural Science Foundation (No.51703068), the Guangdong Province Science & Technology Program (2017A010103015), Program of the Science and Technology Department of Guangzhou, China (201803020039, 201707010343). References Alagi, P., Choi, Y.J., Hong, S.C., 2016a. Preparation of vegetable oil-based polyols with controlled hydroxyl functionalities for thermoplastic polyurethane. Eur. Polym. J. 78, 46–60. Alagi, P., Choi, Y.J., Seog, J., Hong, S.C., 2016b. Efficient and quantitative chemical transformation of vegetable oils to polyols through a thiol-ene reaction for thermoplastic polyurethanes. Ind. Crops Prod. 87, 78–88. Alagi, P., Ghorpade, R., Jang, J.H., Patil, C., Jirimali, H., Gite, V., Hong, S.C., 2018. Functional soybean oil-based polyols as sustainable feedstocks for polyurethane coatings. Ind Crop Prod 113, 249–258. Andjelkovic, D.D., Valverde, M., Henna, P., Li, F., Larock, R.C., 2005. Novel thermosets prepared by cationic copolymerization of various vegetable oils—synthesis and their structure–property relationships. Polymer 46, 9674–9685. Bhoyate, S., Ionescu, M., Kahol, P.K., Gupta, R.K., 2018. Sustainable flame-retardant polyurethanes using renewable resources. Ind Crop Prod 123, 480–488. Blache, H., Mechin, F., Rousseau, A., Fleury, E., Pascault, J.P., Alcouffe, P., Jacquel, N., Saint-Loup, R., 2018. New bio-based thermoplastic polyurethane elastomers from isosorbide and rapeseed oil derivatives. Ind Crop Prod 121, 303–312. Black, M., Rawlins, J.W., 2009. Thiol–ene UV-curable coatings using vegetable oil macromonomers. Eur. Polym. J. 45, 1433–1441. Chiou, B.-S., Schoen, P.E., 2002. Effects of crosslinking on thermal and mechanical properties of polyurethanes. J. Appl. Polym. Sci. 83, 212–223. Demir, M.M., Yilgor, I., Yilgor, E., Erman, B., 2002. Electrospinning of polyurethane fibers. Polymer 43, 3303–3309. Desroches, M., Caillol, S., Lapinte, V., Auvergne, R.M., Boutevin, B., 2011. Synthesis of biobased polyols by thiol−Ene coupling from vegetable oils. Macromolecules 44, 2489–2500. Desroches, M., Escouvois, M., Auvergne, R., Caillol, S., Boutevin, B., 2012. From vegetable oils to polyurethanes: synthetic routes to polyols and main industrial products. Polym. Rev. 52, 38–79. Dumont, M.J., Kharraz, E., Qi, H., 2013. Production of polyols and mono-ols from 10 North-American vegetable oils by ozonolysis and hydrogenation: a characterization study. Ind Crop Prod 49, 830–836. Feng, Y., Liang, H., Yang, Z., Yuan, T., Luo, Y., Li, P., Yang, Z., Zhang, C., 2017. A solventfree and scalable method to prepare soybean-oil-Based polyols by thiol–Ene photoclick reaction and biobased polyurethanes therefrom. ACS Sustain. Chem. Eng. 5,
Fig. 5. Dependence of tensile strength and elongation at break of PU films on the hydroxyl value of the corresponding polyols (Hydroxyl values of olive, rice bran, grape seed and linseed oil based polyol are 190 mg KOH/g, 232 mg KOH/ g, 270 mg KOH/g, 305 mg KOH/g, respectively).
elastomeric polymers with yield points and elastic regions in stressstrain curves. Tensile strength, elongation at break, Young’s modulus and toughness of the films are tabulated in Table 3. PU-LOP has the highest tensile strength of 50.7 MPa while PU-OOP shows the lowest tensile strength of 4.7 MPa. PU-OOP demonstrates highest elongation at break of 331% and PU-ROP shows highest toughness. The tensile strength of the polyurethane films prepared from vegetable oil based polyols obtained by thiol-ene reaction is much higher than those from bio-based polyols obtained by other techniques. For example, the tensile strength of polyurethane films prepared from olive oil and linseed oil by epoxidation/ring opening is 0.4 MPa, and 17.3 MPa, respectively (Zhang et al., 2015). The tensile strength and elongation at break of polyurethane films prepared from bio-based polyols by reduction of epoxidized linseed oil are 35.1 MPa, and 11.9%, respectively (Zhang 5
Industrial Crops & Products 140 (2019) 111711
Y. Shen, et al.
Lligadas, G., Ronda, J.C., Galia, M., Cadiz, V., 2010. Plant oils as platform chemicals for polyurethane synthesis: current state-of-the-Art. Biomacromolecules 11, 2825–2835. Lu, Y., Larock, R.C., 2008. Soybean-oil-based waterborne polyurethane dispersions: effects of polyol functionality and hard segment content on properties. Biomacromolecules 9, 3332–3340. Noreen, A., Zia, K.M., Zuber, M., Tabasum, S., Zahoor, A.F., 2016. Bio-based polyurethane: an efficient and environment friendly coating systems: a review. Prog Org Coat 91, 25–32. Prociak, A., Kuranska, M., Cabulis, U., Ryszkowska, J., Leszczynska, M., Uram, K., Kirpluks, M., 2018. Effect of bio-polyols with different chemical structures on foaming of polyurethane systems and foam properties. Ind Crop Prod 120, 262–270. Stemmelen, M., Pessel, F., Lapinte, V., Caillol, S., Habas, J.P., Robin, J.J., 2011. A fully biobased epoxy resin from vegetable oils: from the synthesis of the precursors by thiol-ene reaction to the study of the final material. J. Polym. Sci. Part A: Polym. Chem. 49, 2434–2444. Thanamongkollit, N., Miller, K.R., Soucek, M.D., 2012. Synthesis of UV-curable tung oil and UV-curable tung oil based alkyd. Prog Org Coat 73, 425–434. Veronese, V.B., Menger, R.K., Forte, M.Md.C., Petzhold, C.L., 2011. Rigid polyurethane foam based on modified vegetable oil. J. Appl. Polym. Sci. 120, 530–537. Zhang, C., Garrison, T.F., Madbouly, S.A., Kessler, M.R., 2017. Recent advances in vegetable oil-based polymers and their composites. Prog. Polym. Sci. Zhang, C.Q., Ding, R., Kessler, M.R., 2014. Reduction of epoxidized vegetable oils: a novel method to prepare bio-based polyols for polyurethanes. Macromol Rapid Comm 35, 1068–1074. Zhang, C.Q., Madbouly, S.A., Kessler, M.R., 2015. Biobased polyurethanes prepared from different vegetable oils. Acs Appl Mater Inter 7, 1226–1233. Zlatanic, A., Lava, C., Zhang, W., Petrovic, Z.S., 2004. Effect of structure on properties of polyols and polyurethanes based on different vegetable oils. Journal Of Polymer Science Part B-Polymer Physics 42, 809–819.
7365–7373. Gupta, T.K., Singh, B.P., Dhakate, S.R., Singh, V.N., Mathur, R.B., 2013. Improved nanoindentation and microwave shielding properties of modified MWCNT reinforced polyurethane composites. J. Mater. Chem. A Mater. Energy Sustain. 1, 9138–9149. Hablot, E., Zheng, D., Bouquey, M., Avérous, L., 2008. Polyurethanes based on castor oil: kinetics, chemical, mechanical and thermal properties. Macromol. Mater. Eng. 293, 922–929. Ionescu, M., Radojcic, D., Wan, X.M., Shrestha, M.L., Petrovic, Z.S., Upshaw, T.A., 2016. Highly functional polyols from castor oil for rigid polyurethanes. Eur. Polym. J. 84, 736–749. Javni, I., Petrović, Z.S., Guo, A., Fuller, R., 2000. Thermal stability of polyurethanes based on vegetable oils. J. Appl. Polym. Sci. 77, 1723–1734. Javni, I., Zhang, W., Petrovic, Z.S., 2003. Effect of different isocyanates on the properties of soy-based polyurethanes. J. Appl. Polym. Sci. 88, 2912–2916. Ji, D., Fang, Z., He, W., Luo, Z.Y., Jiang, X.B., Wang, T.W., Guo, K., 2015. Polyurethane rigid foams formed from different soy-based polyols by the ring opening of epoxidised soybean oil with methanol, phenol, and cyclohexanol. Ind. Crops Prod. 74, 76–82. Kirpluks, M., Kalnbunde, D., Benes, H., Cabulis, U., 2018. Natural oil based highly functional polyols as feedstock for rigid polyurethane foam thermal insulation. Ind Crop Prod 122, 627–636. Li, Q., Zhou, H., Wicks, D.A., Hoyle, C.E., Magers, D.H., Mcalexander, H.R., 2009. Comparison of Small Molecule and Polymeric Urethanes, Thiourethanes, and Dithiourethanes: Hydrogen Bonding and Thermal, Physical, and Mechanical Properties. Macromolecules 42, 1824–1833. Li, Z., Zhang, R.W., Moon, K.S., Liu, Y., Hansen, K., Le, T.R., Wong, C.P., 2013. Highly conductive, flexible, polyurethane-based adhesives for flexible and printed electronics. Adv. Funct. Mater. 23, 1459–1465. Liang, H., Feng, Y., Lu, J., Liu, L., Yang, Z., Luo, Y., Zhang, Y., Zhang, C., 2018. Bio-based cationic waterborne polyurethanes dispersions prepared from different vegetable oils. Ind. Crops Prod. 122, 448–455.
6
Contents lists available at ScienceDirect
Industrial Crops & Products journal homepage: www.elsevier.com/locate/indcrop
Synthesis and characterization of vegetable oil based polyurethanes with tunable thermomechanical performance ⁎
Yingbin Shena,b,f, Jialiang Hec, Zhenxing Xied, Xing Zhoue, Changqing Fange, , Chaoqun Zhangf,
T ⁎
a
Department of Food Science and Engineering, School of Science and Engineering, Jinan University, Guangzhou 510632, Guangdong, China School of Life Sciences, Guangzhou University, Guangzhou 510006, Guangdong, China c School of Food and Bioengineering, Henan University of Science and Technology, Luoyang, Henan 471023, China d Basic School of Medicine, Henan University, Kaifeng 475004, China e Faculty of Printing, Packaging Engineering and Digital Media Technology, Xi’an University of Technology, Xi’an, 710048, China f College of Materials and Energy, South China Agricultural University, Guangzhou 510642, China b
A R T I C LE I N FO
A B S T R A C T
Keywords: Biomass transformation Vegetable oil Polyol Polyurethane Thermomechanical performance
The replacement of petroleum based polymers with the environmental-friendly counterparts derived from renewable resource has received much attention due to the growing concern toward the depletion of the world crude oil stock and environmental problem. In this study, a series of biobased polyurethanes were successfully prepared from polyols obtained by thiol-ene reaction of different plant oils (olive, rice bran, grape seed and linseed oils). Their properties were characterized by dynamic mechanical analysis (DMA), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and tensile test. Their thermomechanical and mechanical properties were compared and discussed to reveal the structure-property relationship. The results show that as the hydroxyl values of the polyols increase, Tgs and tensile strengths of the corresponding polyurethanes increase linearly while the thermal stability decrease. Furthermore, polyurethane from linseed oil had the highest Tg of 65.2 °C and tensile strength of 50.7 MPa. The resulting polyurethane films with tunable thermomechanical performance are promising to find application in coatings, leather, adhesive and so on.
1. Introduction Biobased polymers derived from renewable feedstocks receive more and more attention for their eco-friendly characters, including reducing the consumption of non-renewable sources like petroleum and lowering the greenhouse gas emission (Desroches et al., 2012). The most common used renewable sources are vegetable oils, polysaccharides, lignocellulose and proteins (Zhang et al., 2017). Among them, vegetable oils are one of the most promising candidates to substitute the petroleum derivatives as the monomers of polymers. They are mainly triglycerides of various kinds of fatty acids (Lligadas et al., 2010). Fatty acids are aliphatic carboxylic acids with long carbon chains containing from 8 to 18 carbon atoms and 0˜3 carbon-carbon double bonds, which are determined by the plant type and growth climate of the plants. Specially, some oils inherently possess hydroxyl (castor oil) or epoxy groups (vernonia oil). Multiple functional groups in their structures as mentioned above make them readily modify to the valuable monomers for biobased polymers. Thus, they have been developed into many kinds of polymers from alkyds (Thanamongkollit et al., 2012), vinyl
⁎
resins (Black and Rawlins, 2009) to epoxy resins (Stemmelen et al., 2011) and polyurethanes (Desroches et al., 2011). Of these polymers, polyurethanes (PUs) play the significant role in the modern society for its extensive applications in coatings (Noreen et al., 2016), adhesives (Li et al., 2013), fibers (Demir et al., 2002) and composites (Gupta et al., 2013). Their popularity is based on their excellent properties brought by the unique hydrogen bonding of carbamates, the characteristic bonds of PUs (Li et al., 2009). PUs are obtained by the polyaddition of polyisocyanates and polyols, so properties of PUs could be tuned by changing the type or the molar ratios of these two raw materials (Bhoyate et al., 2018; Blache et al., 2018). Polyisocyanates with rigid ring structure could increase the stiffness of the resulting PUs, thus PUs with diphenylmethane diisocyanate (MDI), toluene diisocyanate (TDI) and isophorone diisocyanate (IPDI) have higher Tgs and tensile strengths than with hexamethylene diisocyanate (HDI) (Javni et al., 2003). Besides, increasing the functional groups number of raw materials could enhance the crosslinking density of the final products, improving the mechanical properties (Lu and Larock, 2008). Finally, the molar ratio of NCO to OH is also the important factor
Corresponding authors. E-mail addresses: [email protected] (C. Fang), [email protected] (C. Zhang).
https://doi.org/10.1016/j.indcrop.2019.111711 Received 28 February 2019; Received in revised form 17 August 2019; Accepted 19 August 2019 0926-6690/ © 2019 Elsevier B.V. All rights reserved.
Industrial Crops & Products 140 (2019) 111711
Y. Shen, et al.
Scheme 1. The representative chemical structures and properties of vegetable oils and the corresponding polyols (Feng et al., 2017; Liang et al., 2018).
(Ionescu et al., 2016). In our previous study, novel biobased polyols were successfully prepared by thiol-ene reaction of soybean oil, and the reaction parameters were optimized for high conversion efficiency and yields (Feng et al., 2017). And the resulting polyurethanes possess the highest elongation at break of 471% and tensile strength of 15.7 MPa. However, to the best of our knowledge, properties of PUs based on these novel polyols from different vegetable oils have not been thoroughly investigated. In this paper, biobased polyurethanes from different vegetable oil based polyols were synthesized and characterized. Their properties were compared and discussed to establish the structure-property relationship. In detail, four biobased polyols from olive, rice bran, grape seed and linseed oil were prepared by thiol-ene reaction and reacted with IPDI to produce a series of bio-based polyurethanes. Their thermomechanical, thermal stability and mechanical properties were characterized by dynamic mechanical analysis (DMA), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and tensile test, respectively. The effect of polyol structure and functionalities on the performance of the resulting PUs was discussed.
to impact the performance of PUs (Chiou and Schoen, 2002). Higher NCO content enhances the rigidity of PUs for the increasing crosslinking density. As limited polyisocyanates are commercially available, polyols from vegetable oils become vital to the properties of biobased PUs. However, because not all vegetable oils inherently bear hydroxyl groups like castor oil, chemical modifications are necessary to transform these renewable sources to valuable polyols. So far, several routes have been successfully developed (Alagi et al., 2018; Kirpluks et al., 2018; Prociak et al., 2018). Dong et al. synthesized three polyols by oxirane ring opening of epoxidized soybean oil with methanol, phenol and cyclohexanol (Ji et al., 2015). The results show that these biobased polyols could partially substitute the petroleum counterparts in the systhesis of polyurethane rigid foams. Dumont et al. prepared ten kinds of polyols from North-American vegetable oils by ozonolysis followed by hydrogenation reaction (Dumont et al., 2013). They found these polyols to bear primary OH groups, which showed high reactivity to the isocyanates. Guo et al. converted the carbon-carbon double bonds of soybean oil to aldehydes through hydroformylation followed by hydrogenation to obtain polyols. The resultant polyurethanes can act as hard rubbers or rigid plastics according to the conversion of polyols. Veronese et al. increased the hydroxyl numbers of the resulting polyols by transesterification of the formiated soy polyol with polyfunctional alcohol (Veronese et al., 2011). The corresponding rigid polyurethane foam had the compression strength around 200 kPa due to the high hydroxyl value of polyols. Recently, an increasing interest has emerged in the application of thiol-ene reaction to transform the renewable vegetable oils into biobased polyols for its virtues of high yields, mild reaction conditions and easy purification (Alagi et al., 2016a, b; Desroches et al., 2011). For example, Ionescu et al. used this reaction to synthesize the high functional castor oil based polyols with hydroxyl value of 286 mg KOH/g
2. Materials and methods 2.1. Materials Linseed oil was purchased from Tianjin Guangfu Fine Chemical Research Institute. Rice bran and grape seed oil were purchased from Jinan Quanrun Rose Product Co., Ltd. Olive oil was purchased from Chengdu Kelong Chemical Reagents Factory. 2-Mercaptoethanol (> 98%) was obtained from Alfa Aesar (China) Chemicals Co., Ltd. 2Hydroxy-2,2-dimethylacetophenone (1173) was supplied by Ryoji Organic Chemical Co., Ltd. Isophorone diisocyanate (IPDI) was obtained from Guangdong Wengjiang Chemical Reagents Co., Ltd. 2
Industrial Crops & Products 140 (2019) 111711
Y. Shen, et al.
(Feng et al., 2017; Liang et al., 2018). The polyurethane films were prepared through the reaction between bio-based polyols and IPDI with molar ratio of 1:1.05. All the films demonstrate good transparency, showing the potential application in coatings (Fig. 1 (a)). The thermomechanical properties for all PU films were characterized by DMA. Thermal stability and mechanical properties of the films were characterized by TGA and tensile testing, respectively. Storage modulus (E´), loss modulus (E") and loss factor of the PU films as functions of temperature from -60 °C to 120 °C are shown in the Fig. 1 (b) and (c). Storage modulus of all the films first slightly declines with the increase of the testing temperature. Once it surpasses a certain temperature, a rapid decrease occurs in E´. At this stage, storage modulus increases with increasing OH number of the polyols from OOP, ROP, GSOP to LOP. Finally, E´curves of all the films demonstrate the rubbery plateau at high temperature. In the curves of loss factor, only one peak was observed, indicating the homogeneous property of PU films. As the hydroxyl values of the polyols increases from OOP, ROP, GSOP to LOP, the peaks of loss factor shift to high temperature and their peak values decline successively. Glass transition temperatures (Tg) were determined by the peak of loss factor curves and summarized in the Table 2. Crosslinking densities (νe) of all the films were calculated from the rubbery moduli according to the kinetic theory of rubber elasticity (Andjelkovic et al., 2005):
Dibutyltin dilaurate (DBTDL) was supplied by Tianjin Fuchen Chemical Reagents Factory. Methyl ethyl ketone was purchased from Tianjin Hongda Chemical Reagents Factory. All materials were used as received without further purification. 2.2. Synthesis of vegetable oil based polyols The thiol-ene reaction of olive, rice bran, grape seed and linseed oil with 2-mercaptoethanol was used to synthesis biobased polyols as previously reported (Feng et al., 2017; Liang et al., 2018). They are identified as OOP, ROP, GSOP and LOP, respectively. The representative chemical structures of vegetable oils and the resulting polyols are shown in Scheme 1. 2.3. Preparation of polyurethanes These novel polyols were mixed with IPDI (5% molar excess) in the presence of DBTDL. The mixtures were first reacted at 60 °C for 1 h with vigorous stirring, and then cast into silicone molds (length × width × thickness: 10 cm × 10 cm × 2 cm) and cured at 85 °C in an oven for 24 h. A small amount of methyl ethyl ketone was added in the mixture before treatment in the oven to remove the trapped air bubbles. The obtained PU films were cut into specific dimensions for thermomechanical and mechanical testing. The recipe composition for the polyurethanes is shown in Table 1.
E´ = 3νeRT´
where T´ is the absolute temperature of films in the rubbery plateau region at Tg +50 °C, and E´ is the corresponding storage modulus at T´. R represents the gas constant. With increasing OH number of the polyols, the crosslinking density of the films increases. Higher cross densities restrict the motion of polymer chain, leading to higher storage modulus and Tg as revealed by DMA (Zhang et al., 2015). DSC is also used to examine the glass transition temperature of all the films, which was determined from the midpoint temperature in the heat capacity change of the DSC scan as shown in Fig. 1(d). Tgs of polyurethanes from DSC and DMA both show the linear relationship with the hydroxyl values of the corresponding polyols as presented in the Fig. 2. With increasing hydroxyl value of polyols, the crosslinking density of PU films increases, leading to the increase of Tgs because of the restriction of molecular chains mobility. This is identical to the reports of Alisa Zlatanic(Zlatanic et al., 2004). The Tgs obtained from DMA are approx. 10–20 °C higher than those measured by DSC because of the different principles underlying these two characterization methods. TGA weight loss and weight loss derivative curves of the PU films are shown in the Fig. 3. According to the weight loss derivative curves, the degradation of the PU films is composed of three stages. The degradation between 200 °C and 330 °C is attributed to decomposition of labile urethane groups into primary amine, secondary amine, olefin and carbon dioxide (Hablot et al., 2008; Javni et al., 2000). As the OH numbers increase from OOP, ROP, GSOP to LOP, the thermal stability of the corresponding PU films decreases due to the increasing urethane contents. The degradation in the range 330˜430 °C was initiated by the chain scission of the vegetable oils. At this stage, all the curves demonstrate the similar trend because of the analogical structure of the triglyceride oils. The degradation of the PU films above 430 °C is corresponding to further thermo-oxidation of the PU films at high temperature. Moreover, temperature of 10% degradation (T10), 50% degradation (T50) and maximum decomposition rates (Tmax) are summarized in the Table 2. According to the T10, T50 and Tmax values, the thermal stability of the PU films decrease with the increase of OH number of the corresponding polyols. The mechanical properties of PU films from different vegetable oilbased polyols were measured by tensile testing. Fig. 4 shows the representative stress-strain curves of PU films which exhibit a broad range of mechanical properties, from soft and rubbery to hard and glassy. PU-
2.4. Characterization Dynamic mechanical analysis (DMA) of PU films (Rectangular specimens of 20 mm × 6 mm × 0.5 mm (length × width × thickness)) was performed with a film-tension mode of 1 Hz using a Netzsch DMA 242C dynamic mechanical analyzer. The samples were cooled and maintained isothermally at -60 °C for 5 min, followed by heating to 125 °C at a rate of 5 °C min−1. The glass transition temperatures (Tgs) of the samples were obtained from the peaks of tan δ curves. Differential scanning calorimetry (DSC) of PU films was measured using a PerkinElmer DSC 6000 thermal analyzer. The following heating programs were conducted on every sample: heating from room temperature to 90 °C at a rate of 20 °C min−1, cooling to -90 °C and holding for 5 min, heating to 90 °C at a rate of 20 °C min−1. 5 mg samples were used for the analysis. Tgs were obtained from the midpoint temperature in the heat capacity change of the second DSC scan. Thermogravimetric analysis (TGA) of the samples was performed on a Netzsch STA 449C thermal analyzer. The samples (approximately 10 mg) were heated from room temperature to 700 °C at a rate of 20 °C min−1 in nitrogen. The tensile properties of samples with size of 50 mm × 10 mm × 0.5 mm (length × width × thickness) were measured by a Shenzhen Suns UTM 5000 universal testing machine with a crosshead speed of 100 mm min−1. Average values of at least three replicates of each sample were taken. 3. Results and discussion Biobased polyols were synthesized by thiol-ene reaction of olive, rice bran, grape seed and linseed oil, and characterized previously Table 1 The recipe composition for the polyurethanes.
PU- OOP PU- ROP PU-GSOP PU-LOP
Polyols (g)
IPDI (g)
2-Hydroxy-2,2-dimethylacetophenone (g)
6 6 6 6
2.37 2.90 3.37 3.81
0.17 0.18 0.19 0.20
(1)
3
Industrial Crops & Products 140 (2019) 111711
Y. Shen, et al.
Fig. 1. (a) The appearance of PU films based on different vegetable oils. Storage modulus (b) and loss factor (c) as the function of temperature for the PU films based on different vegetable oils. (d) DSC curves for the PU films based on different vegetable oils. Table 2 Thermal properties of polyurethanes from different vegetable oil based polyols. DMA Tg (oC)
PU-OOP PU-ROP PU-GSOP PU-LOP
20.6 48.6 55.6 65.2
DSC Tg (oC)
8.7 34.7 42.7 56.9
νe (mol/m3)
208.4 438.7 526.7 674.3
TGA in nitrogen (oC) T10
T50
Tmax(1st/2nd)
293 297 307 299
363 355 359 353
337/417 325/341 321/343 317/345
Fig. 2. Dependence of glass transition temperature of polyurethanes on hydroxyl value of the corresponding polyols. (Hydroxyl values of olive, rice bran, grape seed and linseed oil based polyol are 190 mg KOH/g, 232 mg KOH/g, 270 mg KOH/g, 305 mg KOH/g, respectively).
GSOP and PU-LOP demonstrate the brittle behavior of hard plastic with low elongation at break, and high tensile strengths and Young’s modulus. In contrast, PU-ROP and PU-OOP show typical behavior of
Fig. 3. (a) TGA curves and (b) their derivative curves of polyurethanes from different vegetable oil based polyols.
4
Industrial Crops & Products 140 (2019) 111711
Y. Shen, et al.
et al., 2014). As presented in Fig. 5, tensile strength of the PU films increases linearly with increasing hydroxyl value of the corresponding polyols, while elongation at break displays the exponential reduction. Increasing hydroxyl numbers of the polyols results in an increase in crosslinking densities of the resulting PUs, leading to increase of tensile strength and Young’s modulus, and decrease of elongation at break. 4. Conclusions Four kinds of plant oils including olive, rice bran, grape seed and linseed oil were transformed into polyols by thiol-ene reaction and then reacted with IPDI to prepare bio-based polyurethanes. Tgs and tensile strengths of the resulting PUs increase linearly with the increase of hydroxyl values of the corresponding polyols, while elongation at break decreases exponentially because of the different crosslinking densities. Polyurethane from linseed oil had the highest Tg of 65.2 °C and tensile strength of 50.7 MPa. The thermal stability of the polyurethanes declines with the increase of hydroxyl values of polyols. All the films show excellent thermal stability up to 300 °C. This well-established structureproperty relationship could provide guidance for the design and the practical application of these novel bio-based PUs in the field of coatings, leather, adhesive and so on.
Fig. 4. Stress-strain curves of polyurethanes with different vegetable oil based polyols. Table 3 Mechanical properties of polyurethanes with different vegetable oil based polyols.
PU-OOP PU-ROP PU-GSOP PU-LOP
Tensile strength (MPa)
Elongation at break (%)
Young’s modulus (MPa)
Toughness (MPa)
4.7 ± 0.4 22.6 ± 0.3 37.1 ± 0.6 50.7 ± 2.6
331.5 ± 12.9 56.1 ± 4.3 18.5 ± 3.3 15.1 ± 2.4
1.4 ± 0.1 40.6 ± 3.6 203.9 ± 42.8 342.5 ± 36.2
7.66 10.79 4.94 5.37
Declaration of Competing Interest The authors declare no competing financial interest. Acknowledgements This work was sponsored by the Open Project of Jiangsu Key Laboratory for Biomass Energy and Materials (JSBEM201803), National Natural Science Foundation (No.51703068), the Guangdong Province Science & Technology Program (2017A010103015), Program of the Science and Technology Department of Guangzhou, China (201803020039, 201707010343). References Alagi, P., Choi, Y.J., Hong, S.C., 2016a. Preparation of vegetable oil-based polyols with controlled hydroxyl functionalities for thermoplastic polyurethane. Eur. Polym. J. 78, 46–60. Alagi, P., Choi, Y.J., Seog, J., Hong, S.C., 2016b. Efficient and quantitative chemical transformation of vegetable oils to polyols through a thiol-ene reaction for thermoplastic polyurethanes. Ind. Crops Prod. 87, 78–88. Alagi, P., Ghorpade, R., Jang, J.H., Patil, C., Jirimali, H., Gite, V., Hong, S.C., 2018. Functional soybean oil-based polyols as sustainable feedstocks for polyurethane coatings. Ind Crop Prod 113, 249–258. Andjelkovic, D.D., Valverde, M., Henna, P., Li, F., Larock, R.C., 2005. Novel thermosets prepared by cationic copolymerization of various vegetable oils—synthesis and their structure–property relationships. Polymer 46, 9674–9685. Bhoyate, S., Ionescu, M., Kahol, P.K., Gupta, R.K., 2018. Sustainable flame-retardant polyurethanes using renewable resources. Ind Crop Prod 123, 480–488. Blache, H., Mechin, F., Rousseau, A., Fleury, E., Pascault, J.P., Alcouffe, P., Jacquel, N., Saint-Loup, R., 2018. New bio-based thermoplastic polyurethane elastomers from isosorbide and rapeseed oil derivatives. Ind Crop Prod 121, 303–312. Black, M., Rawlins, J.W., 2009. Thiol–ene UV-curable coatings using vegetable oil macromonomers. Eur. Polym. J. 45, 1433–1441. Chiou, B.-S., Schoen, P.E., 2002. Effects of crosslinking on thermal and mechanical properties of polyurethanes. J. Appl. Polym. Sci. 83, 212–223. Demir, M.M., Yilgor, I., Yilgor, E., Erman, B., 2002. Electrospinning of polyurethane fibers. Polymer 43, 3303–3309. Desroches, M., Caillol, S., Lapinte, V., Auvergne, R.M., Boutevin, B., 2011. Synthesis of biobased polyols by thiol−Ene coupling from vegetable oils. Macromolecules 44, 2489–2500. Desroches, M., Escouvois, M., Auvergne, R., Caillol, S., Boutevin, B., 2012. From vegetable oils to polyurethanes: synthetic routes to polyols and main industrial products. Polym. Rev. 52, 38–79. Dumont, M.J., Kharraz, E., Qi, H., 2013. Production of polyols and mono-ols from 10 North-American vegetable oils by ozonolysis and hydrogenation: a characterization study. Ind Crop Prod 49, 830–836. Feng, Y., Liang, H., Yang, Z., Yuan, T., Luo, Y., Li, P., Yang, Z., Zhang, C., 2017. A solventfree and scalable method to prepare soybean-oil-Based polyols by thiol–Ene photoclick reaction and biobased polyurethanes therefrom. ACS Sustain. Chem. Eng. 5,
Fig. 5. Dependence of tensile strength and elongation at break of PU films on the hydroxyl value of the corresponding polyols (Hydroxyl values of olive, rice bran, grape seed and linseed oil based polyol are 190 mg KOH/g, 232 mg KOH/ g, 270 mg KOH/g, 305 mg KOH/g, respectively).
elastomeric polymers with yield points and elastic regions in stressstrain curves. Tensile strength, elongation at break, Young’s modulus and toughness of the films are tabulated in Table 3. PU-LOP has the highest tensile strength of 50.7 MPa while PU-OOP shows the lowest tensile strength of 4.7 MPa. PU-OOP demonstrates highest elongation at break of 331% and PU-ROP shows highest toughness. The tensile strength of the polyurethane films prepared from vegetable oil based polyols obtained by thiol-ene reaction is much higher than those from bio-based polyols obtained by other techniques. For example, the tensile strength of polyurethane films prepared from olive oil and linseed oil by epoxidation/ring opening is 0.4 MPa, and 17.3 MPa, respectively (Zhang et al., 2015). The tensile strength and elongation at break of polyurethane films prepared from bio-based polyols by reduction of epoxidized linseed oil are 35.1 MPa, and 11.9%, respectively (Zhang 5
Industrial Crops & Products 140 (2019) 111711
Y. Shen, et al.
Lligadas, G., Ronda, J.C., Galia, M., Cadiz, V., 2010. Plant oils as platform chemicals for polyurethane synthesis: current state-of-the-Art. Biomacromolecules 11, 2825–2835. Lu, Y., Larock, R.C., 2008. Soybean-oil-based waterborne polyurethane dispersions: effects of polyol functionality and hard segment content on properties. Biomacromolecules 9, 3332–3340. Noreen, A., Zia, K.M., Zuber, M., Tabasum, S., Zahoor, A.F., 2016. Bio-based polyurethane: an efficient and environment friendly coating systems: a review. Prog Org Coat 91, 25–32. Prociak, A., Kuranska, M., Cabulis, U., Ryszkowska, J., Leszczynska, M., Uram, K., Kirpluks, M., 2018. Effect of bio-polyols with different chemical structures on foaming of polyurethane systems and foam properties. Ind Crop Prod 120, 262–270. Stemmelen, M., Pessel, F., Lapinte, V., Caillol, S., Habas, J.P., Robin, J.J., 2011. A fully biobased epoxy resin from vegetable oils: from the synthesis of the precursors by thiol-ene reaction to the study of the final material. J. Polym. Sci. Part A: Polym. Chem. 49, 2434–2444. Thanamongkollit, N., Miller, K.R., Soucek, M.D., 2012. Synthesis of UV-curable tung oil and UV-curable tung oil based alkyd. Prog Org Coat 73, 425–434. Veronese, V.B., Menger, R.K., Forte, M.Md.C., Petzhold, C.L., 2011. Rigid polyurethane foam based on modified vegetable oil. J. Appl. Polym. Sci. 120, 530–537. Zhang, C., Garrison, T.F., Madbouly, S.A., Kessler, M.R., 2017. Recent advances in vegetable oil-based polymers and their composites. Prog. Polym. Sci. Zhang, C.Q., Ding, R., Kessler, M.R., 2014. Reduction of epoxidized vegetable oils: a novel method to prepare bio-based polyols for polyurethanes. Macromol Rapid Comm 35, 1068–1074. Zhang, C.Q., Madbouly, S.A., Kessler, M.R., 2015. Biobased polyurethanes prepared from different vegetable oils. Acs Appl Mater Inter 7, 1226–1233. Zlatanic, A., Lava, C., Zhang, W., Petrovic, Z.S., 2004. Effect of structure on properties of polyols and polyurethanes based on different vegetable oils. Journal Of Polymer Science Part B-Polymer Physics 42, 809–819.
7365–7373. Gupta, T.K., Singh, B.P., Dhakate, S.R., Singh, V.N., Mathur, R.B., 2013. Improved nanoindentation and microwave shielding properties of modified MWCNT reinforced polyurethane composites. J. Mater. Chem. A Mater. Energy Sustain. 1, 9138–9149. Hablot, E., Zheng, D., Bouquey, M., Avérous, L., 2008. Polyurethanes based on castor oil: kinetics, chemical, mechanical and thermal properties. Macromol. Mater. Eng. 293, 922–929. Ionescu, M., Radojcic, D., Wan, X.M., Shrestha, M.L., Petrovic, Z.S., Upshaw, T.A., 2016. Highly functional polyols from castor oil for rigid polyurethanes. Eur. Polym. J. 84, 736–749. Javni, I., Petrović, Z.S., Guo, A., Fuller, R., 2000. Thermal stability of polyurethanes based on vegetable oils. J. Appl. Polym. Sci. 77, 1723–1734. Javni, I., Zhang, W., Petrovic, Z.S., 2003. Effect of different isocyanates on the properties of soy-based polyurethanes. J. Appl. Polym. Sci. 88, 2912–2916. Ji, D., Fang, Z., He, W., Luo, Z.Y., Jiang, X.B., Wang, T.W., Guo, K., 2015. Polyurethane rigid foams formed from different soy-based polyols by the ring opening of epoxidised soybean oil with methanol, phenol, and cyclohexanol. Ind. Crops Prod. 74, 76–82. Kirpluks, M., Kalnbunde, D., Benes, H., Cabulis, U., 2018. Natural oil based highly functional polyols as feedstock for rigid polyurethane foam thermal insulation. Ind Crop Prod 122, 627–636. Li, Q., Zhou, H., Wicks, D.A., Hoyle, C.E., Magers, D.H., Mcalexander, H.R., 2009. Comparison of Small Molecule and Polymeric Urethanes, Thiourethanes, and Dithiourethanes: Hydrogen Bonding and Thermal, Physical, and Mechanical Properties. Macromolecules 42, 1824–1833. Li, Z., Zhang, R.W., Moon, K.S., Liu, Y., Hansen, K., Le, T.R., Wong, C.P., 2013. Highly conductive, flexible, polyurethane-based adhesives for flexible and printed electronics. Adv. Funct. Mater. 23, 1459–1465. Liang, H., Feng, Y., Lu, J., Liu, L., Yang, Z., Luo, Y., Zhang, Y., Zhang, C., 2018. Bio-based cationic waterborne polyurethanes dispersions prepared from different vegetable oils. Ind. Crops Prod. 122, 448–455.
6