微相分离结构对聚乳酸薄膜性能的调控及其在巨峰葡萄保鲜中的应用

Modulation of Poly (L-lactic acid) Films Properties by Microphase Separation Structure and Its Application in Preservation of Kyoho Grapes

为改善聚乳酸(PLLA)性能并增加其在果蔬保鲜领域应用的可能性,本研究将聚三氟丙基甲基硅氧烷(PTFPMS)和聚乙二醇(PEG)分别与L-丙交酯进行开环反应制备出PLLA-PTFPMS-PLLA(PLTL)和PLLA-PEG-PLLA(PLEL)三嵌段共聚物,进一步以75∶25、50∶50、25∶75的质量比将PLTL和PLEL进行共混得到PLTL/PLEL共混薄膜。实验结果表明,PTFPMS和PEG嵌段的引入提高了PLLA的热学和力学性能,PLLA的T_(g)分别变为57.8℃和43.9℃,其薄膜的断裂伸长率分别达到108.7%和199.7%。将PLTL和PLEL共混成膜后,PLLA的T_(g)变为52.3~46.2℃,PLTL/PLEL共混膜的断裂伸长率可达142.5%~295.8%。在5℃测试环境下,PLTL和PLEL薄膜的CO_(2)透过率分别是PLLA的2.12倍和3.51倍,O_(2)透过率分别是PLLA的1.97倍和0.87倍,其CO_(2)/O_(2)透过比分别为3.3和12.2,另外20℃测试条件下其H_(2)O透过率是PLLA的0.87倍和3.29倍,说明PEG能够大幅度提升CO_(2)和H_(2)O透过率,但对O_(2)透过率贡献不大;而PTFPMS既能够提升CO_(2)透过率也能提升O_(2)透过率,但其自身的疏水性减弱了H_(2)O透过率。两者共混后,PLTL/PLEL薄膜的CO_(2)透过率为PLLA的2.55~3.33倍,O_(2)透过率为PLLA的1.15~1.46倍,CO_(2)/O_(2)透过比达到5.3~8.8,H_(2)O透过率为PLLA的0.92~2.66倍,并且随着测试温度的升高,PLTL/PLEL薄膜的CO_(2)和O_(2)透过率明显提升,说明PLTL/PLEL共混膜在保持优异气体透过性能的同时,拥有适宜生鲜果蔬包装的CO_(2)/O_(2)透过比。将改性后的材料及市售PE保鲜膜应用于巨峰葡萄保鲜,PLTL-PLEL50组在贮藏第10 d已达到巨峰葡萄最适宜的5%O_(2)+8%CO_(2)浓度,可将巨峰葡萄的货架期延长至30 d。

To improve the performance of poly(L-lactic acid)(PLLA) and to increase its potential application in the field of fruit and vegetable preservation,in this study,polytrifluoropropyl methylsiloxane(PTFPMS) and polyethylene glycol(PEG) were used to conduct ring-opening reaction with L-lactide.PLLA-PTFPMS-PLLA(PLTL) and PLLA-PEG-PLLA(PLEL) triblock copolymers were successfully prepared.PLTL/PLEL blend films were obtained by blending PLEL with PLEL at 75∶25,50∶50 and 25∶75.The experimental results show that PTFPMS and PEG blocks improve the flexibility and thermal properties of PLLA,T_(g) of PLLA was changed to 57.8 ℃ and 43.9 ℃,and the elongation at break of PLLA films reaches 108.7% and 199.7%,respectively.The T_(g) of PLLA was changed from 52.3 ℃ to 46.2 ℃.At 5 ℃,the CO_(2) transmittance of PLTL and PLEL films is 2.12 times and 3.51 times of PLLA,and the O_(2) transmittance is 1.97 times and 0.87 times of PLLA,respectively.Moreover,the CO_2/O_(2) transmittance ratio of PLTL and PLEL films is 3.3 and 12.2,at 20 ℃,the H_(2O) transmission rate was 0.87 times and 3.29 times that of PLLA.It shows that PEG can greatly improve CO_(2) transmittance,but has little contribution to O_(2) transmittance.PTFPMS can improve both CO_(2) and O_(2) transmittance.After blending,the CO_2,O_(2) and H_(2O) transmission amounts are 2.55—3.33 times,1.15—1.46 times and 0.92—2.66 times of PLLA,and the CO_2/O_(2) transmission ratio reaches 5.3—8.8.The results indicate that PLTL/PLEL blend film has a CO_2/O_(2) transmittance ratio suitable for fresh fruit and vegetable packaging while maintaining excellent gas transmittance.The modified material and commercially available PE cling film were applied to preserve the grapes.The PLTL-PLEL50 group reached the optimum 5%O_2+8%CO_(2) concentration for grapes on the 10th day of storage,extending the shelf life of grapes to 30 days.