Modulation of Poly(L-lactic acid) Films Properties by Microphase Separation Structure and Its Application in Preservation of Kyoho Grapes
WANG Yangyang1, YUN Xueyan1,*, ZHOU Ziyi1, YUAN Shuai1, SUN Tao1, ALATA Hexig2, DONG Tungalag1,*
1 College of Food Science and Engineering, Inner Mongolia Agricultural University, Hohhot 010018, China 2 College of Physics and Electronic Information, Inner Mongolia Normal University, Hohhot 010022, China
Abstract: 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, Tg 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 Tg of PLLA was changed from 52.3 ℃ to 46.2 ℃. At 5 ℃, the CO2 transmittance of PLTL and PLEL films is 2.12 times and 3.51 times of PLLA, and the O2 transmittance is 1.97 times and 0.87 times of PLLA, respectively. Moreover, the CO2/O2 transmittance ratio of PLTL and PLEL films is 3.3 and 12.2, at 20 ℃, the H2O transmission rate was 0.87 times and 3.29 times that of PLLA. It shows that PEG can greatly improve CO2 transmittance, but has little contribution to O2 transmittance. PTFPMS can improve both CO2 and O2 transmittance. After blending, the CO2, O2 and H2O transmission amounts are 2.55—3.33 times, 1.15—1.46 times and 0.92—2.66 times of PLLA, and the CO2/O2 transmission ratio reaches 5.3—8.8. The results indicate that PLTL/PLEL blend film has a CO2/O2 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%O2+8%CO2 concentration for grapes on the 10th day of storage, extending the shelf life of grapes to 30 days.
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