端羟基聚二甲基硅氧烷嵌段对聚(L-乳酸)气体透过性的影响及气调功能

以端羟基聚二甲基硅氧烷(PDMS)为引发剂,丙交酯为单体,开环聚合制备PLLA-PDMS-PLLA(PLDL)三嵌段共聚物,旨在改善聚(L-乳酸)(PLLA)的柔韧性和气体透过性使其更适合果蔬保鲜包装。通过控制嵌段的比例调控PLDL薄膜的力学性能、气体透过及选择透过性能。采用核磁共振氢谱、凝胶渗透色谱、衰减全放射傅里叶变换红外光谱表征共聚物的结构、组成和相对分子质量;并对薄膜的热性能、气体阻隔性能及力学性能进行了研究。结果表明,PDMS的引入降低了PLLA的结晶度,显著提高了PLLA的柔韧性,其断裂伸长率增加约2.5倍;PLLA的CO2、O2透过率及透过比也显著提高;而水蒸气透过率则随着疏水PDMS链段含量的增加而略微减小。将经改性后的嵌段共聚物薄膜用于蔬菜包装,可将货架期延长至18 d以上。

Effect of Poly-Dimethylsiloxane Blocks on Thermal Properties,Mechanical Properties and Gas Permeability of Polylactic Acid

PLLA-PDMS-PLLA(PLDLx) triblock copolymers were synthesized by ring-opening polymerization of lactide with hydroxy-terminated poly-dimethylsiloxane(PDMS) as initiator to improve the flexibility and gas permeability of polylactic acid(PLLA) for fresh-keeping packaging of vegetables. The mechanical properties, gas permeation and permselectivity of the films were controlled by the ratios of PDMS blocks. The structure, composition and molecular weight of the copolymers were characterized by 1H-NMR, gel permeation chromatography(GPC), total reflectance Fourier transformed infrared(ATR-FT-IR) and modulated differential scanning calorimeter(MDSC). The thermal properties, gas barrier properties and mechanical properties of the films were investigated. The results show that with the introduction of PDMS blocks, the crystallinity of PLLA is reduced. However, the flexibility of PLLA is significantly increased and the elongation at break is increased 2.5 times;the CO2, O2 permeability and permselectivity of the films are improved;the water vapor transmission rate is decreased slightly with the increase of the hydrophobic PDMS segment contents. Finally, the modificated material was used for atmosphere packaging of vegetables and can extend the shelflife to 18 d.