环保型大分子增塑剂分子结构设计及其增塑聚乳酸复合体系性能研究

Compared with other general plastics such as polyolefin, the inherent brittleness of poly(lactic acid) (PLA) severely limits its more widespread implementation.Many low molecular weight plasticizers could greatly improve PLA flexibility, but usually the plasticized PLA systems are not stable, because the low molecular weight plasticizers trend to migrate slowly toward the material surface, leading to phase separation with PLA. Therefore, the plasticized PLA blends will gradually lose the attractive toughness and ultimately regain the embrittlement. This work aims at inhibiting the renew embrittlement of plasticized PLA blends through restraining the migration of plasticizers, so we put forward to design and prepare environmentally friendly completely biodegradable macromolecular plasticizer with different molecular structures, which need to have excellent compatibility with PLA. The macromolecular plasticizers are used for plasticizing modification of PLA by melt blending, The relationship between the molecular structure and molecular weight of macromolecular plasticizers and compatibility, morphology stablity, mechanical properties and aging properties of plasticized PLA blends is studied, so as to finally obtain highly flexible PLA composite materials of performance stability with good comprehensive mechanical properties and good processing performance. The behaviors of crystallization, compatibility and yield deformation of plasticized PLA blends are researched in details using a variety of analytical methods, in order to clarify the mechanism of macromolecule plasticized PLA. Furthermore, the plasticized PLA composite materials will be explored in field of blown film, and thus broadening the application areas of PLA.

同其它聚烯烃类通用塑料相比，聚乳酸（PLA）固有的脆性限制了它的广泛应用。小分子增塑剂能够大幅度提高PLA制品的柔韧性，但是，增塑后的PLA性能不稳定，小分子的增塑剂会缓慢析出到材料的表面，导致与PLA发生相分离，增塑的PLA材料逐渐失去应有的韧性而重新脆化。本项目通过提高增塑剂的抗迁移能力，解决增塑PLA重新脆化的问题，提出通过分子结构设计，制备可完全生物降解环境友好抗迁移的大分子增塑剂，并保持增塑剂与PLA的优良相容性。通过熔融共混对PLA进行增塑改性，研究大分子增塑剂的分子结构及分子量对PLA增塑体系的相容性、相形貌稳定性、力学性能及耐老化性能的影响，最终获得韧性较高、综合力学性能优异、性能稳定和加工性能良好的聚乳酸复合材料。利用各种分析测试方法，研究PLA增塑体系的结晶性、相容性和屈服形变等行为，阐明大分子增塑PLA的机理，进一步探讨增塑的PLA复合材料在吹膜加工方面的应用。

聚乳酸（PLA）作为一种可完全生物降解高分子材料，其固有的脆性限制了它的广泛应用。许多小分子增塑剂能够大幅度提高PLA的柔韧性，但是，增塑后的PLA材料性能并不稳定，这些小分子增塑剂会缓慢析出到材料表面，导致与PLA发生相分离，增塑的PLA材料逐渐失去应有的韧性而重新脆化。本项目通过提高增塑剂分子量，进而提高其抗迁移能力，解决增塑PLA重新脆化的问题。合成了柠檬酸酯类、苯二甲酸酯类、氨基甲酸酯类、聚氨酯类和聚乳酸基共聚物类等可作为PLA的大分子增塑剂。研究大分子增塑PLA体系的相容性、形貌和力学性能等规律。柠檬酸酯类、苯二甲酸酯类大分子增塑剂能够有效降低PLA的玻璃化转变温度（Tg），提高PLA材料的柔韧性，在柠檬酸酯和苯二甲酸酯含量为20wt%时，可使PLA的Tg下降到55~12℃；断裂伸长率达到400%~500%。氨基甲酸酯类大分子增塑剂与PLA有较好的相容性，能明显降低PLA的Tg和熔点（Tm），因而有效降低了PLA的加工温度。该类增塑剂既能提高PLA的柔韧性，又能保持PLA较高的拉伸强度。5~30wt%的增塑剂能使PLA的Tg从61℃降低到57~30℃，Tm从176℃降低到175~165℃；20wt%的增塑剂能使PLA断裂伸长率从5%提高到250%~300%；共混物的拉伸强度保持为46MPa。合成的聚醚-聚酯型聚氨酯（PELU-50），在20wt%的共混比例下，可使PLA的Tg从58.3℃下降到51.4℃，断裂伸长率达到330%，拉伸强度保持为37MPa。合成了聚乳酸基共聚物，包括：PLA-b-PCL、PLA-b-PBS-b-PLA、PLA-b-PBAT-b-PLA和(PLA-b-PGMA)3。这些共聚物被用于和PLA进行多元共混，大幅度提高了PLA的柔韧性和共混体系的稳定性。探索了大分子增塑PLA复合体系的吹膜加工工艺，获得薄膜制品，这将扩大PLA的应用领域。