乳酰基聚氨酯的合成、结构、性能及其在聚乳酸增韧中的应用

Polylactide (PLA) is a hard and brittle material, its tensile strength is approximately 60 MPa, while the elongation at break is only about 5%. The drawback of low toughness has restricted its application as membranes in the industry. Some polyurethane (PU) elastomers are not only flexible but also biodegradable, and thus can be used as an excellent candidate material for toughening PLA. However, most of PUs are incompatible with PLA, thus the effect of toughening PLA by PUs is not satisfactory. In order to improve the compatibility between PLA and PU, this project puts forward to implant lactate repeating units into the PU molecular chains, design and prepare biodegradable lactate-based polyurethanes (La-PU) as toughening agents for PLA. The compatibility of PLA and La-PU with different molecular structures, compositions and molecular weights will be studied in details. The influence of the intermolecular hydrogen bonds formed by the imino groups (-NH-) of La-PU molecules and the carbonyl groups of PLA on the properties of PLA/La-PU blends will be investigated. In this work, we will further explore the mechanism of La-PU toughening PLA and explore the influence of La-PU on PLA materials with regard to the thermal, mechanical, rheological and aging properties, as well as the phase morphological stability. Finally, the stable PLA/La-PU composites with high toughness, high strength, excellent aging resistance and good processability will be obtained. The elongation at break can be reached by 400%~500%, while the tensile strength is maintained at 40~50 MPa for the PLA/La-PU blends, which will be used in the high-end membrane products with high toughness and strength.

聚乳酸（PLA）本身是一种脆性材料，拉伸强度约为60MPa，断裂伸长率仅为5%。这种韧性不足限制了其在薄膜领域的应用。部分聚氨酯（PU）弹性体不仅有优良的柔韧性而且是可生物降解的，可作为一种PLA增韧的极佳候选材料。然而，大多数PU与PLA是不相容的，使PU增韧PLA效果欠佳。本项目拟在PU分子链中嵌入乳酰基来提高其与PLA的相容性，设计制备可生物降解的乳酰基聚氨酯（La-PU）作为PLA的增韧剂。研究不同分子结构、组成和分子量的La-PU与PLA的相容性，考查La-PU分子链中的亚氨基（-NH-）与PLA的羰基形成的分子间氢键对共混物性能的影响，探索La-PU增韧PLA的机理，和其对PLA材料的热、力学、流变和老化性能及相形貌稳定性的影响。最终获得断裂伸长率400%~500%、拉伸强度40~50MPa、抗老化性能优良、加工性能稳定的PLA复合材料，使其能应用于高韧性高强度的薄膜制品领域。

聚乳酸（PLA）本身是一种脆性材料，拉伸强度约为60 MPa，断裂伸长率仅为5%。这种韧性不足限制了其在薄膜领域的应用，因此通过增韧增塑提高PLA柔韧性成为研究的热点。以聚乙二醇、二异氰酸酯和丙交酯为原料合成了含有聚L-乳酸（PLLA）和聚D-乳酸（PDLA）链段的乳酰基聚氨酯PELU和PEDU。当PELU及PEDU含量为10~20 wt%时，和PLLA共混物的断裂伸长率为 250%~350%，拉伸强度为37~42 MPa。相近分子量的PELU与PEDU对PLLA的增韧效果是一致的，在相同共混比例下，PLLA/PEDU共混的强度略高于PLLA/PELU的，因为PEDU中的PDLA链段能和PLLA形成立构复合物。研究了PCL-b-PLLA共聚物对PLLA/聚己内酯（PCL）共混物的热性能、相容性和力学性能的影响。随着PCL-b-PLLA中PLLA链段含量的增加，PLLA与PCL的相容性提高，共混物的拉伸强度增加。当PCL-b-PLLA中PCL/PLLA组成为50/50时，PLLA/PCL/PCL-b-PLLA共混物韧性最佳。高分子量的PCL-b-PLLA对PLLA/PCL的增容效果显著，共混物力学强度也随之增加。分子量大于39 kg/moL的PCL-b-PLLA共聚物具有更好的增容效果。将PLLA分布于体型聚氨酯网格中的结构，制备了体型聚氨酯增塑的聚乳酸复合材料，具有高强度、高模量、高韧性、结构稳定的特性。开发了聚酯多元酸盐作为聚乳酸增塑成核双功能改性剂。可提高聚乳酸的结晶速率和结晶度，能明显降低聚乳酸的结晶温度，可把PLLA的结晶度从44.8%提高到70%，降低聚乳酸的玻璃化转变温度、熔点，改善加工性能。开发的材料有望应用于有高韧性高强度要求的可生物降解薄膜制品领域。