改性纳米碳酸钙增强淀粉基生物降解塑料研究

Starch-based biodegradable plastics are considered one of the most promising biodegradable materials, which are usually prepared from blends of thermoplastic starch (TPS), biodegradable polyesters, and compatibilizer hydroxyl functioned polyesters (HTP). On the account of the issue of food security, the resource utilization of starch is confined by the national policy. Meanwhile, there are competitions with fuel ethanol industry for starch supplies. Therefore, an urgent research topic is proposed, aiming to further reduce cost and improve mechanical properties of starch-based biodegradable plastics at lower starch content and higher biodegradable polyesters, which would promote commercialization application of starch-based biodegradable plastics on a large scale. For this purpose, modified nanometer calcium carbonate is supposed to be blended with starch-based biodegradable plastics in this research project. The technical route is to synthesize dendritic macromolecules with massive ester bonds in the main chain and terminal carboxyl groups. The dendritic macromolecules are then to be used to modify the surface of nanometer calcium carbonate. Above are innovative points of this subject and have not been reported yet. The synthesis technology parameters would be optimized and the mechanism of CaCO3 modification will be investigated. The ratio of modified nanometer calcium carbonate, TPS, biodegradable polyesters, and compatibilizer would be adjusted. Dispersion mechanism of nanometer calcium carbonate in starch-based biodegradable plastic matrix would be studied and processing parameters would be optimized, which are expected to prepare novel biodegradable plastics with lower cost and enhanced mechanical properties.

淀粉基生物降解塑料是最具前景的生物降解塑料之一，由热塑性淀粉和可降解聚酯、以及增容剂羟基功能化聚酯共混制备。由于粮食安全的原因，国家政策限制淀粉的资源化应用，且存在着燃料乙醇行业对淀粉的需求竞争，因此如何在淀粉加入量适当降低，同时多种可降解聚酯价格仍较高的条件下，降低淀粉基生物降解塑料的成本，提高力学性能，使其能够大规模商品化应用，成为亟待解决的课题。为达到上述目标，本课题拟采用改性纳米碳酸钙与淀粉基生物降解塑料共混。技术路线是合成主链含大量酯键、端基为羧基的新型树枝状大分子作为改性剂，对纳米碳酸钙进行表面改性。这些是本课题的创新点，尚未见到报道。优化树枝状大分子合成工艺参数，探索改性碳酸钙的机理。调整改性纳米碳酸钙与热塑性淀粉、可降解聚酯、增容剂的相对比例，研究纳米碳酸钙在淀粉基塑料基质中的分散机制，优化加工参数，以期能够得到成本降低、力学性能提高的新型降解塑料。

淀粉基生物降解塑料是最具前景的生物降解塑料之一，通常由热塑性淀粉（TPS）和可降解树脂共混制备。如何提高其力学性能，使其大规模商品化应用，已成为亟待解决的课题。本课题合成了可降解的端羧基超支化聚酯，创新性的以之改性纳米碳酸钙，改性后加入TPS和可降解树脂共混物以提高其综合力学性能，最终目标是使其达到聚乙烯（PE）的水平。. 分别采用一步法和两步法合成了多种端羧基超支化聚酯，并用于纳米碳酸钙的改性。并对柠檬酸与聚乙二醇6000缩聚进行了合成条件优化，最优条件为反应温度160℃，催化剂对甲苯磺酸加入量为反应物总质量的3.0%，第一步常压反应3h，再0.6kPa减压反应1小时，第二步常减压反应时间均为3h，特性黏度最高为37.6ml/g，优化了此聚酯改性纳米碳酸钙反应条件，结果为加入聚酯的羧基摩尔数与碳酸钙质量3%的硬脂酸相同，DMF中75℃改性1h，吸油值最低为36.0%。还探索和优化了柠檬酸和12-羟基硬脂酸的缩聚及此聚酯对纳米碳酸钙改性条件，得到最低吸油值为23.5。. 采用多种增塑剂在双螺杆挤出机中制备TPS，并优化了甘油增塑TPS的加工条件，最优条件为甘油加入量占原淀粉质量的50%，加工温度175℃，螺杆转速为120r/min，此条件下制备的TPS最有利于后续与可降解树脂共混。分别对TPS和可降解树脂质量比6:4、7:3进行共混，加入改性纳米碳酸钙和（或）两亲性聚酯增容剂，结果表明，加入改性纳米碳酸钙同时提高了共混物的拉伸强度σ和断裂伸长率ε。共混物σ已达到聚乙烯15MPa的水平，在TPS与聚乳酸（PLA）质量比6:4，加入TPS和PLA总质量5%的改性纳米碳酸钙，当σ为12～22MPa时，ε最高为27.3%。经过后续实验研究改性效果更好的纳米碳酸钙，加入TPS与可降解树脂的共混物，有望使其ε继续提高，最终达到PE的ε值160.0%水平。进而使淀粉基生物降解塑料的大规模日常应用成为可能，同时研究改性纳米碳酸钙的增强增韧及多相均匀分散机理，将为包括淀粉基生物降解塑料在内的生物质共混材料的性能增强提供重要理论依据。