摘要
目前,全世界塑料年产量已经超过2亿吨,相应的,塑料废弃物逐渐增加,已引起严重的环境污染。减少废塑料污染的重要方法之一是使用在自然界和生物体内外都可以自然降解、不会对环境造成污染的生物降解材料。在已开发的生物降解材料中,聚乳酸(PLA)和淀粉由于来源于天然资源,具有可完全生物降解,对环境无污染等优点,成为最有前途的可生物降解高分子材料。聚乳酸作为新型完全生物降解脂肪族聚酯,具有良好的生物相容性、力学性能和耐水性,但生产成本远高于传统塑料,限制了它的应用。淀粉作为天然高分子具有来源广泛、价格低廉、可完全生物降解、再生周期短等优点,是重要的生物降解材料之一。但是淀粉是多羟基聚合物,能够形成大量的分子内、分子间氢键,使其本身不具备热塑性,难以成型加工,同时纯淀粉塑料由于其强亲水性使其对湿度敏感,耐水性差。采用廉价的淀粉和性能优良的聚乳酸复合体系成为解决性能与成本之间矛盾的有效办法,国内外学者也在这方面做了一些研究。目前聚乳酸与淀粉共混体系中最主要的问题是疏水性的聚乳酸与亲水性的淀粉之间的界面结合力太弱,即两者相容性较差。热塑性淀粉(TPS)是采用天然淀粉、高直链淀粉或直链淀粉在不添加聚合物,在高温、高压和高湿条件下添加有效的增塑剂进行挤塑或注塑得到的全生物降解新材料。
本文在总结国内外相关研究的基础上,提出并制备了一种由可降解无毒聚乙二醇400(PEG400)改性的聚乳酸／热塑性淀粉复合材料,该材料是先经造粒后经注塑加工而成的复合材料。研究了PEG400加入量的不同对PLA/TPS复合材料加工流变性能、力学性能的影响,并且采用差示扫描量热(DSC)仪和扫描电子显微镜(SEM)对复合材料的微观结构进行分析以及研究了加工工艺条件对复合材料的影响。结果表明所制备的PEG400改性的复合材料在一定程度上改善了聚乳酸和热塑性淀粉之间的相容性,提高了复合材料的塑性。当PEG400的加入量达到3%时,其力学性能达到最佳。另外从加工工艺条件对复合材料的影响可以得出冷却时间为60s,注射压力为10MPa,注射速度为80mm／s时,复合材料体系的力学性能达到最佳。材料有望用于可降解餐具、性能要求不太高的可降解塑料包装等领域。为了进一步对比研究,分析比较了不同改性剂对复合材料力学性能的影响。
另外通过对土埋法和堆肥法降解5个月的复合材料进行力学性能及重量损失测定,可以得出在改性前,样条的降解性能随着热塑性淀粉含量的增加而变得更好；经过PEG400改性后,样条的降解率随着PEG400含量的增加而增加,说明PEG400在一定程度上促进了复合材料的降解。把本次采用的堆肥法和土埋法进行对比,可以得出堆肥法虽然在一定程度上提高了样条的降解率,但对样条降解速率的提高很小,所以还需进一步改进堆肥实验,从而进一步提高样条的降解速度。综合分析样条的力学性能与降解性能,找出了两者的最佳平衡点,即当PEG400的加入量达到3%时,其力学性能和降解性能达到最佳,从而确定了复合材料的最优配方。
World plastics production has more than 200 million tons, its extensive application dues to the rapid increase of waste, have caused serious environmental pollution problems. One important way of waste plastic pollution reduction is to use biodegradable material both in nature and organisms, the biodegradable material will not cause environmental pollution. During the biodegradable materials, poly (lactic acid) and starch become the most promising biodegradable polymer materials as derived from natural resources, with full bio-degradable, environmental pollution, etc. poly (lactic acid) is derived from renewable resources as a new type of fully biodegradable aliphatic polyester, have good biocompatibility, mechanical properties and water resistance, but the cost of production is far higher than traditional plastic, limiting its application. Starch is also one important biodegradable materials with its inexpensive, completely biodegradable, renewable short cycle. However, starch is a polyhydroxy polymer, can form a large number of intermolecular hydrogen bonds, so that it does not have the thermoplastic and is difficult to process, while pure starch plastics is sensitive to moisture and water, so its hydrophilic nature is strong. Cheap starch and poly (lactic acid) composite system is the way to resolve this contradictory of performance and cost effective, foreign scholars have done some research. Present blends of polylactic acid and starch, the most important issue is the poor interface compatibility between the hydrophobic of poly(lactic acid) and hydrophilic of starch. Thermoplastic starch is made of natural starch, high amylose or amylose with adding an effective plasticizer using extrusion or injection molding in high temperature, high pressure and high humidity conditions.
In this paper, PLA/thermoplastic starch (TPS) blends were produced using injection molding machine in the presence of poly(ethylene glycol)(PEG). The rheological and mechanical properties of PLA/TPS were studied by adding different amount of PEG. And thermal analysis (DSC) instrument and scanning electron microscopy (SEM) were used on the microstructure of composite materials, and researched processing conditions impact on composite materials. The results show that the composite materials modified by the PEG400 improved the compatibility between thermoplastic starch and poly(lactic acid), and enhanced plasticity of composite materials. when the addition of polyethylene glycol reach to 3%, the mechanical properties of composite materials achieved the best. From processing conditions we can conclude that mechanical properties of composites will be the best when cooling time 60 seconds, injection pressure 10MPa, injection speed 80mm/s. The composite materials could be used in the biodegradable tableware, biodegradable plastic bags and other fields. For further comparative studies, I analyzed the mechanical properties of composite materials using different modifiers.
By assessment of mechanical properties and weight loss through five months of degradation of composite materials, Results show that:Before the modification, degeneration performance increases along with TPS content increases. After the modification with PEG400, degradation rate increases with the increase of PEG400 concentration, indicating PEG400 promoted the compound materials degeneration to a certain extent. Comparison with soil burial test and composting degradation, we can conclude that although composting degradation increased the degradation rate of samples, but effects is little. Therefore, we need improve composting degradation experiment. Though analyzing the mechanical properties and degradation of samples, I found the optimal balance point of the mechanical properties and degradation of the performance, when the addition of polyethylene glycol reach to 3%, the mechanical properties and degradation of composite materials achieved the best, so I determined the optimal formulation of composite materials.
引文
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