【作者】 刘敏；

【导师】 马秀清；

【作者基本信息】 北京化工大学 ， 机械工程， 2019， 硕士

【摘要】 聚乳酸(PLA)是近些年来备受关注的一种可生物降解材料。从玉米、土豆、小麦和玉米秸秆等可再生的植物资源中提炼出的淀粉或多糖等可以作为合成聚乳酸的原料。聚乳酸因为原料来源充足、加工和制备方法多样且成熟、生产成本较低等优点,因此在各个领域逐渐被用来取代聚乙烯、聚丙烯等通用塑料。热塑性聚氨酯(TPU)是一种介于一般橡胶和塑料之间的特殊的弹性合成材料,由多异氰酸酯、低分子多元醇制备而成。它既具有橡胶的高弹性,又具有热塑性塑料的热塑加工性,同时也具有高模量、高强度、高伸长率、高弹性等优点,被广泛应用于塑料的增韧改性。纳米二氧化硅(SiO2)是三维结构的纳米粒子,由于低成本、高表面活性等优点,也常被用来制备聚合物纳米复合材料。本课题采用TPU对PLA进行增韧改性,研究结果表明TPU能有效改善PLA的韧性,但扫描电镜分析显示PLA与TPU相界面明显,PLA与TPU相容性差。为此向PLA/TPU共混体系中添加SiO2来提高PLA与TPU的相容性,研究结果表明SiO2主要分布在PLA与TPU相界面处,与PLA和TPU都有很好的结合,从而提高了 PLA与TPU的相容性。PLA/TPU/SiO2共混体系的性能受TPU含量、SiO2含量、共混工艺等因素影响,研究结果表明,共混体系的冲击强度随着TPU含量的增多而增高,拉伸强度随TPU含量的增多而降低;随着纳米SiO2含量的增加,PLA/TPU/SiO2共混体系冲击强度有所提高,但拉伸强度呈现下降趋势;双因素正交试验分析得出,纳米SiO2含量比TPU含量对共混体系性能的影响更大;共混工艺对共混体系性能影响的研究中,采用先将PLA与纳米SiO2共混造粒,再将得到的共混物与TPU共混的共混方式得到的共混体系分散相粒径分布最窄,粒径较均匀,冲击性能与拉伸性能均优于其他组别。对实验所用双螺杆挤出机混合段螺杆构型进行设计,模拟并分析了表征不同螺杆构型下共混体系混合能力的部分参数。模拟分析得出8KB+SE+SME的螺杆构型的各项指数均优于其他组别。按照设计的五种螺杆构型实际制备PLA/TPU/Si02共混体系并进行相关性能测试,分析混合段螺杆构型对共混体系性能的影响。实验研究结果表明,混合段螺杆构型对PLA/TPU/Si02共混体系拉伸强度的影响较小,对冲击强度的影响较大;捏合盘块数多有利于TPU的分散混合;先分散元件后分布元件的布置方式有利于PLA/TPU/Si02共混体系冲击强度、拉伸强度的提高。将模拟分析与实验研究进行对比,两部分结果相吻合,结果均显示捏合盘块数多、且采用先分散元件后分布元件的排布方式有利于PLA/TPU/Si02共混体系的综合力学性能和TPU的分散混合。更多还原

【Abstract】 Polylactic acid(PLA)is a kind of biodegradable material which has attracted much attention in recent years.Starch or polysaccharides extracted from renewable plant resources such as corn,potatoes,wheat and corn straw can be used as raw materials for the synthesis of polylactic acid.PLA has been gradually used to replace general plastics such as polyethylene and polypropylene in various fields because of its abundant raw materials,various processing and preparation methods,mature and low production cost.Thermoplastic polyurethane(TPU)is a special elastic synthetic material between rubber and plastics,which is prepared from polyisocyanate and low molecular polyol.It not only has high elasticity of rubber,but also has thermoplastic processability of thermoplastic plastics.It also has high modulus,high strength,high elongation,high elasticity and so on.It is widely used in toughening and modification of plastics.Nano-silica(SiO2)is a three-dimensional nano-particle.Because of its low cost and high surface activity,it is often used to prepare polymer nanocomposites.TPU was used to toughen PLA in this project.The results showed that TPU can effectively improve the toughness of PLA.But SEM analysis showed that the interface between PLA and TPU was obvious,and the compatibility between PLA and TPU was poor.SiO2 was added to PLA/TPU blends to improve the compatibility between PLA and TPU.The results showed that SiO2 was mainly distributed at the interface between PLA and TPU,which had a good combination with PLA and TPU,thus improving the compatibility between PLA and TPU.The properties of PLA/TPU/SiO2 blends are affected by TPU content,SiO2 content and blending process.The results showed that the impact strength of blends increased with the increase of TPU content and tensile strength decreased with the increase of TPU content.With the increase of nano-SiO2 content,the impact strength of the PLA/TPU/SiO2 blends increased,but the tensile strength showed a downward trend.The results of two-factor orthogonal test showed that the content of nano-SiO2 had a greater effect on the properties of the blends than that of TPU.In the study of the effect of blending process on the properties of blends,the dispersed phase size of the blends prepared by the blending process of PLA and nano-SiO2 blended firstly and the obtained blend and TPU blended had the narrowest particle size distribution and uniform particle size,and the impact and tensile properties were better than those of other groups.The screw configuration of the mixing section of the twin screw extruder was designed,and some parameters characterizing the mixing ability of blends with different screw configurations were simulated and analyzed.The simulation results showed that the screw configuration indexes of 8KB+SE+SME are better than those of other groups.The blends prepared with five screw configurations were tested and the influence of five screw configuration on the properties of PLA/TPU/SiO2 blends was analyzed.The results showed that the screw configuration in the mixing section had little effect on tensile strength of PLA/TPU/SiO2 blends,but had a great influence on the impact strength of PLA/TPU/SiO2 blends.The number of kneading disc was more favorable for the dispersion mixing of TPU.The arrangement of distributive element after dispersive element facilitated the improvement of the impact strength and tensile strength of the PLA/TPU/SiO2 blends.The simulation analysis was compared with the experimental study and the results of the two parts coincided with each other.The results showed that large number of kneading discs and the arrangement of distributive element after dispersive element were beneficial to the comprehensive mechanical properties of PLA/TPU/SiO2 blends and the dispersive mixing of TPU.更多还原