CAS-SC: Threading the Needle: Recycling Commodity Plastics

非技术总结：塑料无处不在，几乎在生活的各个方面为社会提供了无数的好处。从医疗植入物到食品包装再到绿色能源生产风车，合成聚合物为世界上许多最苛刻的技术挑战提供了有利的解决方案。然而，这些材料在很大程度上是坚不可摧的，并且正在以惊人的速度在环境中积累。这项研究旨在开发一种经济可行的方法来回收聚乙烯、聚丙烯和聚苯乙烯，这三种塑料占全球塑料总产量的60%以上。与铝和玻璃不同，很少有商业塑料在使用后被回收，这是一种可悲的资源浪费。回收利用的一种策略是在高温下将这些塑料混合在一起，然后重新配制成有用的产品。不幸的是，由于化学上不同的聚合物无法在分子水平上混合，导致相分离，这导致了脆性和机械性能差的材料。在机械变形过程中，界面附着力差会导致裂纹和块体破坏。该项目将探索商业上可行的嵌段共聚物的合成，当与相分离的聚合物混合时，它可以迁移到界面上，从而将塑料区域拼接在一起，并恢复与原始材料相关的优越机械性能。这项研究工作将培养高分子科学与工程领域的博士、本科生和博士后，高分子科学与工程是美国化学和材料工业中最大的领域之一。参与者与当地社区的互动将激励学生及其家人接受科学和工程的高等教育和未来的职业生涯。技术总结：塑料废物危机要求制定新的战略，将聚乙烯（PE）、聚丙烯（iPP）和聚苯乙烯（PS）（占所有合成聚合物的60%以上）在使用后返回到产品原料流中。回收利用的一种方法是将这些塑料熔体混合在一起，然后再配制成有用的商业产品。该项目将探索三嵌段和多嵌段共聚物的合成，这些共聚物位于相分离域界面，导致拓扑约束和共结晶，共同产生界面强度，从而具有与纯均聚物竞争的机械性能。丁二烯和苯乙烯将阴离子聚合，聚丁二烯嵌段催化氢化，生成PE-PX、PS-PX和PS-PE二嵌段、三嵌段和多嵌段共聚物，其中PX是一种随机共聚物，含有约90%的乙烯和10%的乙烯重复单元。PX与iPP熔融混相。这些嵌段共聚物与相应的均聚物对的胶束形成和界面活性将通过小角中子和x射线散射（SANS和SAXS），原子力和透射电子显微镜（AFM和TEM）进行探索。混合物将通过熔体混合配制，并通过拉伸和冲击测试在固态下进行评估。界面附着力将通过剥离试验进行量化。该项目的总体目标是确定共混延展性对嵌段共聚物分子量、组成和结构的依赖性；嵌段共聚物浓度；以及加工条件。这项可持续发展的努力旨在创造一种经济上可行的方法来回收最普遍的商品塑料。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

NON-TECHNICAL SUMMARY:Plastics are ubiquitous, providing innumerable benefits to society across virtually all aspects of life. From medical implants to food packaging to green energy producing windmills, synthetic polymers offer enabling solutions to many of the world’s most demanding technical challenges. However, these materials are largely indestructible and are accumulating in the environment at an alarming rate. This research aims to develop an economically tractable approach to recycling polyethylene, polypropylene, and polystyrene, which together constitute more than 60% of all plastics produced worldwide. Unlike aluminum and glass, few commercial plastics are recycled after use, representing a tragic waste of resources. One strategy for recycling is to blend these plastics together at elevated temperature followed by reformulation into useful products. Unfortunately, this results in brittle and mechanically inferior materials due to the inability of chemically different polymers to mix at a molecular level, leading to phase separation. Poor interfacial adhesion promotes cracks and bulk failure during mechanical deformation. This project will explore the synthesis of commercially viable block copolymers that can migrate to the interface when mixed with phase separated polymers, thereby stitching the plastic domains together and recovering the superior mechanical properties associated with the virgin materials. This research effort will result in the training of Ph.D. and undergraduate students, along with postdocs, in the field of polymer science and engineering, one of the largest segments of the chemical and materials industries in the United States. Interactions of the participants with the local community will inspire students, and their families, to embrace science and engineering for higher education and prospective careers.TECHNICAL SUMMARY:The crisis of plastic waste requires the development of new strategies for returning polyethylene (PE), polypropylene (iPP) and polystyrene (PS), representing more than 60% of all synthetic polymers, to product feed streams after use. One approach to recycling involves melt blending these plastics together, followed by formulation into useful items of commerce. This program will explore the synthesis of triblock and multiblock copolymers that localize at the phase separated domain interface, resulting in topological constraints and cocrystallization, which together create interfacial strength leading to mechanical properties competitive with the pure homopolymers. Butadiene and styrene will be polymerized anionically, and the polybutadiene blocks catalytically hydrogenated, yielding PE-PX, PS-PX, and PS-PE diblock, triblock and multiblock copolymers, where PX is a random copolymer containing approximately 90% ethylethylene and 10% ethylene repeat units. PX is melt miscible with iPP. Micelle formation and interfacial activity of these block copolymers with the respective pairs of homopolymers will be explored using small-angle neutron and X-ray scattering (SANS and SAXS), and atomic force and transmission electron microscopy (AFM and TEM). Blends will be formulated by melt mixing and evaluated in the solid state by tensile and impact testing. Interfacial adhesion will be quantified using peel tests. The overall goals of this program are to establish the dependence of blend ductility on: block copolymer molecular weight, composition, and architecture; block copolymer concentration; and processing conditions. This sustainability effort aims to create an economically viable approach to recycling the most prevalent commodity plastics..This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.