CAS-SC: Threading the Needle: Recycling Commodity Plastics

非技术总结：塑料无处不在，为社会生活的几乎所有方面提供了无数的好处。从医疗植入物到食品包装，再到生产绿色能源的风车，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不可破坏的，并以惊人的速度在环境中积累。该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，这些塑料占全球生产的所有塑料的60%以上。与铝和玻璃不同，很少有商业塑料在使用后被回收，这是一种悲惨的资源浪费。回收利用的一个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不能在分子水平上混合，导致相分离，这导致脆性和机械性能较差的材料。在机械变形过程中，不良的界面粘合促进裂纹和体破坏。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，嵌段共聚物可以迁移到界面，从而将塑料域缝合在一起，并恢复与原始材料相关的上级机械性能。这项研究工作将导致培养博士。高分子科学和工程领域的本科生沿着博士后，这是美国化学和材料工业中最大的部分之一。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，以获得高等教育和未来的职业生涯。技术总结：塑料废物的危机需要开发新的策略，将占所有合成聚合物60%以上的聚乙烯（PE）、聚丙烯（iPP）和聚苯乙烯（PS）回收到使用后的产品进料流中。回收利用的一种方法是将这些塑料熔融混合在一起，然后制成有用的商品。该计划将探索三嵌段和多嵌段共聚物的合成，这些共聚物定位于相分离的结构域界面，导致拓扑约束和共结晶，它们共同创造界面强度，导致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，产生PE-PX、PS-PX和PS-PE二嵌段、三嵌段和多嵌段共聚物，其中PX是含有约90%乙基乙烯和10%乙烯重复单元的无规共聚物。PX可与iPP熔融混溶。胶束的形成和这些嵌段共聚物与各自对均聚物的界面活性将探讨使用小角中子和X-射线散射（SANS和SAXS），原子力和透射电子显微镜（AFM和TEM）。将通过熔融混合配制混合物，并通过拉伸和冲击试验在固态下进行评价。将使用剥离试验对界面粘附力进行定量。该计划的总体目标是建立共混物延展性对以下因素的依赖性：嵌段共聚物分子量、组成和结构;嵌段共聚物浓度;和加工条件。这一可持续发展努力旨在创造一种经济上可行的方法来回收最流行的商品塑料。该奖项反映了NSF的法定使命，并被认为是值得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的支持。

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.