CAS-SC: Threading the Needle: Recycling Commodity Plastics

非技术摘要：塑料无处不在，几乎在生活的方方面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可行的解决方案。然而，这些材料在很大程度上是坚不可摧的，并以惊人的速度在环境中积累。这项研究旨在开发一种经济上易于处理的回收聚乙烯、聚丙烯和聚苯乙烯的方法，这些材料加起来占全球塑料产量的60%以上。与铝和玻璃不同的是，很少有商业塑料在使用后被回收，这是对资源的悲惨浪费。回收的一种策略是将这些塑料在高温下混合在一起，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，从而导致相分离，这导致了脆性和机械性能较差的材料。界面粘结力差会在机械变形过程中导致裂纹和整体破坏。该项目将探索合成商业上可行的嵌段共聚物，当与相分离聚合物混合时，这种嵌段共聚物可以迁移到界面上，从而将塑性区域缝合在一起，并恢复与原始材料相关的优异机械性能。这项研究工作将培养聚合物科学和工程领域的博士和本科生以及博士后，聚合物科学和工程是美国化工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庭接受科学和工程，以接受高等教育和未来的职业生涯。技术摘要：塑料废物的危机要求开发新的策略，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)回收到使用后的饲料流中。回收的一种方法是将这些塑料熔融混合在一起，然后将其制成有用的商业物品。本项目将探索三嵌段和多嵌段共聚物的合成，它们位于相分离的区域界面，导致拓扑约束和共结晶，共同产生界面强度，从而获得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两嵌段、三嵌段和多嵌段共聚物，其中PX是一种含有大约90%的乙撑和10%的乙烯重复单元的随机共聚物。PX与iPP是熔融相容的。我们将使用小角中子和X射线散射(SANS和SAXS)以及原子力和透射电子显微镜(AFM和TEM)来研究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。共混物将通过熔融混合配制，并通过拉伸和冲击试验在固态下进行评估。界面粘附力将通过剥离试验进行量化。该计划的总体目标是建立共混延展性的依赖关系：嵌段共聚物的相对分子质量、组成和结构；嵌段共聚物的浓度；以及加工条件。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普遍的商品塑料。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势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.