Self-Reinforcement via 1D Nanostructure Formation during Melt Blending of Thermoplastics and Thermoplastic Elastomers with Nanophase-Separated UHMWPE/HDPE Wax Reactor Blends

Adding inorganic fillers like glass or carbon fibers is common practice for reinforcing engineering thermoplastics to expand their range of applications in lightweight construction. Albeit the advantages of traditional polymer composites are obvious, the quest for sustainable development and a circular economy is driving the development of recyclable all-polymer composites with a low carbon footprint. Melt blending of commodity high-density polyethylene (HDPE) with reactor blends (RB) comprising nanophase-separated ultrahigh-molecular-weight polyethylene (UHMWPE) substantially improved the toughness/stiffness/strength balance of polyethylene (PE). During processing, the flow-induced formation of nanofiber-like extended-chain UHMWPE one-dimensional (1D) nanostructures accounted for efficient HDPE reinforcement. Herein, we expanded this concept of self-reinforcement and all-polymer composite formation to other thermoplastics and thermoplastic elastomers. Nanophase-separated UHMWPE/HDPE wax reactor blends with ultrabroad bimodal molar distribution served as an additive for melt compounding and injection molding of isotactic polypropylene (iPP), olefin block copolymers (OBC), and a thermoplastic ionomer (Surlyn). Microscopic imaging and evaluation of mechanical properties confirmed the in situ formation of fiberlike UHMWPE 1D nanostructures that efficiently reinforced these thermoplastics and thermoplastic elastomers. The resulting all-polymer composites were a drop-in solution for injection molding of olefinic thermoplastics with unprecedented mechanical properties enabled by the synergy of the characteristics of the matrix material in combination with ultrastrong UHMWPE 1D nanostructures.