Tailored Nanostructured HDPE Wax/UHMWPE Reactor Blends as Additives for Melt-Processable All-Polyethylene Composites and in Situ UHMWPE Fiber Reinforcement

Abstract

Tailored polyethylene reactor blend additives (RB) with ultrabroad bimodal molar mass distributions comprise nanophase-separated ultrahigh molar mass polyethylene (UHMWPE) uniformly dispersed in polyethylene wax. During injection molding of high-density polyethylene (HDPE) together with variable amounts of the nanophase-separated HDPE wax/ UHMWPE (70/30) additive (RB30) flow-induced oriented crystallization affords shish-kebab fiber-like UHMWPE nanostructures accounting for efficient HDPE self-reinforcement. RB additives are readily prepared by ethylene polymerization on silica-supported two-site chromium catalysts which simultaneously produce HDPE wax together with disentangled nanoplateletlike UHMWPE. The presence of HDPE wax is essential for lowering melt viscosity at high UHMWPE content. Since HDPE wax crystallizes onto extended-chain UHMWPE shish to form kebab structures, high HDPE wax content is tolerated without encountering emission problems and impairing mechanical properties as observed in the absence of UHMWPE. This in situ reinforcement substantially improves HDPE toughness/stiffness/strength balance as reflected by simultaneously increased Young's modulus (+365%), tensile strength (+392%), and impact resistance (+197%). The performance of self-reinforced polyethylene (PE-SRC) is far superior to that of melt-blended UHMWPE/HDPE and the majority of PE nanocomposites. Neither hazardous UHMWPE nanoparticles nor alien inorganic nanofillers are required.

Blending ultrahigh‐molecular‐weight polyethylene and poly(ethylene/10‐undecen‐1‐ol) in one nascent particle

“…However, the catalytic activity of the V complex was 28 times that of the Fe complex (see Table ). This indicated that the fraction of each component was comparative in the synthesized blends (see Figure ) …”

“…Cat‐1 could prepare the polymer with a M w of 7.7 × 10 4 g/mol, where no chains showed molecular weights larger than 7 × 10 5 g/mol (see Figure ). UHMWPE was successfully synthesized by Cat‐2 (i.e., M w = 2.6 × 10 6 g/mol), where most of the chains presented molecular weights above 1 × 10 6 g/mol . Interestingly, the M w of the polymer synthesized by the hybrid catalyst covered the whole range of molecular weights; this was attributed to the polymer synthesized by the individual catalyst (i.e., Cat‐1 and Cat‐2).…”

“…Blending multiple polymers (or components) in one nascent particle is another effective procedure in the depression of phase separation and is helpful for intensifying the diffusion and interactions among multiple chains . This blending scale can be endowed by the catalysis of hybrid catalysts that anchor multiple catalysts in one catalytic particle . Generally, two kinds of catalysts are randomly immobilized on one support.…”

Tailored bimodal ultra‐high molecular weight polyethylene particles

“…This concept has been extended to high UHMWPE content blends by Chadwick et al . and Mülhaupt et al . but still provides polymers that are not classed as UHMWPE.…”

“…A dual site catalyst concept similar to the work of Chadwick et al . and Mülhaupt et al . was not deemed to be viable.…”