The world population will rapidly grow from 7 to 9 billion by 2050 and this will parallel a surging annual plastics consumption from today's 350 million tons to well beyond 1 billion tons. The switch from a linear economy with its throwaway culture to a circular economy with efficient reuse of waste plastics is therefore mandatory. Hydrocarbon polymers, accounting for more than half the world's plastics production, enable closed‐loop recycling and effective product‐stewardship systems. High‐molar‐mass hydrocarbons serve as highly versatile, cost‐, resource‐, eco‐ and energy‐efficient, durable lightweight materials produced by solvent‐free, environmentally benign catalytic olefin polymerization. Nanophase separation and alignment of unentangled hydrocarbon polymers afford 100% recyclable self‐reinforcing all‐hydrocarbon composites without requiring the addition of either alien fibers or hazardous nanoparticles. Recycling of durable hydrocarbons is far superior to biodegradation. The facile thermal degradation enables liquefaction and quantitative recovery of low molar mass hydrocarbon oil and gas. Teamed up with biomass‐to‐liquid and carbon dioxide‐to‐fuel conversions, powered by renewable energy, waste hydrocarbons serve as renewable hydrocarbon feedstocks for the synthesis of high molar mass hydrocarbon materials. Herein, an overview is given on how innovations in catalyst and process technology enable tailoring of advanced recyclable hydrocarbon materials meeting the needs of sustainable development and a circular economy.
Scheme 1. Freeze-drying of CNF hydrogels (identified by atomic force microscopy (AFM) height image; z-scale = 4 nm) leading to 2D sheet-like NC aerogels (image taken by scanning electron microscopy (SEM)) due to lamellar ice-templating.
produce all-polymer composite by means of flow-induced crystallization during classical injection molding employed in the state-of-the-art processing of commodity and engineering plastics. Today, progress made in all-polymer composite technology holds great promise for upgrading and diversifying existing thermoplastics. Especially, with respect to converting commodity polymer such as polyolefins into high performance materials. As reviewed by Karger-Kocsis and coworkers, one-step (in situ) and multistep (ex situ) processes have been pioneered to produce all-polymer composites via selfreinforcement resulting from oriented polymer crystallization during polymer processing. [1,2] In one-step strategies, flow-induced crystallization is achieved in extrusion and injection molding processes either by redesigning machines or by employing special precisely controlled processing conditions such as high pressure, processing temperature close to polymer melting temperature, and high frequency. [3,4] However, most one-step processes prolong cycle times, require high investment costs, and are highly incompatible with the existing cost-efficient processing technology established for molding of commodity plastics. In multistep processes, oriented polymer crystallization results from either drawing of fibers or stretching of tapes, respectively, followed by lamination such as hot compaction in the subsequent process step. Again, such processes involving lamination of fibers, stacking of stretched films massively impair both throughput and cost efficiency typical for classical injection molding. [5,6] Flow-induced oriented polymer crystallization and in situ formation of extended-chain polymer microand nanofibers represent the key prerequisite for producing all-polymer composites in one-step processes. The concept of flow-induced polymer coil-stretch transition was pioneered by de Gennes for dilute solutions and by Keller and Kolnaar for elongation flow in polymer melts. [7,8] Only when exceeding a critical polymer molar mass flow-induced crystallization produces shish-kebab structures, in which extended-chain polymers form shish, which nucleate the crystallization of low molecular weight polymer forming kebab. Below the critical mass polymer, chains rapidly relax to the coiled state and fail Nanostructure Composites All-polyethylene composites exhibiting substantially improved toughness/ stiffness balance are readily produced during conventional injection molding of high density polyethylene (HDPE) in the presence of bimodal polyethylene reactor blends (RB40) containing 40 wt% ultrahigh molar mass polyethylene (UHMWPE) dispersed in HDPE wax. Scanning electron microscopy (SEM) and differential scanning calorimetry (DSC) analyses shows that flow-induced crystallization affords extended-chain UHMWPE nanofibers forming shish which nucleates HDPE crystallization producing shish-kebab structures as reinforcing phases. This is unparalleled by melt compounding micron-sized UHMWPE. Injection molding of HDPE with 30 wt% RB40 at 165 °C aff...
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.