Self-Reinforcement of Polypropylene Lid-Shaped Samples Induced by Increasing Shish-Kebab Content: Practical Application of Vibration Injection Technology

Unique Slow Crack Growth Behavior of Isotactic Polypropylene: The Role of Shear Layer-Spherulites Layer Alternated Structure

With the development of polymer science, more attention is being paid to the longevity of polymer products. Slow crack growth (SCG), one of the most important factors that reveal the service life of the products, has been investigated widely in the past decades. Here, we manufactured an isotactic polypropylene (iPP) sample with a novel shear layer–spherulites layer alternated structure using multiflow vibration injection molding (MFVIM). However, the effect of the alternated structure on the SCG behavior has never been reported before. Surprisingly, the results showed that the resistivity of polymer to SCG can be enhanced remarkably due to the special alternated structure. Moreover, this sample shows unique slow crack propagation behavior in contrast to the sample with the same thickness of shear layer, presenting multiple microcracks in the spherulites layer, which can explain the reason of the resistivity improvement of polymer to SCG.

Effects of Phase Morphology on Mechanical Properties: Oriented/Unoriented PP Crystal Combination with Spherical/Microfibrillar PET Phase

In situ microfibrillation and multiflow vibrate injection molding (MFVIM) technologies were combined to control the phase morphology of blended polypropylene (PP) and poly(ethylene terephthalate) (PET), wherein PP is the majority phase. Four kinds of phase structures were formed using different processing methods. As the PET content changes, the best choice of phase structure also changes. When the PP matrix is unoriented, oriented microfibrillar PET can increase the mechanical properties at an appropriate PET content. However, if the PP matrix is an oriented structure (shish-kebab), only the use of unoriented spherical PET can significantly improve the impact strength. Besides this, the compatibilizer polyolefin grafted maleic anhydride (POE-g-MA) can cover the PET in either spherical or microfibrillar shape to form a core⁻shell structure, which tends to improve both the yield and impact strength. We focused on the influence of all composing aspects-fibrillation of the dispersed PET, PP matrix crystalline morphology, and compatibilized interface-on the mechanical properties of PP/PET blends as well as potential synergies between these components. Overall, we provided a theoretical basis for the mechanical recycling of immiscible blends.

Tailoring Hydrocarbon Polymers and All-Hydrocarbon Composites for Circular Economy

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.

New Approach to Optimize Mechanical Properties of the Immiscible Polypropylene/Poly (Ethylene Terephthalate) Blend: Effect of Shish-Kebab and Core-Shell Structure

Improving the mechanical properties of immiscible PP/PET blend is of practical significance especially in the recycling process of multi-layered plastic solid waste. In this work, a multi-flow vibration injection molding technology (MFVIM) was hired to convert the crystalline morphology of the PP matrix from spherulite into shish-kebab. POE⁻g⁻MA was added as compatibilizer, and results showed that the compatibilization effect consisted in the formation of a core-shell structure by dispersing the POE⁻g⁻MA into the PP matrix to encapsulate the PET. It was found that the joint action of shish-kebab crystals and spherical core-shell structure enabled excellent mechanical performance with a balance of strength and toughness for samples containing 10 wt % PET and 4 wt % POE⁻g⁻MA, of which the yield strength and impact strengths were 50.87 MPa and 13.71 kJ/m², respectively. This work demonstrates a new approach to optimize mechanical properties of immiscible PP/PET blends, which is very meaningful for the effective recycling of challenging plastic wastes.