Fabrication of Expanded Ethylene–Propylene–Butene‑1 Copolymer Bead

Ethylene–propylene–butene-1 ternary copolymer (TPP) and ethylene–propylene copolymer (EPC) were fabricated to produce expanded polypropylene (EPP) beads through batch foaming followed by steam-chest molding. The microstructure and thermal behaviors of both TPP and EPC were investigated by nuclear magnetic resonance, gel permeation chromatography, wide-angle X-ray diffraction, analytical temperature rising elution fractionation, and differential scanning calorimetry. EPP beads made of TPP and EPC were prepared by an autoclave batch-foaming process using compressed CO2 as the blowing agent. Polypropylene micropellets (average diameter is approximately 1 mm) were obtained with an underwater micropelletizer system, which shortens the CO2 diffusion distance. The effects of CO2 content on the melting temperature of two types of polypropylene were studied. A magnetic suspension balance was used to measure the solubility of CO2 in semimolten PP. The effects of introducing comonomers on the foaming processing and cell structure of EPP beads were preliminarily investigated. The addition of 1-butene played a significant role in enhancing the mechanical properties and decreasing the energy cost during both batch foaming and steam-chest molding with reduced carbon dioxide emissions.