13X zeolite as Difunctional nucleating agent regulating the crystal form and improving the Foamability of blocked copolymerized polypropylene in supercritical CO₂ foaming process

Comparing with solid counterpart, plastic foams exhibit many merits, such as lightweight, excellent energy absorption, good thermal insulation and sound absorption properties. Blocked copolymerized polypropylene (PPB) is a kind of foamable polymer, but it is challenging to obtain the PPB foam with high expansion ratio, uniform cell structure and good toughness. In this study, 13X zeolite was used as nucleating agent for both crystallization process and foaming process. During the crystallization process, 13X zeolite used as β-nucleating agent not only improved the crystallization behavior but also induced the β-form crystal, thereby improving the toughness of PPB. During the foaming process, 13X zeolite used as cell nucleating agent improved the foamability of PPB by increasing the content of CO₂ dissolved in PPB melt due to its porous structure. The experiment results revealed that when the content of 13X zeolite was 0.5 wt%, the relative content of β-crystal (k_β), the crystallization temperature (T_c) and the impact strength of PPB were greatly increased from 0.17, 114 °C, 838.9 J/m to 0.64, 122 °C, 952.9 J/m respectively. Moreover, at that content, the expansion ratio (R_v) of PPB foam reached the maximum value of 41 times under the optimal foaming temperature and pressure.