Lightweight and strong gelling agent-reinforced injection-molded polypropylene composite foams fabricated using low-pressure CO₂ as the foaming agent

Abstract

Lightweight and strong polymeric foams show high potential application in alleviating the global energy crisis due to their capability of reducing material and resource requirements as well as decreasing energy consumption. However, it is inevitably difficult to produce lightweight polymers with satisfactory mechanical properties. Herein, we report an innovative method to produce high-performance polypropylene (PP) foams by combining a sorbitol gelling agent with the newly developed low-pressure microcellular injection molding (MIM) technique. Carbon dioxide (CO₂) at an ultralow pressure of 5 MPa is used as a foaming agent in the low-pressure MIM process. The addition of a 1, 3:2, 4-bis-O-(4-methyl benzylidene)-D-sorbitol gelling agent (MDBS), which generates an in situ network structure, notably enhances the crystallization, viscoelasticity and melt strength of PP, resulting in PP foams with well-defined cellular structures. Compared with neat PP foams, the added sorbitol gelling agent leads to a four orders of magnitude increase in the cell density of PP foams that have a cell size of approximately 8.4 μm. Remarkably, the tensile toughness and tensile strength of the PP composite foam are approximately 1000 % and 150 % higher than those of the neat PP foam, respectively. These results demonstrate that lightweight and strong PP foams with high ductility can be obtained via the scalable and novel FIM technique, which shows a promising future in many applications, such as automotive, construction and electrical components.