A novel foam injection molding process using gas-laden pellets

Polymeric foams usually employ chemical or physical blowing agents to produce cellular or microcellular structures. A chemical blowing agent (CBA) can be easily and directly mixed with plastic pellets and fed through the hopper while a generally finer microcellular structure can be achieved using a physical blowing agent (PBA). The physical blowing agent route is accomplished by injecting environmentally benign gases (e.g., carbon dioxide, CO ₂, or nitrogen, N ₂) in the super-critical state into the machine barrel to form a single-phase polymer-gas solution that subsequently foams during molding. This paper proposes a new foam injection molding process that enables the ease of processing of the chemical blowing agent method with the foaming characteristics of a physical blowing agent, but in a cost-effective fashion. By using gas-laden (CO ₂ or N ₂) pellets in injection molding, a simple yet cost-effective dosing method can be achieved. This paper presents this new process and the properties of the injection molded foamed parts.