Foam injection molding of phenolic resins

The process of foam injection molding is state of the art for thermoplastic materials, whereas very little research has been carried out applying this technique for thermosetting materials. This publication demonstrates the feasibility of a foam injection molding process with phenolic resin as a thermosetting material. Test series were carried out applying different foaming agents, which differ in their decomposition process. One is exothermic, another one is endothermic and the third creates foam due to thermal expansion. The maximum weight reduction achievable for each foaming agent has been determined by gradually decreasing the shot volume until incomplete filling occurs. The foam structures are analyzed by microsections and evaluated with a digital image processing method. Additionally, the effect on mechanical properties is discussed by evaluating the bending stress. The exothermic foaming agent shows the best foam patterns achieving a maximum weight reduction of approximately 50 %, whereas the endothermic and the thermal foaming agent can reduce the weight by approximately 25 % and 20 % respectively. The bending stress decreases significantly with an increasing proportion of foam in all samples.