By the invention of foam processing techniques using physical blowing agents, the area of foam injection molding has caught the attention of product developers in industry as well as of researchers. Compared to conventional injection molding, the foaming approach delivers a great potential in the manufacturing as well as in the part itself, offering a monetary benefit, being vantages for example automotive and consumer goods producer (Hyde, L.J., Kishbaugh, L.A. and Katterman, J.A. (2002) [1]. How Microcellular Foam Molding Changes the Cost Structure of Injection Molded Automotive Components: A Review of the Process and Automotive Applications, SAE Technical Paper Series). The pros are facing several cons in the part quality,notably an impaired surface finish, an over-pronounced loss in mechanical strength and toughness or some uncertainties in subsequent processing steps like varnishing and plastic welding. Actual researchers are approaching those challenges in different ways (Dassow, J. (2003) [2]. Foamed Parts with Excellent Surface Quality, Kunststoffe-Plast Europe, 93(9): 65). On the one hand, the choice of the appropriate polymeric materials has a big impact on the morphologies and the properties of the obtained foam injection molded parts. The mold as well as the processing parameters have a big effect on the obtainable foam morphologies and thus the final part properties.This study presents some possibilities to control the morphology of structural foams at high-density reductions (>50%) by an intelligent mold and process design. Parameters affecting the morphology of the foamed part like the foaming temperature, the cavity pressure, and the expansion ratio are varied.

Foaming isotactic polypropylene (i-PP) by foam injection molding usually results in inhomogeneous, large cell structures. Possibilities to realize more homogeneous and finer foam morphologies are adjusting processing parameters or adding nucleating agents. Often, inorganic nucleating agents such as talc in concentrations of about 2 wt% are used to influence the foam morphology. This article discusses the use of two benzene trisamide-based nucleating agents to control cell nucleation during foaming of i-PP. These additives form supramolecular nanostructures in the polymer melt acting first as nucleating sites for foam formation and second as nuclei for the polymer crystallization. Foaming was performed by foam injection molding with nitrogen as physical blowing agent. A specially designed variotherm mold technology was utilized to exactly control the foaming temperature, foaming pressure, and expansion ratio. Foamed i-PP samples were prepared with a density reduction of 50% and analyzed with respect to foam structure and mechanical properties. We demonstrate that the benzene trisamide additives have a strong influence on the foam morphology at very low additive concentrations. Only 0.02 wt% of an additive is sufficient to obtain a remarkable reduction of the cell sizes. It appears that the cell struts, those dimensions can be influenced by the additives as well, leads to a significant improvement of the mechanical properties.

Rubber-toughened polypropylene (PP) is an important resin for many engineering applications. Through the structural foaming of materials, material cost-saving and lightweight structures can be achieved. In this study, physical blends of PP and poly(ethylene/octene) at various compositions were characterized for their melt strength and shear viscosity. The high pressure MuCell ® foaming process was used to obtain structural foams with average cell diameters of <50 μm and cell densities of approximately 8 million cells/cm3. This study presents key understandings between material rheology and its suitability for structural foaming that are in turn linked to blend composition and melt temperature.

The production of hard-soft-combinations via multi injection molding gained more and more importance in the last years. This is attributed to different factors. One principle reason is that the use of two-component injection molding technique has many advantages such as cancelling subsequent and complex steps and shortening the process chain. Furthermore this technique allows the combination of the properties of the single components like the high stiffness of the hard component and the elastic properties of the soft component. Because of the incompatibility of some polymers the adhesion on the interface has to be determined. Thereby adhesion is not only influenced by the applied polymers, but also by the injection molding parameters and the characteristics of the mold. Besides already known combinations of thermoplastics with thermoplastic elastomers (TPE), there consists the possibility to apply liquid silicone rubber (LSR) as soft component. A thermoplastic/LSR combination gains in importance due to the specific advantages of LSR to TPE. The faintly adhesion between LSR and thermoplastics is currently one of the key challenges when dealing with those combinations. So it is coercively necessary to improve adhesion between the two components by adding an adhesion promoter. To determine the promoters influence, it is necessary to develop a suitable testing method to investigate e.g. the peel resistance. The current German standard "VDI Richtlinie 2019", which is actually only employed for thermoplastic/TPE combinations, can serve as a model to determine the adhesion of thermoplastic/LSR combinations.

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