Mingjun Yuan

Microcellular Injection Molding

Abstract This paper reviews some of the recent developments of microcellular injection molding, which is capable of producing parts with excellent dimensional stability using lower injection pressure, shorter cycle time, and less material. Process conditions as well as nano/micro-fillers such as nanoclay and core–shell rubber have a strong influence on cell density and cell size, hence, the final material properties of the molded parts. The addition of nano/micro-fillers at optimum loading levels can generally facilitate the formation of microcellular plastics with higher cell density and smaller cell size leading to superior mechanical properties. The novel integration of a solid plastic surface with a microcellular plastic core via the co-injection molding technique has been investigated to achieve Class “A” surfaces and improved material performance. An improved mathematical model has been developed to simulate the cell growth behavior in the microcellular injection molding process.

Crystallization Behavior of Polyamide-6 Microcellular Nanocomposites:

The crystallization behaviors of polyamide-6 (PA-6) and its nanocomposites undergoing the microcellular injection molding process are studied using Transmission Electron Microscopy (TEM), X-ray Diffractometer (XRD), Polarized Optical Microscopy (POM), and Differential Scanning Calorimetry (DSC). The relationships among the morphology, the mechanical property of the molded parts, and the crystallization behavior are investigated. With the addition of nanoclays in microcellular injection molded parts, the growth of the γ-form crystal is suppressed and the formation of γ-form crystals is promoted. Both nanoclay and dissolved gas have a big influence on PA-6 crystalline structures. The existence of nanoclay increases the initial crystallization rate. But with extra addition of nanoclays in the polymer matrix, the increase of crystallization rate is reduced. Microcellular injection molded nanocomposites with proper amount of nanoclays possess the maximum crystallization activation energy and produce a finer and denser microcell structure which leads to better mechanical properties.

Core-Shell Rubber Modified Microcellular Polyamide-6 Composite

This paper presents the effects of processing parameters and submicron core-shell rubber particle filler on the mechanical properties and cell morphology of microcellular injection molded polyamide-6 (PA-6) composites. Three types of materials are studied, namely, neat PA-6 resin, and 0.5 wt% and 3.1 wt% core-shell rubber polybutylacrylate-polymethylmethacrylate-filled PA-6 composites. This study shows that the addition of a small amount (0.5%) of core-shell rubber particles improved the ductility and impact strength of micro-cellular injection molded PA-6 samples. In comparison to the microcellular injection molded PA-6 polymer-clay nanocomposite, the samples with a small amount (0.5%) of core-shell rubber had much higher impact strength and ductility. The small addition of core-shell rubber also reduced cell size and increased cell density of the microcellular injection molded PA-6 parts, in comparison to their neat resin counterparts. On the other hand, at higher core-shell rubber loading, the cell size and density were found to be similar to that of the neat resin.