Research On PLA Microcellular Foaming Injection Molding Process And Equipment

PLA (Poly lactide acid) material is similar with petroleum based plastics in many properties generally, and has good bio-compatibility and biodegradable. Microporous PLA has a good application prospect in packaging, bio-medical and consumer goods and other fields. The pore structure relates with the final product quality of microporous PLA closely. The cell structure of microporous PLA often exist big bubbles and open holes, and bubble distribution is not uniform, which greatly restricts the application of microporous PLA. Expanding mold process of microcellular injection molding technology can control the foam structure of microporous products effectively, being one of the most popular technologies of the current international research on microcellular forming. We used expanding mold process of microcellular injection molding technology, and studied the effect of pressure drop rates on the microporous structure and properties of foaming pure PLA and PLA nano-composite products, then researched the influence of the initial pressure on the structure and thermal insulation performance of the microporous PLA products in the expanding mold process:1. The Appropriate PLA material was studied for microcellular injection molding. Five melt flow rate of PLA materials were molded,and PLA material of the melt flow rate about 11.2g/10min was recommended. The cell diameter was smaller, the cell density was higher,and the mechanical weight amplitude ratio was relatively smaller after foaming;2. According to the principle of expanding mold process, a kind of micro-mould device that can control variable volume was put forward.Controllable weight loss rate of PLA products and microporous structure was achieved. Comparing with the traditional microcellular injection, the weight loss rate was higher, pore structure was better;3. The effect of pressure drop rate on microporous structure,mechanical properties and surface quality of pure PLA and PLA nano-composite was studied through the experiment. The study showed that with the pressure drop rate decreased, the cell morphology of products of the core layer was improved, tensile strength and tensile modulus increased, the impact strength change is not obvious, the surface quality improved. PLA nano-composite materials has been further improved than pure PLA foam structure and performance.4. The cell structure was controlled by changing the injection pressure of microporous PLA products. The research showed that the increase of injection pressure could make the appropriate smaller foam more. Heat conduction rate of non-foamed PL A is higher than that of microporous PLA products. Improving the injection pressure would make the heat conduction rate of microporous PLA products tend to rise. But the excessive high pressure resulted heat conduction rate to decline.