| Polylactic acid (PLA) is a polymer material, being widely used in all walks of life, which is made from plant resources (such as corns), is recognized as the environment-friendly material, and is possessed of great biodegradable and renewable. Generally, foam plastics obtain many excellent properties such as light weight, high impact strength, high specific strength, excellent thermal and sound insulation, moisture absorption strong and so on. PLA foam has many performances as same as environmentally friendly materials and foam plastics. PLA foam has good application prospects, in line with the current trend of environmental protection and sustainable development. Thus, recent studies about PLA foam have aroused widespread concerns and get quick research and development in the field of packaging and consumer goods.This study will use supercritical CO2as a blowing agent for continuous extrusion experiments of PLA foam, under different foamed conditions, making the polylactic acid foam sample. Firstly, this study analyzes the impact of process conditions on abscess shape, abscess density, foam properties and mechanical properties of the foam. Then, the study analyzes the effects to the PLA abscess density, abscess morphology and foaming properties by adding talc. By changing the foamed process conditions, we can improve foam morphology and mechanical properties of PLA cell foam, in order to find the optimal foamed conditions.During foaming the polylactic acid with Supercritical carbon dioxide, we studied how different screw speeds in the same die head temperature affected the polylactic acid foam sample. The results show that different screw speeds get different expansion of polylactic acid. When the screw speed reaches maximum speed setting of the experiment, the expansion of polylactic acid samples is the biggest. The results meet the shear energy nucleation theory,which the presence of shear energy will relatively reduce Gibbs free energy of bubble nucleation, and help to improve the bubble nucleation rate. Second, we studied the effects of temperature on the die head on the foaming properties of polylactic acid. The viscous and elastic of polylactic acid are controlled by the temperature. Due to the higher temperature of the die head such that the viscous and elastic about the melt of the polylactic acid reduce, resulting in the extrusion process, the gas evolution and cell merge. Therefore, the die head temperature rise affects the expansion rate of polylactic acid foam sample and uniformity of the structure of sample hole, thereby reducing the foaming properties of polylactic acid. In this experiment we also study the effect of water on the foaming properties of polylactic acid. We know that the polylactic acid is formed by polylactic acid molecules dehydration. The process is a balance of processes. Because of the presence of moisture will cause the synthesis of polylactic acid for the reverse direction, so that the hydrolysis of the polylactic acid molecules, to reduce the molecular weight of the polylactic acid, which reduces the foaming properties of polylactic acid. Finally, talc is added in a polylactic acid test. We obtain significantly higher expansion ratio of the foam sample than pure sample to a high expansion ratio of the village. Due to the addition of a nucleating agent, it played a role in heterogeneous nucleation, thus, making it melt nucleation sites increased significantly, strengthening the foaming properties of polylactic acid. On the end of the article, the mechanical properties of the foam samples were tested, obtained the influence of four foaming conditions on the mechanical properties of the sample.Polylactic acid foam material has been more and more widely used in various industries. Research foaming methods have a very long-term significance. Using supercritical carbon dioxide continuous extrusion foaming method of polylactic acid will enhance the production efficiency and this method having industrial significance. |
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