Chemical Extrusion Foaming Research Of Modified Polylactic Acid (PLA)

Polylactic acid (PLA) is a kind of biodegradable thermoplastic. In recent years, it has become the research hot spot in all kinds of biodegradable polymers because of its good properties. PLA foams have the advantage of low density and cost, light weight, good absorption and heat insulation, which can be used in a wide field of applications such as packaging, automotive, electronics, daily life and agricultural areas.etc. It is considered as a promising replacement for non-degradable foam products. The reaserch of PLA foams is valuable. The main works are as follows:(1)Two kinds of chain extender:ADR and CX-1, were used in chain extendtion reaction by twin screw extruder. ADR have improved PLA’s apparent viscosity, and reduced the melt flow rate, which lead an improvement to the melt strength. The improvement of ADR to the melt strength of PLA was better than the CX-1, the optimal content of ADR is 0.8.(2)Three chemical agents:foaming agent A (Masterbatch), foaming agent B (the main components are AC and NaHCO3, homemade) and foaming agent C (the main components is AC, homemade), were used to investigate the foamablibity of modified PLA. Three different particle size of CaCO3 were taken as a nucleating agent. The influence of chain extender, blowing agent and nucleating agent on the PLA foam were analyzed respectively, in order to obtain the optimal formula. The best foamed samples were obtained when ADR content is 0.8, foaming agent C content is 1.5, the apparent density of the samples are 0.6 g·cm-3, the cell diameter is about 57um, the cell density is about 7.69×106个·cm-3; CaCO3 has significantly reduced the apparent density, cell diameter and increase the cell density of foamed samples. Good foamed PLA samples have been prepared only when the nanoCaCO3 content is 0.5.(3) Designed three types of die mouth with different straight length, the influence of screw rotation speed, die temperature die pressure, and die structure on the apparent density, cell structure and surface quality of foamed PLA samples were analyzed. The foam samples prepared by die 2# presented the best comprehensive properties, when the screw rotation speed was 20 r/min, the die temperature was 150℃, the apparent density was about 0.48g·cm-3, cell diameter was 50μm, cell density was 1.67X 107个·cm-3. Reducing the die temperature improved the toughness of the foaming samples. The foamed tube samples still remained good properties, the apparent density was about 0.48g·cm-3, cell diameter was 56μm, cell density was 9.87X 106 个·cm-3.