Experimental And Theoretical Study On Chemecal Crosslingking Extruding Polypropylene Foam In One Step

In recent years, plastic foams have been developed into one of the most important branches of the modern plastic industry, and have been widely used in industry, agriculture and automobile, etc.Among polyolefin foams, polypropylene (PP) foam with excellent performances has been drew more attention. It's high crystallization and special relationship between viscosity and temperature make it difficult for PP to be foamed, so the industrialization level improved slowly, and only few developed countries can do it. Moreover, in the traditional technology used to make PP foam, special injection and measuring device or a long technology process is required, which greatly limited the popularization of the foaming technology.In the study, the theory, formula, technology and combination and optimization of apparatus for the crosslinked PP extruding foam in one-step were discussed.By using some testing means, the microcosmic structure of the obtained foam was observed, the effects of the factor of the formula and technologies on the structure and properties of the foam was analyzed, and the foaming process was observed. The result provided some useful theoretical guides for the foaming.In addition, the physical model of the unit cell during the foaming was got and simple mathematical description was made. Also, the rheology of the mixture of crosslinked PP and decomposed gas of AC was analyzed, and the evolving equation which describes the apparent viscosity of the PP melt mixture in the foaming die was gained.In the study, some useful conclusions were drawn as follows:1. Experiments show that it is feasible to get the chemical crosslinked PP extruding foam in one step by the proper crosslinking modification and the corresponding improvement of extruder.2. Die temperature has great effects on the cell structure and foam properties. Only under the reasonable die temperature , the ideal foam can be got, and lower die temperature is more advantageous to reach the foaming.3. The effect of screw rotating speed and die pressure on the cell's structure and foam properties are identical. Foam density is reduced at begin and then increased with the increasing of the screw rotating speed and die pressure, in other words, there exist a optimal value of screw rotating speed and die pressure at which lower density foam can be got.4. The dosage of crosslinking agent DCP and foaming agent AC is fewer than other foaming technology, but the foaming result is ideal on the condition of relative simple technology process and apparatus.