Study on the Extrusion Foam Molding of Polyethylene
|Course||Material Intelligent Systems Engineering|
|Keywords||Recycled PE Thermal degradation Activation Rheological behavior Extruding foam|
The foamed materials have many good performances such as light weight, heat insulation, sound insulation, cushion, low cost, and so on. 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, architecture and automobile, etc.In this study, the dynamics of thermal degradation, activation mechanism of two kinds of high temperature foaming agent, and rheological behavior and melt strength of the recycled PE were investigated, which provided theoretical basis for the recycled PE foaming. Then, the foaming of the recycled PE via a chemical extrusion foam process was studied.The experimental results are shown as follows:1. The thermal degradation kinetics analyses showed that the activation energies of degradation, obtained by the method of Kssinger, Flynn-Wall-Ozawa and Friedman, respectively, were higher in TSSC than in AC, which implied TSSC had higher thermal stability. Thus, it was very meaningful to use TSSC as a foaming agent for the recycled PE which needed processing at high temperature.2. Zinc oxide and zinc stearate were used to coordinate with AC or TSSC. The FTIR spectra showed that some absorption peaks of AC or TSSC were shifted after coordination process compared with untreated AC or TSSC. The coordination with zinc compounds made AC or TSSC easier to thermally decompose, which mainly resulted from the activation of chemical groups in AC or TSSC.3. The rheological behaviors of HDPE, crosslinking HDPE and recycled PE showed that HDPE belonged to the typical non-Newton fluid, the melt strengths of crosslinking HDPE and recycled PE were larger than that of HDPE by the analyses of non-Newton index and viscosity flow activation energy, and the apparent viscosity was not sensitive to temperature so that a slight temperature change would not cause a great fluctuation of melt viscosity.4. The HDPE exhibited low melt strength and led to poor foaming effectiveness. The crosslinking HDPE and recycled PE had higher melt strength, thus improving the performance of the foam products and increasing the foam rate of the products.5. The extrusion foaming experiments showed that the dosage of foaming agent directly affected the foam rate and density. By choosing appropriate process parameters and adding proper amount of foaming agent, the foaming rate of products could be controlled in a certain range, and the different foam products could be obtained.6. The screw temperature had a direct impact on the foaming body performance. If the temperature was too low or too high, the ideal foaming body could not be obtained, because the foaming agent TSSC decomposed insufficiently or excessively so that the melt was not in the appropriate viscoelasticity range to foam. The effects of screw rotating speed and die pressure on the cell structure and foam properties were identical. The foam density was reduced at beginning and then increased with the increase of the screw rotating speed and die pressure, in other words, there existed a optimal value of screw rotating speed and die pressure at which top foam density could be realized.7. The die temperature had great effects on the cell structure and foam properties. Low die temperature was advantageous to foaming. The adopted cooling method also had an impact on foaming effectiveness. Using water cooling method in our study could improve the foam surface quality, the cell structure, and the physical and mechanical properties of foam.