Melt compounding based rotational foam molding technology for manufacture of polypropylene foams

摘要

This paper is intende dotprovide an engineering understanding of the technological potentials for processing polypropylene (PP) foams in rotational foam molding.A process proposal,basd on the melt compounding material-peparationapproach,capable of producing completely foamed,single-alyer,single-piece PP prducts in rotational foam molding,is disclosedin detail.It comprises dispersing a chemical blowing agent (CBA) in the PP matrix using a twin-screw componder,pelletizing the obtained expandable composition,and then producing foams in an uninterrupted rotational foam molding cycle by using the pre-compounded foamable pellets.Several PP grades were deliberately selected to cover a wide range of melt flow rates (MFR),starting from 5.5 up to 35dg/min.After the raw materials participating in the study were characterized using thermal analysis instrumentation,different foamable compositions were formulated in order to prepare both 3-fold and 6-fold foamable pellets from each PP grade.The optimalfoam procesing strategies were identified via a systematic experimental parametric search.Foams with the best cell morphologies were obtained out of the high melt strength PP grades.inaddition,the experimental results revealed that the cell morphology of the processed PP foams is not as good as that of respective PE foams.However,the cell morphologies of the PP foams processed byusing the melt compounding-based appraoched monstrated significant improvements in comparison with those processedby using the dry blending-based approach.