Study On UV Irradiation Grafting Polypropylene

Regular polypropylene using for the preparation of foam materials is limited by its low melt strength and melt viscosity. In this study, UV irradiation was used to improve the melt strength of PP, and the foam products of PP with low foaming ratio were prepared.The grafting reaction occurred in the system under the irradiation of UV light after adding the sensitizer and photosensitizer. The gel content can reach about 30% when the system was given 3000mj/cm2 UV,1.5phr SR444 and 0.2phr BP. The melt mass flow rate of PP after UV irradiation reduced from 3g/10min to 0.22g/10min. Die swell of the melt increase from 2.37 mm to 4.93 mm, which was over 2.4 times the diameter of the die. The melt strength and sag resistance of PP are improved as well as the tensile strength.The thermal properties of PP were improved after modified by UV irradiation. When given 3000mj/cm2 UV, the melting temperature of PP increased from 161.61? to 164.53?, while the crystallization temperature increased from 114.44? to 123.59? and the Vicat softening temperature decreased from 153? to 146.6?. The thermal weight loss temperature of PP increased from 248.74? to 259.07?, and the temperature of the maximum decomposition rate increased from 314.50? to 329.00? when the maximum decomposition rate decreased;When given 3000mj/cm2 and above UV, the cell structure of PP has been significantly improved, with higher foaming rate and better tensile properties. When adding 10.4phr,12.9phr and 15.5phr foaming agent masterbatch, the expanded PP were prepared with the foaming ratio by 3, 4 and 5 times.The apparent morphology, cell structure and mechanical properties of the expanded PP sheet were better when the sheet was extruded at die temperature of 180?, processing temperature of 170?, and screw speed of 45 r/min. The extrusion foaming process was steady and continuous at this processing condition.UV irradiation grafting modification effectively improved the melt strength of polypropylene, and the foam PP sheet with excellent properties was prepared with the foaming ratio by 3 to 5. The foam sheet has the tensile strength of 12.32 MPa and the surface hardness of 60HS with excellent cell microstructure and apparent morphology.