Preparation And Characterization Of Waste-EVA/NR/Rubber Powder Blend Based Foams

At present,a significant amount of polymer foam scraps have appeared quickly because the polymeric foams have developed rapidly according to the increasing requirement of the human.Some reasonable recycling methods are adopted to deal with the scraps to result in reducing not only the production costs but also the environmental pollution caused by the waste or incorrect waste management.In this thesis,the categorization,preparation process,foaming method and mechanism of polymer foams were reviewed briefly.The research progresses of ethylene vinyl acetate(EVA)foams and the recycling utilization of waste EVA resources were described in detail.The EVA/NR/rubber powders mixture were prepared by the melt-mixing firstly in a two-roll mill using the scraps of industrial ethylene vinyl acetate(EVA)foams,natural rubber(NR)and waste rubber powders as the main raw materials and then blending with other additives and fillers,Subsequently,the EVA/NR/rubber powders composite foams were prepared by compression molding using the mixture in a mold.The physical mechanical property of the composite foams was further measured and the effects of different process conditions,additives and feed content of rubber powders on the property of the composite foams were also evaluated.(1)The influences of molding temperature,molding time and molding pressure on the physical and mechanical properties of EVA/NR/rubber powders composite foams were investigated here.The optimum preparation condition of composite foams showed that the molding temperature was 145 oC,the molding time was 30 min and the molding pressure was 12.5Mpa.(2)The influences of the blowing agent(AC)content on the physical and mechanical properties of EVA/NR/rubber powders composite foams were studied.The apparent density of composite foams tended to decrease firstly and increase subsequently with increasing of AC content in the processing conditions.However,the foaming ratios increased firstly and decreased subsequently as increasing of AC content.The maximum value of foaming ratio reached when AC content was 4phr.The mechanical properties ofcomposite foams including hardness and tear strength gradually decreased according to increasing of AC content.(3)The influences of the cross-linking agent(DCP)content on the physical and mechanical properties of EVA/NR/rubber powders composite foams were evaluated.The mechanical properties of composite foams increased with increasing of DCP content.The apparent density of composite foams changed very little when DCP content ranged from0.6phr to 0.8phr.However,the apparent density of composite foams increased with increasing of DCP content above 0.8phr.The maximum value of foaming ratio reached when DCP content was 0.8phr.(4)Properties of EVA/NR/rubber powders composite foams filled with various fillers including carbon black(N330),carbon black(N550)and silica were measured.The mechanical properties of composite foams,such as tensile strength,tear strength,hardness,increased with increasing of the filler content,however,their elongation at break decreased.It was found that some defects and large shrinkage appeared on the surface of composite foams when the filler content was 5phr.(5)The influences of two kinds of calcium carbonate as the nucleating agents on the physical and mechanical properties of EVA/NR/rubber powders composite foams were indicated.The properties of composite foams filled with light calcium carbonate were better than those of composite foams filled with heavy calcium carbonate.(6)The effects of waste rubber powders filling content on the property of EVA/NR/rubber powders composite foams were discussed.The hardness of composite foams increased and their elongation at break decreased with increasing of rubber powders content.The microstructure and thermal property of EVA/NR/rubber powders composite foams were measured by the scanning electron microscopy(SEM),differential scanning calorimetry(DSC)and X-ray diffraction(XRD).Experimental data indicated that the EVA foam scraps possessed the good compatibility with NR and rubber powders in the composite foams.Thus the preparation of EVA/NR/rubber powders composite foams can be provided as a potential practical method for the recycling utilization of EVA foam scraps.