| Thermosetting closed-cell rubber-based composites foam has the characteristics of combustion carbonization,carbon deposition and self-resistance.The flame retardancy is realized by mechanical blending of a large number of flame retardants in practical production.The amount of flame retardant added is not proportional to the actual flame retardancy and reinforcement effect due to their dispersion problem in the matrix.Therefore,it is a great significance to study low loading,high efficiency flame-retardant and excellent mechanical properties of rubber-based composite foam.Styrene butadiene rubber(SBR)is widely used in rubber products because of its easy processing and halogen-free.However,the SBR chain that is stretched and produced internal stress and strain in the vulcanization-foaming process,resultin the low dimensional stability of SBR foams.This paper intends to take SBR as the main foaming matrix,and introduces ethylene-vinyl acetate copolymer(EVA)with crystallization and different inorganic particles to construct organic/inorganic support structures on the cell wall and bubble cavity-wall of closed-cell structure SBR foam respectively,which can improve the dimensional stability and flame-retardant of SBR-based foam.The main research contents include as follow:(1)Based on the cross-linking system of sulfur(S)and dicumyl peroxide(DCP),an organic scaffold structure was constructed with the crystallized EVA to enhance the dimensional stability of SBR foams.The effects of EVA with the different vinyl ester(VA)content on the crystal,compatibility,cell morphology,dimensional stability of SBR/EVA composites were studied,and the anti-shrinkage mechanism of the EVA crystal area as an organic scaffold structure and the combustion performance of SBR/EVA foam were explored.The results showed that the ethylene chain segment crystal region of EVA acted as an organic scaffold structure based on the alternating cross-linking process of DCP and S.As a result,the shrinkage and post-shrinkage of SBR/EVA composite foams decreased to 4.7%and 2.3%.The limiting oxygen index of SBR/EVA composite foam was 19%.(2)EVA was insufficient to counteract the internal stress and strain caused by the stretching of the SBR chains.The ZnO particles that must be added during rubber foaming were constructed on the bubble cavity-wall of SBR/EVA composite foams with closed-cell structure to enhance the dimensional stability and flame-retardant property of SBR/EVA composite foams.The effects of the different ZnO content on the cell morphology,dimensional stability and flame-retardant of SBR/EVA composite foams were studied.The results showed that ZnO particles and their aggregates were successfully constructed on the bubble cavity-wall of SBR/EVA composite foams with closed-cell structure.The shrinkage reduced from 14.2%to 6.4%.The ignition time increased from 53 s to 80 s due to ZnO particles and their aggregates on the bubble cavity-wall dispersed heat accumulation,the limiting oxygen index increased to 21.1%.(3)The enhancement degree of the dimensional stability and flame retardancy of SBR/EVA composite foams was small due to the less content and non-uniform ZnO on the bubble cavity wall of the foam cells.A small amount of bisphenol A epoxy resin(EP)was introduced into the SBR/EVA matrix to conntrol the distribution of ZnO particles on the Bubble cavity-wall of SBR/EVA composite foams to enhance its dimensional stability and flame-retardant property.The effects of the different EP content on the cell morphology,dimensional stability and flame-retardant of SBR/EVA composite foams were studied.The results showed that EP successfully controlled the uniform and dense distribution of ZnO on the bubble cavity-wall of SBR/EVA composite foams.Because ZnO was adhered to the bubble cavity-wall by EP,which reduced the shrinkage of SBR/EVA composite foams to 6.0%.The peak heat release rate of SBR/EVA composite foams decreased from 825 kW/m2 to 584 kW/m2,the limiting oxygen index increased to 23.5%.(4)ZnO has a single structure,no smoke suppression effect,and excessive EP reduced the flame retardant.Magnesium aluminum layered double hydrotalcite(MgAl-LDH)was introduced into the SBR/EVA matrix.A moderate amount of EP was used to control the distribution of MgAl-LDH on the bubble cavity-wall of SBR/EVA composite foams to enhance the dimensional stability and flame-retardant property of SBR/EVA composite foams.The effects of the different ratio of MgAl-LDH and EP on cell morphology,dimensional stability and flame-retardant of SBR/EVA composite foams were studied.The results showed that EP controlled the uniform and dense distribution of MgAl-LDH in the local area of the bubble cavity-wall.When the ratio of MgAl-LDH and EP was 3:1,the shrinkage of SBR/EVA composite foam reduced to 3.4%.The maximum heat release rate of SBR/EVA composite foams decreased to 540 kW/m2,the smoke production rate decreased obviously,the limiting oxygen index increased to 25.8%.(5)MgAl-LDH was uniformly and compactly distributed in the local area of the bubble cavity-wall,which has poor thermal insulation protection on the cell wall.The Magnesium aluminum layered double hydrotalcite and expanded flame-retardant ammonium polyphosphate(MgAl-LDH/APP)was introduced into SBR/EVA matrix,and the distribution of MgAl-LDH/APP in SBR/EVA composite foams was controlled by EP,to enhance the dimensional stability and flame-retardant performance of SBR/EVA/EP composite foams.The effects of the different ratio of MgAl-LDH and APP on the cell morphology,dimensional stability and flame-retardant of SBR/EVA/EP composite foams were studied.The results showed that the large size cell was formed by the growth of MgAl-LDH as heterophane nucleating agent,while the small size cell was formed by the growth of APP as heterophane nucleating agent.As a large number of APP were distributed on the Bubble cavity,resulting in the increase of the shrinkage and post-shrinkage of SBR/EVA/EP composite foams,and the deterioration of the dimensional stability.It is proved that inorganic particles distributed on the bubble cavity-wall can enhance the dimensional stability.When the ratio of MgAl-LDH to APP is 1:4,the peak heat release rate of SBR/EVA foam was reduced to 513 kW/m2.(6)The distribution of inorganic particles in the matrix of SBR/EVA based foam cell wall and on the bubble cavity-wall were respectively controlled.The construction mechanisms of inorganic particles in the matrix of cell wall and on the bubble cavity-wall were studied by means of comparative analysis.The enhancement mechanism of the two distribution states of inorganic particles on the dimensional stability,flame retardancy,physical and mechanical properties of SBR/EVA based foams were studied.The results showed that when the saturation pressure of foaming gas was less than atmospheric pressure,the inorganic particles and their aggregates were constructed on the bubble cavity-wall;When the saturation pressure of foaming gas was greater than atmospheric pressure,the inorganic particles and their aggregates were constructed on the matrix of cell wall.The construction of inorganic particles on the bubble cavity-wall was controlled by EP,acting as a support structure,which increased the shrinkage and post shrinkage of SBR/EVA based foam by 75.7%and 71.6%,respectively.The combustion test showed that inorganic particles were constructed on the bubble cavity-wall to form an insulating protective layer,which enhanced the strength and integrity of the residual layer after combustion,and extended the time of ignition and peak value of the heat release rate. |
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