| High-density polyethylene (HDPE) is a desirable polymer because of its excellent performance, and has been widely used in industry and life fields. But flammability restricts its application to a large extent. In recent years, magnesium hydroxide (MH) becomes one of the most promising flame-retardant inorganic material for its friendly environment. But more than 50wt% MH is needed to achieve flame retardant grade. The processing and mechanical properties have been deteriorated when 50wt% MH is added. To solve those problems mentioned above, the commonly used method is polymer blending. Poly (ethylene-co-vinyl acetate) (EVA) has excellent flexibility, low viscosity, partial polarity. The addition of EVA into the HDPE/MH composites can improve the compatibility between HDPE and MH particles and can obtain complementary advantages.In view of this, the effects of compatibilizer, MH content, EVA with different VA content and EVA content to the structure and properties of HDPE/EVA/MH composites are investigated in this paper, fhe structure and properties were characterized by rheological tests, scanning electron microscopy (SEM), thermal gravimetric analysis (TG), vertical-burning test (UL-94), limiting oxygen index (LOI) and cone calorimeter test (CCT).The HDPE/EVA/MH composites are prepared by a twin-screw extruder through melting extrusion. And the processing performance, mechanical properties, thermal stability and combustion behabviors of HDPE/EVA/MH are discussed. The main purpose of this paper is to investigate the effect of component to the structure and properties so as to develop new balanced properties composites that can be used in many fields. The main work and conclusions are as follows:(1) A large amount of MH is needed to achieve flame retardant effect and so the compatibility will become worse. Two compatibilizers, which are HDPE-g-GMA and HDPE-g-MAH, respectively, are used to improve the compatibility between the matrix and filler. The results show both the two compatibilizer can enhance the interfacial bonding strength, improve the mechanical properties, increase the residue after combustion and flame retardant. Compared HDPE-g-GMA with HDPE-g-MAH, HDPE-g-MAH has a stronger compatibilization effect than HDPE-g-GMA, but HDPE-g-GMA has a more obvious improvement in flame retardant than HDPE-g-MAH.(2) Base on the experiment results above, the effects of magnesium hydroxide on processing properties, mechanical properties, thermal and flame retardancy properties of HDPE-EVA blends compatibilized by HDPE-g-MAH are studied. The conclusions indicate MH can greatly improve the flame retardant properties, especially when MH content is more than 50%(wt%). But at the same time, both the processing properties and mechanical properties deteriorate, which limit its application.(3) In this work, three different EVA, whose VA content are 15%,28%,40%, respectively, are added into the composties and the structure and properties are studied when the ratio of HDPE and EVA is 4:1. The results show the mechanical properties become worse with the increase of VA content while the processing properties show tiny difference. The thermal stability move towards low temperature while the residues at 600℃ are higher than HDPE/MH composites. Among all the samples, the properties are optimized when VA content is 15%.(4) The addition of 50wt% MH content into the composites deteriorates the processing and mechanical properties. In this part, the research focuses on studying the structure and properties of HDPE/EVA/MH composites with different EVA content. Results anysis demonstrate that adding elastomer EVA makes the process easier which results from low viscosityof EVA. The polar group makes the MH particles disperse uniformly and it results in the increase of elongation at break. In addition, the CCT results indicate the heat and toxic gas generated durning combusition decrease when partial EVA replaces HDPE. However, with the increase of EVA, the UL-94 rating can not reach. |
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