Studies On The Strengthening, Thermal Conducting And Flame Retardance Of Polypropylene By Magnesium Hydroxide Sulfate Hydrate Whisker

Magenisum hydroxide sulfate hydrate(MHSH) has the functions of enhancement, filling, flame retardant and smoke suppression and so on, and is often applied in the improvement of the mechanical properties and flame retardance of polymer materials. When used as the reinforced materials, MHSH modified by the traditional methods can improve only slightly the mechanical performance of polypropylene(PP); and the flame retardant property is also limited if not cooperates with other synergistic flame retardant. Although PP composites with good flame retardant performance was prepared by using MHSH and microencapsulate red phosphorus(MRP), few reports deal with the flame-retardant mechanism, detailed depiction on the formation process of intumescent layer in the composites. In addition, the unique structure of MHSH whisker is expected to provide heat conduction channel easily and the study on MHSH in thermal conductivity was rear. Therefore, this article has carried on the detailed research in view of the three aspects above. Specific works are as follow:1) MHSH/PP composite with good mechanical properties was prepared by adopting the dynamic curing method with PP-g-MAH and epoxy resin(EP) as the modifying agent. The results from dynamic torque measurement and SEM tests indicated that the active epoxide groups of EP can react not only with the maleic anhydride groups of PP-g-MAH but also with the hydroxyl groups at the surface of the whisker. We believe that the reactions promoted interfacial adhesion between PP and MHSH. Dynamic curing of the EP in the PP/PP-g-MAH/MHSH composites can further increase interfacial adhesion and thus increase the mechanical properties; When the content of EP in the composites was 2wt%, dynamically cured PP/10wt%PP-g-MAH/20wt%MHSH/2wt%EP composite reaches the highest mechanical properties with tensile strength of 54.2Mpa, flexural strength of 66.9Mpa and impact strength of 36.82J/m, which is 58%, 86% and 66% higher than that of neat PP respectively.2) The effect of MHSH, expanded graphite(EG) and MHSH/EG mixtures on the thermal conductivity of PP composites were investigated. The results showed that the thermal conductivity of PP composites increased with increasing the MHSH, EG, MHSH/EG content. With the addition of 20 phr EG, MHSH/EG had a good synergistic effect on thermal conductivity and biggest synergistic effect(collaborative coefficient equals 1.298) reached with the addition of 10wt% MHSH.3) The synergistic effect of zinc borate(ZB)/MHSH, ammonium polyphosphate(APP)/MHSH, MRP/MHSH on the flame retardant property of PP composites were studied. The results indicated that MHSH associated with MRP had the best synergistic effect. When the additions of MHSH and MRP were 30wt%, 10wt% respectively, the LOI of PP composite was 26.1% and vertical burning reached UL94V-0. The appearance of residue surface after vertical burning was continuous and dense. The synergistic flame retardant mechanism of MHSH/MRP was studied by thermo gravimetric analysis, FTIR, SEM and EDS. The results showed that water from the thermal degradation of MHSH was right absorbed by phosphorus oxide during the high temperature combustion process. The water thinned phosphorus oxide/acid wet, spread and react with combusted residue materials on the surface form a dense intumescent layer in which magnesium sulfate and magnesium phosphate acted as aggregate while phosphate, polyphosphate acted as binder. The intumescent layer resisted and delayed the transmission of combustion materials and energy conduction; thus, good flame retardant PP composite resulted.