The Influence Of Aluminium Hypophosphite On Intumescent Flame Retardant Polypropylene Compound

Polypropylene (PP) represents the largest part in the polymer consumption of the world just behind the polyvinyl chloride and polyethylene. PP is widely used in many fields due to its versatility and a good performance to cost ratio such as building materials, automotive industry, household appliances, electronics, furniture and packaging, etc. However, due to its chemical constitution, the polymer is easily flammable, When PP is burning, the flame is fierce with big heat release, simultaneously has the serious melt drop phenomenon, and its limiting oxygen index is only17～18%, those limit its applications. Therefore, the research of flame retardant polypropylene has been the hot spot in the PP material research.This paper mainly added aluminium hypophosphite (ALHP) to the flame retardant system for flame-retardant PP. From the dates of limiting oxygen index (LOI)、UL-94test and mechanical properties, we studied some important factors affecting to the flame retardancy and mechanical properties, such as the optimum ratio of ALHP and IFR, different loading of IFR、 different loading of ALHP and IFR. Based on the results of experimental tests, we obtain a formulation with better flame retardancy and mechanical properties:when the weight ratio of ALHP to IFR is1/6, the loading of ALHP/IFR is only24%in PP, the flame retardancy of ALHP-IFR-PP could pass UL-94VO rating (0.8mm), and its LOI value reached33.5. It had good mechanical properties, the tensile impact is23.7MPa, the flexural strength is33.3MPa, the notched izod impact is5.3kJ/m2.In order to study the synergistic effects of ALHP to IFR-PP system, this paper researched the thermal degradation under pure nitrogen and air, the combustion behavior of IFR-PP without ALHP, ALHP-PP without IFR, and ALHP-IFR-PP by TGA and CONE. The results of TGA showed that the thermal degradation behavior had been changed due to the addition of ALHP, ALHP could more effectively accelerate the reaction of IFR, between IFR and PP, enhance the char formation in high temperature. The CONE test results revealed that the parameters, HRR, THR and SPR, etc, decreased compared to these of PP.The SEM and XPS were used to research the IFR-PP without ALHP, ALHP-PP without IFR and ALHP-IFR-PP. The result of SEM showed that the ALHP-IFR-PP after burning can form more compact and stabile char layer, preventing the polymer from further burning. The XPS result showed the carbon content on the char residue surface of ALHP-IFR-PP was higher than that of IFR-PP without ALHP, ALHP-PP without IFR, and the AL content on the char residue surface of ALHP-IFR-PP was lower than that of ALHP-PP without PP. The results indicated that the synergistic reaction between ALHP and IFR can effectively promote the char formation of PP during burning, and the protective layer stop the propagation of heat and oxygen to the polymer matrix, resulting in a good flame retardancy.