Study On The Preparation And Properties Of Organic Palygorskite Clay Synergized Intumescent Flame Retardant Polypropylene Composites

Polypropylene(PP) has excellent comprehensive performance of mechanical properties, heat resistance, non-toxic, light weight, corrosion resistance, easy processing and recycling, abundant material source, low cost and excellent performance. Therefore, PP has been widely used in many fields, such as electrical appliances, furniture, machinery, automobiles and construction. But the limit oxygen index(LOI) of PP is very low, only 17.6%, and the disadvantage of flammable with molten droplet, which limited the scope of utilization of the material. Therefore, the development of environmental friendly, low toxicity and low smoking halogen free flame retardant has been drawn more and more attention in the research of flame retardant polypropylene.The intumescent flame retardant(IFR) has high flame retardant efficiency, low smoke, low toxicity and low corrosive gas release, which are widely concerned as a new type composite flame retardant agent at home and abroad in recent years.However, the high loading of IFR, poor compatibility with the matrix, easy absorption of moisture and other shortcomings limited their application. In order to overcome these problems, novel flame retardants or strategies have been developed. In this paper, organic palygorskite clay(OPGS) was introduced to the intumescent flame retardant polypropylene composite material and discovered that OPGS has a synergistic effect in the composite materials. Meanwhile, synergistic effect of the OPGS was studied in the classical intumescent flame retardant polypropylene composite material as well as in the combined IFR system, which acid source, carbon source and the gas source are hold together. The limited oxygen index method(LOI),the vertical combustion(UL- 94), mechanical property testing, scanning electron microscopy(SEM) and thermal gravimetric analysis(TGA) were used to evaluate the synergistic effect of OPGS on intumescent flame retardant polypropylene composite,flame retardant properties, mechanical properties and thermal stability.This thesis consists of three parts:Part I: Literature reviewThis section focuses on the research progress of intumescent flame retardant polypropylene, the classification and mechanism of commonly used halogen free flame retardants, the classification of the synergistic flame retardant and the present situation of the application of palygorskite clay, and puts forward the significance of the subject.Part II: Study on the preparation and properties of PP/IFR/OPGS compositesAmmonium polyphosphate(APP) as acid source and gas source, pentaerythritol(PER) as carbon source to composite the intumescent flame retardant(IFR). And organic palygorskite clay(OPGS) as synergistic agent of intumescent flame retardant and the mechanical properties modifier, filled into polypropylene, prepared the PP/IFR/OPGS composite material. The limited oxygen index method(LOI), the vertical combustion(UL- 94), mechanical property testing, scanning electron microscopy(SEM) and thermal gravimetric analysis(TGA) were used to study the flame retardancy and mechanical properties of the composite material. The results showed that the best addition of intumescent flame retardant APP/PER mass ratio was3:1, and the LOI of the composite increased from 30.3% to 36% when replaced the IFR with the equal quality of mass fraction of 2% OPGS. At the same time, the tensile strength and impact strength are 26.29 MPa and 38.80 MPa respectively. Both the flame retardancy and mechanical properties were improved obviously. TGA test results showed that, at the high temperature, the addition of suitable amount of OPGS could increase the stability of carbon residue. From the SEM images of the carbon residue after the LOI test, we found that adding suitable amount of OPGS could makethe carbon layer stronger and tighter, which could isolate the transfer of oxygen and heat effectively, and thus improve the flame retardancy of the composite.Part III:Study on the preparation and properties of PP/PA- APP/OPGS compositesPiperazine-ammonium polyphosphate(PA- APP) was used as an acid source, the carbon source and the gas source, and the organic palygorskite clay(OPGS) as intumescent flame retardant synergistic agent and the modifier of mechanical properties, filled into polypropylene, prepared the PP/PA-APP/OPGS composite materials. The limited oxygen index method(LOI), the vertical combustion(UL- 94),mechanical property testing, scanning electron microscopy(SEM) and thermal gravimetric analysis(TGA) were used to study the effect of adding amount of intumescent flame retardant agent and synergistic flame retardant of intumescent flame retardant polypropylene composites, mechanical properties and thermal stability of the effects. The results of the experiment on addition amount of the matrix,intumescent flame retardant and synergistic flame retardant and show that the best adding amount of the total mass matrix were 75% and 70% respectively, and the flame retardancy of the composites has been improved when add 2% mass fraction of OPGS instead of the same equality PA-APP. Experimental results showed that when the adding amount of matrix, PA-APP and OPGS is 70%, 28%, 2%, the LOI reached the maximum( 36.7%). The tensile strength and bending strength of the composites increased respectively at the same time. TGA test results showed that, at the high temperature, the adding amount of OPGS is 2% of the total mass, the stability of composite materials is best. Through the SEM test of composite materials, adding suitable amount of OPGS could make the carbon layer stronger and tighter which could isolate oxygen from the composite and reduce the heat release, so as to improve the flame retardant properties of the composite.