Study On The Synthesis Ofphosphorus-Containing Polysiloxanes Andtheir Application In PC/ABS

Polycarbonate/Acrylonitrile-Butadiene-Styrene (PC/ABS) is a kind of engineering plastic with good properties. It combines good physical properties of PC and easy processing of ABS, and has been widely used in automobile panel, parts, mobile-phone housing, power tools which need high heat and flame retardance property. PC/ABS is easily combustible, in order to meet the requirement of some applications, flame retardant formulations are needed in PC/ABS. According to West Electrical and Equipment Directive, WEEE and Restriction of Hazardous Substances Directive, RoHS, some halogen-containing flame retardants are forbidden to use in some applications although they are very effective in most polymers. The halogen-free flame retardant used in PC/ABS are mostly phosphorus-containing flame retardant, they mainly acts in condensed phase to help PC/ABS charring during burning. Organic silicon compounds form char with high thermal stability while burning, and have been used as flame retardant in PC. According to the above discussion, in this paper, organic silicon and phosphorus are successfully combined in one molecular, two kinds of phosphorus-containing polysiloxanes flame retardants are synthesized. The structure and thermal properties of the flame retardants are studied, and then they are applied into PC/ABS, their effects on flame retardancy, thermal property and thermal degradation behavior are also studied.(1) The synthesis and characteristic of phosphorus-containing polysiloxanes First, 9,10-dihydro-9-oxa-10-phospha-phanthrene-10oxide (DOPO) was reacted with vinyl methyl dimethoxysilane (VMDMS) to form a phosphorus-containing siloxane, after hydroxylation and dehydration, a intermediate product named DOPO–VMDMS was obtained. After that, two kinds of phosphorus-containing polysiloxanes (DVN and DVP) were synthesized by condensation of DOPO-VMDMS and N-β-(aminoethyl)-γ-aminopropyl methyl dimethoxysilane (NMDMS) orα,ω-dihydroxide polydimethsiloxane (PDMS). The structure of the intermediate product DOPO–VMDMS and product (DVN and DVP) was characterized by Fourier transform infrared spectroscopy (FTIR), Nuclear Magnetic Resonance (1H NMR, 31P NMR), element analysis and so on. The thermal properties of DVN and DVP were investigated by thermogravimetric analysis (TGA) in both nitrogen and air. It was found that both DVN and DVP had better char yield in air than in nitrogen at 800℃which indicates that oxygen can help the charring progress of polysiloxane..(2) Application of phosphorus-containing polysiloxanes in PC/ABSThe phosphorus-containing polysiloxanes (DVN and DVP) were then incorporated into PC/ABS to improve its flame retardance. The flame retardance of the flame retarded PC/ABS was investigated by LOI, vertical burning test and cone calorimeter, the thermal stability was investigated by TGA, the structure of the char formed after fire were investigated by scanning electron microscopy (SEM). The results show that the LOI values of the flame retarded PC/ABS were increased by incorporation of DVN or DVP, the heat release rate (HRR), effective heat of combustion (EHC), total heat released (THC) and mass loss rate (MLR) were reduced in cone, and the char yield was increased in both cone and TG analysis. But the initial degradation temperature (IDT) in TGA and time to ignition (TTI) in cone were reduced which was caused by the relative early decomposition of phosphorus-containing polysiloxanes comparing with PC/ABS. SEM results reveal that the outer surface of the char layer of flame retarded PC/ASB after the LOI test was smooth and the inner side structure was swollen cells like, which benefits to the flame retardancy of PC/ABS. The char acts as an insulating barrier to reduce both radiant heat of flame and the diffusion of flammable degradation products into the combustion zone.(3) The synergistic effect of OMT and DVP in PC/ABSPC/ASB/OMT and PC/ABS/DVP/OMT were obtained by melting compounding; the flame retardance, thermal stability, the dispersion of OMT, and the structure of the char formed after fire were investigated. The dispersion of OMT in PC/ABS and PC/ABS/DVP was investigated by X-Ray Diffraction (XRD) and transmission electron microscopy (TEM). It was found that OMT in PC/ABS was intercalation structure while in PC/ABS/DVP was intercalation and semi-exfoliation structure. The incorporation of OMT can not improve the LOI and vertical burning test behavior of PC/ABS and PC/ABS/DVP, but it can low down the HRR, increase the TTI and char yield in the cone.(4) Study of the degradation behavior of flame retarded PC/ABSThe degradation behavior of flame retarded PC/ABS were investigated by TGA,TG-FTIR, FTIR and XPS. Flynrr-Wall-Ozawa method was used to calculate the degradation activation energies (E) of flame retarded PC/ABS at different degradation conversion degree (α). The results reveal that comparing with PC/ABS, E of DVN or DVP flame retarded PC/ABS decreased at lowαbut increased at highα. That mean the char formed by flame retarded PC/ABS had better thermal stability than PC/ABS. TG-FTIR and FTIR results convinced that during the degradation of DVP, a cross-linking structure with Si-O-Si formed. XPS results reveal that for PC/ABS/DVP, there are P-Si and phosphorous acids in the char formed after burning.