Synthesis Of Epoxy Polysiloxane And Its Application In Flame Retarded PBT

Polysiloxane is a kind of semi organic polymer of special structure and excellentproperties. With the Si-O molecular backbone and organic groups as side base, it has bothinorganic and organic polymer properties. Studies have shown that polysiloxane has recentlybecome one of the most development green flame retardant. As flame retardant, polysiloxanehas lots of advantages, such as high flame retardancy, no halogen, low smoke, low toxicity,eco-friendly, little affect on mechanical and processing properties of polymer materials.Polybutylene terephthalate(PBT) is a high performance thermoplastic, it is flammablelike other polymers, limiting its further promotion and application. Diethylphosphinate salt asflame retardant has the advantages of high efficience and low amount, so it has been widelyused in flame-retardant of PBT. The main flame retardancy mechanism of diethylphosphinatesalt is that, after thermal decomposition, it will produce large amounts free radical scavengerscontaining phosphorus into the air to inhibit the spread of flame. Thus the flame retarded PBTused diethylphosphinate salt would release large amount of smoke in the combustion process.As smoke causes85%death in fire hazards, it is essential to study flame retarded and lowsmoke PBT composites.Accordingly, a novel functional polysiloxane (EPM) containingepoxy group was designed and synthesized in this study. EPM as synergisticflame retardantand aluminium diethylphosphinate (AlPi) as flame retardant were applied in PBT to obtainflame retarded PBT composites. By the limiting oxygen index (LOI), UL-94vertical burningtest, conecalorimeter test, the flame retarded properties and the amount of smoke of thecomposites were characterized; the thermal decomposition process and the flame retardancymechanism were studied with thermo gravimetric analysis combined with fourier transforminfrared spectroscopy(TG-FTIR) and scanning electron microscopy; the relationship betweenmaterial microstructure and macroscopic properties of composites were analyzed by dynamicmechanical analysis (DMA), differential scanning calorimetry (DSC) and the test of PBTmechanical properties results.Firstly, three different structure chloropropylpolysiloxane (PCSi) were synthesized byγ-chloropropylmethyldiethoxysilane (MCPS) hydrolysis polymerization or copolymerizationwith phenyltrimethoxysilane (PTMS) and methyltrimethoxysilane (MTMS). Then epoxy group was introduced through the chloropropyl group into the PCSi side group to obtain threekinds of epoxy polysiloxane (EPM). The structure of products were characterized by FTIRand1H-NMR, the thermal property was tested by thermo gravimetric analysis(TGA). EPMwith the best thermal performance was used as synergistic flame retardant in the processing ofPBT.The experimental results showed that: maintaining the amount of flame retardant AlPi at11%, the LOI of the PBT/AlPi/EPM composites increased with the amount of EPM increasing.When adding0.6%EPM, the PBT composite achieved UL-94V-0rating, its LOI was37.1%,increased by81%than that of PBT. Thermal gravimetric analysis (TGA) results showed thatat600℃the residue of PBT/AlPi/EPM composite was as high as9.3%,while the PBT/AlPicomposite was7.3%.The smoke release of PBT/AlPi/EPM composite decreased43%compared with the PBT/AlPi composite. SEM tests showed that the carbon layer ofPBT/AlPi/EPM composite was more smooth and dense than PBT/AlPi composite afterburning, thus the flame retardancy of former composite was enhanced. The tensile strength,flexural strength and flexural modulus of PBT/AlPi/EPM composite was54.7MPa,93.2MPaand3.17GPa, compared with PBT, its properties was significantly improved, but theelongation at break and impact strength was declined.