Study On Preparation Of Flame Retarded Polystyrene By Suspension Polymerization

Polystyrene?PS?is a thermoplastic resin with good thermal insulation,good electrical insulation performance,convenience of processing and excellent mechanical properties.It is therefore widely used in all areas of national economy and people's livelihood.However,polystyrene is a fire hazardous material because it is very flammable.Therefore,some flame retardants have been used to obtain PS with desired flame retarded properties.In general,flame retarded polystyrene prepared by melt extrusion method.However,although melt extrusion method is effective,there are still some disadvantage,for example,not good dispersion,volatilization and decomposition of flame retardants during extrusion processing.In industrial production,polystyrene is mainly produced by suspension polymerization.Flame retarded polystyrene is prepared by suspension polymerization with flame retardants together with reaction monomers,which maybe avoid the problems of melt extrusion method and secondary processing.In this thesis,PS nanocomposites were prepared by suspension polymerization with triphenyl phosphate?TPP?and bisphenol-A bis?diphenyl phosphate??BDP?,and the effects on graphite on suspension polymerization were studied.The microstate,formation process and mechanism of TPP nanoparticles,flame retardance properties of PS/TPP nanocomposite and the effects of TPP on suspension polymerization were studied by fourier transform infrared spectrometry?FTIR?,³¹P-nuclear magnetic resonance(³¹P-NMR),x-ray photoelectron spectroscopy?XPS?,scanning electron microscope?SEM?,materials studio software,thermogravimetric?TG?and cone calorimeter measurement method.A comparative study about preparation of polystyrene/triphenyl phosphate?PS/TPP?composites by suspension polymerization and melt extrusion method was developed.Base on the above results,halogen-free expandable polystyrene?EPS/TPP?and expandable polystyrene containing graphite?EPS/G?were prepared by suspension polymerization.?1?PS/TPP nanocomposite was prepared successfully by suspension polymerization.Through FTIR,³¹P-NMR and XPS measurements,there were not chemical changes in the TPP,so it can be considered that TPP had been incorporated into the PS beads in the manner of physical blending.TPP particles were all in nanosized and dispersed homogenously in the PS matrix.?2?The formation process and mechanism of TPP nanoparticles were studied by solubility parameter???,Flory–Huggins parameters???and mesoscopic structures stimulation.The results showed that during the initial suspension polymerization period,TPP firstly dissolved in styrene in molecular level.With the polymerization reaction proceeding,the decreasing compatibility of TPP with PS chains resulted in separation of TPP molecules from PS phase,and the nano-sized TPP droplets gradually formed.?3?With the increase of TPP content,the polymerization time increased,the molecular weight of PS/TPP nanocomposite decreased and the particles size of PS/TPP beads decreased.The onset decomposition temperature of PS/TPP nanocomposite decreased significantly,which were due to the onset decomposition temperature of TPP is prior to PS.?4?The LOI of PS/TPP nanocomposite increased with increase of TPP content.When20 phr TPP was added,the LOI value increased up to 25.4%;the UL-94 rating of PS/TPP nanocomposite reached up to V-2 rating with 10 phr TPP.For CONE analysis,with the increase of TPP content,the heat release rate?HRR?,peak heat release rate?PHRR?,fire growth index?FGI?decreasedthe and time to ignition?TTI?increased significantly,all the above results indicated that TPP can delay the ignition time of PS,improving the flame retardance of PS.?5?Halogen-free expandable polystyrene?EPS/TPP?was prepared by suspension polymerization,which is a flame retarded foaming material with excellent foaming structures.The results showed that TPP had no significant effect on foaming property of EPS/TPP,and the foaming structures of EPS/TPP foaming particles were completely closed-cell structure,the foaming size is uniform.When 15 phr TPP added,the LOI of EPS/TPP was 24.2%,UL-94 was up to V-2 rating and the thermal conductivity was 0.0420W/?m·K?.The above results showed that EPS/TPP obtained good flame retardance while maintain excellent thermal insulating property.?6?A comparative study about preparation of PS/TPP composites by suspension polymerization and melt extrusion method was developed.As shown in SEM images,TPP was in the form of nanosized spheres and distributed homogeneously and uniformly in the PS/TPP-S matrix,which prepared by suspension polymerization,however,TPP particles were agglomerated in the PS/TPP-M matrix prepared by extrusion melt method,and some of the TPP particles were irregular,micron-sized particles.Due to the differences of TPP particles prepared by the two preparation methods,the thermal properties,flame retarded properties?including LOI,UL-94,TTI,PHRR,THR?and mechanical properties of PS/TPP-S is superior to PS/TPP-M.Therefore,it is considered that suspension polymerization is an effective method to prepared polymer nanocomposite.?7?PS/BDP and PS/TPP/BDP nanocomposites were prepared by suspension polymerization.BDP particles were all in nanosized and dispersed homogenously in the PS matrix.The LOI,UL-94 rating,TTI,PHRR,THR and FGI of PS/BDP nanocomposite were all improved with BDP.With the increase of BDP content,the polymerization time increased,the molecular weight of PS/BDP nanocomposite decreased and the particles size of PS/BDP beads decreased.The flame retaredance properties of PS/TPP/BDP nanocomposite improved significantly with TPP and BDP,because TPP and BDP have different decomposion temperature.?8?Base on the exploration of polymerization conditions,polystyrene containing graphite?PS/G?and expandable polystyrene containing graphite?EPS/G?were prepared by suspension polymerization.With the increase of graphite content,the polymerization time increased,the molecular weight and the onset decomposion temperature of PS/G composite decreased.As increasing graphite content the particle size of PS/G beads increased,the instability of suspension polymerization system was found at high amount of graphite.With increasing initiator concentration,the particle size of PS/G beads increased and the PSD became narrower slightly.Changing the concentration of suspending agent was an efficient way to control the particle size although its increase led to the broadening of the PSD.The second addition of suspending agent decreased the particle size and narrowed the concentration of suspending agent as well as keeping the suspension polymerization system stable.Stirring speed was a very efficient way to manipulate the PSD as decreasing the particle size and broader the PSD when it increased and 400 rpm was an appropriate value to obtain PS/G beads with desirable particle size and distribution.With adding 4 phr graphite,EPS/G had low thermal conductivity decreased by 20.6%compared with pure EPS,which had a uniform foam cell size,and many graphite particles distributed homogeneously in the wall of the foams.