Synthesis Of Silicone Microspheres And Its Application In Light Diffusing And Halogen-free Flame Retarded Polycarbonate

LED light source has high photoelectric conversion,and is environment-friendly,thus it has been more and more widely used.However,it is difficult to make effective use of light energy from LED light source for the high brightness and concentrated light distribution,which hinders its wider application.Light diffusing materials can solve these problems by converting point light source into line or area light source.Such materials possibly convert the concentrated bright and dazzling LED light into more uniform and soft light.Polycarbonate?PC?is a kind of transparent engineering thermoplastics with good mechanical properties and heat resistance,which is often used as the substrate for light diffusion materials.Silicone microspheres are thermally stable and can maintain the original spherical shape during the processing of light diffusing PC.Therefore,it is a commonly used light diffusing agent for light diffusing PC.In this paper,poly?methyl silicone?microspheres?PMSM?were prepared from methyltrimethoxysilane using acid-base catalyzed two-step method and were used as the light diffusing agent for PC.The particle size of PMSM was adjusted by changing the ratio of oil to water,the concentration of sodium hydroxide?NaOH?and of emulsifier.PMSM possessed excellent thermal stability with only 1.0 wt% mass loss?mass percent?at the processing temperature of PC?280 oC?.Its refractive index was 1.454,which was significantly different from that of PC?1.586?.Therefore it could endow effective light scattering effect on PC.Based on MATLAB simulation from Mie scattering theory,the average diameter of PMSM was adjusted to about 0.8 ?m for light diffusing PC.Light diffusing PC/PMSM blends were prepared by extrusion and injection.The haze of PC was significantly increased from 13.2% to 76.7% with only 0.1 wt% loading level of PMSM,maenwhile the transmittance was decreased by only 6.5%.PMSM had very efficient light diffusion effect.Since light diffusing PC is flammable,it is necessary to realize the halogen-free flame retardant modification for light diffusing PC.Potassium sulfonate functionalized organosilica microspheres?OM-SO₃K?were prepared from the copolymerization of methyltrimethoxysilane and?3-mercaptopropyl?trimethoxysilane using acid-base catalyzed two-step method and were used as the flame retardant light diffusing agent for PC.The average particle size of OM-SO3 K was controlled to about 1.2 ?m.Its coefficient of variance?CV?was 2.0%,possessing good monodispersion.OM-SO3 K had high thermal stability with only 1.5 wt% mass loss at 280 oC.Its refractive index was 1.470.OM-SO3 K performed efficient light diffusing and flame retardant effect on PC.When the addition amount was 0.3 wt%,the haze of PC was increased from 13.2% to 86.6%,meanwhile the transmittance was maintained at a high level of 81.6%.PC/OM-SO3 K composites passed V-0 rating?3.2 mm?of UL 94 test with limiting oxygen index?LOI?of 37.4 % at only 0.3 wt% OM-SO3 K,as revealed by the results of flammability.The flame retardant effect of OM-SO3 K was originated from the thermal degradation of OM-SO3 K that produced SO2 and H2 O during combustion.The sulfur-containing compounds formed subsequently behaved as acid sources to catalyze the rapid degradation of PC and formed a dense carbon layer.The carbon layer became expanded following the accumulation of pyrolysis gas of PC and it behaved as a protective barrier to inhibit the diffusion of heat and gaseous products.As a result,PC degraded in the lack of oxygen under lower temperature,leading to the reduction in emission of combustible gas and interruption of combustion.