| Poly(butylene terephthalate)(PBT),as one of the five engineering plastics,has a wide range of applications in machinery,automobile,electronic,optical fiber,and other fields for its excellent solvent resistance,chemical corrosion resistance,mechanical properties,dimension stability,dielectric properties and heat resistance.Yet it still has shortcomings such as warp and high notch sensitivity,in addition,domestic PBT material can not meet the requirements due to its low viscosity,leading to the result that optical fiber coating materials used in our country always have to rely on imports,which greatly restricts the application of PBT material in this kind of field.This project is devoted to the study of high viscosity polybutylene terephthalate by means of combining ultraviolet light and extrusion process,the whole process was carried out without adding any initiator,and the product viscosity increased obviously,the properties of the products were stable,as well as,by adjusting the ratio of compound chain extender and extrusion parameters,the molecular weight of poly(butylene terephthalate(PBT)could be controlled,the reaction degree was easy to control,the operation process was simple,the cost was not high,what's more,this kind of method could achieve continuous production which can used in industrial production.Specific research contents and results are as follows:(1)Took advantage of the principle which combined ultraviolet light irradiation with extrusion process,and used the ?two-step? method which combined end-capping reaction with free radical branching reaction,with methyl glycidyl ester of acrylic(GMA)and trimethylolpropane three acrylate(TMPTA)as the composite chain extender and successfully prepared high viscosity poly(butylene terephthalate)(PBT).In the process of extrusion,methyl glycidyl ester of acrylic(GMA)and trimethylolpropane three acrylate(TMPTA)were added to the extruder successively,and the carboxyl group and the epoxy group of PBT reacted with the hydroxyl group of GMA,then the C=C double bond was introduced to the end group of PBT;At a later stage of free radical reaction,the carbon-carbon double bond of GMA,which was successfully grafted onto the PBT chain,as well as that of TMPTA were initiated by UV irradiation and active free radicals were produced,then the free radicals reaction carried out,eventually the extrusion product was the long branches chain polybutylene terephthalate.(2)The effects of extrusion parameters on the properties of long branched chain PBT were studied,the study found that the melting index,crystalline peek and bending strength came to the highest value at 235 ?,5rpm,160 rpm respectively.The varitation of extrusion temperature and feeding speed had little influence on the tensile and impact performance of PBT but engine speed did,the tensile and impact performance of PBT reached the maximum when the engine speed was 160 rpm.In combination,the parameters that the extruding temperature,feeding speed,and engine screw speed were 235 ?,5rpm and 160 rpm respectively were a better set of extrusion process parameters in the process of extrusion.(3)The crystallization properties of long chain branched PBT prepared via adding composite chain extenders during extrusion changed,its crystallization peak moved to higher temperature,the crystallinity and crystal grain size increased while the crystal s tructure and crystal morphology did not change.The long branched chain PBT had obvious different viscoelasticity with pure PBT,including higher complex viscosity,longer relaxation time,and smaller loss coefficient.The vGP diagram showed that the long-branched chain PBT has a comb-like topologic structure.TGA results showed that the existence of branched chain structure has little effect on the thermal stability of PBT,but the mechanical test illustrated that these branched chain structures could improve the mechanical properties of the materials.In addition,the dynamic mechanical properties of PBT were improved after modification. |
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