Study On The Preparation And Performance Of Bright PET/BaSO₄ Composites

Poly(ethylene terephthalate)(PET)is widely used in the fields of the fiber,film and engineering plastics because of its excellent rigid,heat and chemical resistance properties.However,due to its rigid chain,there was heterogeneous optical media in its internal structure,which affected the spread of light in the materials and led the transparency decrease,and all these shortages limited its application as packaging materials and bright fiber.Barium sulphate(BaSO₄),as an inorganic filler,added into PET of certain amounts,could enhance the transparence of PET/BaSO₄ composites, because their refractive indices matched closely.In this thesis,poly(ethylene terephthalate)(PET)/BaSO₄ composites were prepared by melt blending of three different surface properties of BaSO₄,isophthalic acid(IPA),and poly(ethylene terephthalate)in twin-screw extruder,and the properties of the composites were systemically studied.The aim of this study on PET/BaSO₄ composites is to further improve PET properties and to exploit novel applications for PET by providing reliable experimental data.Firstly,the PET/BaSO₄ composites were prepared by two-step melt blending process and the dispersions of three different kinds of BaSO₄ in the PET matrix were observed by scanning electron microscopy(SEM).The results showed that the aggregate extent of BaSO₄ in the polymer matrix increased as the BaSO₄ contents increased and at the same loading,the two treated BaSO₄ were dispersed uniformly in PET matrix with smaller particles size of about 400nm,but the untreated BaSO₄ was badly dispersed and aggregated.The crystallization behaviour of the composites were studied using differential scanning calorimetry(DSC)and X-ray diffraction and the Jeziorny method,Ozawa method and Mo method were employed to describe the non-isothermal crystallization kinetics.The results indicated that all the three different surface characteristic BaSO₄ improved the crystallization temperature and the crystallinity,and also the crystallites size reduced,so all of them acted as nucleating agents during the crystallization of the PET matrix,especially the inorganically modified one.However,when introduced of the IPA,the crystallization of PET/BaSO₄/IPA composites was prevented,and it became more difficult and the sizes of crystallites were smaller with the addition of IPA.The Ozawa analysis seemed not to be suitable,while the Mo's analysis was successfully used.Although the Jeziorny method had some deviations in analyzing the whole crystallization process,it could be applied to analyze the main crystallization process well.The optical performances such as transmittance,haze of the composites were measured using WGT-S transmittance/haze meter.The results indicated that the transparency of PET film increased and the optical properties of materials were improved with the addition of inorganic particulate BaSO₄,especially added small amount,but the haze value increased as the content of BaSO₄ increased.For the influence of surface treatment methods of to BaSO₄ on the optical performance,the transmission of the film had little change,but the composites contained the Al-Si inorganically coated one had lower haze than the other two kinds.Also,the transparency of the materials was enhanced by introduced IPA,and it increased with the content of IPA increased,while the haze for the opposite trend.The results of the film transmittance linear-fit of different thickness showed that the absorption coefficient of the PET/BaSO₄ composites film was small and the reflectance coefficient was low.The calculated reflective index was 1.48,and the theoretical value of maximal transmittance was 92.5 percent of the PET/BaSO₄ composites film.The thermal behavior of the PET/BaSO₄ composites was measured using thermal analyzer(STA 409PC).The thermal gravimetric analysis indicated that the thermal degradation of PET was inhibited by introduced BaSO₄ and enhanced the thermal stability,especially the inorganically modified one,but the effect was not seriously. The improved thermal stability of PET/BaSO₄ composites increased with the increased further loading until the 2.5%loading.However,when introduced of the IPA,the thermal stability of PET/BaSO₄/IPA composites was prevented,and the thermal degradation was serious as the addition of IPA increased.The rheology behavior of the PET/BaSO₄ composites was measured using rotational rheometer(ARES-RFS)in a dynamic mode.It was found that the storage modulus(G′),the loss modulus(G″)and dynamic viscosity of composites decreased with the introduction of BaSO₄.The G′,G″of the composites contained the Al-Si inorganically coated one didn't decreased remarkably,while the dynamic viscosity of the composites contained the untreated one decreased sharply.All of them decreased with increasing of BaSO₄ particles content.And PET/BaSO₄ composites exhibited shear-thinning non-Newtonian fluids behavior as the same as PET.