摘要
聚对苯二甲酸乙二醇酯(PET)具有高的刚性、耐热性和耐化学药品性等优良性能,被广泛应用于纤维、薄膜和工程塑料等领域。但由于其刚性链结构导致其内部结构存在光学介质差异,从而影响光线在材料中的传播,透光性能下降,限制其作为包装材料、大有光纤维等方面的应用。而在PET基体中添加一定量的与其折射率相近的无机微粒BaSO_4,可改善PET材料的光学性能。本论文以三种不同表面特性硫酸钡、间苯二甲酸(IPA)和聚对苯二甲酸乙二醇酯为原料,采用双螺杆挤出机熔融共混法制备了PET/BaSO_4复合材料,并对聚对苯二甲酸乙二醇酯(PET)/硫酸钡复合体系的各种性能进行了系统研究,为大有光PET/BaSO_4复合材料的开发提供可靠的基础数据,具有很强的实际应用意义。
首先采用二阶熔融共混工艺制备了PET/BaSO_4复合材料,并用SEM对硫酸钡的分散性进行了表征,结果表明,随着BaSO_4含量的增加,无机微粒的分散性能越来越差;在相同BaSO_4含量下,经表面处理的BaSO_4在PET基体中表现出较小的粒径,粒径分布在400nm左右,而未处理的BaSO_4在PET基体中有明显的团聚现象,分散均匀性较差。
采用DSC、X射线衍射方法研究了PET/BaSO_4复合体系的结晶行为,并采用Jeziorny法、Ozawa法和Mo法对其非等温结晶动力学进行处理,结果表明,三种不同表面特性BaSO_4的加入都起到异相成核的作用,提高了PET/BaSO_4复合材料的结晶温度和结晶度,细化其晶粒尺寸,尤其是添加硅铝二次包覆处理BaSO_4的成核作用更为显著。而IPA的引入,阻碍了PET/BaSO_4复合材料的结晶行为,且随着IPA含量的增加,PET结晶更困难,晶粒尺寸明显减小。Jeziorny法能很好的描述PET和PET/BaSO_4复合材料的主结晶过程,但对结晶前期和后期不适用,Mo法也能很好的分析PET和PET/BaSO_4复合材料的非等温结晶动力学,但Ozawa法对该体系不适合。
采用WGT-S透光率/雾度测定仪测试了PET/BaSO_4复合体系的透光率、雾度等光学性能,结果表明,无机微粒BaSO_4的加入提高了PET薄膜的透明度,改善材料的光学性能,尤其是BaSO_4添加量较少的PET薄膜透光率更好,但雾度却随着BaSO_4含量的增加而上升。对于不同表面特性的硫酸钡,对PET透光率的影响不大,但含硅铝无机包覆硫酸钡的共混材料雾度较其他两种偏低。IPA的引入能提高材料的透明性,且材料的透光率随IPA含量的增加而增大,而雾度则成相反趋势。由不同厚度薄膜透光率的拟合结果知,PET/BaSO_4复合薄膜的吸收系数很小,反射系数很低,制备的PET/BaSO_4复合材料相对折射率为1.48,该复合材料的理论最大透过率为92.5%。
采用STA 409PC型同步热分析仪研究了PET/BaSO_4复合材料的热性能,研究表明,三种表面特性无机硫酸钡的加入抑制了PET材料的热降解,提高了其热稳定性,尤其是硅铝无机包覆表面处理的硫酸钡,但影响不是很明显。且在一定添加范围内,PET/BaSO_4复合材料的热稳定性随BaSO_4添加量的增加而增强,但当添加量大于2.5%时,表现出分解温度和最大失重温度下降。而IPA的加入,破坏了PET/BaSO_4复合材料的热稳定性,且随着IPA含量的增加,PET/BaSO_4复合材料热降解越严重。
采用ARES-RFS平板流变仪测定了PET/BaSO_4复合材料的流变性,对其动态流变性能作了初步的研究。研究发现:硫酸钡的加入,降低了PET/BaSO_4复合材料的动态储能模量G′与损耗模量G″,但经过硅铝二次包覆处理后硫酸钡降幅较小。随着无机微粒硫酸钡含量的增加,复合体系的G′与G″均有所降低。而硫酸钡的加入降低了填充体系的复数粘度,但没有改变PET切力变稀的流变特性,且随着硫酸钡含量的增加而降低;对于不同表面处理的硫酸钡而言,未经表面处理的硫酸钡降低幅度更大。
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(BaSO_4),as an inorganic filler,added into PET of certain amounts,could enhance the transparence of PET/BaSO_4 composites, because their refractive indices matched closely.In this thesis,poly(ethylene terephthalate)(PET)/BaSO_4 composites were prepared by melt blending of three different surface properties of BaSO_4,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/BaSO_4 composites is to further improve PET properties and to exploit novel applications for PET by providing reliable experimental data.
Firstly,the PET/BaSO_4 composites were prepared by two-step melt blending process and the dispersions of three different kinds of BaSO_4 in the PET matrix were observed by scanning electron microscopy(SEM).The results showed that the aggregate extent of BaSO_4 in the polymer matrix increased as the BaSO_4 contents increased and at the same loading,the two treated BaSO_4 were dispersed uniformly in PET matrix with smaller particles size of about 400nm,but the untreated BaSO_4 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 BaSO_4 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/BaSO_4/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 BaSO_4,especially added small amount,but the haze value increased as the content of BaSO_4 increased.For the influence of surface treatment methods of to BaSO_4 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/BaSO_4 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/BaSO_4 composites film.
The thermal behavior of the PET/BaSO_4 composites was measured using thermal analyzer(STA 409PC).The thermal gravimetric analysis indicated that the thermal degradation of PET was inhibited by introduced BaSO_4 and enhanced the thermal stability,especially the inorganically modified one,but the effect was not seriously. The improved thermal stability of PET/BaSO_4 composites increased with the increased further loading until the 2.5%loading.However,when introduced of the IPA,the thermal stability of PET/BaSO_4/IPA composites was prevented,and the thermal degradation was serious as the addition of IPA increased.
The rheology behavior of the PET/BaSO_4 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 BaSO_4.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 BaSO_4 particles content.And PET/BaSO_4 composites exhibited shear-thinning non-Newtonian fluids behavior as the same as PET.
引文
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