【作者】 张运湘；

【导师】 宋义虎；

【作者基本信息】 浙江大学 ， 高分子材料， 2013， 博士

【摘要】 聚偏氟乙烯(PVDF)具有优异的力学性能、热稳定性、抗化学腐蚀和耐老化性能,可用作太阳能电池背膜。但PVDF熔体强度大、不易吹塑成型,且表面粘接能力差,限制其使用范围。聚甲基丙烯酸甲酯(PMMA)具有强的粘结能力和力学性能,可用来改善PVDF。本文采用熔融共混法制备PVDF/PMMA共混物,研究加工条件和组成对其结构与性能的影响,并采用TiO2提高共混物力学性能。论文进一步采用PVDF/PMMA和丙烯腈-苯乙烯-丙烯酸丁酯共聚物(ASA)来改善聚氯乙烯(PVC)的耐紫外老化性能。首先研究相形态结构对PVDF/PMMA共混物热行为、力学和抗紫外老化性能的影响。经短时熔融共混后(一次加工),共混物呈相分离结构,其相形态结构与共混物的组成和加工条件密切相关。PMMA含量越大,剪切速率越小,加工温度越高,越易形成相分离结构。经长时熔融共混后(二次加工),共混物呈均相结构。共混物异种分子链缠结几率大于同种分子链,有利于均相结构形成。共混体系仅有一个应力松弛峰,不存在长时松弛平台。固态共混物中存在三种松弛行为：结晶区中无定形态PVDF的αc松弛、无定形区中PVDF的αa松弛、和无定形态共混物的αm松弛。PMMA促进PVDF分子链松弛,降低其结晶度和熔融温度,提高其亲水性。共混物相形态结构决定共混物的综合性能,均相体系的拉伸与耐紫外老化性能更好。采用种子乳液聚合法制备具有核-壳结构的TiO2-g-PMMA复合粒子,使TiO2均匀分散在PVDF/PMMA共混物中,降低纳米粒子团聚。TiO2-g-PMMA粒子不改变聚合物基体的玻璃化转变温度和PVDF晶型。TiO2-g-PMMA的PMMA壳使TiO2与基体相的界面极化作用减弱,降低Ti02表面对基体分子链的影响。而TiO2-g-PMMA粒子的复合体系热稳定性高,结构不随热处理(190℃)时间改变。TiO2-g-PMMA复合粒子在共混物中分散性好,其力学增强效果明显优于TiO2。PVDF可提高PVC抗紫外老化性能,但二者相容性差,二元共混物的拉伸性能显著低于PVC。PMMA可改善PVC/PVDF共混物相容性,提高共混物拉伸和抗冲击性能。PVC/PVDF/PMMA共混物具有强的抗紫外老化性能。经紫外老化后,含少量PMMA的三元共混体系的拉伸强度、弹性模量和断裂伸长率均高于二元PVC/PVDF共混物。高含量PMMA共混物的拉伸和抗紫外老化性能随PMMA含量增加而降低。PVC与ASA相容性好,具有协同增韧效果,共混物出现明显的脆韧转变。随ASA含量增加,PVC/ASA共混物的屈服强度和弹性模量逐渐下降,断裂伸长率不断增大。ASA可提高PVC的静态热分解时间、动态热分解温度和维卡软化温度。ASA具有紫外光吸收作用,可阻碍PVC氧化降解反应。PVC/ASA共混物抗紫外老化能力随ASA含量增加而显著增强。共混物经长时间紫外老化后仍保持较高韧性。更多还原

【Abstract】 Polyvinylidene fluoride (PVDF) presents good stability to rigorous temperatures, mechanical strength, chemistry stability, and ageing resistance, which can be used as the solar cell back. However, PVDF has the relatively high melt strength, and therefore it is difficult to blow molding. The cost, processibility, and peel strength limit the application of PVDF in some fields. Polymethyl methacrylate (PMMA) has the strong interfacial adhesion and mechanical properties, which is used to improve the properties of PVDF. The processing conditions, morphologies, and properties of PVDF/PMMA blends prepared by melting compounding were investigated. TiO2particles were added into PVDF/PMMA blends to improve the mechanical properties. PVDF and acrylonitrile-styrene-acrylate (ASA) were introduced to improve the anti-ultraviolet irradiation of PVC. The mechanical and anti-ultraviolet properties of PVC/PVDF/PMMA and PVC/ASA blends were analyzed.The phase separation behavior appeared in PVDF/PMMA blends after short time melt blending (first processing). Phase morphology was related to the shear rate, processing temperature, and PMMA content. PVDF/PMMA blends were the homogeneous structures after long time melt blending (second processing). The chain entanglements densities of different molecules were greater than the same ones, which were good for the compatibility between PVDF and PMMA. There was only one relaxation peak in the stress relaxation spectrum, and no relaxation platform appeared in the long time region. PVDF/PMMA blends had the synergy effect during the molecular chain relaxation process. The solid PVDF/PMMA blends had three kinds of relaxation behaviors:aa and ac relaxation associated with segmental motions in the amorphous phase and the amorphous portions within the crystalline phase of PVDF, respectively, and am relaxation related to the PVDF/PMMA phase. PMMA facilitated the relaxation process of PVDF. The crystallinity of PVDF reduced gradually with the increasing PMMA content, however, the crystal type of which was not change. PMMA improved the hydrophilicity, processing conditions, and adhesion capability of the blends. The thermal decomposition temperatures of PVDF/PMMA blends reduced gradually with increasing PMMA content, however, the decomposition processes of PVDF and PMMA were independent. The microstructures of PVDF/PMMA blends determine the comprehensive performance. The homogeneous blends had the good tensile properties and anti-ultraviolet aging performance.Core-shell structured TiO2-g-PMMA nanoparticles prepared via seeded emulsion polymerization. TiO2-g-PMMA particles were dispersed evenly in PVDF/PMMA blends, which reduced the reunion phenomenon of TiO2nanoparticles. TiO2-g-PMMA particles did not affect the glass transition temperature of polymer matrix, but reducing the PVDF crystallinity. TiO2-g-PMMA was coated with a layer of PMMA, which reduced the interfacial polarization effect between TiO2particles and polymer matrix. TiO2-g-PMMA composites had a good thermal stability, the structures of which did not change under190℃with the increase of heat treatment time. Due to the good dispersion of TiO2-PMMA, the enhancement effect was greater than unmodified TiO2.PVDF was introduced to improve the anti-ultraviolet aging ability of PVC. However, the compatibility between PVC and PVDF was poor, which decreased the tensile properties of PVC/PVDF blends. PMMA improved the compatibility of PVC/PVDF blends, and enhanced the tensile properties and impact resistance. PVC/PVDF/PMMA blends had the strong anti-ultraviolet ability. The blends contain small amount of PMMA could keep good tensile strength, elastic modulus, and elongation at break after long time UV irradiation. However, the tensile properties and anti-ultraviolet performance of blends with high PMMA content decreased gradually with increasing PMMA.There was a good compatibility between PVC and ASA molecular chains. The synergistic toughening effect appeared in PVC/ASA blends due to the interaction between molecular chains. The elongation at break and toughness of PVC/ASA blends increased with the increasing ASA content. ASA improved the static thermal decomposition time, thermal decomposition temperature, and vicat softening temperature of PVC. ASA had the ultraviolet absorption effect, which hindered the oxidation degradation of PVC. PVC/ASA blends had the strong anti-ultraviolet aging ability with increasing ASA content. After a long time ultraviolet aging, PVC/ASA blends could maintain toughness higher than rigid PVC.更多还原