聚丙烯酸酯-纳米二氧化硅接枝复合胶粒在熔融剪切场中的取向重排

以聚丙烯酸酯-硅烷改性二氧化硅（PAcr-MPS-SiO₂）石榴状接枝复合胶粒为分散相，以聚甲基丙烯酸甲酯树脂（PMMA）为连续相，在HAKKA转矩流变仪中进行熔融共混，考察不同交联结构复合胶粒在不同熔融共混条件下的剪切形变行为。发现:微米级复合胶粒在熔融共混过程中既受强力剪切场的诱导作用，同时又受复合胶粒接枝交联结构的约束作用，因而依次会经历球形、椭球形、棒状、微纤状等取向形态，但又不至于出现大规模的撕裂解离现象，从而可在聚合物基体中原位并排生成大量具有较大长径比的微纤状取向结构体。通过改变SiO₂表面MPS改性程度和SiO₂含量调节复合胶粒的交联程度，或通过改变螺杆转速调节熔融剪切场的剪切强度，可在一定范围内调控复合胶粒及其中的接枝SiO₂粒子簇的取向程度。其中，当胶粒凝胶率为40%、共混温度180℃、螺杆转速65 r/min、共混时间12 min时，可得到平均长径比达到11.8的规则并排取向结构。研究可为聚合物基体中原位构建和有效调控一维取向结构提供一种新途径。 

Orientation rearrangement of polyacrylate-nano-silica grafted composite particles in melt shear field

Using guava-like polyacrylate-3-(methacryloyloxy) propyltrimethoxysilane modified silica (PAcr MPS-SiO₂) grafted composite particles as the dispersion phase, and polymethylmethacrylate (PMMA) resin as the continuous phase, their mixture was melt blended in a HAKKA torque rheometer, in order to investigate the dispersion and orientation behavior of the grafted composite particles with different crosslinking structures under various melt shear conditions. It is found that due to the induced effect provided by the strong shear force in the melt-mixed field, and also the restraint effect provided by the widespread grafting cross-linking structure formed with SiO₂ particles as the cross-linking point and the grafted polymer chain as the linking line in PAcr-MPS-SiO₂ particles, the guava-like composite particles are likely to be oriented and rearranged. They can be in turn deformed into sphere, ellipsoid, rod-shaped, microfibril and other oriented morphologies without large-scale tear dissociation, and finally in-situ formed a fibrous orientation structure with a large aspect ratio in the polymer matrix. The degree of orientation of the composite particles and the grafted SiO₂ clusters inside could both be controlled within a certain range, by adjusting the degree of crosslinking of the PAcr-MPS-SiO₂ composite particles from changing the degree of MPS modification on the silica surface, or by adjusting the shear strength of the melt shear field from changing the screw speed. When the gel fraction of the composite particles is 40%, the mixture temperature is 180℃, the screw speed fixed at 65 r/min and the blending time of 12 minutes, an ordered alongside oriented structure with an average aspect ratio of 11.8 can be obtained. Accordingly, we would believe this study could open a new pathway to in-situ construct and effiviently regulate one-dimensional orientation structure in polymer matrix.