Study On Mixing Mechanism And Structural Properties Of Nano-filling Composites Via Volume Elongation Deformation

Melting blend method is one of the most commonly used processing methods for preparing of polymer-nanoparticle composites. The good dispersibility of nanoparticles in polymer matrix is the difficulty of the method. How to control the dispersion of nanoparticles in the matrix effectively is the key to the technology. One of the important influence factors on the dispersion of nanoparticles in the matrix is the processing flow field during the preparation of the polymer-nanoparticle composites. Compared with the traditional polymer processing equipment with screw based on shear deformation, the novel equipment without screw based on volume elongation deformation possesses many advantages, such as short thermal mechanical process, good dispersion and low energy consumption. Eccentric rotor extruder（ERE） is novel polymer plasticizing and conveying equipment based on volume elongation deformation, which can realize the whole processing process of the polymer-nanoparticle composites from solid to melt under the control of volume elongation deformation. The mixing mechanism of nanoparticles with different dimensions in polymer matrix and the dispersion effect of nanoparticles on the properties of nanocomposites were systematically studied by using ERE. The study is of great significance for processing nanocomposites with high performance as well as enriching and developing the processing theory and equipment based on volume elongation deformation.The polymer plasticizing and conveying process of ERE was analyzed in detail. Physical model and mathematical model of straight segment of rotor were established, the result indicates that the polymer plasticizing and conveying process of ERE were controlled by volume elongation deformation. This study revealed the mixing mechanism that the nanoparticles filling composites through continuous periodically “compression-expansion” mixing process realized the nanoparticles gradient gradually dispersing in the matrix.PP/Nano-TiO₂ composites were successfully prepared by ERE based on volume elongation deformation. The dispersion morphology of the composites was observed by SEM and TEM technology. The thermal stability and the crystallization behavior of the composites were studied by TG, DSC and XRD. Furthermore, the rheological properties and mechanical properties of the composites were also investigated in this work. The results show that, the Nano-TiO₂ dispersed homogeneously in PP matrix at nanoscale. The thermal stability of the composites improved significantly by adding the Nano-TiO₂, when the content of Nano-TiO₂ is 5%, the 5% weight loss temperature and 50% weight loss temperature of the composite were increased by 38.4℃and 14.1℃compared with that of pure PP, respectively. The crystallization and melting behavior of the composites were insignificantly influenced by adding Nano-TiO₂. The storage modulus, loss modulus and complex viscosity of the composites are increased; the relaxation process is more complex with the increase of Nano-TiO₂. Compared with the PP/Nano-TiO₂ composites prepared by single screw extruder based on shear deformation, Nano-TiO₂ had better dispersion in the composites prepared by ERE, and the comprehensive mechanical properties were also better.PP/MWCNTs composites were successfully prepared by ERE based on volume elongation deformation. The MWCNTs dispersed evenly in PP matrix, when the content of MWCNTs exceeds 1%, some MWCNTs clusters can be observed in the composites. The thermal stability of the composites were improved significantly, when the content of MWCNTs is 5%, the 5% weight loss temperature increased by 31.4℃ compared with that of pure PP. The MWCNTs plays a role of heterogeneous nucleating agent in the crystallization of PP. XRD test found that γ crystal of PP was observed at 19.9°when the content of MWCNTs was 0.5% in the composite. When the content of MWCNTs exceeds 1%, the rheological properties of the composites had great changes compared with PP.PP/Nano-MMT composites were prepared by ERE. The Nano-MMT dispersed evenly in the composite when the content of Nano-MMT not more than 3%. However, some Nano-MMT aggregates emerged and increased with the increase of Nano-MMT content when Nano-MMT exceeds 3%. TEM test showed that the Nano-MMT existed mainly in stripping state when the Nano-MMT content is low, but when the Nano-MMT content is high, the Nano-MMT existed mainly in intercalation state. The Nano-MMT improves the thermal stability of the composites and at the same time plays a role of heterogeneous nucleating agent in the crystallization of PP. The addition of Nano-MMT can obviously increase the modulus and complex viscosity of PP. When the content of Nano-MMT reached 9%, the modulus and complex viscosity of the PP/Nano-MMT composites reached its maximum value, and the microstructure of the composite changed significantly. When the content of Nano-MMT was among 1%-3%, the comprehensive mechanical properties of the composites were better. Compared with the PP/Nano-MMT composites prepared by TSE, the Nano-MMT had better dispersion in the composites prepared by ERE. Moreover, there are less Nano-MMT aggregates but high extent of stripped state, as a result, the comprehensive mechanical properties of the composites prepared by ERE were better. The processing parameters of the ERE extrusion process influence the properties of the composites significantly. When the processing temperature is around the range of 200-210℃, the rotate speed is around 30-45 rpm, the Nano-MMT in the composites dispersed more evenly, and the interlamellar spacing of Nano-MMT is bigger, the storage modulus and loss modulus of the composites are reached the maximum, and the comprehensive mechanical properties are achieved the optimal value.PP/PS blend and its nanocomposites were prepared by ESE. The PS droplets were well dispersed in PP continuous phase. The addition of Nano-MMT into the composites showed obvious compatibilizing effect. The particles size distribution and mean particles size of PS phase decreased with the increase of Nano-MMT content. The thermal stability and mechanical properties of the PP/PS blend are improved by adding Nano-MMT. The Nano-MMT stripped significantly in the PP/PS/Nano-MMT composites and the interlamellar spacing of Nano-MMT is bigger than that in PP/Nano-MMT composites. Furthermore, compared with the zero-dimensional Nano-TiO₂ and single-dimensional MWCNTs, the two-dimensional Nano-MMT is more effective to improve the compatibility of PP/PS blend. The Nano-MMT in the PP/Nano-MMT composites prepared by ERE stripped and dispersed in the path of a similar sine curve. According to the experimental phenomenon, the dispersion and stripping mechanism of “double sine gradual stripping” based on volume elongation deformation was proposed in this work. However, there are some different in the PP/PS/Nano-MMT composites prepared by ERE, the Nano-MMT completed the intercalation and stripping process under the synergistic action of volume elongation deformation force and interfacial force between PP and PS. In this case, the Nano-MMT in the PP/PS/Nano-MMT composites stripped in a more effective and easier way. According to this experimental phenomenon, the stripping mechanism of “interface induced MMT stripping mechanism based on volume elongation deformation” was proposed in this work.Therefore, based on the theoretical analysis and experimental results, it is known to us that the eccentric rotor extruder based on volume elongation deformation has significant advantages on preparing polymer nanocomposite system. Compared to the shear deformation, volume elongation deformation has better mixing and dispersing effect for polymer nanocomposites. The research findings in this work will provide an important theoretical and experimental basis for the application and promotion of eccentric rotor plasticizing and conveying equipment based on volume elongation deformation.