Study on the Preparation, Structure and Properties of PET/Montmorillonite Based Nanocomposites
|Keywords||PET montmorillonite nanocomposites ionomer rheology behavior elastomer engineering plastic compatibilizer spinnability|
The nanocomposites based on polymer and layered silicate exhibit superior mechanical properties, improved thermal properties, and reduced gas permeability, the nanocomposites of this kind has been recognized as one of the latest evolutionary steps of the polymer technology. The nanocomposites offer attractive potential for diversification and application of poly(ethylene terephthalate), a typical class of conventional polymeric materials, if its mechanical and thermal properties could be remarkably enhanced through compounding layered silicate such as montmorillonite. Therefore studies on PET/montmorillonite nanocomposites are very attractive. However the reported researching work were almost concentrated on the preparation and the characterizations of structure and properties of the nanocomposites, there are less deep research on melt intercalation and dispersion mechanism, nanocomposites application. In this dissertation , firstly the PET-MMT intercalated nanocomposites has been prepared by polymer melt intercalated method, PET and organically modified montmorillonite are blended in twin screw extruder. The structure and properties of SPET/MMT have also been systematically studied, finally the nanocomposites based on recycling PET are applied to engineering plastic and spinning fiber. The main results obtained are as follows:1.The organic ammonium modified MMT of different kinds has been prepared using cation exchange in water. The intercalation effect was characterized by WAXD,FT-IR and TGA. Experimental results showed that the cation ammonium of small molecule had weak influence on MMT intercalation;the interlayer spacing of silicate was not enlarged;organic cation of long chain was good for MMT to be intercalated, with the chain increasing the distance between layers get larger, furthermore compared with the monalkyl cation the dialkyl cation is more propitious to form intercalated structure.Among the cation chosen dioctradecyl dimethyl ammonium chloride is the best for intercalation, the interlayer spacing of MMT modified by this cation is the biggest.2. A series of SPET/MMT nanocomposites were prepared by polymerization intercalation, the property of pure SPET was compared with composites. The results indicated that with increasing the content of DMSIP in the SPET a better dispersion of the MMT layers in the SPET matrix was verified by WAXD, TEM and AFM. Through the comparative DSC studies, the silicates shows a heterogeneous nucleation effect on crystallization of SPET. Because of the dispersion of MMt layers and strong interaction between the SPET matrix and the MMT layers, the nanocomposites show better thermal stability than that of virgin SPET.3. The effects of MMT on crystallizability, thermal stability and mechanical properties of the composite were studies. The intercalated nanocomposites were prepared by melt intercalation. When containing 1% organo-MMT, the MMT was intercalated quite well. The addition of MMT improved the crystallization of PET, and it was found that MMT acted as a nucleating agent in PET, and the crystallization temperature and crystallization rate of PET could be obviously increased. TGA results indicated that MMT layered structure could prevent the movement and volatilization of small molecule resulted from PET decomposing, which could prevent the further decomposition. Consequently, the heat decomposing temperature of PET could be increased, the hot resistance was improved. Incorporation of MMT obviously increased the tensile strength of the PET matrix. The mechanical tests also showed that the comprehensive mechanical property of the composites could be increased by the adding of MMT at the ratio of 1 wt%.4. The multi component nanocomposites of superior toughness were prepared by the elastomer introduced into PET/MMT system. The results of WAXD, TEM and AFM indicated that the "exfoliated" and "intercalated" nanocomposites of PET/MMT/elastomer were obtained. With addition of elastomer, impact toughness of the nanocomposites were greatly improved;SEM micrographs of impact fracture surfaces of nanocomposites show ethylene-glycidyl methacrylate copolymer as a compatibilizer improved the compatibility between PET and elastomer. Crystallization behavior of the composites with different compositions was compared by DSC, indicating that compatibilizer and MMT dispersed in matrix improved the crystallizability of nanocomposites.5. The rheological behavior of these composites was investigated by capillary rheometer. The results showed that all samples exhibit a shear-thinnig behavior, when shear rate increases the viscosity of the melt blends decreases;the viscosity of the melt blends increases with the increase of elastomer content, the introduction of MMT greatly decreased the viscosity of the melt blends. The flow activation energy of PET/elastomer increases as the shear rate increases;after MMT addition the activation energy of composites reduced with shear rate increases. The no-Newtonian index is complicated in three-phase system.6. Based on MMT and PET multi-component engineering plastic was prepared by melt blend. The effect of each component on property of composites was studied. The nucleating system comprised of surlyn and talc powder has evident nucleating effect, so the mould temperature canbe kept in range of 80-100 °C.Glass fiber in matrix influences the composite property greatly, the composite of 30% glass fiber has a excellent integrative property. The elastomer (MABS) and ethylene-glycidyl methacrylate compatibilizer are compatible to other components, which improve mechanical properties. The MMT addition of l%-3% is suitable, the silicate layers can disperse at nanometer, the comprehensive property of nanocomposites is optimal.7. The spinnability of the nanocomposites by melt intercalation was compared with the fiber by intercalation polymerization. Spinnable nanocomposites can be prepared by two intercalation methods. Except that oil uptake is different, the spinning process of PET/MMT and rPET/MMT is close to pure PET. At the same draw ratio after MMT addition the modulus of the fibers from intercalation polymerization and melt intercalation was promoted. For the same sample as draw ratio increases the tensile strength and Youngs modulus of fiber were improved. At the same preparation condition MMT modified PET fiber has higher modulus and lower contraction ratio. MMT introduction into fiber greatly improved the dying ability, the MMT modified fiber can be dyed by dispersion dye in boiling water at atmosphere. For the same sample dying uptake drops with draw ratio increasing, the fiber made by nonacomposites containing MMT and SIPM has a fastest dying rate.