Preparation Of Organic Montmorillonite And Its Effect On The Thermal Stability Of PVC Composites

Research and development of novel polyvinyl chloride (PVC) composites with higher thermal stability have been one of the key goals concentrated on the modification of PVC plastic. The modification of PVC complexed with montmorillonite, can effectively improve the thermal stability of PVC composites. In this dissertation, Using coupling/intercalated second-modification technology, montmorillonite was interface-modified with silane coupling agent, and then modified with methyl methacrylate monomers (MMA) for the secondary modification, thus, a kind of modified montmorillonite (MMT/PMMA) with high thermal stability was obtained. The effects of different reaction conditions on intercalation performance were investigated, and a intercalation-polymerization-modification mechanism was proposed. By means of melt-blending method, exfoliated PVC/PMMA/MMT nanocomposites were prepared, and its structure, thermal stability and rheological properties were studied. The main contents and related achievements are as follows:Using coupling/intercalated second-modification technology, montmorillonite was interface-modified with silane coupling agent, and then modified with MMA for the secondary modification, thus, a kind of modified montmorillonite (MMT/PMMA) with high thermal stability was obtained. FT-IR, XRD, TGA and SEM analyses indicated that the molecular chains of PMMA have been inserted into the interlayer of montmorillonite, formed a partially exfoliated structure. Compared with traditional OMMT, the MMA-modified montmorillonite (MMT/PMMA) exhibited a higher thermal stability. The effects of mass ratio of MMA/MMT, reaction temperature, reaction time, ultrasonic dispersion, dispersion medium and other factors on intercalation performance have also been analyzed. The results showed that, when by ultrasonic-mechanical stirred, the mass ratio of MMA/MMT was 10:10, the reaction temperature was 80℃and reaction time was 6 h, the intercalation performance was the best, and the modified montmorillonite (MMT/PMMA) showed the best thermal stability. PVC/PMMA/MMT nanocomposites were prepared via melt-blending method, XRD and SEM analyses indicated that montmorillonite was completely exfoliated in the PVC matrix irregularly, and the modified montmorillonite and PVC were complexed in nano-size.Congo red static thermal stability tests and static aging tests showed that, compared with PVC and PVC/OMMT, the thermal stability time of PVC/PMMA/MMT nanocomposites was markedly extended, which indicated that the modified montmorillonite (MMT/PMMA) can significantly improve the thermal stability of PVC composites. Rheological tests showed that the modified montmorillonite (MMT/PMMA) had a good compatibility with PVC, The PMMA which played a role of compatibilizer in the composites, can effectively improve the rheological properties and processing properties of PVC/MMT nano-composite plastic. When the mass ratio of PMMA/MMT was 10:10, the addition of MMT/PMMA was 3 phr (parts per hundred of resin), the composite performance of MMT/PMMA with PVC was the best, and the PVC/PMMA/MMT nanocomposites showed the best thermal stability, rheological properties and processing properties.