Preparation And Application Of Acrylic-based Ionomer As A Multi-functional Processing Aid For Pvc

Due to the excellent comprehensive performance, poly(vinyl chloride)(PVC) is one of the five most commonly used plastics and widely used in building materials, light industry, agriculture field and so on. However, it is prone to degrade and hard to fuse during processing. Hence, the thermal stabilizers and processing aids are necessities especially for the rigid PVC products. In the last decades, in respect of environmental protection and health, the traditional stabilizers, such as lead salts and cadmium salts are forbidden. Non-toxic calcium/zinc or rare earth/zinc composite stabilizers attract more and more attention. Nevertheless, metal soaps with short fatty or naphthenic chains are easy to volatilize during PVC processing and reduce heat deformation temperature of PVC products, though they could maintain the transparency of the products due to their good compatibility with PVC. On the other hand, the soaps stabilizers with long alkyl chains may undergo fogging easily owing to their limited compatibility with PVC, which limits their usage in transparent products. Acrylate processing aids (ACR) having a good compatibility with PVC are usually used to promote fusion of PVC in almost all rigid formula and many flexible ones. In this study, a ACR-based ionomer was synthesized with purpose to combine the fusion promotion function of ACR with a good compatibility to PVC and the stabilization function of rare earth compounds.Up to now, few relevant work about ionomer used as stabilizer for PVC is reported and the mechanism is nearly ignored. In this paper, the influence of ion content, acid content, the type of plasticizer and ion type of ionomer on the thermal stabilization, fusion behavior, transparency and mechanical properties of PVC was investigated by congo red test, color comparison, hake torque rheometer and so on. Furthermore, we try to explore the mechanism of stabilizing and promoting fusion of ACR-based ionomer.The results revealed lanthanide-containing ionomer behaves as a good HCl scavenger and shows synergistic effect with ZnSt2for stabilizing rigid PVC. It could improve static stability time and promote fusion of PVC with improvement of minimum and fusion torques. The transparency of the compounds stabilized by this kind of ionomer compares favourably with those stabilized by organotin and liquid Ca/Zn stabilizers. The ionomer has a comparable stabilizing efficiency to the commonly used lanthanide stearate for PVC. Moreover, the ionomer stabilized compounds show better initial discoloration, transparency and tensile strength than those stabilized by LaSt3.Being different from small molecular stabilizer, there is a critical content in ionomer. Increasing stabilizing functional groups further will lead a decrease in stabilizing efficiency of ionomer for PVC which is attributed to formation of cluster because of the serious aggregation of stabilizing functional groups. The aggregation is stable under processing temperature which restricts the reaction between stabilizing functional groups in it and hydrochloride (HCl) or zinc stearate (ZnSt2). The reaction rate between stabilizing functional groups in ionomer and ZnSt2is much slower than that between LaSt3and ZnSt2which endows PVC a better initial discoloration.Acid contents in ionomer strongly influence the structure and functionality of ionomer. The size of aggregation decreases with the acid content increasing, owing to restricting the formation of cluster. This is a positive factor of stabilizing and promoting fusion for PVC. On the other hand, increasing acid content in ionomer will increase dissociation temperature and slower the rate of dissociation which considerably lowers the stabilization and promoting fusion function of the ionomers. It is suggested that there is an optimal acid contents of the ionomer to reach a best functionality.Diisooctyl phthalate (DOP) could only plasticize the matrix of ionomer. So it could improve stabilizing and promoting fusion efficiency of the ionomer containing lower amount of stabilizing functional groups more significantly. Glycerol could improve the stabilization of PVC remarkably, but it will postpone the fusion of PVC. It could plasticize the ionic aggregation region in ionomer, destroy part of the ionic aggregation or lower the dissociation temperature of ionic aggregation. Hence, it could improve stabilizing and promoting fusion efficiency of the ionomer containing higher amount of stabilizing functional groups more significantly.It is more easily to form cluster for calcium-containing ionomer. So its stabilizing and promoting efficiency for PVC is lower than that of lanthanide-containing ionomer with stabilizing functional groups no more than0.8mmol/g. While it is more difficult to form cluster for zinc-containing ionomer, so its promoting fusion efficiency for PVC is better than calcium and lanthanide-containing ionomer. However, zinc ionomer will lead zinc burning which makes its stabilizing efficiency is the worst in these three kinds of ionomer.Epoxy soybean oil could improve the stabilization and promote fusion of PVC. When it is used with ionomer/ZnSt2together, it could make promoting fusion efficiency of zinc-containing ionomer become to be the worst of the three and that of lanthanide-containing ionomer become to be the best one. Epoxy soybean oil/ZnSt2/calcium or zinc-containing ionomer could make PVC fuse faster with a lower viscosity (180℃,65r/min,6min) compared with PVC compound containing the same epoxy soybean oil/zinc stearate/ACR content. Based on these results, it may provide a new method to develop a higher efficient and less energy cost processing aid formula.