Qi-Hui Zhao, Wan-Chan Liu
Beijing Technology and Business University
Institute of Plastics Processing and Application of Light Industry (IPPA)

Key words: PVA, pellet, blowing film
Abstract: Along with the development of the food industry, drink industry, agriculture industry, chemical industry and commodity industry, the need of functional packaging film is larger and larger. Now the plastics packaging film covers 1/3 of the whole plastics packaging material and it have been aroused great attention of the environment problem by the government and during the international trade. So the packaging material with high performance, multi-functional and environment-friendly could meet the environment protection policy. Poly (vinyl alcohol) film gains the attention because of its water-soluble and high-obstruct performance.
PVA film has the following characters:
1) Environment-friendly
2) Water content and water solubility
3) High-obstruct
4) Anlistatig property
5) Heat sealing
6) Oil resistance and the chemical resistance
7) Sanitation property
　Poly (vinyl alcohol) is a kind of polymer with regular molecular structure and a great deal of hydrophilic hydroxides. The intermolecular interaction is strong with high crystallinity. On the other hand, there are strong hydrogen bonds between the molecular so the melt point of PVA is as high as 210°C~240°C. The processing methods such as extrusion and blowing used in PE material could not be used in PVA. The plasticizers such as ester, aether, ketone and advanced alcohols could not act with PVA. So several years ago, PVA could not be used in the extrusion processing. So the extrusion method of PVA is a difficult problem for the entire world.
　The research team of IPPA is through experiments, selecting and design a reasonable plasticizing system, which forms a temperature difference between the melt temperature and decomposition temperature. At the same time, doing some changes to the domestic extruders, so as to overcome the high melt viscosity and bad flow rate performance and could make pellets and blow film of PVA through extrusion method. The quality of the pellets is good and the properties of the PVA are excellent. Comparing to that of wet method, the dry extrusion method of PVA has the advantages of simplemethod, low energy cost, high efficiency, and low invests, etc. At the same time, the PVA pellets provide possibility of extrusion multi-layer high-obstruct material such as film, components, hollow products and it opens the new applications of PVA resin.