Surface modification of selected polymer films by ozonation

Abstract

In this study, three polymer films - high density polyethylene (HDPE), biaxial oriented polypropylene (BOPP) and biaxial oriented polyethylene terephthalate (PET) were oxidized by ozone in distilled water and in the gaseous phase in a specially designed reactor. Ozonation was conducted using different reaction times, applied ozone doses and pH values. Peroxides were generated by ozonation on the surfaces of polymers. Then the peroxide-induced graft polymerixation of hydrophilic monomers improves the biocompatibility of the polymer surfaces. These three films are currently in extensive use, the modified polymer films can be applied more in organic materials packaging and medical fields. These three films were all found to react with ozone to generate peroxides both in distilled water and in gaseous phase. When comparing the peroxide generation rates in distilled water and in ozone gas mixture, it was found that the peroxide generation rates of BOPP and PET in the gaseous phase ozonation were faster than the peroxide generation rates in the aqueous phase ozonation; but the peroxide generation rate of HDPE showed a different trend: its peroxide generation rate in distilled water was faster than when using the ozone mixture in the gaseous phase. Further, among the three polymer films, HDPE obtained the fastest peroxide generation rate in distilled water, while BOPP has the fastest peroxide generation rate in gas phase. The tensile strength and elongation of untreated and ozone treated films were examined. The tensile strength and elongation decreased with increasing ozonation time. For both the aqueous and ozone gas mixtures, the order in which the three polymer films decreased in tensile strength and elongation were: HDPE>BOPP>PETE; but the tensile stength and elongation of BOPP and PET dropped faster when using the ozone gas mixture than when using the aqueous ozone. The results were the opposite of HDPE. After the reaction conditions were investigated, that using the 1.0-wt‰ applied ozone dose and 1.0-hr reaction time was found to be optimal, both to obtain peroxides and to maintain good mechanical strength. After investigation of the reactions with different pH values, it was found that the peroxide density decreased slightly as the pH volume increased. Finally, the ozone-induced graft polymerization of Acryamide (AAm) significantlly increased the hydrophilicity of HDPE films, the FTIR and SEM analysis confirmed the successful graft polymerization of AAm.