Stabilization of nontoxic PVC formulation for gamma irradiation sterilization, I. Effect of additives

In order to investigate the fundamental data for the resistance of gamma radiation sterilization of polyvinylchloride (PVC), the formulations of the additives such as plasticizers of dioctylphthalate, trioctyltrimellitate and polyester, second plasticizers, Ca/Zn nontoxic metallic stabilizers with powder, paste and liquid state, and phosphite stabilizers have been carried out. The control and irradiated PVC samples with 1.5, 2.5 and 4.0 Mrads were characterized by mechanical tester, colorimetry, and extractant in water. The effect of plasticizers observed in the order of dioctylphthalate approximately equal trioctyltrimellitate > polymeric plasticizer. It was observed in the order of Ca/Zn metallic stabilizers of paste > liquid approximately equal powder state for the color change and liquid > paste > powder for the extractant. The mechanism of the discoloration of PVC in our experiment was predominant the formation of polyene by the dehydrochlorination rather than the formation of keton and aldehyde by the oxidation and chain dissociation by the measurement of gel permeation chromatography and mechanical property. The proposed mechanisms of stabilization and discolorization with various additives are also discussed.