Effects Of Plasticizer On Ultraviolet Light Aging Properties Of Poly(Vinyl Chloride)

Poly(vinyl chloride) (PVC). is one of the important commodity plastics withhigh production and low price. The mechanical properties of PVC are controllablefrom soft material to rigid material by varying the addition amount of plasticizer.Therefore, PVC has been widely used practically. Under the effect of heat, UV light,oxygen, radiation, etc., PVC easily degrades with the elimination of hydrogenchloride, the formation of conjugated polyene sequences and photooxidation,leading eventually to the destruction of all the polymer's properties. Therefore, it isnecessary to study the degradation mechanism of PVC and to apply methods toincrease its stability during the synthesis, storage, processing and use of materialsand products based on PVC.This study was based on the UV degradation of PVC samples that containvarious concentrations of different plasticizer and a certain concentratibn stabilizer.The effects of plasticizer on the changes of mechanical properties and chemicalstructures of PVC after UV irradiation were studied by means of ATR-FTIR, UVspectrum, SEM, GPC, DSC, mechanical test and other methods. The main resultswere as followed:1. With increasing of UV light aging time, the elongation at break of rigid andsemi-rigid PVC samples decreases remarkably and tensile strength changesslightly, while both elongation at break and tensile strength of soften PVCreduce.2. During UV irradiation, the chemical structures of PVC change obviously,dehydrochlorination reaction generates conjugated polyene sequence and thecolor of sample surface turns dark (from white to black). The carbonyl groups ofketone,aldehyde and ester were generated during photooxidation.3. Under the UV light, the surface of PVC sample undergoes the roughening, theformation and extend of cracks. The change of surface morphology of soft PVC sample is slower than that of the rigid sample.4. During UV irradiation, both crosslink and chain cleavage reactions take place atthe same time. Chain cleavage is prior in soft samples, its average molecularweight decreases during the whole irradiation time. In rigid samples, crosslinkingis prior at the beginning of UV light irradiation, its average molecular weightincreases, and then decreases with irradiation time increase.5. The samples keep losing weight during UV irradiation, the weight loss rate ofsoft PVC samples is faster than that of rigid sample, for it including plasticizer'svolatilization besides the reaction of dehydrochlorination duringphotodegradation.