Methods Of Testing And Evaluating PVC Recyclate

Poly(vinyl chloride) (PVC) has found broad application in building materials, in the forms of profile, pipe, board, etc. While the buildings are dismantled or reaching the lifetime, PVC products bring about a great deal of wastes inevitably, which poses a threat to the ecological environment. The best solution is reclaiming and reusing, however most of the time the wastes are reclaimed in a degrading way, which means the properties of the recycled products are much inferior to that of the original ones. So evaluating the recycling properties of the recyclate before reuse helps to make full use of these wastes in a reasonable and efficient way, and then to protect environment, economize resource and promote sustainable development.In the present paper, the research progress and achievements in this field around the world were reviewed firstly. Based on this, the idea was proposed, that the properties of the recyclate are mainly determined by its chemical composition, residual thermal stability and the ageing degree of the PVC resin within it. To make use of PVC recyclate scientifically and efficiently, the determining factors above-mentioned must be tested, and then its recycling properties can be assessed. Secondly, PVC resin, crosslinked PVC, thermal stabilizer and filler in recyclate were seperated and analyzed. It indicated that the samples from different source varied in their compositon, which was related to their formula, processing, serving condition and time. Thirdly, the thermogravimetry was employed to test and compare the thermal stability of recycled and virgin PVC. When the conversion of the degrading reaction reached 10% and 20%, the activation energy of degradation in N2, calculated by Flynn-Wall-Ozawa method were 143 kJ/mol and 145 kJ/mol for the virgin one, and both 132 kJ/mol for the recycled one. The values calculated by Kissinger method were 138 kJ/mol and 124 kJ/mol, respectively. Toop equation was applied to predict the lifetime of the two samples when they served under different temperatures, and the value of the virgin sample is 2-9 times longer than that of the recycled one, which indicated that the thermal stability of the recycled sample was worse than that of the virgin one. Fourthly, to understand the relationship between the ageing degree and molecular structure of PVC resin, the PVC samples(formulated with thermal stabilizer) were thermooxidatively aged under 140℃,150℃and 160℃respectively. Then GPC, FTIR and UV-Vis spectrum were employed to characterize the samples aged. The results demonstrated that carbonyl group developed through oxidation reaction on the molecular chain, the number average molecular weight increased with ageing, and HCl shucked off, producing polyene, the length and concentration of the polyene ever-increased with the time of ageing increasing or the temperature rising. The absorbance at 450nm in UV-Vis spectrum was defined as the ageing degree of PVC, then the activation energy of ageing under the condition of the experiment was calculated through Arrhenius equation, that was 113 kJ/mol. Fifthly, the molecular structure of PVC resin within the recycled samples R1, R2, R3, sample N(thermally processed once, not used) and the virgin PVC resin were comprehensively characterized by GPC, FTIR and UV-Vis spectrum. It indicated that the number average molecular weight of R1, R2, R3 and N were higher than that of the virgin resin in varying degrees, and their molecular weight distributions were wider. The sequence of the carbonyl index indicating the oxidation degree, was R3>R2>R1>N>V; There were polyenes with different length and concentration. The sequence of the absorbance at 450nm in UV-Vis spectrum, which indicated the ageing degree, was R1>R2>R3>N>V. The duration that recycled samples R1, R2 and R3 had served at 30℃were roughly calculated, that were 45 years, 15 years and 7 years (theoretical values), respectively. Lastly, the work and achievement were concluded, and the method and approach of assessing recycled PVC were proposed.The achievement of the present paper helps to develop testing menthods for evaluating recycling quality of the PVC recyclate, and the methods to identify the virgin products from recycled ones. It can provide technical support to the recycling of PVC wastes, advancing the healthy development of the recycling industry. It contributes to reducing or even eliminating the harm to environment caused by PVC wastes, and pushing forward the full use of resource. It also affords reference to the recycling of other kinds of plastic wastes.