Thermal Degradation Kinetics of Plasticized Poly (Vinyl Chloride) with Six Different Plasticizers

ABSTRACT

Plasticized PVC formulated with different kinds of normally used plasticizers, including bis(2-ethylhexyl) phthalate (DOP), dioctyl terephthalate (DOTP), acetyl tri-n-butyl citrate (ATBC), acetyl trioctyl citrate (ATOC), trioctyl trimellitate (TOTM), and a new vegetable devived plasticizer, isosorbide ester (ID-37), were prepared by a melt blending method. The effect of plasticizer on the thermal degradation behavior of plasticized PVC was investigated by thermal gravimetric analysis (TGA). The activation energies were calculated by three well known methods, developed by Flynn-Wall-Ozawa (FWO), Friedman and Kissinger, respectively. The TGA conducted in N₂ atmosphere showed that the type of plasticizer had an obvious influence on the thermal stability of plasticized PVC. It was found that the peak temperatures (T_P) of the thermal degradation processes shifted to higher temperature with the increase of the heating rate, with two processes being shown. The activation energy of the first thermal decomposition process (E₁), calculated by the Kissinger method, was between 118 and 130 kJ/mol, while the activation energy of the second thermal decomposition process (E₂) was between 261 and 305 kJ/mol, except 499 kJ/mol for the PVC/TOTM formulation. The corresponding values of E₁ and E₂ obtained by the Flynn-Wall-Ozawa method were similar to the above data. E of the sample with TOTM also showed a higher value than the others; the results demonstrated that the PVC plasticized with TOTM was more thermally stable than with the others. The activation energies for certain conversion degrees were calculated by the Friedman method and the FWO method. The value of activation energy for 20%, 50%, and 80% conversion calculated by the Friedman method, exhibited an apparent difference from that calculated by the Flynn-Wall-Ozawa method; the results showed that the value of E obtained by the Friedman method was much more reasonable than that obtained by the Flynn-Wall-Ozawa method.

KEYWORDS:

• Poly (vinyl chloride) (PVC)
• plasticizer
• thermal degradation kinetics
• activation energy