Kinetics of the stabilizing effect of calcium and zinc stearates in the thermal degradation of PVC: Part I

Differential scanning calorimetry analysis of the thermal treatment of ternary mixtures of ethylene vinyl acetate, polyethylene, and azodicarbonamide

“…The shift of the peaks associated with the ADC thermal decomposition in the mixtures studied compared with the pure ADC might be explained as a result of different effects: There existed an initial effect of the polymeric matrix in the heat transfer inside the sample that contributed to the delay of the peaks in the ternary mixtures as compared with pure ADC. Additionally, the EVA matrix seemed to alter the mechanism of the ADC primary exothermic thermal decomposition (different relative intensities of peaks p1 and p2) that apparently went through different paths than those of the pure components. According to the ADC degradation reactions shown in Figure 1, the heterogeneous reaction iii introduced an autoaccelerating effect13, 14, 18, 34 when the concentration of ADC in the sample increased because of a higher probability of reaction (higher contact time) between the nonreacted ADC and the HNCO gas generated from reactions i and ii in Figure 1. This reaction may have accelerated the global decomposition of the ADC and produced the observed shift to lower temperatures. …”

“…According to the ADC degradation reactions shown in Figure 1, the heterogeneous reaction iii introduced an autoaccelerating effect13, 14, 18, 34 when the concentration of ADC in the sample increased because of a higher probability of reaction (higher contact time) between the nonreacted ADC and the HNCO gas generated from reactions i and ii in Figure 1. This reaction may have accelerated the global decomposition of the ADC and produced the observed shift to lower temperatures.…”

“…In this study, following an exhaustive investigation of the phenomena that happen in the industrial production of commercial EVA that we started in previous studies,9–12 the thermal behavior of EVA–polyethylene (PE)–foaming agent ternary mixtures involved in the production of EVA foams was systematically studied by differential scanning calorimetry (DSC) to examine the possible effects of different compounds and mixtures on the foaming process. In this study, azodicarbonamide (ADC) was used as a foaming agent because it is very frequently used in the production of EVA–PE foams because its decomposition liberates a large volume of gas, which is trapped in the melt 13–15. The decomposition of this chemical goes, according to Stevens and Emblem16 and Lober,17 through the competitive and exothermic reaction pathways shown in Figure 1 to produce solids (urazol and hydrazodicarbonamide) and a gaseous mixture of nitrogen, carbon monoxide, cyanic acid, and ammonia.…”

Kinetic study of the decompositions involved in the thermal degradation of commercial azodicarbonamide

“…The only difference among the curves is that they seem to shift to lower temperatures when increasing the particle size. The origin of this fact in the exothermic decomposition of the ADC could be due to an auto‐accelerating or autocatalyst effect1, 2, 6, 20 of the global decomposition rate, as a consequence of the heterogeneous reaction (r.iii) in Figure 1. When the ADC particle size increases, the reaction rate of this heterogeneous reaction may increase due to a larger contact time of the HNCO gas (produced from reactions r.i and r.ii, Fig.…”

“…Azodicarbonamide (ADC) is a foaming agent frequently used in the production of PVC and EVA‐PE foams because its decomposition liberates a high volume of gas, which is trapped in the melt 1–3. This foaming agent is used in combination with a crosslinking agent to produce the final product.…”