CaZn stabilizers are preferred for use in critical applications because of low toxicity however, they are the least effective option in terms of thermal performance. An alternative stabilizer to replace Pb-based stabilizers such as calcium zinc (CaZn) is investigated. As a consequence, considerable efforts have been expended towards the development of new stabilization systems for PVC processing, which is driven by a desire to move away from stabilizers based on heavy metals. However, in 2003, the European Union passed regulations that stated the use of Pb will be limited in the production of PVC pipes, as well as in a number of other manufacturing processes. These products are widely used for the stabilization of pipe in Europe and Asia (except Japan). Heavy metal-based heat stabilizers such as lead (Pb)-based products are responsible for a large proportion of products in the heat stabilizer group. Recently, heat stabilizers contributed more than 30% of the global PVC additive demand. They can also impart PVC to enhance daylight resistance, weathering, and heat ageing. Therefore, heat stabilizers were widely used to safeguard the vinyl products at all stages by improving the heat resistance of PVC products at high temperatures, preventing the chain reaction of degradation. Hydrochloric acid can also deteriorate the mechanical, thermal, and physical properties of PVC. It also causes the level of color in the sample to range from yellow to black. When PVC is heated to 170–180 ☌, chlorine and hydrogen in the molecules are eliminated, and it releases hydrochloric acid (HCl), which in turn accelerates the thermal degradation process of the number of conjugated double bonds formed during the processing. However, PVC is thermally unstable at processing temperatures. The rigid PVC form has broad acceptance and exhibits a good market growth in major PVC product applications, i.e., pipes, due to its outstanding functional properties and cost competitiveness. It is widely used in various construction applications, including water, sewage, or drainage pipes and in many extruded profiles. Polyvinyl chloride (PVC) is a well-known commodity plastic with a broad spectrum of properties that are rigid, semi-flexible, and flexible. The results indicated that the OBS might decrease the dehydrochlorination rate of PVC, implying that PVC/OBS was more stable than PVC/Pb and PVC/CaZn systems. The non-isothermal kinetic parameter determined by the Kissinger and Flynn–Wall–Ozawa methods of the dehydrochlorination stage of the PVC/OBS was in satisfactory agreement and continued to compare with the PVC/Pb and PVC/CaZn systems. This characteristic was related to a more uniform fusion behavior of the PVC/OBS, i.e., the lowest gelation speed and the longest fusion time. This leads to a longer retention time for the initial color change of the PVC/OBS compared to PVC/Pb or PVC/CaZn systems. The OBS showed a positive effect on preventing the autocatalytic-typed thermal degradation of the PVC samples. A repeated processing cycle of those three types of the heat stabilizers up to four cycles was found to increase the degree of gelation and proved no significant effect on the impact strength and heat resistance of the resulting PVC samples. In addition, the effects of repeated processing cycles on the degree of gelation and the impact strength of the PVC/OBS, PVC/CaZn, and PVC/Pb are also examined. In this paper, the effects of organic based stabilizers (OBS) are investigated and compared with traditional lead (Pb) and calcium zinc (CaZn) heat stabilizers regarding their processability, mechanical property, and thermal degradation behaviors in rigid PVC pipe applications.
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