Synthesis and thermal stabilizing effect on polyvinyl chloride of calcium/zinc carboxylate from palm fatty acid distillate: Effect of metal to fatty acid ratio

Polyvinyl chloride (PVC) has many applications in construction, such as pipes, floors, roofs, walls, frames, and cables. Since it is easily degraded by heat, a heat stabilizer must be added to the PVC resin before it is molded into final products. Mixed calcium/zinc carboxylate has become a popular PVC thermal stabilizer since it is more friendly than the conventional lead base thermal stabilizers and is relatively inexpensive. This research aims to investigate the synthesis and assess the effectiveness of a mixed calcium/zinc thermal stabilizer in stabilizing PVC. The stabilizer was prepared from palm fatty acid distillate (PFAD), and different metal salt-to-fatty acid molar ratios were employed for the study. The synthesis was carried out by a metathesis method at 10% deficiency, stoichiometric, and 10% excess of metal salt-to-fatty acid molar ratio. The stabilizing effects of the obtained metal carboxylates as mixed metal thermal stabilizers have also been evaluated by standard thermal stability tests. The calcium and zinc carboxylates prepared at a 10% deficiency were found to have high pHs and lower metal contents than those at stoichiometric molar ratios due to the presence of residual sodium soap. Their thermal stabilizing effects on PVC are also worst when prepared at a deficient metal salt-to-fatty acid molar ratio. Increasing the metal-to-fatty acid molar ratio above the stoichiometric requirement lowers the thermal stabilizing effect of zinc carboxylate but has little influence on the thermal stabilizing effect of calcium carboxylate obtained. Synthesis at stoichiometric metal salt-to-fatty acid molar ratios is recommended for preparing calcium and zinc carboxylates as mixed metal PVC thermal stabilizers.