Stearic acid or octadecanoic acid is a saturated fatty acid that occurs naturally in plant and animal fats. It has a white color and is often crystalline with a moderate odor. Stearic acid features an 18-carbon chain and is derived from tallow and vegetable sources. The acid and its additives are used in the production of polyvinyl chloride (PVC). Stearic acid’s viscosity depressant properties make it perfect for PVC processing.
How is Stearic Acid produced?
Stearic acid is produced from the hydrolysis of typical vegetable oils, animal oils, and fats. The resulting fatty acid further undergoes crystallization or fractional distillation. Later, pressing methods are used to separate the solid saturated fatty acids from the liquid unsaturated acids.
What Makes Stearic Acid Suitable for PVC processing?
Thermal Stability
Thermal stability is an essential characteristic of PVC, defining the final product’s thermal degradation. Thermal degradation affects the physical and mechanical properties of the PVC. Besides, it also limits the circularity and the recyclability of PVC pipes and other products. For this reason, companies in PVC processing use thermal stabilizers that hinder labile chlorines, replacing them with solid functional groups that can withstand elimination.
To effectively perform this function, a thermal stabilizer has to be compatible with the PVC. Besides, it must be added in a condition that reduces diffusion time without thermal degradation. The salts and esters of stearic acid are used as thermal stabilizers in PVC and polymer processing.
Uses of Calcium Stearate in PVC
The reaction of stearic acid and lime forms calcium stearate, which acts as an internal lubricant in PVC processing. The white, silky and fine powder is used to reduce the friction in PVC grains, making it a suitable internal lubricant. Compared to wax, calcium stearate has a higher softening point and does not get greasy when exposed to high temperatures. Calcium stearate is also used as a releasing agent and an acid scavenger in the PVC processing industry.
Uses of Lead Stearate in PVC
Lead stearate is formed from the reaction of lead and stearic acid. It has a melting point of 105-112 °C and a boiling point of 359.4 °C. The compound is commonly used as a stabilizer in PVC production. It also lubricates plasticized PVC compounds, specifically in covering PVC cables to help minimize electrical conductivity.
Although lead stearate has several benefits, one drawback is that it is highly toxic. It is essential to note that lead stearate should not be used in pieces that are in contact with foodstuff. However, when a lead heat stabilizer is combined with PVC compounds, it exhibits excellent light and heat stability and superior electrical and mechanical properties.
Shop Quality Stearates Today
At Bisley, we supply a wide range of stearates in liquid and solid forms. Whether you need stearic acid, aluminum stearate, glycerol monostearate, zinc stearate or calcium stearate, we will offer a solution to fulfill your needs. We also have a wide range of raw materials to facilitate your foam, PVC, rubbers and plastic processing projects. Contact us to discover more about how we can help.V
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