The Founction of Calcium Stearate in PVC
Calcium stearate,white powder, calcium content: 6.4%-7.0%, free acid is less than 0.1%, volatile content is less than 2%. Melting point is 149-155 degrees. Insoluble in water and most solvents. When heated, it is slightly soluble in ethanol, aromatic compounds, chlorinated hydrocarbons or vegetable oils, mineral oils or paraffins.
Inorganic acids decompose to stearic acid and calcium salts. It has water absorption in the air. We should pay attention to damp proofing when storing and transporting. It is used as nontoxic stabilizer, lubricant, mould release agent and textile waterproof agent for PVC plastics.
Calcium stearate, which is recognized as a physiological safety, acute toxicity: oral LD50:> 10000 mg / kg of rats; oral mice LD50:> 10000 mg / kg. No vulcanization pollution, long-term thermal stability.
Calcium stearate will show some interesting effects on heating. It starts to soften between the temperature of 120⁰C and 130⁰C, and the viscosity does not change until 160⁰C . In the DSC test, there is a crystallization peak indicating the separation of crystalline water. Calcium stearate is not a classic .
Effect and Function
As a lubricant for PVC, it is generally considered as an internal lubricant. Calcium stearate is a stearate with strong alkali calcium and has strong polarity. The chemical active point of PVC resin particles can form a stable complex system with calcium stearate. The two long chain alkyl calcium stearate and its compatibility with PVC and other polar resins are relatively small, which form a partial micro two phase interface inside the PVC resin, that is, the lubricant film.
The microscopic nature of its lubrication is that the local lubrication interface between the non polar long chain alkyl group and the polar resin chain segment is less than the force between the resin chain segments, and because there are many small pores in the resin chain segments, when the resin chain segments shift, the arbitrarily deformed alkyl is squeezed into adjacent areas. In the pores, it reduces the resistance of resin segment displacement and plays an internal lubrication role.
The use of calcium stearate alone in the formula can accelerate plasticization, improve melt viscosity, increase torque, and have a certain effect of demoulding, and the use of paraffin alone shows delayed plasticization, torque reduction, and no release effect.
When the calcium stearate and paraffin wax (polyethylene wax) are used in a certain proportion, the effect is good and the torque of the material can be reduced a lot. This is due to the infiltration of paraffin into the calcium stearate molecules, the strengthening of the lubrication, the strong synergistic effect and the improvement of the dispersing condition of the lubricating agent.