Production method and lubricating effect of calcium stearate

2022-02-17   Pageview:33

Calcium stearate is a white powder, insoluble in water, cold ethanol and ether, soluble in hot benzene, benzene and turpentine and other organic solvents, slightly soluble in hot ethanol and ether. When heated to 400°C, it slowly decomposes and is flammable. In case of strong acid, it decomposes into stearic acid and corresponding calcium salt, which is hygroscopic.

1. The production method of calcium stearate

. Direct method

Add a quantitative amount of stearic acid and CaO to the reaction pot equipped with a stirrer and a thermometer, heat up to melting, slowly add catalyst H2O2 under constant stirring, and vacuumize, control the reaction temperature at 140-150, and react ~. After the reaction is completed, the material is discharged, cooled and pulverized to obtain the product.

. Double decomposition

Dissolve stearic acid in 20 times the mass of hot water, add saturated caustic soda solution, and carry out saponification reaction at about 75% to generate dilute sodium stearate solution. Then the calcium chloride solution with a content of 1074kg/m was added to the sodium stearate solution, and metathesis reaction was carried out at about 65%, and the product calcium stearate was precipitated out. Then it is filtered, washed with water, and dried at about 90°C to obtain the finished product.

2. Lubrication in PVC formulations

Calcium stearate is used as a heat stabilizer for PVC and a lubricant and mold release agent for various plastic processing. When used as a PVC lubricant, it is generally regarded as an internal lubricant. Calcium stearate is the stearate of medium and strong alkali calcium, with strong polarity. The chemically active points of PVC resin particles can form a relatively stable complex system with calcium stearate. The two long-chain alkyl groups of calcium stearate have little compatibility with polar resins such as PVC, and form a local microscopic two-phase interface inside the PVC resin, that is, a lubricating film. The microscopic essence of its lubricating effect is that the force between the local lubricating interface formed by the non-polar long-chain alkyl group and the polar resin segment is smaller than that between the resin segments, and because there are many small pores between the resin segments, Therefore, when the resin segment is displaced, the arbitrarily deformable alkyl group is squeezed into other adjacent pores, thereby reducing the resistance of the resin segment during displacement and acting as internal lubrication.

In practical application, calcium stearate as a PVC lubricant does not only play an internal lubricating role, its lubricating role is more complex, and it will reflect the role of external lubrication when other internal lubrication ratios are relatively high. Moreover, it has a synergistic effect with many lubricants.

In hard products, it can improve the gelation speed when combined with basic lead salt and lead soap. It is also used in food packaging, medical appliances and other soft films and appliances that require non-toxicity. It can be used as a halogen absorber for PE and PP to eliminate the adverse effects of residual catalyst on color and stability. As a plasticizer in rubber processing, it can soften natural rubber and synthetic rubber, and has almost no effect on vulcanization. It is also used as a lubricant for polyolefin fibers and molding compounds, a thickening agent for grease, a waterproofing agent for textiles, a flattening agent for paints, a plasticizer in the manufacture of plastic records, and a lubricant and release agent for phenolic, amino and other thermosetting plastics. Molding agent, lubricant for pencil lead, food grade calcium stearate used as anticaking agent, etc.

The use of calcium stearate alone in the formula can accelerate plasticization, increase melt viscosity, increase torque, and have a certain demoulding effect, while the use of paraffin alone can delay plasticization, reduce torque, and have no demoulding effect. . When calcium stearate and paraffin wax (polyethylene wax) are mixed in a certain proportion, it shows a good effect, and the torque value of the material can be greatly reduced. This is because the paraffin penetrates into the molecules of calcium stearate and strengthens the lubricating effect. , showing a strong synergistic effect, changing the dispersion of lubricants.

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