stearic acid
Stearic acid, or octadecanoic acid, molecular formula c18h36o2, is produced by hydrolysis of oils and fats, mainly for the production of stearates.
Properties: The pure product is a small piece of white waxy crystal with a slight luster.
Melting point: 71.5-72°C 69.6°C;
Boiling point: 232 °C (2.0kpa);
Relative density: 0.9408;
Refractive index: 1.4299; decomposition at 360 °C (also known as 376.1 °C); non-toxic.
Insoluble in water (at 20 °C, only 0.00029 g is dissolved in 100 ml of water).
Slightly soluble in cold ethanol.
Soluble in acetone, benzene, ether, chloroform, carbon tetrachloride, sulfur dioxide, chloroform, chloromethane, hot ethanol, toluene, amyl acetate, etc.
Slowly volatilize at 90-100 ° C. It has the chemical readiness of organic carboxylic acids in general.
Industrial products are 40-97% pure, white or slightly yellow or lumpy, are a mixture of stearic acid and soft lipid acid (hexadecanic acid), and contain a small amount of oleic acid, slightly fatty flavor, non-toxic. There are many types of stearic acid in the product, and it is better to use it as a lubricant with a low iodine and ester value, so that it will not affect the heat resistance and weather resistance of the product.
Uses and effects
It is generally believed that stearic acid is mainly lubricated internally, but it also has superior external lubrication. Stearic acid is a polar group, which has good compatibility with pvc resin, and can play a better internal lubrication effect on the melt, but the stearic acid molecules are associated with hydrogen bonds, so that the polarity of stearic acid decreases and the external lubrication effect is enhanced.
Stearic acid can be used in small amounts to get a great lubrication effect, but also has the effect of preventing crushing. Generally, the amount of addition is 0.2 ~ 0.5phr, and the amount of excessive (0.5phr or more) is not only not good for the lubrication effect, but will damage the transparency of the product, and even cause frost spraying. In order to avoid delaying the gelatinization rate of PVC, it is best to use it in combination with internal lubricants such as butyl stearate.
In practical applications, it should be noted that stearic acid can play an internal lubrication role at low temperatures or a small amount, but when the temperature increases or the amount of use increases, its external lubrication effect gradually takes advantage. Especially in high-filler formulations, the proportion of stearic acid should be selected with extra care, because stearic acid is added to many filler processing processes. Blind use of stearic acid often causes many problems such as poor plasticization, frost spraying, precipitation and so on.
Calcium stearate
Calcium stearate, white powder, calcium content: 6.4%-7.0%, free acid ≤0.1%; volatile ≤ 2.0%, melting point: 149 °C-155 °C. Insoluble in water, insoluble in most solvents.
When heated, it is slightly soluble in ethanol, aromatic compounds, chlorinated hydrocarbons or vegetable oils, mineral oils or paraffins.
In case of inorganic acids decompose into stearic acid and corresponding calcium salts. There is water absorption in the air, and attention should be paid to moisture-proof when storing and transporting. It can be used as a non-toxic stabilizer, lubricant, mold release agent and textile waterproofing agent for PVC plastics.
Calcium stearate, recognized for physiological safety, acute toxicity: oral-rat ld50:> 10,000 mg/kg; oral-mouse ld50:> 10,000 mg/kg. No vulcanization pollution, good long-term thermal stability.
Calcium stearate exhibits some interesting effects when heated. It begins to soften at temperatures between 120°C and 130°C, and the viscosity no longer changes after reaching around 160°C. In the DSC test, there is a crystal peak that indicates the separation of crystalline water. It shows that calcium stearate is not a classic melt.
Effects and effects
When used as a PVC lubricant, it is generally considered an internal lubricant. Calcium stearate is a stearate of medium strong alkali calcium, with strong polarity, the chemical activity point of PVC resin particles can form a relatively stable complex system with calcium stearate. The two long-chain alkyl groups of calcium stearate have less compatibility with polar resins such as PVC, and constitute a local microscopic two-phase interface inside the PVC resin, that is, a lubrication film.
The microscopic nature of its lubrication is that the local lubrication interface formed by the non-polar long chain alkyl group and the force between the polar resin chain segments is less than the force between the resin chain segments, and because there are many small pores between the resin segments, when the resin chain segments are displaced, the alkyl groups that can be arbitrarily deformed are squeezed into other pores adjacent to them, thereby reducing the resistance during the displacement of the resin chain segments and playing 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 release effect, while the use of paraffin wax alone shows delayed plasticization, reduced torque, and no release effect. When calcium stearate and paraffin (polyethylene wax) are mixed in a certain proportion, it shows a good effect, and the torque value of the material can be reduced a lot, which is due to the infiltration of paraffin into the calcium stearate molecules, which strengthens the lubrication effect, shows a strong synergistic effect, and improves the dispersion of the lubricant.
In practical application, calcium stearate as pvc lubricant not only plays an internal lubrication role, its lubrication effect is more complex, in other cases where the proportion of internal lubrication is relatively high, it will reflect the role of external lubrication. Moreover, it has a synergistic effect with many lubricants.