The polyols in calcium zinc stabilizer can replace the unstable chlorine atoms in PVC molecular chain or the polyols can absorb the HCl produced by PVC decomposition. This is not an appropriate understanding. The actual situation should be: Diols have no auxiliary stabilizing effect. Polyols alone do not have a direct stabilizing effect on PVC, because the essence of the action is that polyols are easy to form complex bonds with metal atoms. In the calcium zinc stabilizer system of PVC, polyols are easy to form complexes with ZnCl2 strong Lewis acid. Thus, the autocatalytic effect of ZnCl2 on the decomposition and removal of HCl from PVC was inhibited (i.e. the inhibition of "zinc burning"), and the more hydroxyl groups in polyols, the more obvious the effect was.
Polyols, generally considered to contain 2 or more hydroxyl groups in the molecule, the general formula is CnH2n+2-x(OH)x(x≥2), sweet. Polyols are generally soluble in water, strong solubility for polar substances, viscous liquid or crystalline solid, its boiling point, viscosity, density and melting point increase with the increase of molecular weight. According to the number of hydroxyl groups in the molecule, polyols can be divided into two alcohols, three alcohols, four alcohols, five alcohols, six alcohols, etc. Polyol in polymer chemistry, often used as a monomer of polycondensation reaction to synthesize polyether, polyester or polyurethane, but also as a plasticizer, lubricant, stabilizer and other important raw materials, applied in paint, cosmetics, military, building materials and other fields, sugar alcohol in food processing is an important sweetener.
But in PVC calcium zinc stabilizer, polyol is not the use of the number of copies the better the effect? The answer is not necessarily, I think there are two reasons: first, although hydroxyl is a polar group, polyols and PVC theoretically have good compatibility, but polyols are generally small molecular compounds, hydroxyl is also a hydrophilic group, resulting in polyols soluble in water, in the high temperature processing process of PVC, polyols are easy to be precipitated with the migration of water molecules volatilization; Second, it is also necessary to consider the influence of different types and usage of polyols on coldness. Generally, in the amount, the initial and whiteness of products have a trend of increasing and decreasing. As polyols are generally small molecular compounds, they are easy to be precipitated in the process of processing, and the hydrophilic hydroxyl group is susceptible to moisture and other shortcomings.
At present, the development direction of polyols as the auxiliary stabilizer of calcium and zinc components is through esterification or etherification, and the introduction of aromatic groups, ester groups and epoxy groups, increase the number and molecular weight of the hydroxyl group in the molecule, so as to improve the compatibility with PVC precipitation resistance, or through the melting complex of polyols and zinc atoms to improve the compatibility and stability.