PVC Light Stabilizers

In a broad sense, any additive that improves the thermal stability of a polymer is called a heat stabilizer. Because polyvinyl chloride (PVC) has poor thermal stability, the vast majority of PVC stabilizers in the world are used for polyvinyl chloride. Thus, "PVC stabilizer" usually refers to the heat stabilizer for PVC and its copolymers.

PVC stabilizers are generally classified by chemical composition into basic lead salts, metal soaps, organotins, epoxides, phosphites and polyols. By function they can be divided into primary and auxiliary stabilizers. An auxiliary stabilizer itself has little or no heat-stabilizing effect, but used together with a primary stabilizer it produces a synergistic effect; a primary stabilizer is generally a metal-containing heat stabilizer. Pure organic compounds such as epoxides, phosphites and polyols are generally used as auxiliary stabilizers.

Because good stability of PVC often requires the simultaneous use of several heat stabilizers, some commercial PVC stabilizers are compounded from multiple components into composite stabilizers, such as barium-cadmium and barium-zinc stabilizers. These composite stabilizers usually already contain processing aids such as lubricants needed for PVC processing, for user convenience. Composite stabilizers come in many varieties — powder, paste and liquid forms.

(1) Absorb hydrogen chloride

Me(OOCR)2 + 2HCl → MeCl2 + 2HOOCR

where Me is: Pb, Ba, Cd, Ca, Zn, Sn, Sb, Mg, Sr, etc.

(2) Eliminate unstable chlorine atoms — replace or remove unstable chlorine atoms.

(3) Prevent auto-oxidation: under heat, oxygen and shear stress, PVC is highly susceptible to oxidative degradation by O2.

(4) Adding metal salts of maleic acid can suppress or eliminate double bonds, or shorten and reduce them.