Acid scavengers metal stearates

Traditional substances used as co-stabilisers include polyols, epoxidised soya bean oil, phosphites and certain antioxidants. Arkema markets Stavinor calcium stearate co-stabilisers for use with calcimn-zinc systems. Akcros Chemicals sells P24D, which stands for pyrrolidene-2,4-dione. Siid-Chemie is now marketing a synthetic hydrotalcite, Sorbacid 911, while the PQ Corporation is selling two grades of aluminosilicate (zeolite) imder the name Advera 401. They act as scavengers for acids and metal chlorides, and enable users of tin mercaptides to use less tin, saving on material costs. They also allow stabiUsation to take place with the very low tin levels required by law in food contact applications. 

Referring to the polyolefin industry, metal stearates (especially calcium, sodium and zinc) and s)mthetic dihydrotalcites are of paramount importance as acid scavengers applied in additive formulations. A minor part is occupied by the calcium lactates/lactylates (salts of lactic acid), ZnO and other oxides. 

Acid scavengers neutralize catalyst residues and prevent equipment corrosion. The choice of the acid scavengers can affect the overall acidity/basicity of a resin and influence the reactions of many of the organic additives in the system. Also, the acid scavengers as metallic stearates will impart to the polymer a certain lubricity, mold release or slip properties. As acid scavengers can be used metallic stearates (of sodium, calcium and zinc, zeolites structures (dihydro talcite, both synthetic and natural) CaO and ZnO and other metallic salts based on lactic or benzoic acid. Environmental Products has introduced PTA-210 and PTA-310 for increased thermal stability of PE, EVA, EMA, EVAA, PP, and ionomers. They are used to neutralize acidic catalyst residues. Concentration level is very low (0.2-0.5%). The hydrocaldte L-SSRH introduced by Reheis has a similar effect. 

Metals (copper and copper alloys, nickel, iron) have a strong adverse effect on PE because they accelerate degradation. Metal deactivators (organic molecnles containing heteroatoms or functional groups such as hydroxyl or carboxyl) act by chelation of the metal to form inactive or stable complexes. The concentration used is about 1 %. Acid scavengers (or antiacids) are used to neutralise acidic catalyst residues. Calcium or zinc stearate are commonly used, and also function as internal lubricants. Inserts should be made of light metal or he nickel or chromium plated. 

Synthetic hydrotalcites as inorganic acid scavengers recently became important co-stabilizer in polymer formulations. They are primarily utilized in replacing heavy metal-based stabilizing components such as lead stearate, lead phosphite, dibasic lead phthalate, or ttibasic lead sulfate and the respective cadmium salts. 

Stabilization. For example, calcium stearate may play the role of an associate thermal stabilizer when used in a system with calcium salts of fatty acids. These stabilizers use combinations of two or more metals - one of which (e.g. zinc) produces metal chlorides which accelerate PVC degradation. The presence of large amount of calcium salts helps to convert this chloride to calcium chloride which does not increase the degradation rate of PVC. Also, calcium carbonate can react with hydrogen chloride which is produced as PVC degrades. On the other hand, inclusion of fillers which contain admixtures of metals such as iron, nickel, copper, etc. reduces PVC thermal stability. Fillers also affect UV stabilization by adsorption of HALS stabilizers which immobilizes them and prevents them from performing as radical scavengers. 

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