PVC heat stabilizers mechanism

October 30, 2008 on 7:08 pm | In Tech | No Comments

Where the polymer to improve the heat stability for the purpose of adding additives can be referred to as heat stabilizers. In addition to the small amount of heat stabilizer used in rubber processing and other resin, mainly used for thermal stability of a very prominent problem of PVC processing. As a result, often has said the heat stabilizer refers specifically to the use of PVC and PVC copolymer of heat stabilizers.

The thermal degradation of PVC in the process, almost no single, but generated a lot of HCl. PVC thermal degradation mechanism is very complicated, and similarly, heat stabilizer mechanism is very complex. At present, comprehensive research, the role of heat stabilizer can be summarized in the prevention of type (and HCl, to replace the instability of the Cl atom and the prevention of auto-oxidation) and type remedies (PVC and non-saturated parts of the response, the destruction of carbon ions are) two Species.

As follows:

1. Absorption and HCl, inhibiting its catalytic effect automatically. Stabilizer, including such categories lead salt, soap-type metal organic acids, organic compounds, epoxy compounds, amines, alcohols metal salt and salt-and metal salts, such as mercaptan. They can react with HCl, the suppression of HCl from PVC response.

2. PVC replacement elements of instability in the allyl chloride or t-carbon atom of chlorine atoms, the suppression from PVC. Organotin stabilizers such as PVC and chlorine elements of instability occurred in the original coordination, in the ligand, organic tin and instability in the replacement of chlorine atoms.

3. Polyene structure and the addition reaction, the destruction of large conjugate system formation, to reduce the shading. Unsaturated fatty acid contains a double bond salt or ester, with the PVC molecules conjugated diene double bond addition reaction took place in order to break the yoke of its structure, color suppression.

4. Capturing free radicals to prevent oxidation. If the accession to the phenolic heat stabilizers to block off HCl, is due to give the H-atom to free radicals and free radical molecules degradation of the PVC coupling, can not be formed with the O2 respond to the material, and has a stabilizing effect on the heat. This heat stabilizer may have one or both of several roles.

The ideal of PVC heat stabilizers should be a multi-function material, or some mixture of materials, they can achieve the following:

1. Lively exchange, the instability of the substituents, such as t-Cl connected to the Cl atom or allyl chloride, to form a stable structure;

2. Absorption and processing of PVC and in the process of release of HCl, the elimination of HCl automatic catalytic degradation;

3. Or passive and act as a catalyst for the degradation of the metal ions and other harmful impurities;

4. Through various forms of the chemical reaction can be blocked unsaturated key to the growth inhibiting degradation of coloring;

5. There is the best protection against ultraviolet shielding effects.

Hint:If there is any inconsistency or conflict between the English and Chinese versions, the Chinese version shall prevail for all purposes.

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