Polyvinyl chloride (PVC) is a material widely used in daily life. During heating, PVC softens and degrades and changes color over a range of temperatures. In order to prepare the required PVC products, stabilizers and other additives must be added to the PVC resin.
The mechanism of PVC aging is mainly caused by the free radical chain reaction caused by thermal degradation. According to this mechanism, the presence of double bonds, branched chain points, residual initiator groups, and oxygen-containing structures in PVC is excited by heat or light to produce free radicals. These free radicals trigger a chain reaction in PVC, leading to de-escalation and degradation. The double bond formed by de*** is very active and will continue to occur the formation of conjugated double bonds, resulting in PVC discoloration. The newly generated free radicals can further trigger the degradation of PVC and intensify the degradation reaction.
Phosphite is a co-antioxidant and plays an important role in the antioxidant system. It has excellent hydroperoxide decomposition and resistance to color aberration, and can increase the processing temperature of polymers. When used in combination with hindered phenolic antioxidants and light stabilizers, phosphite esters can also exert a good synergistic effect.
In PVC formulations, phosphite mainly plays a complexing role. When used alone, phosphite has no significant stabilizing effect. But when used together with metal soaps, it can form complexes with metal chlorides, improve the heat and weather resistance of PVC, and maintain transparency. In addition, the combined use of phosphite with organotins, epoxy compounds, etc., can also show synergistic effects.
The stabilizing effect of phosphite on PVC is multifaceted:
1) Capture the *** released during PVC degradation and inhibit its autocatalytic degradation;
2) Replace the unstable allyl chloride atom in the PVC molecule and inhibit the decapitation
3) passivation of harmful metal ions;
4) has antioxidant effect;
5) Inhibits free radical reaction.
In addition, phosphite also has a good effect on improving the transparency of PVC plastics containing lead salts, barium salts and calcium salts.
There are many types of traditional phosphite, including triphenyl phosphite (TPP), monobenzenyldiisodecyl phosphite (PDDP), trinonylphenyl phosphite (TNPP), bisphenol A phosphite (1500), etc. However, with the improvement of environmental protection requirements, the restrictions on the use of nonylphenol, bisphenol A and free phenols are becoming more and more stringent. Traditional phosphite esters are mostly prepared with triphenyl phosphite as the substrate, which does not meet the requirements of environmental protection because it is difficult to avoid the residue of free phenol and bisphenol A.
In order to meet the market's requirements for environmental protection and efficiency, a new phenol-free phosphite antioxidant line has been launched. These antioxidants not only reach the level of traditional antioxidants in terms of performance, but also embody environmentally friendly properties during production and use. This range of novel phosphite compounds includes:
Tridecyl phosphite (TDP).
Tridodecyl phosphite (TLD).
Triadecyl phosphite (TTDP).
Pentaerythritol didecyl diphosphite.
Octacyl pentaerythritol diphosphite.
These new phosphite antioxidants are high in available phosphorus, which means they can provide excellent protection at lower levels of use. They can effectively decompose hydroperoxides, an active substance that causes accelerated aging of polymeric materials. Through this decomposition, these antioxidants effectively extend the life of the material and inhibit the auto-oxidation process of the polymer material.
Thanks to their phenol-free formulation, these new phosphite antioxidants avoid harmful ingredients such as free phenols or bisphenol A that may be found in traditional antioxidants, thereby reducing potential risks to the environment and human health. In addition, the development and use of this new antioxidant not only complies with current environmental regulations, but also reflects the pursuit of sustainable use of resources and green industrial production. With the rapid development of materials science and environmental protection technology, it is expected that these phenol-free phosphite antioxidants will occupy an increasingly important position in the stabilization of PVC and other polymers.