Unexpected reactions/interactions of phosphites within polyolefin stabilisation
| Title |
Unexpected reactions/interactions of phosphites within polyolefin stabilisation |
| Publication year |
2005 |
| Language |
English |
| Author |
Jamtvedt, Svein H. (Norner) |
| Co-Authors |
Øysæd, Harry (Norner) |
| Source |
Addcon World 2005, Hamburg 21-22.09., 2005 |
| Abstract |
Polyolefins are prone to degradation during compounding, converting to final products and end use. The degradation proceeds in a free radical mechanism and will finally destroy the polymer properties. Phenolic antioxidants and phosphites are important stabilisers to protect polyolefins during processing and end use. Phenolic antioxidants give good contribution to process -stability and especially long term heat stability (LTHS) of polyolefins. The main drawback is contribution to discolouration, mainly yellowing. Phosphites are known to give good process stability together with phenolic antioxidants, but very limited contribution to LTHS. High performance phosphites are contributing to a total good colour of the final product. A combination of phenolic antioxidant(s) and phosphite(s) give synergistic effect. The reason for this is that they take care of different degradation products. A surprising reaction with high performance phosphites/phosphonite has been experienced in LPPE based on Cr-catalyst on silica carrier. During storage of such PE at ambient temperature the residual catalyst system is capable of hydrolysing the phosphites. The end result is that original phosphite is not traceable after few months storage, while the starting alkyl phenol, e.g. 2,4-di-tert. butyl phenol, will appear. Process stability test of a few months old granules has shown reduced stability with gels and stripe-formation as the result. A positive surprise with phosphites has been observed in PP. It is possible to boost LTHS significantly with selected phosphites in combination with phenolic antioxidant(s) and thiosynergists (e.g. DSTDP). Normally the role of phosphites has been seen to protect PP during processing and thereby also reduce the reaction the phenolic antioxidant during processing. This will give only marginally (if any) increase in LTHS |