Antioxidants are key to performance. A variety of phosphites are used including the liquid trisnonyl phenyl phosphite (TNPP) and commodity solid phosphite (SP-1). TNPP does not bloom and has global indirect food contact approval (GRAS). The Dover Chemical Corp. has developed a new Liquid Green Phosphite (LGP-11), which is a high molecular weight molecule with low migration, is biodegradable, contains no alkylphenols, and has process and hydrolytic stability. This is currently being patented.
The leading research company in polyolefins is Norner in Scandinavia. The company has recently led research with partners from Sintef, Nexans and BrederoShaw looking at the effect of service conditions on the consumption of antioxidants in polyolefins. The project was based on the performance of PP coatings for oil and gas pipelines, where the pipes require direct electrical heating to avoid the formation of hydrate and wax inside. The specification is a 25 year service life at temperatures up to 115C and at a sea depth of around 350 m. Different types of PP block copolymer were tested including a 25% glass fibre grade.
The results showed that discoloration was affected by wet or dry conditions, time and water depth. Chemical analysis using HPLC and GC revealed the antioxidant consumption in the different types of PP under different conditions, for example there was a 57% consumption of one antioxidant in the glass fibre-reinforced PP during processing. There was a significant effect of raising the sea water pressure conditions (simulating depth) on the loss of some antioxidants. The results of this study indicate the best antioxidants for long-term use in deep sea pipe coatings.
Polyolefins burn well with high heat capacity; therefore flame retardants are important for some products. PP can be a challenge as it is already crystalline and adding filler-type flame retardants can make the material more brittle. THOR has developed a new non-halogen flame retardant to address some of the weaknesses of existing FR systems.
The new AFLAMMIT grades can be used in applications such as thin wall and films, and are based on organic phosphorus chemistry. In tests in LDPE the LOI was around 30 at 5% loading, and there are synergistic effects with other additives like the NOR HALS Flamestab from BASF and Hostavin NOW XP PILLS from Clariant. In PP a loading of 8% gave an LOI of about 26. Various factors affect the loading required including the film thickness, the presence of fillers like carbon black and titanium dioxide, and the MFI.
UV stabilisation is critical in many products. Cytec has produced several tailored products for different markets including CYASORB UV-3853 for PP/TPO automotive interiors to improve gloss retention and CYASORB THT-6460 for agricultural films to resist acid pesticides and mechanical stress. Cynergy R300 is for rotomoulding applications.
