Colour formation and inhibition in catalyst polyethylenes

Transition metal coordination catalysts used in the polymerization of ethylene have evolved over the years. Although catalyst residues have been drastically reduced, they still play an important role in polymer discolouration. This work pursues the identification of the origin and mechanisms involved in the colour formation, focusing mainly in Titanium containing Polyethylene with and without the addition of phenolic antioxidants, monitoring the different reactions that might be involved taking into consideration the antioxidant, catalyst residues, air exposure and polymer. Possible methods for reducing the colour formation via compounds containing different functional groups and their modes of action have been studied, some of them were found very efficient.· Additives were compounded in Ziegler-Natta LLDPE in combination with a highly discolouring bisphenol, 2,2'-isobutyledenebis(4,6dimethylphenol), some of them being successful colour' suppressants. Colour measurements after 5 extrusion passes revealed good performance of some of these additives; reduced yellowing of the polymer was observed (note the polymer contained only phenolic antioxidant and an antacid (zinc stearate)). Complete absence of discolouration was attained in some cases in the absence of oxygen (under a nitrogen atmosphere) and significantly reduced in the presence ofoxygen. Qualitative correlation processing/solution reactions via derivative UVNis was followed for a better understanding ofthe reactions taking place in the discolouration as well as the species involved. Using UVNis spectroscopy it has been monitored how the species were influenced by the introduction of additives with different functionalities and different reaction conditions. Model solution studies also opened a major range of possibilities in investigating several reactions, catalyst and antioxidant behaviour, and clarifies and simplifies the analysis and quantification of the species involved in the discolouration. A clearer understanding of these mechanisms can lead to new applications with this knowledge to Polyethylene formulations and colour stability obtained through different technologies and catalytic systems. This work has also been extended to the effect of different primary antioxidants in the discolouration of polyethylene containing different transitions metal catalysts other than titanium.EThOS - Electronic Theses Online ServiceGBUnited Kingdo