The Mechanistic Action and Performance of Metal Deactivators for Polyolefins

Hussain, Sajid (2021) The Mechanistic Action and Performance of Metal Deactivators for Polyolefins. Doctoral thesis (PhD), Manchester Metropolitan University in collaboration with Addivant UK Ltd.

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Abstract

The main action of metal deactivators is to slow down or reduce the metal-catalysed oxidation of polymers. Although metal ions may be introduced inadvertently to polymers (e.g. by metal polymerisation catalyst residues, fillers, pigments), major problems arise when polymers are used as an insulating material for the manufacture of power cables and copper wires, because copper is a pro-oxidant metal. Over 20 novel metal deactivators have been synthesised and their structures verified by IR, NMR and LC-MS. The molecules have been designed in a systematic manner, to introduce various chelating structures (derivatives of: hydrazine monohydrate; tris-amines; hydrazones; dilauryl dithioprionate; propanehydrazide; triazines) and antioxidant structures (sterically hindered phenols, furans, pyrazolones), with a view to improving the roles of the individual and combined functionalities. The performance of these novel structures has been evaluated in LDPE, oxidised during circulation mode extrusion, using MFI, YI and FTIR spectroscopy. Nearly all the structures have an ability to complex Cu2+ and demonstrate wide ranging performance. Inhibition of oxidative degradation by these antioxidant-metal deactivators is complex and arises from a subtle balance of antioxidant and metal deactivator functions. The work highlights the importance of the complex interplay between different routes to degradation and their inhibition. Here the concentration profile of peroxyl radicals and peroxides that leads to the carbonyls (aldehyde, ketone, ester) that dominate the degradation profile of polymers such as LDPE. The best performance of antioxidant-metal deactivator structures is presented by molecules that optimise metal coordination at multiple sites with proximity to an effective peroxyl and alkoxy radical scavenger (i.e. primary antioxidants, particularly hindered phenols). These principles may be used to tailor antioxidantmetal deactivator ligands to metal redox systems (e.g. Fe2+/Fe3+) and so improve the performance of metal deactivators in a range of commercial applications.