Reactive extrusion was employed to study free-radical grafting of itaconic anhydride (IA) onto polyethylene, using thermally induced peroxide decomposition. IA has the potential to improve adhesion between polyethylene and fibres , for use in composite materials. It was selected because it is less harmful compared to other similar chemicals, such as maleic anhydride.

It was found that an increase in IA concentration lead to an increase in the degree of grafting (DOG), but only up to 6 wt% IA. Using di-cumyl peroxide (DCP) as the initiator, always resulted in a higher degree of grafting than di-tert-butyl peroxide (DTBP) and required less reaction time to achieve the same DOG. However, raising the IA concentration also resulted in an increase in cross-linking, which is an undesirable side reaction.

Increasing the initiator concentration from 0.2 wt% to 2 wt% resulted in a higher DOG, but using 5 wt% had similar results than using 0.2 wt% due to termination by disproportionation, which is more prevalent at high initiator concentrations. Degradation was clearly observed by the inability to form a continuous extrudate during extrusion as well as discolourasion.

A residence time of more than 50 seconds, using DCP and 120 seconds for DTBP didn’t offer any further increase in the DOG and also resulted in more pronounced degradation of mechanical properties, such as tensile strength, modulus and ductility. Optimising grafting is therefore a tradeoff between maximal DOG and minimising side reactions, therefore, and conditions do not necessarily correspond to a maximum DOG.