Usage of atmosphere pressure plasma for rapid polyethylene functionalisation exhibiting only minor ageing

The inert surface of polyethylene (PE) hinders its application in composites field. Here we report a rapid func-tionalisation method of molten PE using atmosphere pressure plasma with dry air as gas source to enhance its polarity. Treatment distance (between 10 mm and 30 mm) and treatment time (between 5 s and 20 s) are two key factors to impact the degree of functionalisation of PE. Various oxygen-containing groups, such as ketone groups (C--O), ether groups (C-O-C) and hydroxy groups (-OH), were introduced into molecules during plasma treatment. Furthermore, based on the higher relative C--O content, PE in molten state was functionalised more rapidly than that in solid state. The static water contact angle dropped from 107 degrees of once-molten PE to 84.5 degrees of plasma treated PE at 20 mm for 20 s, which demonstrated the improved hydrophilicity of treated PE. Cross -linking structure preferred to be formed in plasma treated PE resulting in higher complex viscosity. The drop of crystallisation enthalpy and increase of half crystallisation time of plasma treated PE were due to cross-linking structure. The relative C--O content in plasma treated PE remained constant even after 7 days showing only minor ageing effect. Plasma treatment is a rapid and economic method to improve polarity of PE in molten state, which provides a promising route to improve interfacial compatibility of PE-based composite.

Automated summary

This article reports a method of using plasma to functionalize molten polyethylene, enhancing its polarity. Oxygen-containing functional groups were successfully introduced into the molecules of polyethylene through plasma treatment. The treated polyethylene showed improved hydrophilicity and increased viscosity due to the formation of cross-linking structures.