Low-frequency plasma activation of nylon 6
Applied Surface Science 2021, 544, 148929. https://doi.org/10.1016/j.apsusc.2021.148929
Polymers such as nylon 6 are integral to many industrial and consumer products. However, the low friction, smooth surface and poor wettability that are often the characteristics that cause them to be chosen, also mean that they are hard to retain in place due to the inability of adhesive to bond the surface. Chemical treatments to enhance adhesion are possible, but bring with them issues of environmental toxicity. Plasma processing offers a dry, rapid and clean route to increasing wettability and this paper details the characterisation of such a process using low frequency plasma rather than RF or microwave. As bonding is between an adhesive and the top monolayer of substrate molecules, it is important to fully characterise this interface. It is also vital to ensure that plasma parameters are consistent and optimised; the Hiden EQP plasma probe can analyse the plasma reaction kinetics and determine the ion energy distribution function in technical plasmas during processing, even in pulsed systems.
In this work, the XPS data show chemical bonding between the oxygen from the plasma and carbon groups on the surface, however, this could easily arise from loosely attached oxidative surface debris. The static SIMS is necessary as it can characterise entire monomer units ejected from the surface, confirming that the chains are still intact and that the hydroxly and carboxylic acid groups have been incorporated into the nylon structure – a requirement for strong adhesive bonding to the bulk material.
The Hiden Compact SIMS instrument, used for these static SIMS measurements, is a highly cost effective, semi-portable, self contained, SIMS tool capable of acquiring static SIMS spectra in a matter of seconds and with the ability to chemically image the surface and make concentration measurements as a function of depth.