μPlasma surface modification of thermoplastic composites and their ageing behaviour

Che, Chang ORCID: 0000-0002-8669-8205 (2024). μPlasma surface modification of thermoplastic composites and their ageing behaviour. University of Birmingham. Ph.D.

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Abstract

Thermoplastic polymers generally exhibit relatively low surface energies, and this often results in limited adhesion when bonded to other materials. Plasma surface modification offers the potential to overcome this challenge through functionalisation of the polymer surfaces, and thereby enhance the bond strength between dissimilar materials. In this study, glass fibre reinforced polyamide 6 (GFPA6), high-density polyethylene (HDPE), polyamide 12 (PA12) and polyamide 6 (PA6) was modified using a novel μPlasma surface treatment technique. The physical and chemical changes following μPlasma surface modification of the polymer surfaces were characterised using Atomic Force Microscopy (AFM), Fourier Transform Infrared Spectroscopy (FTIR), and Raman Spectroscopy. These techniques confirmed an increase in surface polarity, roughness, and surface energy following μPlasma treatment. Following single μPlasma treatment scan of GFPA6 samples, a substantial enhancement in wettability (with contact angles decreasing by 46.3°, 47.3°, 42.6°, and 50.1° for GFPA6, HDPE, PA12, and PA6 respectively) was observed. However, the effect of the μPlasma modification was subject to a rapid ageing phenomenon in 5 hours. The ageing process was slower when the GFPA6 material was pre-dried and stored in low humidity conditions, thereby demonstrating the importance of the presence of moisture on the rate of ageing. The ageing process of three polymers (HDPE, PA12, and PA6) with different hydrophilicity over five hours was modelled using a modified stretched exponential function Kohlrausch–Williams–Watts (KWW) model, and it was found to be dependent on the hydrophilicity of the polymers, with higher hydrophilicities resulting in faster ageing. The effectiveness of the adhesive bond of GFPA6-epoxy-aluminium joint with GFPA6 being treated by μPlasma was evaluated. Significant increases in the tensile shear strength of the joint from 1kN to 2.3kN were observed, with no ageing phenomenon after 24 days. These observations, coupled with the atmospheric nature of the technique, points to great potential as a rapid, on-line, and effective, polymer surface treatment technique.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

Supervisor(s):