Improvement of adhesive bonding of thermoplastic polymers by different surface treatments

Abstract

Injection moulded samples of six species of thermoplastic polymers were exposed to different surface treatments and successively glued together to form single lap shear joints. Lap shear strength and failure mode of these specimens were examined. The surfaces obtained after treatment were characterized by electron spectroscopy for chemical analysis, contact angle measurements and atomic force microscopy.

Adhesion Improvement of Thermoplastics-Based Composites by Atmospheric Plasma and UV Treatments

“…This indicates that the improvement of adhesion properties using plasma or UV is caused by different mechanisms. In [20] contact angles post-treatment were found to increase. This contradicts the results detailed in [21] and [22].…”

“…An important consideration for the viability of a surface treatment in industry is the treatment stability. In [20] it was found that the lap shear strength of UV treated semi-crystalline samples of polymers remained relatively consistent for up to 30 days. This is an advantage of UV treatment with respect to plasma treatment as, currently, a material treated with plasma has to be bonded almost immediately, meaning that surface treatment and adhesive bonding must occur in two very close facilities.…”

“…Most research has been performed using excimer UV lasers or UV lamps: the main difference between these two is that a laser is monochromatic, coherent and directional, focusing on very small spots on the surface of the material samples, while a lamp is generally non-monochromatic, non-coherent and multi-directional, lighting up wide areas of the surface. In [20] polymers including PEEK, PPS, PEI and PES were treated with both plasma and a UV excimer laser to compare the effects of each treatment method. For both plasma and UV treatment a substantial increase was seen in lap shear strength when compared to untreated materials.…”

“…This discrepancy may be due to the different types of UV treatment used or the increased treatment time. Shi et al [22] achieved their highest fracture toughness after exposing substrates for 30 minutes while the UV pulse duration in [20] was only 20 ns. Zeiler et al [20] used an atomic force microscope to measure the roughness of each surface post-treatment and they attributed to an increased roughness a larger bonding area and better conditions for mechanical interlocking.…”

“…Shi et al [22] achieved their highest fracture toughness after exposing substrates for 30 minutes while the UV pulse duration in [20] was only 20 ns. Zeiler et al [20] used an atomic force microscope to measure the roughness of each surface post-treatment and they attributed to an increased roughness a larger bonding area and better conditions for mechanical interlocking. Similar experiments detailed in [23] and [24] used vacuum UV treatment rather than excimer lasers and found that the treatment caused the surface to flatten and smoothen on a microscale.…”