Abstract
Poly(hexamethylene adipamide), nylon 66, is a popular plastic that requires high surface wettability and strong adhesive bonds for many applications. However, pristine nylon is difficult to bond due to its hydrophobic nature and poor surface wettability. The objective of this work was to modify the physio-chemical surface properties of nylon 66 via a novel atmospheric plasma surface treatment approach using oxygen (O2) or water vapor (H2O) plasma glow. The surface hydrophilicity of the plasma-treated nylon surface was substantially enhanced immediately after either helium (He)/H2O or He/O2 plasma surface treatment. The average water contact angle was reduced from 65 degrees to ~30 degrees after He/H2O plasma and ~40 degrees after He/O2 plasma treatments. The improved hydrophilicity was also evidenced by the increased intensities of the surface oxygen and hydroxyl bonds in the X-ray photoelectron spectra. The interfacial adhesion strength of nylon surfaces before and after plasma treatment was further evaluated by uniaxial tensile tests of nylon single-joint lap shears bonded with three adhesives, i.e., thermoset epoxy resins EPON 825/ JEFFAMINE D-230 and EPON825/JEFFAMINE D-2000, and the thermoelastic polyurethane adhesive Sikaflex 252. The most significant improvements in bond strengths due to plasma treatment were found for lap shears bonded with the EPON 825/JEFFAMINE D-230 epoxy resin; their shear strengths with maximum loads were more than doubled—from 299–451 to 693–1594 N—after plasma treatment and were further enhanced by a factor of four to 895–1857 N after a subsequent silane treatment. In contrast, the bond strength of lap shears bonded with EPON 825/JEFFAMINE D-2000 and Sikaflex was not significantly improved because of the different a, re-affirming the importance of adhesive bulk properties This work presents the preliminary success of effective surface functionalization leading to enhanced interfacial adhesive bonds for nylon 66 via the development of scalable atmospheric plasma surface treatments.
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