Effect of atmospheric plasma treatment on the interfacial properties of glass fibre-reinforced polypropylene/polyamide blend composites

An innovative plasma treatment was applied to glass fibre-reinforced thermoplastic composites to enhance interfacial adhesion between the polypropylene/polyamide (PP/PA6) blend and glass fibres. Plasma modification improves bulk functionalities, strengthens bonding within the blend, and enhances polymer-glass fibre interfacial interactions, improving material strength and performance. In this study, an Atmospheric Pressure Plasma Jet (APPJ) with air as the working gas was applied during the melt compounding of PP/PA6 blends in a twin-screw extruder. Two inverse compositions (90/10 and 10/90 wt% PP/PA6) were used to compare the effect of plasma treatment on both blends. The chord modulus of the plasma-treated PP/PA6 blends increased by 15 % and 27 % for the 90-PP/10-PA6 and 10-PP/90-PA6 blends, respectively. Plasma-treated 90-PP/10-PA6 and 10-PP/90-PA6 blends reinforced with 18 wt% short glass fibres exhibited improvements in interfacial shear strength by 22.6 % and 5 %, and chord modulus by 33 % and 46 %, respectively. Morphological analysis of cryofracture samples of the blends showed a decrease in droplet size and better dispersion of the minor phase within the blend. Micrographs of tensile fracture surfaces and microbond pull-out samples, along with fibre length distribution analysis, revealed enhanced fibre–matrix interfacial bonding after plasma treatment. Rheological analysis revealed that the viscosities of the blends were retained after plasma treatment, suggesting that the polymers underwent some chain scission, generating reactive sites that enhanced bonding with plasma-induced functionalities and improved interfacial adhesion within the polymers and with the fibres.