Combining polymer extrusion with plasma surface modification to optimize adhesion in additive manufacturing

Increasing interest in 3D-printed high-performance polymers is observed due to their excellent mechanical properties and high resistance to thermal and chemical degradation. Models prepared by using material extrusion techniques have low interlaminar strength. The reason is the lamination principle itself as the models are prepared using layer-by-layer deposition and solidification of fused material which results in low interlaminar strength because of weak adhesion bonding and ultimately ends in poor rupture strength. Despite the other various process parameters; infill density, infill pattern, and line thickness it is evident that interlaminar bindings also have a strong effect on the mechanical sustainability of models. Functionalization of a material surface by using atmospheric pressure plasma containing some active species (ions, electrons, free radicles) is used to enhance the surface free energy (SFE) and wettability by activation of functional groups on material interfaces. Atmospheric pressure plasma jet (APPJ) and ring-shaped plasma source (RSPS) were mounted on a commercially available 3D-printer to treat the polymers using helium and oxygen as feed gas to generate plasma. Both systems are different in terms of plasma treatment and plasma dosage. In this research, the characterization of plasma was performed preliminary to get optimized parameters (plasma flame size, plasma dose, dissipated power, etc.) to treat polymers including polypropylene (PP), polyamide (PA6), polylactic acid (PLA), and acrylonitrile butadiene styrene (ABS). Investigations on contact angle and SFE were made before and after the plasma treatment of printed polymers. Fourier transform infrared (FTIR) measurements were carried out to evaluate surface chemistry and X-ray photon spectroscopy (XPS) was performed to endorse the results. Improvements in adhesion strength were confirmed by performing cross-cut tests. Surface morphology and surface roughness of polymer surfaces was investigated with the help of laser scanning microscopy (LSM) and scanning electron microscopy (SEM). Finally, a 10-18% increase in the rupture force of used polymers has been noticed with different plasma systems. Additionally, a 133% increase in rupture force was noticed for epoxy-infiltrated plasma-treated ABS polymer.