This research focused on enhancement of mechanical properties in carbon fiber (CF)-filler-reinforced linear low-density polyethylene (PE) matrix composites. A hand layup method using an oven was used as the fabrication method. Improvement in adhesion was achieved by oxygen plasma treatment to the PE matrix. CF and PE were initially mixed by normal stirring, ultrasonication and mechanical stirring before being filtered and dried for fabrication. Better tensile results were observed with a plasma-treated polyethylene (PEP)/10 wt.% CF combination, with a maximum tensile strength of 21.5 MPa and improvement in the properties of up to 12.57% compared to non-plasma PE with the same CF addition. The addition of carbon fibers at 13 and 15 wt.% resulted in a reduction in the tensile strength properties to 18.2 MPa and 17.7 MPa, respectively. This reduction in tensile strength was due to agglomeration of CF with plasma- and non-plasma-treated PE. The fabrication condition of 180 °C temperature for 20 min showed better tensile properties than other conditions. The SEM results following tensile testing revealed enhanced CF filler adherence with plasma PE results, as well as fewer surface deformations. A higher flexural strength of 25.87 MPa was observed for the plasma treated PE/7 wt.% CF combination.

Plasma treatment of polyethylene powder was carried out in low-pressure gaseous plasma sustained in a semi-industrial reactor powered with a microwave source, in which it was specifically worked with the residual atmosphere. Timed applications of plasma-treated powder in air atmosphere were carried out to study their influence on the adhesion. Based on wettability and adhesion, a treatment time of 5 min was selected for the study of other working gases (nitrogen, oxygen, hydrogen, argon and a mixture of nitrogen and hydrogen). The measurements of wettability showed the highest adhesion increase for nitrogen. The highest increase of adhesion and of surface oxygen contain shown by oxygen treatment. By contrast, treatment with hydrogen resulted in increased roughness of the sintered surface of the powder. The selection of appropriate working gases which are not standard in industrial processes enables one to atypically regulate the adhesion or wettability.

This paper describes a newly developed testing method for determination of the adhesivity of a film sintered from thermoplastic powder. This method is based on the modified EN 15337 standard. Application of this method enables an effective development of thermoplastic composites with enhanced adhesion between reinforcement and matrix and/or high-quality joints between plastics and dissimilar materials. The proposed method was successfully tested on a series of polyethylene powders treated in the oxygen atmosphere for 0–1200 s. Adhesion to metal and glass substrates in dependence on treatment conditions is described along with powder wettability and X-ray photoelectron spectroscopy analysis. The results show an increase in adhesion to metal by 580% and to glass by 1670% for the longest treatment time, compared to a nontreated powder. Sintering of treated powders revealed a strong influence of treatment time on the melting process. The XPS analysis confirmed the formation of new oxygen groups (C–O, C=O, O–C=O). The method reveals a specific behavior of powders based on treatment conditions, which is crucial for the optimization of plasma treatment for the improved adhesion, applicability of polymer powders, and a development of composite materials.