Tribological and Nanomechanical Behavior of Liquid Wood

Abstract

During the last decades, there has been an increased interest in the use of lignin-based composites following the ideas of developing green materials for fossil-based raw materials substitution. The biopolymer Arboform is a mixture of lignin, plant fibers, and additives, which is nowadays successfully used in many applications. As a thermoplastic, it can be molded and is therefore also called “liquid wood.” In this paper, we report a study comparing the nanomechanical and tribological properties of Arboform (AR), and Aramid-reinforced Arboform (AR-AF) composite biopolymers. The samples were produced in an industrial-scale injection molding machine. Nanoindentation experiments have revealed that, in both series of biopolymer samples, an increase in temperature or a change in the injection direction from 0 deg to 90 deg produces an increase in hardness. On the other hand, Young's modulus is slightly affected by the increase in temperature, and not affected by the injection angle. Tribological characterization has shown that all samples, except the AR-AF injected at 175 °C, present noticeable wear and have a similar friction coefficients μ ∼ 0.44–0.49 at Hertzian contact pressures p0 between 90 and 130 MPa. Interestingly, the reinforced polymer produced at 175 °C shows no wear and low friction of μ ∼ 0.19 at p0 = 90 MPa. Our results show that the reinforced Arboform biopolymers are a good candidate to replace other polymers in many mechanical and tribological applications.