One-Component Polyurethane Adhesive filled with Milled Carbon Fiber and its Effect on Hydrothermal Stability of Beech Glued Joints In Wood Material Science and Engineering

Abstract

The effect of fibres of various lengths, thicknesses, origins, and quantities on mechanical and other properties of polymer matrices is well-known, including carbon fibres. These were used in the form of milled carbon fibres (MCF) to fill a one-component polyurethane (1C-PUR) commercial adhesive to determine hydrothermal resistance of beech-bonded joints tested in shear. The effect of MCF (1%, 3%, 5%, and 7%) was first tested on thin adhesive films before and after exposure to cold water (20°C) and boiling (wet state test and after drying). A good bond of 1C-PUR to MCF was demonstrated, with tensile mechanical properties significantly increased after the addition of 3% and 5% MCF in all tested environments. The aqueous environment, especially boiling water, led to a deterioration in mechanical properties, but after drying, there was a recovery and, in many composite films, an improvement. This was due to a change in adhesive’s domain structure, as demonstrated by differential scanning calorimetry. An increase in hydrothermal resistance of glued wood joints with MCF (1%, 3%, and 5%) was not demonstrated based on tensile shear strength. However, considering the achieved wood failure, it was proven that MCF has a positive effect on stress transfer into the wood adherend.