Effects of air-plasma treatment in enhancing the mechanical properties of oriented strand boards

Abstract

In this work, through surface modification of poplar strands with a non-thermal type of plasma, we produced oriented strand board (OSB) panels with high loading capacity (fabricated with a target density of 0.7 g/cm3 and phenol-formaldehyde resin in a content of 7%). At the processing power of 4.5 kW, the plasma-induced efficient etching effect and chemical grafting contributed greatly to improving the wettability of strands surfaces, resulting in the 68.3% increase of resin coverage and the formation of consecutive bond-lines within the structures of OSB. Furthermore, the adhesive distribution within wood surface layers and adhesion efficiency were intensively analyzed by means of X-ray computed tomography imaging, the results demonstrated that the plasma-based surface modification considerably increased the penetration depth of the resin into the wood volume, making it easier to form mechanical interlocking in wood-resin interphase. Further nanoindentation analysis on the resin-infiltrated cell walls revealed the substantial reinforcement of bonding interphase after plasma modification. In bonding performance tests, the internal bond strength of plasma-modified OSB reached up to 1.22 MPa, nearly 3.6 times the value recommended by ISO 16894: OSB panels type 4. Meanwhile, the loadbearing property was improved significantly, which was not only reflected in the enhanced bending strength and elastic modulus, but was also confirmed by strain distribution along the thickness direction recorded using digital image correlation technique.