Composites surface modified wood

Okino and co-workers produced composites from acetylated rubberwood (Okino etal., 2001) and acetylated cypress (Okino etal., 2004), bonded using a UF resin. The composites exhibited inferior mechanical properties compared to those produced from unmodified wood. The reduction in mechanical properties is undoubtedly due to poor wetting and weak interaction of the surface of the modified wood with the UF resin due to a reduction of H-bonding sites on the acetylated wood surface. 

In a study conducted by Yuan et al, argon and air-plasma treatments were used to modify the surface of wood fibers in order to improve the compatibility between the wood fibers and a polypropylene matrix [55]. The improvement in the mechanical properties of the resulting composites, as depicted by SEM, was attributed to an increase in the surface roughness of the wood fibers following plasma treatment. The increase in surface roughness can facilitate better mechanical interlocking, but the increase in... 

Chemical compounds which contain reactive groups such as the methanol group (-CH2OH) as in methanolamine compounds are able to form stable, covalent bonds with cellulose fibres. This treatment decreases the moisture pick-up and increases the wet strength of reinforced plastics. Isocyanates are also suitable to modify the chemical structure via its reaction with the OH groups of cellulose. The mechanical properties of composites reinforced with wood-fibre and PVC or PS can be improved by an isocyanate treatment of those cellulose fibres or the polymer matrix. The improvement of the properties of the composites can be explained by the reduction in the number of OH groups responsible for moisture uptake and consequently the increase in the hydrophobicity of the fibre s surface... 

Since wood flour is hydrophilic and plastic used in WPG is hydrophobic, the compatibility of these two is low. Low compatibility of components has a bad influence on the mechanical properties or durability of the composite. Generally, for WPGs, a plastic material in which the base plastic is modifled with maleic acid is used [33-38]. The maleic acid-modifled plastic is prepared by adding maleic acid in a side chain within the main chain of the base plastic (the model of maleic acid modified PP is shown in Figure 5.32). Since the main chain of a maleic acid-modified plastic is the same as that of the base plastic, compatibility is high. On the other hand, the maleic acid-modified portion of the side chain acts on the hydroxyl group on the surface of wood flour and modifies the wood flour surface (Figure 5.32). Thus compatibility between the wood flour and the base plastic is improved [39, 40]. 

Bryne, L.E., Lausmaa, J., Emstsson, M., Engfund, F., Walinder, M.E.P. Ageing of modified wood. Part 2 determination of surface composition of acetylated, furfurylated, and thermally modified wood by XPS and ToF-SIMS. Holzforschung 64, 305-313 (2010)... 

Fabiyi, J.S., McDonald, A.G., Stark, N.M. Surface characterization of weathered wood-plastic composites produced from modified wood flour. In Proceedings of the 9th International Conference on Wood and Biofiber Plastic Composites, Forest Products Society, Madison, p. 271 WI (2007)... 

Graft copolymers of polypropylene (PP) and maleic anhydride have shown to be very effective additives for wood cellulose/PP composites [50]. Thus cellulose fibers have been surface modified with polypropylene-maleic anhydride copolymer. The modified fibers have been compounded with polypropylene [51]. 

Pulpstones. Improvements have been made in the composition and speed of the grinding wheel, in methods of feeding the wood and pressing it against the stone, in control of power to the stones, and in the size and capacity of the units. The first pulpstones were manufactured from quarried sandstone, but have been replaced by carbide and alumina embedded in a softer ceramic matrix, in which the harder grit particles project from the surface of the wheel (see Abrasives). The abrasive segments ate made up of three basic manufactured abrasive siUcon carbide, aluminum oxide, or a modified aluminum oxide. Synthetic stones have the mechanical strength to operate at peripheral surface speeds of about 1200—1400 m /min (3900 to 4600 ft/min) under conditions that consume 0.37—3.7 MJ/s (500—5000 hp) pet stone. 

In Roman times tar and pitch from Pinaceae resinous wood were used to treat the inner surface of amphorae to store fluids such as wine [ 145,149] and to seal ship planks [89,144], Heating treatments applied to natural resins and resinous wood profoundly modify the chemical composition of the original material. Diterpenoid compounds undergo aromati-zation, demethylation and decarboxylation reactions, with the formation of new compounds of a lower molecular weight that show a high degree of aromatisation [87,88]. In tar and pitch produced from Pinaceae resin and woods, retene is considered as a stable end product of these reaction pathways and nor-abietatrienes, simonellite and tetrahydroretene represent the intermediates of these reactions [87,89,150]. 

---