Wood fibres surfaces

An important chemical modification method is the chemical coupling method, which improves the interfacial adhesion. The fibre surface is treated with a compound, that forms a bridge of chemical bonds between fibre and matrix. The increase in the mechanical properties of the fibreboards due to chemical modification is an indication of improved interaction and stress transfer between the components. Some authors have reported that softening and increased thermo-plasticity of wood fibre surface facilitates contact and dispersion of the fibre with thermoplastics [61, 62]. 

Polyelectrolyte Complexes for Tailoring of Wood Fibre Surfaces... 

Ankerfors, C., Wagberg, L. Polyelectrolyte complexes for tailoring of wood fibre surfaces. Adv. Polym. Sci. 256, 1-24 (2014)... 

The production of MDF from allylated wood fibres has also been reported (Ogawa and Ohkoshi, 1997). The IBS of the 4 mm thick boards was superior to control boards (unmodified fibres bonded with PF resin), provided that the temperature of the allylation reaction and board density was sufficiently high. The MOR was markedly inferior to that of control boards in all cases (c. 10 MPa for allylated compared with c. 60 MPa for controls, at a board density of 800 kg m ). Blending of the allylated fibres with acetylated fibres caused a decrease in IBS, but did not affect MOR. It is perhaps significant that no free-radical initiator was used during hot-pressing in either study, which may account for the lack of reactivity of the allylated surfaces. 

Figure 5.25 Scanning electron micrographs of fracture surfaces of polypropylene/wood fibres composites. Left with maleated PP right without MAPP...

The interface between plastic and wood fibres strongly influences the mechanical properties of a plastic/wood fibre composite. A means for evaluating the effectiveness of surface treatment on the wood fibres in the PVC/wood fibre composites is presented that investigated the adhesion between PVC and laminated wood veneers. Wood veneers were first treated with gamma-aminopropyltriethoxysilane, dichlorodiethylsilane, phthalic anhydride, and maleated PP for surface modification. The chemical modification made on the wood surfaces was then characterised by different complementary surface analytical techniques X-ray photoelectron spectroscopy and surface tension measurements. 63 refs. 

In summary the temperature of the wood surface is determined by the cooling effect of evaporation, rising from the initial wet-bulb temperature when the surface is wet to the dry-bulb temperature as the wood approaches the equilibrium moisture content. With permeable woods the surface temperature remains at the wet-bulb for a considerable proportion of the schedule. With impermeable woods the surface temperature soon begins to rise toward the dry-bulb temperature, as there is no mass flow of water from the interior to keep the surface moist and above fibre saturation. 

The surface properties of cellulose, wood fibre, and naper are of great importance in the production and utilization of paper and board. Phenomena as diverse as the formation of fibre-fibre bonds in papermaking and the ink-paper interaction during printing processes are certainly influenced by the surface properties of fibres and sheet. With the development of increasingly sophisti-... 

Kharazipour et al." reported a one component system, where laccase treated wood fibres with no additional adhesive were used for MDF-boards preparation. The wood fibres were incubated with laccase for 2-7 days. After the incubation excess water was removed and the fibres were hot pressed to desired boards. The incubation time was later reduced to 12 hrs. The results indicated that the technical values obtained from the enzymatically bound MDF-boards met the German Standards. Felby et al. has also shown that production of MDF boards can be carried out without synthetic adhesives. They have studied the possible reaction mechanism involved in bonding. Although the mechanism is not completely understood, it presumably involves direct oxidation of fibre surface lignin and parallel radicalization of solubilized or colloidal lignin. These radicals will react further without... 

The effect of the modification of the fibre surface consists in the shift of the sound absorption maximum towards higher frequency range and is accompanied by the decrease of the sound absorption coefficient a. The reduction of the coefficient a is not large. It amounts 2.5 % in the case of composites with pine wood and rapeseed straw Californium. For the samples with beech wood filler the coefficient a remains unaffected after modification. The exception is the composite containing the rapeseed straw Kaszub as a filler that shows the decreasing in the sound absorption of 7%. The reduction of the a coefficient value at the frequency related to the maximum of the sound absorption can be associated with the increase in the density of the composite after modification (Table 1) due to better adhesion between filler particles and polypropylene matrix. The fact implies that the specific acoustic impedance of... 

Fabrics made of glass or carbon fibres may also be used to make fibre reinforced composites on site. Normally a layer of adhesive is applied to the timber surface, one or more layers of the fabric are then pressed into the adhesive and a new layer of adhesive is applied to it, resulting, after cure, in a fibre reinforced composite. The principal direction of the fabric is normally oriented parallel to the wood fibres to improve bending strength and stiffness. 

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