Cell Wall Impregnation with Monomers

Nakagami and Yokota (1983) impregnated wood with a solution containing methacrylic acid, trifluoracetic acid and sulphuric acid, to form a covalent bond with the cell wall polymers. The methacrylic-reacted wood was then impregnated with styrene, or methylmethacrylate, to form cross-links with the reacted cell wall polymers. Improved dimensional stability was obtained, although degradation of the wood was also observed. 

A solution of styrene in methanol to impregnate wood samples, followed by polymerization, was used by Furuno and Goto (1979). Penetration of the monomer into the cell wall was determined by solvent extraction of samples after polymerization. This removed lumen located polymer, whilst leaving the cell wall bound polymer in place. This showed that the concentration of cell wall bound polymer increased in proportion to the monomer content in methanol, up to a maximum of 80% of the monomer in the solvent. No cell wall penetration was observed for treatment with neat monomer. This was also found for bulking of the wood, as determined from external dimensions of the samples. Improvements in ASE were obtained as a result of the presence of cell wall bound polymer. To achieve similar ASE values with lumen located polymer required very high polymer loadings. 

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Monomer (or oligomer) impregnation, with subsequent polymerization within the cell wall. 

It is also possible first to react the polymers that still remain in the cell wall with a simple reactive chemical and then to follow this with impregnation of a polymerizable monomer (15). The simple bonded bulking chemical provides dimensional stability, and the polymerized monomer provides strength (i6). 

Wood polymer composites are produced by impregnating the wood with different monomers, for example, styrene (St), methylmethacrylate (MMA), acrylonitrile (AN), and unsaturated polyester (UPE). These monomers can transfer into homopolymer or grafted on the wood cell wall during polymerization process, which can be initiated by y-radiation, high temperature, or chemical catalysts. 

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