Methyl isocyanate-modified southern pine

In the reaction of wood hydroxyls with isocyanates, a nitrogen-containing ester is formed. A limited reduction of fungal attack was reported earlier in beechwood modified with diisocyanate (13). Considerably more decay protection than acetylation has been shown in the methyl and allyl isocyanate modifications. Little decay was evident in methyl isocyanate-modified southern pine at WPGs between 14% and 19% in laboratory assay using G. trabeum. 

Figure 4. IR spectra of methyl isocyanate-modified southern pine. Key ...

Evidence that chemical reaction has taken place with wood cell wall hydroxyl groups is evident from the infrared (IR) spectra of methyl isocyanate-modified southern pine (Figure 3). All samples run in the IR were first milled to pass a 40-mesh screen and extracted first with benzene/ethanol (2/1, v/v) followed by water in a Soxhlet extractor. Any unreacted reagent and isocyanate homopolymer formed during the reaction with wood would be removed by this extraction procedure. The spectrum for unreacted... 

Figure 3. Infrared spectra of methyl isocyanate-modified southern pine. Key A, unreacted wood (control) B, 17.7 WPG C, 47.2 WPG D, holocellulose from sample treated to 17.7 WPG E, lignin from sample treated to 47.2 WPG.

Additional evidence that bonding has occurred in the cell wall of methyl isocyanate-modified southern pine can be seen by considering the volume increase in the treated wood and comparing that to the theoretical volume of chemical added after thorough leaching of the treated wood. If the chemical has entered the wood cell wall, the increase in wood volume as a result of modification should be proportional to the volume of chemical added. 

Figure 4. Antishrink efficiency of methyl isocyanate-modified southern pine as a function of WPG. Key O, ASE, , ASE2 A, ASE3 , ASEt.

Table VIII. Distribution of nitrogen in methyl isocyanate-modified southern pine on a whole wood basis—...

Southern pine with a dual treatment of chemical modification with butylene oxide or butyl isocyanate followed by lumen-fill treatment with methyl methacrylate, or southern pine impregnated with methyl methacrylate and polymerized in situ, resulted in modified woods that were resistant to accelerated weathering and to ultraviolet light alone. Physical, chemical, and microscopic changes occurring as a result of ultraviolet light irradiation are described. 

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