This study selected acylate monomers/oligomers as the nanoparticle transportation chemicals to produce high value-added wood surface densification products. The effect of nanoparticles in the formulations on the Brinell surface hardness, impact resistance and abrasion resistance was evaluated in this project. It was found that the addition of nanoparticles showed significant effect on mechanical properties of surface densification wood products. Different ratio of monomer/oligomers formulation and their viscosities on the chemical retention and penetration properties were investigated. Lower viscosity formulation presented better penetration and higher chemical retention with same surface densification process.
Two optimized advanced surface densification processes were developed to improve the efficiency and lower the chemical retention thus to decrease the cost of final value-added surface densification wood products. The first optimized advanced densification process that prepared surface-densified wood product by replacing the traditional time-consuming pressurization stage with only a short vacuum process was investigated. Formulations with nanoparticles were successfully impregnated into maple and oak engineered wood flooring planks by using a vacuum time from 30 s to 10 min without further pressurizing during the impregnation process. The properties of these short vacuum process impregnated wood products were also comparable to or even superior to the conventional vacuum/pressure impregnated wood products. The Brinell surface hardness of impregnated maple wood were improved 205% with a 30s vacuum process and oak wood were improved 108% with 60s vacuum process. The second optimized advanced surface densification process contained three steps process. The 1st step consists on application of a layer of resin on the wood surface by roller or curtain coater; the 2nd step is using a 60s vacuum to penetrate the resin into the wood surface to a target depth 1-2 mm; the 3rd step is to cure the impregnated wood with UV/thermal dual in situ polymerization process. The chemical retention decreased drastically with this approach compare to conventional vacuum/pressure impregnation process. 22% improvement of the Brinell surface hardness was found through this low cost approach.
Electron beam (EB) and UV/thermal dual cure process which was industrial viable online in situ polymerization process have been successfully developed to cure the surface densification wood products. The efficacy of EB and UV/thermal dual cure was validated by differential scanning calorimetry (DSC) and photo-DSC characterization. The results showed that EB cure is a powerful instant online polymerization method to cure the fully penetrated chemical surface densification wood products with a relative high capital investment on equipment. UV/thermal dual cure method is a cost-effective approach to polymerize the roller/coater resin application and vacuum penetration surface densified wood products.
In general, this study implied that reduce cost from surface densification process is possible through application of resin by roller/curtain coater followed with a short vacuum process to penetrate the resin into wood surface. This work also implied that in situ UV/thermal dual cure could replace the high cost EB cure surface densification products, which in turn, favour our industrial to adopt this technology cost-effectively.