This study investigated the feasibility of using wood flour (WF) as a partial substitute in polymeric methylene diphenyl diisocyanate (pMDI) resin and compared its performance with soy flour (SF) substituted in pMDI resin. The physical and mechanical properties of experimental particleboards made with WF and SF substituted in pMDI resin at different substitution percentages were evaluated. The viscosity for the WF at different substitution ratios (5%, 10%, 20%, and 30%) ranged from 314.7 to 6,256.3 cP, whereas SF-substituted resin ranged from 249.7 to 1,291.8 cP. During the production of the boards, it was observed that because of the high viscosity of WF substituted in pMDI resin above 10 percent, it was exceedingly difficult to apply it through spraying and brushing, either to wood particles or veneers. Dimensional stability test results established that the incorporation of SF assisted in mitigating board thickness swelling. The results from the study showed that panels made with SF substituted in pMDI resin at 5 and 10 percent exhibited the overall best performance in all the properties considered compared with panels made with WF substituted in pMDI resin.

This study evaluated the possibility of using different fillers—cellulose nanocrystal, cellulose microcrystalline, wood flour, soy flour, talc, and calcium carbonate—as partial substitutes in polymeric methylene diphenyl diisocyanate (pMDI) resin. There has been concern recently regarding the use of pMDI resin due to the environmental effect of isocyanate, which is dominantly present in the resin, as well as the cost of the resin. Different fillers were used in this study as substitutes at their allowable substitution percentages. This study focused on the possibility of replacing more pMDI resin with biodegradable filler without compromising the integrity of the resin; the mechanical strength of plywood from both southern yellow pine and oak was evaluated. Fourier-transform infrared spectroscopy, scanning electron microscopy, and thermogravimetric analysis were conducted to study the effect of modification on the bond-line quality of the final product. The effects of different fillers on adhesion properties of the pMDI resin were tested on the plywood according to the American Society for Testing and Materials (ASTM D–906-64) standard. The results showed that shear strength of the modified pMDI resins ranged from 0.3 to 1.083 MPa and 0.35 to 1.178 MPa for oak and pine plywoods, respectively. The modified samples with soy flour showed significant improvement in the shear strength with 261 and 236 percent higher shear strength than the control (pMDI) for samples from hardwood and softwood, respectively. Partial substitution of pMDI resin with soy flour at 30 percent substitution substantially improves the adhesion properties of pMDI resin.