Urea formaldehyde (UF) resins are widely used thermosetting polymers in adhesives, finishes, molded objects, etc. The existence of crystalline regions has been detected in UF resins. These crystalline regions are believed to be beneficial for the hydrolytic stability or water resistance and advanced mechanical properties of the resin. In this study, characterization was conducted on crystalline regions of a cured UF resin with a formaldehyde to urea (F/U) molar ratio of 1.2. A slow scanned X-ray diffraction (XRD) pattern was obtained to estimate the crystalline percentage, grain sizes, and interplanar spacing (d-spacing) of the resin crystalline structures. The results showed that the crystalline regions accounted for nearly 14.48% of the resin. From the XRD pattern, the estimated grain size of 4.1 nm was accounted for the peak (two theta degrees, 2θ) of 21.55°, 4.1 nm for 24.35°, 4.2 nm for 31.18°, and 4.8 nm for 40.43°, respectively. Furthermore, a selected area electron diffraction (SAD) pattern of the resin was obtained to confirm the results. The calculated d-spacing values were 2.2242 Å for the peak (2θ) of 21.55°, 1.2833 Å for 24.35°, and 1.0978 Å for 31.18°, respectively. The obtained SAD pattern matched the corresponding XRD pattern of a UF resin. This work provides information for studying the mechanism of formation and the application of crystalline regions of UF resins.

Elastic constants of wood are fundamental parameters used in finite element analysis of wood structures. However, few studies and standards regulate the dimensions of sample used to measure elastic constants of wood. The size effect on mechanical properties (i.e., elastic constants and proportional limit stresses) of European beech (Fagus sylvatica L.) wood was studied with five different sizes samples. The data of experiments were inputted into a finite element model of self-designed chair and the loading capacity of chair was investigated by finite element method (FEM) and experiment. The results showed that nonlinear relationships were found between proportional limit stresses, cross-sectional area, and height of specimen by response surface method with R² greater than 0.72 in longitudinal, radial, and tangential directions. Elastic moduli and shear moduli increased with the height of specimen when cross-sectional area was kept constant, and decreased with an increased cross-sectional area of specimen, when the height was a constant, while the trends of Poisson’s ratio were not as expected. The comparisons between experiment and FEM suggested that the accuracy of FEM simulation increase with the raise of width-height ratio (≤1) of specimens used to determine the elastic constants. It is recommended to use small cubic wood specimen to determine the elastic mechanical properties used for finite element analysis of beech wood structures. Further research to find optimized wood specimen dimensions to get mechanical properties for FEM is quite necessary.

Developing a Renewable Hybrid Resin System. Part I: Characterization of Co-Polymers of Isocyanate with Different Molecular Weights of Phenolic Resins

The mechanism underlying thermal degradation of oriented strand board was tested under a humid environment. Near-infrared reflectance (NIR) spectroscopy coupled with chemometric modeling was utilized to better understand the degradation of functional groups over time. The flexural properties, internal bond (IB), water absorption, and thickness swelling were tested after exposure to various times of 0, 3, 6, and 9 weeks in a climate-controlled laboratory to 76.7°C and 60 percent relative humidity. The largest reduction in all flexural and physical properties occurred during the first 3 weeks of exposure and then leveled off thereafter, while IB decreased significantly through the 9-week period (α = 0.05). Chemometric models built from NIR spectra revealed pertinent chemical changes in wood chemistry and resin components.

The feasibility of applying an innovative process to manufacture composite decking boards with quartersawn or starsawn southern pine lumber bonded with phenol resorcinol formaldehyde (PRF) and polyurethane (PU) adhesives was studied. It was feasible to make quatersawn-based composite decking panels with possible improved surface qualities. Accelerated aging tests showed that composite quartersawn decking samples were more resistant to aging than flatsawn decking samples in terms of shear strength, especially after exposure to 12 wet–dry aging cycles. Compared with the PRF adhesive, the PU adhesive resulted in greater initial dry shear strength but had lower shear strength after the accelerated aging test. Furthermore, the amount of wood failure increased for the PRF-bonded samples and decreased for the PU-bonded samples after accelerated aging tests. Compared with solid quartersawn decking boards, the quartersawn composite decking boards had the same modulus of rupture and modulus of elasticity.