he objective of this research was to investigate the feasibility of using the pyrolysis bio-oil as part of a binder system for wood-based composites. Liquid products obtained from pyrolysis process of pine wood were mixed with reactants, such as isocyanate. The adhesive binder system was blended with flakes to fabricate flakeboard. The effect of the resin content and the mix ratio of the adhesive on the physical and mechanical properties of the flakeboard were examined. Dynamic mechanical analysis (DMA) was also employed to investigate the thermal properties of the adhesives. The results indicated that a bio-oil content of 25% showed comparable properties to those produced by pure pMDI adhesive. A good correlation between the DMA results and the mechanical properties of the flakeboard was also obtained. The increase of bio-oil content in the adhesive system improved the curing speed but reduced the adhesive stiffness.

The effect of cyclic moisture infiltration on connections in light-frame wood buildings has received limited research attention. Specifically, the connections between wood-based sheathing materials (OSB, plywood) and solid wood studs are of interest. A comprehensive understanding of connection performance will enhance structure and material design, thereby improving the overall integrity and robustness of light-frame structures. The focus of this research project was to evaluate the strength and stiffness of wood-frame connections exposed to cyclic humidity conditioning. Nailed sheathing/stud connection samples were tested for lateral resistance following various periods of moisture exposure. Elastic stiffness, 5% offset yield load, maximum yield load, and failure yield were computed and analyzed using the data collected. The parameters were compared among connection specimens receiving either 0, 1, 5, 10, 15, 25, or 40 periods of cyclic moisture conditioning. In addition, the bearing resistances of the materials were investigated for application to the general dowel equations for calculating lateral connection values, the current basis for design of single dowel-type fastener connections between wood-based members. An x-ray density profilometer was used to observe the de-densification processes within the composite sheathing materials throughout the moisture conditioning regime. Results indicated moderate to extreme changes in the performance of cycled connections involving lower density sheathing materials. Higher density sheathing materials performed favorably at each cycle test period. Comparisons to the yield model were similar to the control results, but usually differed as cycling increased. Analysis of connection performance following cyclic moisture loading is a vital component in developing a holistic model for service-life prediction of nailed connections in light-frame residential construction. / Master of Science

Oriented strandboard (OSB) is a wood-based composite product with the largest market share for residential and commercial construction. OSB composite products have introduced variability in their physical and mechanical properties due to their raw material and process variation. Reliable in-line non-destructive evaluation (NDE) devices are needed to rapidly determine OSB panel product quality during and after the manufacturing process. Wood specific gravity (SG) and moisture content (MC) play an important role in the wood composite manufacturing process. A real-time after-press monitoring device for locating SG and MC variations can supply information needed to control and improve mat formation, hot press schedules, detect MC-related problems, reduce product variation, and perform final product quality inspection. No real-time non-contact NDE methods are available for simultaneous detection of MC and SG variation. In this research, the radio frequency (RF) scanning technique was used to evaluate the MC and SG of OSB. The numerical simulation method assisted in developing RF sensors to nondestructively evaluate MC and SG of OSB composite specimens. MC and SG prediction models were derived based on RF testing results. The model behavior between relative humidity conditioned method and oven-drying conditioning method were compared. The results indicated the RF scanning technique can be successfully used as a NDE tool to measure MC and SG of OSB panel products. Numerical simulation can help deciding RF sensor geometry successfully and accurately. The MC and SG of OSB can be predicted with the models developed with the procedure used in this study. The RF scanning results are not only influenced by material physical properties, but also influenced by their MC conditioning method, such as relative humidity conditioned method and oven-drying conditioning method.

A numerical model based on fundamental engineering principles was developed and validated to establish a relationship between process parameters and the final properties of woodbased composite boards. The model simulates the mat formation, then compresses the reconstituted mat to its final thickness in a virtual press. The number of interacting variables during the hot-compression process is prohibitively large to assess a wide variety of data by experimental means. Therefore, the main advantage of the model based approach that the effect of the hot-compression parameters on the final properties of wood-based composite boards can be monitored without extensive experimentation. The mat formation part of the model is based on the Monte Carlo simulation technique to reproduce the spatial structure of the mat. The dimensions and the density of each flake are considered as random variables in the model, which follow certain probability density distributions. The parameters of these distributions are derived from data collected on industrial flakes by using an image analysis technique. The model can simulate the structure of a threelayer oriented strandboard (OSB) mat as well as the structure of random fiber networks. A grid is superimposed on the simulated mat and the number of flakes, the thickness, and the density of the mat at each grid point are computed. Additionally, the model predicts the change in several void volume fractions within the mat and the contact area between the flakes during consolidation. The void volume fractions are directly related to the physical properties of the mat, such as thermal conductivity, diffusivity, and permeability, and the contact area is an indicator of the effectively bonded area within the mat. The heat and mass transfer part of the model predicts the change of air content, moisture content, and temperature at designated mesh points in the cross section of the mat during the hotcompression. The water content is subdivided into vapor and bound water components. The free water component is not considered in the model due to the low (typically 6-7 %) initial moisture content of the flakes. The gas phase (air and vapor) moves by bulk flow and diffusion, while the bound water only moves by diffusion across the mat. The heat flow occurs by conduction and convection. The spatial derivatives of the resulting coupled partial differential equations are discretized by finite differences. The resulting ordinary differential equation in time is solved by a differential-algebraic system solver (DDASSL). The internal environment within the mat can be predicted among different initial and boundary conditions by this part of the hot-compression model. In the next phase of the research, the viscoelastic (time, temperature, and moisture dependent) response of the flakes was modeled using the time-temperature-moisture superposition principle of polymers. A master curve was created from data available in the literature, which describes the changing relaxation modulus of the flakes as a function of moisture and temperature at different locations in the mat. Then the flake mat was compressed in a virtual press. The stress-strain response is highly nonlinear due to the cellular structure of the mat. Hooke's Law was modified with a nonlinear strain function to account for the behavior of the flake mat in transverse compression. This part of the model gives insight into the vertical density profile formation through the thickness of the mat. Laboratory boards were produced to validate the model. A split-plot experimental design, with three different initial mat moisture contents (5, 8.5, 12 %), three final densities (609, 641, 673 kg êm3 or 38, 40, 42 lb ê ft3), two press platen temperatures (150, 200 °C), and three different press closing times (40, 60, 80 s) was applied to investigate the effect of production parameters on the internal mat conditions and the formation of the vertical density profile. The temperature and gas pressure at six locations in the mat, and the resultant density profiles of the laboratory boards, were measured. Adequate agreement was found between the model predicted and the experimentally measured temperature, pressure, and vertical density profiles. The complete model uses pressing parameters (press platen temperature, press schedule) and mat properties (flake dimensions and orientation, density distribution, initial moisture content and temperature) to predict the resulting internal conditions and vertical density profile formation within the compressed board. The density profile is related to all the relevant mechanical properties (bending strength, modulus of elasticity, internal bond strength) of the final board. The model can assist in the optimization of the parameters for hot-pressing woodbased composites and improve the performance of the final panel. / Ph. D.

Low moisture veneer and regions of sapwood within hickory engineered wood flooring bonded with soy-flour adhesive are thought to be factors leading to potential performance deficiencies. The goal of this research was to gain a broader understanding of bonding low moisture hickory veneer with soy-based adhesive. Soyad® is of particular interest due to its novel cross-linking chemistry. Impacts of moisture content and wood region (heartwood versus sapwood) were analyzed with dry and wet shear bond strength tests, measurement of percent wood failure, lathe check characterization, and adhesive bondline thickness and penetration depth measurement. Impact of wood region and type (hickory versus red oak) was assessed by comparing wood buffering capacity and delamination following three-cycle water soaking. Dry and wet shear strength values met expectations for engineered wood flooring yet percentage wood failure results were uniformly very low for all combinations of moisture levels and wood regions. In contrast, delamination following wet and dry cycling was minor and within minimum requirements for all specimens tested. The influence of moisture level, wood region and type were inconsistent; statistically significant relationships were not evident within the moisture range studied. However, different wood regions and types exhibited differing veneer buffering capacities that had potential to interfere with pH requirements of Soyad®. Additional study of buffering capacity and resin cure is recommended to determine the significance of the buffering capacity results found in this study. / Master of Science / Performance issues including debonding and delamination have been reported for hickory engineered wood flooring products constructed using a soy-flour based adhesive. Sapwood regions within the composite and extremely low moisture veneer were provided by industry as possible factors that resulted in performance deficiencies. The goal of this research project was to gain a broader understanding of bonding low moisture hickory veneer with Soyad® adhesive. Soy-flour adhesive systems offer many environmental, health, and durability advantages. Soyad® is of particular interest due to its use of natural, renewable soy flour, a novel cross-linking resin, and no added formaldehyde. Test specimens were prepared using heartwood of hickory and red oak and sapwood of hickory. Analytical tests included determination of certain chemical properties of the adhesive and wood veneer, measurement of strength properties of the adhesive bond, and assessment of delamination tendencies of bonded panels following water soaking. Results indicate that moisture levels and the different growth regions and wood type had an inconsistent impact on the bond strengths yet percent wood failure was uniformly low and considered unacceptable by industry. Although this research established a foundation of basic knowledge, more information about adhesive bonding of wood with the recently developed soy based adhesives is needed to optimize the systems and provide technological advancements that lead to more efficient and safe utilization of woody materials from the forest.

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