Browsing by Author "Kamke, Frederick A."

Now showing 1 - 20 of 39
  • Thumbnail Image
    The adoption of innovative wood processing technologies in the building products industry
    Cohen, David H. (Virginia Polytechnic Institute and State University, 1989)
    The strategic importance of the adoption of innovative processing technologies was analyzed for building products businesses. This study examined the two components of wood building products businesses: the structural panel industry and the softwood Iumber industry. To ensure that the relevance of adopting of innovative processing technologies was examined within an accurate contextual environment, additional important strategies and performance were also measured. A mail survey of the seventy-five largest North American producers of these two products provided the primary data necessary to investigate the strategic importance of process technology adoption, forward vertical integration, relative market share, grade sector focus, and investment intensity on firm performance as measured by profitability surrogates and changes in relative market share. This survey collected direct measures of the proportion of 1987 production produced by respondent firms that used controlled distribution channels and each of twentythree processes indicative of innovative technologies in the manufacture of building products. Information concerning the other strategic and performance factors was collected from secondary data sources. Results indicate that the adoption of innovative processing technologies has a positive impact on firm profitability. Investment intensity and grade sector focus also contributed to superior profitability. Forward vertical integration, and relative market share had no impact in differences between performance levels for the firms studied. Technologies were examined for underlying dimensions that group different process technologies together. Firms were clustered according to their level of adoption of innovative processing technologies and these clusters were then described according to a variety of firm-dependent characteristics, strategies, and performance measures. A strategy-performance model was developed for standardized, industrial product-markets and empirically tested using the data collected for the building products industry as an industry representative of this type of competitive environment.
  • Thumbnail Image
    Analysis of Calcutta bamboo for structural composite materials
    Ahmad, Mansur (Virginia Tech, 2000-08-11)
    Land use issues have dramatically changed the timber supply outlook for our nation's forest products industry. Since demand for wood products shows no sign of abating, alternative products must be developed. Bamboo is a very promising alternative raw material for the manufacture of structural composite products. It is fast growing, economical, renewable and abundant throughout the world. Bamboo has physical and mechanical properties that are comparable to many commercial timber species, and thus, may easily be processed using existing technology from the wood-based composites industry. Bamboo can be cultivated in the U.S., and thus has the potential to relieve some of the harvesting pressure from our nation's forestlands. However, the use of specific bamboo species for structural composite products will require a thorough investigation of the material as well as its interaction with other components. Thus, the primary objective of this dissertation is to determine the properties of Calcutta bamboo and its interaction with adhesives. The properties investigated were relative density, dimensional stability, equilibrium moisture content, bending strength and stiffness, tensile strength, pH, buffer capacity, wettability and the adhesive penetration. In addition to this, a prototype bamboo parallel strip lumber (BPSL) was manufactured and tested for its physical and mechanical properties. The relationships among the properties of Calcutta bamboo and the prototype bamboo composite were also investigated. As the result of these investigations, it is concluded that Calcutta bamboo is technically a suitable raw material for structural composite products. This result may also be applicable for the utilization of other bamboo species, thus aiding companies in decisions regarding investment in bamboo plantations and manufacturing facilities in the U.S, Malaysia and other parts of the world. The primary benefits from this research may be the development of new products to serve growing markets, and thereby relieving some of the pressure to harvest forestlands.
  • Thumbnail Image
    Aspects of Wood Adhesion: Applications of 13C CP/MAS NMR and Fracture Testing
    Schmidt, Robert G. (Virginia Tech, 1998-01-28)
    Phenol Formaldehyde (PF) and polymeric isocyanate (pMDI) are the two main types of adhesives used in the production of structural wood-based composites. Much is unknown about various aspects of adhesion between these two types of resins and wood. The present research describes the development of techniques which will permit an enhanced understanding of 1.) the extent of cure of PF within a wood based composite, 2.) the scale of molecular level interactions between PF and pMDI and wood, 3.) mechanical performance and durability of wood-adhesive bonds. Correlations were established between conventional methods of characterization of neat PF (thermomechanical analysis, swelling studies) and measurements made using 13C CP/MAS NMR. These correlations were then utilized to characterize PF cured in the presence of wood. The use of 13C labeled PF allowed estimates of relative degrees of resin conversion to be made. The use of 13C and deuterium labeled PF allowed qualitative estimates of resin molecular rigidity to be made. The scale of molecular level interactions between PF and pMDI and wood was probed using NMR relaxation experiments. Evidence was shown to suggest the formation of an interpenetrating polymer network (IPN) morphology existing at both types of wood-resin interphases. The formation of the IPN morphology was strongly influenced by resin molecular weight, cure temperature and the presence of solvent. A new test geometry for the evaluation of the fracture toughness of wood-adhesive bonds was developed. Consistent and reliable results were obtained. It was found that low molecular weight PF possessed enhanced durability over high molecular weight.
  • Thumbnail Image
    Behavior of wood under transverse compression
    Kasal, Bohumil (Virginia Tech, 1989-01-05)
    The increasing demand on wood and wood products, and the simultaneously decreasing quality of wood as a raw material leads to the increasing significance of wood-based composites such as particleboard or flakeboard. The resulting mechanical and physical properties are to the large extend dictated by the densification of the wood component. To be able to predict the density of the material, the behavior of structural elements must be known. A theory developed for rigid plastic foams was modified and applied to the deformation of wood in transverse compression. A testing procedure for high strain compression over a range of temperatures was developed. In addition, a stochastic model for prediction of high strain behavior was developed. Wood of yellow poplar (Liriodendron tulipuera) was used as the experimental material.
  • Thumbnail Image
    Changes in Oriented Strandboard Permeability During Hot-Pressing
    Hood, Jonathan Patrick (Virginia Tech, 2004-06-04)
    Convective heat transfer during hot pressing in wood-based composite panel manufacturing is widely accepted as the most important means of heat transport for resin curing. The rate of convective heat transfer to the panel core is controlled by its permeability. Permeability in the plane of the panel also controls the flow of vapor to the panel edges, thereby influencing the potential for panel "blowing". This research considers how flake thickness, flake alignment and changing mat density during hot-pressing influences OSB mat permeability, through its thickness and in the plane of the panel. Some previous research exists but it fails to address the affects of horizontal and vertical density gradients as well as flake alignment. An apparatus was designed to allow cold pressing of aligned flakes to desired densities while enabling permeability measurements through the mat thickness. An additional apparatus was designed to allow the measuring of permeability in the plane of the mat. These designs permitted permeability measurements in mats that had no vertical density gradient, allowing for the direct study of permeability versus density (compaction ratio). Superficial permeability was determined using Darcy's law and for each sample, multiple readings were made at five different pressure differentials. Permeability through the mat thickness was highly dependent on compaction ratio and to a lesser extent flake thickness. As the compaction ratio is increased, the initial reduction in permeability is severe, once higher compaction ratios are achieved the reduction in permeability is less pronounced. Permeability decreased with decreasing flake thickness. Permeability in the plane of the mat decreases with increasing compaction ratio but in a less severe manner than through the mat thickness. In this case, the permeability-compaction ratio relationship appears linear in nature. Again, permeability decreases with decreasing flake thickness.
  • Thumbnail Image
    Characterizing the Durability of PF and pMDI Adhesive Wood Composites Through Fracture Testing
    Scoville, Christopher R. (Virginia Tech, 2001-06-13)
    The increased use of wood composites in building materials results in a need for a better understanding of wood adhesion. The effects of water and temperature exposure on the durability of wood products were assessed using the double-cantilever beam (DCB) method of fracture testing. The relative durability of phenol-formaldehyde (PF) and isocyanate (pMDI) adhesives was compared using a 2-hour boil test and an environmental test. The feasibility of using oriented strandboard (OSB), oriented strand lumber (OSL) and parallel strand lumber (PSL) for the DCB fracture method was assessed. The fracture resistance of PF was reduced significantly by the aging exposures. The fracture resistance of pMDI did not decrease after the 2-hour boil test. The DCB fracture method was shown to be useful with a square-grooved machined specimen using OSB and OSL.
  • Thumbnail Image
    Comparative Analysis of Inactivated Wood Surfaces
    Sernek, Milan (Virginia Tech, 2002-04-24)
    A wood surface, which is exposed to a high temperature condition, can experience inactivation. Surface inactivation results in reduced ability of an adhesive to properly wet, flow, penetrate, and cure. Thus, an inactivated wood surface does not bond well with adhesives. The changes in surface chemistry, wettability, and adhesion of inactivated wood surfaces, including heartwood of yellow-poplar (Liriodendron tulipifera) and southern pine (Pinus taeda), were studied. Wood samples were dried from the green moisture content condition in a convection oven at five different temperature levels ranging from 50 to 200 °C. The comparative characterization of the surface was done by X-ray photoelectron spectroscopy (XPS), sessile drop wettability, and fracture testing of adhesive bonds. The oxygen to carbon ratio (O/C) decreased and the C1/C2 ratio increased with drying temperature. The C1 component is related to carbon-carbon or carbon-hydrogen bonds, and the C2 component represents single carbon-oxygen bond. A low O/C ratio and a high C1/C2 ratio reflected a high concentration of non-polar wood components (extractives/VOCs) on the wood surface, which modified the wood surface from hydrophilic to more hydrophobic. Wettability was directly related to the O/C ratio and inversely related to the C1/C2 ratio. Contact angle decreased with time and increased with the temperature of exposure. Southern pine had a lower wettability than yellow-poplar, which was due to a greater concentration of non-polar hydrocarbon-type extractives and heat-generated volatiles on the surface. Solvent extraction prior to drying did not improved wettability, whereas, extraction after drying improved wettability. A contribution of extractives migration and VOCs generation played a significant role in the heat-induced inactivation process of southern pine. The maximum strain energy release rate (Gmax) showed that surface inactivation was insignificant for yellow-poplar when exposed to drying temperatures < 187°C. The southern pine was most susceptible to inactivation at drying temperatures > 156°C, particularly when bonded with phenol-formaldehyde (PF) adhesive. Chemical treatments improved the wettability of inactivated wood surfaces, but an improvement in adhesion was not evident for specimens bonded with polyvinyl-acetate (PVA) adhesive. NaOH surface treatment was most effective for improving adhesion of the PF adhesive bond.
  • Thumbnail Image
    Computational Steering in the Problem Solving Environment WBCSim
    Shu, Jiang; Watson, Layne T.; Ramakrishnan, Naren; Kamke, Frederick A.; Deshpande, Shubhangi (Department of Computer Science, Virginia Polytechnic Institute & State University, 2009)
    Computational steering allows scientists to interactively control a numerical experiment and adjust parameters of the computation on-the-fly and explore “what if ” analysis. Computational steering effectively reduces computational time, makes research more efficient, and opens up new product design opportunities. There are several problem solving environments (PSEs) featuring computational steering. However, there is hardly any work explaining how to enable computational steering for PSEs embedded with legacy simulation codes. This paper describes a practical approach to implement computational steering for such PSEs by using WBCSim as an example. WBCSim is a Web based simulation system designed to increase the productivity of wood scientists conducting research on wood-based composites manufacturing processes. WBCSim serves as a prototypical example for the design, construction, and evaluation of small-scale PSEs. Various changes have been made to support computational steering across the three layers—client, server, developer—comprising the WBCSim system. A detailed description of the WBCSim system architecture is presented, along with a typical scenario of computational steering usage.
  • Thumbnail Image
    Cure of aqueous phenol-formaldehyde resin at elevated water vapor pressures
    Ballerini, Aldo A. (Virginia Tech, 1994-11-19)
    The intent of this research was to enhance our knowledge of aqueous phenolformaldehyde resin cure as it is affected by the elevated water vapor pressures that occur during hot-pressing of a wood-based composite. Microdielectric spectroscopy (DEA) was used to monitor the cure reaction, and thermomechanical analysis (TMA), swelling tests and scanning electron microscopy (SEM) techniques were used to characterize the final resin-network. Microdielectric results showed that as the water vapor pressure of the sy stem increases the time to gelation increases. It was also found that the injection of saturated water vapor sharply decreased the gelation time when compared to the other water vapor environmental conditions. In addition, it was found that the higher the water vapor pressure the lower the residual ion viscosity. Thermomechanical analysis and swelling test experiments showed that as the water vapor pressure increases the glass transition temperature and the cross-link density of the cured resin-network decreases. Considerable differences in the morphology of the network were found using SEM. Thus, it can be established that during the curing process under elevated water vapor pressures of a liquid phenol-formaldehyde adhesive some water is trapped into the resin network and it is acting as a plasticizer. A theoretical approach to model the cure kinetics of phenol-formaldehyde has been developed. The model is based on the occurrence of two simultaneous processes (condensation polymerization and evaporation of water) and on the concentration dependency of the activation energy of polymerization.
  • Thumbnail Image
    Data Driven Surrogate Based Optimization in the Problem Solving Environment WBCSim
    Deshpande, Shubhangi; Watson, Layne T.; Shu, Jiang; Kamke, Frederick A.; Ramakrishnan, Naren (Department of Computer Science, Virginia Polytechnic Institute & State University, 2009)
    Large scale, multidisciplinary, engineering designs are always difficult due to the complexity and dimensionality of these problems. Direct coupling between the analysis codes and the optimization routines can be prohibitively time consuming due to the complexity of the underlying simulation codes. One way of tackling this problem is by constructing computationally cheap(er) approximations of the expensive simulations, that mimic the behavior of the simulation model as closely as possible. This paper presents a data driven, surrogate based optimization algorithm that uses a trust region based sequential approximate optimization (SAO) framework and a statistical sampling approach based on design of experiment (DOE) arrays. The algorithm is implemented using techniques from two packages—SURFPACK and SHEPPACK that provide a collection of approximation algorithms to build the surrogates and three different DOE techniques—full factorial (FF), Latin hypercube sampling (LHS), and central composite design (CCD)—are used to train the surrogates. The results are compared with the optimization results obtained by directly coupling an optimizer with the simulation code. The biggest concern in using the SAO framework based on statistical sampling is the generation of the required database. As the number of design variables grows, the computational cost of generating the required database grows rapidly. A data driven approach is proposed to tackle this situation, where the trick is to run the expensive simulation if and only if a nearby data point does not exist in the cumulatively growing database. Over time the database matures and is enriched as more and more optimizations are performed. Results show that the proposed methodology dramatically reduces the total number of calls to the expensive simulation runs during the optimization process.
  • Thumbnail Image
    The development of a durability procedure for pallets with structural panel decking
    Cao, Jiqiang (Virginia Tech, 1993-05-07)
    The Pallet Design System (PDS) is a widely accepted engineering procedure for comparing the performance of competing pallet designs. As part of a new version of the PDS, the objective of this study was to develop a durability model for pallets with structural panel decking. An accelerated rough material handling test system, "the VPI unit-load material handling FasTrack" , was developed to simulate pallets used in the unit-load material handling environments. 100 pallets representing 14 different designs were tested in the "FasTrack." Damages to these pallets were recorded after each test cycle. A procedure relating damage to repair cost was developed. The effect of panel-deck pallet design on the resistance to damage was evaluated in terms of the total number of damaged parts and average damage cost or repair cost. Test results indicate that panel grade and type, species of related wood parts, size of stringer and deckboards, joints, and pallet configurations affect the resistance of panel deck pallet to damage. The plots of average total damage cost, Cu adjusted for repair as a function of test cycle, U, fit the equation: Ct = aU - 1. The equation provided good fits to all the pallet designs tested. Using the initial purchase prices, the average cost and the economic life were calculated for all the pallet designs. The VPI "FasTrack" was calibrated based on the number of physical handlings and the amortized life. Three typical in-field handling environments were compared with the VPI "FasTrack". It concluded that the 30-cycle test period in the VPI "FasTrack" simulates between 2 to 5 years of field uses depending on the field handling system being simulated. Thirty Canadian Pallet Council (CPC) pallets with known 7 years of amortized life in the field were tested in the VPI "FasTrack". The 30-cycle test in the VPI system simulated 6 years of use in the similar handling environment of the CPC pallet used by the grocery industry in Canada. The average total damage costs for different pallet designs were related to pallet structural characteristics using multivariate regression analysis. The shear resistance through the thickness of the top panel deck, bottom deck flexural strength, pallet flexural strength, fastener withdrawal resistance, and pallet configuration were used to predict the total damage cost. A multiple regression model was developed. The model was verified by comparing the predicted values with the tested values of 12 panel deck pallets representing 2 designs. The results indicated that the model is reliable for the future predictions.
  • Thumbnail Image
    Economic Feasibility of Implementing a Resin Distribution Measurement System for MDF Fiber
    Scott, Keith Alan (Virginia Tech, 2001-04-11)
    There have been successful techniques developed to measure resin distribution of phenol-formaldehyde adhesive on several types of wood surfaces. However, a technique that quantitatively measures UF resin on wood surfaces has been a problem because UF resin is colorless on wood fiber. The first objective of this study was to develop a technique to quantitatively measure surface area coverage and statistical distribution of urea-formaldehyde (UF) resin on medium density fiberboard (MDF) fiber. Two techniques were evaluated to quantitatively measure UF resin. One technique treated the resinated fiber with a reactive stain, such that the resin and wood could be distinguished and separated using digital image analysis. An epi-fluorescence microscope, color video camera, A/D image capture board, and image analysis software were used to measure the percent of resin coverage on the wood surface. The measured resin coverage of the treated fibers did not correlate with the target resin loading level. The other technique added ultraviolet dye to the resin and measured the distribution of resin with an image analysis system. The results of a mill trial confirmed the accuracy of the technique. This system has potential to be incorporated into a mill setting, which will provide MDF mills with a method of determining how resin is being distributed on their fiber. The second objective of this study was to identify factors that would influence the technique's acceptance among MDF mills. A questionnaire was developed, pretested, and sent to every MDF mill in the United States. The method of adding UV dye into the resin was favorable to most mills and could be tested either on-site or by a third-party company. This allows MDF mills to determine potential problems with their blending process. This method saves time and money since it is a proactive measure rather than a reactive measure. It should also lead to a more uniform and consistent product, which is the goal of every MDF mill.
  • Thumbnail Image
    Evaluation of Phenol Formaldehyde Resin Cure Rate
    Scott, Brian Cameron (Virginia Tech, 2005-04-29)
    Cure time is often the bottleneck of composite manufacturing processes, therefore it is important to understand the cure of today's thermosetting adhesives. This research attempts to characterize the cure rate of two commercial phenol-formaldehyde adhesives. Two methods are used, parallel-plate rheometry and dielectric spectroscopy. Viscosity data from a parallel-plate rheometer may be used to track the advance of polymerization as a function of temperature. This data can then be used to optimize press conditions and reduce production times and costs. The research will further examine resin cure through dielectric analysis; such a technique could monitor resin cure directly and in real-time press situations. Hot-pressing processes could conceivably no longer require a set press schedule; instead they would be individually set based on dielectric data for every press batch. Such a system may lead to a more efficient and uniform product because press times could be based on individual press cycles instead of entire product lines. A more likely scenario, however, is the use of in situ adhesive cure monitoring for troubleshooting or press schedule development. This research characterized the cure of two phenol-formaldehyde resins using parallel-plate rheometry, fringe-field dielectric analysis, and parallel-plate dielectric analysis. The general shape of the storage modulus vs. time curve and the gel and vitrification points in a temperature ramp were found. Both dielectric analysis techniques were able to characterize trends in the resin cure and detect points such as vitrification. The two techniques were also found to be comparable when the cure profiles of similar conditions were examined.
  • Thumbnail Image
    An Experiment Management Component for the WBCSim Problem Solving Environment
    Shu, Jiang (Virginia Tech, 2002-12-13)
    This thesis describes a computing environment WBCSim and its experiment management component. WBCSim is a web-based simulation system used to increase the productivity of wood scientists conducting research on wood-based composite and material manufacturing processes. This experiment management component integrates a web-based graphical front end, server scripts, and a database management system to allow scientists to easily save, retrieve, and perform customized operations on experimental data. A detailed description of the system architecture and the experiment management component is presented, along with a typical scenario of usage.
  • Thumbnail Image
    Experiment Management for the Problem Solving Environment WBCSim
    Shu, Jiang (Virginia Tech, 2009-08-10)
    A problem solving environment (PSE) is a computational system that provides a complete and convenient set of high level tools for solving problems from a specific domain. This thesis takes an in-depth look at the experiment management aspect of PSEs, which can be divided into three levels: 1) data management, 2) change management, and 3) execution management. At the data management level, anything related to an experiment (computer simulation) should be stored and documented. A database management system can be used to store the simulation runs for a PSE. Then various high level interfaces can be provided to allow users to save, retrieve, search, and compare these simulation runs. At the change management level, a scientist should only focus on how to solve a problem in the experiment domain. Aside from running experiments, a scientist may only consider how to define a new model, how to modify an existing model, and how to interpret an experiment result. By using XML to describe a simulation model and unify various implementation layers, changing an existing model in a PSE can be intuitive and fast. At the execution management level, how an experiment is executed is the main concern. By providing a computational steering capability, a scientist can pause, examine, and compare the intermediate results from a simulation. Contrasted with the traditional way of running a lengthy simulation to see the result at the end, computational steering can leverage the user's expert knowledge on the fly (during the simulation run) and provide new insights and new product design opportunities. This thesis illustrates these concepts and implementation by using WBCSim as an example. WBCSim is a PSE that increases the productivity of wood scientists conducting research on wood-based composite materials and manufacturing processes. It integrates Fortran 90 simulation codes with a Web based graphical front end, an optimization tool, and various visualization tools. The WBCSim project was begun in 1997 with support from United States Department of Agriculture, Department of Energy, and Virginia Tech. It has since been used by students in several wood science classes, by graduate students and faculty, and by researchers at several forest products companies. WBCSim also serves as a test bed for the design, construction, and evaluation of useful, production quality PSEs.
  • Thumbnail Image
    Experimental apparatus for measuring moisture transfer in porous materials subject to relative humidity and temperature differences
    Crimm, Robert Prentiss (Virginia Tech, 1992-04-15)
    A detailed design was developed of an apparatus to measure moisture transfer in porous materials. The apparatus is to be used to collect data to aid in the development of mathematical models which accurately describe this phenomena. The apparatus consists of dual environmental chambers between which a specimen material is sealed. The temperature of each chamber is controlled separately allowing nonisothermal test conditions. The relative humidity is maintained without the use of saturated salt solutions. The moisture transfer rate is measured by periodically weighing a desiccant column used to absorb moisture as result of diffusion across the specimen. The apparatus was built and used to verify a heat transfer model written to predict its thermal characteristics. The chamber temperature capabilities are 5°C to 60°C with up to a 20°C temperature difference across the specimen. The relative humidity limits are based on the heat transfer into or out of the system. High relative humidities (75 to 85 percent) are possible at chamber temperatures close to ambient, but decrease sharply at the extremely high or low temperatures and during nonisothermal operation. The apparatus maintains a constant temperature within ±0.4°C of the setpoint when subjected to varying ambient temperatures. The spatial temperature variation close to the sample (within 25 mm) is within approximately ​​​​±1°C of the average chamber temperature. The relative humidity can be manually controlled to within ±.7 percent RH. Automated control, complicated by a response lag, was within ±1 percent RH.
  • Thumbnail Image
    Flexural behavior of a glass fiber reinforced wood fiber composite
    Smulski, Stephen John (Virginia Polytechnic Institute and State University, 1985)
    The static and dynamic flexural properties of a wood fiber matrix internally reinforced with continuous glass fibers were investigated. When modelled as a sandwich composite, the static flexural modulus of elasticity (MOE) of glass fiber reinforced hardboard could be successfully predicted from the static flexural MOE of the wood fiber matrix, and the tensile MOE and effective volume fraction of the glass fiber reinforcement. Under the same assumption, the composite modulus of rupture (MOR) is a function of the reinforcement tensile MOE and effective volume fraction, and the matrix stress at failure. The composite MOR was predicted on this basis with limited success. The static flexural modulus of elasticity, dynamic modulus of elasticity, and modulus of rupture of glass fiber reinforced hardboard increased with increasing effective reinforcement volume fraction. The logarithmic decrement of the composite decreased with increasing effective reinforcement volume fraction. Excellent linear correlation found among flexural properties determined in destructive static tests and nondestructive dynamic tests demonstrated the usefulness of dynamic test methods for flexural property evaluation. The short-term flexural creep behavior of glass fiber reinforced hardboard was accurately described by a 4-element linear viscoelastic model. Excellent agreement existed between predicted and observed creep deflections based on nonlinear regression estimates of model parameters.
  • Thumbnail Image
    Investigating the Surface Energy and Bond Performance of Compression Densified Wood
    Jennings, Jessica D. (Virginia Tech, 1997-09-10)
    The bond performance and surface energy of hygro-thermal compression densified wood were studied using comparisons to hygro-thermally treated and control yellow-poplar (Liriodendron tulipifera). Bond performance was studied using opening mode double cantilever beam fracture testing and cyclic boiling of one half of all fracture samples. Phenol formaldehyde film (PF-film) and polymeric diphenylmethane diisocyanate (pMDI) were the two different adhesives used to bond fracture samples. Hygro-thermal samples bonded with PF-film had significantly higher fracture toughness than control samples, while no difference was found for densified samples. Densified samples bonded with pMDI had significantly higher fracture toughness than control samples while no change was seen for hygro-thermal samples. Boil cycling reduced fracture toughness of hygro-thermal fracture samples only, irrespective of adhesive type. Surface energy was studied using sessile drop contact angle measurement and the Chang model of acid-base, surface energy component calculation. Water, glycerol, formamide, ethylene glycol, and -Bromonapthalene were used as probe liquids. Densified and hygro-thermally treated yellow-poplar had significantly higher contact angles than control samples. The contact angle trends for densified and hygro-thermally treated wood were found to be the same. Total surface energy as well as the polar and acid components of surface energy decreased with hygro-thermal treatment. The dispersive and base components of surface energy increased with hygro-thermal treatment.
  • Thumbnail Image
    An Investigation of Nailed Connection Performance in a Cyclic Humidity Environment
    Smith, Jeffrey Scott (Virginia Tech, 2004-07-23)
    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.
  • Thumbnail Image
    Investigation of the Wood/Phenol-Formaldehyde Adhesive Interphase Morphology
    Laborie, Marie-Pierre Genevieve (Virginia Tech, 2002-02-01)
    This work addresses the morphology of the wood/ Phenol-Formaldehyde (PF) adhesive interphase using yellow-poplar. In this case, morphology refers to the scale or dimension of adhesive penetration into wood. The objective is to develop methods for revealing ever smaller levels of wood/resin morphology. Dynamic techniques that are commonly utilized in polymer blend studies are investigated as potential methods for probing the wood/ adhesive interphase morphology. These are Dynamic Mechanical Analysis (DMA) and solid state NMR using CP/MAS. PF resin molecular weight is manipulated to promote or inhibit resin penetration in wood, using a very low or a very high molecular weight PF resin. With DMA, the influence of PF resin on wood softening is investigated. It is first demonstrated that the cooperativity analysis according to the Ngai coupling model of relaxation successfully applies to the in-situ lignin glass transition of yellow-poplar and spruce woods. No significant difference in intermolecular coupling is detected between the two woods. It is then demonstrated that combining simple DMA measurements with the cooperativity analysis yields ample sensitivity to the interphase morphology. From simple DMA temperature scans, a low molecular weight PF (PF-Low) does not influence lignin glass transition temperature. However, the Ngai coupling model of relaxation indicates that intermolecular coupling is enhanced with the low molecular weight PF. This behavior is ascribed to the low molecular weight PF penetrating lignin on a nanometer scale and polymerizing in-situ. On the other hand, a high molecular weight resin with a broad distribution of olecular weights (PF-High) lowers lignin glass transition temperature dramatically. This plasticizing effect is ascribed to a small fraction of the PF resin being low enough in molecular weight to penetrate lignin on a nanoscale, but being too dispersed for forming a crosslinked network. With CP/MAS NMR, intermolecular cross-polarization experiments are found unsuitable to probe the angstrom scale morphology of the wood adhesive interphase. However, observing the influence of the PF resins on the spin lattice relaxation time in the rotating frame, HT1r, and the cross-polarization time (TCH) is useful for probing the interphase morphology. None of the resins significantly affects the cross-polarization time, suggesting that angstrom scale penetration does not occur with a low nor a high molecular weight PF resin. However, the low molecular weight PF substantially modifies wood polymer HT1r, indicating that the nanometer scale environment of wood polymers is altered. On the other hand, the high molecular weight PF resin has no effect on wood HT1r. On average, the high molecular weight PF does not penetrate wood on a nanometer scale. Interestingly, the low molecular weight PF resin disrupts the spin coupling that is typical among wood components. Spin coupling between wood components is insensitive to the high molecular weight PF. Finally, it is noteworthy that the two PF resins have significantly different T1r 's in-situ. The low molecular weight resin T1r lies within the range of wood relaxations, suggesting some degree of spin coupling. On the other hand, the T1r of the high molecular weight PF appears outside the range of wood relaxations. Spin coupling between the high molecular weight resin and wood components is therefore inefficient. The CP/MAS NMR and DMA studies converge to identify nanometer scale penetration of the low molecular weight PF in wood. On the other hand, the high molecular weight PF resin forms separate domains from wood, although a very small fraction of the PF-High is able to penetrate wood polymers on a nanoscale.