Ultrasonic Atomization of pMDI Wood Resin

A novel, patent-pending approach to the application of wood resins based on an ultrasonic principle was developed in this study. Liquid polymeric methane diphenyl-diisocyanate (pMDI) resin was successfully atomized using a bench-scale 25 kHz ultrasonic atomizer. The optimal average sizes of the resin droplets generated at a flow rate of 0.7 mL/min and power input of 5.0 J/s were about 90 μm. In addition to fewer fine droplets than that produced by conventional spinning-disk atomizers, the droplets of pMDI resin produced by the ultrasonic atomizer had a more uniform droplet size distribution. These results indicate the potential advantages of implementing ultrasonic atomization in oriented strandboard production, including elimination of the hazardous fraction of fine resin droplets and potential production cost savings from improved resin efficiency. The ultrasonic atomization of wood resins appears to be a promising alternative to the spinning-disk atomizer

Short-Term Creep Tests on Phenol-Resorcinol-Formaldehyde (PRF) Resin Undergoing Moisture Content Changes

The objective of the study was to develop an experimental technique that would allow determination of the hygro-mechanical properties of thin uniform resin films undergoing moisture content changes; and to use the technique for assessment of the hygro-mechanical performance of phenol-resorcinol-formaldehyde (PRF) resin.Creep tests on 6 small specimens of PRF film under constant stress (50% of the short-term ultimate stress level), at room temperature (23°C ± 2°C) and controlled relative humidity (RH) conditions (drying or wetting) were carried out. Digital images of the specimens were acquired using a CCD camera at discrete time intervals during the experiments. Displacements were then measured by comparing successive images using digital image correlation principles. Separation of strain components from total strain recorded during the creep tests was carried out by using data from two reference tests performed on the same material: 1) free deformations of unloaded specimens during drying or wetting conditions, and 2) creep under equilibrium conditions.The experimental method developed for the study provided a tool to determine hygro-mechanical properties of thin resin films. Quantitative data on material properties of hygroscopic resins determined by means of the technique may be used for modeling the behavior of adhesive bonds as well as adhesive bonded materials in varying climate conditions. The PRF resin revealed a distinct mechano-sorptive behavior, though it seems to be less significant than that reported for wood in transverse directions

Stereomicroscopic optical method for the assessment of load transfer patterns across the wood-adhesive bond interphase

The mechanical performance of wood-based composites is determined by the mechanical properties of their individual components and the effective load transfer between these components. In laminated wood composites, this load transfer is facilitated by the adhesive bond. The experimental methodology developed in this study measures and analyzes the full-field deformation and strain distributions across the loaded wood-adhesive interphase at a micromechanical level. Optical measurements were performed based on the principles of digital image correlation by a stereomicroscopic camera system. This system allows the monitoring of in-plane deformations as well as out-of-plane displacements, providing full-field 3D surface strain maps across the adhesive bond. These measurements can be used to improve the understanding of the load transfer between the adherents and the contribution of the adhesive to the mechanical properties of the bulk composite and serve as a quantitative input for numerical modeling and simulations aimed at the improvement of the products.Keywords: digital image correlation (DIC), optical measurement, micromechanics, load transfer, adhesive interphas

Moment-Curvature Analysis of Coupled Bending and Mechanosorptive Response of Red Spruce Beams

In this study, an expanded comprehensive numerical approach to predict hygromechanical behavior of beams is proposed that rigorously couples spatially varying time-dependent moisture content fluctuation with uniaxial stress-strain relations. The constitutive model, consisting of elastic, viscoelastic, and two mechanosorptive strain elements connected in series, was used in a layered moment-curvature flexural analysis. The procedure is numerical and is able to take into account effect of moisture content changes, different mechanosorptive behavior in tension and compression, and cross-sectional hygroexpansion. The overall trend and magnitude of predicted deflections are in good agreement with experimental results. Results demonstrated that complex beam behavior in a varying environment can be predicted by a simple model with well-defined material characteristics generated through relatively simple 18-h uniaxial experiments

IMAGING WOOD PLASTIC COMPOSITES (WPCs): X-RAY COMPUTED TOMOGRAPHY, A FEW OTHER PROMISING TECHNIQUES, AND WHY WE SHOULD PAY ATTENTION

Wood plastic composites are complex, anisotropic, and heterogeneous materials. A key to increasing the share of the WPC materials in the market is developing stronger, highly engineered WPCs characterized by greater structural performance and increased durability. These are achieved by enhanced manufacturing processes, more efficient profile designs, and new formulations providing better interaction between the wood particles and the plastic matrix. Significant progress in this area is hard to imagine without better understanding of the composite performance and internal bond durability on the micro-mechanical level, and reliable modeling based on that understanding. The objective of this paper is to present a brief review of promising material characterization techniques based on advanced imaging technologies and inverse problem methodology, which seem particularly suitable for complex heterogeneous composites. Full-field imaging techniques and specifically X-ray computed tomography (CT) combined with numerical modeling tools have a potential to advance the fundamental knowledge on the effect of manufacturing parameters on the micromechanics of such materials and their response to loads and environmental exposure

Strain distribution and load transfer in the polymer-wood particle bond in wood plastic composites

This is the publisher’s final pdf. The published article is copyrighted by Walter de Gruyter GmbH and can be found at: http://www.degruyter.com/view/j/hfsg.The load transfer between wood particles and\ud the matrix was analyzed by observation of the strain patterns\ud in thin films of high density polyethylene (HDPE)\ud with embedded wood particles subjected to tensile loading.\ud Optical measurement techniques based on the digital\ud image correlation (DIC) principle were employed for quantitative\ud measurement of strain distributions on the surfaces\ud of the specimens. Interpretation of these measurements in\ud terms of load transfer between the particle and the matrix\ud below the surface proved challenging and required a structured\ud approach. In this paper, quantitative descriptors were\ud selected as synthesized metrics to support the quantitative\ud interpretation of the measured strains. X-ray computed\ud tomography (XCT) scans were used to assess the effect of\ud the position of the particles in the film specimens on the\ud strains patterns observed on the surface

On the need for reliable rolling shear characteristics in CLT lamellas and for efficient related test methods

Effective modeling of structural behavior of cross-laminated timber (CLT) elements requires reliable input on the mechanical properties of its laminations. The cross-lamination of layers provides for dimensional stability of CLT elements. In this arrangement, however, all laminations in shear walls and the layers of floor elements oriented perpendicular to the major strength axis transfer shear stress in the radial–tangential plane, often referred to as rolling shear. It is among the least documented characteristics of wood, since it had been of marginal interest for structural lumber and engineered wood composites until the emergence of CLT. While the numerical models may easily account for the contribution of rolling shear in the immediate and long-term deformations of laminated panels, simulations are charged with wide margins of uncertainty because of shortage of reliable experimental data. Rolling shear is not the easiest property to measure, and it received only limited coverage in the literature [1-7]. What has been documented was that the rolling shear strength and stiffness in the cross-layers in CLT floor panels is related to the species, density, growth ring orientation, and manufacturing parameters, but there is no evidence for a meaningful correlation with the grade of lumber, whether established by visual or machine grading. In the presentation, we will discuss the pressing need for reliable data on rolling shear characteristics in clear wood and in structural lumber, their statistical distributions in species important for CLT industry, as well as for efficient test methods to allow generation of relevant data in timely manner. Prototype methods and preliminary data will be presented