Karl Englund

Stress wave sorting of red maple logs for structural quality

Existing log grading procedures in the United States make only visual assessments of log quality. These procedures do not incorporate estimates of the modulus of elasticity (MOE) of logs. It is questionable whether the visual grading procedures currently used for logs adequately assess the potential quality of structural products manufactured from them, especially those for which MOE is of primary concern. The purpose of this study was to investigate the use of stress wave nondestructive evaluation techniques to sort red maple logs for the potential quality of lumber obtained from them. Ninety-five red maple logs were nondestructively evaluated using longitudinal stress wave techniques and sorted into four stress wave grades. The logs were then sawn into cants and lumber. The same procedure was used to obtain stress wave times in the cants and lumber. The lumber specimens were then dried and graded using a transverse vibration technique. The results of this study showed that good relationships existed between stress wave times measured in logs, cants, and the lumber produced from the logs. It was found that log stress wave grades have positive relationships with the lumber grades. Logs with high stress wave grades produced high-grade lumber. These findings indicate that the longitudinal stress wave technique has potential in sorting logs and cants for the production of high MOE products.

Fungal Upgrading of Wheat Straw for Straw-Thermoplastics Production

Combining biologic pretreatment with storage is an innovative approach for improving feedstock characteristics and cost, but the magnitude of responses of such systems to upsets is unknown. Unsterile wheat straw stems were upgraded for 12 wk with Pleurotus ostreatus at constant temperature to estimate the variation in final compositions with variations in initial moisture and inoculum. Degradation rates and conversions increased with both moisture and inoculum. A regression analysis indicated that system performance was quite stable with respect to inoculum and moisture content after 6 wk of treatment. Scale-up by 150× indicated that system stability and final straw composition are sensitive to inoculum source, history, and inoculation method. Comparative testing of straw-thermoplastic composites produced from upgraded stems is under way.

Application of micromechanical models to tensile properties of wood–plastic composites

Wood–plastic composites (WPC) were produced with white birch pulp fibers of different aspect ratios (length-to-diameter), high-density polyethylene, and using two common processes: extrusion or injection molding. Three additive levels were also used: no additive, compatibility agent, and process lubricant. Fiber size was measured with an optical fiber quality analyzer. Tensile properties of WPC were measured and modeled as a function of fiber aspect ratio. Models were fitted to experimental values using the minimum sum of squared error method. A shift from the oriented fiber case (injection molding) to the randomly oriented fiber case (extrusion) was achieved using a fiber orientation factor. Fiber/matrix stress transfer increased with increasing fiber aspect ratio. Stress transfer was reduced with the use of process lubricant. Unexpectedly, the compatibility agent had the same effect. Fiber strength and stiffness contributions to the composite were lower than those of intrinsic fiber properties.

Water sorption and mechanical performance of preheated wood/ thermoplastic composites

Wood samples heat treated at 175°C, 190°C, and 205°C with different amounts of high density polyethylene and coupling agent were used for the production of wood/plastic composites. Measuring water sorption, thickness swelling, and diffusion coefficients of composites for a 40-week period immersion in water showed that composites with wood treatment at 190°C and 205°C had considerably higher water resistance. Adding a coupling agent reduced water sorption, thickness swelling, and diffusion coefficients, more pronounced in composites with untreated wood. Measurements of flexural properties in a control state and after 4 and 12 weeks immersion periods in water proved that heat treatment is an effective way to ease detrimental effects of water on mechanical properties. Modulus of elasticity showed more sensitivity to water exposure than modulus of rupture. Strain at maximum load increased after water exposure. Treating wood at 190°C resulted in good flexural properties and excellent water resistance.

Recycling of carbon fiber-reinforced thermoplastic composite wastes from the aerospace industry:

Post-industrial trimmings and off-cuts of carbon fiber/polyether ether ketone composite were successfully recycled into new composite products. The original composites were thermally characterized by dynamic thermomechanical analysis, differential scanning calorimetry, and thermogravimetric analysis. Melt-bonding and thermoset adhesives were used to bond the carbon fiber/polyether ether ketone. Performance of the bond was evaluated through double lap-shear tests. The carbon fiber/polyether ether ketone scraps were mechanically refined to a variety of elemental sizes, subsequently subjected to high-temperature hot pressing to form panel composites. The influences of element size and processing temperature were evaluated through mechanical testing.

Influence of atmospheric pressure plasma treatments on the surface properties of ligno-cellulosic substrates

Abstract The paper aims at the investigation of atmospheric pressure weakly ionized plasmas with argon and acetylene to deposit plasma-polymerized coatings on wood veneers (birch, maple), cellulose paper, and pine wood flour to modify their surface properties, in particular their topography and wettability. The treatment was performed in a reactor containing an array of high-voltage needles and a grounded metallic mesh as electrodes. The deposition occurred in the discharge downstream of the plasma region. The plasma-polymerized acetylene deposits form spherical nodules on the surface of the substrates and change their wettability from hydrophilic to hydrophobic. The water contact angles of the veneer were determined with a goniometer. The capillary rise was combined with the Washburn equation to assess the change in hydrophilicity of the plasma-treated wood flour.

Rheological properties and tunable thermoplasticity of phenolic rich fraction of pyrolysis bio-oil.

In this work we report on the preparation, characterization, and properties of a thermally treated lignin-derived, phenolic-rich fraction (PRF) of wood pyrolysis bio-oil obtained by ethyl acetate extraction. The PRF was characterized for viscoelastic and rheological behavior using dynamic mechanical analysis (DMA) and cone and plate rheology. A unique thermoplastic behavior was evidenced. Heat-treated PRFs acquire high modulus but show low temperatures of thermal flow which can be systematically manipulated through the thermal pretreatment. Loss of volatiles, changes in molecular weight, and glass transition temperature (Tg) were investigated using thermogravimetric analysis (TGA), mass spectrometry (MS), and differential scanning calorimetry (DSC), respectively. Underlying mechanisms for the thermal and rheological behavior are discussed with regard to interactions between pyrolytic lignin nanoparticles present in the system and the role of volatile materials on determining the properties of the material resembling in several aspects to colloidal suspension systems. Low thermal flow temperatures and reversible thermal effects can be attributed to association of pyrolytic lignin particles due to intermolecular interactions that are easily ruptured at higher temperatures. The thermoplastic behavior of PRF and its low Tg is of particular interest, as it gives opportunities for application of this fraction in several melt processing and adhesive technologies.

Interrelationship between lignin-rich dichloromethane extracts of hot water-treated wood fibers and high-density polyethylene (HDPE) in wood plastic composite (WPC) production

Abstract Hot water extraction (HWE) partially removes hemicelluloses from wood while leaving the majority of the lignin and cellulose; however, the lignin partially migrates to the inner surfaces of the cell wall where it can be deposited as a layer that is sometimes visible as droplets. This lignin-rich material was isolated via Soxhlet extraction with dichloromethane to investigate its rheological behavior in blends with high-density polyethylene (HDPE), a common material in wood plastic composites (WPCs). Pyrolysis gas-chromatography/mass spectrometry (Py-GC/MS) and electrospray ion mass spectrometry (ESI/MS) confirmed that the isolated material is constituted mainly of low-molecular-weight lignin oligomers. The blends of HDPE/isolated lignin, in varying ratios, were tested by means of dynamic rheology. A “shoulder” was found in plots “shear storage moduli (G′) vs. frequency sweep” and a shift of the terminal zone to lower frequencies was observed. Apparently, this shoulder is caused by the elastic contribution of the interfacial tension between the blend components. The rheology of WPCs produced from HWE wood and HDPE shows a similar shoulder in G′ plots, suggesting that the HDPE/lignin blends are in part responsible for the shape of the G′ curves.

Point-to-Point Corona Discharge in Admixtures of Argon, Oxygen, and Acetylene

Multipoint-to-multipoint and multipoint-to-plane electrode geometries have been investigated to enhance corona discharge modes in atmospheric pressure weakly ionized plasma. This paper presents a new geometry approach by a protrusion array over the grounded screen along with a high-voltage (HV) needle array to obtain higher coulombic discharge. It has been observed that needle-to-grounded-screen-protrusion configuration enhances the discharge modes, especially the back corona is enhanced significantly near the protrusions in Ar/C2H2 plasma. A corona mode map has been developed to depict the optimal discharge zones at various HV gaps. Similar investigations were performed in Ar/O2 plasma to study the nature of the current pulses and discharge modes.

Tack and shear strength of hybrid adhesive systems made of phenol-formaldehyde, dextrin and fish glue, and acrylic pressure-sensitive adhesive

Abstract The development of adhesives that have good initial adhesion (tack) that provides improved mat integrity during shape-forming of wood composites has been the subject of recent research. Hybrid adhesives were made based on thermosetting phenol-formaldehyde (PF), to which three tacky adhesives were added: high tack fish glue (FG), dextrin glue (DX) and a commercial acrylic, pressure-sensitive adhesive (PSA). Tacky adhesives were blended with PF at weight levels of 25%, 50% and 75%. The time-dependent tack development of the resulting hybrid adhesives was evaluated by means of a texture analyzer. The bond strength of adhesives was measured after curing by shear block test. PF/DX blends exhibited the highest tack during longer open times, while blends of PF and FG had low tack during shorter times. PF/PSA blends lost their bond strength completely after being heated at the curing temperature of PF. PF/FG blends did not show a significant decrease in bond strength compared to pure PF. The addition of DX had no effect on shear strength at ratios <75%.