Monlin Kuo

Comparison of protein-based adhesive resins for wood composites

The search for new value-added uses for oilseed and animal proteins led us to develop protein-based wood adhesives. Low-fat soy and peanut flours and blood meal were hydrolyzed in an alkaline state, and PF-cross-linked protein resins were formulated by reacting the protein hydrolyzates with phenol-formaldehyde (PF) in solid-tosolid ratios ranging from 70% to 50% hydrolyzates and 30% to 50% PF. Physical properties of medium density fiberboard (MDF) bonded with protein-based phenolic resins were compared to those of boards bonded with ureaformaldehyde (UF) and PF resins, and flakeboard bonded with soy protein-based phenolic resin was compared to PF-bonded board. As MDF binders, adhesive properties of protein-based phenolic resins depended upon protein content of proteinacious materials. MDF board bonded with blood-based phenolic resin was comparable to PF-bonded board and met the requirements for exterior MDF. Boards bonded with soy-protein-based phenolic resin met requirements for interior MDF, while peanut-based phenolic failed to meet some of the requirements. Flakeboard bonded with soy-protein-based phenolic resins was inferior to PF-bonded board but outperformed PF-bonded board in accelerated aging tests. Although they exhibit a slow curing rate, the cost effectiveness and superior dimensional stability of protein-based phenolic resins may make them attractive for some uses.

Ultrastructural changes of photodegradation of wood surfaces exposed to UV

Red pine sapwood transvcrse and radial surfaccs werc exposcd to ultraviolet (UV) light for 3 to 40 days. Effcct of UV Irradiation on ultrastructural changcs of ccll walls wcrc studicd by scanning (SEM) and transmission (TEM) elcctron microscopy. SEM study of transvcrse scctions showcd that during initial stagcs of UV Irradiation, lignin in ccll corncrs and in the compound middlc lamcllac was prcfcrcntially dcgradcd and that the radial middtc lamcllac suhstaincd a grcatcr rate of UV dcgradation than did thc tangcntial middle lamellae. Massive ccll wall dcgradation, äs indicatcd by ccll walll thinning, did not occur until surfaccs wcrc exposcd to UVIight for morc than 10 days. TEM study of radial cell wall surfaces indicatcd that lignin lining the warty laycr was rcmovcd by UV Irradiation in 3 days and that warts wcrc dcstroycd by a U Virradiation in 7 days. UVirradiation of cell wall surfaccs produccd a substantial amount of watcr-solublc dcgradation products. After 30 days of UVirradiation, the S3 laycr was totally rcmovcd and rcvcalcd thc very fragile S2 layer.

Ensiling Corn Stover: Effect of Feedstock Preservation on Particleboard Performance

Ensilage is a truncated solid‐state fermentation in which anaerobically produced organic acids accumulate to reduce pH and limit microbial activity. Ensilage can be used to both preserve and pretreat biomass feedstock for further downstream conversion into chemicals, fuels, and/or fiber products. This study examined the ensilage of enzyme‐treated corn stover as a feedstock for particleboard manufacturing. Corn stover at three different particle size ranges (<100, <10, and <5 mm) was ensiled with and without a commercial enzyme mixture having a cellulase:hemicellulase ratio of 2.54:1, applied at a hemicellulase rate of 1670 IU/kg dry mass. Triplicate 20 L mini‐silos were destructively sampled and analyzed on days 0, 1, 7, 21, 63, and 189. Analysis included produced organic acids and water‐soluble carbohydrates, fiber fractions, pH, and microorganisms, including Lactobacillusspp. and clostridia were monitored. On days 0, 21, and 189, the triplicate samples were mixed evenly and assembled into particleboard using 10% ISU 2 resin, a soy‐based adhesive. Particleboard panels were subjected to industry standard tests for modulus of rupture (MOR), modulus of elasticity (MOE), internal bonding strength (IB), thickness swell (TS), and water absorption at 2 h boiling and 24 h soaking. Enzyme addition did improve the ensilage process, as indicated by sustained lower pH (P < 0.0001), higher water‐soluble carbohydrates (P < 0.05), and increased lactic acid production (P < 0.0001). The middle particle size range (<10 mm) demonstrated the most promising results during the ensilage process. Compared with fresh stover, the ensilage process did increase IB of stover particleboard by 33% (P < 0.05) and decrease water adsorption at 2 h boiling and 24 h soaking significantly (P < 0.05). Particleboard panels produced from substrate ensiled with enzymes showed a significant reduction in water adsorption of 12% at 2 h boiling testing. On the basis of these results, ensilage can be used as a long‐term feedstock preservation method for particleboard production from corn stover. Enzyme‐amended ensilage not only improved stover preservation but also enhanced the properties of particleboard products.

Alkali Treated Kraft Lignin as a Component in Flakeboard Resins

Summary Southern pine kraft lignin was reacted with NaOH (15 and 20% based on dry lignin) at 170, 200, and 250°C for 30 and 60 min. Sweetgum flake boards bonded with phenolic resins containing 50% hydroxymethylated lignin prepared from some of the alkali treated lignins wcre compared with boards bonded with a neat PFresin. Results indicate that boards bonded with lignin-containing resins have a satisfactory bending strength. Boards bonded with resins prepared by reacting lignins with phenol and formaldehyde have better internal bond strength and durability than those bonded with lignin-extended resins. However, there is no evident advantage in using alkali treated lignin in the manufacture of phenol-ligninformaldehyde resins for flakeboard application. NMR spectral analyses indicated that the phenolic hydroxyl content of alkali treated lignins increases with increasing severity of reaction condition. The increase in the phenolic hydroxyl content, however, is accompanied by a decrease in free C5 positions in the guaiacyl moieties due to the formation of GC5-C5G and GCS-CH2-C5G bonds during the reaction. Because of condensation of C5 positions, the degree of hydroxymcthylation of alkali treated lignins with formaldehyde also decreases with increasing severity of the reaction.

Cellular Distribution of Extractives in Redwood and Incense Cedar - Part I. Radial Variation in Cell-Wall Extractive Content

Substantial amounts of extractives were found to be located in the cell walls of redwood and incense cedar heartwood. On the average, incense cedar heartwood contained about 40% less cellwall extractives than redwood heartwood. Redwood outer, intermediate, and inner heartwood contained 50.6 %, 77.6%, and 74.1% cell-wall extractives in these respective regions. The corresponding values for incense cedar heartwood were 39.3 °0, 60.7 °0 and 72.5 %.

Cellular Distribution of Extractives in Redwood and Incense Cedar - Part II. Microscopic Observation of the Location of Cell Wall and Cell Cavity Extractives

Many redwood and incense cedar heartwood tracheid walls and pit structures were deposited with extractives but in varying amounts. Latewood tracheids contained more extractives than earlywood tracheids. Polyphenolic extractives in the cell wall were concentrated in the S 2 layer of the secondary wall. Within the S 2 layer, the inner and outer portions had a higher extractive concentration than the central portion of the layer. There was a general trend for the concentration of extractives to decrease from the lumen inward towards the middle lamella, suggesting that extractives, when they are deposited, infiltrate into the cell wall in the same sequence.

Influence of extractives on bonding properties of white and southern red oak

Abstract White and southern red oak veneers were subjected to four methods of drying followed by five surface treatments. The four drying methods were mill drying at 350°F, laboratory drying at 350 and 212°F, and air drying. The five surface treatments were no treatment, surface scraping, soaking and dipping in 1% NaOH aqueous solution, and water extraction. Plywood panels were prepared by using a phenol-formaldehyde resin. Even with the best drying-surface treatment combination, wood failure was only 35% for white oak and 39% for southern red oak. Overall, mill drying was the best drying method. Soaking the veneers in 1% NaOH solution significantly increased the bond quality. Mill drying of veneers caused water-soluble extractives to migrate from the interior portions to veneer and lathe check surfaces. SEM examinations of the glue failure surface revealed that gluelines failed to adhere to the cell walls. Difficulties in bonding white and southern red oak veneers may be caused by extractive contamination.

NDE OF LUMBER AND NATURAL FIBER BASED PRODUCTS WITH AIR COUPLED ULTRASOUND

Due to the porous nature of wood and natural fiber based products, conventional fluid or gel coupled ultrasonic inspection is unsuitable. Air‐coupled ultrasonic transmission scanning, being non‐contact, is ideally suited for inspecting lumber, wood and natural fiber based products. We report here several successful applications of air‐coupled ultrasound for the inspection of wood. Air‐coupled ultrasonic scan at 120 kHz can easily detect “sinker‐stock” lumber in which bacterial damage of ray tissue cells had occurred during anaerobic pond storage. Channels in ash lumber board caused by insect bore were imaged in transmission scan. Delamination and material inhomogeneities were mapped out in manufactured wood and natural fiber products including medium density fiberboards, compression molded shredded waste wood with formaldehyde resin, and acoustic panels molded with kenaf fibers. The study has demonstrated some of the capabilities of air‐coupled ultrasound in the NDE of forest products.

Preliminary study on chicken feather protein-based wood adhesives

Abstract The objective of this preliminary study was to partially replace phenol in the synthesis of phenol-formaldehyde resin with feather protein. Feather protein–based resins, which contained one part feather protein and two parts phenol, were formulated under the conditions of two feather protein hydrolysis methods (with and without presence of phenol during hydrolysis), two formaldehyde/phenol molar ratios (1.8 and 2.0), and three pH levels (9.5, 10.5, and 11.5). Southern pine fiberboard bonded with feather protein–based resins was fabricated and bending strength, bending stiffness, internal bonding strength, and percent thickness swell were evaluated. Results indicated that the test parameters all significantly affected resin quality. The resin formulated with feather protein hydrolyzed in the presence of phenol, using a F/P ratio of 2.0, and at a pH of 10.5 performed as well as the neat PF resin. Based on our findings, feather protein is a potential cost-effective material for the production of PF-type adhesive resins.

Biomass Protein Adhesives for Biocomposite Manufacturing

This study examines the use of high protein biomass residuals as a partial substitute for formaldehyde based adhesives, combining the biomass with alternative fiber sources including papermill sludge and corn stover. Short-term in-vessel composting was used for biological drying, to reduce moisture and odor while minimizing fiber degradation. Resulting biomass-fiber mixtures were combined with 4 and 6% melamine urea formaldehyde adhesive and subjected to industry standard tests for modulus of rupture, modulus of elasticity, internal bonding strength, wet swelling, and formaldehyde emissions. Results demonstrate the effectiveness of biomass protein as a component of adhesive systems, and indicate considerable potential for combining these residuals into environmentally friendly building materials.