Chung-Yun Hse

Effects of Reaction pH on Properties and Performance of Urea-Formaldehyde Resins

Urea formaldehyde resins were formulated with combination variables of three reaction pH (1.0, 4.8, and 8.0) and four molar ratios of formaldehyde to urea (2.5, 3.0, 3.5, and 4.0). The resins were prepared by placing all formaldehyde and water in reaction kettle and pH was adjusted with sulfuric acid and sodium hydroxide, respectively. Urea was added in 15 equal parts at 1-minute intervals. The proportion of high molecular weight products in the resin increased substantially äs the reaction pH decreased. Furthermore, the F/U molar interacted with reaction pH to effect resin molecular weight. At acidic pH, the high molecular weight products increased äs F/U ratio decresed; while, at alkaline pH, little difference was evident between the high or low molecular weight products at various F/U ratios. The formation of a high percentage of uron derivatives under strong acidic conditions also indicated these resins differed considerable from conventional UF resins formulated in the past. Panels bonded with resins catalyzed at strong acidic conditions resulted in lowest formaldehyde emission but slightly lower bonding strength. Of the three pH conditions evaluated in the study, both weak and strong acid catalysts Systems are not commonly used in conventional UF resin formulation. Based on the bond strength and formaldehyde emission data, however, the weak acid catalysts seems to provide the best compromise between the strong acid and the conventional alkaline-acid catalyst System currently used for formulating UF resin wood adhesives.

Curing property and plywood adhesive performance of resol-type phenol-urea-formaldehyde cocondensed resins

The curing processes and thermal properties of resol-type phenol-urea-formaldehyde cocondensed resins, which were prepared by alkaline treatments of the cocondensed resins once synthesized from UF-concentrate and phenol, were investigated by torsional braid analysis. The resol-type cocondensed resins displayed almost the same curing behaviors and heat-resistance as a commercial resol. Their apparent activation energies determined by measuring temperature dependence of gel time were almost identical with that of resol, and quite different from that of UF resin. Their plywood adhesive performances were evaluated with a cyclic 4-hour boil test and a 72 hour boil test. The plywood test results passed the requirements for the JAS special grade structural plywood

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.

Rapid prediction of wood crystallinity in Pinus elliotii plantation wood by near-infrared spectroscopy

Crystallinity is an important property of woody materials; it responds to tree growth traits, structure, and chemical composition, and has a significant effect on Young’s modulus, dimensional stability, density, and hardness, etc. The ability of near-infrared (NIR) spectroscopy coupled with multivariate analysis to rapidly predict the crystallinity of slash pine (Pinus elliotii) plantation wood was investigated. The results showed that the NIR data could be correlated with the X-ray diffraction (XRD)-determined crystallinity of slash pine wood by use of partial least squares (PLS) regression, producing excellent coefficients of determination, r2, and root mean square error of calibration, RMSEC. The use of either reduced spectral ranges or the selection of certain wavelengths consistent with known chemical absorptions did not have any detrimental effect on the quality of PLS models allowing the use of inexpensive, small, and portable spectrometers. These studies show that NIR spectroscopy can be used to rapidly predict the crystallinity of slash pine wood.

Utilization of softwood kraft lignin as adhesive for the manufacture of reconstituted wood

Abstract Reaction conditions for hydroxymethylation of pine kraft lignin (KL) were optimized by kinetic studies of the reaction. Characterization of the resulting hydroxymethylated kraft lignin (HMKL) indicated that about 0.36 mole of the - CH2OH/C9 unit was introduced into the lignin under the optimal reaction conditions, of which about 0.33 mole was introduced into C-5 of guaiacyl moieties via Lederer-Manasse reaction. This result was confirmed by 13C-NMR spectrum of 13C enriched HMKL prepared from KL and 13CH2O (about 7 atomic%) under the same reaction conditions. Lignin-phenolic resins were formulated by blending the HMKL with phenol-formaldehyde (PF). A 50/50 blending of HMKL/PF resulted in a bond strength of about 65 psi in laboratory boards made with sweetgum flakes. In general, bond strength increased with an increase in the PF. Studies on effects of process and wood variables indicate that such resin could yield satisfactory boards made with red oak, black gum, red maple, post oak and sweetgum fl...

An Investigation of Selected Factors that Influence Hardwood Wettability

Summary Wettability of sanded and non-sanded transverse and tangential sections of 22 southern hardwoods species was judged by measurement of contact angles using phenol formaldehyde resins. As expected, contact angle values on transverse sections were higher than those on tangential sections for both sanded and non-sanded surfaces. On sanded surfaces, hackberry had the highest mean contact angle (64.7°), and black oak had the lowest mean contact angle (50.1°). On non-sanded surfaces, winged elm had the highest mean contact angle (59.1°), and sweetgum had the lowest mean contact angle (45.9°). In addition, 4 of the 22 species (southern red oak, sweetgum, white oak, and post oak) were selected to investigate the effect of oven-drying, air-drying, and free-drying on wettability. The mean transverse contact was 2.1°–29.0° and 5.1°–31.5° higher than radial and tangential values, respectively. The contact angle pattern typically displayed for a given species and plane was generally oven-dry > air-dry > freeze-dry. The species pattern for most methods and planes was: sweetgum > white oak > post oak > southern red oak. White oak and post oak gave similar contact angle values.

Fractionation of heavy metals in liquefied chromated copper arsenate 9-treated wood sludge using a modified BCR-sequential extraction procedure

Chromated copper arsenate (CCA)-treated wood was liquefied with polyethylene glycol/glycerin and sulfuric acid. After liquefaction, most CCA metals (98% As, 92% Cr, and 83% Cu) were removed from liquefied CCA-treated wood by precipitation with calcium hydroxide. The original CCA-treated wood and liquefied CCA-treated wood sludge were fractionated by a modified Community Bureau of Reference (BCR) sequential extraction procedure. The purpose of the BCR-sequential extraction used in this study was to examine the availability of CCA metals in treated wood for reuse. Both As and Cr had a slightly higher concentration in the sludge sample than in original CCA-treated wood. The sequential extraction showed that As and Cr were principally existed in an oxidizable fraction (As, 67%; Cr, 88%) in original CCA-treated wood. Only 1% of both As and Cr were extracted by hot nitric acid with the last extraction step. The distribution of As and Cr changed markedly in liquefied CCA-treated wood sludge. The amount of As in the exchangeable/acid extractable fraction increased from 16% to 85% while the amount of Cr increased from 3% to 54%. Only about 3% of As was present in the oxidizable fraction. However, there was still about 34% of Cr in the same fraction. Based on these results from sequential extraction procedures, it can be concluded that the accessibilities of CCA metals increase markedly by the liquefaction-precipitation process.

Isolation and characterization of cellulose nanofibers from bamboo using microwave liquefaction combined with chemical treatment and ultrasonication

Cellulose nanofibers were successfully isolated from bamboo using microwave liquefaction combined with chemical treatment and ultrasonic nanofibrillation processes. The microwave liquefaction could eliminate almost all the lignin in bamboo, resulting in high cellulose content residues within 7min, and the cellulose enriched residues could be readily purified by subsequent chemical treatments with lower chemical charging and quickly. The results of wet chemistry analyses, SEM images, and FTIR and X-ray spectra indicated the combination of microwave liquefaction and chemical treatment was significantly efficient in removing non-cellulosic compounds. Ultrasonication was used to separate the nanofibrils from the purified residues to extract nanofibers. The TEM images confirmed the presence of elementary fibrils, nano-sized fibril bundles, and aggregated fibril bundles. As evidenced by the TGA analysis, cellulose nanofibers isolated by this novel technique had high thermal stability indicating that the isolated nanofibers could possibly be applied as reinforcing elements in biomaterials.

Chemical groups and structural characterization of lignin via thiol-mediated demethylation

Abstract A new approach to increase the reactivity of lignin by thiol-mediated demethylation was investigated in this study. Demethylated lignin was characterized by the changes in its hydroxyl and methoxyl groups, molecular weight, and other properties using titration and spectroscopy methods including FT-IR, 1H NMR, UV, and GPC. The total, phenolic, and aliphatic hydroxyl contents in lignin increased while the methoxyl content decreased after demethylation reaction, which indicated the occurrence of demethylation reaction. The results from FT-IR and UV analysis also indicated that the kraft lignin in this study contains mainly guaiacyl moiety and demethylated lignin has a higher guaiacyl content than original lignin. The average molecular weight of lignin decreased after demethylation reaction due to the cleavage of ether linkages in lignin macromolecules. No severe degradation of lignin was observed during the demethylation reaction.

Liquefaction of CCA-treated wood and elimination of metals from the solvent by precipitation

Abstract Spent chromated copper arsenate (CCA)-treated wood was liquefied in polyethylene glycol 400/glycerin (2:1w/w). Sulfuric acid (95–98%) and ferrous salts (FeSO4·7H2O or FeCl2·4H2O) were used as catalysts and additives, respectively. The resulting liquefied CCA-treated wood was diluted with aqueous solvents and was then mixed with complexion/precipitation agents, followed by precipitation or filtration to remove the toxic metal-bearing sediment. As a result, more than 90% of Cu, Cr or As was removed.