Hiromu Kajita

The modification of wood by treatment with low molecular weight phenol-formaldehyde resin: a properties enhancement with neutralized phenolic-resin and resin penetration into wood cell walls

To enhance dimensional stability and biological properties, low molecular weight phenolic resins of a conventional alkaline type and neutralized type were impregnated into Japanese cedar wood (Cryptomeria japonica D. Don) and heat-cured. The treatment with the neutralized type resin retained the original wood color, whereas the alkaline treatment changed the color of wood to red-brown. The concentrations of the resin solutions and the weight gains due to the resin loading of wood after treatment were highly correlated, and the target resin loading could be assessed from the solution concentration. A high dimensional stability of 60% antiswelling efficiency was attained when both types of resins were impregnated at about 30% resin loading and no significant difference was recognized between the two. To suppress decay attack from brown-rot and white-rot fungi, 15% and 10% resin loading due to treatment was required for the neutralized and alkaline types of phenolic resins, respectively. The penetration of resin into wood cell walls was investigated by means of light microscopy, Scanning Electron Microscopy (SEM), and Electron Probe X-ray Microanalysis (EPMA). A m-Bromophenol-formaldehyde resin of three levels of an average molecular weight was used to detect the presence of resin by bromine signals. The phenolic resins with low and medium molecular weights (290 and 470) were shown to penetrate into the cell walls the furthest, thereby contributing to the enhancement of dimensional stability and decay resistance in the resin-impregnated wood. Also, for phenolic resin with a high molecular weight (820), only the resin components of low molecular weight appeared to be present in the walls, making very little contribution to the dimensional stability.

Improvement mechanism of bondability in UF-bonded reed and wheat straw boards by silane coupling agent and extraction treatments

The effects of silane coupling agents and extractives on the wettability of reed and wheat straws were investigated. The inherent wettability of these materials was low but could be significantly improved by treating with silane coupling agents. The degree of improvement achieved by each silane coupling agent was different: Vinyl silane had almost no effect on wettability, epoxide silane was found to be more effective for reed straw, and amino silane was better for wheat straw. The wettability of these materials could also be improved by ethanol-benzene extraction, which resulted in more improvement in wheat straw than reed straw. The analyses of untreated reed and wheat straws by electron spectroscopy for chemical analysis (ESCA) revealed that there was much silicon on both the outer and inner surfaces of the former but only on the outer surface of the latter. The influence of hot-water extractives and silane coupling agents on the gelation time and pH of urea formaldehyde (UF) resin was also examined. The addition of extractives was found to increase the gelation time. Amino silane greatly retarded the gelation of OF resin, whereas epoxide and vinyl silanes had no influence on resin gelation. This retardation was found to be due to an increase in the pH of the resin.

Chemical treatment of wood for musical instruments

After a review of the structure of wood concerning its acoustic properties and a discussion of the merits and demerits of wood as a material for making soundboards of stringed instruments, the effects of three chemical treatments (a low molecular weight phenolic resin treatment, a resorcin/formaldehyde treatment, and a saligenin/formaldehyde treatment) on the acoustic properties of Sitka spruce wood are reported and compared with those of formaldehyde treatment. All three chemical treatments increased the specific dynamic Young’s modulus and greatly decreased damping (tan δ) without greatly increasing specific gravity. The range was almost equivalent to that with formaldehyde treatment whose superb effects have already been confirmed in the violin. With saligenin/formaldehyde treatment, the frequency dependence of tan δ could be controlled over a wide range by changing the saligenin concentration. In all treatments, hygroscopicity was reduced and dimensional stability was improved significantly.

Chemical characteristics of surfaces of hardwood and softwood deteriorated by weathering

The factors that cause weather-induced deterioration of wood surfaces were determined by chemical and spectroscopic analyses. Albizzia (Paraserianthes falcata Becker.) and sugi (Cryptomeria japonica D. Don) were exposed to two temperate conditions of natural weathering with and without rainfall and to accelerated conditions of artificial weathering coupled with ultraviolet (UV) light irradiation and water flashing. Infrared spectroscopic analysis showed that the oxidative reaction of lignin was observed under all conditions of weathering for both wood species. However, a marked decrease in lignin and hemicellulose content were recognized when albizzia woods were exposed to weathering with water. Lignin content in the softwood sugi did not decrease as much as in albizzia even in the presence of water, but the modification of lignin macromolecules was assumed to be accelerated by water, as seen by electron spin resonance spectroscopy. These results showed that the presence of water promotes the weathering deterioration of wood under UV irradiation.

Improvement of physical and biological properties of particleboards by impregnation with phenolic resin

SummaryParticleboards were treated with a low molecular-weight phenol-formaldehyde resin and their properties were evaluated. Particles were dipped into aqueous solutions of resin or sprayed with resin solutions before spraying the conventional phenol-formaldehyde resin adhesive, or sprayed with a mixture of low molecular-weight resin and the adhesive resin in a single step. Though mechanical properties and dimensional stability of the phenolic-resin-treated boards were affected considerably by the incorporated resin loading (IRL), the methods of treatment did not produce significantly different results. After boiling for 2-hours, the boards treated at 10% IRL retained 80% of their strength values in the dry condition. The internal bond strength increased with increasing IRL values, and the boards with 20% IRL showed twice the value of untreated controls at the same level of board density. Treated particleboards showed a dramatic reduction in the rate of swelling even at low resin loading. Results obtained from accelerated laboratory tests of biodegradation suggested that incorporated resin-solids worked well to enhance decay and termite resistance of particleboards. For a brown-rot fungus, the weight loss was substantially reduced at 15% IRL, whereas attack was suppressed almost entirely even at low resin loadings for the white-rot fungus.

Durability evaluation of particleboards by accelerated aging tests

SummarySpecimens of four commercially produced particleboards were exposed to various accelerated aging treatments: 1) 6-cycle ASTM D-1037 exposure, 2) 6-cycle WCAMA exposure, 3) BS 5669 test, 4) cyclic soak-dry test, and 5) cyclic boil-dry test. Thickness swelling (TS) and internal bond strength (IB) were measured after each step of each cycle. Phenol and phenol (face)/isocyanate (core)bonded boards are more durable than urea and melamine urea bonded boards. The effect of treatment 1) is most severe on TS and IB retention, followed in order by treatments 2), 5), 4) and 3). When the value of springback reached about 35%, IB became equal to zero.

Chemically modified particleboards.

ABSTRACT Studies were carried out on chemically modified particle- and/or fiber-boards to improve their mechanical properties, dimensional stability, and biological properties. The technology developed from chemical modification of solid wood was applied to these reconstituted wood products. This report describes the production and properties of the chemically modified boards.

Oriented strand and fiber boards.

ABSTRACT Oriented mat-forming methods that employ mechanical and electrostatic orientation were studied. The effects of some variables on the degree of particle alignment and on the physical and mechanical properties of oriented boards were investigated. A production system applying the electrostatic method, in which electrodes are located only on the reverse side of the forming belt, is proposed.

Wood and Wood Based Materials. Effects of Moisture Content on Bending Properties and Creep Behavior of Phenolic-Resin-Treated Particleboards.

Low molecular-weight (Mn=369) phenolic impregnating resin and high molecular-weight (Mn=1143) bonding phenolic resin were mixed and sprayed on Japanese cedar (Cryptomeria japonica) semi-strand (22.8mm×2.6mm×0.6mm) particles, and then 10mm thick single-layer particleboards (PBs) (SG=0.7) were produced. The effects of moisture content (MC) on bending properties and creep behavior of the PBs were investigated. The maximum value of modulus of rupture (MOR) was achieved at 7 to 9 percent MC, and at 19 to 28 percent MC the PBs retained 60 to 70 percent of the MOR value in the oven dry condition. The modulus of elasticity of PBs decreased with increasing MC. The creep compliance of PBs increased with increasing MC and decreased with increasing total resin content. The creep compliance after 48 hours under bending load at 7 to 9 percent MC was about 1.8 times the value in the dry condition.