The permeability of moisture through the paint film on the wood surface seems to differ from that in the case of an isolated paint film. The main difference is that the swelling of the wooden basis caused by the adsorption of moisture expands the paint on the wood surface, and that subsequently the expansion of the film gives rise to high permeability of moisture through it. In this paper discussion is made on the method to determine the permeability of the paint film on the wood surface on the measurement of the rate of moisture adsorption and desorption of wood coated with four kinds of paint, i.e. aminoalkyd resin paint (AA), nitrocellulose lacquer (NC), polyester resin paint (PE) and polyurethane resin paint (PU). From the adsorption and desorption curves for the painted wood (Fig. 1 and 2), the adsorption and desorption curves for the wooden basis are plotted in Fig. 4 and 5, assuming distribution of moisture within the paint film and the wooden basis which is schematically shown in Fig. 3. The rate of moisture permeation is obtained from inclination of the curves in Fig. 4 and 5, and is plotted against the average moisture content of the wooden basis in Fig. 6. The coefficient of moisture permeation, P, has been calculated, using eq. 5, where Q/tA is the rate of moisture adsorption or desorption from the unit area of the surface, l the thickness of the paint film, ua the equilibrium moisture content for wood at the surrounding humidity, and ub the moisture content of the wooden basis. The coefficient, P, is plotted against the average moisture content of the wooden basis in Fig. 7. The figure shows that the coefficient, P, is slightly increasing with the increasing moisture content of the wooden basis. The comparison of the measured P values with those calculated by eq. 6 from diffusion coefficient, D, density, ρ, and k-value of the isolated paint film shown in Table II indicates that the nature of moisture permeation of the paint film on the wood surface differs from that in the case of an isolated paint film.
This report is made of the measurement of the changes of viscoelastic and dielectric properties and infrared spectrum during curing of polyurethane resin, and of their comparison with the internal stress produced during the formation of the thin resin layer on wood. The results are summarized as follows: (1) In the results on the apparent dielectric loss, is traced the process of freezing in the rotational motion of the segments along the main chain of polymer which contributes to α relaxation. (2) The two peaks are observed in the curve of logarithmic decrement, and they are attributed to the structural changes due to the transition, liquid-to-rubber and rubber-to-glass respectively. (3) The following equation on the modulus of dynamic rigidity has been induced from the results of infrared absorption measurement, and it agrees well with the experimental values. G(t)=ΔG(1-e-t/τ)+G0 τ in this equation is the average relaxation time of the rotational motion of segments along the main chain of polymer, and equals to the reciprocal of rate constant on the reaction between NCO and OH groups. The apparent activation energy calculated from the slope of ln τ-T-1 curve is 6.65kcal/mol. (4) The changes of the internal stress produced during curing of resin layer on wood are also expressed by the segmental motion along the main chain of polymer.
In order to protect wooden boards from weather and wear, to mask their defects and to improve their paintability, studies on the effect on wooden boards of overlaying them with phenolic resin impregnated paper (Phenolic resin sheets) have been carried out by many workers. This paper is a review of the previous papers which have been reported by the author on the phenolic resin sheet overlaid on plywoods. The phenolic resin sheets, or the kraft paper (Base paper) varying in thickness and in resin content, were overlaid on both sides of lauan plywoods either on the strength of their own resinousness or with the use of film glue. The plywoods thus overlaid with the phenolic resin sheets and other plywoods as they were both left exposed outdoors for six years in Tokyo facing south, inclined at 45 degrees to the land surface. The weathered plywoods were respectively examined after the six years' exposure in respect of their water absorbing property, mechanical properties and adhesion strength. From the results it is concluded that by overlaying wood with phenolic resin sheets the two factors mentioned below give the wood effective weather resistance power. (1) Ninty grams per square meter or more solid resin in the overlaying material. (2) Sixteen kilograms per 15 millimeters wide or stronger tensile strength of the cured resin sheet, including the strength of the film glue when it is used, in the cross-grain direction of the face veneer.
In view of the fact that the wettability of wood is an important factor in processing woodworks, chemical and all otherwise, including adhesion, surface coating and impregnation, it is a matter of regret that little study on the wettability of wood has so far been made, and that the method of measurement in that line has not yet been established. In the present paper the principle of the capillary rise method is discussed as an indirect method for measuring the wettability of wood. Wood meal prepared from red lauan (Shorea negrosensis Foxw) timber was used for this experiment, and water was used as wetting liquid. Several glass tubes (Each 300mm high, 2.65cm inside diameter) were filled uniformly with wood meal, and their lower ends were brought down to the water level by means of the sample level adjuster, and the height of the water rising in the wood meal column was measured. The weight of the water absorbed in the wood meal was measured at the same time by means of an apparatus using an U-gauge (An unbonded wire strain gauge type transducer).
As one of the methods for chemical modification of wood, the graft polymerization of MMA to wood was carried out in aqueous suspension in the absence of radical initiators. The wood samples used in the experiment were the hot water extracted and the alcohol-benzene extracted birch wood powder (40-60 mesh). The polymerization was made within glass tubes sealed in vacuum, at 85°C for definite times. The results of the experiment are as follows. (1) The yield of total polymer in the presence of wood takes lower value than the yield of thermal polymerization (That is, the conversion in the absence of wood). It is found that the wood extractives supplied from the wood during the polymerization play an important part in retardation of the polymerization of MMA. Furthermore, in this polymerization system, the wood extractives have no effect on graft polymerization, but they retard homopolymer formation, so that, the more wood extractives there exist, the higher the grafting efficiency is. (2) The graft yield increases linearly with the polymerization time after some induction period, but there is no variation of grafting efficiency with the polymerization time in each definite polymerization condition. (3) When the amount of wood and MMA is fixed and that of the water is variable, the graft yield takes the maximum value with certain amount of water, beyond which the grafting efficiency decreases simultaneously. It can be argued from this that in the condition where the small amount of water exists, the polymerization of MMA occurs predominatingly within the cell wall of the wood, and that in the case where the water exists richly, the polymerization occurs substantially outside the cell-wall of the wood. (4) When both the amount of wood and water is fixed and that of MMA is variable, such a phenomenon as is described in (3) occurs as to the amount of MMA.