In order to investigate an optimum relation between temperature and duration at hot-pressing in the dry-process hardboard manufacturing system, experiments were designed, utilizing oak fiber mat containing 2% phenolic resin and 1.5% wax, hot-pressed under two-stage pressing diagram (Figs. 1, 2), in which the second stage hold pressures were elevated with higher temperatures.
Thermal decomposing reaction was found during the hot-pressing of mats (Fig. 5). Reaction was the first order one and the specific rate constant at each temperature could be calculated as Table 1 from the data of Fig. 6. Also activation energy could be found as 24.3kcal/mole, which was comparable with other investigators (Literature 11).
On the basis of manufacturing quality board economically, for example, having 400kg/cm² of modulus of rupture and 25% of water absorption without defects such as puncture, blown out or dark spot, following hyperbolic relation could be derived (Figs. 8, 9) : t (T-162) =4900 (z-1.7) where t : Total hot-pressing duration in seconds.T : Hot-platen temperature in °C.z : Board thickness in mm.This shows that the presence of thermal decomposition is necessary on the dry-process hardboard manufacturing and satisfactory board would not be obtained, if mats were hot-pressed below 162°C. Also this equation cannot apply to thinner boards than 1.7mm. It is found empirically that, in case of thinner boards than 2.0mm, hot-pressing temperature must be lowered to avoid the occurrence of defects, compared with a thicker board manufacturing. This is based on the reason that thinner mats are easily compressed to higher densities under higher temperatures and longer pressing durations as employed in the thicker boards. Other reasons are press operational difficulties and press construction economics accompanied with rapid press cycle in the thinner boards.
Mat moisture is another important process variable which make board defective at pressing, because the compression of mats is accelerated with the presence of moisture. From the experience, punctures or dark spots would be often found over 1.2g/cm³ of the board densities. Optimum correlation was found between mat moisture and pressing schedule, particularly for the first stage duration, and an equation could be derived as follows (Fig. 10) : t₁ (m-3) =0.83 (279-T) where t₁ : The first stage holding duration in seconds.m : Fiber mat moisture content in %.T : Hot-platen temperature in °C. From this equation, it would be found that temperatures higher than 279°C would be unnecessary for manufacturing satisfactory boards. The results of Fig. 812 would be useful for mill operation with lower fraction defective production of the dry-process hardboard.

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The changes of polysaccharides during ordinary and two per cent sodium borohydride added kraft cooking of Shirakaba birch were studied. The cooking cycle was divided in five stages, in each stage the changes of polysaccharide from wood residue (pulp) and cooking liquor were observed.
The effects of borohydride addition to yield of pulp were considerably large at first stage, but only small toward the end of the cooking cycle.
Addition of borohydride saves the peeling reaction of polysaccharides, and consequently alkali consumption will be lowered. According to avoid the lowering the yield of pulp by high hydrogen ion concentration, low ratio of effective-to-wood must be used.
Stabilization of xylan by borohydride is not so noticeable as glucomannan. Even in ordinary kraft cooking liquor, much amount of xylan was found. Addition of borohydride increased the amount of xylan in cooking liquor and stabilization of xylan in cooking liquor was higher than that in wood residue. Xylan had also different behavior in this point from glucomannan.
These facts indicate that xylan is more soluble in alkali and has higher resistance to peeling reaction than glucomannan. It seems to be due to branching structure of xylan. Recent report³²⁾ about chemistry of xylan indicates the presence of branching in xylan molecule.

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Small-scale pilot-plant experiments were conducted on the evaporation of decalcified sulfite spent liquor (I) in a long-tube vertical evaporator. The evaporator used had only one heating tube 2.54cm in ID and 3.5m in length (heating surface 0.28m²). The feed concentration was varied from 10 to 50% (by wt.). In all cases, the feed rate was 34±2l/h, the boiling point was 95±1.0°C., and the temperature drop was 10.0±1°C. Also, for purposes of comparison, kraft black liquor (II) was evaporated under similar conditions in the same evaporator.
The over-all heat-transfer coefficients U (kcal/m²h°C) in the evaporation of I from given initial concentrations were as follows : (The initial and final concentrations in weight per cent are given in order in parentheses.) 2, 800 (10, 20%), 2, 600 (20, 30%), 2, 400 (27, 40%), 2, 100 (36, 50%), and 1, 700 (45, 60%). The boiling point rises were 2.7, 4.0 and 5.0°C., respectively, at concentrations of 40, 50 and 55%. The values of U in the evaporation of II under similar conditions were nearly equal to the corresponding values found in the experiments with I. The boiling point rises were 4.0, 6.4 and 8.0°C respectively, at concentration of 4.0, 50 and 55%.

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