Лако-красочные материалы — производство

As mentioned earlier, the single largest commercial use of soybean flour in wood glues during the recent past has been as a blend with other adhesive proteins, mainly blood and casein, for bonding interior-grade plywood, doors, and millwork. These blended formula­tions exploit several unique properties of the soybean glues themselves and incorporate useful adhesive characteristics from the other protein materials.

1. Soybean-Blood Glues

For example, a blend of soybean flour with spray-dried soluble animal blood, a fairly expensive but very efficient adhesive protein, yields a glue with the best properties of each material [37]: namely, the cost becomes moderate and the consistency ideal for wood product assembly (slightly granular) because of the soybean flour. The hot-press curing time is very short and the cured glue bonds are considerably more water resistant because of the blood’s thermosetting properties. Fortunately, both proteins require the same neu­tral wetting procedure and strongly alkaline dispersion steps. They are otherwise compa­tible in all proportions, yielding a series of cost/performance-related adhesives. Soybean- blood blend glues were by far the most widely used protein hot-press adhesives for interior structural plywood from the early 1940s until about 1960 [13]. Also, when the oil embargo

Amount

________________________________________________________________________________________________________________________ (kg)

Water at 16-21°C 80.0

Dried soluble animal blood 35.0a

Adhesive-grade soybean flourb 8.5a

74-p. m Wood flourc 5.0a

Pine oil or diesel oil defoamer: mix 4 min or until smooth in a counterrotating mixer 1.5a

Water at 16-21°C: mix 2min or until smooth 195

Fresh hydrated lime (as a slurry in) 4.0

Water at 16-21°C: mix 1 min 8.0

Sodium silicate solution: mix 1 min 22.5d

50% Sodium hydroxide solution: mix 5 min 8.0

Powdered hexamethylenetetramine: mix 3 min 1.0

aNormally dry-blended for easier handling and dust control. b44% protein, specific surface 3000-6000 cm2/g. c0.074 mm (200 mesh) and finer. d8.90% Na2O, 28.70% SiO2, 41° Baume.

of 1973 quickly placed phenolic resin adhesives on allocation through petrochemica1 restrictions, the plywood industry immediately returned to the use of soybean-blood hot-press glues for interior structural grades. Typical examples of low and high-blood- content soybean-blend glues are described in Tables 5 and 6.

Both glues are ready to use when mixed and have a working life of 6-8 h at inside temperatures. Several points of difference between these glues should be noted:

1. The water content of the high-blood-glue formulation is much larger, which offsets most of the material cost increase. This is possible because the ‘‘water

requirement’’ of alkaline-dispersed blood is much higher than that of soybean flour.

2. The order of addition of alkaline dispersing agents in the high-blood mix is partially reversed. Experience has shown that this helps impart a more granular consistency to the dispersed blood, which is otherwise very slick and smooth.

3. The final addition of hexamethylenetetramine illustrates the use of a formalde­hyde donor to partially denature or cross-link the dispersed proteins. This adds further granular character to the mixed glue, lengthens its working life, and improves the water and mold resistance of the cured adhesive film.

4. As with straight soybean glues, the low-blood-content formulation requires a mold-inhibiting ingredient to meet plywood performance standards, whereas the high-blood-content glue does not [24].