Adhesive and hydrophobic properties of alkalimodified soy protein (AMSP) and trypsin-modified soy protein (TMSP) on wood were investigated. Modifying soy protein (i) under moderate alkaline conditions (pH 10.0 at 50°C) and (ii) with trypsin, enhanced adhesive strengths (730 and 743 N, respectively) compared with unmodified soy protein (340 N). Hydrophobicities of AMSP, TMSP, and unmodified soy protein isolate by sodium dodecyl sulfate binding and 1-anilino-8-naphthatene sulfonate methods were 7.6, 6.4, 5.0 and 39, 27, 13, respectively. Modified soy protein adhesives with higher hydrophobicities (AMSP and TMSP) had enhanced water-resistance properties.alone may not yield optimal results, combination treatments of alkaline pH coupled with a moderate temperature were explored.Water resistance is an important glue property that determines adhesive bond durability (11). To improve water resistance of soy protein glue, several cross-linking agents, such as calcium salts and carbon disulfide, have been used (11). Adhesives prepared from soy meal have poor water resistance due to the presence of carbohydrates (1 t). Improved adhesive strength and water resistance have been observed in glue prepared from trypsin-modified soy protein (TMSP) (13). Since limited information is available on the adhesive and water-resistance properties of soy protein isolates (SPI) modified by combinations of alkali and heat treatments, we investigated the effects of these treatments.Preparation of modified protein: TMSP. TMSP was prepared according to the method described by Kalapathy et aL (13). A 7% solution of SPI with trypsin (E/S = 1:50, pH 8.0) was incubated at 37°C for 1 h in a shaker (180 rpm). The enzyme was inactivated by heating at 90°C for 3 min, and the product was frozen and freeze-dried~ Degree of hydrolysis. Degree of hydrolysis was determined by measuring insoluble nitrogen in 10% trichloro

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Fibers were produced from soy protein isolate by both wet-spinning and extrusion. In the wet-spinning process, aged, alkaline protein solution was forced through a spinnerette into an acid coagulating bath. In the extrusion process, a twinscrew extruder forced a protein isolate-water mixture through a die. The physical properties of the fibers were measured at various water activities. The fibers produced by both methods were brittle and lacked tensile strength (tenacity). The addition of glycerol reduced brittleness in extruded fibers. Zinc and calcium ions decreased the brittleness of wet-spun fibers. The tenacity of soy fibers was significantly improved by post-spinning treatments, including acetic anhydride, acetaldehyde, glyoxal, glutaraldehyde, a combination of glutaraldehyde and acetic anhydride, and stretching. The best extruded fibers were produced with a mixture of 45% soy protein, 15% glycerol, and 40% water, finished with a combination of glutaraldehyde and acetic anhydride and then stretched to 150% their original lengths. The best wet-spun fibers were produced with a 19.61% soy protein suspension at pH 12.1; coagulated in a 4% hydrochloric acid solution that contained 3.3% sodium chloride, 3.3% zinc chloride, and 3.3% calcium chloride; and followed by treatment with 25% glutaraldehyde and stretching to 1 70% their original lengths.

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Adhesive properties of trypsin‐modified soy proteins (TMSP) on woods were investigated. A simple method developed in our laboratory, consisting of measuring the force required to shear the bond between glued wood pieces in the Instron universal testing machine, was used to examine adhesive strength of modified soy proteins on wood. Adhesive strength of TMSP was measured for cold‐pressed (ambient temperature for 2 h) and hot‐pressed (60, 80, 100, and 120°C for times varying from 0.5 to 2.5 h) woods. Of the woods examined, soft maple gave the highest strength [743 Newtons (N) at a protein glue concentration of 2 mg/cm2]. For soft maple and cold‐pressing, TMSP at 2 mg/cm2 gave twice the adhesive strength of unmodified protein controls, 743 vs. 340 N. Also, the adhesive strength of TMSP increased from 284 to 743 N as glue concentration was increased from 1 to 2 mg/cm2. However, hot‐pressing of wood pieces beyond 1 h at 120°C and 30% relative humidity resulted in decreased adhesive strengths of TMSP compared to controls. Further, adhesive strengths of hot‐pressed glued wood samples decreased when the relative humidity at which they were kept for curing increased from 30 to 60%. This negative effect of increased humidity on adhesive strengths of glued wood pieces was not observed with cold‐pressed TMSP.