Modification Of Defatted Soy Flour Made Wood Adhesive

With the restrictions of formaldehyde emission in wood processing product more and more stringency on the worldwide, searching for a non-formaldehyde wood adhesive has become an important research topic of timber industry. Soy as an ideal adhesive material has many advantages, such as renewable, easy cultivation, low cost, environmental performance. But traditional soy based adhesives have not water-resistance, need for modification. Therefore, focus on the modification of soy based adhesive has become a research hotspot of timber industry on the worldwide.In this paper, defatted soy flour (DSF) was used for raw materials, and the effects of the acid (acid H), base (base N), acid-base (H acid and base N) and acid-salt-base (acid H, salt F and base N) on soy based adhesive were investigated at first; secondly, the influences of reagents'reaction time on water-resistant bonding strength of soy based adhesive were researched; third, the optimum formula was used for studied the hot-pressing technology of plywood; then Fourier Infrared Spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) were used for analysis the products which from preparation of the modified soy based adhesive, and then the effects of active substance (melamine, dicyandiamide, urea, acrylamide and triethanolamine) on water-resistant bonding strength of modified soy based adhesive were studied further; final, the FTIR, XPS and thermal gravimetric (TG) were used for analysis the products which from process of soy based adhesive modified by active substances to researched the mechanism of increasing water-resistant bonding strength .The dried bonding strength of the plywood which bond with traditional soy based adhesive was 1.70MPa. But all the samples will be delaminated and water-resistant bonding strength was 0MPa, when the plywood test with the request of China National Standard (GB9846.3-2004, plywood typeⅡ). So, the traditional soy based adhesive is the adhesive typeⅢ.The acid H with 38% concentration (38%H) for the modification factor, the effects of 38%H usage (5.9%, 11.9%, 17.8% relative the mass of DSF, the same below) on water-resistant bonding strength of modified soy based adhesive was studied. The results showed that, 38%H can improve the water-resistant bonding strength of modified soy based adhesive, the results were decrease after rise; the best water-resistant bonding strength was 0.48MPa when the usage of 38%H was 11.9%.The base N with concentration 30% (30%N) as a modifier of the soy based adhesive, the study showed that the water-resistant bonding strength of soy based adhesive decrease with the usage of 30%N increase; the best water-resistant bonding strength was 0.43MPa, when the usage of 30%N was 26.6%, but the modified effect of 30%N less than 38%H.The soy based adhesive modified with different ratio acid H and base N, the results show that moderate proportion of 38%H and 30%N have positive correlation on water-resistant bonding strength of modified soy based adhesive; when the usage of 38%H and 30%N were 11.9% and 39.9%, the water-resistant bonding strength of modified soy based adhesive increased to 0.61MPa.The L9 (34) orthogonal test was used on research soy based adhesive which modified by acid, salt and base (H-F-N-DSF). Results show that the salt F and base N have significant impact on water-resistant bonding strength of modified soy based adhesive; when the usage of salt F was 1% or 3%, the water-resistant bonding strength of modified soy based adhesive were better, but 3% salt F results to modified soy based adhesive form lots of bubble and difficult to operation; the water-resistant bonding strength of modified soy based adhesive reached 0.64MPa, when quality of ingredients were DSF: H2O: 38%H: F: 30%N=100: 400: 11.9: 1: 39.9; when the usage of salt F was 0.01 in this formula, the water-resistant bonding strength of modified soy based adhesive enhanced to 0.85MPa, reached the request of China National Standard (GB9846.3-2004,plywood typeⅡ), but the qualified sample only 70%. Therefore, continue to study the formula (DSF: H2O: 38%H: F: 30%N=100: 400: 11.9: 0.01: 39.9) was need.The L9 (34) orthogonal test was used for research reaction time of reagents on the production of H-F-N-DSF. Results showed that reagents reaction time on the production of H-F-N-DSF have an affect on the water-resistance bonding strength, and effects as follow: stirring time of DSF mixed with water (stage A)> the reaction time of the mixture salt F and 38%H was added (stage B)> the reaction time after 30%N was added (stage C), among the three-stage, stage B have significant impact; when the reaction time of stage A, stage B and stage C were 60min, 30min and 10min, the best water-resistance bonding strength of H-F-N-DSF was 0.89MPa, and the qualified sample was 80%.The L9 (34) orthogonal test was used on research hot-pressing technology of H-F-N-DSF. Results showed that hot-pressing technology of H-F-N-DSF have an affect on the water-resistance bonding strength, and effects as follow: hot-pressing temperature> unit pressure> hot-pressing time, among the hot-pressing technology, hot-pressing temperature have significant impact; when hot-pressing temperature, unit pressure and hot-pressing time were 140℃, 1.0MPa and 1.25 min ? mm-1, the best water-resistance bonding strength of H-F-N-DSF was 0.91MPa, and the qualified sample was 70%.FTIR was used for analysis the products which from preparation of H-F-N-DSF, the analysis showed that amide identity absorption bands I,ⅡandⅢwere existence in all samples; when soy based adhesive was modified by acid and salt will form lots of–COOH and -NH3+, and identity absorption peaks of C=O in -COOH appeared on 1537cm-1, the amide absorption bandsⅡdecreased from 1570cm-1 to 1537cm-1; further modified by adding 30% N, that neutralized with -COOH, the 1725cm-1 absorption peak disappeared, and form width strong peak with 1650.75cm-1 absorption; curing H-F-N-DSF does not exist-NH3+, the amide absorption bandsⅡ(1570 cm-1) reappear.XPS was used for analysis the products which from preparation of H-F-N-DSF, the analysis showed that the C1s binding energy of elements C have five states, that was 284.6eV, 286.1eV, 287.7eV, 289.1eV and 289.2eV; the N1s binding energy of elements N have two states, that was 399.8eV and 401.11eV; the O1s binding energy of elements O have three states, that was 532.00eV, 532.98eV and 533.77eV; from this, we can analyze, after DSF was modified by the acid and salt, the high-level structure of protein was damaged and a small amount of amido link was hydrolyzed by acid and some decarboxylation happened on the carboxyl, elements C and O of surface decrease compared with the DSF; after adding base, amido bond acid hydrolysis was terminated and the basic hydrolysis occurrence, and part of amino on peptide linkage was removed and escaped as ammonia, and the content of element N decreased, element O increased; after modified soy based adhesive curing, new amido bond formation, the content of surface element O decreased rapidly.In the above analysis, active substances were used for modified H-F-N-DSF to enhance its stability and water resistance. The results showed that, in the range of the experiment, the water-resistant bonding strength of modified soy based adhesive were instability when melamine, urea and triethanolamine as modifiers; dicyandiamide was a good modifier, the water-resistant bonding strength of H-F-N-DSF which modified by 4.5% dicyandiamide reached 0.80MPa, and the qualified sample was 80%; the optimum formula of H-F-N-DSF modified by dicyandiamide (H-F-N-S-DSF) as follow: DSF: H2O: 38%H: F: Dicyandiamide: 30%N=100: 400: 11.9: 0.01: 4.5: 39.9. FTIR was used for analysis H-F-N-S-DSF, the analysis showed that characteristic absorption peaks of–C≡N and -C=N in Dicyandiamide still existence, after Dicyandiamide reaction 1 hour; after the H-F-N-S-DSF curing the characteristic absorption peaks of -NH3 + (1596.84 cm-1) disappeared, new amido bond of H-F-N-S-DSF was formed during cure and cross-linking each other.XPS was used for analysis H-F-N-S-DSF, the analysis found that after the Dicyandiamide was added the surface content of elements N and O improved; the surface content of element N decreased when base was added, which indicated that amido bond acid hydrolysis was terminated and the basic hydrolysis occurrence, and part of amino on peptide linkage was removed and escaped as ammonia. In H-F-N-S-DSF, the surface content of element O reduced, which illustrated that the primary amino groups generated by acid hydrolysis of Dicyandiamide were combined with -COO- and formed of -COONH3- structure, and part of the hydrophobic groups turn out, the stability of raise; after H-F-N-S-DSF curing, the surface content of element O continued to decline, which indicated that the active groups of H-F-N-S-DSF further polycondensation and cross-linking as -COONH3- structure in the curing process.TG was used for analysis on the DSF, H-F-N-DSF and H-F-N-S-DSF, the analysis found that the maximum weight loss rate of DSF was 1.85%/min at 76.2℃, the largest weight loss rate of H-N-S-DSF was 2.48%/min at 67.0℃, and the largest weight loss rate of H-F-N-S-DSF corresponding to the minimum temperature for the 51.7℃, weight loss rate was 3.61%/min; which indicated that its water binding (van der Waals force) decreases after the soy based adhesives were modified, some hydrophobic group of protein molecules outward, a better water-resistance structure was formed; when the temperature reached 130℃, the three samples have the same weight loss rate, in other side, the number of new generate amide H-F-N-S-DSF> H-F-N-DSF, so, the cross-linked structure of H-F-N-S-DSF was more stable.By the cost estimates, H-F-N-S-DSF for 1666 yuan/ton, high than UF resin adhesive 308 yuan/ton, but H-F-N-S-DSF did not contain free formaldehyde, have good environmental performance.The final formula of modified soy based adhesive (mass ratio of ingredients) as follows: DSF: H2O: 38%H: F: Dicyandiamide: 30%N=100: 400: 11.9: 0.01: 4.5: 39.9, and hot-pressing technology are pressing temperature 140℃, unit pressure 1.0MPa, hot-pressing time 1.25min?mm-1; the water-resistant bonding strength of plywood reached the request of China National Standard (GB9846.3-2004,plywood typeⅡ,≥0.80MPa), the qualified samples≥80%, good stability; the cost of modified soy based adhesive is slightly higher than the UF resin adhesive, but it has good environmental performance and ecological benefit significantly.