Research On The Soy-based Wood Adhesives By Composite Modification

Along with national real estate, architecture fitment industry and furniture manufacturing boom and the advance of living standards, man-made board industry develops rapidly. Wood adhesives consumed quantities increase sharply year after year, aldehyde based adhesives occupy above 80% of the cumulative production of wood adhesives. Limited resources for petrochemical products, and increasing concern about environmental problems have prompted the development of new, adhesive materials from renewable, environmental friendly resources. Adhesives based on soy protein just satisfy the request, according with the eternal theme of mankindevolutions--diminution of environmental pollution and efficiently utilization of resources,responding to the strategy of sustainable development in the world.However, unmodified soy protein adhesives had low water resistance and low decay resistance which could not satisfy the demand of adhesive used in wood industry. The text started with the analysis about the performance deficiency of soy-based adhesives. Physics and chemistry performance indexes of defatted soy flour material were tested. The research selected the suitable modifier to enhance the hydrophobic strength and adopted the methods of composite with many modifiers by stages. At the same time , an investigation was conducted on samples of the original defatted soy flour, traditional soy adhesives and production of every stage, the FTIR was applied to this process for preliminary discussion about the chemical mechanism of waterproof development by composite modification of soy-based adhesives.The dry strength of traditional soy adhesive was 1．75 MPa. According to the new rule GB/T 9846．7-2004, traditional soy adhesive belongs to the III kind glue. But delamination rate was 100% after water-soaking according to the demand of the II kind glue.Results of Sodium Dodecyl Sulfate (SDS)-modified soy protein experiments showed hydrophobic strength reached 0．71MPa. Single factor experiment on the effects of pH value, temperature and reaction time on hydrophobic strength was conducted firstly, then orthogonal experiment L(3) was carried out. The best technology condition was pH 8, reaction temperature with 35℃, reaction time with 4h which were the reference values for the composite modification experiment.O-dihydroxybenzene was selected as urease depressor in the urea-modified experiment. The repressing experiment was carried out by adopting method of pH value increment. Results showed soy urease activity could be depressed above 90% with adding above 0．1% o-dihydroxybenzene. Urea-modified soy protein adhesives gave the highest strength 0．48MPa with a urea concentration of 3mol/L, waterproof was to some extend improved comparing with traditional soy adhesives.Effects of temperature and pH value on hydrophobic strength were investigated under acetic anhydride concentrations (1．2%,1．8%,2．4%,3．0%)for acetylation modification which gave the highest strength 0．72MPa, Results obtained the best constituted values including temperature and pH under different acetic anhydride concentrations which would provide the right reaction condition for the composite modification experiment. Take anhydride concentration 1．8% for example, analysis about the effects of pH on acylation degree under different temperatures were investigated by adopting ninhydrin-standard to measure the acylation degree of soy protein.Composite modification orthogonal experiment L₁₆ (4⁵) took the soy four concentration, SDS concentration, urea concentration, anhydride concentration and PAPI addition as variables. The test results proclaimed that PAPI addition and soy flour concentration had a greater effect on the modified adhesives. The best prescription was soy four concentration 21 %, SDS concentration 1．0 %, urea concentration 1．5mol/L, anhydride concentration 1．2% and PAPI addition 20%. The best technology of pressing board was obtained with a hot-press temperature of 130oC, a specific pressure of 1．2 MPa and a hot-press time of 1．0 min/mm. The maximum hydrophobic strength was 0．94 MPa in terms of the best prescription and technology of pressing board that could meet the waterproof requirement ofâ…¡kind glue in the GB/T9846．1～9846．8-2004 "Plywood".Absorbed peaks of principal characteristic groups did not change obviously from the comparison between spectrograms of traditional soy adhesive sample and soy flour; characteristic peaks were transformed broad peak into acute peak shape nearby 3400 cm^-1 in the spectrogram of SDS-modified production,because massive non-polar groups of protein were exposed under the condition of SDS , it enhanced the waterproof; characteristic peaks were transformed acute peak into broad peak shape nearby 3400 cm^-1 in the spectrogram of Urea-modified production, because secondary structure of protein was unfolded and massive polar groups were exposed by urea-modification; main characteristic peck changed from double peak to double spike(approaching singlet) that could be seen from IR spectra of acetic anhydride-modified production because of the transformation of primary amino group into secondary amino group, it could be explained that acetic anhydride had cross linking reaction with the of free amino of protein; from the comparison between IR spectra of composite modification adhesives after and before curing, it could be found that absorbed peaks of isocyanate group disappeared which showed isocyanate group had cross linking reaction with reactive hydrogen of protein under the condition of high temperature, so the performance of wet strength obtained obvious advance.Analysis of chemism concluded that, SDS-modification could unfold the tertiary structure of protein and move some inside hydrophobic side chains outward and thus increase water resistance; hydroxyl function between urea and soy protein in the second period broke the hydrogen bond in the protein system, then secondary structure was unfolded suitably to offer joints for the ultimate cross-linking reaction; amino caitons of protein was closed by neutral acetyl in the third period of acetylation, and the protein molecular static electricity action was weakened to decrease intermolecular accumulation effect; PAPI had cross linking reaction with reactive hydrogen of soy protein to reduce the hydrophilic groups and thus enhance hydrophobic strength of modified soy adhesives.Under the precondition of meeting the waterproof requirement of II kind glue, the unit price of soy-base adhesive by composite modification were 3243 and 2819 yuan per ton respectively when the adding amounts of PAPI base on the soy adhesive main agent were 20% and 15%. The free formaldehyde of modified soy-based adhesive is zero. The soy is innoxious, environmental friendly and has abundant sources, notable society benefit and zoology benefit are of notability as well.