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Study on the Low Toxic Urea-formaldehyde Resin Adhesive under the Low Curing Temperature

Author: WengXianYing
Tutor: LinQiaoJia
School: Fujian Agriculture and Forestry University
Course: Wood Science and Technology
Keywords: Urea-formaldehyde resin Curing agent Modifier Bonding strength
CLC: TQ433.431
Type: Master's thesis
Year: 2008
Downloads: 488
Quote: 2
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Abstract


With the sharp drop in worldwide quality natural forest timber resources, the full implementation of China's natural forest resources protection project, the structure of the timber resources of a fundamental change, development and production of small diameter wood thinned wood glued wood material, wood composites alternative natural high quality wood, will become the mainstream of the future development of the wood-based panel industry, adhesives and bonding technology will be the key protection. Urea-formaldehyde resin adhesive in the maximum amount of variety. But the existence of the shortcomings of poor water resistance, the adhesive layer is more brittle, especially high content of free formaldehyde and formaldehyde emission during use excessive serious pollution of the environment of the production environment and the use of wood glued products. Therefore, the study of low toxic urea-formaldehyde resin is the development direction of the wood glue. Although low toxic urea-formaldehyde resin free formaldehyde content is low, low formaldehyde emission of glued products, but it's curing slower, require high curing temperature, detrimental to their development. By synthesizing formaldehyde (F) and urea (U) molar ratio of urea-formaldehyde resin, and detection of its performance, from which preferably a kind of low molar ratio of urea-formaldehyde resin. Selection of different modifiers (white latex, PAPI, resorcinol) and a different curing agent (chloride, toluenesulfonyl chloride, ethylenediamine dihydrochloride, oxalic acid, hydrochloric acid, phosphoric acid, zinc sulfate, oxalic acid ethyl ester, trimethyl phosphate, ammonium persulfate, methenamine, triethanolamine)-modified urea-formaldehyde resin discussed modifying agent and a curing agent in a single and composite under different circumstances, the curing temperature and the bonding strength of the urea-formaldehyde resin impact. In addition, by means of Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), analysis of samples of the various stages of the urea-formaldehyde resin modified, to investigate the changes in its internal activity groups and the curing reaction mechanism. The test results show that the performance of urea-formaldehyde resin, urea-formaldehyde resin viscosity, solid content decreased with the F / U molar ratio increases significantly shorter curing time, the bonding strength of the upward trend. But the free formaldehyde content is reduced with the F / U molar ratio of reducing, when the molar ratio as low as 1.3 or less, the change of the free formaldehyde. In this study, F / U molar ratio of 1.3 urea-formaldehyde resin as an object of study. Single factor test method to examine the impact of the single-component curing agent and single modifier on the pH and water bonding strength of the urea formaldehyde resin. The results show that using a single-component curing agent, ethylenediamine hydrochloride or p-toluenesulfonyl chloride to glue pH decreased speed faster than ammonium chloride. When the ammonium chloride was added in an amount of 0.6% of the amount of urea-formaldehyde resin, bonding strength, and ethylenediamine hydrochloride and p-toluenesulfonyl chloride in an amount of 0.2% and 0.4%, respectively, the bonding strength is relatively good. Single modifier, white latex or PAPI added little glue the pH; PAPI the white latex significant modification effect of urea-formaldehyde resin, the addition of the two were at 12% wet bonding strength reaches its maximum, and was 1.43MPa and 1.02MPa respectively. Compound modifier of the effect of modified urea-formaldehyde resin is: white latex and PAPI together than separate effect. When both the amount of 9% and 6%, respectively, the bonding strength is best for 1.61MPa. In addition, the added resorcinol glue pH value is not wet bonding strength of the effect is not obvious. , Then added with 0.4% of ammonium chloride at the main agent in the urea-formaldehyde resin was added 5% of flour, and 9% of the white latex and 3% PAPI bicomponent curing agent, and results showed: with the curing agent additives, hydrochloric acid, oxalic acid, increase of the amount was added with phosphoric acid, pH value decreased rapidly glue; aid is ammonium sulfate, zinc sulfate, diethyl oxalate and trimethyl phosphate, with the increase in the amount added, glue pH value changes little. When the hot pressing temperature of 60 ° C, the modified urea formaldehyde resin adhesive bonding strength to achieve the plywood the requirements of the national standard II. Wherein the bicomponent curing agent consisting of ammonium chloride, and ammonium persulfate, ammonium chloride and zinc sulfate, high bonding strength of 1.49 MPa and 1.44 MPa, respectively. Multi-component curing agent research results show that the upward trend: With the curing agent adjuvants Urotropine and triethanolamine added, glue pH value. Hot pressing temperature of 60 ° C, the same as the main agent of the curing agent, with the different additives, the added amount adjuvants and different varieties of modified urea-formaldehyde resin bonding strength is also different. , Phosphate and ammonium persulfate mixed use, allows the bonding strength of the resin reached reached 1.55 MPa.; Triethanolamine added, leading to lower resin bonding strength. Selected curing agent (p-toluenesulfonyl chloride, ethylene diamine hydrochloride), white latex, PAPI and resorcinol influencing factors, each factor to take three levels, in accordance with the L 9 ( 3 4 ) the orthogonal design three curing agent and modifier combination of programs, test results show that the degree of influence of a curing agent for the p-toluenesulfonyl chloride and ethylenediamine hydrochloride more significant. In order to investigate factors using different formulations of the urea-formaldehyde resin, a curing agent, pressing temperature, unit of pressure, pressing time, respectively, L 9 (3 4 ) and L 16 (4 5 ) orthogonal table design the 3 the platen trial program, the results showed that: hot pressing temperature and curing agent significant impact on ST. Best platen technology: hot pressing temperature 55 ° C, unit of pressure 1.5MPa, hot pressing time 19min; curing agent of choice, there are two: the three-component consisting of ammonium chloride, oxalic acid, methenamine curing agent; chloride and phosphoric acid composition of two-component curing agent. Two-component curing agent consisting of ammonium chloride and phosphate in the hot press temperature of 40 ° C, the water of the modified urea-formaldehyde resin bonding strength of 1.06MPa, to reach the water requirements of the national standard II plywood. Infrared spectroscopy were sampled from the various stages of the gel of the urea-formaldehyde resin, can be seen, adding white latex in the urea-formaldehyde resin, changing the infrared spectra of a urea-formaldehyde resin in the intensity of the characteristic absorption peak, indicating that the resin part of the hydrogen bonds are broken the enhanced hydrophobic resin: Add PAPI, increases the asymmetric stretching vibration of the isocyanate group in the infrared spectrum, characteristic absorption peaks. Iso cyanate ester group and a hydroxymethyl group of the characteristics after the acidic substance modified urea-aldehyde resin glue absorption peak intensity weakened portion iso cyanate ester group with urea aldehyde resin containing active hydrogen groups GROUP occurs an addition polymerization reaction, and the resin hydroxyalkyl the meth also occurred partially cross-linking reaction. Can be seen from the differential scanning calorimetry, DSC spectrum of pure urea-formaldehyde resin is obvious exothermic peak in the curve the white latex join the curve in a more obvious exothermic peak around 35 ℃; PAPI added, the curve in a more obvious exothermic peak around 25 ℃. After ammonium chloride was added in the modified resin, the resin DSC exothermic peak is moved from the 115 ℃ to 90 ℃, described the role of the curing agent, the curing temperature of the resin is reduced. The test of the composite curing system, the curing agent additives of oxalic acid, hydrochloric acid, phosphoric acid added to the curing temperature of the urea-formaldehyde resin further reduced, methenamine added so that the curing temperature of the resin is increased. Of ammonium persulfate was added no significant suction in the curve, the exothermic peak. In this study, using modifier and curing agent of low molar ratio urea-formaldehyde resin was systematically modified to reduce the low molar ratio urea-formaldehyde resin curing temperature, provide a theoretical basis for the expansion of the application of urea-formaldehyde resin in different wood-based panels .

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CLC: > Industrial Technology > Chemical Industry > Adhesive Industry > Synthetic adhesive > Rubber, resin as raw material adhesive > Synthetic resin adhesive of the raw materials > Phenol-formaldehyde , urea- aldehyde adhesive
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