2017; Rastegarfar et al. Fig. Sci. DCqI ')@t Q*^C$l ZTEUla##.eC7tCC]-Ra8bcs,d+;hE2cOvAA
%A?k3TK'qf16ok5.-A21l6_"[5~v4. Adhes. On the other hand, the adhesives curing and increase in the mechanical strength continued to day 30. Article submitted: July 30, 2018; Peer review completed: September 17, 2018; Revised version received: October 13, 2018; Accepted: October 17, 2018; Published: December 6, 2018. Two-step sequential liquefaction of lignocellulosic biomass by crude glycerol for the production of polyols and polyurethane foams, Bioresour Technol. DOI:10.1007/s12010-013-0300-5. Water-absorbing polyurethane foams from liquefied starch, J. Appl. 4. Ionescu, M. (2005). 
In other words, the temperature can increase the degradation of lignocellulosic material. At the present time, commercial polyurethane adhesives are prepared from a reaction between petroleum-based polyol and diisocyanate. The third stage (90% weight loss) occurred at 680 and 622 C in PU PMDI and PU TDI, respectively, due to the decomposition of lignin or the char formed in during thermal degradation (Khoon Poh et al. 2003; Mishra 2010). The peak at 1738 cm-1 belongs to C=O stretching in acetyl groups of hemicelluloses and at 1427 cm-1 belongs to aromatic skeletal vibration combined with CH2 symmetrical bending mode of hydroxymethyl in crystalline cellulose and a-C-O- stretching band at 1248 cm-1, which confirmed the formation of ester bonds (Bodirlau and Teaca 2009; Meilan et al. Contact information: a: Department of Wood and Paper Science and Technology, Faculty of Natural Resources, Tarbiat Modares University, Noor, Iran; b: Department of Polymer Engineering and Color Technology, Amirkabir University of Technology, Tehran, Iran; * Corresponding author: rabi.behrooz@modares.ac.ir. Effect of NCO/OH ratio on the gel time of polyurethane adhesives, FTIR spectroscopy of the polyurethane adhesives. In contrast, the well-packed structure of crystalline cellulose is liquefied more slowly and continues until the latest stages of the liquefaction process (Hu et al. On the other hand, all of the NCO groups of isocyanate reacted with OH group of polyol to form urethane. Therefore, formulation and producton methods of, are important. Characterization of Polyurethane Wood Adhesive Prepared from Liquefied Sawdust by Ethylene Carbonate, Soheyla Daneshvar,a Rabi Behrooz,a,* Saeed Kazemi Najafi,a and Gity Mir Mohamad Sadeghi b, Keywords: Polyurethane adhesives; Liquefaction; Ethylene carbonate; Beech sawdust; Biopolyol. 2014). Two grams of biopolyols were dissolved in 50 mL of ethanol. Identification and comparison of oil compounds derived from pyrolysis of beach sound wood and decayed wood using Gas Chromatography and Mass Spectrometry (GC/MS), Iran. Polyurethane polyester elastomer: Innovative environmental friendly wood adhesive from modied PETs and hydroxyl liquid natural rubber polyols, Int.
Sci. As a result, the reactions between EC and the lignocellulosic components such as cellulose, hemicelluloses, and lignin accelerate. 2003; Somani et al. The sawdust was dried in an oven at 105 C overnight before use. Synthesis of polyurethane wood adhesives from obtained bio polyol. Biochem. The acid number was determined in accordance with ASTM D4662-08 (2012). Diisocyanate with a linear structure is more easily connected to OH groups (Somani et al. The hydroxyl number was determined in accordance with ASTM D4274-05D (2012). Table 4 shows that a NCO/OH ratio of 1.7 in PU TDI and 1.5, 1.7 in PU PMDI with an additional excess of isocyanate failed due to the cohesive failure (CF) and substrate failure (SF) (Desai et al. The highest value of average lap shear strength in both types of adhesives was obtained at a NCO/OH ratio 1.7. Urethane bonds can form between the polyol and isocyanate in polyurethane adhesives. 2015). 2003). Ethylene carbonate was used as a solvent and sulfuric acid as a catalyst in the liquefaction. The adhesive was applied onto the surface of the wood in a bonding section of 30 25 mm2. Prod. Furthermore, Table 2 shows that the effect of the solvent on lignocellulosic material was increased by extending the liquefaction temperature and time. According to the obtained results, an increase in the NCO/OH ratio from 0.7 to 1.7 in the both types of adhesives increased the lap shear strength.
According to ASTM D906-98 (2003), the beech wood pieces were converted into strips at 253003mm3 and then prior to application were polished with sand paper (Desai et al. More than 30 percent of the forest cover consists of Fagus orientalis (beech) species; thus, a large amount of this raw material could be used in the preparation of biopolyol (Hassani et al. DOI: 10.15376/biores.1.2. Liquefaction of crop residues for polyol production, BioResources 1(2), 248-256. Hu, S., and Li, Y. Biotech. Catalysts are used as reaction accelerators and gel time reducers in consumable adhesives. 30(2), 243-255. This was done because with catalyst value 3%, the acid number of polyol was very high, which is not suitable for the preparation of polyurethane adhesive. 4.
8.Trend of green strength of polyurethane adhesives 1 to 30 days. Khoon Poh, A., Choy Sin, L., Sit Foon, C., and Cheng Hock, C. (2014). 3. ,f3E$E2 Table 2 shows the characteristics of the obtained polyols. Gel time is one of the important parameters in preparation adhesives. (2015). The liquefied product was diluted by a universal diluent, 1, 4-dioxane, in excess of 80%. Determination of optimal gel time for the application of adhesives is very significant because represents usability of adhesive during work. where B is the volume of blank solution (mL); S is the volume of NaOH standard solution required for titration (mL); W is the sample weight (g); N is the equivalent concentration of NaOH standard solution (mol/L). Polyols, which are important compounds of polyurethane adhesives (PU), were prepared in this work from renewable sources. Characteristics of Liquefaction Products (Polyol) at Different Temperatures and Times (3% Catalyst), Fig. Chen, H. Z., Zhang, Y. The spectra of wood sawdust show that a strong broad OH stretching at 3411 cm-1 and C-H stretching in methyl and methylene groups (2854 to 2926 cm-1). Table 2. For preparation, adhesives were used from polyol (130 C, 120 min), isocyanate (PMDI, TDI), and glycerol as cross linkers and DBTL as catalyst. Adhes. Residue (%) = [(Mass of residue) Mass of starting sawdust)] 100 (1), Determination of acid and hydroxyl number of biopolyols. The appearance of this band confirms the reaction of OH polyol with NCO isocyanate. Liquefaction and characterization of acid hydrolysis residue of corncob in polyhydric alcohols, Ind. DOI: 10.1016/j.biortech.2014.03.072. 1996; Yamada and Ono 1999; Liang et al. Recently, liquefaction processes for the complete conversion of lignocellulosic material into liquid products have been developed using solvents such as polyhydric alcohols [ethylene glycol (EG), polyethylene glycol (PEG), crude glycerol and glycerin] and cyclic carbonate [ethylene carbonate (EC) and propylene carbonate (PC)] in the presence of an acid catalyst under atmospheric conditions (Ono et al. LIQUID / JUICE WORM FERTILIZERS / hmus lquido /, FOOD PRODUCTS FORMULATIONS ENCYCLOPEDIA - 2 TEXTBOOKS PDF, FOOD PRODUCTS FORMULATIONS ENCYCLOPEDIA - 1 TEXTBOOKS PDF, PERFUME AND COLOR COSMETIC FORMULATIONS ENCYCLOPEDIA TEXT BOOKS, HAIR CARE PRODUCTS FORMULATIONS ENCYCLOPEDIA TEXTBOOKS, SKIN CARE PRODUCTS FORMULATIONS ENCYCLOPEDIA TEXTBOOKS, HERBAL COSMETIC FORMULATIONS ENCYCLOPEDIA TEXTBOOKS, INDUSTRIAL PAINTS FORMULATIONS ENCYCLOPEDIA - 2 TEXTBOOKS, INDUSTRIAL PAINTS FORMULATIONS ENCYCLOPEDIA - 1 TEXTBOOKS, POLYURETHANE COATINGS AND PAINTS FORMULATIONS ENCYCLOPEDIA E - TEXTBOOKS, EPOXY COATINGS & PAINTS FORMULATIONS ENCYCLOPEDIA TEXTBOOKS, CONSTRUCTION CHEMICALS FORMULATIONS ENCYCLOPEDIA - 2 E - TEXTBOOKS, CONSTRUCTION CHEMICALS FORMULATIONS ENCYCLOPEDIA - 1 E - TEXTBOOKS, AEROSOL SPRAY FORMULATIONS ENCYCLOPEDIA E - TEXTBOOKS, DETERGENT PRODUCTS FORMULATIONS E - TEXTBOOKS, INDUSTRIAL DETERGENT FORMULATIONS E - TEXTBOOKS, DISINFECTANT PRODUCTS FORMULATION AND PRODUCTION PROCESS, LUBRICATING OILS FORMULATIONS E TEXTBOOKS, AUTO CARE PRODUCTS FORMULATIONS E - TEXTBOOKS, PLANT NUTRITION FERTILIZERS AND PROTECTION FERTILIZERS & SPECIAL FERTILIZERS TEXTBOOKS, CHEMICAL FERTILIZER FORMULATIONS E - TEXTBOOKS, ORGANIC FERTILIZER FORMULATIONS E - TEXTBOOKS, INDUSTRIAL PRODUCTS FORMULATIONS ENCYCLOPEDIA - 1 E - TEXTBOOKS, INDUSTRIAL PRODUCTS FORMULATIONS ENCYCLOPEDIA - 2 E - TEXTBOOKS, HERBICIDE FORMULATIONS AND PRODUCTIONS ARTICLES, FUNGICIDE FORMULATIONS AND APPLICATIONS ARTICLES, DETERGENT PRODUCTION & FILLING AND SEALING MACHINES, FOOD FORMULATIONS AND FOOD PROCESSING BOOK ARTICLES, ADHESIVES & GUM & GLUE AND SEALANTS ARTICLES, SKIN CARE & HAIR CARE AND COSMETICS RAW MATERIALS, INDUSTRIAL PAINT FORMULATIONS ARTICLE - 2, POLYURETHANE COATINGS AND PAINTS ARTICLES, FOOD PRODUCTS FORMULATIONS ENCYCLOPEDIA VIDEOS, CONSTRUCTION CHEMICALS FORMULATIONS ENCYCLOPEDIA - 2 VIDEOS, CONSTRUCTION CHEMICALS FORMULATIONS ENCYCLOPEDIA - 1 VIDEOS, LUBRICATING OILS FORMULATIONS ENCYCLOPEDIA VIDEOS, AGRICULTURAL CHEMICALS ENCYCLOPEDIA VIDEOS, AEROSOL SPRAY FORMULATIONS ENCYCLOPEDIA VIDEOS, ORGANIC FERTILIZERS FORMULATIONS ENCYCLOPEDIA VIDEOS, INDUSTRIAL DETERGENT FORMULATIONS ENCYCLOPEDIA VIDEOS, DETERGENT FORMULATIONS ENCYCLOPEDIA VIDEOS, DISINFECTANT PRODUCTS FORMULATIONS ENCYCLOPEDIA VIDEOS, EPOXY COATINGS AND PAINTS FORMULATIONS ENCYCLOPEDIA VIDEOS, POLYURETHANE COATINGS AND PAINTS FORMULATIONS ENCYCLOPEDIA VIDEOS, INDUSTRIAL PAINTS FORMULATIONS ENCYCLOPEDIA VIDEOS - 1, INDUSTRIAL PAINTS FORMULATIONS ENCYCLOPEDIA VIDEOS - 2, CAR CARE PRODUCTS FORMULATIONS ENCYCLOPEDIA VIDEOS, HERBAL COSMETIC FORMULATIONS ENCYCLOPEDIDA VIDEOS, CHEMICAL FERTILIZER FORMULATIONS ENCYCLOPEDIA VIDEOS, HERBICIDE FORMULATIONS ENCYCLOPEDIA FREE EXAMPLES, FUNGICIDE FORMULATIONS ENCYCLOPEDIA FREE EXAMPLE, INSECTICIDE FORMULATIONS ENCYCLOPEDIA FREE EXAMPLE, FOOD PRODUCTS FORMULATIONS ENCYCLOPEDIA - 2 FREE EXAMPLES, FOOD PRODUCTS FORMULATIONS ENCYCLOPEDIA - 1 FREE EXAMPLES, PERFUME AND COLOR COSMETICS FORMULATIONS ENCYCLOPEDIA, SKIN CARE PRODUCTS FORMULATIONS ENCYCLOPEDIA FREE EXAMPLES, HERBAL COSMETIC ENCYCLOPEDIA PRODUCTION EXAMPLES, INDUSTRIAL PAINTS AND FREE FORMULATIONS - 2, INDUSTRIAL PAINTS AND FREE FORMULATIONS - 1, POLYURETHANE COATINGS AND PAINTS FREE FORMULATIONS, EPOXY COATINGS AND PAINTS FREE FORMULATIONS, CONSTRUCTION CHEMICALS FORMULATIONS ENCYCLOPEDIA - 2 FREE EXAMPLES, CONSTRUCTION CHEMICALS FORMULATIONS ENCYCLOPEDIA - 1 FREE EXAMPLES, LUBRICATING OIL FORMULATIONS ENCYCLOPEDIA FREE EXAMPLES, CHEMICAL FERTILIZERS FORMULATIONS ENCYCLOPEDIA FREE EXAMPLES, ORGANIC FERTILIZERS FORMULATIONS ENCYCLOPEDIA FREE EXAMPLES, INDUSTRIAL DETERGENT ENCYCLOPEDIA FREE SAMPLES, DETERGENT FORMULATION ENCYCLOPEDIA FREE EXAMPLES, AUTO CARE PRODUCTS FORMULATION ENCYCLOPEDIA FREE EXAMPLES, DISINFECTANT PRODUCTS FORMULATIONS ENCYCLOPEDIA FREE EXAMPLES, INDUSTRIAL PRODUCTS FORMULATIONS ENCYCLOPEDIA - 1 FREE SAMPLE, INDUSTRIAL PRODUCTS FORMULATIONS ENCYCLOPEDIA - 2 FREE SAMPLE, AEROSOL SPRAY FORMULATIONS ENCYCLOPEDIA FREE SAMPLES. Hu, S., Wan, C., and Li, Y. 78(1), 319-325. Beech sawdust at a low liquefaction temperature is decomposed slowly, so the residue content is decreased gradually, but at high temperatures the rate of degradation increases. Usually, isocyanates containing NCO groups used in polyurethane adhesives production industries are 2,4 and 2,6 toluene diisocyanate (TDI) and poly 4,4 diphenyl methane diisocyanate (PMDI). Adhesives from waste paper by means of phenolation, Adhesion 59(1-4), 135-145. The rate of liquefaction of cellulose and hardwood with cyclic carbonates such as EC and PC is faster than that of polyhydric alcohols. The formation of more crosslink during the preparation of adhesives reduces the gel time of adhesives (Desai et al. According to the characterization of liquefied products in the first phase, the liquefaction process is not suitable at low or high temperatures. One desirable property of polyurethane adhesives is its resistance against chemical materials, moisture, and temperature. Jellinek, H. H. G., and Dankle, S. R. (1983). (2014).Polyols and polyurethanes from the liquefaction of lignocellulosic biomass, ChemSusChem 7(1), 66-72.DOI:10.1002/cssc.201300760. FTIR results showed that due to the presence of hydroxyl groups (OH), beechwood sawdust can be a source of polyol. Then 20 mL of dioxane/water solution (4/1, V/V) and 5 mL of distilled water were added to the beaker soluble and the mixture was titrated with 1 mol/L NaOH. The application rate of the adhesive onto the beech wood surface bonding area was 0.2 mg/mm2. %PDF-1.5
%
Combination of the Polyurethane Adhesives, Fig.
Table 4. The experimental method adopted was as described by Xie and Chen (2005): 32.5g of liquefying reagent as solvent and 0.97g catalyst (3 wt% for the liquefying reagent) were added to a three-neck flask (250 mL), which was equipped with a stirrer, thermometer, and reflux condense. Acid-catalyzed liquefaction of bagasse in the presence of polyhydric alcohol, Appl. The NCO/OH ratio in adhesive formulation has the greatest effect on adhesive strength characteristic. Lap shear strength tests were carried out according to ASTM D906-98 (2003). Sci. 2. 2. Basic Components of 2C Pur and polyreaction. J. Adhes. One gram of biopolyol was added into a 150 mL beaker, and then biopolyol with 10 mL of phathalic anhydride solution (150 g phathalic anhydride dissolved in 900 mL of dioxane and 100 mL pyridine) was dissolved. DOI: 10.1016/j.biortech.2011.09.125. As shown in Table 4, the average lap shear strength in PU PMDI was higher than PU TDI because diisocyanate (PMDI) has a linear structure whereas diisocyanate (TDI) has a ring structure. DOI: 10.1080/01694243.2014.883772. Due to the declining availability of fossil fuels, in addition to environmental concerns, renewable sources such as agricultural wastes and wood waste have been used for the production of biopolyol (Kong et al. The lap shear strength of the wood samples was determined by the SANTAM model STM-20 (Tehran, Iran) and was pulled at a rate of 5 mm/min (Somani et al. 10(4), 275-281. On the other hand, with the addition of excess isocyanate to the adhesive mixture created more reactions between NCO groups and OH groups, which led to an increase the cross-linking density due to the formation of urethane bonds as well as formation adhesives with higher mechanical properties. The bands observed at around 1611 and 1604 cm-1 for PU PMDI and PU TDI, respectively, correspond to conjugated double bonds in the aromatic ring of the hard segment. The catalyst content exhibited great influence on the residue content, acid, and hydroxyl numbers. 2012). endstream
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Fig. Abundant lignocellulosic wastes are available from hardwood forests in the north of Iran. Finally, TGA analysis showed that the PU PMDI had better thermal stability than the PU TDI. 1996). J. Phys. 2016). 3, Acid number(mg KOH/g) =((C-B)N56.1)W (3). 60(11), 1939-1949. Table 5. Second Phase: Effects of Reaction Time and Catalyst Value. Fig. 54(1-2), 93-104.DOI: 10.1.1.575.5877. 9 shows, by increasing the NCO/OH ratio from 0.7 to 1.7 the gel time of adhesives was decreased.
2006; Hu et al. The peaks of 3300 and 3500 cm-1 in both sample belong to OH groups. foams prepared from liquefied sawdust by crude glycerol and polyethylene glycol, Polym Res. Preparation of polyurethane wood adhesives by polyols formulated with polyester polyols based on castor oil, Int. An increase in the hydroxyl number is usually due to the cleavage of the ether linkage of lignin and cellulose units (Xie and Chen 2005). 2003). 2003). 0
Beech wood sawdust was liquefied using ethylene carbonate as a new solvent and sulfuric acid as a catalyst in the two phases. The first stage of decomposition (10% weight loss) occurred between 230 and 238C in PU PMDI and PU TDI, respectively, due to the decomposition of urethane bonding which led to the formation of CO2, alcohols, amines, aldehydes, CO, etc. Yamada and Ono (1999) and Liang et al. endstream
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Z., and Xie, S. P. (2012). 2016). Chemistry and Technology of Polyols for Polyurethanes, Rapra Technology Ltd., Shrewsbury, UK. The preparation of polyurethane adhesives and the formation of urethane bands are mainly identified by the absence of OH groups and the appearance of NH bands (Somani et al. These results suggest that the increases in acid numbers of the polyol of wood sawdust during the liquefaction process are mainly because of oxidation of the polysaccharides or depolymerization of the wood components (Zhang et al. Liquefaction temperature had a great influence on the characteristics of polyol such as acid and hydroxyl numbers and yield. 41(1), 127-131. Production and characterization of biopolyols and polyurethane foams from crude glycerol based liquefaction of soybean straw, Bioresource Technol. 2014; Najafi Moghadam et al. When the NCO/OH ratio in the polyurethane adhesives is higher than 1, adhesive bonding strength due to perfect reaction between (OH) polyol and (NCO) isocyanate and formation of a urethane bond will be increased. The polysaccharide components (cellulose and hemicelluloses) each contain two or three hydroxyl groups per monomer unit (Chen et al. Fig.
2016). Table 3 and Fig. The polyol, glycerol as a cross-linker (1, 2, 3, 4, 5%), and dibutyltindilaurate (DBTL) as a catalyst (0.1, 0.2, 0.3, 0.4, 0.5%) were mixed together and stirred at 400 rpm with a stirrer for approximately 3 min at room temperature. Kong, X., Liu, G., and Curtis, G. M. (2011). The average lap shear strength in the polyurethane adhesives was obtained in range of 1.561 MPa for PU PMDI and 1.49 MPa for PU TDI (Somani et al. hbbd```b``! 79, 67-72.
Furthermore, the spectrum of polyol shows that the widespread peak at 3340 cm-1 corresponds to the OH stretching vibration. The formulation of PU adhesives is shown in Table 1. Then two surfaces of wood were placed together under pressure of 2.5 kg at room temperature for 24 h. The prepared samples were conditioned at 25 C and relative humidity of 50% 5% for 7 days. Thermogravimetric analysis for both of types PU adhesives (PU PMDI and PU TDI) was performed on according to ASTM D3850-94 (2006) using Model Q600 (TA Instruments, New Castle, DE, USA) at a heating rate of 10 C/min under nitrogen flow, in the range of 30 to 700 C. Therefore, high quantities of beech wood waste produced, and these can be converted into valuable products such as polyols. Typical Properties of 2 components polyurethane adhesives. Beech wood sawdust, due to the presence of xylan content, shows a carbonyl band at 1738 cm-1. Effects of the liquefaction time on the hydroxyl and acid number (1.5%) of sulfuric acid and temperatures a: 130 C, b: 140 C, Table 3. where C is the volume of NaOH standard solution at the equivalence point(ml); Bis the volume of blank solution(ml); W is the sample weight(g), and N is the equivalent concentration of NaOH standard solution (mol/L). 2012). The resistances of polyurethane adhesives (chemical, mechanical, and physical) are determined by their formulations. (2000) found that increases in the acid number of the liquefied products (polyol) during the liquefaction process are mainly because of oxidation of the polysaccharides or depolymerization of the wood component. 3, by extending the reaction time from 20 to 60 min the residue content decreased. 23(4), 269-275. The carbonyl groups were observed at 1720 and 1715 cm-1 in PU PMDI and PU TDI, respectively. The initial weight loss in both adhesives (PU PMDI and PU TDI) at 100C is due to evaporation of water in the system and the release of volatile substances. Polyurethane adhesives 2 components can be elastic or rigid adhesive, depending on the structure of thermoset or elastomer which acquires the adhesive once it has solidified or cured. 9. The liquefaction process has the ability to convert wood sawdust into substances that are soluble. Resin Polyols with low molecular weight. 1shows the preparation of polyol from beech wood sawdust by using the liquefaction process with ethylene carbonate of solvent. Fig. Res. TGA of the polyurethane adhesives. Yao, Y. G., Yoshioka, M., and Shiraishi, N. (1996). Adhes. Dx _( hX?c B
Fig. The liquefied products obtained at low temperatures have low hydroxyl numbers and yields and at high temperatures have low hydroxyl numbers and high acid numbers.
As above mentioned, beech wood was selected for this study due to its regional availability and considerable application in most wood industries in Iran. ASTM D3850-12 (2006). This molar ratio was considered for continuing the study on adhesives properties. Transmittance measurements were conducted using the KBr pellet method. Hydroxyl groups of the polyols are functional groups in polyurethane production and the strength of polyurethane products depends on the hydroxyl value and the acid number of polyol. 115 0 obj
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Then the flask was immersed in a silicon oil bath that had been preheated. The hydroxyl number was calculated using Eq. Although treatment at 140 C has slightly similar results to results at 130 C, reducing energy consumption in the industry is a significant issue. Figure 7 clearly shows that the peak at 1427 cm-1 corresponding to wood sawdust decreased in the liquefied sample (polyol). Hardener - low molecular weight prepolymers with isocyanate finishes. 28(11), 1020-1033. Meilan, A. C., Goodman, A., Baron, M., and Rodriguez, J. G. (2014). Selective liquefaction of wheat straw in phenol and its fractionation, Appl. 2003). In this study, SPSS software and one-way ANOVA were used to analyze the data. (2017). The second stage of decomposition (50% weight loss) occurred at 393 and 337C in PU PMDI and PU TDI, respectively, due to decomposition of the hard segments of isocyanate. Chemical Resistance of Wood Bonded Adhesives. Moreover, excessive NCO groups can increase the reaction of isocyanate with hydroxyl groups of woods; thus free NCO groups penetrate into the woods top layer, leading to an increase in the adhesion force between the adhesives and the substrates (woods). Table 3 and Fig. Fig. In this study, the residue content at 110C and 40 min (46.2%) was higher than at 160C (18.5%). Figure 4 shows the relationship between liquefaction temperature and the hydroxyl and acid number of liquefied products of beech wood sawdust. 2003; Khoon Poh et al. Xie, T., and Chen, F. (2005). All rights reserved. 3. The temperature then was raised to a desired level. In the event of decrease or increase at this time, the adhesion strength will changed and there is a probability the reducing of adhesive bond strength. `9tH 2011). 6 show the effects of the liquefaction time on the yield and residue content. 8, the average lap shear strength of adhesives PU PMDI and PU TDI had the highest value on day 30. Amorphous and crystalline structures of wood sawdust during the liquefaction process could be converted into small components with a large number active hydroxyl groups appropriate for chemical reaction. 5, when the reaction time was set to 120 min, the acid and hydroxyl number also increased. Synthesis of polyurethane wood adhesives was carried out by a reaction of polyol with two types of diisocyanate (PMDI and TDI), as shown in Fig. 2016). DOI:10.1016/j.ijadhadh.2016.04.004. Figure 11 shows that the thermal stability of PU PMDI is higher than that of PU TDI, because the thermal stability of diisocyanate with a linear structure is greater than that of diisocyanate with a ring structure (Somani et al. 
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