Properties of a low viscosity urea-formaldehyde resin prepared through a new synthetic route.INTRODUCTION
adj having the property of becoming irreversibly rigid or hardened with the application of heat. In dentistry the term is used in connection with resins. polymers such as urea formaldehyde formaldehyde (fôrmăl`dəhīd'), HCHO, the simplest aldehyde. It melts at −92°C;, boils at −21°C;, and is soluble in water, alcohol, and ether; at STP, it is a flammable, poisonous, colorless gas with a suffocating and melamine melamine (mĕl`əmēn'), common name for 2,4,6-triamino-1,3,5-triazine. Melamine is a trimer (see polymer) of cyanamide, H2NC≡N, and is synthesized from calcium carbide. formaldehyde are the mostly widely used amino resins (Conner, 1996; Pizzi, et al., 2001 and Updegraff, 1990). However, the acceptance of amino resins as a universal material in many engineering areas such as in the coating industry is impeded by some of its inherent qualities such as brittleness, poor water resistance and formaldehyde emission (Lowel, 1990; Conner, 1996). These disadvantages limit the rage of uses of amino resins.
Conner (1996) reported that the procedure for the synthesis of urea formaldehyde (UF) resins offers a wide range of conditions that make the synthesis of these resins with important properties such as gel time, tack and spreadibility of the uncured resin possible. Also formaldehyde emissions and the durability of the cured resin can be controlled and specifically tailored for the final end use of the resins. The considerable environmental interest for further reduction of formaldehyde has necessitated intensification of research into modification and improvement of properties of UF resins.
At present, the commercial production of urea formaldehyde resins is carried out in two major steps (Conner, 1996). The first step is characterized by methylation methylation,
n a phase-II detoxification pathway in the liver; methyl groups combine with toxins to rid the body of various substances.
(meth´ reaction in the absence of condensation reactions under basic condition. In the second step, the reaction mixture is brought to acidic side with a pH of about 5 with the condensation reaction being carried out until a desired viscosity is reached.
Various reports (Lowel, 1990; Conner, 1996; Achi, 2003) have shown that the resins from the above synthetic route are too hard and brittle to be used as a paint binder. This has created interest in an alternative synthetic route that can produce a resin with appropriate properties for application in a coating industry.
In our previous work a novel synthetic route (one-step process, OSP (Online Service Provider) See online service.
OSP - Optical Signal Processor ) was used to develop and assess the potential of UF resin as a paint binder (Barminas and Osemeahon, 2006). To offer formulators with varied options to tailor performance, the effect of viscosity was examined and used to prepare a low UF resin for possible application in the coating industry.
MATERIALS AND METHODS
The one-step-process used involved preparing trimethylol urea by reacting one mole (6.0 g) of urea with three moles (24.3 ml) of 37% (w/v) formaldehyde using 0.2 g of sodium dihydrogen phosphate (Chen, et al., 2004). The pH of the solution was adjusted to 6 using 0.5 M [H.sub.2]S[O.sub.4] and 1.0 M NaOH solutions. The solution was then heated in thermostatically controlled water bath at 70[degrees]C. The reaction was allowed to proceed for 2 h after which the sample was removed and kept at room temperature (30[degrees]C). The samples with different viscosities used in this experiment were obtained by removing 25 ml of resin from the synthesized resin at 24 h intervals for a period of 120 h and their viscosities determined.
Films of the resins with different viscosities were cast on petri dishes by using solution casting method (Mirmohseni and Hassanzadeh, 2000). These resins were allowed to cure and set for seven days at 30[degrees]C. The physical properties of these films were investigated.
Determination of Viscosity and Gel Point
The method reported by Barminas and Osemeahon (2006) was adopted for the determination of viscosity and gel point of the UF resins. Five different readings were taken for each sample and the average value calculated.
Determination of Density, Turbidity turbidity /tur·bid·i·ty/ (ter-bid´i-te) cloudiness; disturbance of solids (sediment) in a solution, so that it is not clear.tur´bid
The cloudiness or lack of transparency of a solution. , Melting point melting point, temperature at which a substance changes its state from solid to liquid. Under standard atmospheric pressure different pure crystalline solids will each melt at a different specific temperature; thus melting point is a characteristic of a substance and and Refractive Index A property of a material that changes the speed of light, computed as the ratio of the speed of light in a vacuum to the speed of light through the material. When light travels at an angle between two different materials, their refractive indices determine the angle of transmission
The above properties were determined according to according to
1. As stated or indicated by; on the authority of: according to historians.
2. In keeping with: according to instructions.
3. standard methods (AOAC, 2000). The density of the different resins was determined by taking the weight of a known volume of resin inside a density bottle using metler (Model, At400) weighing balance. Five readings were made for each sample and average value calculated. The turbidity of the resin samples was determined by using Hanna microprocessor turbidity meter (Model, H193703). The melting point of the different film samples were determined by using Galenkamp melting point apparatus (model MFB600-010F). The refractive indices Many materials have a well-characterized refractive index, but these indices depend strongly upon the frequency of light. Therefore, any numeric value for the index is meaningless unless the associated frequency is specified. of resin samples were determined with Abbe refractometer refractometer /re·frac·tom·e·ter/ (re?frak-tom´e-ter)
1. an instrument for measuring the refractive power of the eye.
Determination of Moisture Uptake
The moisture uptakes of the different resin films were determined gravimetrically. Known weights of each of the samples were introduced into a desiccator des·ic·cate
v. des·ic·cat·ed, des·ic·cat·ing, des·ic·cates
1. To dry out thoroughly.
2. To preserve (foods) by removing the moisture. See Synonyms at dry.
3. containing a saturated solution of sodium chloride sodium chloride, NaCl, common salt. Properties
Sodium chloride is readily soluble in water and insoluble or only slightly soluble in most other liquids. It forms small, transparent, colorless to white cubic crystals. . The wet weights of each sample were then monitored until a constant weight was obtained. The differences between the wet weight and dry weight of each sample were then recorded as the moisture intake by resin. Triplicate determinations were made for each sample and average value recorded.
Determination of Formaldehyde Emission
Formaldehyde emission test was performed by using the standard 2 h desiccator test as reported by Kim (2001). The evaluation of the absorbed formaldehyde by the 25 ml water was obtained from standard calibration curves derived from refractometric technique using Abbe refractometer.
Tensile properties (tensile strength tensile strength
Ratio of the maximum load a material can support without fracture when being stretched to the original area of a cross section of the material. When stresses less than the tensile strength are removed, a material completely or partially returns to its and elongation elongation, in astronomy, the angular distance between two points in the sky as measured from a third point. The elongation of a planet is usually measured as the angular distance from the sun to the planet as measured from the earth. at break were measured as described by Wang and Gen, (2002) using Instron Testing Machine testing machine
Machine used in materials science to determine the properties of a material. Machines have been devised to measure tensile strength, strength in compression, shear, and bending (see strength of materials), ductility, hardness, impact strength ( (Model 1026). In brief, resin films of dimension 50 mm long, 10 mm wide and 0.15 mm thick were brought to rupture at a clamp rate of 20 mm/min and a full load of 20 kg. A number of five runs were taken for each sample and the average elongation were taken and expressed as the percentage increase in length.
Dry Time and Water Solubility Water is a bent, polar compound and possesses the ability to Hydrogen bond. As a result, it has unique solubility characteristics as a solvent and functions differently at different temperatures. Polarity
Water Solubility, US Geological Survey
The relative degree of cure was expressed in the form of dry time (dry to touch). This was measured by the qualitative finger-marking test (Ali, et al., 2001). The solubility solubility
Degree to which a substance dissolves in a solvent to make a solution (usually expressed as grams of solute per litre of solvent). Solubility of one fluid (liquid or gas) in another may be complete (totally miscible; e.g. of methylol urea in water was obtained by mixing 1 ml of the resin with 5ml of distilled water Noun 1. distilled water - water that has been purified by distillation
H2O, water - binary compound that occurs at room temperature as a clear colorless odorless tasteless liquid; freezes into ice below 0 degrees centigrade and boils above 100 degrees centigrade; at room temperature (30[degrees]C). A clear transparent solution indicated water solubility while a cloudy solution or white precipitate (Old Chem.) A heavy white amorphous powder (
RESULTS AND DISCUSSION
The melting point of a polymer has a direct bearing to its thermal property (Bindu, et al., 2001). It is related to its molecular weight, degree of crosslinking and the level of rigidity of the polymer (Park, et al., 2001). Figure 1 shows the effect of viscosity on the melting point of methylol urea. The melting point initially increased rapidly with viscosity and slowly approached an asymptotic value at the gel point. This type of behavior agrees with the reports of Ma, et al., (2002) and Markovic, et al., (2001) which was attributed to differences in molecular weight and cross-link density. At the beginning, the molecular weight increased with increases in viscosity until an optimum growth was obtained. At the gel point, the resin may be characterized by molecular rearrangement and crosslinking of resin molecules. This gives an account of the plateau regime seen in Figure 1(Nakason, et al., 2001).
[FIGURE 1 OMITTED]
Gloss is an important factor of many coating products. The gloss of paint coatings with or without pigments is a function of refractive index of the surface, the angle of incidence of the beam of light, the nature of light and the nature of the material (Trezza and Krochta, 2001). Figure 2 shows the effect of viscosity on the refractive index of urea formaldehyde resin. It can be seen that the refractive index increased rapidly within 2-5 mPa.s viscosity levels. After this the rate decreased with further increase in viscosity of the resin. This observation is due to the differences in molecular weight and crosslink density among the different samples with different viscosities (Trezza and Krochta, 2001; Johnson and Wilke, 2001).
[FIGURE 2 OMITTED]
In the coating industry, the density of the paint binder has a profound influence on factors such as pigment dispersion, brushability of paint, flow, leveling and sagging (Lowel, 1990). The effect of viscosity on density of urea formaldehyde is shown in Figure 3, where density increased with viscosity until the gel point. This was then followed by a constant regime with further increase viscosity. The increase in density with increase viscosity is due to increase in molecular weight while the constant regime may be attributed to gelation gelation /ge·la·tion/ (je-la´shun) conversion of a sol into a gel.
1. Solidification by cooling or freezing.
2. The process of forming a gel.
3. (Sekaran, et al., 2001).
[FIGURE 3 OMITTED]
The interaction of structural network of polymer resins with water is both of fundamental and technical interest (Nogueria, et al., 2001). Water uptake affects vital properties of the polymer material such as the physical, mechanical, thermal and structural properties (Hu, et al., 2001 and Nogueria, et al., 2001). One of the major draw backs of urea formaldehyde resins is their poor water resistant (Conner, 1996). In the paint making industry, the moisture uptake of the paint binder is very crucial because it is responsible for blistering and broominess of paint film (Barminas and Osemeahon, 2006).
Figure 4 shows the effect of viscosity on the moisture uptake of urea formaldehyde resin. It can be observed that the moisture uptake decreases with increase in viscosity and then became constant beyond the gel point. This result can be explained in terms of the differences in crosslink density at different viscosity (Nogueria, et al., 2001 and Hu, et al., 2001). As the viscosity of the resin increases, the molecular weight and hence crosslink density also increases until the gel point is reached after which the crosslink density remain constant.
One of the major draw backs of urea formaldehyde resin is the emission of the hazardous formaldehyde during cure (Kim, 2001; El-Naggar, et al., 2003; Pizzi, et al., 2001). In the development of paint binder from urea formaldehyde resin serious effort must be made to reduce formaldehyde emission levels to an acceptable level (Barminas and Osemeahon, 2006).
Figure 5 shows the effect of viscosity on formaldehyde emission of urea formaldehyde. It can be observed that the formaldehyde emission increased with increase in viscosity. This result may be ascribed to two reasons: firstly, it may be due to increase in the rate of condensation reactions with increase in viscosity thereby increasing the rate of emission of formaldehyde in the process (Nakason, et al., 2001; Trumbo, et al., 2001 Liang and Wang, 2001). Secondly it may be due to increase in stress during resin cure with increase in viscosity.
[FIGURE 4 OMITTED]
Reduction in stress during resin cure reduces emission (El-Naggar, et al., 2003). Low viscosity gives rise to low molecular weight, which favors molecular chain mobility that enhances flexibility of polymer network; flexibility reduces stress during resin cure and reduction of stress reduces emission (El-Naggar, et al., 2003; Chain and Yi, 2001).
[FIGURE 5 OMITTED]
The effect of viscosity on the tensile strength and elongation at break are shown in Table 1. The tensile strength decreased while the elongation at break increased with increase in viscosity. This trend is expected and might be due to increase in molecular weight and crosslink density with increase in viscosity (Tai and Li, 2001; Ma, et al., 2002). Viscosities of 2.07 and 3.04 (mPa.s) gave elongation at break of 124.61 and 121.64%, respectively. These values qualify these samples as being ductile ductile /duc·tile/ (duk´til) susceptible of being drawn out without breaking.
Easily molded or shaped.
susceptible of being drawn out without breaking. having met the minimum requirement of 120% elongation at break (Tai and Li, 2001). This behavior is a typical characteristic for ductile polymers. However, beyond 3.04 (mPa.s) viscosities the polymers became brittle and lose its ductility ductility, ability of a metal to plastically deform without breaking or fracturing, with the cohesion between the molecules remaining sufficient to hold them together (see adhesion and cohesion). Ductility is important in wire drawing and sheet stamping. .
Solubility in Water
In the development of amino resins for emulsion paint formulation, the solubility of the resin in water is paramount. It is important both from the technical and processing point of view. This is more so because the solubility of resins decreases with increase in viscosity (Lowel, 1990, Park, et al., 2001). Table 2 shows the effect of viscosity on the solubility of urea formaldehyde resin in water. Below a viscosity of 11.90 mPa.s, the resin is soluble and beyond this point the resin is insoluble. This result is attributed to differences in molecular weight and crosslink density (Lowel, 1990). Perhaps, the viscosity of 11.90 mP.s seems to represent the gel point of the resin. Thus processing of the amino resin Noun 1. amino resin - a plastic (synthetic resin) made from amino compounds; used as an adhesive and as a coating for paper and textiles
amino plastic, aminoplast for emulsion paint formulation could be suggested below this viscosity value.
The time it takes for a paint to dry after application is an important factor for the paint formulator. This is because if the paint dries too fast, it will be prone to brittleness and if it dries too slowly, the paint may be subjected to pickup dirt (Trumbo, et al., 2001). Table 3 shows the effect of viscosity on the dry time of urea formaldehyde resin. Results of the study showed that the dry time decreased with increase in viscosity. This can be explained in terms of increase in molecular weight and crosslink density with increase in viscosity (Lowel, 1990).
Table 4 compares some physical properties of low viscosity with those of the conventional urea formaldehyde resins synthesized by different authors. All the properties of the low viscosity urea-formaldehyde resins were much lower than those of the conventional types. These are positive results that could be used to solve the problems of poor water resistance, hardness, and formaldehyde emission associated with the traditional urea formaldehyde resins. The drastic reduction in formaldehyde emission signals the arrival of a better and an environmentally friendly Environmentally friendly, also referred to as nature friendly, is a term used to refer to goods and services considered to inflict minimal harm on the environment. urea formaldehyde resin. Hence low viscosity resin shows potential properties for possible applications in paint coatings.
Some physical properties of the low viscosity urea formaldehyde were compared with some paint binders. The viscosity of the synthesized resin was close to 3.11 mPa.s for rubber seed oil-modified alkyd al·kyd
A widely used durable synthetic resin derived from glycerol and phthalic anhydride. Also called alkyd resin.
[alky(l) + (aci)d.]
Noun 1. resins (Aigbodion and Pilla ., 2002), but much lower than 38.00 mPa.s (Gawdzik and Matynia, 2002) and 45.00 mPa.s (Gawdzik et al., 2000) obtained for epoxy-based divinyl ester and epoxy epoxy
Any of a class of thermosetting polymers, polyethers built up from monomers with an ether group that takes the form of a three-membered epoxide ring. The familiar two-part epoxy adhesives consist of a resin with epoxide rings at the ends of its molecules and a curing fumerate resins, respectively. The refractive index of our resin (1.4080) is also similar to 1.4838 found for when protein isolate biopolymer bi·o·pol·y·mer
A macromolecule, such as a protein or nucleic acid, that is formed in a living organism.
any protein or nucleic acid produced by a living organism. (Trezza and Krochta, 2001).
The density of the resin, 0.532 g/[cm.sup.3] is lower than 1.04 g/[cm.sup.3] (Gawdzik and Matynia, 2002), 1.07 g/[cm.sup.3] (Gawdzik et al., 2000) and 0.96 g/[cm.sup.3] (Starostina et al., 2001) reported for epoxy-based divinyl ester, fumerate and aromatic amine-modified polyethylene resins, respectively. The melting point of 128[degrees]C is lower than values determined for resins such as epoxy-based divinyl ester; 197[degrees]C (Gawdzik and Matynia, 2002), styrene-modified epoxy-resin; 200[degrees]C (Yoon and McGrath, 2001), and aromatic amine-modified polyethylene; 133[degrees]C (Starostina et al., 2001). The melting point is however higher than 110[degrees]C and 101[degrees]C evaluated for epoxy fumerate resin (Gawdzik et al., 2000) and epoxy resins (Hu et al., 2001), respectively.
The moisture uptake (3.10 %) of the low viscosity amino resin is much lower than 8.6 % for copolymer copolymer: see polymer. latex (Wu et al., 2000) and 17.2% aqueous aqueous /aque·ous/ (a´kwe-us)
1. watery; prepared with water.
2. see under humor.
adj. polyurethane (Lee and Kim, 2001). The elongation at break for the low viscosity resin was 124.6%, which is lower than 170% reported for glycidyl methacrylate methacrylate /meth·ac·ry·late/ (meth-ak´ri-lat) an ester of methacrylic acid, or the resin derived from polymerization of the ester. See also acrylic resins, under resin. and piperazin (Hong et al., 2001). This behavior may be relevant in modifying the creep behaviors of resin composites used in the coating industry.
This experiment examined the effect of viscosity on some physical properties of methylol urea synthesized through the OSP synthetic route. It shows that viscosity has a significant influence on the properties of methylol urea derived from OSP. Amino resins with viscosity less than 3.0 mPa.s may be a new class of amino resin composites for application in the coating industry. The properties of the resin when compared with properties of some conventional paint binders revealed that urea formaldehyde resin synthesized with low viscosity using the OSP synthetic route, might meet the requirements of the coating industry.
(1.) Achi, S. S. 2003. Basic Principles of Coating Technology. Shemang Graphics, Zaria Nigeria.
(2.) Aigbodion, I. A. and Pilla, C. K. S. 2001. J. Appl. Polym. Sci., 79 : 2431-2438.
(3.) Ajayi, J. O., Omizegba, F. I., Barminas, J. T. and Osemeahon, S. A. 2005. European Journal of Scientific Research. 4: 21-32.
(4.) Ali, M. M., Ooi, T. L., Salmiah, A., Ishaku, S. and Ishak, Z. A. M. 2001. J. Appl. Polym. Sci., 79: 2156-2163.
(5.) AOAC . 2000. Official Method of Analysis International, 17th edition (Horwitz, W., Editor). Gaithersburg Mongland, USA.
(6.) Barminas, J. T.and Osemeahon, S. A. 2006. European Journal Sci Research (in press).
(7.) Bindu, L. R., Nair, C. P. and Nina, K. N. 2001. J. Appl. Polym. Sci., 80: 1664-1674.
(8.) Chain, K. S. and Yi, S. 2001. J. Polym. Sci. 82: 879-888.
(9.) Chen, C., Lue, J. and Yen, C. 2004. J. Appl. Polym. Sci., 83: 1242-1251.
(10.) Conner, H. A. (1996). Urea-formaldehyde Adhesive Resins. In: Encyclopedia of Polymer Materials Vol 2(Joseph, C., Salamone, J. Clapol, Demby, A. and Aller, M., Editors)
(11.) El-Naggar, A. M., Kandeel, K. A., Khafaga, M. R. and Zahran, A. H. 2003. J. Appl. Polym. Sci., 82: 2869-2881.
(12.) Gawdzik, B. and Matynia, T. 2002. J. Appl. Polym. Sci., 81: 2062-2067.
(13.) Gawdzik, B., Matynia, T. and Osypiuk, J. 2000. J. Appl. Polym. Sci. 79:1201-1206.
(14.) Hong, W. J., Kim, H. K., Yu, J. A. and Kim, Y. B. 2005. J. Appl. Polym. Sci. 84: 1178-1184.
(15.) Hu, X., Fan, J. and Yue, C. Y. 2001. J. Appl. Polym. Sci., 80: 2437-2445.
(16.) Johnson, B. M. and Wilkes, G. L. 2002. J. Appl. Polym. Sci; 81: 2944-2963.
(17.) Kim, G. M. 2002. J. Appl. Polym. Sci., 80: 2800-2814.
(18.) Lee, J. S. and Kim, B. K. 2003. J. Appl. Polym. Sci., 82: 1315-1322.
(19.) Liang, G. and Wang, G. 2002. J. Appl. Polym. Sci., 81: 2918-2922.
(20.) Lowel, H. J. 1990. Coatings. In: Encyclopedia of Polymer Science Polymer science or macromolecular science is the subfield of materials science concerned with polymers, primarily synthetic polymers such as plastics. The field of polymer science includes researchers in multiple disciplines including chemistry, physics, and engineering. and Engineering, Vol.3 (Kroschwitz, J. I., Mark, H. F., Bikales, N. M., Overberger, C. G. and Menges, G., Editors).
(21.) Ma, Z., Pang, X., Zhang, J.and Ding, H. 2005. J. Appl. Polym. Sci., 84: 1223-1232.
(22.) Markovic, S., Dunfic, B., Zlatanic, A. and Djon Lagic, J. 2001. J. Appl. Polym. Sci., 80: 1902-1914.
(23.) Mirmohseni, A. and Hassanzadeh, V. 2000. J. Appl. Polym. Sci., 79: 1062-1065.
(24.) Nakason, C., Kaesman, A., Homsin, S. and Kiatkanjornewong 2002. J. Appl. Polym. Sci., 81: 2803-2813.
(25.) Nogueira, P. C., Ramirez, A., Torres, M. I., Abad, J., Cano, I., Lopez-Bueno I. and. Barral, L. 2001. J. Appl. Polym. Sci. 80: 71-80.
(26.) Park, H., Yang, I., Wu, J., Kim, M., Hahm, H., K, K.S. and Rhee, H. 2002. J. Appl. Polym. Sci. 81: 1614-1623.
(27.) Pizzi, A., Beaujean, M., Zhao, C., Properzi, M. and Z. Huang. 2001. J. Appl. Sci, 84: 2561 -2571.
(28.) Sekaran, G., Thamizharasi, S. and Ramasami, T. 2002. J. Appl. Polym. Sci. 81: 1567-1571.
(29.) Starostina, A. I., Stoyanov, O. V., Bogdanova, S. A., Deberdeev, R. J. A., Kurnosor V. V. and Zaikov, G. E. 2000. J. Appl. Polym. Sci., 79:388-397.
(30.) Tai, M. C. and Li, R. K. Y. 2001. J. Appl. Polym. Sci., 80: 2718 -2728.
(31.) Trezza, A. T. and Krochta, J. M. 2000. J. Appl. Polym. Sci., 79: 2221-2229.
(32.) Trumbo, D. I., Mole, E. B., Travino, S. A. and Denbrink, V. M. 2003. J. Appl. Polym. Sci., 82: 1030-1039.
(33.) Updegraff, H. I. 1990. Amino Resins. In: Encyclopedia of Polymer Science and Engineering Vol 1 (Kroschwitz, I., Mark, H. F., Bikales, N. M., Olerberger, C. G. and G. Menges editors).
(34.) Wang, H. and Gen, C. 2005. J. Appl. Polym. Sci. 84: 797-805.
(35.) Wu, Y., Duan, H., Yu, Y. and Zhang, C. 2004. J. Appl. Polym. Sci., 83:333-336.
(36.) Yoon, T. and Mcgrath, J. E. 2001. J. Appl. Polym. Sci., 80: 1504-1513.
S. A. Osemeahon and J.T. Barminas
Department of Chemistry, Federal University of Technology, Yola , P. M. B. 2076 Yola, Nigeria Yola is the capital city and administrative center of Adamawa State, Nigeria. Located on the Benue River, it has a population of 88,500 (2004). Established in 1841, Yola was the capital of a Fulani state until it was taken by the British in 1901. * Email: firstname.lastname@example.org
Table 1: Effect of Viscosity on the Tensile Strength and Elongation at break of methylol urea Viscosity (mPa.s) Tensile strength Elongation at (mN-[m.sup.-2]) break (%) 2.07 0.13 124.61 3.04 0.16 121.64 4.85 0.33 40.83 11.91 2.4 19.20 85.65 5.7 4.45 124.74 10.5 3.60 Table 2: Effect of Viscosity on the Solubility of Methylol urea in water at room temperature (30[degrees]C) Viscosity (mPa.s) Solubility properties in water 2.07 Soluble 3.04 Soluble 4.85 Soluble 11.91 Slightly Soluble 85.65 Insoluble 124.74 Insoluble Table 3: Effect of viscosity on the dry time of methylol urea Viscosity (mPa.s) Dry time (h) 2.07 48 3.04 36 4.85 24 11.91 12 85.65 6 124.74 6 Table 4: Comparison of some physical properties of low viscosity urea formaldehyde (2.07 mPa.s) with convectional urea formaldehyde Low viscosity Conventional Property urea formaldehyde urea formaldehyde Moisture uptake (%) 3.1 18.0 Melting point ([degrees]C) 128 200 Formaldehyde emission (ppm) 0.08 0.70 Density (g/[cm.sup.3]) 1.0532 1.1764 Property Reference Moisture uptake (%) Ajayi, et al., 2005 Melting point ([degrees]C) Ajayi, et al., 2005 Formaldehyde emission (ppm) Kim, 2001 Density (g/[cm.sup.3]) Ajayi, et al., 2005