(B) Synthesis of Cationic UF Resins
Urea-formaldehyde resin is referred to as urea-formaldehyde resin, which is formed by the polymerization of urea and formaldehyde. UF resins are classified into anionic and cationic types. The anionic UF resin is not easily combined with negatively charged fibers, the retention rate is low, and the wet strength effect is poor. The cationic UF resin is a modified cationic UF resin obtained by modifying an anionic UF resin. The wet strength obtained by the modified cationic UF resin can reach 50% or more of the dry strength, and the wet strength can be improved without affecting the other properties of the paper. At the same time, it can also make the paper crack length, burst resistance, folding degree and sizing degree increase correspondingly.
UF resin is a colorless (or grass yellow) clear, uniform, syrupy liquid that mixes with water in any ratio without precipitation. With ionic properties, cationic and anionic. When added to the pulp, the resin is absorbed by the fibers and retained on the fibers. Cationic UF resins are commonly used in the industry.
1. Synthetic method of ethylenediamine modified urea formaldehyde resin
(1) Characteristics: Ethylenediamine modified urea resin is a cationic resin. Because it is cationic, it has a stronger effect of humidification than unmodified urea formaldehyde resin. In addition, it also has good water solubility, is not easy to gel, is easy to manufacture and has low cost. It is made of urea and formaldehyde first, with the addition of ethylenediamine and other auxiliary chemicals.
(2) Raw Material: Urea (95%-100% Crystallized) 1mol
Formaldehyde (51% aqueous solution) 2.5mol
Ethylenediamine (98-100%) 0.1mol
Hydrochloric acid (38%) 0.1mol
Sodium hydroxide (25%) is suitable for controlling the pH of the resin solution
Formic acid (90%) is suitable for controlling the pH of the resin solution
(3) Equipment: measuring cylinder, balance, pH test paper, burette, heater (50Â°C-100Â°C), container with thermometer, stirrer and reflux condenser.
(4) Synthesis steps: A. Ethylene diamine salt was formed by reacting 9.5 ml of acid with 6.1 ml of ethylenediamine, and then 147 ml of formaldehyde solution was placed in a vessel equipped with a thermometer, a stirrer, and a reflux condenser.
B. The pH was controlled at 7.0-8.0, followed by 60 g of urea. The pH of the reaction solution was still controlled at 7.0 or higher.
C. The temperature was then raised. When the temperature gradually increased to 95Â°C, the pH was adjusted to 4.2 with formic acid. Due to the basicity of ethylenediamine, the pH of the reaction solution was increased to 6.2 and then reduced to 4.0 with formic acid. After about 20 minutes, the pH of the reaction solution was stabilized at 5.2-5.6, and the resin reaction was maintained. Performed at 95Â°C.
D. When the viscosity of the resin liquid reaches about 100 cp, the resin liquid is naturally cooled to 65-75[deg.] C. and the resin reaction is continued.
E. When the desired viscosity of the resin solution (about 0.15 Pa.s) is reached, it is rapidly cooled to room temperature, and the resin solution is adjusted to 7.2-7.6 with 25% NaOH solution. The solid content of the resin liquid obtained at this time is about 51% to 53%, and is diluted with water to a concentration of about 45%.
(5) Storage method: The resin solution with a concentration of 45% is stored below 20Â°C.
2. Synthetic method of polyamine modified urea formaldehyde resin
(1) Characteristics: The polyamine modified urea-formaldehyde resin is also a cationic resin. Because it has two active groups, it has a strong effect of humidification. In addition, it has a wide range of pH values â€‹â€‹and good Stability and other advantages.
If the polyamine-modified urea-formaldehyde resin has a sufficient molecular weight, when it is cured by adding it to the pulp, the resin forms a reticulated body structure, ie, the resin molecules and the pulp fibers are joined together in the longitudinal direction, so that the wet strength of the paper is remarkably increased.
(2) Raw materials: urea 200g (pure)
Diethylenetriamine 1/3 and Triethylenetetramine 2/3 148g (Pure)
Ethylene glycol 100ml (pure)
Formaldehyde (37%) 124g
NaOH (10%) 17ml
(3) Containers: scales, beakers, oil bath heaters, thermometers, stirrers, pH test papers and indicators, measuring cylinders, etc.
(4) Synthesis method: A, urea 220, 148 g of diethylenetriamine 1/3 and triethylene tetraamine 2/3, and heated to 145-150Â°C in 64 minutes (oil bath heating).
B. Incubate for 15 minutes at 145-150Â°C.
C. After the temperature was lowered to 135Â° C., ethylene glycol 100 ml was added.
D. Stir and cool to room temperature to obtain a polyurea intermediate having a pH of 11.
E. Polyurea intermediate 1015.g and formaldehyde (37%) 102 g were heated together to 80Â°C.
F. Incubate 20mim at 80Â°C and pH 9.
G. Cool to 70Â° C., add 85% H3PO44.6 ml, water 65 ml, adjust the pH to 5.5, and incubate for 65 minutes.
H. Subsequently, 17% NaOH (17 ml), 37% HCHO (22 ml), and water (103 ml) were added, and the mixture was cooled to room temperature with stirring to obtain a polyamine modified urea resin having a pH of 4.
(5) Storage main method: Usually stored in a cool, ventilated and dry place, the storage period is 6 months.
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