Woodworking hand made puzzle glue
Time：2013/09/18 8:45:49 Hits：1730
Woodworking hand made puzzle glue
Experiment method is as follows:
An experimental introduction
Urea-formaldehyde resin is a condensation from the urea and formaldehyde synthetic resin, is currently the most widely used types of adhesives, it is also used in wood processing industry the largest synthetic resin adhesive, the industry accounted for 80% of the amount of adhesive used above.
Urea-formaldehyde resin can be used in addition to wood adhesives, can also be applied to textiles, paper, musical instruments and other treatment agents, coatings, composites and plastics.
Second, the purpose of the experiment
Through this experimental study and practice, so that students understand the basic urea formaldehyde resin synthesis process, so as to enhance understanding of the principles for the polycondensation reaction, the synthesis of urea formaldehyde resin grasp principles and basic synthesis process.
Third, security and protection
Experiments used in formic acid and sodium hydroxide may have some corrosion, if accidentally come into contact with skin, wash immediately with water; should avoid splashing into the eyes, such as accidentally splashed into the eyes, rinse immediately with plenty of water and immediately to the hospital for medical treatment.
Formaldehyde solution is a solution with a strong irritant volatile, the weighing of formaldehyde solution, because it may cause eye irritation tears; very few people may be allergic to formaldehyde, formaldehyde solution thus weighing rash or itching should immediately stop the experiment and the air circulation.
Fourth, the experimental principle
The synthesis of urea-formaldehyde resin can be alkali - acid - alkali or acid synthesis - alkali process, the latter reaction rate, complex process, and the product side reactions and other issues, so the industry usually alkali - acid - alkaline urea-formaldehyde resin prepared by synthesis , the preparation process is usually divided into two phases: the addition reaction and the polycondensation reaction.
A) urea and formaldehyde in neutral or weakly alkaline medium by addition reaction of a methylol urea and bis (hydroxymethyl) urea. Under special conditions, excess formaldehyde, they can generate three or four methylol urea, methylol ureas, but the four methylol ureas had never been isolated.
Five, formulation design
Determine the performance of urea-formaldehyde resin is one of the key factors during the synthesis of urea / formaldehyde (F / U) molar ratio. In general, F / U molar ratio, the high degree of hydroxymethyl resin, crosslinking density after curing, the bonding strength is high; while the high F / U molar ratio of the resin curing time is short, easy to cure; but With the F / U molar ratio increases, the free formaldehyde content was increased, and the urea-formaldehyde resin decreased water resistance. So in order to prepare a good overall performance are urea-formaldehyde resin, the first step is to choose the appropriate F / U molar ratio, and then use the appropriate synthesis process.
In this study, the synthesis of secondary preparation of urea urea-formaldehyde resin adhesive, the first is used for the synthesis of urea urea-formaldehyde resin binder, adhesive properties to determine the final resin, urea is the first in a weak base addition reaction conditions, Then under acidic polycondensation reaction; second is to reduce the final of urea formaldehyde resins, urea applied in a neutral or weakly alkaline conditions with a system of free formaldehyde addition reaction.
Industrially, the amount of urea first posed F / U molar ratio is usually between 1.5-2.5. Low F / U molar ratio is conducive to reducing urea formaldehyde resin of free formaldehyde release, improved resin water resistance, but will make the bonding strength is reduced, the curing time extension; Gao F / U molar ratio, urea-formaldehyde resin bonding strength , fast curing time, but will make curing urea-formaldehyde resin, formaldehyde releasing improved water resistance decreases. Therefore, you should first select the appropriate amount of urea.
This experiment requires the ultimate synthesis of urea-formaldehyde resin total F / U molar ratio of 1.30, and twice that number of moles of formaldehyde urea molar ratio of the sum.
Six, reagents and instruments
About 36.5% formaldehyde solution, 98% urea, 30% formic acid, 30% sodium hydroxide solution, distilled water;
500mL three bottles, a reflux condenser, a stirrer, water bath, pH meter, beaker, dropper dropper, sampling tubes, suction ear ball;
Also owned calculator.
Seven, experimental procedures
1) Calculation formula feeding
(A) the final F / U = 1.30; final total mass of urea-formaldehyde resin 350g or so.
(2) choose the first and second plus the amount of urea and formaldehyde solution accurately calculate the amount of the first and second plus urea quality;
(3) according to the last experiment, "Determination of formaldehyde" in the formaldehyde content analysis to calculate the actual amount of formaldehyde solution should be invested.
2) the aqueous solution of formaldehyde measured-necked flask, starting stirrer, and gradually adjusted to pH with NaOH 8.6;
3) adding the first batch of urea, heated to 85 ℃, 85 ℃ reaction conditions at 30min, pay attention to controlling the reaction temperature.
4) with formic acid of the reaction solution was adjusted to pH 5.0, and the reaction conditions in this 60min.
5) of the reaction solution was adjusted to pH 6.5 by adding a second batch of urea reaction conditions at 75 ℃ 10min.
6) The pH was adjusted to 8.0 and cooled. The material.
Eight, the commentary
Please keep the synthesized urea-formaldehyde resin obtained, please indicate the group and the name on the bottle, stored in the laboratory, but also in subsequent experiments applied.
Nine, lab reports
A) Write an experimental report.
2) self-description of this experiment, urea-formaldehyde resin experimental principles and experimental process.
3) Discussion of how to maximize the methylol urea-formaldehyde resin content.
4) Discussion of the two, your own qualitative description of the synthesized urea formaldehyde resin content analysis how to reduce the free formaldehyde content of the resin.
