Waste cotton and sawdust are used as raw materials, and are hydrolyzed into alkali cellulose ether under the action of 18% alkali and a series of additives. Then use epoxy resin for grafting, the molar ratio of epoxy resin and alkali fiber is 0.5:1.0, the reaction temperature is 100°C, the reaction time is 5.0h, the catalyst dosage is 1%, and the etherification grafting rate is 32%. The obtained epoxy cellulose ether is blended with 0.6mol Cel-Ep and 0.4mol CAB to synthesize a new coating product with good performance. The product structure was confirmed with IR.
Key words: cellulose ether; synthesis; CAB; coating properties
Cellulose ether is a natural polymer, which is formed by condensation of β-glucose. Cellulose has a high degree of polymerization, a good degree of orientation, and good chemical stability. It can be obtained by chemically treating cellulose (esterification or etherification). A series of cellulose derivatives, these products are widely used in plastics, biodegradable lunch boxes, high-end automotive coatings, auto parts, printing inks, adhesives, etc. At present, new modified cellulose varieties are constantly emerging, and the application fields are constantly expanding, gradually forming a fiber industry system. This topic is to use sawdust or waste cotton to be hydrolyzed into short fibers by lye, and then chemically grafted and modified to form a new type of coating that has not been reported in the document.
1. Experiment
1.1 Reagents and instruments
Waste cotton (washed and dried), NaOH, 1,4-butanediol, methanol, thiourea, urea, epoxy resin, acetic anhydride, butyric acid, trichloroethane, formic acid, glyoxal, toluene, CAB, etc. (Purity is CP grade). The Magna-IR 550 infrared spectrometer produced by Nicolet Company of the United States was used to prepare the samples by solvent tetrahydrofuran coating. Tu-4 viscometer, FVXD3-1 type constant temperature self-controlled electric stirring reaction kettle, produced by Weihai Xiangwei Chemical Machinery Factory; rotational viscometer NDJ-7, Z-10MP5 type, produced by Shanghai Tianping Instrument Factory; molecular weight is measured by Ubbelohde viscosity; The preparation and testing of the paint film shall be carried out according to the national standard GB-79.
1.2 Reaction principle
1.3 Synthesis
Synthesis of epoxy cellulose: Add 100g of chopped cotton fiber to a constant temperature self-controlled electric stirring reactor, add an oxidant and react for 10 minutes, then add alcohol and alkali to make a lye with a concentration of 18%. Add accelerators A, B, etc. for impregnation. React at a certain temperature under vacuum for 12 hours, filter, dry and weigh 50g of alkalized cellulose, add mixed solvent to make a slurry, add catalyst and epoxy resin with specific molecular weight, heat up to 90~110℃ for etherification reaction 4.0~ 6.0h until the reactants are miscible. Add formic acid to neutralize and remove excess alkali, separate the aqueous solution and solvent, wash with 80 ℃ hot water to remove sodium salt, and dry for later use. The intrinsic viscosity was measured with an Ubbelohde viscometer and the viscosity-average molecular weight was calculated according to the literature.
Acetate butyl cellulose is prepared according to the literature method, weigh 57.2g of refined cotton, add 55g of acetic anhydride, 79g of butyric acid, 9.5g of magnesium acetate, 5.1g of sulfuric acid, use butyl acetate as solvent, and react at a certain temperature until qualified , neutralized by adding sodium acetate, precipitated, filtered, washed, filtered, and dried for later use. Take Cel-Ep, add appropriate amount of CAB and specific mixed solvent, heat up and stir for 0.5h to form a uniform thick liquid, and the coating film preparation and performance test follow the GB-79 method.
Determination of the degree of esterification of cellulose acetate: first dissolve cellulose acetate in dimethyl sulfoxide, add a metered amount of alkali solution to heat and hydrolyze, and titrate the hydrolyzed solution with NaOH standard solution to calculate the total consumption of alkali. Determination of water content: Place the sample in an oven at 100~105°C to dry for 0.2h, weigh and calculate the water absorption after cooling. Determination of alkali absorption: weigh a quantitative sample, dissolve it in hot water, add methyl violet indicator, and then titrate with 0.05mol/L H2SO4. Determination of expansion degree: Weigh 50g sample, crush it and put it into a graduated tube, read the volume after electric vibration, and compare it with the volume of unalkalined cellulose powder to calculate the expansion degree.
2. Results and discussion
2.1 The relationship between alkali concentration and cellulose swelling degree
The reaction of cellulose with a certain concentration of NaOH solution can destroy the regular and orderly crystallization of cellulose and make the cellulose swell. And various degradations occur in lye, reducing the degree of polymerization. Experiments show that the degree of swelling of cellulose and the amount of alkali binding or adsorption increase with the concentration of alkali. The degree of hydrolysis increases with the increase of temperature. When the alkali concentration reaches 20%, the degree of hydrolysis is 6.8% at t=100°C; the degree of hydrolysis is 14% at t=135°C. At the same time, the experiment shows that when the alkali is more than 30%, the degree of hydrolysis of cellulose chain scission is significantly reduced. When the alkali concentration reaches 18%, the adsorption capacity and swelling degree of water are the maximum, the concentration continues to increase, drops sharply to a plateau, and then changes steadily. At the same time, this change is quite sensitive to the influence of temperature. Under the same alkali concentration, when the temperature is low (<20°C), the swelling degree of cellulose is large, and the adsorption amount of water is large; at high temperature, the swelling degree and water adsorption amount are significant. reduce.
Alkali fibers with different water content and alkali content were determined by X-ray diffraction analysis method according to the literature. In actual operation, 18%~20% lye is used to control a certain reaction temperature to increase the swelling degree of cellulose. Experiments show that the cellulose reacted by heating for 6~12h can be dissolved in polar solvents. Based on this fact, the author thinks that the solubility of cellulose plays a decisive role in the degree of hydrogen bond destruction between cellulose molecules in the crystalline segment, followed by the degree of hydrogen bond destruction of intramolecular glucose groups C3-C2. The greater the degree of hydrogen bond destruction, the greater the swelling degree of the alkali fiber, and the hydrogen bond is completely destroyed, and the final hydrolyzate is a water-soluble substance.
2.2 Effect of Accelerator
Adding high-boiling-point alcohol during cellulose alkalization can increase the reaction temperature, and adding a small amount of propellant such as lower alcohol and thiourea (or urea) can greatly promote the penetration and swelling of cellulose. As the concentration of alcohol increases, the alkali absorption of cellulose increases, and there is a sudden change point when the concentration is 20%, which may be that the monofunctional alcohol penetrates into the cellulose molecules to form hydrogen bonds with cellulose, preventing the cellulose molecules The hydrogen bonds between chains and molecular chains increase the degree of disorder, increase the surface area, and increase the amount of alkali adsorption. However, under the same conditions, the alkali absorption of wood chips is low, and the curve changes in a fluctuating state. It may be related to the low content of cellulose in wood chips, which contains a large amount of lignin, which hinders the penetration of alcohol, and has good water resistance and alkali resistance.
2.3 Etherification
Add 1% B catalyst, control different reaction temperatures, and carry out etherification modification with epoxy resin and alkali fiber. The etherification reaction activity is low at 80°C. The grafting rate of Cel is only 28%, and the etherification activity is nearly doubled at 110°C. Considering the reaction conditions such as solvent, the reaction temperature is 100°C, and the reaction time is 2.5h, and the grafting rate of Cel can reach 41%. In addition, at the initial stage of the etherification reaction (<1.0h), due to the heterogeneous reaction between alkali cellulose and epoxy resin, the grafting rate is low. With the increase of Cel etherification degree, it gradually turns into a homogeneous reaction, so the reaction The activity increased sharply, and the grafting rate increased.
2.4 Relationship between Cel grafting rate and solubility
Experiments have shown that after grafting epoxy resin with alkali cellulose, the physical properties such as product viscosity, adhesion, water resistance, and thermal stability can be significantly improved. Solubility test The product with Cel grafting rate <40% can be dissolved in lower alcohol-ester, alkyd resin, polyacrylic acid resin, acrylic pimaric acid and other resins. Cel-Ep resin has obvious solubilizing effect.
Combined with the coating film test, the blends with a grafting rate of 32%~42% generally have better compatibility, and the blends with a grafting rate of <30% have poor compatibility and low gloss of the coating film; the grafting rate is higher than 42%, the boiling water resistance, alcohol resistance, and polar organic solvent resistance of the coating film are reduced. In order to improve the material compatibility and coating performance, the author added CAB according to the formula in Table 1 to further solubilize and modify to promote the co-existence of Cel-Ep and CAB. The mixture forms an approximate homogeneous system. The composition interface thickness of the blend tends to be very thin and try to be in the state of nano-cells.
2.5 Relationship between Cel—Ep/CAB blending ratio and physical properties
Using Cel-Ep to blend with CAB, the coating test results show that cellulose acetate can significantly improve the coating properties of the material, especially the drying speed. The pure component of Cel-Ep is difficult to dry at room temperature. After adding CAB, the two materials have obvious performance complementarity.
2.6 FTIR spectrum detection
3. Conclusion
(1) Cotton cellulose can swell at 80°C with >18% concentrated alkali and a series of additives, increase the reaction temperature, prolong the reaction time, increase the degree of swelling and degradation until it is completely hydrolyzed.
(2) Etherification reaction, the Cel-Ep molar feed ratio is 2, the reaction temperature is 100°C, the time is 5h, the catalyst dosage is 1%, and the etherification grafting rate can reach 32%~42%.
(3) Blending modification, when the molar ratio of Cel-Ep:CAB=3:2, the performance of the synthesized product is good, but pure Cel-Ep cannot be used as a coating, only as an adhesive.