Microcrystalline cellulose (MCC) with a definite degree of polymerization obtained by acid hydrolysis of cellulose cotton pulp was used as raw material. Under the activation of sodium hydroxide, it was reacted with 1,4-butane sultone (BS) to obtain A cellulose butyl sulfonate (SBC) water reducer with good water solubility was developed. The product structure was characterized by infrared spectroscopy (FT-IR), nuclear magnetic resonance spectroscopy (NMR), scanning electron microscopy (SEM), X-ray diffraction (XRD) and other analytical methods, and the polymerization degree, raw material ratio, and reaction of MCC were investigated. Effects of synthetic process conditions such as temperature, reaction time, and type of suspending agent on the water-reducing performance of the product. The results show that: when the degree of polymerization of the raw material MCC is 45, the mass ratio of the reactants is: AGU (cellulose glucoside unit): n (NaOH): n (BS) = 1.0: 2.1: 2.2, The suspending agent is isopropanol, the activation time of the raw material at room temperature is 2 h, and the synthesis time of the product is 5 h. When the temperature is 80°C, the obtained product has the highest degree of substitution of butanesulfonic acid groups, and the product has the best water-reducing performance.
Key words: cellulose; cellulose butylsulfonate; water reducing agent; water reducing performance
1、Introduction
Concrete superplasticizer is one of the indispensable components of modern concrete. It is precisely because of the appearance of water reducing agent that the high workability, good durability and even high strength of concrete can be guaranteed. The currently widely used high-efficiency water reducers mainly include the following categories: naphthalene-based water reducer (SNF), sulfonated melamine resin-based water-reducer (SMF), sulfamate-based water-reducer (ASP), modified Lignosulfonate superplasticizer (ML), and polycarboxylate superplasticizer (PC), which is currently researched more actively. Analyzing the synthesis process of water reducers, most of the previous traditional condensate water reducers use formaldehyde with a strong pungent smell as raw material for polycondensation reaction, and the sulfonation process is generally carried out with highly corrosive fuming sulfuric acid or concentrated sulfuric acid. This will inevitably cause adverse effects on workers and the surrounding environment, and will also generate a large amount of waste residue and waste liquid, which is not conducive to sustainable development; however, although polycarboxylate water reducers have the advantages of small loss of concrete over time, low dosage, good flow It has the advantages of high density and no toxic substances such as formaldehyde, but it is difficult to promote it in China due to the high price. From the analysis of the source of raw materials, it is not difficult to find that most of the above-mentioned water reducers are synthesized based on petrochemical products/by-products, while petroleum, as a non-renewable resource, is increasingly scarce and its price is constantly rising. Therefore, how to use cheap and abundant natural renewable resources as raw materials to develop new high-performance concrete superplasticizers has become an important research direction for concrete superplasticizers.
Cellulose is a linear macromolecule formed by connecting many D-glucopyranose with β-(1-4) glycosidic bonds. There are three hydroxyl groups on each glucopyranosyl ring. Proper treatment can obtain a certain reactivity. In this paper, cellulose cotton pulp was used as the initial raw material, and after acid hydrolysis to obtain microcrystalline cellulose with a suitable degree of polymerization, it was activated by sodium hydroxide and reacted with 1,4-butane sultone to prepare butyl sulfonate Acid cellulose ether superplasticizer, and the influencing factors of each reaction were discussed.
2. Experiment
2.1 Raw materials
Cellulose cotton pulp, polymerization degree 576, Xinjiang Aoyang Technology Co., Ltd.; 1,4-butane sultone (BS), industrial grade, produced by Shanghai Jiachen Chemical Co., Ltd.; 52.5R ordinary Portland cement, Urumqi Provided by the cement factory; China ISO standard sand, produced by Xiamen Ace Ou Standard Sand Co., Ltd.; sodium hydroxide, hydrochloric acid, isopropanol, anhydrous methanol, ethyl acetate, n-butanol, petroleum ether, etc., are all analytically pure, commercially available.
2.2 Experimental method
Weigh a certain amount of cotton pulp and grind it properly, put it into a three-neck bottle, add a certain concentration of dilute hydrochloric acid, stir to heat up and hydrolyze for a certain period of time, cool to room temperature, filter, wash with water until neutral, and vacuum dry at 50°C to obtain After having microcrystalline cellulose raw materials with different degrees of polymerization, measure their degree of polymerization according to the literature, put it in a three-necked reaction bottle, suspend it with a suspending agent 10 times its mass, add a certain amount of sodium hydroxide aqueous solution under stirring, Stir and activate at room temperature for a certain period of time, add the calculated amount of 1,4-butane sultone (BS), heat up to the reaction temperature, react at constant temperature for a certain period of time, cool the product to room temperature, and obtain the crude product by suction filtration. Rinse with water and methanol for 3 times, and filter with suction to obtain the final product, namely cellulose butylsulfonate water reducer (SBC).
2.3 Product analysis and characterization
2.3.1 Determination of product sulfur content and calculation of degree of substitution
The FLASHEA-PE2400 elemental analyzer was used to conduct elemental analysis on the dried cellulose butyl sulfonate water reducer product to determine the sulfur content.
2.3.2 Determination of fluidity of mortar
Measured according to 6.5 in GB8076-2008. That is, first measure the water/cement/standard sand mixture on the NLD-3 cement mortar fluidity tester when the expansion diameter is (180±2)mm. cement, the measured benchmark water consumption is 230g), and then add a water reducing agent whose mass is 1% of the cement mass to the water, according to cement/water reducing agent/standard water/standard sand=450g/4.5g/230 g/ The ratio of 1350 g is placed in a JJ-5 cement mortar mixer and stirred evenly, and the expanded diameter of the mortar on the mortar fluidity tester is measured, which is the measured mortar fluidity.
2.3.3 Product Characterization
The sample was characterized by FT-IR using the EQUINOX 55 type Fourier transform infrared spectrometer of Bruker Company; the H NMR spectrum of the sample was characterized by the INOVA ZAB-HS plow superconducting nuclear magnetic resonance instrument of Varian Company; The morphology of the product was observed under a microscope; XRD analysis was carried out on the sample by using an X-ray diffractometer of MAC Company M18XHF22-SRA.
3. Results and discussion
3.1 Characterization results
3.1.1 FT-IR characterization results
Infrared analysis was carried out on the raw material microcrystalline cellulose with a degree of polymerization Dp=45 and the product SBC synthesized from this raw material. Since the absorption peaks of S-C and S-H are very weak, they are not suitable for identification, while S=O has a strong absorption peak. Therefore, whether there is a sulfonic acid group in the molecular structure can be determined by confirming the existence of the S=O peak. Obviously, in the cellulose spectrum, there is a strong absorption peak at a wave number of 3344 cm-1, which is attributed to the hydroxyl stretching vibration peak in cellulose; the stronger absorption peak at a wave number of 2923 cm-1 is the stretching vibration peak of methylene (-CH2). Vibration peak; the series of bands composed of 1031, 1051, 1114, and 1165cm-1 reflect the absorption peak of hydroxyl stretching vibration and the absorption peak of ether bond (C-O-C) bending vibration; the wave number 1646cm-1 reflects the hydrogen formed by hydroxyl and free water The bond absorption peak; the band of 1432~1318cm-1 reflects the existence of cellulose crystal structure. In the IR spectrum of SBC, the intensity of the band 1432~1318cm-1 weakens; while the intensity of the absorption peak at 1653 cm-1 increases, indicating that the ability to form hydrogen bonds is strengthened; 1040, 605cm-1 appears stronger Absorption peaks, and these two are not reflected in the infrared spectrum of cellulose, the former is the characteristic absorption peak of the S=O bond, and the latter is the characteristic absorption peak of the S-O bond. Based on the above analysis, it can be seen that after the etherification reaction of cellulose, there are sulfonic acid groups in its molecular chain.
3.1.2 H NMR characterization results
The H NMR spectrum of cellulose butyl sulfonate can be seen: within γ=1.74~2.92 is the hydrogen proton chemical shift of cyclobutyl, and within γ=3.33~4.52 is the cellulose anhydroglucose unit The chemical shift of the oxygen proton in γ=4.52~6 is the chemical shift of the methylene proton in the butylsulfonic acid group connected to oxygen, and there is no peak at γ=6~7, indicating that the product is not Other protons exist.
3.1.3 SEM characterization results
SEM observation of cellulose cotton pulp, microcrystalline cellulose and product cellulose butylsulfonate. By analyzing the SEM analysis results of cellulose cotton pulp, microcrystalline cellulose and the product cellulose butanesulfonate (SBC), it is found that the microcrystalline cellulose obtained after hydrolysis with HCL can significantly change the structure of cellulose fibers. The fibrous structure was destroyed, and fine agglomerated cellulose particles were obtained. The SBC obtained by further reacting with BS had no fibrous structure and basically transformed into an amorphous structure, which was beneficial to its dissolution in water.
3.1.4 XRD characterization results
The crystallinity of cellulose and its derivatives refers to the percentage of the crystalline region formed by the cellulose unit structure in the whole. When cellulose and its derivatives undergo a chemical reaction, the hydrogen bonds in the molecule and between molecules are destroyed, and the crystalline region will become an amorphous region, thereby reducing the crystallinity. Therefore, the change in crystallinity before and after the reaction is a measure of cellulose One of the criteria to participate in the response or not. XRD analysis was performed on microcrystalline cellulose and the product cellulose butanesulfonate. It can be seen by comparison that after etherification, the crystallinity changes fundamentally, and the product has completely transformed into an amorphous structure, so that it can be dissolved in water.
3.2 The effect of the degree of polymerization of raw materials on the water-reducing performance of the product
The fluidity of the mortar directly reflects the water-reducing performance of the product, and the sulfur content of the product is one of the most important factors affecting the fluidity of the mortar. The fluidity of the mortar measures the water-reducing performance of the product.
After changing the hydrolysis reaction conditions to prepare MCC with different degrees of polymerization, according to the above method, select a certain synthesis process to prepare SBC products, measure the sulfur content to calculate the product substitution degree, and add the SBC products to the water/cement/standard sand mixing system Measure the fluidity of the mortar.
It can be seen from the experimental results that within the research range, when the polymerization degree of the microcrystalline cellulose raw material is high, the sulfur content (substitution degree) of the product and the fluidity of the mortar are low. This is because: the molecular weight of the raw material is small, which is conducive to the uniform mixing of the raw material And the penetration of etherification agent, thereby improving the degree of etherification of the product. However, the product water reduction rate does not rise in a straight line with the decrease of the degree of polymerization of raw materials. The experimental results show that the mortar fluidity of the cement mortar mixture mixed with SBC prepared by using microcrystalline cellulose with a degree of polymerization Dp<96 (molecular weight<15552) is greater than 180 mm (which is greater than that without water reducer). benchmark fluidity), indicating that SBC can be prepared by using cellulose with a molecular weight of less than 15552, and a certain water reducing rate can be obtained; SBC is prepared by using microcrystalline cellulose with a degree of polymerization of 45 (molecular weight: 7290), and added to the concrete mixture , the measured fluidity of the mortar is the largest, so it is considered that the cellulose with a degree of polymerization of about 45 is most suitable for the preparation of SBC; when the degree of polymerization of raw materials is greater than 45, the fluidity of the mortar gradually decreases, which means that the water reducing rate decreases. This is because when the molecular weight is large, on the one hand, the viscosity of the mixture system will increase, the dispersion uniformity of the cement will be deteriorated, and the dispersion in concrete will be slow, which will affect the dispersion effect; on the other hand, when the molecular weight is large, The macromolecules of the superplasticizer are in a random coil conformation, which is relatively difficult to adsorb on the surface of cement particles. But when the degree of polymerization of the raw material is less than 45, although the sulfur content (substitution degree) of the product is relatively large, the fluidity of the mortar mixture also begins to decrease, but the decrease is very small. The reason is that when the molecular weight of the water reducing agent is small, although the molecular diffusion is easy and has good wettability, the adsorption fastness of the molecule is larger than that of the molecule, and the water transport chain is very short, and the friction between the particles is large, which is harmful to concrete. The dispersion effect is not as good as that of the water reducer with larger molecular weight. Therefore, it is very important to properly control the molecular weight of pig face (cellulose segment) to improve the performance of the water reducer.
3.3 The effect of reaction conditions on the water-reducing performance of the product
It is found through experiments that in addition to the degree of polymerization of MCC, the ratio of reactants, reaction temperature, activation of raw materials, product synthesis time, and type of suspending agent all affect the water-reducing performance of the product.
3.3.1 Reactant ratio
(1) The dosage of BS
Under the conditions determined by other process parameters (the degree of polymerization of MCC is 45, n(MCC):n(NaOH)=1:2.1, the suspending agent is isopropanol, the activation time of cellulose at room temperature is 2h, the synthesis temperature is 80°C, and the synthesis time 5h), to investigate the effect of the amount of etherification agent 1,4-butane sultone (BS) on the degree of substitution of butanesulfonic acid groups of the product and the fluidity of the mortar.
It can be seen that as the amount of BS increases, the degree of substitution of butanesulfonic acid groups and the fluidity of the mortar increase significantly. When the ratio of BS to MCC reaches 2.2:1, the fluidity of DS and the mortar reaches the maximum. value, it is considered that the water-reducing performance is the best at this time. The BS value continued to increase, and both the degree of substitution and the fluidity of the mortar began to decrease. This is because when BS is excessive, BS will react with NaOH to generate H-O-(CH2)4SO3Na. Therefore, this paper chooses the optimal material ratio of BS to MCC as 2.2:1.
(2) The dosage of NaOH
Under the conditions determined by other process parameters (the degree of polymerization of MCC is 45, n(BS):n(MCC)=2.2:1. The suspending agent is isopropanol, the activation time of cellulose at room temperature is 2h, the synthesis temperature is 80°C, and the synthesis time 5h), to investigate the effect of the amount of sodium hydroxide on the degree of substitution of butanesulfonic acid groups in the product and the fluidity of the mortar.
It can be seen that, with the increase of the reduction amount, the degree of substitution of SBC increases rapidly, and begins to decrease after reaching the highest value. This is because, when the NaOH content is high, there are too many free bases in the system, and the probability of side reactions increases, resulting in more etherification agents (BS) participating in side reactions, thereby reducing the degree of substitution of sulfonic acid groups in the product. At a higher temperature, the presence of too much NaOH will also degrade the cellulose, and the water-reducing performance of the product will be affected at a lower degree of polymerization. According to the experimental results, when the molar ratio of NaOH to MCC is about 2.1, the degree of substitution is the largest, so this paper determines that the molar ratio of NaOH to MCC is 2.1:1.0.
3.3.2 Effect of reaction temperature on product water-reducing performance
Under the conditions determined by other process parameters (the degree of polymerization of MCC is 45, n(MCC):n(NaOH):n(BS)=1:2.1:2.2, the suspending agent is isopropanol, and the activation time of cellulose at room temperature is 2h. Time 5h), the influence of synthesis reaction temperature on the degree of substitution of butanesulfonic acid groups in the product was investigated.
It can be seen that as the reaction temperature increases, the sulfonic acid substitution degree DS of SBC gradually increases, but when the reaction temperature exceeds 80 °C, DS shows a downward trend. The etherification reaction between 1,4-butane sultone and cellulose is an endothermic reaction, and increasing the reaction temperature is beneficial to the reaction between etherifying agent and cellulose hydroxyl group, but with the increase of temperature, the effect of NaOH and cellulose gradually increases. It becomes strong, causing the cellulose to degrade and fall off, resulting in a decrease in the molecular weight of cellulose and the generation of small molecular sugars. The reaction of such small molecules with etherifying agents is relatively easy, and more etherifying agents will be consumed, affecting the degree of substitution of the product. Therefore, this thesis considers that the most suitable reaction temperature for the etherification reaction of BS and cellulose is 80℃.
3.3.3 Effect of reaction time on product water-reducing performance
The reaction time is divided into room temperature activation of raw materials and constant temperature synthesis time of products.
(1) Room temperature activation time of raw materials
Under the above optimal process conditions (MCC degree of polymerization is 45, n(MCC):n(NaOH):n(BS)=1:2.1:2.2, suspending agent is isopropanol, synthesis reaction temperature is 80°C, the product Constant temperature synthesis time 5h), investigate the influence of room temperature activation time on the degree of substitution of the product butanesulfonic acid group.
It can be seen that the degree of substitution of the butanesulfonic acid group of the product SBC increases first and then decreases with the prolongation of the activation time. The analysis reason may be that with the increase of NaOH action time, the degradation of cellulose is serious. Decrease the molecular weight of cellulose to generate small molecular sugars. The reaction of such small molecules with etherifying agents is relatively easy, and more etherifying agents will be consumed, affecting the degree of substitution of the product. Therefore, this paper considers that the room temperature activation time of raw materials is 2h.
(2) Product synthesis time
Under the optimal process conditions above, the effect of activation time at room temperature on the degree of substitution of the product’s butanesulfonic acid group was investigated. It can be seen that with the prolongation of the reaction time, the degree of substitution first increases, but when the reaction time reaches 5h, the DS shows a downward trend. This is related to the free base present in the etherification reaction of cellulose. At higher temperatures, the prolongation of the reaction time leads to an increase in the degree of alkali hydrolysis of cellulose, a shortening of the cellulose molecular chain, a decrease in the molecular weight of the product, and an increase in side reactions, resulting in substitution. degree decreases. In this experiment, the ideal synthesis time is 5h.
3.3.4 The effect of the type of suspending agent on the water-reducing performance of the product
Under the optimal process conditions (MCC polymerization degree is 45, n(MCC):n(NaOH):n(BS)=1:2.1:2.2, the activation time of raw materials at room temperature is 2h, the constant temperature synthesis time of products is 5h, and the synthesis reaction temperature 80 ℃), respectively choose isopropanol, ethanol, n-butanol, ethyl acetate and petroleum ether as suspending agents, and discuss their influence on the water-reducing performance of the product.
Obviously, isopropanol, n-butanol and ethyl acetate can all be used as suspending agent in this etherification reaction. The role of the suspending agent, in addition to dispersing the reactants, can control the reaction temperature. The boiling point of isopropanol is 82.3°C, so isopropanol is used as a suspending agent, the temperature of the system can be controlled near the optimum reaction temperature, and the degree of substitution of butanesulfonic acid groups in the product and the fluidity of the mortar are relatively high; while the boiling point of ethanol is too high Low, the reaction temperature does not meet the requirements, the degree of substitution of butanesulfonic acid groups in the product and the fluidity of the mortar are low; petroleum ether may participate in the reaction, so no dispersed product can be obtained.
4 Conclusion
(1) Using cotton pulp as the initial raw material, microcrystalline cellulose (MCC) with a suitable degree of polymerization was prepared, activated by NaOH, and reacted with 1,4-butane sultone to prepare water-soluble butylsulfonic acid Cellulose ether, that is, cellulose-based water reducer. The structure of the product was characterized, and it was found that after the etherification reaction of cellulose, there were sulfonic acid groups on its molecular chain, which had transformed into an amorphous structure, and the water reducer product had good water solubility;
(2) Through experiments, it is found that when the degree of polymerization of microcrystalline cellulose is 45, the water-reducing performance of the obtained product is the best; under the condition that the degree of polymerization of raw materials is determined, the ratio of reactants is n(MCC):n(NaOH):n( BS)=1:2.1:2.2, the activation time of raw materials at room temperature is 2h, the product synthesis temperature is 80°C, and the synthesis time is 5h. Water performance is optimal.