Synthesis and application of water reducing agent for butane sulfonate cellulose ether

Abstract: After acid hydrolysis of cellulose cotton pulp to obtain microcrystalline cellulose cord (MCC) with a definite degree of polymerization, it was used as raw material, activated by sodium hydroxide, and 1,4-butane sultone (BS) After the reaction, a butylsulfonate cellulose ether (SBC) water reducer with good water solubility was obtained. The structure of the product was characterized by means of infrared spectroscopy (FTIR), nuclear magnetic resonance spectroscopy, scanning electron microscopy (SEM), and X-ray diffraction (XRD), and the synthesis of MCC polymerization degree, raw material ratio, reaction temperature, and reaction time were investigated. The effect of process conditions on the water-reducing performance of the product, and the performance of concrete mixed with SBC was measured. The results show that: when the degree of polymerization of the raw material MCC is 45, the reactant molar ratio n (AGU, cellulose glucoside unit): n (Na0H): n (BS) = 1.0: 2.1: 2.2, the raw material room temperature When the activation time is 2 h, the product synthesis time is 5 h, and the synthesis reaction temperature is 80 °C, the water-reducing performance of the obtained SBC product is the best, reaching the quality index of high-efficiency water-reducing agent (retarding type) in GB8076-2008.

Key words:cellulose; cellulose butylsulfonate; water reducing agent; water reducing performance

0、Preface

Because a large number of hydroxyl groups in the cellulose molecular chain are easily derivatized by esterification or etherification with some compounds under certain conditions, and some water-soluble cellulose derivatives show thickening and dispersion under certain conditions. , emulsification, solubilization, film-forming, protective colloid and other properties, and has a wide range of raw material sources, biodegradable, safe use and other characteristics, so water-soluble cellulose derivatives have been widely used in various industries. In the field of construction, research on cellulose derivatives as water reducers has also received attention, but no systematic preparation process for cellulose-based water reducers has yet been formed. Most of the existing cellulose derivatives that can be used as concrete water reducers are cellulose mixed ethers/mixed esters, which need to be prepared through multi-step chemical reactions, the reaction time is long, the consumption of reagents is large, and the application effect is low. There is still a certain gap with the current commercial water reducer, so it is necessary to further conduct in-depth and systematic research on the synthesis conditions and applications of cellulose-based water reducers, and explore its mechanism of action as a water reducer. This paper systematically studies the preparation of butyl sulfonate by reacting with 1,4-butane sultone using cotton pulp as the basic raw material and obtaining microcrystalline cellulose with a suitable degree of polymerization through acid hydrolysis. The technological process of acid cellulose ether superplasticizer is discussed, and the application performance of the product is discussed.

1. Preparation principle of cellulose-based water reducer

Cellulose is a linear macromolecule composed of many D-glucopyranose linked by β-(1-4) glycosidic bonds.

It can be seen that there are a large number of hydroxyl groups on the cellulose molecular chain, which has the characteristics of easy chemical reaction, easy modification and utilization, etc., and ionic groups that can interact with the surface of cement particles can be introduced into the cellulose molecular chain to prepare water-reducing agent.

The possibility of starch and cellulose ion derivatives as biodegradable dispersants for mortar/concrete was studied by Vieim et al. The results show that the higher the degree of hydrolysis of starch and cellulose, the lower the viscosity of the aqueous solution of the derivatized products, and the more obvious the fluidity of cement-based materials is. In the acid medium, the 1-4-B-glucosidic bond in the molecule of cellulose will be broken, which not only reduces the degree of polymerization, but also has the characteristics of being used as a mortar/concrete dispersant, and increases the number of hydroxyl groups. Reactivity can be improved.

Therefore, the idea of preparing cellulose-based water reducer in this study is to use cellulose cotton pulp as the initial raw material, after acid hydrolysis to obtain microcrystalline cellulose with a suitable degree of polymerization, and activate it with 1,4 - Butane sultone reaction to prepare butylsulfonate cellulose ether (SBC) water reducer.

The acidolysis reaction mechanism of cellulose can be divided into three stages: the glycoside oxygen atom on the cellulose is rapidly protonated; the positive charge on the glycoside oxygen is slowly transferred to Cl, and then a carbocation is formed and the glycosidic bond is broken; the water rapidly Attacks carbocations to give free glycosidic groups and reform hydronium ions. This process continues to cause successive breaks of cellulose molecular chains.

Sodium hydroxide activates cellulose, which can improve the accessibility of cellulose and make it easier for the hydroxyl groups on each glucose unit (AGU) of cellulose to undergo chemical reactions.

The synthesis process of cellulose-based water reducer, first, NaOH and cellulose generate alkali cellulose, and then, alkali cellulose and 1,4-butane sultone (BS) undergo etherification reaction to obtain butyl sulfonate fiber Plain ether (SBC) superplasticizer. At the same time, due to the presence of free sodium hydroxide in the system, side reactions with BS will occur, and a small amount of small molecular by-products will be obtained.

The generated butyl sulfonate cellulose ether contains strong hydrophilic butyl sulfonic acid groups. At the same time, the hydrogen bond association between the original cellulose molecules is destroyed, so that it cannot be crystallized, so it is soluble in water and has a surfactant The basic structure, when the degree of polymerization is appropriate, should be used as a dispersant for cement paste.

2. Test

2.1 Main 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.; P·0 52.5R grade cement, both Provided by Urumqi Cement Factory; China ISO standard sand, produced by Xiamen Ace Ou Standard Sand Co., Ltd.; sodium hydroxide, hydrochloric acid, isopropanol, anhydrous methanol, etc., are all analytically pure and commercially available.

2.2 Synthesis method

Weigh a certain amount of cotton pulp, put it into a three-neck bottle after proper crushing, add a certain concentration of dilute hydrochloric acid, heat up and hydrolyze for a certain period of time under stirring, cool to room temperature, filter, wash with water until neutral, and vacuum dry at 50°C to obtain Microcrystalline cellulose (MCC) raw materials with different degrees of polymerization. Determine the degree of polymerization of MCC according to the literature, put it into a three-necked reaction bottle, suspend it with isopropanol 10 times the mass of MCC, 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) is heated up to the reaction temperature, reacted at constant temperature for a certain period of time, the product is cooled to room temperature, and the crude product is obtained by suction filtration, then rinsed 3 times with anhydrous methanol, and suction filtration, The final product is obtained, namely butyl sulfonate cellulose ether superplasticizer (SBC).

2.3 Product Structure Characterization

Bruker Company EQUINOX 55 Fourier Transform Infrared Spectrometer was used to characterize the sample by FTlR; Varian Company INOVA ZAB-HS Superconducting NMR Spectrometer was used to characterize the lH NMR spectrum of the sample; LEO Company 1430VP Scanning Electron Microscope was used to observe Morphology of the product; XRD characterization of the sample was carried out by using a MAC company M18XHF22-SRA X-ray diffractometer.

2.4 Concrete performance testing

The fluidity of the mortar directly reflects the water-reducing performance of the product. Therefore, in this test, the fluidity of the mortar mixed with the SBC product is used to measure the water-reducing performance of the product.

The fluidity of the mortar is measured in accordance with 6.5 in GB 8076-2008. First, measure the water: cement: standard sand mixture required for the standard water consumption when the slump is (180±2) mm (this test uses P·O 52.5R grade cement, the measured standard water consumption is 230 g), and then Add water-reducing agent with a mass of 1% of the cement mass to the water, charge according to the ratio of cement: water-reducing agent: standard water: standard sand = 450:4.5:230:1 350, stir and mix well, and measure the mortar The expansion diameter on the jumping table is the fluidity of the measured mortar.

Refer to GB/T 8076-2008 concrete mixture test method to determine other properties of concrete.

3. Results and discussion

3.1 Characterization results

3.1.1 FTIR characterization results

Infrared analysis was performed on raw cellulose and product SBC.

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, it is determined whether there is a sulfonic acid group in the molecular structure by determining whether the S=O peak exists or not. Obviously, in the cellulose spectrum, there is a strong absorption peak at wave number 3 344 cm-1, which is attributed to the hydroxyl stretching vibration peak in cellulose; the strong absorption peak at wave number 2 923 cm-1 is methylene (-CH2 ) stretching vibration peak; the series of bands composed of 1031, 1051, 1114, and 1165cm-1 reflect the hydroxyl stretching vibration absorption peak and the ether bond (C-O-C) bending vibration absorption peak; the wave number 1646cm-1 reflects the formation of hydroxyl and free water The hydrogen 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 1653cm-1 increases, indicating that the ability to form hydrogen bonds is strengthened; strong absorption occurs at 1040 and 605cm-1 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

From the H NMR spectrum of cellulose butyl sulfonate, it can be seen that the hydrogen proton chemical shift of the butyl group is within γ=1.74~2.92, and the hydrogen proton chemical shift of the cellulose glucoside unit at γ=3.33~4.52 , no peak appears between γ=6~7, indicating that there are no other protons in the product.

3.1.3 SEM characterization results

SEM analysis was performed on cellulose cotton pulp, microcrystalline cellulose and the product cellulose butylsulfonate. By analyzing the SEM analysis results of cellulose cotton pulp, microcrystalline cellulose and the product cellulose butane sulfonate (SBC), it was found that the microcrystalline cellulose obtained after hydrolysis with HCL can significantly change the structure of cellulose fibers. The fibrous structure is destroyed, and fine agglomerated cellulose particles are obtained. The SBC obtained by further reacting with BS has no fibrous structure, and basically transforms into an amorphous structure, which is beneficial to its dissolution in water.

3.1.3 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 the chemical reaction of cellulose and its derivatives occurs, the hydrogen bonds in the molecule and between the molecules are destroyed, and the crystalline region will transform into an amorphous region, thereby reducing the crystallinity. Therefore, the change of crystallinity before and after the reaction is a measure of cellulose One of the criteria for participating in the response or not. X-ray diffraction analysis was performed on microcrystalline cellulose and the product cellulose butylsulfonate. It can be seen from the 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

After changing the hydrolysis reaction conditions to obtain MCC with different degrees of polymerization, select a certain synthesis process according to the aforementioned preparation method (the molar ratio of the reactants is n(MCC):n(NaOH):n(BS)=1:2.1:2.2 , the synthesis reaction temperature is 80°C, the activation time of the microcrystalline cellulose raw material at room temperature is 2 hours, and the product synthesis time is 5 hours), the SBC product is prepared, and the SBC water reducer is added to the mixing system (cement: water reducer: water: Standard sand = 450:4.5:230:1350) to measure the fluidity R of the mortar.

It can be seen from the test results that within the research range, when the degree of polymerization of the microcrystalline cellulose raw material is higher, the fluidity of the mortar is lower. Obviously, it is because the molecular weight of raw materials is large, which is conducive to the uniform mixing of raw materials and the penetration of etherification agent, thereby improving the degree of etherification of the product. However, the water-reducing performance of the product does not increase in a straight line with the decrease of the degree of polymerization of the raw materials. The test 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 is low. If it is greater than 180 mm (the benchmark fluidity when no water reducing agent is added), it means that SBC can be prepared by using microcrystalline cellulose with a degree of polymerization less than 96, and a certain water reducing rate can be obtained; SBC can be prepared by using microcrystalline cellulose with a degree of polymerization of 45. When it is added to the concrete mixture, the fluidity of the mortar is the largest, so it is considered that microcrystalline cellulose with a degree of polymerization of about 45 is most suitable for the preparation of SBC; the degree of polymerization of raw materials is greater than 45, and the fluidity of the mortar gradually decreases. Both the water reduction rate is reduced. 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 superplasticizer macromolecule is in random coil conformation, which is relatively difficult to adsorb on the surface of cement particles. However, when the degree of polymerization of the raw materials is less than 45, the fluidity of the mortar begins to decline again. 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 relatively large. , and the hydrophobic chain segment is very short, the friction between particles is relatively large, and the dispersion effect on concrete is not as good as that of a water reducer with a larger molecular weight. Therefore, it is very important to properly control the molecular weight of the main chain (that is, the cellulose segment) to improve the water reducing performance of the water reducing agent.

3.3 The influence of the preparation process of SBC 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 and synthesis time of products all affect the water-reducing performance of the product.

3.3.1 Mixing ratio of reactants

(1) The dosage of BS. Under the conditions of other determined process parameters (the degree of polymerization of MCC is 45, n(MCC):n(NaOH)=1:2.1, the activation time of cellulose at room temperature is 2 h, the synthesis temperature is 80°C, and the synthesis time is 5 h), The effect of the amount of etherifying agent 1,4--butane sultone (BS) on the water-reducing performance of the product was investigated.

Obviously, as the amount of BS increases, the fluidity of the mortar increases significantly. When the molar ratio of BS to MCC reaches 2.2:1, the fluidity of the mortar reaches the maximum value. It is considered that the water-reducing performance of the product is the best at this time. The amount of BS continued to increase, and the fluidity of the mortar began to decrease. This is because when the amount of BS is used in excess, many side reactions will occur. Therefore, the optimum molar ratio of Bs to MCC was chosen as 2.2:1 in this experiment.

(2) The amount of NaOH used. Under the conditions of other determined process parameters (Mcc degree of polymerization is 45, n(BS):n(MCC)=2.2:1, cellulose activation time at room temperature is 2 h, synthesis temperature is 80°C, synthesis time is 5 h), The effect of the amount of sodium hydroxide on the water-reducing performance of the product was investigated.

With the increase of the amount of alkali, the fluidity of the mortar mixed with SBC increased rapidly, and then began to decrease after reaching the highest value. This is because, when the NaOH content is large, there are too many free alkalis in the system, and the probability of side reactions increases, causing more etherification agents (BS) to participate in side reactions, reducing the degree of etherification of the product, thereby affecting the product. Water reducing performance. In addition, at higher temperatures, the presence of too much NaOH will also degrade cellulose. The degree of polymerization decreases, which affects the water-reducing performance of the product. According to the test results, when the molar ratio of NaOH to MCC is about 2.1, the fluidity of the mortar is the largest, so it is determined that the optimal molar ratio of NaOH to MCC is 2.1:1.0.

3.3.2 Reaction temperature

Under the conditions determined by other process parameters (MCC degree of polymerization is 45, n(MCC):n(NaOH):n(BS)=1:2.1:2.2, cellulose room temperature activation time 2 h synthesis time 5 h), to investigate the influence of the synthesis reaction temperature on the water-reducing performance of the product. It can be seen that as the reaction temperature increases, the fluidity of the mortar increases gradually, but when the reaction temperature exceeds 80°C, the fluidity of the mortar decreases.

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 the etherifying agent and the hydroxyl group of cellulose, but as the temperature increases, the effect of NaOH and cellulose gradually changes. Strongly, the cellulose degrades and falls off, resulting in a decrease in the molecular weight of the cellulose and the formation of small molecular sugars. The reaction of such small molecules with etherifying agents is relatively easy, and more etherifying agents will be consumed, which will affect the degree of etherification of the product. Therefore, it is considered that the most suitable reaction temperature for the etherification reaction of BS and cellulose is 80°C.

3.3.3 Reaction time

The reaction time is divided into the activation of raw materials and the synthesis time of products.

(1) Raw material activation time. Under the above optimal process conditions (MCC degree of polymerization is 45, n(MCC):n(NaOH):n(BS)=1:2.1:2.2, synthesis reaction temperature is 80°C, synthesis time is 5 h), the raw materials were investigated The effect of activation time at room temperature on the water-reducing performance of the product.

The fluidity of mortar mixed with SBC increases first and then decreases with the prolongation of the activation time at room temperature. The reason may be that with the increase of NaOH action time, the degradation of cellulose is serious, which reduces the molecular weight of cellulose and generates small molecular sugars. The reaction between such small molecules and etherification agent is relatively easy, and more etherification agent will be consumed, which will affect the degree of etherification of the product, thereby deteriorating the water-reducing performance of the product. Therefore, the room temperature activation time of raw materials is considered to be 2 h.

(2) Product synthesis time. Under the above optimal process conditions, the influence of product synthesis time on the water-reducing performance of the product was investigated.

As the synthesis reaction time prolongs, the fluidity of the mortar mixed with SBC increases gradually, but when the reaction time exceeds 5 h, the fluidity of the mortar decreases. This is related to the free alkali existing in the etherification reaction of cellulose. At higher temperatures, the prolongation of the reaction time will lead 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 The degree of etherification decreases, thus affecting the water-reducing performance of the product. In this experiment, the optimal synthesis reaction time was considered to be 5 h.

3.4 Application of SBC

3.4.1 Dosage of SBC

Under optimal synthesis conditions (MCC degree of polymerization is 45, n(MCC):n(NaOH):n(BS)=1:2.1.2.2, activation time at room temperature is 2 h, synthesis time is 5 h, synthesis reaction temperature is 80°C ), scale up the preparation of SBC superplasticizer products, and mix it with water: cement: standard sand mixture in different proportions to measure the fluidity of the mortar.

It can be seen that when the amount of SBC superplasticizer is 0.5% to 1.0% of the amount of cement (the amount of water reducer mentioned in the article is the percentage of solid powder in the cement mass), the fluidity of mortar increases with the increase of the amount. However, when the dosage is between 1.0% and 1.5%, the fluidity of the mortar decreases slightly with the increase of the dosage, but the change is not significant. Therefore, it is believed that the optimal dosage of butyl sulfonate cellulose ether superplasticizer is 1.0% of the cement dosage.

3.4.2 Properties of concrete mixed with SBC

According to GB 8076-2008, the concrete performance was determined when the SBC content was 1%.

This product is light yellow solid powder, neutral, non-toxic, non-flammable and explosive, soluble in water, stable in chemical and physical properties. The water-reducing performance of the product has reached the quality index of high-efficiency water-reducing agent (retarding type) in GB8076-2008.

3.4.3 Water-reducing performance of SBC in different cement mixtures

In this paper, according to 1% of the cement mass, the SBC water reducer is mixed with the water: cement: standard sand mixture mixed with different types of cement to measure the fluidity of the mortar.

It can be seen from the test process that the prepared butyl sulfonate cellulose ether superplasticizer (SBC) exhibited good water-reducing and dispersing effects on the three kinds of cement mentioned in the table, and did not show any incompatibility with cement Phenomenon. It shows that SBC has good compatibility with cement and has good water retention.

4 Conclusion

(1) Using cotton pulp as the initial raw material, after preparing microcrystalline cellulose (MCC) with a suitable degree of polymerization, it was activated by NaOH and reacted with 1,4-butane sultone to prepare water-soluble butylsulfonic acid Cellulose ether superplasticizer. The structure of the product was characterized, and it was found that after the etherification reaction of cellulose, there were sulfonic acid groups in its molecular chain, and it had transformed into an amorphous structure.

(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 optimal; under the condition that the degree of polymerization of raw materials is determined, the mixing ratio of reactants is n(MCC):n(NaOH):n(BS )=1:2.1:2.2, when the activation time of the raw materials at room temperature is 2 h, the synthesis temperature of the product is 80°C, and the synthesis time is 5 h, the water-reducing performance of the obtained product is the best.

(3) The optimal dosage of butyl sulfonate cellulose ether superplasticizer is 1.0% of the cement dosage, and it has good adaptability to various cements.

(4) The plasticizing effect is good at the optimal dosage, and the water reducing performance reaches the quality index of high-efficiency water reducing agent (retarding type) in GB 8076-2008.