Views: 1 Author: Site Editor Publish Time: 2023-03-29 Origin: Site
Abstract: Cellulose cotton paddle meal and 1,4-butanal sulfur (BS) are synthesized by ingotisulfonic acid cellulose ether (SBC). Using infrared spectrum (FTIR), 13C solid carbon spectrum (13 CP MAS), scanning electron microscope, XRD (XRD) and other characteristics, the product structure was inspected, and the cellulose aggregation, raw material ratio, reaction temperature The impact of synthetic process parameters such as reaction time on SBC water reduction water reduction performance. The surface tension and water-SBC-cement system of butenylsulfonic spiny ether hydrolysis have studied the water reduction mechanism of SBC water reducing agents. The research results show that the SBC water reduction agent almost does not change the surface tension of the water. The orientation capacity of the qi-liquid interface is small and does not cause an air to the concrete; The surface has the same charge and excludes each other to cause the cement particles to disperse, thereby reducing the water reduction effect.
Keywords: cellulose; butyl sulfonic acid cellulose ether; water reducing agent; water reduction mechanism
The water reducing agent refers to an exterior agent that can improve the harmony, or the same harmony, which can reduce the amount of concrete water and increase the strength of the concrete. At present, the more common high -efficiency water reducing agents are mainly in the following categories: N Water reducing agent (SNF), sulfide hydride resin water reduction agent (SMF), amino sulfonate water reduction agent (ASP), and Modified lignin sulfonate water reduction agent (ML) and currently active polycarboxylic acid water reduction agent (PC). As far as the synthesis process is concerned, most of the previous traditional shrinkage water reduction agents are mostly used to react with strong irritating formaldehyde as raw materials. The sulfide process is generally carried out by strong corrosive smoke sulfur acid or concentrated sulfuric acid. This will inevitably cause adverse effects on the production workers and the surrounding environment, and it will also produce a large amount of waste residue and a large amount of waste liquid, which is not conducive to sustainable development; although the polycar carboxylic acid reduction agent has less loss of concrete, mixed The advantages of low quantity, large flow, and no toxic substances such as formaldehyde are not used, but there are certain promotion difficulties in China due to high prices. From the analysis of the source of raw materials, it is not difficult to find that the above -mentioned water reduction agents are mostly based on petrochemical products, which are synthesized by by -products, and petroleums are increasingly scarce and prices are constantly higher. Therefore, how to develop a new high -performance concrete water reducing agent with cheap and rich natural renewable resources has become a research hotspot of concrete water reducing agents.
Due to the extensive source of cellulose, renewable, and having the characteristics of chemical reactions with some reagents, easy modification and utilization, the study of water -soluble cellulose derivatives as a water reducing agent has been concerned. This work uses cellulose cotton paste as the initial raw material. After the microcrystalline cellulose with a suitable polymerization is obtained by acid hydrolysis, the cellulose is reacted with the 1,4-butanide dectus to the activation of sodium hydroxide. Base -efficient water reduction agent and discussed its water reduction mechanism.
1.1 The main raw materials
Cellulose cotton paste, aggregate 576, Xinjiang Aoyang Technology Co., Ltd.; 1,4 one -butanal sulfide (BS), industrial grade, Shanghai Jiachen Chemical Co., Ltd.; 52.5R ordinary silicate cement, Urumqi cement, Factory provides: China is ISO standard sand, Xiamen Aisoubiao Sand Co., Ltd.; sodium hydroxide, hydrochloric acid, isopenol, etc. are all analytical and commercially available.
1.2 Preparation of SBC water reduction agent
Called a certain amount of cotton pulp, put it in a three -mouth bottle in appropriate crushing, add a certain concentration of dilute hydrochloric acid, stir down and heat the water for a certain time, cool to room temperature, filter and water to neutral, dry the vacuum at 50 ° C, get the vacuum at 50 ° C, get dry at 50 ° C, get dry at 50 ° C, get dry at 50 ° C, get dry at 50 ° C, and get dry at 50 ° C. Micro -crystal cellulose raw materials (MCC) with different polymerization. After determining the polymerization degree according to the literature, place it into a three -port reactor, and use 10 times the beopropyl of isopropanol with 10 times the quality of the microcrystalline fibrin, and add a certain amount of sodium hydroxide aquatic solution under the mixing. Later, add 1,4 one -butylsulne (BS) of the calculated amount, increase the temperature to the reaction temperature, the constant temperature reaction for a certain period of time, cool the product to room temperature, draw the filter to get rough products, then rinse with methanol 3 times, filter the filtration 3 times, filtrate , Obtain the final product, a tanl sulfonic acid cellulose ether (SBC).
1.3 Product structure representation
Use Bruker Equinox 55 Fourier to change infrared spectrometer to the FHR characteristics of the sample. In the appearance, Mac 8XHF22 One SRA -type X -ray diffraction instrument perform XRD characteristics on the sample.
1.4 Product water reduction performance analysis
The size of the glue sand directly reflects the water reduction performance of the product. Therefore, this work uses the glue sand flow of SBC products to measure the water reduction performance of the product.
The liquidity of glue sand is determined in accordance with the regulations of 6.5 in GB 8076--2008. That is, first determine the water / standard sand mixture on the NLD type 3 cement glue liquidity measurement in the NLD one -3 cement sandy glue device (180 ± 2) mm. Cement, measured the benchmark water volume of 230 g), and then add a water reduction with a mass of 1 % of the cement quality to the water, according to the cement / water reducing agent / benchmark water / standard sand) = 450g / 4.5g / 230g / The proportion of 1350g is placed in the JJ-5 cement glue sand mixer and stirred and mixed, and the diameter of the gum sand on the glue sand flow measurement is the measured gum fluidity.
1.5 Product water reduction mechanism analysis
This experiment analyzes the water reducing mechanism of SBC water reduction agent by measuring the potential of the SBC and one cement system and the SBC aqueous solution of the SBC water solution.
1.5.1 Measurement of the potential
U.S. Brookhaven-type Zeta potential analyzer is used to measure the potential of the SBC water-reduced water-SBC-cement system. That is, according to the water and ash ratio of 400: 1 Add cement to a water reduction agent solution or distilled water with a certain concentration, stir 5 min, set up 10 min, then take the upper layer clearing, inject the electrophoresis, measure the pure position, each one, each one The sample is measured 3 times, and its average value is used as the potential at this concentration.
1.5.2 Surface tension measurement
The surface tension of the SBC water reduction aquatic solution is determined using the platinum plate method. Pour the water solution of different concentrations into the surface tension of the solution in the JK98B fully automatic tension instrument sample. Each sample is measured 3 times, and its average value is taken as the surface tension of the concentration solution (the platinum plate must be washed and burned red before each measurement, and it is used to cool and used it).
2. Results and Discussion
2.1 Characterization results
2.1.1 FTIR characterization results
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 presence or absence of the S=O peak. Obviously, in the cellulose spectrum, there is a strong absorption peak at wave number 3344 cm-1, which is attributed to the hydroxyl stretching vibration peak in cellulose; the strong absorption peak at wave number 2923 cm-1 is methylene (-CH2) The stretching vibration peak; the series of bands composed of 1031 cm-1, 1051 cm-1, 1114 cm-1, and 1 165 cm'-1 reflect the absorption peak of hydroxyl stretching vibration and the bending vibration absorption peak of ether bond (C—O—C): The wavenumber at 1646 cm-1 reflects the hydrogen bond absorption peak formed by hydroxyl and free water; the band at 1432-1318 cm-1 reflects the existence of cellulose crystal structure. In the IR spectrum of SBC, the intensity of the band 1318-1432 cm-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 cm-1, 605 cm-1 A strong absorption peak appears at 1, but these two are not reflected in the infrared spectrum of cellulose, the former is the characteristic absorption peak of S=0 bond, and the latter is the characteristic absorption peak of 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.
2.1.2 Characterization results of 13CP MAS
From the 13CP MAS spectrum of the raw material, it can be seen that the chemical shift 102.8 corresponds to C-1, 76.3~70.0 correspond to C-2, C-3, C-5 respectively, and the chemical shift 64.2 corresponds to C-1 -6, due to the weak intensity of C-4, could not be reflected. In addition to the carbon spectrum of cellulose molecules in the 13CPMAS spectrum of the crystallized SBC, the chemical shifts of 20-30.34 and 48.02 correspond to the methylene C of the alkyl ether. It can be seen that the NMR research results are consistent with the FHR characterization results, indicating that the butylsulfonic acid group has been introduced into the cellulose molecular chain through the etherification reaction.
2.1.3 SEM characterization results
By analyzing the SEM results of cellulose cotton pulp, MCC and the product SBC, it was found that the MCC obtained after HCI hydrolysis can significantly change the structure of cellulose fibers, destroy the fibril structure, and obtain fine agglomerated cellulose particles, which can further react with BS The obtained SBC has no fibrous structure and basically transformed into an amorphous structure, which is beneficial to its dissolution in water.
2.1.4 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 transform into 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 for participating in the response or not. X-ray diffraction analysis of microcrystalline cellulose and product cellulose butanesulfonate. Through comparison, it can be seen that after etherification, the crystallinity has changed fundamentally, and the product has completely transformed into an amorphous structure, so that it can be dissolved in water.
2.2 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 (DP), according to the preparation method in Section 1.2, select a certain synthesis process [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 microcrystalline cellulose raw material at room temperature is 2 h, and the product synthesis time is 5 h] Prepare SBC products, and add SBC water reducer to water/cement/standard sand In the mixing system (cement/water reducer/water/standard sand=450g/4.5g/230g/1350g) measure the fluidity of the mortar.
In the research range, when the degree of polymerization of the microcrystalline cellulose raw material is high, the fluidity of the mortar is low. The reason is obviously that the molecular weight of the raw material is small, which is conducive to the uniform mixing of the raw material and the penetration of the etherification agent, thereby improving the etherification of the product. degree. However, the water-reducing performance of the product does not increase in a straight line as the degree of polymerization of the raw material decreases. The experimental results show that the mortar fluidity of the cement mortar mixtures mixed with SBC made of microcrystalline cellulose with a degree of polymerization DP<96 is greater than 180 mm (the benchmark fluidity when no water reducer is added), indicating that Using microcrystalline cellulose with a degree of polymerization of less than 96 to prepare SBC can obtain a certain water reducing rate: use microcrystalline cellulose with a degree of polymerization of 45 to prepare SBC, add it to the concrete mixture, and measure the fluidity of the mortar to be the largest Therefore, it is considered that microcrystalline cellulose with a degree of polymerization of about 45 is most suitable for making various SBCs; if the degree of polymerization of raw materials is greater than 45, the fluidity of the mortar will gradually decrease, that is, the water reducing rate will decrease. This is obviously 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 the coagulation will be slow, which will affect the dispersion effect; on the other hand, the large molecular weight hour. The macromolecules of the superplasticizer are in a regular coil conformation, which is relatively difficult to adsorb on the surface of cement particles. But when the degree of polymerization of the raw materials is less than 45 屙, the fluidity of the mortar begins to decline again, but the decline is small. The reason is that when the molecular weight of the water reducing agent is small, although it is easy to diffuse and has good wettability, the molecule has a relatively large adsorption fastness, and the molecule is small, and the hydrophobic chain segment is very short, and the friction between the particles is relatively large. The dispersion effect of concrete is not as good as that of superplasticizer with larger molecular weight. Therefore, it is very important to properly control the molecular weight of the main chain (ie, the cellulose segment) to improve the water-reducing performance of the water-reducing agent.
2.3 The influence of the preparation process of SBC on the water-reducing performance of the product
Through experiments, it was found that in addition to the degree of polymerization of MCC, the ratio of reactants, reaction temperature, raw material activation and product synthesis time all affect the water-reducing performance of the product.
2.3.1 Ratio of reactants
(1) The amount of BS is under the conditions determined by other process parameters 【MCC polymerization degree is 45, n(MCC):n(NaOH)=1:2.1, cellulose activation time at room temperature is 2h, synthesis temperature is 80°C, 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. It can be seen from this that with the increase of the amount of BS, 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 Onga molar ratio of BS to MCC was chosen to be 2.2:1 in this work.
(2) The amount of NaOH is determined under the conditions of other process parameters [MCC degree of polymerization is 45, n(BS):n(MCC)=2.2:1, activation time of cellulose at room temperature is 2 h, synthesis temperature is 80°C, synthesis time 5 h] to investigate the effect of the amount of sodium hydroxide on the water-reducing performance of the product. It can be seen that as the amount of alkali increases, the fluidity of the mortar mixed with SBC increases rapidly, and begins to decrease after reaching the highest value. This is because when the NaOH content is large, there is too much free alkali 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, and thus affecting Product water-reducing performance. In addition, at a higher temperature, the presence of too much NaOH will also degrade the cellulose, and the degree of aggregation will decrease, which will affect the water-reducing performance of the product. According to the experimental results, the molar ratio of NaOH to MCC is around 2.1. The fluidity of the mortar is the largest, so the optimum molar ratio of NaOH to MCC is determined to be 2.1:1.0.
2.3.2 Reaction temperature
Under the condition of other process parameters determined [MCC polymerization degree is 45, n(MCC):n(NaOH):n(BS)=1:2.1:2.2, cellulose activation time at room temperature is 2 h, synthesis time is 5 h ], to investigate the effect of 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 gradually increases, but when the reaction temperature exceeds 80°C, the fluidity of the mortar tends to decrease.
The etherification reaction of 1,4-butane sultone and cellulose belongs to endothermic reaction, increasing the reaction temperature is beneficial to the reaction of etherifying agent and cellulose hydroxyl, but with the increase of temperature, the effect of NaOH and cellulose gradually 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, which will affect the degree of etherification of the product. Therefore, the author of this paper believes that the suitable reaction temperature for the etherification reaction of BS and cellulose is 80°C.
2.3.3 Reaction time
The reaction time includes the activation time of raw materials and the synthesis time of products.
(1) The activation time of raw materials is under the above optimal process conditions [MCC polymerization degree is 45. n(MCC):n(NaOH):n(BS)=1:2.1:2.2, the synthesis reaction temperature was 80°C, and the synthesis time was 5 h], to investigate the effect of the activation time of raw materials at room temperature on the water-reducing performance of the product . It can be seen that the fluidity of the 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 of such small molecules with etherifying agents is relatively easy. More etherification agent will be consumed, which will affect the degree of etherification of the product, thus making the water-reducing performance of the product worse. Therefore, this paper considers that the activation time of raw materials at room temperature is 2 h.
(2) Product synthesis time Under the above-mentioned optimal process conditions, it can be seen from the investigation of the influence of product synthesis time on product water-reducing performance that as the synthesis reaction time prolongs, the fluidity of the mortar mixed with SBC increases gradually. When the reaction time exceeds 5 h, R tends to decrease. This is related to the presence of free alkali 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. The cellulose molecular chain becomes shorter, the molecular weight of the product decreases, and the side reactions increase, resulting in a decrease in the degree of etherification of the product, thereby affecting the water-reducing performance of the product. In this experiment, the optimal synthesis reaction time was considered to be 5 h.
2.4 Water reduction mechanism of SBC products
When the water reducer is added to the cement mixture, it will be quickly adsorbed on the surface of the cement particles, changing the properties of the cement-water-solid-liquid system, charge distribution, steric hindrance, etc., thereby affecting the dispersion properties of the cement particles in the liquid . In this paper, the water-reducing mechanism of SBC superplasticizer products is revealed through the research on the potential of water-SBC-cement system and the surface tension of water-SBC solution.
2.4.1 Surface tension
In order to investigate the activity of the water reducer, the surface tension of the aqueous solution of the SBC water reducer with different concentrations was measured. It can be seen that the SBC water reducer hardly changes the surface tension of the water. According to Chen Jiankui's point of view, this type of water reducing agent has little orientation ability at the air-liquid interface and has no air-entraining effect on concrete. Therefore, the author believes that cellulose butyl sulfonate is a non-air-entraining water reducer.
By changing the amount of SBC superplasticizer and measuring the potential of the water-SBC-cement system, it can be seen that due to the addition of SBC superplasticizer, it is adsorbed on the surface of cement particles, which changes the potential of cement particles. As the amount of SBC increases, the potential of the water-SBC-cement system gradually decreases, and the absolute value gradually increases. Finally, the potential change tends to be gentle, and the absolute value of the relaxation potential reaches the maximum.
This is because the main mineral components of cement are C3S, C2S, C3A and C4AF, among which the particles of silicate hydrate are negatively charged in the aqueous dispersion system, while the particles of aluminate hydrate are positively charged. In the early stage of cement hydration, c3A first undergoes hydration reaction, so the cement particles are positively charged. With the addition of SBC superplasticizer into the cement mixture, the potential of the electric double layer on the surface of cement particles changes due to the adsorption of superplasticizer molecules by cement particles. The electric potential changes from positive to negative. The greater the concentration of SBC, the more the amount adsorbed on the surface of cement particles, therefore, the more the potential of the surface of cement particles is increased.
Through the above experimental analysis. The author believes that when the SBC water reducer is added to the water-cement dispersion system, a layer of gelatinized adsorption film is formed on the surface of the cement particles. Therefore, electrostatic repulsion is generated between particles, so that they are not agglomerated, and are almost dispersed as individual individual particles. As a result, the part of water that was originally surrounded by the flocculation structure is released, which contributes to the fluidity of the concrete mixture; the part of the particle surface that was originally cohesive with each other is liberated, and also participates in early hydration, resulting in a water-reducing effect. .
(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, that is, cellulose-based water reducer. And characterize the structure of the product, found that after cellulose etherification reaction. There are sulfonic acid groups on its molecular chain, and it has been transformed into an amorphous structure.
(2) The experiment found that when the degree of polymerization of the microcrystalline fiber is 45, the water-reducing performance of the obtained product is the best; under the condition that the degree of polymerization of the raw materials is determined, the ratio of the 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 butylsulfonate cellulose ether product is the best.
(3) The research results on the surface tension of different concentrations of SBC superplasticizer aqueous solutions show that cellulose butyl sulfonate is a non-air-entraining superplasticizer.
(4) When butyl sulfonate cellulose ether water reducer is added to the water-cement dispersion system, a layer of gelatinous adsorption film is formed on the surface of cement particles, which are adsorbed on the surface of cement particles after ionization in the solution Make the cement particles carry the same negative charge, and repel each other to cause the dispersion of the mud particles, so that they will not agglomerate, and the effect of water reduction will appear.