Synthesis and properties of Water-soluble cellulose ether superplasticizer

In addition, cotton cellulose was prepared to level Ling-off degree of polymerization and was reacted with sodium hydroxide, 1,4 monobutylsulfonolate (1,4, butanesultone). sulfobutylated cellulose ether (SBC) with good water solubility was obtained. The effects of reaction temperature, reaction time and raw material ratio on butyl sulfonate cellulose ether were studied. The optimal reaction conditions were obtained, and the structure of the product was characterized by FTIR. By studying the effect of SBC on the properties of cement paste and mortar, it is found that the product has similar water reducing effect to naphthalene series water reducing agent, and the fluidity retention is better than naphthalene series water reducing agent. The SBC with different characteristic viscosity and sulfur content has different degree of retarding property for cement paste. Therefore, SBC is expected to become a retarding water reducing agent, retarding high efficiency water reducing agent, even high efficiency water reducing agent. Its properties are mainly determined by its molecular structure.

Key words: cellulose; Equilibrium degree of polymerization; Butyl sulfonate cellulose ether; Water reducing agent

The development and application of high-performance concrete is closely related to the research and development of concrete water-reducing agent. It is because of the appearance of water-reducing agent that the concrete can ensure high workability, good durability and even high strength. At present, there are mainly the following kinds of highly effective water reducing agents widely used: naphthalene series water reducing agent (SNF), sulfonated amine resin series water reducing agent (SMF), amino sulfonate series water reducing agent (ASP), modified lignosulfonate series water reducing agent (ML), and polycarboxylic acid series water reducing agent (PC), which is more active in current research. Polycarboxylic acid superplasticizer has the advantages of small time loss, low dosage and high fluidity of concrete. However, due to high price, it is difficult to popularize in China. Therefore, naphthalene superplasticizer is still the main application in China. Most of the condensing water-reducing agents use formaldehyde and other volatile substances with low relative molecular weight, which may harm the environment in the synthesis and use process.

The development of concrete admixtures at home and abroad is faced with the shortage of chemical raw materials, price rise and other problems. How to use cheap and abundant natural renewable resources as raw materials to develop new high performance concrete admixtures will become an important subject of concrete admixtures research. Starch and cellulose are the main representatives of this kind of resources. Because of their wide source of raw materials, renewable, easy to react with some reagents, their derivatives are widely used in various fields. At present, the research of sulfonated starch as water reducing agent has made some progress. In recent years, the research on water-soluble cellulose derivatives as water-reducing agents has also attracted people’s attention. Liu Weizhe et al. used cotton wool fiber as raw material to synthesize cellulose sulfate with different relative molecular weight and degree of substitution. When its degree of substitution is in a certain range, it can improve the fluidity of cement slurry and the strength of cement consolidation body. The patent says that some polysaccharide derivatives through chemical reaction to introduce strong hydrophilic groups, can be obtained on cement with good dispersion of water-soluble polysaccharide derivatives, such as sodium carboxymethyl cellulose, carboxymethyl hydroxyethyl cellulose, carboxymethyl sulfonate cellulose and so on. However, Knaus et al. found that CMHEC seems not suitable for use as concrete water reducing agent. Only when sulfonic acid group is introduced into CMC and CMHEC molecules, and its relative molecular weight is 1.0 ×105 ~ 1.5 ×105 g/mol, it may have the function of concrete water reducing agent. There are different opinions on whether some water-soluble cellulose derivatives are suitable for use as water-reducing agents, and there are many kinds of water-soluble cellulose derivatives, so it is necessary to conduct in-depth and systematic research on the synthesis and application of new cellulose derivatives.

In this paper, cotton cellulose was used as the starting material to prepare balanced polymerization degree cellulose, and then through sodium hydroxide alkalization, select the appropriate reaction temperature, reaction time and 1,4 monobutyl sulfonolactone reaction, the introduction of sulfonic acid group on cellulose molecules, the obtained water-soluble butyl sulfonic acid cellulose ether (SBC) structure analysis and application experiment. The possibility of using it as water reducing agent was discussed.

1. Experiment

1.1 Raw materials and instruments

Absorbent cotton; Sodium hydroxide (analytical pure); Hydrochloric acid (36% ~ 37% aqueous solution, analytically pure); Isopropyl alcohol (analytically pure); 1,4 monobutyl sulfonolactone (industrial grade, provided by Siping Fine Chemical Plant); 32.5R ordinary Portland cement (Dalian Onoda Cement Factory); Naphthalene series superplasticizer (SNF, Dalian Sicca).

Spectrum One-B Fourier Transform infrared spectrometer, produced by Perkin Elmer.

IRIS Advantage Inductively Coupled Plasma Emission Spectrometer (IcP-AEs), manufactured by Thermo Jarrell Ash Co.

ZETAPLUS potential analyzer (Brookhaven Instruments, USA) was used to measure the potential of cement slurry mixed with SBC.

1.2 Preparation method of SBC

Firstly, the balanced polymerization degree cellulose was prepared according to the methods described in the literature. A certain amount of cotton cellulose was weighed and added into a three-way flask. Under the protection of nitrogen, dilute hydrochloric acid with a concentration of 6% was added, and the mixture was stirred strongly. Then it was suspended with isopropyl alcohol in a three-mouth flask, alkalized for a certain time with 30% sodium hydroxide aqueous solution, weighed a certain amount of 1,4 monobutyl sulfonolactone, and dropped into the three-mouth flask, stirred at the same time, and kept the temperature of constant temperature water bath stable. After the reaction for a certain time, the product was cooled to room temperature, precipitated with isopropyl alcohol, pumped and filtered, and the crude product was obtained. After rinsing with methanol aqueous solution for several times, pumped and filtered, the product was finally vacuum dried at 60℃ for use.

1.3 SBC performance measurement

The product SBC was dissolved in 0.1 mol/L NaNO3 aqueous solution, and the viscosity of each dilution point of the sample was measured by the Ustner viscometer to calculate its characteristic viscosity. The sulfur content of the product was determined by ICP – AES instrument. SBC samples were extracted by acetone, vacuum dried, and then about 5 mg samples were ground and pressed together with KBr for sample preparation. Infrared spectrum test was conducted on SBC and cellulose samples. Cement suspension was prepared with water-cement ratio of 400 and water reducing agent content of 1% of cement mass. Its potential was tested within 3 min.

Cement slurry fluidity and cement mortar water reduction rate are measured according to GB/T 8077-2000 “Test method for uniformity of concrete admixture”, mw/me= 0.35. The setting time test of cement paste is carried out in accordance with GB/T 1346-2001 “Test Method for Water Consumption, Setting Time and Stability of Cement Standard Consistency”. Cement mortar compressive strength according to GB/T 17671-1999 “cement mortar strength test Method (IS0 method)” the method of determination.

2. Results and discussion

2.1 IR analysis of SBC

Infrared spectra of raw cellulose and product SBC. Because the absorption peak of S — C and S — H is very weak, it is not suitable for identification, while s=o has a strong absorption peak. Therefore, the existence of sulfonic acid group in the molecular structure can be determined by determining the existence of S=O peak. According to the infrared spectra of raw material cellulose and product SBC, in the cellulose spectra, there is a strong absorption peak near the wave number 3350 cm-1, which is classified as the hydroxyl stretching vibration peak in cellulose. The stronger absorption peak near wave number 2 900 cm-1 is methylene (CH2 1) stretching vibration peak. A series of bands consisting of 1060, 1170, 1120 and 1010 cm-1 reflect the stretching vibration absorption peaks of hydroxyl group and the bending vibration absorption peaks of ether bond (C — o — C). The wave number around 1650 cm-1 reflects the hydrogen bond absorption peak formed by hydroxyl group and free water. The band 1440~1340 cm-1 shows the crystalline structure of cellulose. In the IR spectra of SBC, the intensity of band 1440~1340 cm-1 is weakened. The strength of the absorption peak near 1650 cm-1 increased, indicating that the ability to form hydrogen bonds was strengthened. Strong absorption peaks appeared at 1180,628 cm-1, which were not reflected in the infrared spectroscopy of cellulose. The former was the characteristic absorption peak of s=o bond, while the latter was the characteristic absorption peak of s=o bond. According to the above analysis, sulfonic acid group exists on the molecular chain of cellulose after etherification reaction.

2.2 Influence of reaction conditions on SBC performance

It can be seen from the relationship between the reaction conditions and the properties of SBC that the temperature, reaction time and material ratio affect the properties of the synthesized products. The solubility of SBC products is determined by the length of time required for 1g product to completely dissolve in 100mL deionized water at room temperature; In the water reduction rate test of mortar, SBC content is 1.0% of cement mass. In addition, since cellulose is mainly composed of anhydroglucose unit (AGU), the amount of cellulose is calculated as AGU when the reactant ratio is calculated. Compared with SBCl ~ SBC5, SBC6 has lower intrinsic viscosity and higher sulfur content, and the water reduction rate of the mortar is 11.2%. The characteristic viscosity of SBC can reflect its relative molecular mass. High characteristic viscosity indicates that its relative molecular mass is large. However, at this time, the viscosity of aqueous solution with the same concentration will inevitably increase, and the free movement of macromolecules will be limited, which is not conducive to its adsorption on the surface of cement particles, thus affecting the play of the water reducing dispersion performance of SBC. The sulfur content of SBC is high, indicating that butyl sulfonate substitution degree is high, SBC molecular chain carries more charge number, and cement particles surface effect is strong, so its dispersion of cement particles is also strong.

In the etherification of cellulose, in order to improve the etherification degree and product quality, the method of multiple alkalization etherification is generally used. SBC7 and SBC8 are the products obtained by repeated alkalization etherification for 1 and 2 times, respectively. Obviously, their characteristic viscosity is low and sulfur content is high, the final water solubility is good, the water reduction rate of cement mortar can reach 14.8% and 16.5%, respectively. Therefore, in the following tests, SBC6, SBC7 and SBC8 are used as research objects to discuss their application effects in cement paste and mortar.

2.3 Influence of SBC on cement properties

2.3.1 Influence of SBC on the fluidity of cement paste

Influence curve of water reducing agent content on fluidity of cement paste. SNF is a naphthalene series superplasticizer. It can be seen from the influence curve of the content of water reducing agent on the fluidity of cement paste, when the content of SBC8 is less than 1.0%, the fluidity of cement paste gradually increases with the increase of the content, and the effect is similar to that of SNF. When the content exceeds 1.0%, the growth of the fluidity of the slurry gradually slows down, and the curve enters the platform area. It can be considered that the saturated content of SBC8 is about 1.0%. SBC6 and SBC7 also had a similar trend to SBC8, but their saturation content was significantly higher than SBC8, and the improvement degree of clean slurry fluidity was not as high as SBC8. However, the saturated content of SNF is about 0.7% ~ 0.8%. When the content of SNF continues to increase, the fluidity of the slurry also continues to increase, but according to the bleeding ring, it can be concluded that the increase at this time is partly caused by the segregation of bleeding water by cement slurry. In conclusion, although the saturated content of SBC is higher than that of SNF, there is still no obvious bleeding phenomenon when the content of SBC exceeds its saturated content by a lot. Therefore, it can be preliminarily judged that SBC has the effect of reducing water and also has certain water retention, which is different from SNF. This work needs to be further studied.

It can be seen from the relation curve between the fluidity of cement paste with 1.0% water-reducing agent content and time that the fluidity loss of cement paste mixed with SBC is very small within 120min, especially SBC6, whose initial fluidity is only about 200mm, and the loss of fluidity is less than 20%. The warp loss of slurry fluidity was in the order of SNF>SBC8>SBC7>SBC6. Studies have shown that naphthalene superplasticizer is mainly absorbed on the surface of cement particles by plane repulsive force. With the progress of hydration, the residual water reducing agent molecules in the slurry are reduced, so that the adsorbed water reducing agent molecules on the surface of cement particles are also gradually reduced. The repulsion between particles is weakened, and cement particles produce physical condensation, which shows a decrease in the fluidity of net slurry. Therefore, the flow loss of cement slurry mixed with naphthalene superplasticizer is greater. However, most naphthalene series water reducing agents used in engineering have been properly mixed to improve this defect. Thus, in terms of liquidity retention, SBC is superior to SNF.

2.3.2 Influence of potential and setting time of cement paste

After adding water reducing agent to cement mix, the cement particles adsorbed water reducing agent molecules, so the potential electrical properties of cement particles can be changed from positive to negative, and the absolute value increases obviously. The absolute value of particle potential of cement mixed with SNF is higher than that of SBC. At the same time, the setting time of the cement paste mixed with SBC was extended to different degrees compared with the blank sample, and the setting time was in the order of SBC6>SBC7>SBC8 from long to short. It can be seen that with the decrease of SBC characteristic viscosity and the increase of sulfur content, the setting time of cement paste is gradually shortened. This is because SBC belongs to polypolysaccharide derivatives, and there are more hydroxyl groups on the molecular chain, which has different degrees of retarding effect on the hydration reaction of Portland cement. There are roughly four kinds of retarding agent mechanism, and the retarding mechanism of SBC is roughly as follows: In the alkaline medium of cement hydration, the hydroxyl group and free Ca2+ form unstable complex, so that the concentration of Ca2 10 in the liquid phase decreases, but also may be adsorbed on the surface of cement particles and hydration products on the surface of 02- to form hydrogen bonds, and other hydroxyl groups and water molecules through hydrogen bond association, so that the surface of cement particles formed a layer of stable solvated water film. Thus, the hydration process of cement is inhibited. However, the number of hydroxyl groups in the chain of SBC with different sulfur content is quite different, so their influence on the cement hydration process must be different.

2.3.3 Mortar water reduction rate and strength test

As the performance of mortar can reflect the performance of concrete to some extent, this paper mainly studies the performance of mortar mixed with SBC. The water consumption of mortar was adjusted according to the standard of testing the water reduction rate of mortar, so that the mortar sample expansion reached (180±5)mm, and 40 mm×40 mlTl×160 mill specimens were prepared to test the compressive strength of each age. Compared with blank specimens without water-reducing agent, the strength of mortar specimens with water-reducing agent in each age has been improved in different degrees. The compressive strength of specimens doped with 1.0% SNF increased by 46%, 35% and 20% respectively at 3, 7 and 28 days. The influence of SBC6, SBC7 and SBC8 on the compressive strength of mortar is not the same. The strength of the mortar mixed with SBC6 increases little at each age, and the strength of the mortar at 3 d, 7 d and 28d increases by 15%, 3% and 2% respectively. The compressive strength of the mortar mixed with SBC8 increased greatly, and its strength at 3, 7 and 28 days increased by 61%, 45% and 18%, respectively, indicating that SBC8 has strong water-reducing and strengthening effect on cement mortar.

2.3.4 Influence of SBC molecular structure properties

Combined with the above analysis on the influence of SBC on cement paste and mortar, it is not difficult to find that the molecular structure of SBC, such as the characteristic viscosity (related to its relative molecular weight, general characteristic viscosity is high, its relative molecular weight is high), sulfur content (related to the degree of substitution of strong hydrophilic groups on the molecular chain, high sulfur content is high degree of substitution, And vice versa) determines the application performance of SBC. When the content of SBC8 with low intrinsic viscosity and high sulfur content is low, it can have strong dispersion ability to cement particles, and the saturation content is also low, about 1.0%. The extension of the setting time of cement paste is relatively short. The compressive strength of mortar with the same fluidity increases obviously at each age. However, SBC6 with high intrinsic viscosity and low sulfur content has a smaller fluidity when its content is low. However, when its content is increased to about 1.5%, its dispersion ability to cement particles is also considerable. However, the setting time of the pure slurry is prolonged more, which shows the characteristics of slow setting. The improvement of mortar compressive strength under different ages is limited. In general, SBC is better than SNF in mortar fluidity retention.

3. Conclusion

1. Cellulose with balanced polymerization degree was prepared from cellulose, which was etherized with 1,4 monobutyl sulfonolactone after NaOH alkalization, and then water-soluble butyl sulfonolactone was prepared. The optimum reaction conditions of the product are as follows: row (Na0H); By (AGU); n(BS) -2.5:1.0:1.7, reaction time was 4.5h, reaction temperature was 75℃. Repeated alkalization and etherification can reduce the characteristic viscosity and increase the sulfur content of the product.

2. SBC with appropriate characteristic viscosity and sulfur content can significantly improve the fluidity of cement slurry and improve the fluidity loss. When the water reduction rate of mortar reaches 16.5%, the compressive strength of mortar specimen at each age increases obviously.

3. The application of SBC as a water-reducing agent shows a certain degree of retardation. Under the condition of appropriate characteristic viscosity, it is possible to obtain high efficiency water reducing agent by increasing sulfur content and reducing retarding degree. Referring to the relevant national standards of concrete admixtures, SBC is expected to become a water reducing agent with practical application value, retarding water reducing agent, retarding high efficiency water reducing agent, and even high efficiency water reducing agent.