The use of plant materials for the synthesis of superplasticizer

The paper presents data on the synthesis of phloroglucinol-furfural modifier (1,3,5-trihydroxybenzene-2-furaldehyde oligomer) based on 2-furaldehyde (furfural) and 1,3,5-trihydroxybenzene (phloroglucinol). The synthesis of a modifier with different molar ratios of phloroglucinol/furfural was carried out. It was found that an increase in the molar ratio leads to an increase in the plasticizing ability of the modifier. The optimal concentration of the catalyst was determined to be equal to 50% by weight of phloroglucinol. Two chemical forms of the modifier were obtained: H-form and Na-form. The structure of various forms of the modifier has been studied by scanning electron microscopy. It was found that the oligomers used in the work for the synthesis of the modifier, in addition to 2-furyl methyl alcohol, do not have plasticizing properties. Purified 2-furyl methyl alcohol has weak plasticizing properties. It is shown that to achieve the best plasticizing effect, it is necessary to gradually introduce a condensing agent into the reaction mixture. With gradual introduction, a complete condensation reaction occurs between the monomers, which affects the improvement of the plasticizing properties of the resulting product. The spread of the cement mixture when using 0.3% of the additive based on the mass of cement in terms of dry matter is 19 cm.


Introduction
Currently, due to major environmental problems, as well as a serious shortage of mineral resources in construction, there are active developments in the use of plant biorenewable raw materials. A special role is given to the use of agricultural waste. In this regard, furfural is promising, obtained by acidcatalyzed dehydration of polysaccharide-containing agricultural waste [1,2], including corn cobs, beet pulp, bran, sawdust and other waste.
Furfural and its derivatives are widely used in many industries such as plastics, pharmaceuticals and agricultural chemicals, etc. Furfural is widely used in industry due to its good solubility and its easy recuperation by steam distillation. Today all major oil companies use furfural as selective solvent in the refining of lubricating oils.
Orlova [3] found that furfural can be used for the production of binders, including highly filled composites with high mechanical characteristics. Orlova has developed low viscosity furfural binders with a gel time of 40-60 min.
Analysis of literature sources shows that furfural can be used as a modifier (plasticizing additive) in cement compositions. Dr. Al-Hubboubi et al. [4] established an increase in the corrosion resistance of concrete by introducing furfural into the concrete mixture in an amount of 3%. The studies presented in the work showed that furfural dramatically reduces the corrosion rate; the inhibition efficiencies were 62.7 and 63.8% due to 3% furfural addition to 35 and 45 MPa-concretes respectively [4].  Hussain et al. found that the addition of furfural to Iraqi cement significantly improved mechanical properties. It has been established that with the introduction of even 1% furfural, a plasticizing effect is already observed, and the greatest effect is achieved with the introduction of 3% furfural [5].
In works [6,7] it is shown that furfural and its derivatives have a good plasticizing effect and can be used for the production of superplasticizers. It is known that superplasticizers are used to regulate the mobility and structure formation of cement mixtures [8]. Superplasticizers are surfactants, so their main property is the ability of their molecules to adsorb on the surface of cement particles, with the formation of a very thin mono-or bimolecular layer, which increases the zeta potential on the surface of cement particles. As a result, the interfacial cohesion energy of the particles decreases and the degree of disaggregation of the particles increases [8][9][10]. The released immobilized water acts as a plasticizing agent. The adsorbed layer reduces the microroughness of the particles, thereby reducing the coefficient of friction between them. And, finally, the appearance of an electric charge of the same name during the adsorption of superplasticizer molecules on the surface of cement particles excludes the possibility of their adhesion under the action of electrostatic forces, thereby reducing the viscosity of the suspension. Along with the growth of crystals of neoplasms in the process of hydration, the repulsive effect of molecules with the same electric charge ceases, and the mobility of the concrete solution decreases [11][12][13][14]. As a result, with the addition of a super-plasticizer, the proportion of fine fractions of cement particles increases almost 2 times [15][16].
This paper presents the results of using furfural for the synthesis of phloroglucinol-furfural modifier for cement mixtures.

Materials and methods
The following reagents were used to synthesize the modifier: -2-furaldehyde (furfural) -an organic substance of the class of aldehydes with a heterocyclic core, which is a dark brown liquid with a density of 1.16 g/cm 3 in accordance with GOST 10437-80. The mass fraction of 2-furaldehyde was 99.8%. The chemical formula of furfural is C 5 H 4 O 2 .
-1,3,5-trihydroxybenzene (phloroglucinol) is an organic substance of a class of phenols with a benzene nucleus, to which three hydroxyl groups are attached at positions 1,3,5. This compound is a transparent needle-like crystals with a melting point of 215 °C. Chemical formula C 6 H 6 O 3 .
The plasticizing properties of the obtained modifier were determined on Portland cement grade PC500 D0. The values of the results of physical and mechanical tests of the original Portland cement without mineral additives are presented in Table 1. The study of the mobility of the modified cement suspensions was carried out using a mini-cone by determining the diameter of the spreading of the cement suspension under the action of gravity.

Results and discussions
The synthesis of phloroglucinol-furfural modifier (1,3,5-trihydroxybenzene-2-furaldehyde oligomer) is a multistage process consisting of several stages: preparation of a solution with a given concentration of phloroglucinol and catalyst, heating the solution to the optimal temperature, adding furfural, heating the reaction mixture at a certain amount of time and its further slow cooling.
In the course of the study, for the synthesis of the modifier, several samples were prepared with different molar ratios of phloroglucinol / furfural. Having carried out the synthesis and studied the obtained oligomers, we can say that with an increase in the molar ratio, the plasticizing ability of the modifier increases. Also, the optimal concentration of the catalyst was found equal to 50% by weight of phloroglucinol. The medium of the modifier must be alkaline (pH = 11), since at pH less than 5 the modifier passes into its insoluble form (Fig. 1). Temperature is also important during synthesis. After numerous studies, the optimal synthesis temperature was found equal to 70 ° C. Heating of the reaction mixture should be uniform, using a water jacket.
Two chemical forms of the modifier were obtained: H-form and Na-form. The H-form was obtained from a 20% modifier solution acidified with mineral acid to pH less than 5. Figure 2 shows SEM-images of various forms of the obtained modifier. Analysis of Figure 2 showed that the shape and size of the Na-form and H-form of the obtained modifier are significantly different. The Na-form particles have a smooth surface and rather large sizes, reaching several microns. In addition, the particles are lamellar with dense packing, pores are practically absent. H-shaped particles, on the contrary, have an uneven, highly rough surface. However, Determination of the plasticizing ability of the obtained modifier and the starting monomers was carried out using a miniconus according to the methodology developed at the Research, Design and Technological Institute of Concrete and Reinforced Concrete named after A. A. Gvozdev in Russia. The process of determining the plasticizing ability is shown schematically in Figure 3. The cement paste is loaded into a mini-cone, then it is lifted and the diameter of the spreading of the mixture is measured. Were prepared a series of cement pastes with different consistencies of the investigated plasticizing additive. In this case, the water-cement ratio in all experiments was the same 0.4. Analysis of the data obtained showed that without the addition of a plasticizing additive, the spreading diameter of the cement paste is minimal (4.5 cm). With an increase in the amount of added additive, a significant increase in the diameter of the mini-cone spread is observed. The minimum dosage of phloroglucinol / furfural additive at which the maximum plasticizing effect is achieved is 0.3% by weight of the cement. Thus, the optimal dosage of the developed plasticizing additive is 0.3% of the cement weight (calculated on dry matter).
Cement mixtures were prepared with the same concentration of monomers and synthesized oligomers. The miniconus was filled with these mixtures, after which the cone was raised and the amount of spreading of the mixtures was measured with an accuracy of 0.5 cm using a ruler. The control mixture without added additives has a spread of 4.5 cm. The obtained data on the spread of the cone are presented in Table 2.
Analysis of the data presented in Table 1 showed that the monomers used in the work for the synthesis of the modifier, except for 2-furyl methyl alcohol, do not have plasticizing properties. Purified 2-furyl methyl alcohol has weak plasticizing properties. When used, the spread of the minicone increases by 1.6 times. However, this is not sufficient for using the oligomer as a superplasticizer.
With the introduction of synthesized phloroglucinol / furfural additive, the value of the spread of the miniconus increases significantly: with the instant introduction of the condensing agent (2furaldehyde) by 3.5 times and 4.2 times with the gradual introduction of the condensing agent in comparison with the cement slurry without the additive. The improved plasticizing properties of phloroglucinol / furfural additive with the gradual introduction of the condensing agent is most likely due to the fact that with the gradual introduction of the condensing agent into the reaction mixture, a complete condensation reaction occurs between the monomers. It can be assumed that with the instant introduction of the condensing agent, the reaction of disproportionation of the condensing agent additionally occurs with the formation of 2-furyl methyl alcohol.

Summary
The paper presents studies on the possibility of obtaining a plasticizing modifier based on 2furaldehyde (furfural) and 1,3,5-trihydroxybenzene (phloroglucinol) for cement mixtures. The optimal concentration of the catalyst was determined to be equal to 50% by weight of phloroglucinol. It was found that the medium of the modifier should be alkaline (pH = 11), since at pH less than 5 the modifier transforms into its insoluble form. Two chemical forms of the modifier were obtained: H-form and Na-form. The H-form was obtained from a 20% modifier solution acidified with mineral acid to pH less than 5.
It was found that to achieve the best plasticizing effect, it is necessary to gradually introduce a condensing agent into the reaction mixture. With gradual introduction, a complete condensation reaction occurs between the monomers, which affects the improvement of the plasticizing properties of the resulting product. The spread of the cement mixture when using 0.3% of the additive based on the weight of cement in terms of dry matter is 19 cm. According to GOST 24211-2008, 1,3,5trihydroxybenzene-2-furaldehyde oligomer belongs to the plasticizing additive of group I.