Preparation Of Carboxymethyl Starch With High Degree Of Substitution And Its Application In Mortar

According to the present status of carboxymethyl starch and its application, the research of preparation of carboxymethyl starch was significant. A series of preparation of carboxymethyl starch with high degree of substitution and its application in mortar were studied in this paper.Carboxymethyl starch (CMS) with high degree of substitution (DS) was prepared in alcohol medium by chloroactic acid and sodium hydroxide. The effects of single factor variation such as the dosage of ethanol, the concentration of ethanol and the amount of alkali were studied. On the basis of one-factor experiments, we select alkalization temperature and time, etherification temperature and time, the dosage of etherifying agent as the variables, DS as the experiments index, using L16(45) orthogonal experiment. The optimum processing conditions for preparation of starch were obtained:the molar ratio of starch, chloroactic acid and sodium hydroxide was 1:1.4:2.4, alkalization under 25℃for 1h, etherification under 55℃for 3h. Under these conditions, the DS of carboxymethyl starch obtained was 0.82 and the solution viscosity was 1800cp, light transmission was 82.4%(pH 6.8). In the infrared spectroscopy, typical absorbance peaks of-COO at 1619 cm-land 1420 cm-1were observed and the peak at 1600 cm-1was from the aether group. With the increase of DS, the solution viscosity and light transmission of carboxymethyl starch also increased, so it can be further used in many fields.Mortar is an essential construction material. Water-soluble polymer was added in the mortar to improve the construction performances, such as water retaining, thickening, retarding, adhering and so on. The high degree of substitution of derivatized starch was anionic water-soluble polymer, and its water solubility, viscosity and viscosity stability improved. In this paper, carboxymethyl starch with high degree of substitution (DS) 0.8 and low degree of substitution (DS) 0.2 were added in mortar for the same test, according to JGJ/T 70-2009 "standard for test method of basic properties of construction mortar". The water retention, apparent density, setting time, compressive strength and bond strength of mortar were discussed when compounded with about 0.05% to 0.5% of CMS. The results shows that CMS with high DS was better in water retention and consistency, lower in apparent density, similar in retardation, compared with CMS with low DS. For air entrainment, CMS with different degree of substitution could reduce compressive strength of mortar, so it should be added appropriately. CMS with high degree of substitution also could increase the adhesive strength of hardened mortar, thereby increasing the durability of mortar. Compared with other water-soluble polymer such as cellulose ethers and gum powder, in application to the mortar, CMS with high DS was superior for its raw material easy to get, low cost, similar in performance. According to different types of mortar and different uses, CMS could be added appropriately or compounded with other polymer, with good prospects for development.