Foreword

Cellulose is the oldest and rich natural polymer compound on the earth, which is not exhausted, and the most valuable natural renewable resources of human beings. Cellulose is cheaper, which can be characterized by biodegradation, low calorie, non-toxic and biological compatibility. The base ring of the cellulose molar is dehydrated glucose, its molecular formula: (C6H10O5) n. Among them, 44.44% carbon containing 44.44%, hydrogen is 49.39%, and each glucose residue contains three alcohol hydroxyl groups, including 2 sidewase hydroxyl groups and 1 primroll hydroxyl group, which plays a decisiveness of cellulose. Impact [1]. The cellulose can obtain a series of cellulose derivatives by chemically modifying it. Natural cellulose is alkalized, etherified, purified, and drying can be prepared to obtain cellulose ether [2]. Cellulose ether is one of the important derivatives of cellulose, can be widely used in food, medicine, cosmetics, building materials, papermaking, coatings, textile printing, daily chemical, oil mining and other industries [3], with solubility, viscosity , Stability, non-toxic, biocompatibility, etc. There are different classifications depending on the substitution of cellulose ether. Substituents on cellulose ether are often significant for their properties. Different from the substituent, the cellulose ether has the types of MC, HEC, CMC, HPMC, HEMC, and refer to Fig. 1. This paper mainly discusses the different physical and chemical properties and applications of HPMC, HEMC in the construction industry.

1 structure

1.1HPMC

Hydroxypropyl Methyl Cellulose, Scrubrication HPMC After the chemical reaction, the etherification reaction was then prepared in the process of oxygen propane and chloromethane. The methoxy group on the methoxy group on the oxygen group on the glucose cycloalkyl, the hydroxyl group is substituted with a hydroxypropoxy, and the structure is as shown in Fig. 2. HPMC has thermal gel properties, no ionic charge thereof, does not function with metal salts or ionic compounds, strong anterliosis, and good dispersion, emulsification, thickening, bonding, water, water, and rubber properties.

1.2Hemc

Hydroxythyl methyl Cellulose, referred to as HEMC, producing a slightly different HPMC, after alkalization of cellulose, replace the hydroxyl propylene oxide with ethylene oxide, and substituted hydroxyl groups on the glucose cycloyl group. The structure is shown in Figure 3. The chemical structure of HEMC has more hydrophilic groups relative to HPMC, so it is more stable at high temperatures and has good thermal stability. Compared to common HPMC cellulose ethers, it has relatively high gel temperatures and more advantage in high temperature applications. Like HPMC, HEMC also has good ribbics, dispersion, emulsification, thickening, bonding, water-saving, gumming performance [4].

2 physical and chemical properties

Physical and chemical properties of the fluid ether industry detection standards include: appearance, fineness, dry weight loss rate, sulfate, solution pH, solution light transmittance, solution viscosity, gel temperature, group content, etc. (excluding mortar application experiment [7].

Appearance, fineness, dry weight loss rate, sulfate, pH value, and light transmittance, viscosity, etc. are related to the product itself, function, different manufacturers, and discussions here.

2.1 Cellulose ether group content

Due to the difference in HPMC and HEMC substituents, the cellulose ether sample can be heated in a closed reactor, and under the catalysis of adipic acid, the substituted alkoxy group is quantified, and the corresponding iodine is formed. The alkane is extracted with a neighbornebenzene extraction product, and the extract is injected into the gas phase chromatograph to perform the separation of the component, and the hydroxypropoxy and hydroxyethoxy can be identified by separating the time. The internal standard method is used to calculate the content of the components to be tested in the sample [7]. Figure 5 is a meteorological spectrum spectrum of HPMC, and Figure 6 is a glyph chromatographic spectrum (containing methoxy, hydroxyethoxy, hydroxypropoxy) for calibration. It is not difficult to find that the separation time of the hydroxyethoxy group is interposed with a methoxy and hydroxypropoxy, and the group type is determined by comparing the separation time of the standard solution. The group type and peak area are calculated by calculating the group content by the peak time. In general, the methoxy content of HPMC is 16% to 30%, and the hydroxypropoxy may be 4% to 32%; HEMC's methoxy content is 22% to 30%, hydroxyethoxy 2% ~ 14 %.

2.2 Gel Temperature

The gel temperature is an important indicator of cellulose ether. The cellulose ether aqueous solution has a thermoegel property. As the temperature increases, the viscosity is decreasing, and when the solution temperature reaches a certain value, the cellulose ether solution is no longer a transparent, but a white gum is formed, and the viscosity is finally lost. The gel temperature test method refers to: The cellulose ether sample is formulated into a concentration of 0.2% cellulose ether solution, slow heating in the water bath until the solution appears white turbidity and even white gel, and completely lost viscosity, at this time the temperature of the solution The gel temperature of cellulose ether [7]. Figure 7 is randomly selected 8 test gel temperatures each of the cellulose ether products at home and abroad. As a result, the HEMC overall gel temperature is slightly higher than HPMC. In general, HPMC gel temperatures at 60 ° C to 75 ° C, HEMC at 75 ° C to 90 ° C.

HPMC methoxy, hydroxypropoxy content ratio has a certain effect on the water solubility, water supply capacity, surface activity and gel temperature of the product. Usually, the hydroxypropylene content is high, the hydroxypropoxy content is good, the surface activity is good, but the gel temperature is low; the hydroxypropoxy content is appropriate, and the methoxy content can be improved, and the gel temperature can be improved. However, the hydroxypropylene content is too high, and the gel temperature is lowered, water solubility and surface activity are deteriorated. Therefore, the cellulose ether manufacturer must ensure product quality and stability by strict control of the group.

3 Application of Construction Industry

HPMC and HEMC have a similar role in building materials. It can be used as a dispersing agent, a water retention agent, a thickener, and a bonding, mainly used in the molding of cement mortar and gypsum articles. It is used in cement mortar to increase its bonding, construction, reducing flocculation, improve viscosity and shrinkage, and water-keeping, reducing the water loss of concrete, increasing strength, preventing cracks and water-soluble salts. There is widely used in cement-based tamping mortar, gypsum plaques, gypsum products, masonry mortar, plate filling materials, filling agents, tile binders, self-leveling materials, etc. In the coating, it can be used in the latex coating and the water-soluble resin coating component as a film forming agent, a thickener, an emulsifier, and a stabilizer to make the coating film have good abrasion resistance, uniform coating and adhesion, and improve it. Surface tension, stability of acid base and compatibility to metal pigments. Due to the good viscosity storage stability, it is particularly suitable for use in emulsified coatings as dispersants. All in all, although there is very little dosage in the system, it has a large role, wide application [5].

The gel temperature of cellulose ether determines its thermal stability in the application. The gel temperature of HPMC is usually at 60 ° C to 75 ° C, depending on the model, group content, different production processes of different manufacturers. Due to the characteristics of the HEMC group, it has a higher gel temperature, typically at 80 ° C or more, so that stability under high temperature conditions is due to HPMC. In practical applications, in the hot construction environment in summer, the same viscosity and dosing HEMC has a large advantage of HPMC compared to HPMC compared to water storage properties in moist mortar. Especially in the south, the mortar will sometimes be constructed at high temperatures, the cellulose ether having a gel temperature will lose the thickening of cellulose ether at high temperatures, water retainability, thus accelerating cement fixed line and mortar Hardening, directly affects construction and anti-cracking [6].

Since there is more hydrophilic groups in the HEMC itself, it has better hydrophilic, and the product of the same viscosity is under the same dosage, and the water retaining rate of HEMC in the mortar is slightly higher than HEMC. In addition, HEMC's anti-gravist capacity is relatively better. So HEMC is better to use to tile the tile rubber.

However, the mainstream cellulose ether of the domestic construction industry is mainly HPMC, because of its species, the price is low, and the comprehensive cost free choice, high-quality HPMC is not more than HEMC. With the development of domestic building markets, especially the improvement of mechanized construction, and the improvement of building quality requirements, HPMC will continue to increase. At present, the domestic production of HPMC has a very small factory, fierce competition, cellulose ether's investment, short construction cycle, wide application, current market situation, due to serious industrial disorder, industry profits continue to decrease, and recently Environmentally friendly, restrictions on raw materials, etc. Due to the constant compression of the large environment, cellulose ether manufacturers, suppliers should improve the level of equipment, increase their own innovation, pay attention to environmental resources, and continue to improve the quality of HPMC. The main HPMC suppliers in China include: Guangdong Longhu Technology Co., Ltd., Tianpu Chemical Co., Ltd., Shandong Yun Chemical Co., Ltd., Shanghai Huicheng fine chemical industry. Although some applications are excellent in HPMC, most manufacturers are not mature due to domestic manufacturers, and the product quality is general, and the price is expensive. Therefore, the domestic relatively small use, and it is more common in foreign countries. More imported suppliers are like Tao, Bayer.