Industrial Applications of Cellulose Ethers for Construction Chemicals and Product Overview

Cellulose polymers are chain monomers that form repeating structures. Cellulose molecules are defined as polymeric structures formed by the combination of anhydroglucose monomers with the formula (C6 H10 O5)n. Cellulose polymers consist of monomers bonded with a linear angle of 1800 degrees with chain lengths between 500-1000 Angstroms, sensitive to oxidation, containing three functional (replaceable) hydroxyl (OH)- groups and possess hydrophilic (water-loving) properties bonded through hydrogen bonding. Cellulose is a fibrous crystalline structure containing an average of 5000 glycol units bonded through hydrogen bonding between molecular hydroxyl (OH)- groups. The microcrystalline lattice structure that forms the macrocapillary structure increases the consistency of the water phase between air cells and serves as a physical barrier holding the air cells in suspension. The gel formed with microcrystalline cellulose breaks down when an external force is applied, and reforms with minimal viscosity loss when the force is removed. Thanks to this property, liquid solutions of cellulose exhibit thixotropic flow characteristics. Each anhydroglucose unit in the cellulose structure contains three functional hydroxyl (OH)- groups; the functional groups are available for modification. Because of this property, various derivatives of cellulose can be developed with very broad industrial applications such as paints, inks, cement-based construction chemicals, plaster, varnish, detergents, cosmetics, food, petrochemicals and textiles. The low molecular weight bonds of the functional hydroxyl (OH)- groups in cellulose are broken and cleaved in concentrated acidic (70% H2SO4, 40% HCl) or dilute alkaline (10% NaOH) solutions, thereby obtaining cellulose derivatives with different physical and chemical properties. The most important industrial derivatives of cellulose are cellulose ethers (Methyl Cellulose- MC, Methyl Hydroxyethyl Cellulose-MHEC, Methyl Hydroxypropyl Cellulose-MHPC, Hydroxyethyl Cellulose -HEC, Carboxymethyl cellulose-CMC), cellulose esters (Cellulose Acetate) and nitrocelluloses. Cellulose ethers are obtained as a result of the reaction of an appropriate alcohol with sulfate or chlorine salts (monochloromethane CH3Cl) in an alkaline environment. Alkaline cellulose is prepared as an intermediate product, and the degree of etherification is determined by the reaction temperature as well as the chain length of the cellulose, the chemical properties of the alkali and the water ratio. [caption id="attachment_103540" align="aligncenter"] Figure 1. Chemical structure of cellulose molecule[/caption] The degree of etherification is the main factor determining the physical (water retention, viscosity, color, particle size, odor, etc.) and chemical (pH range, molecular weight, reaction with solvents, etc.) properties of cellulose. I would like to emphasize once more that the modified cellulose ethers put into industrial use (For example: Walocel MKX 45000 PP 10, Walocel M KX 25000 PP 25 L, Walocel MC 65, Methocel 327, Cellosize QP 30000 H, Cellosize QP 100 MH, etc.) are obtained through chemical reaction. The modified celluloses we sell commercially are not products obtained through physical mixing (powder mixing) but are modified cellulose ethers obtained through chemical reaction. In cement-based applications, the preference for products obtained through chemical reaction when selecting cellulose ether is an important criterion. Celluloses are products with high water retention capacity and macro capillary structure. However, high temperatures (above 500C) cause cellulose degradation and loss of water absorption and swelling capacity. Viscosity measurement (generally of 1% or 2% solutions) is one of the most important parameters in selecting cellulose ether and determining its properties. Although the term viscosity has many similar definitions, it is generally defined as the resistance of liquids to flow. According to the cellulose molecule chain theory; low chain cellulose molecules have low viscosity, while high chain cellulose molecules have high viscosity. Fluids with low viscosity have high fluidity, while fluids with high viscosity have low fluidity. The science dealing with the deformation and flow properties of fluids under the influence of mechanical forces is called Rheology.

Below, the relationship between viscosity and flow properties is explained according to the Newton model:

Viscosity (μ): Shear stress/shear rate Viscosity (μ): Shear stress /Shear rate μ = (Newton/m2 ) x Second = Pascal (N/m2 ) x Second = Pa.s 1 Pascal x Second = 10 Poise = 1000 mPa.S = 1000 centipoise (cP) The flow model of a fluid is determined according to the graph plotted between shear stress and shear rate. Accordingly, flows are classified as Newtonian or non-Newtonian flows. Gases, solutions and non-colloidal liquids are Newtonian fluids. Most liquids such as high concentration suspensions and polymer solutions do not exhibit Newtonian behavior. In Newtonian flow, shear stress and shear rate are directly proportional to each other. The proportionality constant gives the viscosity value and does not change with the rate of shear deformation. To describe the flow behavior of such materials, knowing only the viscosity value is sufficient. Viscosity measurement is performed in industry using different measurement methods; the most commonly used methods are Haake Rotovisco, Brookfield and Höppler viscometers, and viscosity values give different results from each other. [caption id="attachment_103556" align="aligncenter"] Figure 2. Newtonian and non-Newtonian flow behaviors[/caption] The viscosity of Newtonian fluids such as water, milk, sugar solution and mineral oil depends only on temperature, not on shear rate and time. The viscosity of a non-Newtonian fluid depends on shear rate and time. If the viscosity of a non-Newtonian fluid depends on temperature, shear rate and time, such a fluid is called a "Time-Dependent Non-Newtonian Fluid". Depending on how the viscosity changes over time, the flow behavior is characterized as thixotropic or rheopectic. Thixotropy is not a separate flow type but is considered as a time-dependent structural change of existing flow types and is a frequently occurring phenomenon in dispersed systems. In thixotropy, it is observed that stress reversibly decreases viscosity. When the stress is removed, the structure returns to its original state. Depending on how viscosity changes with shear rate, the flow behavior is called "shear thinning or shear thickening". In shear thinning fluids, viscosity decreases with increasing shear rate, while in shear thickening fluids, viscosity increases with increasing shear rate. Shear thinning fluids (paints, shampoo, fruit juice concentrate, ketchup) are called pseudoplastic, and shear thickening fluids (clay, sugar solutions, corn starch-water mixture, water-sand mixture, concentrated starch suspensions) are called "Dilatant Fluids". Pseudoplastic fluids exhibit plastic behavior under low stresses and viscous behavior under high stress forces. Several of the described different rheological behaviors can be observed in a single substance at different stress levels and different mixing times. Cellulose ethers used as rheological agents in water-based decorative paints, cement-based construction chemicals and plaster applications are one of the important inputs that regulate the viscosity, flow properties, application time and ease of application of the product. As Kimsel Kimya, with decades of experience we offer a wide range of exclusive cellulose ether-based product portfolio for building materials. This product range includes well-known brands such as Walocel and Methocel cellulose ethers with the following characteristics: •High water retention capacity unchanged with temperature (Open Time), • Selective consistency adjustment for easy handling (Workability), • Precise control of rheology for slip resistance and good workability (Slip Resistance), •Stabilization of air voids (Stability), •Improved surface adhesion strength (high bond strength under normal conditions, after heat aging, freeze-thaw, and water soaking). Potential applications range from tile and ceramic adhesives and joint fillers to fillers, surface levelers, plasters and adhesives for exterior facade thermal insulation systems to plaster and cement-based renders. Walocel MKX 70000 PP 01: Cement-based tile and ceramic adhesives, Walocel MC 65: Cement-based tile and ceramic adhesives, Walocel MKX 45000 PP 10: Cement-based adhesives and renders, Walocel MKX 25000 PP 25 L: Cement-based thermal insulation renders and adhesives, Methocel 327: Cement-based thermal insulation renders and adhesives, Walocel MKX 15000 PP 20: Cement-based grout and repair mortar, Walocel MKX 6000 PF 01: Cement-based joint filler,

Walocel MT 400 PFV: Cement-based self-leveling.

Sources •Fırat University Engineering Faculty Chemical Engineering Department, Fluid Mechanics Lecture Notes (Instructor Prof. Dr. Dursun Özer) • Dow Construction Chemicals. High Performance Products and Solutions for the Construction Industry. Turkey Version 2012 www.dowcc.eu • Dow Construction Chemicals Regional Marketing Manager Beyhan Gözoğul. 2012 Training Notes • Rheology Handbook. 2002 Elementis Specialties, Inc.

Ertuğrul Günaydın Chemical Engineer Product Manager Kimsel