Cellulosic thickeners

Cellulosic thickeners are among the most commonly used thickeners for decorative latex-based paints. They are produced by chemical modifications of cellulose such as carboxymethylation or etherification. The most widely used derivatives are hydroxyethyl cellulose, ethylhydroxyethyl cellulose, methylhydroxyethyl cellulose, methylhydroxypropyl cellulose, and sodium carboxymethyl cellulose. The important characteristics that control the properties of different grades of individual derivatives are degree of polymerization, degree of substitution and molar substitution. 

There is no best cellulosic thickener for all types of waterbased paints rather, experimental study is needed to select the best suitable thickener for a given system because various performance para- 

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Another important application of NR is for bonding ceramic tiles, although it needs special compounding with clay filler and cellulose thickener. Water-borne NR adhesives can also be used for bonding canvas and leather shoes and interior trim in some automotive applications. 

In petroleum and oxygenate finish removers, the major ingredient is normally acetone, methyl elliyl ketone, or toluene. Cosolvcnts include methanol, n-butanol, sec-butyl alcohol, or xylene. Sodium hydroxide or amines are used to activate the remover. Paraffin wax is used as an evaporadon retarder though its effectiveness is limited because it is highly soluble in the petroleum solvents. Cellulose thickeners are sometimes added to liquid formulas to assist in pulling the paraffin wax from the liquid to form a vapor barrier or to make a thick formula. Corrosion inhibitors are added to stabilize the formula for packaging (qv). 

Aicoramnosan. [Vevy] Hydroxydhyl-cellulose thickener, suspending s oit stabilizer for vinyl polymerization binder in ceramic glazes used in paper and textile sizing. 

Recent improvements in the sensitivity IS) of the vacuum-suction fiberdrawing technique for elongational viscosity measurements have permitted the evaluation of cellulose-thickened coatings with a small-particle latex 16), The data (Table I) indicate that the DUEV involves contributions not only from the thickener but also from the components of the formulation. On the basis of earlier observations 17), this contribution was assumed to arise from high-aspect ratio flocculents formed by the latex and pigment in extension. 

Hydrophobically modified alkali-swellable latex thickeners (Chapter 25) can also be used as cothickeners for HEURs, and, like hydrophobically modified HEC, do not suppress the ICI viscosity of HEURs. Therefore, blend ratios of HEUR/hydrophobically modified alkali-swellable latex systems will have less HEUR thickener and be less expensive than HEUR/cellulosic systems. Some hydrophobically modified alkali-swellable latexes are even more cost-efficient than cellulosic thickeners, so a further savings may be realized. Another advantage to this approach is that the HEUR/hydrophobically modified alkali-swellable latex thickener systems are not biodegradable however. 

The reduction of scrub resistance is the main disadvantage of HEUR/ hydrophobically modified alkali-swellable latex thickener systems 18, 19). Hydrophobically modified alkali-swellable latex-thickened paints often show increased water and alkali sensitivity, reduced wet and dry adhesion, and lower scrub resistance than similar cellulosic-thickened paints. 

Associative thickener blended with mid-M W HEC cellulosic thickener (50/50). 

Secondly, damage can been as product separation. Coatings contain varying amounts of solids depending on its function. To keep these solids suspended in a water medium, other additives such as cellulosic thickeners and LAS surfactants are used. These components can be attacked by microorganisms and can be broken down. As this happens, their ability to function properly diminishes and the solid matter of the formulation settles to the bottom of the container. 

SPECIAL CELLULOSIC THICKENERS 4.1 Hydration Retarded Cellulosics... 

Figure 5 Possible Points of Enzyme Attack on Conventional Cellulosic Thickeners...

The goal is to offer to paint formulators an easy way to convert from cellulosic thickeners to designed rheology modifiers maintaining rheology profile and overall properties. 

The cellulosic thickeners market has had low growth in the past recent years when the demand for liquid polymer type thickeners has been greater. This because of the trend to full liquid production line and easily - tailored systems. Paints manufacturers wait for cost effectiveness from suppliers with improved, more efficient and competitively priced products. 

In other types of production with no cellulosic premix, blending cycle times are nevertheless reduced dry cellulosic thickener has to be added slowly and needs time to swell and build up viscosity, whereas die new product can be added more quickly and reacts immediately. 

Most of the time, cellulosic diickeners are pre-dissolved in a separate tank and used under a liquid form in the manufacturing process. In general, this premix is a blend of cellulosic thickener, water, biocide and defoamer. This colloid solution is made to be pumpable and large enough to be used in several paint batches. 

The main causes of viscosity loss of cellulose ethers are of microbial (b u teria, fungi and enzyme) and chemical (redox process) natures. Biocides are used to kill bacteria and fVingi but they are usually not effective against enzymes. The enzymatic liquefaction is known to be the strongest process. Studies have been made on different cellulosic thickeners with bacteria, fungi and commercial cellulase enzyme juid the overall conclusion was that cellulase is the most significant cause of viscosity loss. ... 

Generally contamination in a colloid solution can appear after only 24 hours resulting in a decreased efficiency of cellulosic thickeners and can contaminate the paints which then show visual deterioration like phase separation and the development of a characteristic odour. This issue is a problem for the paint industry as it first leads to an increase in formulating costs linked to larger amount of thickener in order to obtain the required viscosity and secondly to the excessive costs associated with claims when contaminated paints are returned. 

The introduction of these new rheology modifiers provides paints manufacturers with a very attractive alternative to cellulosic thickeners. These rheology modifiers are the first acrylic associative thickeners that offer a similar rheology, in-can feeling, appearance, and application properties as cellulosic thickeners. They also show some key advantages compared to cellulosic thickeners. Supplied as liquids, they are easier to handle and because of their polymeric chemistry, they are less sensitive to microbial attack In application trials, professional painters found that new rheology modifier based paint performs similarly to cellulose thickened paint but with a better spattering resistance. 

However, what makes this new technology very attractive is that it offers opportunity for major cost savings. These rheology modifiers function more efficiently than cellulosic thickeners giving the possibility to decrease raw material costs. In addition, productivity improvements are possible and have been confirmed by customers. 

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