Agent thickening

The identification and quantitative determination of polysaccharides plays a role in the examination of thickening agents, balast material etc. 

These derivatives of the monosaccharide structural units are then qualitatively and quantitatively analyzed by gas chromatography on capillary columns. In more difficult cases, a preliminary separation of acidic and neutral polysaccharides on an ion exchanger is recommended. Methanolysis or hydrolysis of polysaccharides containing uronic acids and anhydro sugars are critical due to losses of these labile building blocks. 

Reductive cleavage of the permethylated polysaccharide is recommended as a gentle alternative to hydrolysis. In this process, partially methylated anhydroalditolacetates are formed as shown in Fig. 4.42, using a galactomannan as an example. Conclusions about the structure of the polysaccharide can be drawn from the result of the qualitative and quantitative analysis, which is carried out by gas chromatography/mass 

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Cellulosics. CeUulosic adhesives are obtained by modification of cellulose [9004-34-6] (qv) which comes from cotton linters and wood pulp. Cellulose can be nitrated to provide cellulose nitrate [9004-70-0] which is soluble in organic solvents. When cellulose nitrate is dissolved in amyl acetate [628-63-7] for example, a general purpose solvent-based adhesive which is both waterproof and flexible is formed. Cellulose esterification leads to materials such as cellulose acetate [9004-35-7], which has been used as a pressure-sensitive adhesive tape backing. Cellulose can also be ethoxylated, providing hydroxyethylceUulose which is useful as a thickening agent for poly(vinyl acetate) emulsion adhesives. Etherification leads to materials such as methylceUulose [9004-67-5] which are soluble in water and can be modified with glyceral [56-81-5] to produce adhesives used as wallpaper paste (see Cellulose esters Cellulose ethers). 

Synthetic lubricants are made with neopentyl glycol in the base-stock polyester (24). Excellent thermal stabiHty and viscosity control are imparted to special high performance aviation lubricants by the inclusion of polyester thickening agents made from neopentyl glycol (25,26) (see LUBRICATION AND lubricants). Neopentyl glycol is also used to manufacture polymeric plasticizers that exhibit the improved thermal, hydrolytic, and uv stabiHty necessary for use in some exterior appHcations (27). 

Gel Shampoos. These shampoos are generally versions of the clear product but consist of higher concentrations of the cleansing and thickening agents. They are usually packaged in tube form for dispensing purposes. 

Semipermanent hair color products are formulated at an alkaline pH, usually between 8.5 and 10. At this pH the cuticle of the hair lifts away from the hair a Httie, allowing for easier penetration of dye. An alkyl amine buffered with an organic acid normally is used to obtain the desired pH. The formulations contain a mixture of solvents and surfactants to solubilize the dyes and a thickening agent is added so that the product stays on the hair without mnning or dripping. A 20—30 min appHcation time is normal for this type of product. A representative formula for a semipermanent dye product is given in Table 7. 

The viscosity of solutions is quite temperature dependent increasing the temperature leads to a reduction in viscosity, which approaches zero at approximately 60°C (322). The viscosity is relatively stable from pH 3—10 and is compatible with a number of inorganic salts other than sodium. The production of succinoglycan and its potential use in foods and industrial processes as a thickening agent has been described (322). 

Solvent Evaporation. This encapsulation technology involves removing a volatile solvent from either an oil-in-water, oil-in-oil, or water-in-oH-in-water emulsion (19,20). In most cases, the shell material is dissolved in a volatile solvent such as methylene chloride or ethyl acetate. The active agent to be encapsulated is either dissolved, dispersed, or emulsified into this solution. Water-soluble core materials like hormonal polypeptides are dissolved in water that contains a thickening agent before dispersion in the volatile solvent phase that contains the shell material. This dispersed aqueous phase is gelled thermally to entrap the polypeptide in the dispersed aqueous phase before solvent evaporation occurs (21). 

Typical cosolvents include methanol [67-56-17, ethanol [64-17-5] isopropyl alcohol [67-65-OJ, or toluene. The selection of cosolvents depends on the requirement of the formula and their interaction with other ingredients. Methanol is a common cosolvent in methylene chloride formulas since it has good solvency and is needed to swell ceUulose-type thickening agents. A typical methylene chloride formula used to strip wood is as follows (7). 

Hydroxyethyl cellulose (HEC), a nonionic thickening agent, is prepared from alkali cellulose and ethylene oxide in the presence of isopropyl alcohol (46). HEC is used in drilling muds, but more commonly in completion fluids where its acid-degradable nature is advantageous. Magnesium oxide stabilizes the viscosity-building action of HEC in salt brines up to 135°C (47). HEC concentrations are ca 0.6—6 kg/m (0.2—21b/bbl). 

For products intended to remain stable dispersions for an extended period, a particle size of 2 p.m or less is desirable. A thickening agent is usuaUy added after the reaction has been completed and the mixture is cooled in order to prevent settling and agglomeration. Examples of thickeners are guar gum, xanthan gum, and hydroxyethylceUulose. The final products are generaUy between 40 and 50% soUds, with a viscosity of 1500 5000 mPa-s(=cP). 

Carbohydrates. Carbohydrates (240—244) of any form are easily sulfated in the presence of solvent, using sulfating reagents such as SO —pyridine, SO —triethjlamine, SO.—trimethyl amine, or chlorosulfonic acid—pyridine. As an example, starch (qv) is sulfated using SO.—trimethyl amine at 0 to 5°C in aqueous media (16). Sulfated carbohydrate products find some use in industry as thickening agents. 

Starch succinates [39316-70-6] are also used as thickening agents in foods. The 1-octenylsuccinate half-ester [52906-93-17, sold as its sodium salt [66829-29-6], has surface active (emulsifying) properties. 

In hair coloring a light ash blond shade may require as Httie as 0.5—1% of intermediates, whereas a tme black may require up to about 5%. In principle, the formulator blends precursors that yield red, blue, and yellow dyes. The base in which the components are dissolved or suspended is similar to that used in simple bleaches and may include alkanolamides, various types of surfactants, thickening agents, and solvents. Removal of undesirable dyes is achieved by treating the discolored hair with a powerful reductant of the sulfite family. 

Toothpaste contains an abrasive (qv), flavor, a humectant system, a surfactant, a binding and thickening agent, color, and one or more therapeutic or cosmetic agents. 

The process of textile print coloration can be divided into three steps. First, the colorant is appHed as pigment dispersion, dye dispersion, or dye solution from a vehicle caUed print paste or printing ink, containing in addition to the colorant such solutions or dispersions of chemicals as may be required by the colorant or textile substrate to improve and assist in dye solubUity, dispersion stabUity, pH, lubricity, hygroscopicity, rate of dye fixation to the substrate, and colorant-fiber bonding. The required viscosity characteristics of a print paste are achieved by addition of natural or synthetic thickening agents or by use of emulsions. 

If you combine petroleum based or synthetic based oil with a suitable thickening agent, you get grease. The thickening agent can represent between 3% and 30% of the total volume of grease. 

An example of the first type is the emulsion stabiliser as exemplified by sodium oleyl sulphate, cetyl pyridinium chloride and poly(ethylene oxide) derivatives. For a number of applications it is desirable that the latex be thickened before use, in which case thickening agents such as water-soluble cellulose ethers or certain alginates or methacrylates may be employed. Antifoams such as silicone oils are occasionally required. 

Poly(acrylic acid) is insoluble in its monomer but soluble in water. It does not become thermoplastic when heated. The sodium and ammonium salts have been used as emulsion-thickening agents, in particular for rubber latex. The polymer of methacrylic acid (Figure 15.13 (VI)) is similar in properties. 

The polymers are of interest as water-soluble packaging films for a wide variety of domestic and industrial materials. (Additional advantages of the poly(ethylene oxide)s are that they remain dry to the feel at high humidities and may be heat sealed.) The materials are also of use in a number of solution application such as textile sizes and thickening agents. As a water-soluble film they are competitive with poly(vinyl alcohol) whereas in their solution applications they meet competition from many longer established natural and synthetic water-soluble polymers. 

A number of water-soluble cellulose ethers are marketed." Methyl cellulose is prepared by a method similar to that used for ethyl cellulose. A degree of substitution of 1.6-1.8 is usual since the resultant ether is soluble in cold water but not in hot. It is used as a thickening agent and emulsifier in cosmetics, as a paper size, in pharmaceuticals, in ceramics and in leather tanning operations. 

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