Thickener poly , derivatives

Suitable protective coUoids for the preparation of acryhc suspension polymers include ceUulose derivatives, polyacrylate salts, starch, poly(vinyl alcohol), gelatin, talc, clay, and clay derivatives (95). These materials are added to prevent the monomer droplets from coalescing during polymerisation (110). Thickeners such as glycerol, glycols, polyglycols, and inorganic salts ate also often added to improve the quahty of acryhc suspension polymers (95). 

Other thickeners used include derivatives of ceUulose such as methylceUulose, hydroxypropylmethylceUulose, and ceUulose gum natural gums such as tragacanth and xanthan (see Cellulose ethers Gums) the carboxyvinyl polymers and the poly(vinyl alcohol)s. The magnesium aluminum siHcates, glycol stearates, and fatty alcohols in shampoos also can affect viscosity. 

Functional derivatives of polyethylene, particularly poly(vinyl alcohol) and poly(acryLic acid) and derivatives, have received attention because of their water-solubility and disposal iato the aqueous environment. Poly(vinyl alcohol) is used ia a wide variety of appHcations, including textiles, paper, plastic films, etc, and poly(acryLic acid) is widely used ia detergents as a builder, a super-absorbent for diapers and feminine hygiene products, for water treatment, ia thickeners, as pigment dispersant, etc (see Vinyl polymers, vinyl alcohol polymers). 

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. 

Fishermen periodically recover chemical weapons and are burned through accidental exposure to sulphur mustard. This is because when sulphur mustard comes in contact with cold water a tarry substance forms around the exterior while the interior remains viscous over a period of many decades. The exterior consists mainly of precipitates derived from thickening agents (Fishermen then break open the crusty exteriors as they haul their catches into their boats and may then become exposed or contaminate their vessels as a result). The chemical composition of the tarry exterior is not well understood partly because it varies from case to case. Various polymer materials, such as alloprene and poly [methyl methacrylate] (PMMA), for example, were sometimes combined with sulphur mustard to lower its freezing temperature. Solvents such as chlorobenzene, have also been combined with sulphur mustard. Finally, sulphur mustard was often mixed with arsenic-containing agents, such as lewisite and diphenychloroarsine. 

The most commonly used suspending agents are cellulose derivatives, poly-aciylate salts, starch, poly(vinyl alcohol), gelatin, talc, and clay derivatives (95). The important function these agents must serve is to prevent the coalescence of monomer droplets during the course of the polymerization (114). Thickeners can also be added to improve suspension quality (95). Other additives such as lauryl alcohol, stearyl acid or cetyl alcohol lubricants and di- or trivinyl benzene, dial-lyl esters of dibasic acids, and glycol dimethacrylates cross-linkers are used to improve bead imiformity and bead performance properties. 

In many cases it will be necessary to increase the viscosity of the adhesive with thickener. Examples of this are thick bed or gap filling adhesives, or adhesives for use on porous substrates. Naturally occurring materials are sometimes used, such as karaya gum casein also tends to increase viscosity as well as behaving as a stabilizer. However, it is now more usual to use synthetic polymers such as methyl cellulose and similar derivatives, and poly acrylates. 

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