Applications to AB cements

Broadly speaking, in the study of AB cements derived from poly-carboxylic acids, the band of interest falls in the region 1550-1620 cm (Mehrota Bohra, 1983 Bellamy, 1975). This band is the asymmetric stretch of the carboxylate group and its exact position depends on both the nature of the bonding involved (i.e. whether purely ionic or partially covalent), and the nature of any chelation by the carboxylate group (Bellamy, 1975). 

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The theory of Bronsted (1923) and Lowry (1923a, b) is of more general applicability to AB cements. Their definition of an acid as a substance that gives up a proton differs little from that of Arrhenius. However, the same is not true of their definition of a base as a substance capable of accepting protons which is far wider than that of Arrhenius, which is limited to hydroxides yielding hydroxide ions in aqueous solution. These concepts of Bronsted and Lowry can be defined by the simple equation (Finston Rychtman, 1982) ... 

The Arrhenius definition is not suitable for AB cements for several reasons. It cannot be applied to zinc oxide eugenol cements, for these are non-aqueous, nor to the metal oxychloride and oxysulphate cements, where the acid component is not a protonic acid. Indeed, the theory is, strictly speaking, not applicable at all to AB cements where the base is not a water-soluble hydroxide but either an insoluble oxide or a silicate. 

Aluminosilicate glasses are used in certain AB cement formulations, and the acid-base balance in them is important. The Bronsted-Lowry theory cannot be applied to these aluminosilicate glasses it does not recognize silica as an acid, because silica is an aprotic acid. However, for most purposes the Bronsted-Lowry theory is a suitable conceptual framework although not of universal application in AB cement theory. 

Acid-base (AB) cements have been known since the mid 19th century. They are formed by the interaction of an acid and a base, a reaction which yields a cementitious salt hydrogel (Wilson, 1978) and offers an alternative route to that of polymerization for the formation of macro-molecular materials. They are quick-setting materials, some of which have unusual properties for cements, such as adhesion and translucency. They find diverse applications, ranging from the biomedical to the industrial. 

The ability of the polyelectrolyte-based AB cements (Chapter 5) to bond to a variety of substrates, combined with their rapid development of strength - they can become load-bearing within minutes of preparation -suggests that they have applications as rapid-repair and handyman materials. 

Consistency, working time, setting time and hardening of an AB cement can be assessed only imperfectly in the laboratory. These properties are important to the clinician but are very difficult to define in terms of laboratory tests. The consistency or workability of a cement paste relates to internal forces of cohesion, represented by the yield stress, rather than to viscosity, since cements behave as plastic bodies and not as Newtonian liquids. The optimum stiffness or consistency required of a cement paste depends upon its application. 

Such cementing compositions are obtained by adding ABS types to common cements used in subterranean applications (85,86). When ABS is added to water-extended slurries, a cementing composition is created with a lower Young s modulus while achieving high compressive and tensile strengths. 

AcrylonitrUe-butadiene-styrene (ABS). ABS plastic is a copolymer made from the three monomers-acrylonitrile (at least 15 percent), butadiene, and styrene. It is a rigid plastic with good impact resistance at temperatures down to -40°F and up to Y16°P. ABS is used mainly for drain-waste-ventilation (DWV) pipe and fittings, but it also is used in solvent cement for installing pipe in various applications. The most conunon applications for ABS pipe material are ... 

MAJOR APPLICATIONS Hoses where oil, fuel, chemicals, and solutions are transported. Oil-drilling industry. Powder and particulate forms in cements and adhesives. Modification of PVC and ABS to improve impact resistance. 

Typical interior holding adhesive applications are listed in Table 2. One of their major functions is to retain vinyl or ABS films against interior door or sidewall trim panels. The ABS or vinyl sheet material is often vacuum drawn into recesses in the door or trim panel. It may have a tendency to pop loose and creep away from concavities or from the backside of the panels. This behavior, which may be expected whenever the sheet material is under tension, is overcome by the use of adhesives such as epoxies which do not cold flow and which begin to cure when heated in the vacuum forming operation. For panels where there is less tension on the sheet material, hot melts or solvent cements may be used. An example is the use of a hot melt hemming adhesive to secure plastic sheet when it is wrapped over the edge of a door or trim panel. 

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