History and introduction

2 Zinc oxide eugenol ZOE) cements 9.2.1 Introduction and history 

The ZOE cement has a long history. Eugenol is the essential constituent of oil of cloves, which has been used medically since the fourth century 

Polymers are important. Approximately 60 million tonnes are made annually. Indeed most of the organic chemicals manufactured are used to make polymers. These chemicals obviously include monomers, but indirectly the polymer industry consumes enormous quantities of organic materials for solvents, antioxidants, stabilizers, plasticizers etc. Apart from fuel (for transport and heat) and speciality chemicals like ethylene glycol (anti-freeze), pharmaceutical and agrochemicals etc., it can be stated that the end-use of most organic chemicals is in the production, directly or indirectly, of polymers. 

The term polymer describes materials which are large molecules. They are also called resins and macromolecules by industrialists and academics respectively. The main classes of polymers are plastics, elastomers (or rubbers), fibres and films. Polymers are effect chemicals—that is, they fulfil a particular application. Originally they were made—or accidentally discovered as in the case of polyethylene (PE) or polytetrafluoroethylene (PTFE)—and end-uses found for them. However, increased knowledge of properties such as toughness and strength together with experience gained with fillers and plasticizers, makes it possible to predict the properties of new polymers, copolymers or blends to the extent that the new polymeric materials are manufactured to serve a particular application. 

The early history of polymers is really the conversion of natural polymers into useful materials. Examples include the vulcanization of rubber (Goodyear, 1839), celluloid (which is plasticized cellulose nitrate—Hyatt, 1868), and cellulose-derived fibres, e.g. cuprammonia rayon (Despeisses, 1890) and viscose rayon (Cross, Bevan and Beadle, 1892). The first truly synthetic polymer, that is, one made from laboratory chemicals, was Bakelite (Bakeland, 1907). This was made from phenol and formaldehyde. Bakeland probably did not know the chemical structure of the Bakelite, but he did realize that organic chemicals containing multiple functionality yielded insoluble materials. The various phenol-formaldehyde resins (PF), e.g. Bakelite and novolacs, were thus obtained in an empirical manner. 

It is of interest to note that from that time nearly all the synthetic pioneering work on polymers has been carried out in industrial laboratories. This started with Carothers (Du Pont) in 1930, who studied the formation of aliphatic polyesters from diols and diacids but abandoned them in favour of aliphatic polyamides (nylons) when the polyesters were not suitable for fibres (wool and silk proteins are polyamides). It is continuing at the present time with the development of high performance aromatic polymers such as Nomex (Du Pont), Kevlar (Du Pont) and PEEK (ICI). 

Although polymers are effect chemicals and serve a particular end-use, many of the initial applications were ill-advised and attempted to substitute for metals without designing for the physical properties of the plastic. This led to the stereotyped image of plastics as cheap and nasty . Synthetic fibres were a notable exception. However, over the last 25 years recognition of the 

Thin-layer chromatography (TLC) is a rapid, simple, versatile, sensitive, inexpensive technique for the separation of substances. The mobile phase in TLC is a liquid 

TLC is useful both as an analytical and a preparative technique, and substances tentatively identified by TLC may be further characterized by various analytical techniques such as nuclear magnetic resonance spectrometry, mass spectrometry, or gas liquid chromatography. Moreover, many specific chemical detection tests are available to help identify substances separated by TLC. TLC is a microanalytical procedure and provides for separations and at least tentative identification of substances in the milligram (mg), microgram (/ig), and nanogram (ng) range. TLC can provide the biochemist with a method of eluting separated substances from plates for quantitative analyses. Recent studies indicate that elution techniques may not be the best alternative for quantitative analyses of many substances separated by TLC and that the preferred method may involve quantitative in situ densitometric analysis [1,2]. 

It is not easy to determine when the detergent industry came into existence. The problem was to define exactly what is being referred to as a synthetic detergent. For example, in the United States the term surfactants was used, while in Europe the term tenside was applied to point out the detergent industry. 

Many general definitions of a detergent have been suggested [4]  

Detergent. A product that after formulation is devised to promote the development of detergency. 

Surface active agent. A chemical compound, which when dissolved or dispersed in a liquid, is absorbed at an interface giving rise to a number of important chemical properties. The compound includes in its molecule one group that has an affinity for polar surfaces, ensuring solubilization in water, and a group that has little affinity for water. 

Amphiphilic product. A product that contains in its structure one or more hydrophilic groups and one or more hydrophobic groups. 

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Breitenstein BD, Newton CE, Norris HT. 1985. Parti Introduction and history of the case. Health Phys 49(4) 565-567. 

Cartwright AC. Introduction and history of pharmaceutical regulation. In Cartwright AC, Matthews BR, eds. Pharmaceutical Product Licensing. Requirements for Europe. Chichester EUis Horwood, 1991 29 5. 

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