Existing chemicals chemical substances Synthetic

Not surprisingly, there are many synthetic chemicals and formulations commercially available. In Europe alone more than 100000 chemicals (not formulations) are on the European Inventory of Existing Commercial Chemical Substances (EINECS), which lists chemicals on the market before September 1981. This list differentiates between existing and all new chemicals produced since 1981 that have to be notified. During the period between 1981 and 2000 more than 2700 new substances were notified in Europe (Figure 1.3). For new substances, the obligatory notification system requires the manufacturer or importer to provide information suitable for risk assessment to be submitted to the competent authorities. The details required are dependent on the production volume or import quantities of the chemical. 

All thermoplastic adhesives require heating in order to melt the polymer, hence the name hot-melt. Unlike the majority of structural adhesives, there is no chemical curing reaction. Initially based on natural substances, synthetic hot-melt adhesives first became available in the 1950 s. A great many polymers exist as thermoplastics, providing a wide range of potential hot-melts. Each adhesive formulation contains a cocktail of compounds to modify the properties. These include tackifiers to promote adhesion and waxes to reduce viscosity and cost. 

Substances prepared under carefully controlled conditions and using very pure chemicals, in a modern laboratory, for example, contain only the basic component elements, those that determine the actual composition and nature of the substances. Natural substances, whether of mineral or biological origin, and also most synthetic (human-made) substances contain, in addition to their main components, impurities foreign to their basic composition. Most impurities usually enter substances such as minerals, for example, in relatively small amounts, when the substances are created. Others, such as those in some rocks and the wood of trees, do so in the course of their existence. Once within a substance, impurities become an integral part of the host substance and impair the purity of the substance. Although they alter the actual composition of substances, impurities do not affect their basic properties. 

There exists a list of permitted additives. This list is concerned only with chemical synthetics (substances obtained by a chemical reaction other than degradation). It means that the substances on the list are those which either do not occur naturally or are not obtained from natural sources. Of the substances which are not on the list it is not always possible to decide whether these may be used in food. The antioxidants and foodstuffs in which a limited amount of antioxidant is permitted are given in Table 12.11. Only the above-mentioned foods may contain antioxidants, except -tocopherol which may be generally used in foods as an antioxidant. 

The third possibility for synthesizing polymeric substances is the modification of existant natural or synthetic macromolecules (see Chap. 5). These processes can either be chemical or physical. Chemical modifications are reactions on macromolecules without degradation of the main chain (macromolecular substitution routes, polymer-analogous reactions ) like, for example, hydrolysis. 

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