Categories of additives

In Sec. 1.4 we discussed the classification of polymers into the categories of addition or condensation. At that time we noted that these classifications could be based on the following ... 

In Europe, the formation of the European Economic Community has created a requirement to bring food additive approvals of the member nations into alignment, so as to eliminate differences in laws that hinder the movement of foodstuffs among these nations. Historically the member countries have differed widely in approaches to food additive approval and their tendency to approve new additives. At the time of this writing, a framework directive for food additives and several specific directives for various categories of additives are nearing completion (3). 

There are now far more categories of additives than a few decades ago. The corresponding changes in additive technology are driven partly by the desire to produce plastics which are ever more closely specified for particular purposes. The benefits of plastics additives are not marginal. As outlined before, they are not simply optional extras but essential ingredients, which make all... 

The directive makes provision for rules regarding most categories of additive to be made in a further comprehensive directive. These additive categories, listed in Annex I of the Directive, are shown in Table 2.1. 

Table 2.1 Categories of additives listed in annex I of Directive 89/107/EEC...

Antioxidants should be labelled on the retail package with the specific chemical name or with the EC number. The legislation of member states of the EU is influenced by the decision taken within the EC. Some food standards are fully based on EC Directives and some are still based on national considerations. There may be differences between European states, for instance, the utilisation of ascorbic acid as antioxidant for egg products is permitted in France but prohibited in Germany. These differences concern usually the utilisation of antioxidants in various food commodities. The specification of antioxidants mentioned in EC Directives are respected by all member states. But it is still generally required that individual countries of the European Union as well as the central organisation should be approached. The requirements appearing in the EC Directives on additives must be applied by the member states. This means in the first place that for those categories of additives for which a Community positive list exists, member states may not authorise any additives which do not appear on the positive list. 

The second example27 belongs to the category of addition via onium-type intermediates . It exemplifies how the choice of the electrophile may affect the stereochemical course of the cyclization. When the hydroxy cnones rac-4a, b were treated with mercury(II) trifluoroacetate, both (E)- and (Z)-enone afforded basically the same yield and distribution of the diastereomer-ic cyclization products rac-5a, b. However, when phenylselenenyl chloride was used as electrophile, the (Z/Zj-isomers rac-4a, b produced quite contrasting ratios of the products rac-5 a, b. This result was interpreted in terms of EjZ equilibration in a single-bonded cationic adduct of the mercuric ions vs. nucleophilic attack on a rigid epi-selenonium ion27. 

Cell lines differ in the defined proteins they require for optimal cell growth. Usually, addition of insulin (I) and transferrin (T), along with the trace element selenium (S), is sufficient to enable most cell lines to grow in rich balanced nutrient media, such as the ones listed above. However, several categories of additives may enhance or be required for cell growth and/or production of the desired... 

A wide variety of other chemical entities are specifically incorporated into plastics to achieve desired goals of structure, performance, and processing ease. A short list of the major categories of additives is provided in Table 3. 

Lemma 4.1.5 Let A be a small-cocomplete abelian category in which lirp preserves exactness of sequences. Then with F the category of additive functors from A] to A , there is a functor (—)cts F —> F and a functorial map Dcts —> H (D G F) such that ... 

Food additives have been used for centuries to improve food quality. Smoke, alcohols, and spices have been extensively used for the last 10,000 years as additives for food preservation. The above-mentioned additives as well as a restricted number of additives comprised the main food additives until the Industrial Revolution. The Industrial Revolution brought so many changes in foods and asked for improved quality as well as quantity of the manufactured foods. For this reason many chemical substances were developed either for preservation or for color and/or odor enhancement. In the 1960s, over 2500 different chemical substances were used toward food manufacturing. In the United States over 2500 different additives were used to manufacture over 15,000 different foods. The desire for nutritional, functional, and tasty foods is an ongoing process. An additive is used to improve the shape, color, aroma, and extend the shelf life of a food. The following categories of additives are described ... 

In contrast to use of the term in other categories of additives, external plasticizers refer to additives blended homogeneously into the resin. The term internal plasticizer refers to modification of the molecular structure of the polymer by incorporating comonomers that provide greater flexibility. 

Side-shields on eye glasses or complete eye-shields fall in the category of additional desirable protection, but one that is often foregone in order to make the somewhat lesser protection by ordinary glasses acceptable and hence enforceable. 

Generally, divalent and tiivalent cations enhance the effectiveness of these anions more than monovalent ions do. This category of additives affects mainly the hydration of the alite phase, thus accelerating the development of early strength. The setting time is also shortened, but less effectively than with admixtures that increase the pH of the hquid phase. 

There is considerable overlap within this category of additives. A particular material, such as glass, may be employed in one application and be considered a reinforcement, but in another application it is called a filler. However, most commonly, a reinforcement is defined as an additive that improves the mechanical properties (e.g., strength) of the polymer system. A filler is defined as an additive that takes up space in the system, generally to reduce cost. A few of the most important additives within this category are described here. 

Many chemical compounds in foods (as well as in feeds for livestock) are added intentionally as food additives. The purpose is to protect foods against spoilage, oxidation and increase some aspects of the food quality (e.g., nutritional value, aroma, taste, colour or texture). Preservatives, colours and flavours are the best-known additives, but there are in fact many categories of additives, each tailored to a specific purpose. 

The different components involved in the formulated sols used for membrane coating can be classified in three categories as reported on Table 7-2. The first category consists of the compounds usually employed in the conventional sol-gel process whereas the second category has to do with additives preventing crack formation in supported layers. The third category of additives is related to the design of new membranes properties. Indeed, in order... 

TABLE 7-2. THE DIFFERENT CATEGORIES OF ADDITIVES INVOLVED IN SOL FORMULATION FOR MEMBRANE TOP-LAYER PROCESSING... 

Different categories of additives or additive systems are used to this purpose ... 

The explanation of the role of this second category of additives is primarily phenomenological. It considers the respective values of the diffusion coefficients and the mobility of the boimdaries ... 

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