Additives for plastics

After commercial polymers are manufactured in bulk, various additives are incorporated in order to make them suitable for specific end uses. These additives 

Plasticizers are high-boiling-point liquids (and sometimes solids) that, when mixed with polymers, give a softer and more flexible material. Box 2.1 gives dioctyl phthalate as a common plasticizer for PVC. On its addition, the polymer (which is a hard, rigid solid at room temperature) becomes a rubberlike 

Commercial polymer Largely amorphous, slightly branched with monomers joined in head-to-tail sequence. 

Lubricant Prevents sticking of compounds to processing equipment. Calcium or lead stearate forms a thin liquid film between the polymer and equipment. In addition, internal lubricants are used, which lower the melt viscosity to improve the flow of material. These are montan wax, glyceryl monostearate, cetyl pahnitate, or aluminum stearate. 

Filler Reduces cost, increases hardness, reduces tackiness, and improves electrical insulation and hot deformation resistance. Materials used are china clay for electrical insulation and, for other works, calcium carbonate, talc, magnesium carbonate, barium sulfate, silicas and silicates, and asbestos. 

Only very few polymers (thermoplastics, duroplastics, elastomers, converted natural products) can be processed and used as synthesized. The effects of heat and oxygen would damage them before they could even be processed. Then there are the environmental conditions applied during storage and use of the semifinished 

Besides the necessary protection against these damaging effects, use of these materials demands a considerable number of additive substances that influence the properties, processability, or appearance of the polymer materials [29, 30]. The result is a large number of irreplaceable additives that make processable resins, molding compounds and top-grade molding materials, i.e., technical materials, out of the primary products. 

To obtain an overview of the great variety of additives, they can be arranged in three types according to their purpose and function [31, 32]. 

A general statement that should be kept in mind before the individual additives are described is as follows Common to all additives is the fact that their effects depend on their solubility in the specific polymer [29, 30, 33]. The relative parameters are their chemical structure, the temperature, and the crystallinity of the matrix. Additives can only be dissolved, for instance, in the amorphous phase of semicrystalline thermoplastics, in which the additive concentration is increased during cooling from the molten state [33]. This is advantageous in terms of stabilization, since oxygen and solvent atoms are only capable of permeation through the increased lattice vacancies of the amorphous phase with its many defects. 

The bulk properties of a polymer ean often be altered considerably by the incorporation of additives. Probably the most well-known examples of this occur in rubber technology where variations in the choice of additives can produce such widely differing products as tyres, battery boxes, latex foam upholstery, elastic bands and erasers. It is also possible to achieve variations as extensive as this amongst plastics materials, in particular with PVC from which rigid rainwater piping, baby pants, conveyor belting, footballs and domestic insulating flex may all be prepared. 

In some cases an additive may be encountered in a variety of polymers for a wide range of end uses, for example certain antioxidants. In other instances the additive may be very specific to a certain polymer for a particular end use. 

Physically, additives may be divided into four groups, solids, rubbers, liquids and gases, the last of these being employed for making cellular polymers. In terms of function there are rather larger numbers of groups, of which the following are the most important  

In general, additives should have the following features unless by virtue of their function such requirements are excluded  

Example Concentration of additive Solubility at ambient temperature Solubility at processing temperature Expected effect 

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J. S. Murphy (ed.), Additives for Plastics, Elsevier Advanced Technology, Oxford (2001). 

Phillip Townsend Associates Inc., Chemical Additives for Plastics Apparent Supplier Strategies, Houston, TX... 

U. SchOnhausen, Positive List I. Additives for Plastics, Elastomers and Synthetic Fibres for Food Contact Applications, Ciba-Geigy Ltd, Basel (1993). 

Table 10.9 Apparent supplier strategies for chemical additives for plastics...

J. Murphy, The Additives for Plastics Handbook, Elsevier Science Ltd, Oxford (1996, 2001)... 

R. B. Seymour, Filers and Other Additives for Plastics. Audio Course nasties Institute of America, Hoboken, NJ. (1981). 

Stepek, J. and H. Daoust Additives for Plastics, Springer-Verlag, New York, NY, 1983. 

Substances that are also used as additives for plastic processing and applications will be treated in Chapter 3. In the following the two most important substance classes in the first category are discussed. 

Characteristic functions and the representative structures of plastics additives providing marketable and durable materials are included in this chapter. Types of additives for plastics used in contact with food are listed in Table 3-1. Similar additives as for PS are used for elastomer-modified plastics forming multilayer systems (blends) and used rather exceptionally in contact with food, such as high-impact polystyrene (HIPS) or acrylonitrile-butadiene-styrene polymer (ABS). Some of the additives, stabilizers in particular, are very reactive and are present in the plastic matrix in a chemically transformed form. 

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