Additives Which Modify Physical Properties 1 Plasticizers

Additives which alter physical properties either during processing or in the final plastic include plasticizers, fillers, lubricants and flow promoters, impact modifiers and foaming agents. 

Polymer additives or modifiers may be generally grouped into those which alter physical properties, those which change chemical properties and those which affect the appearance of the finished plastic product... 

Plastics additives may be divided into two main categories —those which modify polymer properties by physical means, such as plasticisers, lubricants, impact modifiers, fillers, pigments, etc, and additives which achieve their effect by chemical reactions such as PVC heat stabilisers, antioxidants, ultraviolet absorbers and flame retardants. In selecting them, however, care must be taken to match the additives to the polymer they are intended to protect, taking into account such factors as compatibility, efficiency and possible synergism of two or more additives in the particular polymer under consideration. 

Plastics are semi-synthetic or synthetic materials which can be manipulated to form films, fibres, foams or three-dimensional olgects. Natural polymers from plants, insects and animals are not discussed in this book. Synthetic paints, synthetic textiles and photographic film contain plastics but will not be discussed in this book because their conservation is the focus of specialist publications (Chiantore and Rava, 2005 Learner, 2005 Timar-Balazsy and Eastop, 1998 Lavedrine et al., 2003). Plastics are based on polymers, also known as macromolecules, which are large molecules made by joining together many smaller ones. The chemical and physical properties of liquid polymers are modified with additives and shaped to convert them into solids with dimensionally stable forms. 

II. Commercial polymers for the most part do not occur as pure materials. Many are modified by additives which impart certain desired physical properties. An example is the case of polyvinylchloride, which in its pure state is a rigid insoluble material. Plasticizer additives can be used, e.g., di-2-ethylhexyl-phthalate (commonly referred to as dioctylphthalate), to soften this chlorinated hydrocarbon and make it workable. 

---