Basic Concepts for Plastic Response

Abstract

This chapter following the general introduction is devoted to provide the reader with the basic concepts related to the understanding of the fundamental necessary properties of a polymeric material to perform as a plastic material and then to be used in the corresponding applications. The main objective of this chapter is to highlight the structural properties requested to a plastic material and to what extent they can be reached with differentiated molecular structures of the macromolecular chains forming the polymer. Indeed, the plastic behaviour can be found in molecularly different materials, but the precise response requested by many specialized applications in our present style of life is obtained by a well-thought analysis of relationships between detailed molecular structure and ultimate properties. Indeed, the selection of a plastic material among the available products is determined by the requested mechanical response. This last is determined by the type of mechanical stress applied and by the working temperature. Then, the suitability of a plastic polymer to be used for the production of a defined commercial item is based on the determination of its thermal and mechanical features, which allow predicting its behaviour during customer use. Moreover, as the shape of final commercial items is obtained by moulding from the melt, the properties of the molten fully liquid polymer (Rheological properties) must be known before going to an industrial production, including information on how they are modulated by the molecular structure of the polymer. This chapter is consequently devoted to discuss in detail the physical properties, which are presently considered basic for a polymeric material to be classified as a plastic and how they are dependent on macromolecules chemical structure. Thermal, mechanical and rheological features are described separately for sake of clarity even if strictly interrelated. Even if in the commercial use the term plastic is used also for some amorphous polymers, which can be shaped by melt moulding, the real plastic polymer is necessarily consisting of two phases, either physically or chemically different. Then, several commercial plastics are obtained by blending two distinct polymers. Therefore, the mechanical, thermal and rheological properties of blends will be also considered.