The chapter provides an overview of polymer science, covering synthesis, polymer characterization, rheology, mechanical properties, and applications. The chapter delves into the definition of polymers, their historical development, and various classification systems. It also explores the importance of polymers for human survival and discusses the fundamentals of polymer science. The chapter continues by discussing the properties and applications of polymers, including an examination of polymer solution properties, mechanical properties, and the wide range of applications in different industries. Also explored is synthesis and construction of polymers, which form the foundation of their physical nature. This leads to the crucial topic of structure-property relationships, examining how molecular interactions and arrangements impact polymer properties. Furthermore, the chapter explores different types of polymers and their applications, spanning from thermoplastics to thermoset polymers, natural polymers to biopolymers. The chapter concludes by discussing polymer processing techniques.
TopIntroduction
Polymers, which are large molecules composed of repeated smaller chemical units, have been fundamental to the development of life (Alberts et al., 2014). They can exist in linear chains or interconnected structures, forming 3D networks. The basic unit of a polymer is called a monomer. For example, vinyl chloride is the monomer of poly(vinyl chloride), which has a repeating unit of -CH2CHCl-. The length of a polymer chain is determined by the number of repeat units and is referred to as the degree of polymerization (DP) (Callister Jr. & Rethwisch, 2018).
Polymers can be classified into biological and non-biological materials. Biological polymers are essential components of life, including enzymes, nucleic acids, and proteins, while cellulose, natural rubber, wool, and starch are examples of biopolymers with simpler structures found in plants (Alberts et al., 2014; Callister Jr. & Rethwisch, 2018). Polymers play indispensable roles in various aspects of human life, from clothing and shelter to food. Synthetic polymers, such as fibers, plastics, and elastomers, are crucial for modern living (Alberts et al., 2014). Biopolymers can be further categorized as naturally occurring polymers found in nature, like cellulose and starch, or as biobased polymers artificially synthesized from natural resources. Natural polymers, such as proteins, cellulose, and natural rubber, are abundant in nature and can be extracted from renewable sources like plants and animals (Alberts et al., 2014). Fibers encompass a wide range of materials, including natural and synthetic, organic and inorganic, and are defined based on their shape (Callister Jr. & Rethwisch, 2018). For example, fibers are generally required to have a length at least 100 times greater than their diameter. Nylon, polyester, and polyolefins are examples of artificial fibers, while cotton, wool, and flax are natural fibers with lengths typically 1000-3000 times their diameter (Callister Jr. & Rethwisch, 2018).
In recent years, polymers have become prevalent in daily life, both in the form of natural and synthetic polymers. Polymers can be found in various forms such as solid plastics, fibers, elastomers, foams, films, coatings, and adhesives, with a wide range of properties from hard to soft. One useful classification of polymers is based on their response to thermal treatments. Thermoplastic polymers can melt when heated and resolidify upon cooling without undergoing significant structural or property changes. Examples include polyethylene, polystyrene, and nylon. In contrast, thermoset polymers do not melt but undergo irreversible chemical changes and form crosslinked networks when exposed to high temperatures (Callister Jr. & Rethwisch, 2018).
Polymer classification can also be based on the polymerization mechanism, distinguishing between condensation (step-growth) and addition (chain-growth) polymerization. Condensation polymerization involves the reaction between two functionalized monomers, leading to the formation of larger molecules and the elimination of a small molecule like water. This process is typically slower and requires longer reaction times to achieve high molecular weight polymers (Callister Jr. & Rethwisch, 2018).
Understanding the physical structure of polymers, referred to as the secondary structure, is crucial for understanding their properties. The size of a polymer molecule is described by its molecular weight, while the shape is influenced by the nature of the repeating unit and how the units are linked together, described by configuration and conformation (Callister Jr. & Rethwisch, 2018).
As we know small molecules have three states of matter namely, solid state, liquid state and gaseous state. Solid state particles are very tightly packed and have very little or no motion. Solid state particles are very tightly packed and have very little or no motion. In other hand particles in liquid state are more loosely packed and can move. Particles of gas are very loosely packed and move faster with great energy. Unlike small molecules, polymers behave differently due to their high molecular weight and involve a large number of atoms. The principal properties of polymers can be classified into mechanical, electrical, thermal, surface contact, and optical properties, which determine the flexibility and strength of the polymer (Callister Jr. & Rethwisch, 2018).