The Effect of UV Light and Weather on Plastics and Elastomers

Laurence W. McKeen

• Publisher: William Andrew
• Year: 2019
• ISBN:
  9780128172711
• Edition: 4
• Topic: Tecnología e ingeniería
• Subtopic: Ciencias de los materiales

The Effect of UV Light and Weather on Plastics and Elastomers, Fourth Edition, provides critical data on the effect of UV light and weathering on plastics and elastomers, enabling engineers, designers and R&D professionals to select the right materials when developing plastics products for a range of industries and applications. This information will also support academic researchers and scientists in developing polymeric materials for advanced applications.

• Provides vital data on the effects of weather and UV light exposure on plastics and elastomers
• Offers practical guidance for engineers and scientists working with plastics for outdoor applications
• Expanded revision includes the latest data, polymer classes and newly available materials, including bio-based polymers and plastics for 3D printing

1

Introduction to Plastics and Polymers

Abstract

This chapter is an introduction to polymer chemistry. It includes polymerization chemistry and the different types of polymers and how they differ from each other. Discussed are the subjects of copolymers, branching, cross-linking, steric hindrance, isomerism, crystallinity, and other factors that affect the molecular structures of the polymers used to make plastics. Since plastics are rarely “neat,” reinforcement, fillers, and additives are reviewed. The influence of molecular structure on properties is examined. A basic understanding of plastic and polymer chemistry will make the discussion of plastics easier to understand and it also provides a basis for the introductions of the plastic families in later chapters.

Keywords

Polymerization; isomers; molecular attractions; amorphous; crystallinity; additives

The basic component of plastic and elastomer materials is polymer. The word polymer is derived from the Greek term “many parts.” Polymers are large molecules composed of many repeat units, called monomers that have been chemically bonded into long chains. Since World War II, the chemical industry has developed a large quantity of synthetic polymers to satisfy the material needs for a diverse range of products, including paints, coatings, fibers, films, elastomers, and structural plastics. Literally thousands of materials can be called “plastics,” although the term today is typically reserved for polymeric materials, excluding fibers, which can be molded or formed into solid or semisolid objects. As of the beginning of 2012, IDES The Plastics Web (http://www.ides.com) listed over 85,000 different grades of plastic from over 800 suppliers.

There are three introductory chapters to this book. The first chapter is a review of polymer chemistry and plastic formulation. It lays the basis for the discussion on weather processes, property measurement, and all the data chapters. The second chapter is a review of weathering and ultraviolet (UV) light exposure. This includes the various ways to expose test plaques including natural exposures and accelerated exposures. The physical and chemical processes involved with weather and light exposure are explained. The third chapter is on plastic properties. First discussed are the physical properties. Second are the mechanical properties such as tensile strength, elongation, modulus, and tear resistance. Third are thermal properties such as melting point, glass transition temperature, and melt index which affect use, production, and processing of films.

The chapters that follow are the data chapters. Each chapter covers plastics that fall into particular types based on the chemistry of the polymer. Each of these chapters reviews the chemical structures of the polymers used to make the plastics. In many cases, photochemistry and photodegradation reactions are discussed. Typical stabilizers are mentioned and then data are presented in text, tabular, and/or graphical form.

The subject of this first chapter includes polymerization chemistry and the different types of polymers and how they can differ from each other. Since plastics are rarely “neat,” reinforcement, fillers, and additives are reviewed. A basic understanding of plastic and polymer chemistry will make the discussion of properties of specific films easier to understand and it also provides a basis for the introductions of the plastic families in later chapters. This section is taken from The Effect of Temperature and Other Factors on Plastics [1] and Permeability Properties of Plastics and Elastomers [2], but it has been rewritten, expanded, and refocused on polymers as they relate plastics that may be exposure to various weathering processes.

1.1 Polymerization

Polymerization is the process of chemically bonding monomer building blocks to form large molecules. Commercial polymer molecules are usually thousands of repeat units long. Polymerization can proceed by one of several methods. The two most common methods are called addition and condensation polymerization.

1.1.1 Addition Polymerization

In addition polymerization (sometimes called chain-growth polymerization), a chain reaction adds new monomer units to the growing polymer molecule one at a time through double or triple bonds in the monomer. The polymerization process takes place in three distinct steps:

1. 1. Chain initiation—usually by means of an initiator which starts the polymerization process. The reactive initiation molecule can be a radical (free radical polymerization), cation (cationic polymerization), anion (anionic polymerization), and/or organo...