Classes of Polymers
Polymers can be classified into several categories based on their structure, properties, and applications. These classes include thermoplastics, thermosetting polymers, elastomers, and fibers. Thermoplastics can be melted and reshaped, while thermosetting polymers become permanently hardened after curing. Elastomers are known for their elasticity, and fibers are long, thread-like polymers used in textiles and composites.
8 Key excerpts on "Classes of Polymers"
eBook - ePubAdditive Manufacturing
Science and Technology
- Emrah Celik(Author)
- 2020(Publication Date)
- De Gruyter(Publisher)
...2 Additive manufacturing of polymers 2.1 Classification of polymers Polymers are a class of engineering materials that are composed of chains of repeating chemical units called monomers. In fact, the word “Polymer” is derived from two Greek words, “Poly” and “Mer,” which mean “many” and “units,” respectively [ 28 ]. Repeating units or monomers can be just a few atoms or they might be complicated ring-shaped structures containing many more molecules. Natural polymers such as proteins, cellulose, enzymes, starches, and nucleic acids are found in living organisms and they perform important biological functions. Other natural polymers are derived from plants and animals and these natural polymer materials include wood, rubber, cotton, wool, leather, and silk. It was, however, a different type of polymers, nonnatural, or synthetic ones, which revolutionized our world in the past 50 years. Synthetic polymers such as plastics, rubbers, and epoxies are synthesized from petroleum-based organic molecules. These materials can be produced inexpensively, and their properties can be engineered to be superior to their natural counterparts. In many applications, metal and wood parts have been successfully replaced by synthetic polymers that provided lower cost, lightweight, and corrosion/chemical resistance advantages. Polymers can be classified into three major groups according to their molecular orientation as shown in Figure 2.1. As a result of their unique microstructure, each group of polymers, thermoplastics, thermosets, and elastomers possesses different physical behaviors. Details of each category and the AM technologies to fabricate these materials are described in the next section. Figure 2.1: Classification of polymeric materials. 2.1.1 Thermoplastics Thermoplastic polymers have linear or slightly branched molecular structures as shown in Figure 2.1. Molecules in a thermoplastic polymer are held together by relatively weak intermolecular forces...
eBook - ePubPrinting on Polymers
Fundamentals and Applications
- Joanna Izdebska-Podsiad?y, Sabu Thomas(Authors)
- 2015(Publication Date)
- William Andrew(Publisher)
...2 Polymeric Materials—Structure, Properties, and Applications C.V. Pious, and Sabu Thomas International and Interuniversity Center for Nanoscience and Nanotechnology, Mahatma Gandhi University, Kottayam, India Abstract Polymers dominate all other classes of materials due to their wide spectrum of properties and possibility of further modification by the addition of ingredients. This chapter gives a brief introduction to polymeric materials, followed by a discussion on their structure, properties, and applications. The structural features of polymeric chains at the molecular level and ways to control polymer architecture are discussed. Different properties of polymers such as thermal, electrical, and mechanical are presented in brief. Properties and applications of some important polymers and some specialty polymers are also included. Keywords Application of polymers; Electrical properties; Mechanical properties; Polymer structure; Thermal properties Outline 2.1 Introduction 21 2.2 Structure of a Polymer 25 Configuration 25 Conformation 26 2.2.1 Classification of Polymers 26 2.2.1.1 Crystalline and Amorphous Polymers 26 2.2.1.2 Thermoplastics and Thermosetting Plastics 26 2.2.1.3 Homopolymers and Copolymers 27 2.2.2 Designing the Structure of Polymers 27 2.3 Properties of Polymers 28 2.3.1 Thermal Properties 28 2.3.1.1 Thermal Transitions of Polymers 28 2.3.1.2 Thermal Stability of Polymers 29 2.3.1.3 Coefficient of Thermal Expansion and Thermal Conductivity 29 2.3.2 Mechanical Properties 31 2.3.3 Electrical Properties of Polymers 32 2.3.4 Polymer Blends 32 2.3.5 Polymer Composites 33 2.3.6 Polymer Nanocomposites 33 2.4 Application of Polymers 33 2.4.1 Application of Commodity...
- Sherif D. El Wakil(Author)
- 2019(Publication Date)
- CRC Press(Publisher)
...The second method of classification groups polymers into chemical families, each of which has the same monomer. As an example, the ethenic family is based on ethylene as the monomer, and different polymers (members of this family such as polyvinyl alcohol or polystyrene) can be made by changing substituent groups on the basic monomer, as shown in Figure 8.2. As we will see later, this enables us to study most polymeric materials by covering just a limited number of families instead of considering thousands of polymers individually. But before reviewing the commonly used chemical families of polymers, let us discuss in depth their elevated-temperature behavior. Based on this behavior, polymers can be split into two groups: thermoplastics and thermosets. FIGURE 8.2 Structural formula of some polymers of the ethenic group. 8.2.1 Thermoplastics Thermoplastics generally have linear structures, meaning that their molecules look like linear chains having little breadth but significant length. This structure, as shown in Figure 8.3, is analogous to a bowl of spaghetti. Bonds between the various molecular chains are mainly of the van der Waals type (i.e., secondary forces). Therefore, this type of polymer softens by heating and can then flow viscously to take a desired shape because elevated temperatures tend to decrease the intermolecular coherence of the linear chains. When the solidified polymers are reheated and melted again, they can be given a different shape. This characteristic enables plastics fabricators to recycle thermoplastic scrap, thus increasing the efficiency of raw material utilization. FIGURE 8.3 The molecular chains of a thermoplastic polymer. Usually, a thermoplastic polymer consists of a mixture of molecular chains having different lengths...
- Shashanka Rajendrachari, Orhan Uzun(Authors)
- 2021(Publication Date)
- Bentham Science Publishers(Publisher)
...The synthesis, properties, and applications of various thermoplastic and thermosetting plastics are reported in this chapter. Various processing techniques used in polymers are discussed in great detail. Knowledge of understanding the atomic or molecular structure of polymers can provide greater insight into improving them. Fig. (22)) Structural foam [ 32 ]. QUESTIONS 1) What are polymers? Mention their properties and applications. 2) Write a note on the classification of polymers. 3) What are natural and synthetic polymers? Give some examples. 4) Explain linear, branched, cross-linked and graft polymers with examples each. 5) Define the term ‘Tacticity’ and mention its different types. 6) What are atactic, syndiotactic and isotactic polymers? 7) Differentiate between thermoplastics and thermosetting polymers. 8) What are homopolymers and co-polymers? 9) Define the polymerization process and explain the different types of polymerization processes. 10) Differentiate between addition and condensation polymerization. 11) Explain the various stages involved in free radical mechanism during addition polymerization. 12) Explain the various stages involved in the anionic and cationic polymerization mechanism. 13) Which is the monomer used to prepare polyethylene and mention the properties and applications of polyethylene. 14) Differentiate between low density and high-density polyethylene. 15) Explain the synthesis, properties and applications of following polymers: (a) PVC (b) Polypropylene (c) Polystyrene (d) Nylon-6 (e) Nylon-6,6 (f) Nylon-6,10 (g) Bakelite 16) What is meant by the processing of polymers and mention different techniques used to process polymers. 17) Write a note on the following molding techniques: a). Injection Molding b) Blow Molding c) Compression Molding d) Film Insert Molding e) Gas Assist Molding f) Rotational Molding g) Structural Foam Molding REFERENCES [1] Astra Polymers http://www.astra-polymers.com/. [2] Arla Plast A.B....
eBook - ePubThermoplastic Material Selection
A Practical Guide
- Eric R. Larson(Author)
- 2015(Publication Date)
- William Andrew(Publisher)
...Materials at the lower end of the cost spectrum are often referred to as commodity materials, those in the middle are often referred to as engineering plastics, and those at the high end are often referred to as specialty plastics. This method of classification is commonly used within the industry, and is discussed in greater detail in the next chapter. 3.5.4. Elasticity Another means of classification is to organize materials based on their flexibility. We often have specific uses for materials that are stiff and rigid, and other uses for materials that are flexible and elastic. While this kind of classification is often helpful on a general level, in reality it often becomes cumbersome, since many materials can be formulated in a variety of stiffnesses. It is mostly used to describe a general category of highly flexible materials, known as thermoplastics elastomers. These will be discussed in greater detail in the next chapter. 3.6. A Final Word about Property Data Property data for the characterization of a given thermoplastic material is generated under highly controlled conditions. First of all, the test specimens have a defined shape. They are made from a prime grade of material, usually with no additives of any kind. The processing conditions are highly controlled, and if any secondary operations are employed (CNC machining, laser or water jet cutting, etc.), the specimens are thoroughly annealed to remove any internal stresses. These specimens are then subjected to the prescribed test procedures, and the resulting data is published as “typical property data.” Perhaps somewhere in the footnotes there should be a disclaimer, This is as good as it gets. Your actual mileage may vary. 3.7. The Amazing World of Thermoplastics So here we have these new materials called thermoplastics...
eBook - ePubFundamentals of Polymer Science
An Introductory Text, Second Edition
- Michael M. Coleman, Paul C. Painter(Authors)
- 2019(Publication Date)
- CRC Press(Publisher)
...CHAPTER 1 The Nature of Polymeric Materials “He fixed thee mid this dance of plastic circumstance” —Robert Browning A. WHAT ARE POLYMERS—WHAT IS POLYMER SCIENCE? Simply stated, polymers are very large molecules (macromolecules) that are comprised or built up of smaller units or monomers. The arrangements of these units, the various types of chains that can be synthesized and the shapes that these chains can bend themselves into, result in a class of materials that are characterized by an enormous and intriguing range of properties. Some of these are unique to polymers (e.g., rubber elasticity) and, as we shall see, are simply a consequence of their size and chain-like structure. Polymer science is also a relatively new discipline and one that is characterized by extraordinary breadth. It involves aspects of organic chemistry, physical chemistry, analytical chemistry, physics (particularly theories of the solid state and solutions), chemical and mechanical engineering and, for some special types of polymers, electrical engineering. Clearly, no one person has an in-depth knowledge of all these fields. Most polymer scientists seek a broad overview of the subject that is then usually supplemented by a more detailed knowledge of a particular area. This book is a first step towards the former and to give a flavor for the diversity of this subject matter we will commence with an outline of some of the areas we will cover. Polymer Synthesis Many polymer scientists think that it is unlikely that we will ever again see any new thermoplastic take the world by storm (i.e., achieve levels of production comparable to polyethylene or polystyrene), but it should be kept in mind that similar things were being said round about 1950, just before high density polyethylene and isotactic polypropylene made their debut (some of this terminology will be defined shortly). Today, there are two good reasons to think they may be right, however...
eBook - ePubMaterials in Construction
An Introduction
- G. D. Taylor(Author)
- 2013(Publication Date)
- Routledge(Publisher)
...9 Plastics DOI: 10.4324/9781315839158-9 Chapter summary Importance of carbon. Polymerisation of plastics. Classification. Thermoplastics, elastomers and thermosets. Plastics in fire. Applications. Recycling of plastics. 9.1 Introduction The tenti ‘plastic’ refers to the fact that many plastics become soft and malleable when heated, though a more accurate description would be ‘polymeric materials’ which are almost always of organic origin; that is, based on carbon. These materials have in general the following attractions: They have low density — usually around that of water. An almost infinite range of plastics can be produced, based on the bonding versatility of the carbon atom. Many plastics are quite inert; they do not absorb water and are unaffected by frost, pollutants, dilute acids and alkalis. Hence surface protection from moisture is unnecessary. They are readily moulded or shaped. They are good thermal insulators, especially in foamed form. Some shortcomings of organic polymers are: They are often susceptible to ultraviolet deterioration. They have high thermal movement. They have low stiffness (elastic modulus). They have generally low resistance to heat and some are susceptible to fire, especially in foam or sheet form. They rely (currently) largely on fossil fuels as the raw material. Table 9.1 Environmental consideration: plastics Consideration Assessment Raw material availability Limited since plastics are in general a by-product of oil Extraction Risk of pollution — for example, from oil waste or discharge from sinking of ships Energy used in manufacture High, since chemical processes required Health/safety hazards Possible fire hazard; some plastics contain halogens Waste disposal/recyclability Many types do not degrade on disposal; recycling techniques are currently being developed The technology of plastics is being continually developed and the solution to some of the above problems, at least in part, is likely in the foreseeable future...
eBook - ePub- S.K. Duggal(Author)
- 2017(Publication Date)
- Routledge(Publisher)
...Chapter 15 POLYMERIC MATERIALS 15.1 Introduction 15.2 Polymerisation Mechanism 15.3 Depolymerisation 15.4 Rubbers 15.5 Plastics 15.6 Constituents of Plastics 15.7 Fabrication of Commercial Articles 15.8 Applications of Plastic 15.9 Properties of Plastics 15.10 Effect of Temperature on Mechanical Properties Exercises 15.1 Introduction High polymers, also known as macromolecules, are large molecules of colloidal dimensions (10 -3 to 10 -6 mm in diameter) have high molecular weight (10,000 to millions). Small molecules called monomers undergo polymerisation reaction and form macromolecules. The examples of polymeric materials are resins, plastics and rubbers. 15.2 Polymerisation Mechanism Polymerisation may be defined as the union of two smaller molecules of similar or different types with or without elimination of water resulting in the formation of new C-C linkages. The mechanism by which polymerisation takes place may be addition or condensation. A monomer for polymerisation should be bi- or poly functional, i.e. it must contain two or more functional groups. Some of the other functional groups are hydroxyl acid, amino acid, di-amino acid, di-acids, di-or polyalcohols. The structures depend on the functionability of monomers. In case of a bi-functional monomer there will be two reactive groups at its ends. These groups may align side by side to form a straight chain like molecule as shown in Fig. 15.1. The monomer units are linked by primary covalent bonds and the different chains are held together by secondary force of molecular attraction. However, during the chain growth side chains may also develop leading to branched chain molecules as shown in Fig. 15.2. In case of poly-functional groups the monomer molecules are connected to each other by covalent bonds and form a three-dimensional network (Fig. 15.3). Fig. 15.1 Linear Chain Polymer Formation by a Reaction of bi-functional Molecule Fig. 15.2 Branched-Chain Polymer Fig...
