Amorphous Polymer
Amorphous polymers are large molecules with a random, disordered arrangement of their molecular chains, as opposed to a crystalline structure. This lack of long-range order gives amorphous polymers unique properties, such as transparency and flexibility. They are commonly used in a wide range of applications, including packaging materials, adhesives, and coatings.
5 Key excerpts on "Amorphous Polymer"
eBook - ePub- Leslie H. Sperling(Author)
- 2015(Publication Date)
- Wiley-Interscience(Publisher)
...CHAPTER 5 THE AMORPHOUS STATE The bulk state, sometimes called the condensed or solid state, includes both amorphous and crystalline polymers. As opposed to polymer solutions, generally there is no solvent present. This state comprises polymers as ordinarily observed, such as plastics, elastomers, fibers, adhesives, and coatings. While Amorphous Polymers do not contain any crystalline regions, “crystalline” polymers generally are only semicrystalline, containing appreciable amounts of amorphous material. When a crystalline polymer is melted, the melt is amorphous. In treating the kinetics and thermodynamics of crystallization, the transformation from the amorphous state to the crystalline state and back again is constantly being considered. The subjects of amorphous and crystalline polymers are treated in the next two chapters. This will be followed by a discussion of liquid crystalline polymers, Chapter 7. Although polymers in the bulk state may contain plasticizers, fillers, and other components, this chapter emphasizes the polymer molecular organization itself. A few definitions are in order. Depending on temperature and structure, Amorphous Polymers exhibit widely different physical and mechanical behavior patterns. At low temperatures, Amorphous Polymers are glassy, hard, and brittle. As the temperature is raised, they go through the glass–rubber transition. The glass transition temperature (T g) is defined as the temperature at which the polymer softens because of the onset of long-range coordinated molecular motion. This is the subject of Chapter 8. Above T g, cross-linked Amorphous Polymers exhibit rubber elasticity. An example is styrene–butadiene rubber (SBR), widely used in materials ranging from rubber bands to automotive tires. Rubber elasticity is treated in Chapter 9. Linear Amorphous Polymers flow above T g. Polymers that cannot crystallize usually have some irregularity in their structure...
eBook - ePubPolypropylene
The Definitive User's Guide and Databook
- Clive Maier, Theresa Calafut(Authors)
- 1998(Publication Date)
- William Andrew(Publisher)
...Polymer chains have been shown to form helical structures, but the unit cell and lamellar structures have not yet been well resolved. Experiments indicate a lack of lamellar order in addition to a low density and small size of ordered structures. These characteristics result in high clarity, useful in quenched film applications. [ 770, 772, 769 ] 2.2.6 Amorphous polypropylene In atactic polypropylene, with its random molecular structure, molecules cannot crystallize in an ordered form, and a polymer with low crystallinity is formed. Low crystallinity polymers consist of ordered, crystalline regions surrounded by disordered, spaghetti-like amorphous material with entangled polymer chains. [ 772, 769 ] Amorphous polypropylene has no defined melting point. It behaves like an elastic and plastic material and is tough and flexible. It is used for hot melts and pressure sensitive adhesives, films for sound insulation, and for modifying rubber, polyethylenes, bitumen, and asphalt. [ 747 ] 2.3 Effect of morphology on characteristics of polypropylene Due to the ordered crystal structure, semicrystalline polymers generally have high strength and are more chemically resistant than Amorphous Polymers. Semicrystalline materials are more opaque and can be used at higher temperatures, while amorphous materials are generally more transparent and have greater toughness and ductility. [ 772 ] 2.3.1 Melting point The crystalline structure of a solid semicrystalline polymer disappears at the melting point, T m, when the material undergoes a phase change from solid to liquid. At the melting point, physical properties of the material, such as density, refractive index, heat capacity, and transparency, change abruptly as the material becomes a viscous liquid. Melting points are commonly measured using differential scanning calorimetry (DSC). [ 769, 772 ] The melting point of a polymer varies with the amount of crystallinity...
eBook - ePubMaterial Selection for Thermoplastic Parts
Practical and Advanced Information
- Michel Biron(Author)
- 2015(Publication Date)
- William Andrew(Publisher)
...At best, they can be used like fillers after grinding. • The infusibility prevents assembly by welding. 2.3.3. Crystalline and Amorphous TPs, Glass Transition Temperature Polymers can be amorphous (randomly arranged chains), crystalline (well-ordered chains), or semicrystalline (see Figure 2.8). 2.3.3.1. Amorphous Polymers Amorphous chains of an Amorphous Polymer are randomly arranged. The degree of crystallinity (the weight fraction or the volume fraction of crystalline material) is zero. Amorphous Polymers slowly soften when heated above their glass transition temperature (Tg). As examples, we can quote among others, polymethylmethacrylate (PMMA), polycarbonate (PC), polyvinylchloride (PVC), styrene acrylonitrile (SAN), acrylonitrile butadiene styrene (ABS), PS, polyphenylene ether (PPE), polysulfone, special amorphous polyamides (PAs), and so on. When the temperature rises, mechanical properties decrease relatively slowly until the threshold of the glass transition temperature, which is the boundary of their ability to withstand low continuous efforts and also limits their dimensional stability under stress. In the absence of a constraint, dimensional stability can be maintained up to 20–50 °C above the glass transition temperature. Above Tg, these TPs are extremely viscous liquids and it is necessary to reach significantly higher temperatures to sufficiently lower viscosities allowing the extrusion or injection. Only amorphous TPs can be transparent. 2.3.3.2. Crystalline and Semicrystalline Polymers For crystalline polymers, crystalline chains are ordered into compact domains. The degree of crystallinity is 1. Most often, polymers are semicrystalline containing regions of 3D ordering and amorphous regions without any order; the degree of crystallinity (weight fraction or volume fraction of crystalline material) ranges from near 0 up to near 1...
eBook - ePubPlastics
Microstructure and Engineering Applications
- Nigel Mills, Mike Jenkins, Stephen Kukureka(Authors)
- 2020(Publication Date)
- Butterworth-Heinemann(Publisher)
...Chapter 3 Amorphous Polymers and the glass transition Abstract The consideration of polymers on a molecular level continues in this chapter, the focus of which is Amorphous Polymers. The three-dimensional shape, motion and glass-to-liquid transition behaviour will be considered in terms of the chemical structure of the polymer, and the measurement of the glass-to-liquid transition temperature (T g) will be introduced using thermomechanical analysis. Knowledge of the T g in polymers is important as it relates to the mechanisms by which the shapes of plastics products are set during processing; noncrystallizable polymers must be cooled to temperatures below T g to stabilize the shape of the part. The effect of molecular mobility and intermolecular forces on the elastic moduli of rubbers and glassy polymers will also be considered. Keywords Amorphous Polymers; Bulk modulus; Glass transition; Molecular weight; Rubbers 3.1 Introduction 3.2 Modelling the shape of a polymer molecule 3.2.1 Conformations of the C–C bond 3.2.2 Walks on a diamond lattice 3.2.3 Effect of molecular weight on molecular size 3.2.4 Entanglements in polymer melts 3.2.5 Network chain elasticity 3.2.6 Rubbers 3.3 The glass transition temperature 3.3.1 Rotational and translational motions in the liquid state 3.3.2 Sub- T g motion 3.3.3 Control of the T g 3.3.4 Free volume 3.3.5 Measurement of T g using thermomechanical analysis 3.3.6 Glass microstructure 3.3.7 Elastic moduli of glasses 3.1. Introduction The consideration of polymers on a molecular level continues in this chapter, the focus of which is Amorphous Polymers. The three-dimensional shape, motion and glass-to-liquid transition behaviour will be considered in terms of the chemical structure of the polymer, and the measurement of the glass-to-liquid transition temperature (T g) will be introduced using thermomechanical analysis...
eBook - ePub- Marianne Gilbert(Author)
- 2016(Publication Date)
- Butterworth-Heinemann(Publisher)
...With some of these materials it may be difficult to achieve the gaseous state or even the liquid state because of thermal decomposition, but in general these three phases, with sharply defined boundaries, are discernible. Thus at a fixed ambient pressure, the melting point and the boiling point of a material such as pure water occur at definite temperatures. In polymers, changes of state are less well defined and may well occur over a finite temperature range. The behavior of linear Amorphous Polymers, crystalline polymers, and thermosetting structures are considered in turn. 3.2. Amorphous Polymers 3.2.1. Physical States in Amorphous Polymers An Amorphous Polymer will be produced if the molecules are irregular, and possibly bulky. They consist of a mass of entangled polymer chains, with no short range order. This structure controls properties. For example, an amorphous plastic is typically hard, transparent, and often brittle. A specific linear Amorphous Polymer, such as poly(methyl methacrylate) (PMMA) or polystyrene (PS), can exist in a number of states according to the temperature and the average molar mass of the polymer. This is shown diagrammatically in Figure 3.1. (It should be noted that for simplicity, transitions below T g (see Section 3.2.3) are not included in this figure.) Figure 3.1 Schematic diagram showing transition behavior in Amorphous Polymers. At low molar masses (e.g., M 1), typical of organic glasses, the polymer will be solid below the glass transition temperature, T g, while above that temperature it will be liquid. The transition in behavior for such substances polymers will be quite sharp; above T g the molecules have sufficient energy to move independently of each other, that is, they are capable of viscous flow. Conversely, below T g the molecules have insufficient energy for flow and the mass behaves as a rigid solid. At some temperature well above T g, the material will start to boil provided this is below the decomposition temperature...
