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Molecular degradation

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Series: ASM Technical Books
Publisher: ASM International
Published: 01 December 2003
DOI: 10.31399/asm.tb.cfap.t69780359
EISBN: 978-1-62708-281-5
..., creep rupture, environmental stress cracking, molecular degradation, and fatigue. In the case of failure involving fracture, the determination of the failure mode involves identifying how the crack initiated and how it subsequently extended. This is usually ascertained using a number of visual-based...
Book Chapter

Series: ASM Technical Books
Publisher: ASM International
Published: 01 August 2013
DOI: 10.31399/asm.tb.ems.t53730099
EISBN: 978-1-62708-283-9
... Abstract This chapter discusses the structural classifications, molecular configuration, degradation, properties, and uses of polymers. It describes thermoplastic and thermosetting polymers, degree of polymerization, branching, cross-linking, and copolymers. It also discusses glass transition...
Series: ASM Technical Books
Publisher: ASM International
Published: 01 December 2003
DOI: 10.31399/asm.tb.cfap.t69780146
EISBN: 978-1-62708-281-5
.... Environmental conditions can promote brittle fracture in normally ductile plastics at levels of stress or strain well below those that would usually cause failure at all. Actual degradation of a polymer, which reduces molecular weight and therefore mechanical properties, does not need to be particularly...
Book Chapter

Series: ASM Technical Books
Publisher: ASM International
Published: 01 December 2003
DOI: 10.31399/asm.tb.cfap.t69780336
EISBN: 978-1-62708-281-5
...), polypropylene (PP), and polystyrene (PS), do not support microbial growth. Low-molecular-weight hydrocarbons, however, can be degraded by microbes. They are taken up by microbial cells, activated by attachment to coenzyme-A, and converted to cellular metabolites within the microbial cell, as shown in Fig. 1...
Series: ASM Technical Books
Publisher: ASM International
Published: 01 November 2012
DOI: 10.31399/asm.tb.ffub.t53610327
EISBN: 978-1-62708-303-4
... be cognizant of the poor ultraviolet (UV) resistance of most, though not all, engineering plastics and the resulting requirement for a UV absorber. Thermosets and Thermoplastics Polymeric plastics are classified as either thermosets or thermoplastics ( Fig. 12 ). Thermosets are low-molecular-weight, low...
Book Chapter

Series: ASM Technical Books
Publisher: ASM International
Published: 01 December 2003
DOI: 10.31399/asm.tb.cfap.t69780343
EISBN: 978-1-62708-281-5
... pertinent to structure analysis. This is followed by a review of the characterization of plastics by infrared and nuclear magnetic resonance spectroscopy. The article then provides information on the distribution of molecular weight of an engineering plastic. It further discusses the methods used in thermal...
Book Chapter

Series: ASM Technical Books
Publisher: ASM International
Published: 01 December 2003
DOI: 10.31399/asm.tb.cfap.t69780329
EISBN: 978-1-62708-281-5
... stresses all combine to produce changes in the chemical composition of the material. These changes may take the form of polymer molecular weight reduction due to main-chain cleavage, the formation of cross links, or the formation of oxidized and other functional groups. As the chemical composition...
Book Chapter

Series: ASM Technical Books
Publisher: ASM International
Published: 01 November 2010
DOI: 10.31399/asm.tb.scm.t52870063
EISBN: 978-1-62708-314-0
... matrices for advanced composites are classified as either thermosets or thermoplastics. Thermosets are low molecular weight, low viscosity monomers (≈2000 centipoise) that are converted during curing into three-dimensional crosslinked structures that are infusible and insoluble. Crosslinking ( Fig. 3.1...
Series: ASM Technical Books
Publisher: ASM International
Published: 01 November 2010
DOI: 10.31399/asm.tb.scm.t52870401
EISBN: 978-1-62708-314-0
..., paint systems are useful in protecting composite structures from ultraviolet (UV) radiation. Ultraviolet radiation is the band of light from 300 to about 4000 Å. It can cause degradation through molecular weight change and crosslinking in the resin system. However, this damage is generally limited...
Series: ASM Technical Books
Publisher: ASM International
Published: 01 November 2010
DOI: 10.31399/asm.tb.omfrc.t53030237
EISBN: 978-1-62708-349-2
.... One of the first indicators of degradation is the change in the surface appearance or gloss, followed by a change in the color of the surface resin. The change in the molecular composition may extend only a few nanometers on the surface but can continue to progress into the bulk of the composite...
Series: ASM Technical Books
Publisher: ASM International
Published: 01 December 2003
DOI: 10.31399/asm.tb.cfap.t69780028
EISBN: 978-1-62708-281-5
... Abstract This article describes in more detail the fundamental building-block level, atomic, then expands to a discussion of molecular considerations, intermolecular structures, and finally supermolecular issues. An explanation of important thermal, mechanical, and physical properties...
Series: ASM Technical Books
Publisher: ASM International
Published: 01 December 2003
DOI: 10.31399/asm.tb.cfap.t69780314
EISBN: 978-1-62708-281-5
... range is approximately halved when the relative humidity is reduced from 100 to 75%. As indicated in the discussion on thermoplastic polyesters, the hydrolytic degradation leads to a progressive reduction in molecular weight and eventually to a loss of mechanical properties. In the study...
Series: ASM Technical Books
Publisher: ASM International
Published: 01 December 2003
DOI: 10.31399/asm.tb.cfap.t69780105
EISBN: 978-1-62708-281-5
... of molecular weight (MW) by viscosity measurements. This is followed by a discussion of the use of cone and plate and parallel plate geometries in determining the viscoelastic properties of a polymer melt. Details on some of the chromatographic techniques that allow determination of MW and MW distribution...
Book Chapter

Series: ASM Technical Books
Publisher: ASM International
Published: 01 October 2012
DOI: 10.31399/asm.tb.lmub.t53550325
EISBN: 978-1-62708-307-2
.... This reduction in molecular weight often is first evidenced by a reduction in physical strength and, most frequently, in impact strength, as the plastic embrittles. As the degradation reaction continues, other physical properties drop off, and eventually the electrical properties are affected. For this reason...
Series: ASM Technical Books
Publisher: ASM International
Published: 01 December 2003
DOI: 10.31399/asm.tb.cfap.t69780003
EISBN: 978-1-62708-281-5
... to form a polymer. These variations in structure within the molecule may involve stereoisomerism, branching, molecular weight and distribution, end groups and impurities, and copolymerization. Polymer size is quantified primarily by molecular weight (MW), molecular-weight distribution (MWD), and branching...
Series: ASM Technical Books
Publisher: ASM International
Published: 01 December 2003
DOI: 10.31399/asm.tb.cfap.t69780267
EISBN: 978-1-62708-281-5
... in the beginning but drops to a lower value after some sliding. Because of the presence of frictional stress and heat, the PTFE molecular chains are oriented in the direction of sliding, and a transfer film is deposited onto the counterface. The molecular orientation in PTFE is responsible for the drop in friction...
Series: ASM Technical Books
Publisher: ASM International
Published: 01 December 2003
DOI: 10.31399/asm.tb.cfap.t69780404
EISBN: 978-1-62708-281-5
... are not properly stabilized. Mechanical stress is known to enhance degradative effects. Degradation usually involves molecular-weight reduction by one of several mechanisms ( Ref 9 ). Surface embrittlement and consequent microcracking occur. This promotes crack initiation and possibly assists crack propagation...
Series: ASM Technical Books
Publisher: ASM International
Published: 01 December 2003
DOI: 10.31399/asm.tb.cfap.t69780115
EISBN: 978-1-62708-281-5
... becomes rubbery. The T g is also a measure of the onset of long-range molecular movement in the plastic. Because the transition from glass to rubber is not a thermodynamic transition, but rather a manifestation of viscoelasticity, the exact value of the T g depends on the method used to measure...
Series: ASM Technical Books
Publisher: ASM International
Published: 01 December 2003
DOI: 10.31399/asm.tb.cfap.t69780089
EISBN: 978-1-62708-281-5
... form of chromatography is the major characterization technique used for analyzing uncured thermoset systems. Chromatography, combined with various spectroscopic methods and elemental analysis for molecular structure identification, forms the backbone of quality assurance testing schemes...
Series: ASM Technical Books
Publisher: ASM International
Published: 01 December 2003
DOI: 10.31399/asm.tb.cfap.t69780238
EISBN: 978-1-62708-281-5
... of the test; and the molecular properties of the polymer. These factors are of considerable interest and practicality for the safe design of structural polymeric components subjected to repetitive loading. When designing for the fatigue life of an engineering plastic, one of two distinct philosophies...