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Molecular degradation

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Series: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.homegoods.c0090424
EISBN: 978-1-62708-222-8
... is a common breakdown product produced during the decomposition of polycarbonate. The conclusion was that the most likely cause of the molecular degradation was improper drying and/or exposure to excessive heat during the injection molding process that in turn caused the material degradation. Brackets...
Series: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.auto.c0090451
EISBN: 978-1-62708-218-1
... process had exposed the resin to relatively high temperatures, which caused substantial molecular degradation, thus limiting the part's ability to withstand the stresses. The drying temperature was found to be significantly higher than the recommendation for the PET resin, and the testing itself exposed...
Series: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.modes.c0090460
EISBN: 978-1-62708-234-1
... of molecular degradation caused by the service conditions. Specifically, the part material had undergone severe chemical attack, including oxidation and hydrolysis, through contact with silver chloride. The source of the silver chloride was not established, but one potential source was photographic silver...
Series: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.modes.c0090463
EISBN: 978-1-62708-234-1
... inserts. Investigation supported the conclusion that the switch housings failed via brittle fracture, likely through a creep mechanism. The failure was caused by severe embrittlement of the housing resin associated with massive molecular degradation produced during the molding process. A potential...
Series: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.auto.c0090442
EISBN: 978-1-62708-218-1
... degradation of the failed part material, and the thermograms supported this. The conclusion was that the failed sleeves had cracked due to embrittlement associated with severe degradation and the corresponding molecular weight reduction. The reduction in molecular weight significantly reduced the mechanical...
Series: ASM Handbook Archive
Volume: 11
Publisher: ASM International
Published: 01 January 2002
DOI: 10.31399/asm.hb.v11.a0003525
EISBN: 978-1-62708-180-1
..., including catastrophic mechanisms, such as brittle fracture, ductile overload, 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...
Image
Published: 15 May 2022
Fig. 17 Micrograph showing cracking on the failed housing boss. A localized zone of mud cracking and discoloration characteristic of molecular degradation is present. More
Series: ASM Handbook
Volume: 11B
Publisher: ASM International
Published: 15 May 2022
DOI: 10.31399/asm.hb.v11B.a0006933
EISBN: 978-1-62708-395-9
... of contaminants is illustrated in Examples 3 and 8 in Ref 4 . Degradation Fourier transform infrared spectroscopy is a valuable tool in assessing a failed component material for degradation such as oxidation and hydrolysis. Molecular degradation, often involving molecular weight reduction, has...
Series: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.homegoods.c0090448
EISBN: 978-1-62708-222-8
... had been degraded, producing a reduction in the molecular weight and reducing both the mechanical integrity and chemical-resistance properties of the parts. Crystallization Electrical appliances Grease Housings Injection molding Molding resins Undercrystallization Polycarbonate...
Series: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.chem.c0090454
EISBN: 978-1-62708-220-4
... of the vessel. The cracking extended transversely through the wall initially, and subsequently, circumferentially around the wall. Throughout the examination, no signs of postmolding molecular degradation or chemical attack were found. Fig. 1 Scanning electron image showing features associated...
Series: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.modes.c9001593
EISBN: 978-1-62708-234-1
... resins as a result of melt processing, where molecular weight can increase due to thermal induced crosslinking. The magnitude of the change, however, is low and the melt flow rate results suggest good retention of molecular weight through the molding process, without molecular degradation. Discussion...
Series: ASM Handbook
Volume: 11B
Publisher: ASM International
Published: 15 May 2022
DOI: 10.31399/asm.hb.v11B.a0006867
EISBN: 978-1-62708-395-9
... reagent. Finally, there are some chemicals that cause actual degradation of the polymer, breaking the macromolecular chains, reducing molecular weight, and diminishing polymer properties as a result. This article examines each of these effects. The discussion also covers the effects of surface...
Series: ASM Handbook
Volume: 11B
Publisher: ASM International
Published: 15 May 2022
DOI: 10.31399/asm.hb.v11B.a0006916
EISBN: 978-1-62708-395-9
... be compared to the virgin resin to determine the extent of degradation due to the molding process, since degraded material would be lower in viscosity because of its reduced molecular weight. Figure 4 shows the results of a relative viscosity test conducted on normally ductile nylon wire ties that failed...
Image
Published: 15 May 2022
Fig. 1 General concept of plastic degradation by microorganisms. (a) Enzymes from bacteria attached to high-molecular-weight fibers. (b) Assumed transport of mono- and oligomers into the cell and microbial metabolism. Today, only a few enzymes involved in plastic degradation have been More
Series: ASM Handbook Archive
Volume: 11
Publisher: ASM International
Published: 01 January 2002
DOI: 10.31399/asm.hb.v11.a0003550
EISBN: 978-1-62708-180-1
... on plastics is to actually degrade the polymer; that is, to break down the polymer chains into lower molecular weight compounds that no longer have the desirable strength or toughness properties of the original. Certain polymer types are more susceptible than others to specific degradation mechanisms, but all...
Series: ASM Handbook
Volume: 11B
Publisher: ASM International
Published: 15 May 2022
DOI: 10.31399/asm.hb.v11B.a0006920
EISBN: 978-1-62708-395-9
... the mechanism and rate of the subsequent degradation reactions are typically not influenced. Temperature Influences Even though the formation of excited molecular states is initiated by the absorption of photons, the subsequent deactivation and degradation reactions are influenced by the temperature...
Series: ASM Handbook
Volume: 11B
Publisher: ASM International
Published: 15 May 2022
DOI: 10.31399/asm.hb.v11B.a0006917
EISBN: 978-1-62708-395-9
... semicrystalline polymers, as mentioned previously, molding has a direct effect on the level of chain entanglement and the molecular weight of the molded article. If the material undergoes molecular degradation during processing, the polymer chains can be substantially shortened, which reduces inherent...
Series: ASM Handbook
Volume: 11B
Publisher: ASM International
Published: 15 May 2022
DOI: 10.31399/asm.hb.v11B.a0006866
EISBN: 978-1-62708-395-9
... degradation by microorganisms. (a) Enzymes from bacteria attached to high-molecular-weight fibers. (b) Assumed transport of mono- and oligomers into the cell and microbial metabolism. Today, only a few enzymes involved in plastic degradation have been characterized. It is not clear if native plastic binding...
Series: ASM Handbook
Volume: 11B
Publisher: ASM International
Published: 15 May 2022
DOI: 10.31399/asm.hb.v11B.a0006915
EISBN: 978-1-62708-395-9
... effect on solubility, chemical resistance, and softening point. Silicon Silicon is found primarily in silicones, where it imparts low surface energy and resistance to oxidation. Phosphorus Low-molecular-weight phosphorus-containing additives or co-monomers are used as flame retardants...
Series: ASM Handbook
Volume: 11B
Publisher: ASM International
Published: 15 May 2022
DOI: 10.31399/asm.hb.v11B.a0006931
EISBN: 978-1-62708-395-9
... a particular analytical technique. Practical information derived from polymer analysis methods Table 2 Practical information derived from polymer analysis methods Test method Property Practical information provided Gel permeation chromatography (GPC)⁠; molecular weight distribution...