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Factors Controlling Lifetimes of Polyhydroxyalkanoates and their Composites in the Natural Environment
Published in Martin Koller, The Handbook of Polyhydroxyalkanoates, 2020
Bronwyn Laycock, Steven Pratt, Alan Werker, Paul A. Lant
Environmental Stress Cracking (ESC) is a particular challenge for biocomposites, and follows exposure to corrosive environmental chemicals while under tensile stress, causing crazing, and ultimately resulting in brittle failure [150]. This process has recently been reviewed by Robeson [151], with the mechanisms being discussed in detail. As mentioned in Section 14.3.2, surfactants can have this effect on biopolymers, as can solvents and many other organic chemicals, particularly caustic ones (NaOH) [152].
>Mechanisms of ageing
Published in Frank Collins, Frédéric Blin, Ageing of Infrastructure, 2018
Environmental stress cracking (ESC) is characterised by the degradation of a plastic resin by a chemical agent while under stress. Loading allows chemical solvents to enter the plastic via surface crazing and cracking, thereby adversely affecting the polymer chains. The more rapidly that the chemical agent is absorbed, the faster the polymer will be subjected to crazing and subsequent failure. The types of failure are typically brittle fracture, evidence of multiple cracks and smooth fracture surfaces. This is common with amorphous plastics with low molecular weight and lower crystallinity while subjected to tensile stress, and the types of aggressive chemical agents include organic esters, ketones, aldehydes, aromatic hydrocarbons and chlorinated hydrocarbons.
Polyurethanes in Biomedical Applications
Published in Nina M. K. Lamba, Kimberly A. Woodhouse, Stuart L. Cooper, Polyurethanes in Biomedical Applications, 2017
Nina M. K. Lamba, Kimberly A. Woodhouse, Stuart L. Cooper
Environmental stress cracking (ESC) of a material occurs under conditions that provide an active chemical agent, and tensile stress. The failure of pacemaker leads was believed to be caused by environmental stress cracking. SEM studies by Scheuer-Leeser et al. showed that cracking occurred primarily at points of flexure of the lead, such as the J-curve of atrial leads, the distal tip of ventricular leads, and ligature sites.34 A subsequent alteration in the manufacturing process was made, in order to reduce the residual stress in the material, and increase control over annealing, extrusion and molding procedures. Leads manufactured after this modification was implemented were much more successful. Protective sleeves were also introduced at points of ligature. In addition, a slightly harder polyurethane, Pellethane 2363-55D, was investigated and utilized. Both the 55D and 80A grades of Pellethane are synthesized from the same reagents, but Pellethane 2363-55D has a higher hard to soft segment ratio. Studies comparing the degree of surface cracking on explanted surfaces of Pellethane grades show that Pellethane 2363-55D is indeed less susceptible to surface cracking than Pellethane 2363-80A.38 Further studies of environmental stress cracking of polyurethanes in the biological environment have reported that cracks may appear within six months of implantation although they do not propagate more than 20–30 µm within three years.39 Cracking also may lead to a reduction in the tensile strength of the lead, although this is dependent on the extent of cracking and the thickness of the insulator. There also may be a fall in the impedance of a lead, although this is not believed to be clinically significant.40 Severe cracking, however, may provide a breach in the insulating layer allowing permeation of fluid into the core, promoting oxidation of the metal wires. The metal ions may then promote degradation of the material from the inside.41
Gamma induced changes in the structural and optical properties of Makrofol LS 1–1 polycarbonate
Published in Radiation Effects and Defects in Solids, 2019
Ionizing radiations are powerful means for enhancing the physical properties of polymers. Gamma irradiation of polymeric materials leads mainly to chain scission and crosslinking. The two processes coexist and either one may predominate depending not only upon the chemical structure of the polymer but also upon the conditions of irradiation. This may lead to sharp changes in the physical properties of the polymer. On the other hand, polycarbonate is an amorphous engineering thermoplastic notable for its high impact resistance. It has reasonably good temperature resistance, good dimensional stability and low creep but some what limited chemical resistance and is prone to environmental stress cracking (1). It is widely used today to prepare track-etched membranes. Polycarbonate particle track-etched membranes are used as templates in nano-tubes and nano-wires manufacturing (2). In addition, the use of radiation in polymer technology is essential with a view to achieve some desired improvements in polymer properties (3). It is already an established fact that interaction of radiation with polymers leads also to chain aggregation, formation of double bonds and molecular emission. As a consequence of this, the physico-chemical properties like optical, structural and chemical properties of the polymer are modified (4–12). The study of these changes may enhance their applications in different fields, e.g. for the evolution of high radiation doses (13). Radiation-induced modifications in polycarbonate have been studied extensively (14–19). The effect of radiations on polycarbonate is primarily chain scission. However, at increased doses, active sites or branching points created by scission may lead to crosslinks The present study deals with the investigation of the effect of gamma irradiation on the structural and optical properties of Makrofol LS 1–1 polymer not only to obtain information concerning the interaction of gamma with Makrofol, but also to study the feasibility of enhancing its properties, improving its performance in different fields.