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Degradation Pathways of Various Plastics
Published in Hyunjung Kim, Microplastics, 2023
Hyunjung Kim, Sadia Ilyas, Gukhwa Hwang
The most significant damage occurs from highly reactive ozone in the atmosphere, which can attack the double bonds of some plastics and elastomers by ozonolysis. The ozonolysis leads to the interaction of ozone molecule reacts with the double bond to produce an unstable, reactive ozonide (polyatomic anion). The rapid decomposition of the ozonide results in double bond cleavage and ultimately polymer chain breaking. The chain breaking by ozonolysis leads to a decrease in molecular weight and a reduction in material strength that can further cause brittlement and material cracking. For example, in elastomers, ozone can induce cracking on surfaces exposed to the atmosphere, and this ozone-cracking effect is often seen in old car tires. However, elastomers like Neoprene have good ozone resistance because the double bonds in the polymer chain are protected from attack by ozone due to the presence of chlorine in polymer backbone which decreases the electron density in the double bonds, thereby reducing the tendency to react with ozone (Davis et al., 2010).
Plastics Properties and Testing
Published in Manas Chanda, Plastics Technology Handbook, 2017
The stress corrosion resistance of polymers depends on the magnitude of the stress, the nature of the environment, the temperature, and the molecular weight of the specimen. Ozone cracking is a typical example of stress corrosion cracking of polymers. The critical energy for crack propagation (τc) in ozone cracking varies very little from one polymer to another and is about 100 erg/cm2 (0.1 J/m2). This value is much lower that the τc values for mechanical fracture, which are about 107 erg/cm2 (104 J/m2).
Development of an Apparatus for Testing of High-Temperature Static Seals
Published in Tribology Transactions, 2021
Abdolkarim Sheikhansari, Jonathan Knapton, Diego Benito, Ben Shaw, Ehsan Alborzi, Simon Blakey
In order for the seals to work effectively, it is necessary to design the groove so that it provides 7–30% of compression on the seal in a direction normal to the action of pressure. The compression percentage is based on the design standards and seal cross section (2). Once the stress is released, the seal is not restored to its original dimensions, known as compression set. Caused by physical relaxation and chemical degradation, the compression set effect along with stress relaxation degrades the performance of the seals (3). Other O-ring failure modes include extrusion and nibbling, spiral failure, abrasion, weather and ozone cracking, heat aging and oxidation, plasticizer extraction, installation damage, gas expansion rupture, and failure due to backup rings (1, 4). What is not necessarily known a priori is which failure mode is likely for which specific seal design. In order to assess this, it is necessary to monitor the performance of any candidate seal in a representative environment.
Lysis characteristics and mechanism of excess sludge degraded by ozone and ultrasonic treatment
Published in Environmental Technology, 2020
Junfeng Wang, Hai Li, Yaqi Liu, Changming Zhong, Zhijiang Luo, Dan Li
It can be seen from Figure 2 that the effect of ozone-assisted ultrasonication on the lysis of excess sludge is better than that of ozone and ultrasonic respective. The maximum value of SCOD for ozonation synergetic ultrasonic process was 1792 mg/L, the maximum SCOD for ozonation sludge was 1597 mg/L, and the maximum value of SCOD for ultrasonic residual sludge was 1484 mg/L. The preliminary analysis is due to the effect of ultrasound on ozone cracking excess sludge. On the other hand, the cavitation caused by ultrasonic waves also destroyed the structure of the excess sludge, enhanced the mass transfer rate and decomposition rate of ozone, promoted the production of free radicals by ozone, increased the oxidizing ability of ozone, and could be more easily degraded the internal substances [13].