Polymer Surfaces oxidative degradation

XPS and SIMS are both surface sensitive and surface-specific techniques that may be used to probe surface oxidation/degradation of polymers. They use X-rays and ions, respectively, to characterise surface species. Both XPS and SIMS are operated under ultra-high vacuum, UHV, conditions. 

For a ToF-SIMS investigation of the surface oxidative degradation of low-density polyethylene (LDPE), the polymer was exposed to 1802 rather than 1602 in order to be able to readily discriminate oxygen introduced by the ageing process from that in the polymer prior to ageing [102], Figure 36 shows an example series of ToF-SIMS spectra from this investigation, which shows the clear separation of the lsO species from the lsO species. In the study, close correlation was observed between the intensity of the lsO carbonyl species determined by mid-infrared spectroscopy with the ToF-SIMS 180- peak intensity as a function of 1802 exposure time. ToF-SIMS spectra obtained from microtomed cross-sections showed no... 

The durability in use and reuse of the hydrocarbon polymers and their performance during recycling can be readily controlled. Since the catabolic enzymes cannot biodegrade polymers in the inhospitable hydrophobic environment at the polymer surface, oxidatively resistant hydrocarbon polymers are essentially non-degradable. As was seen in Chapter 9, extensive modification of the polymer surface is a prerequisite to biological attack. In particular, both thermal and photooxidation can be employed to provided a suitable surface environment for microbial colonization and the rate at which these processes occur can be controlled by the use of the appropriate antioxidants and stabilizers [7]. Photooxidation of the hydrocarbon polymers is particularly relevant to the control of litter, whereas thermal oxidation is a prerequisite for aerobic composting. 

UV stabilisers protect polymers by restricting UV penetration to the surface and therefore confine the damage to surface layers. Protection is important because the energy possessed by UV radiation is sufficient to break chemical bonds. The initial breakage can either be by a radical (Norrish type I) or non-radical (Norrish type II) pathway. The effects are similar to degradation of the polymer by oxidation routes the radical intermediates can be neutralised by anti-oxidants. 

Adhesion of non-polar polymers is sometimes improved by oxidation, so essentially what is normally thought of as degradation may be used to introduce an enhancing surface property. Nevertheless, in both cases the oxidation process modifies the polymer surfaces, and the analysis tools can be rather similar, see, e.g., Ref. [101]. 

Oxidation Resistance. Oxidation in high-temperature adhesive joints involves reaction of the adhesive polymer with oxygen in the air as well as reaction with certain metal surfaces (e.g., ferrous metals). Oxidative degradation is initiated by the action of highly... 

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