Natural ageing degradation

Figure 5.6 GALDI mass spectra of dammar, fresh (a) and naturally aged under different conditions in a window after 7 weeks (b), as well as in the dark (c), under museum conditions (d) and in a window after 31 weeks (e) [36]. Strong oxidation and degradation can be seen after a few weeks under all ageing conditions, and the ageing patterns are very similar. Oxidation under museum conditions is not much more pronounced than in darkness...

Figure 5.7 GALDI mass spectra of mastic. Commercially available mastic (a) in an advanced state of oxidation as can be seen by comparison with really fresh mastic a few days after harvesting (b). As with dammar, oxidation and degradation progress quickly in both light and darkness. The same mastic as in (b) is depicted after natural ageing in the dark after 7 weeks (c), and in a window after 7 weeks (d) and 42 weeks (e)...

The practical conclusion is that if comparisons are to be made between accelerated and natural ageing results or attempts made to predict degradation at lower temperatures from accelerated tests, the existence of degradation gradients is likely to have significant effect. Also, predictions made from tests on thin test pieces may be misleading if applied to thick products. 

A comparison of the state of degradation of historical silk fabrics with those of artificially aged contemporary fabrics would be very useful in any effort to determine the mechanisms by which naturally aged silk is degraded. Such knowledge would also aid in the selection and evaluation of stabilizers to slow the degradation process. For these reasons, the historical fabrics were evaluated. 

The poor performance of the calcium bicarbonate treated fibers is not so readily understood. However, a very likely explanation is the greatly increased sensitivity of naturally aged (and hence partially degraded) cellulose to alkaline materials. One may speculate that the calcium carbonate that was formed in the fibers was acting as an initiator of depolymerization reactions that are base catalyzed. 

Alkaline degradation reactions are largely controlled by the carbonyl content of cellulose (27-29). Because the carbonyl levels go up as natural aging proceeds, one should expect that an 800-year-old textile would be much more likely to be adversely affected by alkali than would new, unoxidized cellulose. The vast majority of the conservation... 

Case studies. The CL immunochemical techniques was applied on genuine old samples in order to evaluate its performance in samples with a natural aging and degradation of target proteins. A sample collected from a wood painting by Nicolo Rondinelli (c. 1450 - c. 1510), an Italian painter of the Renaissance period, was analyzed. Experimental results showed the presence of ovalbumin in the upper-most painting layer, probably due to the use of an egg-based varnish (Fig. 2). 

One of the drawback of radiation crosslinking of NR latex is the poor ageing property of the film. This poor ageing property may be coming from two causes natural antioxidant degrade under radiation and autoxidation due to the presence of trapped radical in NR matrix. 

Abstract The chemical and biochemical degradation and calcification are investigated as processes that alter the physical and mechanical properties of implanted polymers. The principles of oxidative, hydrolytic and enzymatic degradation and calcification of polymers in the body are discussed and the natural ageing of polymers in vivo and in vitro and the accelerated ageing of polymers are examined. The use of accelerated ageng is described as a method to predict changes in the physical and mechanical properties of polymers in vivo. 

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