Additive degradation techniques

For samples that meet the solubility requirements of the SEC approach, analyses were also reported for additives in polymers such as PVC and PS [28,29]. Direct SEC analysis of PVC additives such as plasticisers and thermal stabilisers in dissolution mode has been described [28,30,31 ]. In the analysis of a dissolved PS sample using a SEC column of narrow pore size, the group of additives was separated on a normal-phase column after elution of the polymer peak [21]. Column-loading capacity of HPSEC for the analysis of additives, their degradation products and any other low-MW compounds present in plastics has been evaluated for PS/HMBT, PVC/TNPP and PVC/TETO (glyceryl tri[l-14C] epoxyoleate) [31]. It was shown that HPSEC can be used to separate low-MW compounds from relatively large amounts of polymers without serious loss of resolution of the additives the technique has also been used for the group analysis of chlorohydrin transformation products of the TETO model compound [32]. 

Only a few methods for the specific degradation of polysaccharides were known when an earlier article on structural polysaccharide chemistry appeared in this Series.3 The Smith degradation,4 which has become the most frequently used, had only just been introduced. Since then, a number of specific degradation techniques have been developed. In addition, there have also been some modifications and improvements to existing methods. In this article, chemical methods for specific or selective degradation of polysaccharides, and their applications in structural analysis, will be discussed. Enzymic methods, which may be of considerable value, have already been treated in this Series.5... 

Other sulfur-selective chemical degradation techniques (work in progress) will probably yield additional information to further resolve remaining questions with respect to structure, origin and thermal behaviour of these sulfur-rich geopolymers. 

In systems where metal catalysis of oxidation is an issue, the use of a metal chelator such as ethylenediaminetetraacetic acid is recommended to inhibit oxidation. Additionally, as with previous degradation techniques, the oxidation samples should be stored at low temperature (below 5 °C) to preserve the... 

NBO is still probably the most commonly employed chemical degradation technique for lignin analysis. This acceptance is related to the fact that NBO provides in satisfactory yield p-hydroxybenzaldehyde, vanillin, and syringaldehyde from lignin H, G, and S units, together with smaller amounts of the corresponding benzoic acids (Figure 2.2). In addition, NBO yields small amount of 5-carboxyvanillin,... 

Reconstruction method used Choice of filters with a selected cutoff frequency in the filtered backprojection reconstruction method may introduce additional degradation of the spatial resolution of the scanner. For example, a filter with a too high cutoff value introduces noise and thus degrades spatial resolution. An error (KT) due to the reconstruction technique is usually a factor of 1.2-1.5 depending on the method (Huesman, 1977). 

Techniques such as this can obviously provide much valuable information on additive degradation occurring in polymers at elevated temperatures. 

In addition to identifying structural units, degradative techniques can provide information about additives, impurities, residuals, structural defects, etc. However, in all determinations, it is absolutely necessary to maintain identical conditions so that the fragmentation of macromolecules will be reproducible. Pyrolytic methylation is also used for the identification of polymers [246]. 

This photolytic degradation technique enables additives to be identified and determined in polymers in amounts down to 0.01%. 

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