Polymers degradation analytical detection

Well before the advent of modern analytical instruments, it was demonstrated by chemical techniques that shear-induced polymer degradation occurred by homoly-tic bond scission. The presence of free radicals was detected photometrically after chemical reaction with a strong UV-absorbing radical scavenger like DPPH, or by analysis of the stable products formed from subsequent reactions of the generated radicals. The apparition of time-resolved ESR spectroscopy in the 1950s permitted identification of the structure of the macroradicals and elucidation of the kinetics and mechanisms of its formation and decay [15]. 

Many experimental findings can at first glance be interpreted as some form of polymer degradation. But, scientifically valid data must try to make up the balance of the polymer and its degradation products to avoid false interpretation due to adsorption phenomena, inappropriate analytical tools or detection limits, or changes in its chemical identity. 

The analytical detection of residues and metabolites was possible from a laboratory degradation test using a mineral bed matrix. Tosin and co-workers [88] described such a test system and the detection of the metabolite, 4,4 -diaminodiphenylmethane (a known toxic substance) as a result of the degradation of the polyurethane caprolactone copolymer. In particular, the problems arising due to high concentrations of organic substances in the matrix (humic substances) were avoided. However, it may be difficult to detect metabolites from a certain polymer when it is not known what to search for. The success of such methods and analysis procedures as a primary source of information may therefore not be assured. Nevertheless, such investigations could be helpful to discover the causes of ecotoxic effects already observed from other experiments. 

When the analyte is present in the polymer at very low concentrations some special precautions are needed to enhance the sensitivity of the extraction process, i.e. to lower the detection limit. The sample may be concentrated prior to analysis by SCF or solvent evaporation (at as low a temperature as possible to avoid degradation or partial loss of volatile analytes). Alternatively, a larger amount of polymer sample may be extracted (followed by LVI). Samples may also be concentrated or matrix effects minimised by using SPE [573,574],... 

Quite a number of recent papers have concentrated on techniques which allow the gravimetric detection of only a few femtograms of an analyte [105]. In one of these, PAHs could be measured in concentration of down to a few ng ml-1 in degraded oil when a piezoelectric quartz crystal coated with Mi-polymers imprinted either with a fresh or with a degraded lubricant was immersed into the... 

The results presented by Breck et al (68) for saturated chain polymers do not coneider the possibility)that very small amounts of hydroperoxide groups c n be formed along the saturated-ohain polymers. Such small amounts of hydroperoxides can not be detected by common analytical methods but may be sufficient for the initiation of an oxidative degradation mechanism of polymers. 

Alternatively, the container may contain an opacifying agent, e.g., titanium dioxide. The use of multilayered bags was demonstrated to inhibit photochemical decomposition of vitamin E in TPN fat emulsions (Allwood and Martin, 2000). PVC films discolor on irradiative exposure due to photochemical degradation of the polymer (Hollande and Laurent, 1997). Plastic containers for parenteral use may contain several additives, e.g., antioxidants, stabilizers, plasticizers, lubricants, impact modifiers, and coloring matter when justified and authorized. In an appendix, the European Pharmacopoeia presents a list of plastic additives that may be used (European Pharmacopoeia, 2002). The additives should not be extracted by the contents in such quantities as to alter efficacy or stability of the product or to present any risk of toxicity (European Pharmacopoeia, 2002). However, organic additives extracted in concentrations below the detection limits of the analytical methods authorized by the European Pharmacopoeia may be sufficient to initiate photosensitized reactions in the formulation. 

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