Polymer degradation, physical factor

We are interested in the effect of weathering on polymers for two distinctly different reasons. We may wish to retard it, so that our products survive longer in outdoor applications, or we may wish to accelerate it, so that products degrade rapidly when exposed to the elements. In either case, we need a way of predicting the response of polymers to the factors that produce measurable changes in their chemical and physical characteristics. Ideally, we would like to be able to obtain these results in as short a period of time as possible. 

A systematic study of both physical and chemical aspects in plastics pyrolysis was launched in the Cycleplast project [6]. Thermal degradation of commodity polymers, including kinetic factors and mechanism, were systematically investigated by Professor Bockhom and collaborators, using thermogravimetry, linked with mass spectrometry, as well as closed loop laboratory-scale pyrolysis reactors. The resulting kinetic parameters are discussed further. 

It must be therefore taken into consideration that the physical loss of stabilizers may influence the r ults of the accelerated ageing test This is true mainly in tests where the polymer degradation is accelerated by physical factors having very different intensities to those applied under practical conditions. 

Solution NMR is widely used in polymer processing for the qualitative and quantitative analyses of tacti-city, end-groups, degradation products, chain defects, and monomer sequence distribution.A typical application is in the characterization of monomer sequence distribution by quantitative NMR spec-troscopy. For example. Fig. 7 shows a typical NMR spectrum of ethylene-co-l-butene. From the relative peak areas, it is possible to determine the fractions of the two monomers, their reactivity ratios, the triad distribution, and the blockiness or randomness of the monomer distributions. All of these structure factors play an important role in the polymer s physical and mechanical properties. 

Microbial contamination of polymer emulsions is discussed, and is shown to depend on a large number of chemical and physical factors. An integrated approach to prevention and cure is recommended, and attention to raw material and water quality, plant design and hygiene, and the use of broad spectrum biocides such as those based on isothiazolin-3, is suggested. Conditions of temperature, pH and redox should be considered, it is stated, when using such biocides to avoid degradation. 

Polymer degradation is highly dependent on chemical and physical factors. The chemical factors vill be examined in relation to thermal degradation (see Section 15.4.2). This section vill be focused exclusively on the influence of physical factors on polymer degradation. 

In conclusion, the literature shows that in most cases LA/GA polymers exhibited comparable in vitro and in vivo degradation behaviours. Examination of corresponding data suggests that whenever differences are observed, effects of physical factors (temperature, stirring, pH) or physiological ones related to implantation sites (subcutaneous, intramuscular or in bony tissues) should be considered prior to invoking enzymatic activities. 

The main environmental factors active in the topsoil and their possible effects on polymer degradation are summarised in Table 3.3 and described in the following paragraphs, differentiating between physical properties, chemical-physical properties and biological properties. 

Antioxidants and stabilizers were used on a trial-and-error basis more than 100 years ago. Real scientific and technological progress is relatively recent. It was ushered in by the development of a basic understanding of the underlying mechanisms of polymer degradation. This has made it possible to ascribe specific chemical and physical functions to antioxidants and stabilizers according to their mode of action in the oxidative process. An important aspect in the development of antioxidants is that their effectiveness does not only depend on the chemical inhibition process but also on physical factors such as solubility of antioxidants and their compatibility with the polymer, diffusion and migration phenomena within the polymer matrix, volatility and extractability of antioxidants. Some historical perspectives of this development has been reviewed recently. ... 

Copolyesters (such as BIOMAX ) which combine aromatic esters with aliphatic esters or other polymer units (e.g. ethers and amides) provide the opportunity to adjust and control the degradation rates. These added degrees of freedom on polymer composition provide the opportunity to rebalance the polymer to more specifically match application performance in physical properties, while still maintaining the ability to adjust the copolyesters to complement the degradation of natural products for the production of methane or humic substances. Since application performance requirements and application specific environmental factors and degradation expectations vary broadly, copolyesters are, and will continue to be, an important class of degradable polyesters. 

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