Thermal properties aging, effect

Bulhons, T.A., McGrath, J.E., Loos, A.C. Thermal-oxidative aging effects on the properties of a carbon fiber-reinforced phenylethynyl-terarinated poly(etherimide). Compos. Sci. Technol. 63, 1737-1748 (2003)... 

The term thermal properties is open to more than one interpretation. Specific heat, thermal conductivity and diffusivity clearly come under this heading but the term can be taken to also include heat ageing, low temperature tests and fire resistance. However, these are more properly dealt with, as in this volume, under Effect of Temperature. Thermal analysis is a group of techniques in which a property of a sample is monitored against temperature, or time at a temperature, and, therefore, is also generally concerned with measuring the effect of temperature. Nevertheless, for convenience, a brief overview of thermal analysis is given here. 

Thermal Properties - Properties related to the effects of heat on physical systems such as materials and heat transport. The effects of heat include the effects on stmcture, geometry, performance, aging, stress-strain behavior, etc. 

The thermal properties are conductivity, diffusivity, and specific heat. Other properties are sometimes included under this title but thermal expansion, transition points, low temperature properties, and heat aging are more properly the effects of temperature (Chapter 12). Thermal analysis in all its various forms is also a study of the effect of temperature rather than measurements concerning the transport of heat, although thermal analysis techniques can be used to measure thermal transport properties. 

The standard recommends using at least three to four temperatures, but this really is the absolute minimum for a viable TI value to be calculated, and at each temperature there must be sufficient results to define clearly the change in property value down to and beyond the threshold limit so that this may be estimated by interpolation and not extrapolation. It is clear that the determination of TI is a time-consuming and expensive process. It must also be borne in mind that the calculated TI value may not equate with any precision to the true service temperature at which a product may be used. In practice it is likely that several properties may be influential in determining the viability of the product, and each of these will almost certainly have a different TI value. Nevertheless, the TI value remains a useful indicator for comparing the relative long-term effects of thermally induced aging in plastics. 

To date, various block copolymers have been produced using biological systems. This includes poly(3HB-fo-4HB) [17], P(3HB)-f>-poly(3-hydroxyvalerate-co-3-hydroxyheptanoate) [18], PHB-f -poly(hydroxyhexanoate) [19], poly 3HB-fc-poly(3-hydroxyheptanoate) [P(3HP)] [20], P(3HP)-f -poly(4-hydroxybutyrate) [P(4HB)] [21], poly(3-hydroxyhexanoate)-fe-poly(3-hydroxydecanoate)-co-[3-hydroxydodecanoate (3HDD)] [22] and poly[3-HDD-f -poly(3-hydroxy-9-decanoate)] [23]. These studies were motivated by the fact that although random copolymers, such as poly(3HB-co-3HV) and poly(3HB-co-4HB), exhibit useful mechanical and thermal properties they suffer from a deterioration of polymer properties due to the effect of ageing. It was found that all block copolymers exhibited improved properties compared with the two relative homopolymers, random and blend polymers. Various... 

Tyrosine-derived polycarbonates provided a convenient model system to study the effect of pendent chain length on the thermal properties and the enthalpy relaxation (physical aging). It is noteworthy that enthalpy relaxation kinetics are not usually reported in the biomedical literature and that a recent study by Tangpasuthadol (Tangpasuthadol, 1995) represents one of the first attempts to evaluate physical aging in a degradable biomedical polymer. 

Outstanding properties high and low working temperatures, chemical resistance, abrasion resistance, memory effect, thermal and aging stability WU, T-S, Plastics Additives Compounding, 9, 6, 40-3, 2007. 

In Both plasticized (semi-rigid and flexible) PVC materials as well as PVC in solutions, the rate of their thermal degradation and effective stabilization are caused by essentially different fundamental phenomena in comparison to aging of PVC in absence of the solvent Both stmcture and macromolecular dynamics render the significant influence on its stability, i.e. chemical nature of the solvent (plasticizer), its basicity, specific and non-specific solvation, degree of PVC in a solution (solubility), segmental mobility of macromolecules, thermodynamic properties of the solvent (plasticizer), formation of associates, aggregates, etc. 

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