Polymer ageing: physics, chemistry or engineering? Time to reflect

Abstract

Polymer ageing may involve physical ageing without chemical reaction occurring; chemical changes such as crosslinking during curing of a thermoset; thermal conditioning at elevated temperature; photochemical ageing, as occurs in weathering. This review concentrates on examples involving a combination of two or more of these effects, and with the consequential changes in engineering properties. Events on the molecular level lead to change in the morphology and macroscopic physical properties. For example, in a semi-crystalline polymer, chain scission caused by photo-oxidation, may lead to secondary crystallisation ('chemi-crystallisation'), increasing density, and causing an increase in Young's modulus and reducing ductility. Similar effects may be observed in glassy polymers, due to chain scission accelerating physical ageing. Such effects are particularly common when rapid cooling during moulding has left the polymer in a state far from equilibrium. A common symptom is a change in the residual stress distribution in polymer mouldings and this is discussed.

Thirty Years of Luminescent Solar Concentrator Research: Solar Energy for the Built Environment

“…[102,130] In addition, as the waveguides age due to exposure to the elements and in particular ultraviolet light, generates brittleness, opacity, and a host of reaction species that generate a yellow tint to the plate and act as absorptive light 'traps'. [200] To combat these loss mechanisms, research into copolymer systems has demonstrated enhanced photostability over single component systems. [131] During the transition from the excited state to the ground state of the dye molecule, electron transfer takes place from the dye to the main copolymer (here polystyrene-co-methylmethacrylate) chain, which may increase the photostability of the dye.…”

Controlled degradation of biocomposites ENR/PCL containing natural antioxidants

“…The greatest interest in PCL was observed during the 1970-1980 decade, when it was primarily used as a drug carrier. Due to its good rheological and viscoelastic properties and therefore its ease of processing, PCL has an advantage over other polyesters [16][17][18][19][20][21][22][23].…”

Mechanical, dielectric, and physicochemical properties of impregnating resin based on unsaturated polyesterimides

“…This is also related to the post-reticulation that occurs in the PEI resin during the different measurements, which provides less mobility to the polymer network. In addition, processed polymers are usually in a nonequilibrium state at the end of the shaping process; thus, heating occurs during measurements operates as an annealing that allows the network tending toward an equilibrium state with a structural recovery [27]. The macroscopic properties of the thermosets depend on the cross-link density [15].…”