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- Additives (1)
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The influence of weathering on the fire retardancy of polymers is investigated by means of a cone calorimeter test, before and after artificial weathering. The surface degradation was monitored using different techniques (ATR–FTIR, microscopy, colour measurement). Different kinds of polymeric materials were chosen, all as they are used in practice: polycarbonate (PC) blends, polyamide (PA) and polypropylene (PP) flame-retarded with arylphosphate, melamine cyanurate (MC) and intumescent formulation based on ammonium polyphosphate (APP), respectively.
All samples show material degradation at the surface due to weathering. No significant weathering influence occurs on the flame retardancy when it is a bulk property, as was observed for aryl phosphates in PC blends and MC in PA. When the fire retardancy is dominated by a surface mechanism, dependence on the duration of weathering is detected: for intumescent formulations based on ammonium APP in PP, a worsening in the formation of the intumescent network was observed.
Der Anteil von Polymeren als Funktions- und Konstruktionswerkstoffe in dauerhaften medizinischen Anwendungen steigt beständig. Derartige Materialien müssen den mechanischen, biologischen und chemischen Bedingungen im Körper widerstehen (u.a. Abrieb, Hydrolyse, Degradation) und gleichzeitig gut verträglich sein. Der sichere Einsatz von polymeren Materialien erfordert die Kenntnisse über ihre Langzeitstabilität unter verschiedenen äußeren Bedingungen. Diese sind nicht nur beeinflusst durch die unmittelbare Umgebung in vivo, sondern auch durch die Historie der verwendeten Materialien. Dazu zählen u. a. erhöhte Temperaturen unter sauerstoffhaltiger Atmosphäre während der Verarbeitung oder die Exposition von ionisierender Strahlung oder reaktiven Radikalen während der Sterilisation.
After several months of operation, many photovoltaic (PV) modules develop a discolouration defect called snail trails which appear as irregular dark traces across the cells. These traces are caused by silver nanoparticles accumulating within the encapsulation foil directly above the grid finger. In this work we systematically investigate combinations of encapsulation and back-sheet foils with respect to their susceptibility for snail trails. We can show that certain additive compositions within the encapsulation and back sheet foils are critical for the formation of the discolouring silver nanoparticles. We suggest a reaction model explaining the formation of snail trails from a chemical point of view. This fundamental understanding allows the rapid testing of foils for their snail trail sensitivity as well as the special design of resistant foils.
Influence of weathering on the stability of flame retardancy in polymeric materials for outdoor use
(2009)
Discoloration Effects of High-Dose gamma-Irradiation and Long-Term Thermal Aging of (U) HMW-PE
(2017)
Two polyethylene types with ultra-high (UHMWPE) and high molecular weight (HMW-PE) used as neutron radiation shielding materials in casks for radioactive waste were irradiated with doses up to 600 kGy using a 60Co gammasource. Subsequently, thermal aging at 125∘C was applied for up to one year. Degradation effects in the materials were characterized using colorimetry, UV-Visspectroscopy, IR spectroscopy, and DSC. Both materials exhibited a yellowing upon irradiation.The discoloration of UHMW-PE disappeared again after thermal aging.Therefore, the yellowing is assumed to originate fromannealable color centers in the formof free radicals that are trapped in the crystalline regions of the polymer and recombine at elevated temperatures. For the antioxidantcontaining HMWPE, yellowing was observed after both irradiation and thermal aging. The color change was correlated mainly to decomposition products of the antioxidant in addition to trapped radicals as in UHMW-PE. Additionally, black spots appeared after thermal aging of HMW-PE.