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The increased interest in the use of polymer composites with natural, biodegradable and renewable fillers is the result of increased awareness of the environment. Therefore, the search for new materials that meet the above expectations is becoming a current issue. The article presents the results of research on composites containing pistachio shells (Pistacia vera L.), which are common agricultural waste, with unsaturated polyester resin based on post-consumer recycled poly(ethylene terephthalate) and vinyl ester resin based on bisphenol-A. The environmentally friendly polymeric cobalt solution was used as the accelerator. In order to study the degradation of the composites, accelerated ageing, immersion in various solvents, and high temperature were used. From the obtained results, it can be observed that accelerated aging resulted in the additional cross-linking of the resin, while the filler absorbed the UV light. During immersion, the polymer matrix was degraded in acetone, whereas the incorporation of pistachio increases its water sorption and the plasticisation effect was also observed. The alkali environment initiated the hydrolysis of ester linkages. The vinyl ester resin-based materials were more chemically and thermally resistant than those from the unsaturated polyester. [ABSTRACT FROM AUTHOR]

In this work, a novel procedure for fast assessment of the material residual stability is proposed. The method resides in integral isoconversional kinetic analysis of the thermal oxidation of unaged material employing the Berthelot–Hood temperature function. Subsequently, the obtained conversion-independent kinetic parameter D is also employed for samples aged in various regimes. The value of conversion-dependent parameter A for aged samples is calculated from the oxidation onset temperature measured at 5 °C min−1. The residual stabilities are then calculated as a simple ratio of the parameter A of aged material to that of the unaged one. The method has been applied and verified for the samples of low-density polyethylene aged by thermal, radiation and combined ageing. The method can also be employed for high-throughput screening of the effect of various stabilizers and antioxidants in a given organic matrix. [ABSTRACT FROM AUTHOR]

Micro-differential scanning calorimetry was used to reveal the deterioration patterns of collagen in vegetable-tanned leather. The influence of both the tannin type, i.e. hydrolysable or condensed, and collagen animal species, i.e. calf and sheep, was investigated. Comparison with the behaviour of unmodified collagen in parchment was made to explain the thermal destabilisation and denaturation of the chemically modified collagen in leather. Both leather and parchment were subjected to accelerate ageing by heating at 70 °C in controlled atmosphere at 30 % RH. The synergistic effect of the daylight exposure was studied by irradiating the samples in the visible domain with 4000 lx. The destabilisation effect induced by the hydrothermal ageing treatment was evident since the 8th day and reached a critical level after 32-day ageing time. The formation of damaged intermediate states with progressively lower thermal stability was the main feature of the deterioration pattern independent of the tannin type and collagen species. Quebracho-tanned calf leather was the most resistant against ageing, whereas chestnut-tanned sheep leather underwent de-tanning after a 32-day ageing period. Exposure to visible light irradiation induced an evident thermal stabilisation due to cross-link formation. The balance between thermal stabilisation and destabilisation processes in leather during visible light exposure was influenced by the tannin type. [ABSTRACT FROM AUTHOR]

Oxidation induction times (OIT) and oxidation onset temperatures (OOT) of a low density polyethylene melt were evaluated in air using DSC. Good regression fits to OOT data were obtained using global values for the activation energy ( E) that are specific for each antioxidant but assumed independent of concentration. Gimzewski’s postulate that OIT and OOT correspond to the same level of antioxidant depletion was tested by attempting to predict OIT values from OOT generated model parameters. The deviations between predicted and experimental OIT values were comparable in magnitude to the inherent scatter in the data. However, regression of the dynamic OOT data yielded statistically significant lower values for the activation energy than are obtained by direct regression of isothermal data. [ABSTRACT FROM AUTHOR]

After improvements were made to a modified Polymer Labs MkIII DMTA instrument to facilitate repeatable controlled humidity (RH) experiments using isothermal and thermal scanning conditions, the viscoelastic properties of titanium white pigmented artists’ acrylic emulsion films were measured in tensile mode. The effects of temperature, relative humidity and accelerated ageing regimes on two brands of titanium white paints were explored. These paints are highly responsive to changes in temperature and relative humidity, formulation differences affect properties slightly, and while light ageing had a negligible effect, thermal ageing resulted in decreased storage modulus and increased film density. [ABSTRACT FROM AUTHOR]

Degradation of poly(ester-urethanes), poly(ether-urethanes) and poly(acrylic-urethanes), as a base for automotive paintings in interior applications, has been studied by DSC. The samples were clearcoat and black-pigmented paints, unstabilized and stabilized with HALS Tinuvin 292, UV absorber Tinuvin 1130 and antioxidant Hostanox O3, exposed to weathering in Xenotest and in Arizona desert. From the dependences of oxidation onset temperature on the heating rate, the kinetic parameters enabling to calculate the oxidation induction time for a chosen temperature have been obtained. From the values of oxidation induction time, the protection factors of the additives and the residual stability of the polymer after an ageing stress has been evaluated. It has been shown that the equivalence between the two methods of weathering depends on the polymer composition. A new criterion for the evaluation of synergism/antagonism of additives in the stabilizing mixture has been proposed. [ABSTRACT FROM AUTHOR]

Methods for kinetic description of induction periods, based on the single-step kinetics approximation and various expressions of the temperature functions, are presented. The formulas for evaluation of both isothermal and non-isothermal lengths of induction periods are derived. Use of the formulas is demonstrated on the thermooxidative degradation of polyolefines. The kinetic parameters obtained from isothermal and non-isothermal experiments are compared and possible reasons of inconsistencies are analyzed. Applications of the determination of induction periods for thermooxidation of various systems are reviewed. The theory outlined in this paper can be applied not only for thermooxidation in condensed phase, but also for other processes exhibiting the induction period, such as the curing of rubber compounds, recrystallization of nickel sulfide and crystallization of silicate and metal glasses. [ABSTRACT FROM AUTHOR]