Accelerating aging physical stability

Similar to cleaning operations, consolidation and adhesion treatments are usually under analytical control. Measurements of the chemical, morphological, and physical properties of the consolidated material are indispensable to assure the efficiency of the operation. Changes in mechanical strength, color, and gloss, as well as chemical composition are assessed. Studies of stability of consolidants are frequently performed by means of namral and accelerated aging trials. 

To approach physical stability problems of suspensions, effectiveness and stability of surfactants as well as salt concentrations must be checked with accelerated aging. In addition, unit operations affecting particle size distribution, surface area, and surfactant effectiveness should be approached, taking into account that different types of distributions, for instance, volume or number weighted, give a different average diameter for an equal sample [43],... 

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. 

Service lifetime prediction of polymers and/or polymer based materials may be undertaken from different types of tests, such as creep behavior tests (linear and non-linear creep, physical aging, time-dependent plasticity), fatigue behavior tests (stress transfer and normalized life prediction models, empirical fatigue theories, fracture mechanics theory and strength degradation) and standard accelerated aging tests (chemical resistance, thermal stability, liquid absorption) [32]. 

Two different approaches for lifetime prediction are presented. The underlying lifetime limiting processes have been identified in two cases. Mathematical expressions of chemical/physical relevance were used for the lifetime predictions for PE hot-water pipes and cables insulated with plasticized PVC. Accelerated testing, extrapolation and validation of the extrapolation by assessment of the remaining lifetime of objects aged during service conditions for 25 years were successfully applied to cables insulated with chlorosulfonated polyethylene. Polyolefin pipes exposed to chlorinated water showed a very complex deterioration scenario and it was only possible to find a method suitable for predicting the time for the depletion of the stabilizer system. 

Recently, La Mantia et al reported a study of LLDPE/clay nanocomposites with appropriate additives [103], The photochemical behavior of nanocomposites without and with different UV stabilizers was studied under artificial accelerated conditions of ageing. Addition of a metal deactivator to the LLDPE-clay nanocomposites was also compared. Stabilizing effect on the physical properties such as elongation at break and tensile strength were described. The most effective photostabilization of these LLDPE/clay nanocomposites was achieved in presence of the metal deactivator. 

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