Dynamic processes, deterioration

This report deals with dynamic processes of the deterioration of polymers often used as paints and finishes in housing, and also refers to their influence as the reduction in protective performance on the durability of reinforced concrete. The deterioration processes of polymers by the simiiltaneous action of ultraviolet (UV) light and diffusive oxygen is explained theoretically based upon unsteady state dynamics. The parabolic law (/t" law) is derived for a typical path for the progress of the deterioration of polymers inwards from the surface (l), and compared with some experimental data. The same parabolic law involving a constant term was also derived for the carbonation of concrete, which well explains the retardation effects of finishes on the carbonation (2). 

Adaptive Control. An adaptive control strategy is one in which the controller characteristics, ie, the algorithm or the control parameters within it, are automatically adjusted for changes in the dynamic characteristics of the process itself (34). The incentives for an adaptive control strategy generally arise from two factors common in many process plants (/) the process and portions thereof are really nonlinear and (2) the process state, environment, and equipment s performance all vary over time. Because of these factors, the process gain and process time constants vary with process conditions, eg, flow rates and temperatures, and over time. Often such variations do not cause an unacceptable problem. In some instances, however, these variations do cause deterioration in control performance, and the controllers need to be retuned for the different conditions. 

The sensitivity of Magnetic Resonance (MR) to the local concentration, molecular dynamics and molecular environment of these nuclei make it well suited for the study of deterioration processes in concrete materials. Hydrogen (water), lithium, sodium, chlorine and potassium are all MR sensitive nuclei and play an important role in cement chemistry. The ability of MRI to spatially resolve and non-destructively examine test samples as a function of treatment or exposure has the potential to provide new insight to better understand deterioration mechanisms and mass transport properties of concrete materials. 

The materials are melt-process able and a critical stress for flow is observed, similar to conventional PP/EPDM-based TPVs. Application of static crosslinking leads to (partial) connectivity of the rubber particles via chemical bridging of grafted PE chains. Dynamic preparation conditions caused the connected structure to break-up, which led to a significant enhancement of the mechanical properties and the melt processability. The addition of 25-80 wt% extender oil resulted in a reduced complex viscosity and yield stress in the melt, without deteriorating the mechanical properties. The relatively good elastic recovery and excellent final properties of these high hardness TPVs can be explained in terms of the submicrometer rubber dispersions. 

The glass transition processes in foods may result from a rapid removal of water from solids. Based on that, e.g., the Tg values of anhydrous polysaccharides are high, and the food materials may decompose at temperatures below Tg (Kokini et al 1994 Roos and Karel, 1991b). The glass temperature transition affects viscosity, stickiness, crispness, collapse, crystallization, and ice formation, and can strongly influence deteriorative reaction rates. This provides a new theoretical and experimental framework for the study of food systems to unify structural and functional aspects of foods, described in terms of water dynamics and glass dynamics. 

Varying Concerns. Conservators concerns tend to lie in preservation of objects of value, rather than in analysis of wood or a better understanding of the process of wood deterioration. Conservators often deal with one-of-a-kind objects that require immediate attention in order to continue to exist as objects of interest. Therefore, conservators feel that they need to have highly reliable preservation methods available to them. The situational dynamic of conservation emphasizes the use of low-risk established techniques in the production of preserved objects rather than research into degradation processes or methods of preservation, a situation that tends to inhibit basic research in conservation laboratories. 

From the viewpoint of prediction of service lives, the photochemical deterioration processes of polymers used as paints and finishes are theoretically analyzed based upon unsteady state dynamics. Theoretical results are compared with experimental data under natural and accelerated exposure. Infrared spectra and scanning micrographs show that the deterioration proceeds continuously inwards from the surface, but differently with the exposure conditions. Parabolic (/t ) law was derived approximately for the increase in the depth of the deteriorated layer of polymers with time. Paying attention to the influence of the deterioration of polymeric finishes, the parabolic law involving a constant term was also derived for the progress of carbonation of concrete. These parabolic laws well predict the progress of deterioration and explain the protective function of finishes on reinforced concrete. 

Dynamic Analysis of Deterioration Processes of Polymeric feterials... 

The photochemical deterioration processes of polymeric materials often used as paints and finishes are studied both theoretically and experimentally. Theoretical models for the deterioration processes are developed based upon unsteady state dynamics. The results were compared with experimental data under outdoor and accelerated aging... 

Even if the principal cause of corrosion is carbonation or chloride penetration, construction defects (voids, honeycombs, early cracks, etc.) or other processes of deterioration (sulfate, freeze-thaw, dynamic loading, etc.) can contribute to the damage of the structure. These should be detected in order to take appropriate measures in the repair work. Furthermore, the condition of the structure with regard to stability must be investigated in order to define if strengthening is required. 

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