ABSTRACT
Thermoplastic materials have established a reputation for long-term reliability in low-pressure gas and water distribution pipe systems. However, occasional Slow Crack Growth (SCG) and Rapid Crack Propagation (RCP) failures still occur. SCG may initiate only a small leak, but it has the potential to trigger RCP, which is much rarer but more catastrophic and destructive. RCP can create a long, straight or meandering axial crack path at speeds of up to hundreds of meters per second. It is driven by internal (residual) and external (pressure) loads and resisted by molecular and morphological characteristics of the polymer. The safe installation and operation of a pipe throughout its service lifetime therefore requires knowledge of its resistance to RCP, particularly when using new materials. In this context, the RCP resistance of five different polyamide (PA) 12 grades was investigated using the ISO 13477 Small-Scale Steady State (S4) test. Since these grades differed not only in molecular weight but also in their use of additives (impact modifiers and pigments), structure-property relationships could be deduced from S4 test results. A new method is proposed for correlating these results more efficiently to evaluate each grade using the crack arrest lengths from individual S4 test specimens.
ABSTRACT
The encapsulation of pharmaceutical drug molecules in silica gels during the sol-gel synthesis and their kinetic release profile in aqueous solutions were systematically investigated in dependence of synthesis pH(S) and extraction pH(E) values. Six pH values in the range from 1 to 6 were chosen in a 6 × 6 two-dimensional matrix to screen the first-order initial dissolution rate constant and the total amount of released drug. Characteristic differences are discovered in such two-dimensional pH mapping profiles for the molecules with different ionization behavior and they are explained by surface imprinting and encapsulation processes. Remarkably, these encapsulations must occur either in the particles of the sol solutions or during the rapid liquid-solid transition of the spray-drying process employed in this study. This pH mapping method is suggested as a novel tool to probe noncovalent imprinting and encapsulation processes in sol-gel-derived materials with embedded guest molecules.
