Polymer PermeabilityJ. Comyn Polymers are permeable, whilst ceramics, glasses and metals are gener ally impermeable. This may seem a disadvantage in that polymeric containers may allow loss or contamination of their contents and aggressive substances such as water will diffuse into polymeric struc tures such as adhesive joints or fibre-reinforced composites and cause weakening. However, in some cases permeability is an advantage, and one particular area where this is so is in the use of polymers in drug delivery systems. Also, without permeable polymers, we would not enjoy the wide range of dyed fabrics used in clothing and furnishing. The fundamental reason for the permeability of polymers is their relatively high level of molecular motion, a factor which also leads to their high levels of creep in comparison with ceramics, glasses and metals. The aim of this volume is to examine some timely applied aspects of polymer permeability. In the first chapter basic issues in the mathema tics of diffusion are introduced, and this is followed by two chapters where the fundamental aspects of diffusion in polymers are presented. The following chapters, then, each examine some area of applied science where permeability is a key issue. Each chapter is reasonably self-contained and intended to be informative without frequent outside reference. This inevitably leads to some repetition, but it is hoped that this is not excessive. |
Contents
Introduction to Polymer Permeability and the Mathematics of Diffusion | 1 |
Permeation of Gases and Vapours in Polymers | 11 |
Case II Sorption | 75 |
Effects of Oxygen Permeation and Stabiliser Migration on Polymer Degradation | 119 |
Diffusion and Adhesion | 177 |
The Role of Polymer Permeability in the Control of Drug Release | 217 |
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absorption activation energy addition adhesive amorphous phase antioxidants barrier properties behaviour C. E. Rogers calculated cellulose Chem chemical chloride coating component composite concentration profiles constant containing controlled release copolymers crosslinking crystalline curves D. R. Paul decrease dependence diffusion coefficient diffusion process dosage forms drug release effect epoxide equation equilibrium experimental factors fibre Fickian film free volume front front velocity function gases glass transition temperature Henry's law humidity hygroelasticity increase initial interactions interface Irganox joints kinetics kJ mol¯¹ linear liquid low density polyethylene materials matrix measured mechanism membrane method moisture molar mass molecular observed oxidation oxygen packaging parameters penetrant molecules permeability permeation Pharm Phys plastic plasticisation polyamide polyisobutene polymer polymeric polyolefins polypropylene polystyrene predicted pressure reservoir device resin rubber sample shelf-life shown in Fig solubility solution sorbed stabilisers stress structure surface swelling temperature theory thickness tion transport uptake values water vapour