Krijn Dijkstra

Modelling the moisture vapour transmission rate through segmented block co-poly(ether–ester) based breathable films

Abstract Water permeability is an important property of films used in, for instance, protective clothing or construction applications. There are a number of standardised test methods available for evaluating the permeability of films. In one class of tests, there is a direct contact between the polymer film and water; in another class of tests there is an air layer between water and the film. This paper deals with the modelling of water permeability of two commercial types of segmented block co-poly(ether–ester). Water transport in the films is modelled assuming a simple Fickian diffusion behaviour, sorption isotherms are described in terms of either a Zimm–Lundberg based cluster model or Henrys law. Mass transport in the air layer is described in analogy with heat transport for the classical Benard problem. Using this analysis it is shown that water permeability for both films and for both types of tests can be predicted as a function of the film thickness. There is a good agreement between the model predictions and the experiment.

Polyamide-rubber blends: microscopic studies of the deformation zone

The morphology of injection moulded samples of polyamide—polybutadiene blends (85.15) with an average particle size of 0.3 μm was studied. The samples were fractured in a notched tensile test at crosshead speeds of 10−4 and 1 ms −1 and the structure of the deformation zone was studied using various techniques: polarized light microscopy, scanning electron microscopy, transmission electron microscopy on stained cut samples and carbon replicas, and selected area electron diffraction transmission electron microscopy. The deformation zone of samples tested at 10−4 ms−1 was found to consist of two layers. Far from the fracture surface a layer was observed with more or less round cavities and with cavities in the rubber particles, while near the fracture surface a layer with strongly deformed cavities (length/diameter ratio of 5–10) could be seen. In the samples tested at 1 ms−1 the deformation zone was found to have three layers. In addition to the two previous layers an extra layer next to the fracture plane was found. This layer was 2–3 μm thick with round rubber particles and no orientation of the matrix material. This indicates that, at the high deformation speed of the test, relaxation in the melt took place, suggesting that the material around the crack tip was molten during fracture.