Arjen Boersma

Mobility and solubility of antioxidants and oxygen in glassy polymers. III. Influence of deformation and orientation on oxygen permeability

The mobility of small molecules in a glassy polymer is largely determined by the amount of free volume present in the material. The amount of free volume can be altered by changing the physical state of the polymer. Plastic deformation under compression reduces this amount, whereas the application of a tensile stress increases it. Furthermore, orientation of a polymer introduces an anisotropy in the free volume. The change in free volume was monitored by oxygen permeation experiments. A clear correlation was found between the draw ratio, plastic deformation and stress on the one hand and oxygen permeability on the other. Since the mobility of oxygen is an important parameter for the stabilisation of a polymer against oxidation, the physical state of the polymer can have a significant influence on the service life of the product.

Mobility and solubility of antioxidants and oxygen in glassy polymers II. Influence of physical ageing on antioxidant and oxygen mobility

The mobility of small molecules in a glassy polymer is largely determined by the amount of free volume present in the material. The amount of free volume can be altered by changing the physical state of the polymer. Physical ageing reduces this amount, whereas the thermal rejuvenation increases it. The change in free volume was monitored by oxygen permeation and antioxidant sorption experiments. A clear correlation was found between the physical ageing on the one hand and oxygen permeability on the other. Since the mobility of antioxidants and oxygen are important parameters for the stabilisation of a polymer against oxidation, the physical state of the polymer can have a significant influence on the service life of the product.

Dielectric study on size effects in polymer laminates and blends

In this article we will focus on the dielectric properties of laminates and blends of a partially conducting (the liquid crystalline copolyesteramide Vectra B950) and an insulating (polypropylene or mica) phase. Dielectric spectroscopy was used as a tool to obtain information about the influence of the dimensions of the conducting phase in these laminates and blends. With decreasing thickness of the conducting layer in the laminates, the measured permittivities deviate more and more from the values predicted using conventional dielectric mixture models. From this discrepancy it is possible to calculate the thickness of the charge layer (=Debye length) in the conducting phase and the thickness of this phase itself, using a model derived by Trukhan. This model incorporates not only conduction, but also diffusion of the charges. Similar experiments were performed on a system of Vectra B950 particles in a polypropylene matrix. After the derivation of a new model, which combines the Trukhan model for space charges with the Bottcher equation for dielectric mixtures, we could make a distinction between samples containing large and small particles. For samples containing small particles, it is even possible to determine the variation in particle sizes. However, the use of a Debye length of 1.1 µm obtained from the laminates resulted in particle sizes that were two times higher than the actual values.

Interfacial tension between a liquid crystalline polyesteramide and polypropylene obtained by dielectric spectroscopy

Dielectric spectroscopy is an unexplored technique in the elucidation of the morphology of polymer blends. Especially the appearance of interfacial polarization can reveal important information about the microstructure ofa polymer blend. A model system of liquid crystalline polymer fibers lined up in a thermoplastic matrix was investigated. After heating above the melting temperature of both phases, the fibers developed distortions which grew with time. Dielectric spectroscopy was used to follow the change in shape of the distorted fibers. The use of only two frequencies made it possible to increase the number of relevant data points in the initial stages of the fiber breakup process. From these measurements it was possible to calculate the growth rate and hence the interfacial tension between the two polymers.

Average particle size in polymer blends obtained by dielectric spectroscopy

Previously we focussed on the dielectric properties of laminates and blends consisting of a weakly conducting and an insulating phase. Dielectric spectroscopy was used as a tool to obtain information about the dimensions of the conducting phase. With decreasing thickness of the conducting layer in the laminates, the permittivities measured were found to deviate more and more from those predicted by the conventional, series mixture rule. This discrepancy allowed us to calculate the thickness of the ionic charge layer (or the Debye length) in the conducting phase and also the thickness of this phase itself, using a model derived by Trukhan. His mixture model incorporates not only conduction, but also diffusion of charges. DS was also performed on a blend of Vectra B particles in a polypropylene matrix. After deriving a new model, which combined Trukhans model with Bottchers equation for dielectric mixtures, we could calculate the average particle size. Here we will discuss which average particle size is actually determined by dielectric measurements.