Filler Controlled Morphology in Polymer Blends
Doctoral thesis, 1997
The morphology of a polymer blend can be altered very dramatically when a filler is added. Depending on the mutual interactions of the polymers and their individual interactions with the filler, many different filler distributions are possible. Inverse gas chromatography was the key tool to quantify the polymer-solid interaction potentials in terms of Lewis acid-base properties. These forecasted interaction strengths at the whisker-polymer interface coincided with the observed preferential adsorption. Selective adsorption of the minority polymer component made it form three-dimensional web structures with the whiskers in the matrix of the majority component. This ability to form co-continuous structures was quantified as electrical conductivity of blends containing the intrinsically conducting polymer poly(3-octyl thiophene). For a properly selected majority polymer the conductivity of the three-component composite increased several orders of magnitude.
Interactions between polyamide-6 and the whisker surface are strong enough to perturb crystallization in a zone by the interface. Selective adsorption was exploited to create virtually highly filled composites as a non-interacting polymer was added as a processing aid. That polymer was extracted and left extreme composites comprising only whiskers and polamide-6 interphase. In order to collect data for derivation of a crystallinity gradient by the filler surface, the ratio of polyamide-6 to processing aid was varied.
Once a beneficial phase morphology has been achieved, successive processing can easily rupture it unless its rheological limitations are considered. For example, the high shear rates created during injection molding ruined the co-continuous structure created during compounding of poly(styrene-co-acrylonitrile)/polyamide-6/whiskers. However, the ruptured morphology could have been restored by annealing at the processing temperature.
In blends with components of comparable polymer-whisker interaction strength and substantial viscosity difference the whiskers are absorbed by the phase that minimizes the viscosity of the three-component system. Accordingly the whiskers were absorbed by the high viscosity phase unless supporting transformation of the minority low viscosity phase from dispersed to continuous. Such transformations and other shear induced morphological changes were followed as viscoelastic changes during steady and/or harmonic shear. This methodology has the prospects to become a valid instrument to optimize the processing route of blends and multicomponent systems.
filled polymer blends
Lewis acid-base properties
polymer solid interactions