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Polyimide-silica hybrids based on polyamic acid and an acetylene-terminated isoimide as matrices for carbon fibre composites

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posted on 2017-06-07, 15:25 authored by Constantinos Xenopoulos
A study was carried out on formulations of organic-inorganic hybrids and their subsequent use as matrices for unidirectional carbon fibre-reinforced composites. The hybrids consist of low molecular weight polyimide precursors and silica which is generated in-situ via the sol-gel route. A special feature of these systems is the use of organofunctional trialkoxysilanes as coupling agents for the two phases and for controlling the resultant morphology. Enhancements are obtained in physicochemical, thermal and mechanical properties of hybrids through morphological modifications achieved in the parent polyimide and silicate materials. Small variations to the composition of the precursors display a substantial effect both on the kinetics of the associated reactions and the final properties of hybrids, often as a result of a change in miscibility of the organic and the inorganic components of the system. The processability of the matrix was evaluated with respect to the fabrication of composites, which in this case is strongly influenced by the gelation behaviour of both the organic pre-polymer and also the inorganic sol-gel component. The kinetics of gelation reactions were examined by dynamic viscometry and by practical tests based on visual observation of the cessation of flow. Differential scanning calorimetry, infrared spectroscopy, thermogravimetric analysis and electron microscopy formed part of the evaluation of the matrix materials. Composites were produced by application of the matrix solution from a variety of formulations on pre-tensioned fibres, followed by vacuum drying and curing under pressure at high temperatures. The properties of these composites were determined by such methods as dynamic mechanical thermal analysis, flexural testing and thermomechanical analysis. From the results obtained in this study, it is concluded that the inclusion of silicate phase in a polyimide matrix in the form of fine co-continuous networks improves the thermal and mechanical properties of the base material, although these are dependent on the overall silicate content and the amount of the coupling agent. High loadings of the coupling agent can cause degradation by chain scission and a reduction of the crosslinking density of the organic pre-polymer.

Funding

Defence and Evaluation Research Agency (DERA)

History

School

  • Aeronautical, Automotive, Chemical and Materials Engineering

Department

  • Materials

Publisher

© C. Xenopoulos

Publisher statement

This work is made available according to the conditions of the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0) licence. Full details of this licence are available at: https://creativecommons.org/licenses/by-nc-nd/4.0/

Publication date

1999

Notes

A Doctoral Thesis. Submitted in partial fulfilment of the requirements for the award of Doctor of Philosophy of Loughborough University.

Language

  • en

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