Post doctoral Project:
Damage healing in composite materials
employing supramolecular polymers
Start / End:
August 2009 - July 2011
This research is sponsored by IOP/SenterNovem,
part of Agentschap.nl.
UNIVERSITY OF TWENTE.
Faculty of Engineering Technology
Chair of Production Technology
Address: Building Horst, Room N131
P.O. Box 217
7500 AE Enschede
Phone: +31 (0)534892569
Damage healing of fibre reinforced composite material with a thermoplastic matrix material based on supramolecular polymers.
This is a collaborative research project between Production Technology Group at the University of Twente and Supramolecular Polymer Chemistry Group at the Technical University of Eindhoven.
The project is supported by IOP Self Healing Materials, no. SHM08727.
Supramolecular polymers (SMP’s) are a new and interesting class of polymers that use non-covalent bonds to hold the repeating units together. Several types of such polymers exist of which the hydrogen-bonded polymers with ureidopyrimidinone (UPy) groups are very promising for healing of cracks due to their thermo-reversible behaviour.
Healing of delamination damage in fibre reinforced composite material can be done by heating matrix to a sufficiently high temperature. Matrix is expected to flow into the damaged regions to close cracks. Then, polymer molecules of the matrix material will be able to diffuse to either side of the damaged regions to actually heal/weld it.
The research project concentrates on the possibilities and limitations of supramolecular polymers. The project comprises both experimental work, including composite manufacturing and composites testing, and theoretical modelling for optimisation purposes.
The experimental work is carried out to determine the healing behaviour of a delaminated region as a function of local and global conditions (e.g. stress, temperature, time). The quality of the healed interface is determined by mechanical testing and microscopy. The results of the experimental work are used to create a composite healing model. The model’s main purpose is to facilitate the optimisation of the self healing properties of the thermoplastic composite material. The model simulates the time dependent healing of the damage upon heating and cooling. It provides the general mechanical properties of the composite material in various stages of healing.
As a start readily available supramolecular polymers, supplied by SupraPolix BV, were used as an adhesive layer between multilayered carbon fibre / polyetherimide (CF/PEI) unidirectional composite materials. A polyol functionalized with UPy-groups, supramolecular polymer SP1 (supplied by SupraPolix) was investigated to assess its self-healing adhesive properties. At room temperature, SP1 is a rubber-like viscoelastic solid with low tensile modulus. The viscosity of the SP1 was determined as a function of temperature up to 150 °C. Above this temperature irreversible changes occur to the UPy-groups that destroy their reversible character.
After Double Cantilever Beam (DCB) tests and separation of sample sides, a thin layer of a supramolecular polymer was applied to bond both sample sides. After a healing cycle at specific conditions (temperature, pressure, time) the DCB-test was repeated. On average a value of GIc = 0.6 kJ/m2 was determined as compared to a value of GIc = 1.2 kJ/m2 in the case of CF/PEI samples without supramolecular adhesive layer. Performing the healing cycle again under the same conditions, without adding more supramolecular polymer as adhesive at the crack interface, shows that the same GIc (0.6 kJ/m2) values can be reached. These results indicate that the supramolecular polymers have the potential to heal delamination type of damage in continuous fibre reinforced composite materials.
Next research efforts are directed to the synthesis and mechanical characterization of polymers that could be used as matrix material for fibre reinforced structural composites with sufficiently high modulus and toughness.