Flexible supramolecular matrix based self-healing composites

FLEXIBLE SUPRAMOLECULAR MATRIX BASED SELF-HEALING

COMPOSITES

F. Sordo 1, V. Michaud 1

1 _{Laboratory of Polymer and Composite Technology (LTC), Ecole Polytechnique Fédérale de}

Lausanne(EPFL), CH-1015 Lausanne, Switzerland – e-mail: federica.sordo@epfl.ch; veronique.michaud@epfl.ch

Keywords: flexible composite, self-healing, supramolecular system, adhesion study, processing

ABSTRACT

Supramolecular polymers gained a great success in the last years as self-healing materials and many different systems have been developed. These polymers combine the advantages of intrinsic and autonomic self-healing systems.

In 2010, Montarnal et al. developed a class of epoxy-based hybrid networks that combine both chemical and supramolecular hydrogen-bonding crosslinks and that are characterized by self-healing properties. These polymers are moreover a priori compatible with composite processing techniques, such as vacuum infusion. For this reason the development of composite materials including the self-healing ability of this type of matrix represent a promising way forward.

In this poster, we will present the development of supramolecular matrix based self-healing composite materials. A supramolecular network with 50% of epoxy cross-links will be used as matrix material, and glass fibers as reinforcements. In particular, attention will be focused on the set up of the composite processing window, and on the self-healing behavior of the obtained materials themselves as well as at the interface between the matrix and the reinforcement. The latter will be studied through pull-out tests on single fiber model composites.

This PhD research work is part of the SHeMat project "Training Network for Self-Healing Materials: from Concepts to Market", a training and research network funded within the scope of the “Seventh Framework Programme” by the European Commission’s “Marie Curie” programme.

1. INTRODUCTION

In 2010 Montarnal et al.[1], combined the chemistry of epoxides with supramolecular chemistry, and thus developed an intrinsic hybrid-supramolecular self-healing polymer which network is constituted by both chemical and physical bonds (hydrogen bonds). The aim of this project is to further characterize the self-healing properties of this class of supramolecular polymers and to evaluate their potential as matrices in textile composite materials. The mechanism of interaction of these polymers towards various materials used as reinforcements is analyzed, as well as the possibility of observing healing effects at the interface after fiber debonding.

2. MATERIALS

For this part of the project, the industrial Reverlink HR-NR® produced by Arkema was used as matrix material. The recommended cure cycle is 130°C for 24 hours. The resulting product presents a supramolecular hybrid network composed of 50% of supramolecular hydrogen bonds and 50% of covalent bonds (this composition corresponds to HN-50-HC synthesized by Montarnal et al.[1]). A low viscosity epoxy resin (LME 10435, Huntsman) cured for 7 hours at 80°C using a polyamine preparation (LME 10436, Huntsman) as hardener in 100:123 weight ratio, was used to produce a soft epoxy material as material of reference for the interface properties study. 125 μm diameter optical glass fibers (FGN 50/125, Alcatel) were used for the adhesion study. For composite processing, a glass fiber mat and plain glass woven fabric was used.

3. METHODS

The curing process of Reverlink HR-NR® was studied with an AR 2000 ex (TA instruments) rheometer, with 25mm Al parallel plates geometry, using a time sweep method with 1% of applied strain, and 1 Hz.

The sensitivity towards humidity was evaluated by subjecting the material to two different relative humidity environments (25%RH, climatized room, and 22°C-90%RH obtained using a KNO3 saturated solution in a dessicator) and measuring the

weight percentage of moisture absorption, and in parallel by evaluating the water uptake after samples immersion in distilled water at 23°C (ASTM D570).

The healing properties of Reverlink HR-NR® were evaluated trough tensile tests using a tensile testing machine UTS TestSysteme (Germany) with a 50 N load cell and a constant crosshead displacement rate of 25 mm/min. Dog-bone specimens (ASTM D412) were produced by pouring the liquid unreacted resin in a silicon mold and curing them. The healing of the samples was measured by cutting them with a razor blade in the Gauge length and bringing back the cut surfaces in contact together. The healing efficiency was calculated by comparing the stress at break values of mended samples after different healing times and of virgin samples.

The adhesion properties and the matrix-fiber interface healing behavior after debonding of Reverlink HR-NR® towards glass fibers were evaluated with pull-out tests and SEM analysis. Pull-out samples were realized pouring the resin in cylindrical molds (10mm of diameter and different heights) in which a glass fiber passed through the center and they were tested on a tensile testing machine UTS TestSysteme (Germany) with a 1000 N load cell and a constant crosshead displacement rate of 1 mm/min. While the adhesion properties of the supramolecular polymer were evaluated through a traditional single fiber pull-out test, the healing properties at the interface study was carried out with a partial pull-out of the fiber, followed by a complete pull-out test at different healing times. Pull-out tests using a soft epoxy resin (LME 10435, Huntsman) as polymeric matrix were also performed in order to compare the Reverlink HR-NR® properties. SEM morphological analysis on pull-out specimens was performed using a Philips (FEI) XLF-30 FEG scanning electron microscope. The tensile tests as well as the pull-out tests and the SEM analysis are still in progress. First impregnation trials were performed impregnating 10 layers of glass fiber mat and of glass woven fabrics with Reverlink HR-NR® using a vacuum resin infusion technique (VIP).

4. RESULTS

Figure 1(a) and (b) report the dynamic shear modulus (G’ and G’’) and the complex viscosity values of Reverlink HR-NR® at 130°C respectively in function of the curing time. The gel time is 194 minutes and the processing window of circa 120 minutes. The same test was performed at different temperatures and using multiple steps curing processes in order to evaluate the best curing process able to reduce the total curing time, maintaining the gel time and processing window values, that are advantageous for a composite processing.

Figure 1 : (a) LogG’ and Log G” and (b) complex viscosity values in function of curing time at 130°C.

The moisture and water uptake curves reported in Figure 2 show the material sensitivity towards humidity. Consequently it is important to pay attention to the storage conditions as well as at the environmental conditions during tests.

Figure 2: Moisture content and water absorption in weight percentage in function of the exposure time.

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Figure 3 presents a SEM image of a pull-out sample. The image clearly shows the good wettability and adhesion of the supramolecular matrix on the glass fiber.

Figure 3 : SEM image of a glass fiber Figure 4 : Glass fiber mats impregnated embedded in Reverlink HR-NR®. with Reverlink HR-NR®.

Finally, impregnation trials were performed on 10 layers of glass fiber mats and glass woven fabrics using a vacuum infusion technique (VIP). In Figure 4 an example of glass fiber mats impregnated plate is reported, demonstrating the feasibility of the infusion processed developed for these materials.

5. CONCLUSIONS

Rheological and vacuum infusion processing analysis showed that Reverlink HR-NR® is a suitable matrix for composite processing, although sensitive to humidity. Self-healing and pull-out tests are still in progress, but from SEM analysis it is possible to already observe a good interaction between the polymeric matrix and glass fiber.

ACKNOWLEDGEMENTS

J.P Disson of Arkema is gratefully acknowledged for providing Reverlink HR-NR® and for technical discussions, as well as F. Tournilhac, L. Leibler and N. Lourero of ESPCI for collaboration.

REFERENCES

[1] D. Montarnal, F. Tournilhac, M. Hidalgo, L. Leibler, Epoxy-based networks combining chemical and supramolecular hydrogen-bonding crosslinks, Journal of Polymer Science: Part A : Polymer Chemistry 48 (2010) 1133-1141.