Auto-Repairing silicones in CAble DEvelopment – ARCADE

First, a model, published material for which self-mending is known, will be studied in detail to explore the broken interfaces and their reparation. Second, we will use different strategies to modify a commercial TPE (a silicone urea copolymer) so as to render it self-mendable. Third, all three academic partners will work to prepare different families of elementary silane stickers, graft them on silicone chains and at the surface of silica particles, and process them to generate improved materials.

At IMP, we have carried out two sets of study. The first one was, as proposed in Task 1, to adapt Leibler/Wang chemistry to prepare self-mending silicone materials. Doing so, it turned out that the chemistry was less straightforward and reproducible than described. We have then conducted a systematic model study to understand each step of the synthesis, and are now confident with the chemistry behind it. We are currently applying this technique to grafted aminated silicones and have already prepared two generations of very soft silicone materials. The self-healing ability has not been proven for these materials so far. In another strategy, corresponding to the Task 3, we have set our own chemistry to tailor both the nature of the functional groups introduced in the polymer, and the extent of molar mass elongation. We are currently testing one cicatrizing material.
At UPMC, as scheduled in Task 2, five TPEs have been synthesized by condensation between amino-terminated PDMS and several diisocyanates. Chain stoppers were designed to bring dynamic properties to the materials. About 20 chain stoppers have been synthesized and evaluated as additives in TPEs. Several of them show very encouraging self-healing properties.
The MATEIS laboratory has participated in the characterization of the materials. A post-doc who started 03 april 2017 will gather more results soon.

One material exhibits a very relevant self-healing property, as shown on the Figure attached.

Communications:
1. ISPO 2017, Copenhagen (Poster, L. Fauvre and INSA)
2. EPF 2017, Lyon (Poster, L. Simonin and UPMC)
Patent:
One in preparation (UPMC).

The ARCADE project aims at generating elastomeric materials whose properties meet the requirements of the rubber industry in terms of hardness, strain and stress at break, while possessing unique, efficient self-healing properties. The final application is very challenging: we aim at generating cable sheaths typically used in French TGVs, where specifications require both “real” mechanical and insulation properties at elevated temperature and auto-reparation ability at room-temperature.

Such goal is a real challenge since:
i) strong mechanical properties are generally associated with high crosslinking density and thus slow molecular mobility, which can hinder the self-healing mechanism that a priori proceeds via chain diffusion;
ii) rising the temperature generally decreases supramolecular forces and thus soften thermoplastic elastomer (TPE) materials that are targeted here.

The innovating strategy proposed to debunk these difficulties consists in functionalizing both the polymer matrix and the surface of the silica filler with different stickers, enabling several levels of (weak and strong) supramolecular interactions in the material, the intensity of which will be controlled also with the temperature.

A convergent approach is singled out, involving the simultaneous, separate competencies of all partners (supramolecular chemistry, macromolecular chemistry, material physical chemistry) to multiply the chances of success.
4 tasks have been selected, 3 conducted in the row by the 3 academic partners, and 1 transverse task ensured by the industrial partner and the physical-chemists from the consortium.

First, a model, published material for which self-mending is known, will be studied in detail to explore the broken interfaces and their reparation, using the complementary expertise of the partners.
Second, we will use different strategies, according to the different partners’ knowledge, to modify a commercial TPE (a silicone urea copolymer) so as to render it self-mendable.
Third, all three academic partners will work hand in hand to prepare different families of elementary silane stickers, graft them on silicone chains and at the surface of silica particles, and process them to generate improved materials.
The transverse task will consist in testing mechanically the bulk properties of the new materials, in an academic lab for conventional characterizations and in the industrial research center for specific, application-driven testing.

The expected outputs of this project are in step with the fundamental and applied challenges. We want to understand the physical chemistry behind the self-repairing polymer systems, while mastering the processing of materials made of silicone (which procedure could be applied to other types of polymers) of practical uses for the elastomer industry.