Self-Healing Surlyn Ionomer and Polybutadiene Thermoplastic Elastomer Blend via two-way Shape Memory Effect

ABSTRACT: When it comes to the intrinsic self-healing of polymer composites, many thermally actuated polymers rely on endothermic process for polymer surface rebinding to occur as well as a means to trigger crack closure. One of the well-researched areas into the mechanisms for such crack closure is the close then heal (CTH) method of self-healing. For self-healing to occur, the cracked surfaces need to be sufficiently brought in close contact to enable healing to take place and heat is a popular means of actuation for the driving force needed for this to occur. Nonetheless, application of these heat triggered self-repair of composites in very low temperature environment or inadequate heating supply reduces reaction time, efficiency of crack closure and success of effectual self-healing.

This study aims at fabricating a thermoplastic elastomer system made from poly (ethylene-co-methacrylic acid) under the trade name Surlyn® 9520 as the thermoplastic phase and cis-1,4- polybutadiene (PBD) employed as the elastomeric phase material. Both materials have been shown to possess two-way shape memory effect, with both experiencing repeatable elongations upon cooling (EUC) and contraction upon heating (CUH), as a result of proper one-time programming that introduces internal stress into the polymer networks and enables energy storage. By exploring the reversible melting/crystallization in the polymer network, this study aims at achieving a driving force enough to narrow and eventually close a crack in the material, thereby promoting proper self-healing.

Different concentration ratios of Surlyn and PBD were prepared to study the performance of the thermoplastic-elastomer blend. Preliminary DMA analysis shows that all the samples are represented by single tan delta peaks which appear between the reported glass transition temperatures of the constituent materials. This is indicative of the compatibility of the thermoplastic-elastomer blend. The glass transition temperatures across the various concentration ratios is currently being verified using differential scanning calorimeter. Each of the blend ratios will be tested for shape fixity and stress recovery, then further employed to investigate their ability to close cracks in the material. Preliminary tensile tests show that the samples with higher concentration of thermoplastic phase show better tensile strength as high as over 35% more in some cases. It is anticipated that this will translate into high closure stress that will help close the two fractured surfaces before healing proceeds.

Characterization works are continuing, while the shape memory behavior efficiency of the blend is being studied in order to explore and optimally utilize this important property of this recyclable material.

KEYWORDS: thermoplastic elastomer, shape memory polymer, close-then-heal, crack closure, self-healing