Self-Healing Polymer Composites with Enhanced Strength for Use in Protective Textiles

Self-healing materials have the potential to increase the lifetime of products exponentially through both non-reversible healing and reversible healing processes. For instance, non-reversible healing has been demonstrated with the use of micro-spheres filled with healing-compounds used to mitigate micro-crack propagation in materials like concrete or asphalt. Upon use, however, micro-sphere rupture is irreversible. Reversible self-healing traditionally takes the form of polymeric or rubber materials designed to exhibit both covalent and ionic bonds within the same material. Reversible self-healing materials not only repair other products but can have extended lifetimes themselves. However, reversible self-healing materials are often mechanically weak when compared to non-reversible self-healing materials, thereby, limiting applications. In this work we report mechanical results of aramid nanofiber (ANF) reinforcement of polycaprolactone (PCL). These results and future testing will then be applied to self-healing polymer materials to observe the mechanical reinforcement factors.<br/> <br/>To fabricate the aramid nanofibers, macroscale fibers were broken down through hydrolysis in a dimethyl sulfoxide and potassium hydroxide solution. Fibers were then reformed through the addition of water and filtered to remove larger fibers. Following filtration, the remaining fibers were suspended in PCL that had been pre-dissolved in trifluoroethanol. The ANF/PCL suspension was sonicated for dispersion of the nanofibers within the polymer matrix. For this study, the samples examined were: 1) PCL melted and impregnated with ANFs before solidifying, 2) PCL that was solvent-dissolved before ANFs were blended into the liquid polymer and then let dry to evaporate solvent, 3) and solvent-dissolved PCL/ANF composites (1 and 2 wt%) that were embedded with ANFs before solvent was evaporated from the samples. Mechanical testing for this study included compressive, tensile and split-Hopkinson pressure bar (SHPB). Results of this testing demonstrated an increase of compressive yield strength by 22 %, an increase in tensile Young’s modulus by 28 %, and a decrease in ultimate strength by 32 %. SHPB testing also revealed an increase in dynamic resistance when absorbing impacts at speeds ranging from 10 to 22 m/s where impact duration lasted as much as 23 % longer. Further testing will be performed to characterize shear performance of the samples as well as the Charpy impact energy absorption. Transmission electron microscopy and energy dispersive spectroscopy will be used to correlate embedded fiber morphologies and distributions with mechanical properties.<br/> <br/>The primary objective of this work is to provide self-healing textiles with enhanced strength for soldiers in the field to maintain protection following damage of protective gear or uniforms. Following determination of a preferable aramid concentration in a reinforced polymer matrix, the polymer will be electrospun into fibrous textiles for further mechanical testing, to monitor properties following impact and self-repair, and determine sustainability.