Rubbery nanofibers by co-electrospinning of almost immiscible NBR and PCL blends

The paper presents a simple method for producing rubbery nanofibers without additional crosslinking required. Electrospinning's fast solvent evaporation is able to induce in liquid NBR/PCL pairs thermoplastic elastomeric (TPE) structure that holds stable over time without any further processing. The slight relative solubility of the polymers pair promotes a homogeneous blend formation with low Tg regions of blended NBR/PCL, avoiding phase separation. Such nanofibers show also a PCL-like crystal phase that is surprisingly higher than plain PCL nanofibrous counterpart and seemingly promoted by NBR/PCL interaction at molecular scale. The obtained nanofibrous-TPE morphology is reproducible, stable with time up to at least two years and is detected in a wide range of blend compositions (up to 80%wt NBR). Such a morphology reflects in good mechanical properties, which are analysed with a fitting model taking into account nanofibrous structure. Its impressive fitting ability helps interpretation of tensile tests behavior, carried out via normalization of force data with respect to sample mass, highlighting the contribution of liquid rubber in improving both elastic modulus and properties at failure. Such rubbery nanofibers represent a cost-effective powerful tool for the production of advanced self-damping composite materials with improved overall mechanical properties.