Abstract
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.
Highlights
Nanofibers represent a powerful tool to design advanced structural and functional materials [1], and it is growing more and more the number of their applications, such as in biomedical devices, filtration media, wearable devices and electronics [2,3,4,5]
Carboxylated nitrile butadiene rubber (NBR) NIPOL 1072CGX was purchased from Zeon Chemicals [68%mol butadiene (Bu), 28%mol acrylonitrile (ACN), 4%mol methacrylic acid (MAA)]
A carboxylated Nitrile Butadiene Rubber (NBR) polymer containing 4%mol methacrylic acid (MAA) was investigated, the latter comonomer used for furthering miscibility with epoxy resins
Summary
Nanofibers represent a powerful tool to design advanced structural and functional materials [1], and it is growing more and more the number of their applications, such as in biomedical devices, filtration media, wearable devices and electronics [2,3,4,5]. Toughening is a requirement for brittle materials and can be attained by addition of already cross-linked rubbery particles, coreshell particles with rubbery core and glassy shell for easiness of handling, or liquid rubber homogeneously mixed to the polymers [9,10] Within this frame, the possibility of manufacturing rubbery nanofibers to be used as toughener for, as an example, local modification of epoxy resin systems, in particular in composite materials, appears as an optimal combination of the two previously introduced toughening approaches. Upon evaluation of the thermodynamic and the processing peculiarities, the production of nanofibrous membranes containing up to 80%wt of linear (non-cross-linked) carboxylated Nitrile Butadiene Rubber (NBR), commonly named Nipol, is presented Such carboxylated rubber precursor was chosen for its renowned compatibility with epoxy resins, for the modification of whom this work is intended. The obtained results demonstrate that, via electrospinning of liquid rubber with PCL, it is possible to attain the formation of a TPE-like structure that keeps together the fibers without the need for a chemical crosslinking, but it provides excellent mechanical properties to the membrane without the need of additional treatment
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