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The aim of this work was to reveal the moisture absorption–desorption–resorption characteristics of epoxy and epoxy-based nanocomposites filled with different multiwall carbon nanotubes (MWCNTs) by investigating the reversibility of the moisture effect on their thermomechanical properties. Two types of MWCNTs with average diameters of 9.5 and 140 nm were used. For the neat epoxy and nanocomposite samples, the moisture absorption and resorption tests were performed in atmospheres with 47%, 73%, and 91% relative humidity at room temperature. Dynamic mechanical analysis was employed to evaluate the hygrothermal ageing effect for unconditioned and environmentally “aged” samples. It was found that moisture sorption was not fully reversible, and the extent of the irreversibility on thermomechanical properties was different for the epoxy and the nanocomposite. The addition of both types of MWCNTs to the epoxy resin reduced sorption characteristics for all sorption tests, improved the hygrothermal and reduced the swelling rate after the moisture absorption–desorption.

The creep-recovery behaviour of two types of high density polyethylene (HDPE) filled with multiwall carbon nanotubes (MWCNT) is investigated. Nanocomposites with various contents of MWCNT were produced by using a commercially available masterbatch aimed to transfer the gained knowledge to an assessment of properties of industrial-scale products. Nanocomposites are characterized by the improved creep resistance compared to the neat polymers. Incorporation of 10 wt.% of MWCNT into the polymers resulted in a decrease of creep and residual strains for more than 3 and 5 times, respectively. The reinforcing effect of the nanofiller appeared also in a great increase of the elastic modulus (up to 100%) and ultimate strength (up to 60%) as well as a decrease of the coefficient of linear thermal expansion (down to 17%) of HDPE. Carbon nanotubes, being also good heat conductors, greatly contributed to the improvement of polyethylene’s thermal conductivity (up to 60%). Electrical percolation is determined below 2 wt.% of MWCNT. The electrical resistance changes monitored during creep-recovery tests are well correlated with the overall strain changes and residual strains in nanocomposites, that approve their in situ strain sensing capability during inelastic and long-term deformation.

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