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The dimensional stability of paper products is a well-known problem, affecting multiple engineering applications. The macroscopic response of paper to moisture variations is governed by complex mechanisms originating in the material at all length-scales down to the fiber-level. Therefore, a recently-developed method, based on Global Digital Height Correlation of surface topographies is here exploited to measure the full-field hygro-expansion of single fibers, i. e. a surface strain tensor map over the full field of view is obtained as function of time. From the strain field, the longitudinal and transverse hygro-expansion and principle strains can be calculated. Long- and intermediate-duration dynamic tests are conducted on softwood and hardwood fibers. A large spread in the softwood fiber’s transverse and longitudinal hygro-expansion coefficient ratio was found, while hardwood fibers behave more consistently. Computing the principle strain ratios reduces this spread, as it takes into account the variations of the deformation direction, which is directly affected by the micro-fibril angle (MFA). Furthermore, long-duration tests allow identification of the half-times at which the fibers equilibrate. Finally, the determined major strain angles for all fibers are consistent with the MFA ranges reported in the literature.

Whisker multiwalled carbon nanotubes (WMWCNTs) and multiwalled carbon nanotubes (MWCNTs) were synthesized via chemical vapor deposition (CVD), and were characterized by scanning electron microscope (SEM), X-ray diffraction (XRD) and Raman spectroscopy. Paper fibers were used as matrix material, WMWCNTs and MWCNTs as functional material. Paper fibers were mixed with dispersed WMWCNTs and MWCNTs by speed-cutting procedure in water. Then the composite papers were fabricated by vacuum filtration method. The electrochemical performance of the supercapacitor was tested by cyclic voltammetry, galvanostatic charge/discharge. The testing results indicate the supercapacitor has a maximum capacitance of 120F/g at a scan rate of 1mV/s and has a specific capacitance of 51.5F/g at 0.4A/g. The maximum energy density and power density reach 63.7Wh/kg and 3.99kW/kg respectively in the current range of 0.4-1.4A/g.