Electrically conductive kraft lignin-based carbon filler for polymers

Commercial kraft lignin was thermostabilised by heating up to 250 °C at a rate of 0.01 °C min−1 in ambient atmosphere. Subsequent carbonisation at 2000 °C in argon atmosphere yielded carbon microparticles containing ordered graphitic domains. Micromechanical characterisation by nanoindentation yielded average values of 1.39 GPa for hardness and 8.2 GPa for the indentation modulus of carbon particles. Composite films of polycaprolactone with different carbon content were prepared by means of solvent evaporation casting. Tensile testing revealed an increase in composite stiffness while strength and elongation at break decreased with the loaded amount of carbon microparticles. Electrical conductivity of the composites was exemplarily observed for a carbon microparticle loading of 15% (w/w). Using a composite film as strain sensor in three-point bending, high sensitivity of electrical conductivity towards the applied strain was observed.