Strength of individual hardwood fibres and fibre to fibre joints

In the present study hardwood fibre strength and fibre to fibre joint strength measurements using bleached, industrial eucalyptus kraft pulp have been performed. The device used for the measurements was a micro bond tester developed at Graz University of Technology. Results were compared to those obtained in previous studies dealing with both, hardwood and softwood. The mean force to break individual hardwood joints ( $$1.82\,\pm \,0.48\,\hbox {mN}$$ ) was found to be 72 % smaller than that of unbleached softwood joints and is mainly governed by the bonded area of the joints. Furthermore, the optically bonded area (OBA) of hardwood fibre to fibre joints was investigated. OBA of hardwood joints is about 81 % smaller than those of softwood and the reduction is attributed to smaller width and lower collapsibility of the fibres. Compared to softwood, the force per unit OBA of hardwood is 1.72 times higher ( $$5.32\,\pm \,1.46\,\hbox {MPa}$$ ). This difference is believed to be due to the well known size effect. Single fibre tensile testing resulted in a mean breaking load of $$38.81\,\pm \,16.31\,\hbox {mN}$$ and show a 76 % reduction when compared to softwood. The reduction is attributed to the smaller cross sectional area and the effect of bleaching.