Self-reinforcing composites from commercial chemical pulps via partial dissolution with NaOH/urea

Self-reinforcing composites (SRCs) were produced from various commercially available chemical pulp fibers by the partial dissolution method using aqueous sodium hydroxide/urea (NaOH/urea) solvent. Surfaces of fibers dissolve during solvent treatment and in regeneration stage form a matrix between fibers improving mechanical properties. The ability of solvent to dissolve cellulose from fiber surfaces have large influence on properties of produced SRCs. The potential for use of bleached spruce, eucalyptus, bleached and unbleached pine, and abaca pulp as raw materials for SCR was investigated by producing SRCs and comparing the field-emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), tensile strength to the untreated counterparts. Also, a short crush index test is measured for cellulose based SRCs for first time in this study, which is widely used test illustrating compression resistance. The tensile test results showed that bleached pulps and eucalyptus had the largest increase in mechanical strength by a factor of more than 2 up to a value of 52 kNm/kg. In unbleached pine, the lignin seems to hinder the dissolution process, leading to smaller improvements of mechanical properties, while the solvent was not able to dissolve abaca fibers at all. Further, it was found that good solubility and a high amount of regenerated cellulose matrix does not inevitably mean better mechanical properties in SRCs.