Intensification of lyocell dissolution process and dope characteristics using pre-swelled cellulosic pulp

Abstract

Transformation of pulp into regenerated lyocell fibre involves a critical step of cellulose dissolution in aqueous NMMO solution. The objective of this work is to investigate the effect of using pre-swelled pulps derived from hardwood kraft sulphate (H-KS) and softwood kraft sulphate (S-KS) process, on cellulose dissolution. Pre-swelling at temperatures follows from 30 °C to 75 °C results in lowering of pulp crystallinity, and hence, was hypothesized to form a homogeneous solution with lower power consumption during the dissolution process. Experimental torque moments (proportional to power consumption) of the un-swelled and pre-swelled pulps at different temperatures were compared and correlated with the cellulose dissolution process. Further, a time based morphological study of cellulose dissolution was performed with the help of a microscopic investigation method. The quality of the dissolved dope was evaluated by optical image analysis, refractive index (RI), dope composition and thermal analysis (TGA/DSC). It was observed that by using pre-swelled pulps, homogeneous cellulose solution could be formed at lower processing temperature, consuming less time and power thereby making the lyocell process more energy-efficient and sustainable.