The Effect of Consistency and Freeness on the Yield Stress of Chemical Pulp Fibre Suspensions

Abstract

To study the influence of mechanical treatments on the yield stress of chemical pulp suspensions, a traditional rheometer, coupled with local velocity measurements (ultrasonic Doppler velocimetry), was used to measure the yield stress of two types of commercial chemical pulp suspensions with different freeness values at mass concentrations (consistencies) ranging from 0.5 to 1.5%. Over the range of consistencies tested, the yield stress was found to depend on the consistency through a power law relationship for all tested samples. Moreover, the results showed that as the freeness decreased, the yield stress of hardwood suspensions increased to a maximum value then decreased. This variation in yield stress was also observed in softwood suspensions with mass concentrations above 1%. However, when the consistency was lower than 0.75%, the yield stress of softwood suspensions increased with decreasing freeness.This behaviour can be understood based on the underlying fibre properties of fibrillation, curl, and stiffness, suggesting that fibre morphology plays a significant role on the yield stress of pulp suspensions over the concentration range studied.

The influence of consistency and fibre length on the yield stress of OCC pulp fibre suspensions

“…3). This result was attributed to the fact that there were more fibres per volume of suspension at a high pulp consistency; this increased the fibre-fibre interactions, resulting in a higher yield stress (Sha et al 2015). Moreover, the yield stress for each fraction of AOCC pulp was slightly higher than the corresponding fraction of COCC pulp under the studied fibre concentrations (Fig.…”

Extraction of Polyphenols and Valorization of Fibers from Istrian-Grown Pomegranate (Punica granatum L.)

“…It is well known that curled fibers produce papers with poorer tensile properties while increasing resistance to fracture and tear. Compared to softwood, the pomegranate peel fibers present a 50% to 60% lower curl, being more in line with hardwood or alternative non-wood pulps [ 52 , 53 , 54 ].…”