Mechanical retention – Influence of filler floc size and grammage of the fibre web

Abstract

An investigation of the impact of particle size on the mechanical retention of particles in a fibre network has been conducted. The particles used were five sets of quartz particle fractions having fairly narrow particle size distributions with average particle size ranging from a few μm to around 100 μm. The particles were used to model flocculated filler aggregates as part of a larger study of the effect of pre-flocculation on mechanical retention. Pre-flocculation of the filler is a possible strategy to increase the filler content of paper without deterioration of strength properties. A modified laboratory hand sheet former, known as the Rapid Drainage Device (RDD) was used. The major modification consisted of a long pipe that acted as a suction leg, which provides a dewatering vacuum at the same level as on a paper machine. The experimental results showed that mechanical filler retention increased linearly with particle size and grammage of the fibre layer above a critical grammage which depended on particle size. The linear relation was also seen in a pilot scale trial on the FEX pilot-paper machine at Innventia. During this trial fine paper was produced using pre-flocculated filler where the mean particle size of the flocs and fibres was measured in the flow to the headbox. The results from this pilot trial show that mechanical retention is an important part of the total filler retention. Drainage time and therefore drainage resistance increased with the grammage of the fibre layer and amount of quartz particle added. Drainage time, compared at total grammage (i.e. the sum of fibre and quartz particle grammage) was lowest for a fraction of medium-sized particles, with a median size of 35 mm. There was no obvious effect on retention or drainage resistance of a change in the dewatering pressure from 27.5 to 41.5 kPa.

Fines mobility and distribution in streaming fibre networks: experimental evidence and numerical modeling

“…In summary, we find from the sampled fibre-fines fraction a (1) depletion of fibre-fines outside the network, speculated to result from fibre-fines interaction with the fibre network, (2) a consequent accumulation of fibre-fines confined to the network interface, and (3) a homogenous distribution of fibre-fines at bulk concentration in the network core. The accumulation of fibres-fines at the network interface indicates a hindered fibre-fines transport through the network pores: fibre-fines may be caged and retained as in a filter that is formed by intersecting fibres [comparable to the mechanical retention argument of fines in formed fibre networks (Athley et al 2012)]. A consequence is, that the mobility of fibre-fines in the streaming network will depend on the network structure.…”

“…Fines are retained in the established network, which was shown to be a size exclusion process, i.e. fines that are larger than the pore size of the formed network are retained (Athley et al 2012). The relative motion of fines in the network is hence a function of the fibrefines size and the fibre network's pore structure.…”

Size and shape characterization of fines and fillers - a review

“…Several studies were found where FBRM was used to study the flocculation of fillers (e.g. Alfano et al 1998;Fuente et al 2003;Athley et al 2012;Björk et al 2012). Additionally, one study was found where FBRM was used to study the retention of inorganic microparticles for papermaking (Gerli et al 2000).…”

Electromechanical properties of paper‐derived potassium sodium niobate piezoelectric ceramics

“…Achieving a high solid content, that is, retention of filler in a paper sheet is critical in achieving ceramic components with mechanical stability 1 . Retention can be increased by various mechanisms, distinguishing between mechanical retention (hooking of the powder particles to the fibers) and chemical retention (coagulation and flocculation processes in the suspension, which increase the effective particle size) 3,4 …”

“…wileyonlinelibrary.com/journal/jace 6755 can be increased by various mechanisms, distinguishing between mechanical retention (hooking of the powder particles to the fibers) and chemical retention (coagulation and flocculation processes in the suspension, which increase the effective particle size). 3,4 Although the paper-derived ceramic processing technique has been mainly used for high-temperature refractory ceramics, such as Al 2 O 3 , 5 SiC, 2 and Ti 3 SiC 2 , 6 it is also feasible to fabricate electro-active ceramic materials. 7 For example, Menge et al 7 demonstrated the fabrication of ferroelectric BaTiO 3 with acceptable functional properties using the paper-derived method.…”