Pulp Suspension Research Articles

Starch‐based fixative with proper substitution degree for controlling dissolved and colloidal substances in a bleached chemithermomechanical pulp

Starch‐based fixatives (SBF), specifically low molecular weight, highly‐cationic starches (LHCS), have been reported to efficiently control dissolved and colloidal substances (DCS) in pulp suspensions, and to enhance paper strengths. However, as their degree of substitution (DS) was as high as 0.65, their preparation cost was very high. In this study, two products with lower DSs of just 0.08 (LHCS 0.08) and 0.22 (LHCS 0.22) were prepared and compared to a traditional polyamine (PA) fixative. It was found that the novel LHCSs interacted more readily with the anionic pulp fibers while the PA interacted more readily with the anionic DCS. Consequently, both LHCS 0.08 and LHCS 0.22 increased the paper strength more than the PA. Moreover, it was found that the LHCS 0.22 was most efficient in fixing the colloidal substances onto fibers, while the PA was most efficient in neutralizing the dissolved substances. We conclude that LHCS with DS as low as 0.22 can be used as a good fixative, however, starch with DS of only 0.08 is not efficient enough.

Carboxymethylated nanofibrillated cellulose: effect of monovalent electrolytes on the rheological properties

The effect of the ionic strength on the properties of a carboxymethylated nanofibrillated cellulose (NFC) system was investigated through rheological studies. It was shown that homogenization of pulp suspensions containing a high amount of a monovalent electrolyte leads to the production of NFC systems displaying a lower magnitude in the rheological response as compared with systems prepared at lower ionic strengths conditions. It was further shown that increasing the ionic strength of NFC suspensions after their manufacturing also results in a lowering of the rheological response. The decreased rheological response in the former case was postulated to be caused by a lowering of the delamination deficiency of the homogenization process, due to decreased swelling of the carboxymethylated pulp, caused by the screening of the charges. In the latter case (post-addition of the electrolyte), the lowering of the rheological response was postulated to be due to the compression of the electrostatic double layer, when the electrostatic repulsion between the charged fibrils diminished in the presence of the electrolyte.

Modeling the effect of fiber orientation on local yield stress in flow of pulp suspensions

A model that takes into account the local yield stress in pulp suspensions (2-3%) was derived. In this model the yield stress was assumed to decrease due to a reduction in the number of contact points between fibers in a network when the fibers are oriented in the shear field. The local yield stress described by the number of contact points multiplied by the friction force in the fiber connections was implemented in a CFD solver to describe the yield stress in the non-Newtonian single-phase Bingham model. Model results were compared with experimental UVP data from a study performed earlier on the flow of pulp suspensions at two concentrations after a sudden expansion. First model parameters were estimated with experimental data from a case with a concentration of 1.8% and an inflow velocity of 1.2 m/s. Then the model was used to predict five other cases. The proposed model was able to capture both the decrease in centerline velocity and the increase in the width of the jets at higher inflow velocities. At low inflow velocities the predicted jet lengths were too short compared to the experimental measured jet length due to under prediction of fiber alignment.

Cassava Pulp Hydrolysis under Microwave Irradiation with Oxalic Acid Catalyst for Ethanol Production

Microwave irradiation is an alternative method of starch hydrolysis that offers a rapid process. The aim of this research was to improve microwave-assisted hydrolysis of cassava pulp by using oxalic acid as a catalyst. Suspension of cassava pulp in 0.5% oxalic acid (1 g/20 mL) was subjected to microwave irradiation at 140-230 °C for 5 minutes, with 4 minutes of pre-heating. One gram of fractured activated carbon made of coconut shell was added into a number of suspensions that were subjected to the same conditions of microwave irradiation. The soluble fraction of the hydrolysates was analyzed for its total soluble solids, malto-oligomer distribution, glucose content, pH value, and formation of brown compounds. The effects of the combined severity parameter at a substrate concentration of 5-12.5% on the glucose yield were also evaluated. The highest glucose yield (78% of dry matter) was obtained after hydrolysis at 180 °C without activated carbon addition. Heating above 180 °C reduced the glucose yield and increased the pH and the formation of brown compounds. The use of activated carbon in microwave-assisted acid hydrolysis of cassava pulp reduced the glucose yield, but suppressed the formation of brown compounds. The highest glucose yield (70-80% of dry matter) was attained at a severity parameter of 1.3-1.5.

A quantitative analysis of turbulent drag reduction in a hydrocyclone

Turbulent drag reduction has been observed to occur over a wide range of additive systems, such as solution of synthetic or natural polymers, and fibre suspensions. In this study, the influence of softwood kraft pulp fibres and synthetic polymer additives on turbulent drag reduction (DR) in a hydrocyclone is investigated. It was demonstrated that cellulose fibre suspensions and aqueous polymeric solutions reduce the fluid energy losses in comparison to water during hydrocyclone operation within the range of reject ratios studied. A maximum drag reduction of 58 % and 55 % was found to occur at a volume split fraction of 50 % for a 0.9 % fibre suspension and a 300 ppm anionic polyacrylamide solution, respectively. Polymer degradation or polymer chain decay displayed adverse effects for 100 ppm and 150 ppm solutions after 22 min of run time at 11.2 kW pumping power and a reject ratio of 25 %. Synergistic effects were observed with pulp suspensions containing both cationic and anionic polyacrylamide (CPAM and APAM, respectively); a maximum DR of 41 % was observed for a 0.7 % fibre suspension containing 100–300 ppm of polymer at a reject ratio of 50 %. Similarly to aqueous polymer solutions, the degradation of 300 ppm APAM or CPAM in a 0.7 % fibre suspension decreased the observed DR up to 38 % after 30 min of run time at 11.2 kW pumping power and a reject ratio of 25 %. The near 43 % reduction in CPAM concentration, due to surface adsorption, when present in a 0.7 % fibre suspension assisted in quantifying the DR variations observed between suspensions containing APAM or CPAM.

Improvements of Strength and Retention of Cotton Handsheet by Additives(II)

Guar gum is added to the pulp suspension at the suction side of the fan pump just before the sheet is formed on either a fourdrinier or cylinder machine. Guar gum replaced and supplements these hemicelluloses in paper bonding with many advantages, which include improved sheet formation with a more random distribution of pulp fibers. But, guar gum has serious storage problem. This material has easily decayed after High-temperature conditions such as summer. In this study, various properties of cotton handsheet were measured to solve the problem of deformation while storing guar gum and to improve the durability. After aging, which is one of the durability tests, cotton handsheet with 0.2% and 0.3% of A-PAM showed improved mechanical properties and bursting index and folding endurance of cotton handsheet with 0.3% of A-PAM were similar to those with guar gum. The yellowness loss of cotton handsheet with synthetic polymers was lower than those with guar gum.

CFD analysis on a turbulence generator of medium consistency pump

Medium concentration paper suspension is a water-air-fibre three phase suspension. It has complicated physical features. When concentration exceeds 7%, it stops flowing and acts like a solid. A generator suspension is installed before the impeller to disturb the flocs and networks to make it start to flow. In this paper, CFD method is adopted to study the effects of the turbulence generator. As there is not a mature model to describe the characteristic of pulp suspension, Newtonian fluid is used to get the general property of the turbulence generator. In the CFD simulation, apparent viscosity of the pulp suspension is used to characterize the mixture. Firstly, numerical method is applied to get the turbulence generator properties in different rotational speed and different viscosity. From another point of view, air contained in the suspension is separate initially by means of centrifugal force. As it is difficult to describe a practical model of pulp suspension, it is simplified to be a water-air two-phase mixture. Several air contents are simulated to study the air distribution in the turbulence generator. The results show that there are three main effects of turbulence generator. Firstly, it has an entrainment effect of the suspension to make it into the pump. Secondly, it stirs the pulp suspension to bring it into flowing. Last, air is centralized in the shaft centre and pre-separated in the turbulence generator. So, the turbulence generator can pre-treat the pulp suspension to make the MC pump transport suspension successfully.

Experimental Study on a Medium Consistency Pump

An experimental testing rig is built to study the performance of a centrifugal pump used in medium consistency technology (MC technology). Pump performances are tested in different pulp concentration, degas pressure differential, and tip clearance ratio. The results show that in medium concentration, pump head and efficiency decreases with increase of pulp concentration. There is a critical concentration above which pump performance drops. Gas separation effect is influenced by the pressure differential over the degas system and the air content in the pulp suspension. In high concentration and small tip clearance conditions, friction loss increases a great deal and results in an efficiency reduction.

Fabrication of X Zeolite Based Modified Nano TiO2Photocatalytic Paper for Removal of VOC Pollutants under Visible Light

Photocatalytic papers were fabricated from 13X zeolite based modified nano titanium dioxide (TiO2) for activation under visible light irradiation. Codoped nitrogen–iron nano titania (N–Fe–TiO2) sol was synthesized and supported on 13X zeolite powder at different fractions and added to the paper pulp suspension. The products were characterized by XRD, SEM, EDS, and UV–vis diffuse reflectance spectra analysis. The photodegradation activity of the papers was investigated under batch conditions for the removal of acetaldehyde in air as an indoor pollutant under visible light irradiation. The results revealed that the fabricated paper was active under visible light irradiation and the photocatalytic efficiency of zeolite-based N–Fe–TiO2 paper was 2.1-fold that of unmodified pure TiO2 containing paper.

The development of a near-wall boundary layer over a flat plate in concentrated pulp fiber suspensions

The development of a boundary layer over a flat plate placed in a square pipe was studied in pulp suspensions at concentrations of 0.5, 1 and 1.8% at flow velocities of 0.24-0.96 m/s. Laser Doppler Anemometry (LDA) was used to measure velocities in the boundary layer from y=0-3 mm at x=0, 5, 10, 20 and 30 mm, where x=0 mm was the position where the flow met the plate. During the measurement time the pressure drop over the plate was also measured and it was concluded that the flow was in the rolling friction regime. The results of boundary layer thickness show that an increase in velocity or a decrease in concentration gave a thicker boundary layer in contrast to a laminar Newtonian boundary layer. In a power law fluid, boundary layer thickness decreases with an increase in shear thinning or velocity. Furthermore, in the pulp suspensions, a boundary layer with a constant thickness was reached 20 mm from the plate edge in contrast to a Newtonian and a shear thinning boundary layer which continued to increase along the plate. The difference in boundary layer development is believed to depend on the two-phase effects in pulp suspensions.

Effect of the combination of biobeating and NFC on the physico-mechanical properties of paper

The combined effect of enzymatic treatment (biobeating) and NFC addition on the mechanical and physical properties of a papermaking pulp suspension was investigated. The influence of pH, consistency of pulp and reaction time of the enzyme on the pulp strength was evaluated by measuring the breaking length of paper sheets made thereof. The results showed that the enzymatic treatment improved mechanical properties of fibres without modifying drainability. After biobeating, NFC was added to the enzyme-treated pulps. Mechanical properties were enhanced, obtaining length at break values similar to those observed in commercial printing/writing paper. Opacity remained constant, whereas porosity was gradually reduced as more amount of NFC was added. The presence of NFC also reduced drainability, although it remained at suitable levels for the papermaking industry. The results suggest that the combination of biobeating and NFC addition can be considered as an alternative to mechanical beating.

Effects on Pulp Properties of Magnesium Hydroxide in Peroxide Bleaching

High alkalinity in peroxide bleaching has traditionally been achieved using sodium hydroxide and sodium silicate. In the present work, partial and total substitution of traditional sodium-based peroxide bleaching auxiliary chemicals with a highly pure magnesium hydroxide-based bleaching additive was studied on two high-brightness mechanical pulp types from Norwegian spruce (Picea abies): pressure groundwood and thermomechanical pulp. Peroxide bleaching with 3.0% charge was carried out on both pulps to a given brightness level. The bleached pulp was studied with respect to electrical conductivity, zeta potential, and water retention value. The bleaching filtrate was measured for total organic carbon content, biological and chemical oxygen demand, cationic demand, extractives content, and turbidity. The main results from this study were that the cationic demand and electrical conductivity of the bleaching filtrate were significantly lowered for both pulps when a magnesium-based bleaching process was used. At the same time, the zeta potential of the dilute pulp suspension was only slightly affected. Magnesium hydroxide-based peroxide bleaching seems to increase the water retention value of the pulp, especially on fines-rich pressure groundwood, predicting a good strength potential of the pulp. The bleaching filtrate from the magnesium hydroxide-based process was significantly cleaner in all categories measured, which indicates that this is an environmentally sound concept.

Effect of the Number of Passes through Grinder on the Pore Characteristics of Nanofibrillated Cellulose Mat

In this study, we investigated the effect of the number of passes through agrinder on the pore characteristics of nanofibrillated cellulose (NFC) mat. The beaten pulp suspension was used to make NFC suspension using a grinder. To evaluate the pore characteristics of a NFC mat, the surface morphology of the dried NFC mat was observed with FE-SEM and the specific surface area was analyzed with BET nitrogen gas adsorption. The structure of NFC mat was changed with the different number of passes and drying methods. The specific surface area of NFC mat increased with the increase in the number of passes. The 20-passed NFC mat had 20 times larger specific surface area (<TEX>$141m^2/g$</TEX>) compared to the 0-passed NFC mat. The specific surface area was strongly correlated with the average pore size in NFC mat. The average pore diameter in NFC mat was calculated from the gas sorption isotherms using BJH model. The value was 13 - 15 nm, indicating that the NFC mat had mesoporous structure.

Permeability Parameters of Pulp Fibers from Filtration Resistance Data and Their Application to Pulp Dewatering

The drainage resistance of pulp fibers can be characterized by means of a specific surface area and the specific volume. These parameters can be used to determine the impact not only of processing the pulp fibers but also to compare and distinguish between different pulp mixes. We determined the specific surface area and specific volume of hardwood kraft pulp fibers by measuring the rate of filtrate flow under different applied pressures by a modified filtration apparatus. The specific surface area and specific volume can be used as parameters for monitoring fiber changes due to source and variation, determination of polymer dosage (retention, drainage aids, and flocculation control), and so on. The specific surface area serves as an indicator of the flocculation state of the pulp suspension, while the specific volume indicates the hydration of the fibers. Two mathematical models to describe dewatering of fibrous suspensions under varying pressure were applied. The first is based on conventional cake filt...

Gas dispersion in pulp-suspension flow in the presence of an in-line mechanical mixer

Dispersion of gas in pulp suspensions was investigated downstream of an in-line mechanical mixer for fibre mass concentrations from 0% to 3.0%, superficial liquid/pulp velocities from 0.5 to 3.0m/s, superficial gas velocities from 0.11 to 0.44m/s and impeller speeds from 0 to 800rpm, based on electrical resistance tomography (ERT) and a gas mixing index, derived from the standard deviation of local gas holdup. When buoyancy was less significant, bubbles dispersed uniformly in the high-shear zone just downstream of the impeller, with considerably better mixing than without the impeller. Reflocculation then likely occurred downstream, accelerating bubble coalescence and demixing, especially for higher suspension concentrations. For buoyancy-dominated flow, however, the impeller disrupted the fibre networks, and buoyancy caused the gas to segregate to the top of the pipe, resulting in worse mixing than for no impeller. Gas dispersion improved downstream at higher fibre mass concentrations, likely due to re-forming of fibre networks causing liquid/pulp slugs and elongated bubble flow at the top of the pipe, whereas stratified flow occurred at lower concentrations. Mixing improved with decreasing impeller speed, likely because fibre networks re-established more rapidly.

The behaviour of mineral matter in fine coal flotation using saline water

In this study the behaviour of mineral matter in the flotation of a fine coal sample using saline water was investigated. For a comparison, de-ionised water was tested in parallel. It was found that saline water increased the recovery of mineral matter while increasing the combustible recovery. By calculating the degree of entrainment in the flotation of the coal sample and also the ash after combustion, coupled with the froth image analysis and rheology measurements of froth and pulp suspensions, the entrainment and entrapment of mineral matter in coal flotation were examined. Compared to de-ionised water, saline water increased the entrainment across the size range and the increase in entrainment was more pronounced for particles smaller than 38μm. However, entrapment played a more important role in recovering mineral matter smaller than 38μm in coal flotation using both de-ionised and saline water. Saline water significantly increased the entrapment through enhancing the aggregation of coal particles.

Rheological characterization of high concentrated MFC gel from kenaf unbleached pulp

Microfibrillated Cellulose (MFC) was isolated from unbleached kraft pulp derived from kenaf bast fiber. MFC gels with different concentrations were manufactured from pulp with varying initial consistencies. The MFC was diluted to a consistency of around one percent using distilled water and was further homogenized by passing through a microfluidizer. In order to gain an understanding of the relative changes in behavior of the resulting MFC gels, their rheological properties were characterized. Results show that all of the gels exhibit a shear-thinning behavior. It was also determined that the rheological characteristics improved with increasing gel concentration, which was achieved by using higher pulp suspension consistencies. Diluted MFC that was derived from highly concentrated MFC had more variable modulus under the same strain and frequency compared to poorly concentrated MFC. But such a strong effect was not observed for viscosity. Additionally, the value of G′, ranging from 76 to 5325 Pa under the studied concentrations, was found to be fourfold the value of G″. In the low frequency range, G′ was almost independent of frequency, but was dependent on gel consistency with a coefficient of 3, indicating that MFC gels are elastic. These results show that it is possible to produce MFC gels with good rheological properties from high consistency kenaf pulp suspensions.

Accessibility of cellulose: Structural changes and their reversibility in aqueous media

During various processing treatments, the accessibility of cellulose in cellulosic fibers reduces, which is often interpreted as cellulose microfibril aggregation. This affects the reactivity of cellulose in further processing to novel cellulosic products such as nanocellulose. In this study, the effect of aqueous treatments at elevated temperatures and various pH on accessibility of an oxygen delignified eucalyptus kraft pulp was evaluated by using deuteration combined with Fourier-transform infrared (FT-IR) spectroscopy and water retention value (WRV) test. Acidic treatments reduced WRV and caused irreversible deuteration of the pulp. However, alkaline treatments increased WRV and caused reversible deuteration of the pulp. Both deuteration and reprotonation of the deuterated pulp followed the same slow, first-order dynamics. This led us to propose that incubation of alkaline cellulosic pulp suspensions at elevated temperatures does not only lead to reduction in accessibility but also to a dynamic interconversion between accessible and inaccessible regions.

Pilot-Scale Examination of Mixing Liquid into Pulp Fiber Suspensions in the Presence of an In-Line Mechanical Mixer

The quality of liquid mixing into the main stream for an in-line mechanical mixer was investigated for water and pulp suspensions over a range of mass concentrations (0–3.0%), main-stream velocities (0.5–3.0 m/s), jet velocities (3.8–12.6 m/s), and rotational speeds (0–800 rpm) based on electrical resistance tomography and a modified mixing index, derived from the coefficient of variation of conductivity values. The mixing quality was worse when the jet penetrated to the far wall of the pipe for all fiber mass concentrations investigated, whereas this only applied at higher mass concentrations without the impeller. For water flow, the residence time had a significant effect on mixing at higher impeller speeds. With the impeller present, the mixing quality in pulp suspensions improved substantially and was similar to that for water when the flow approached the turbulent regime, with a considerably lower main-stream velocity required for mixing compared to a tee mixer alone. At higher mass concentrations, the energy supplied was insufficient to provide the same level of turbulence as that in water, even at the highest main-stream velocity and impeller speed examined. Improved mixing with increasing impeller speed primarily occurred in the high-shear zone around the impeller, with turbulence decaying rapidly downstream, likely aided by reflocculation.

Using ultrasonic Doppler velocimetry to investigate the mixing of non-Newtonian fluids

Mixing is a critical unit operation, which is widely used in chemical and allied industries. Mixing of non-Newtonian fluids is a challenging task due to the complex rheology exhibited by these fluids. Pseudoplastic fluids with yield stress are an important class of non-Newtonian fluids. In this study, we utilized ultrasonic Doppler velocimetry (UDV) to explore the flow field generated by different impellers in the agitation of xanthan gum solutions and pulp suspensions, which are yield-pseudoplastic fluids.