Microparticle Retention System Research Articles

Synthesis of nanocomposites from polyacrylamide and graphene oxide: Application as flocculants for water purification

Polyacrylamide/graphene (PAM/GO) based nanocomposites were synthesized and applied as flocculating agent for cleansing the solvent phase. In order to obtain the better dispersion of the graphene nanoplatelets in matrix the functionalization was carried out using acid and upon analytical characterization the successful fine dispersion of FGNp was found in the PAM matrix. The influence of GO concentrations on viscosity, charge demand, flocculating and dewatering with ambient micrometer-sized ground calcium carbonate (GCC) was well evaluated and elucidated. It was found that on increasing the GO content in the PAM/GO nanocomposites, the filtered weight of GCC suspensions also increases, and the filtrate turbidity decreased and it was also observed that on adding the GO both η and supernatant turbidity reduced: by growing GO concentrations, there was a fall in η and turbidity of cleaned water. The retention mechanism proceeds through a parallel method to microparticle retention system which is done via bridge/patch among pulp and filler.

Unmodified Starch Granules for Strengthening Mineral-Filled Cellulosic Fiber Networks Promoted by Starch Pretreatment with a Cationic Polymer Flocculant in Combination with the Use of an Anionic Microparticulate Material

The efficient use of renewable resources (e.g., starch) is essential to the green economy. On the basis of commercially available microparticle retention and drainage systems, the process concept of trapping unmodified starch granules in mineral-filled cellulosic fiber networks for strength enhancement by incorporation of cationic polymer flocculant pretreated/bridged starch granules in combination with the use of an anionic microparticulate material was discussed and demonstrated. Specifically, a high molecular weight cationic polyacrylamide and a modified bentonite, which are commercially available in the market, were used as the polymer flocculant and the anionic microparticulate material, respectively. The paper strength loss upon the addition of precipitated calcium carbonate filler particles was significantly mitigated by employing such a concept, which may provide an alternative strategy for improving the strength properties of mineral-filled paper grades.

Evaluation of the Flocculation and Reflocculation Performance of a System with Calcium Carbonate, Cationic Acrylamide Co-polymers, and Bentonite Microparticles

Flocculation, flocs resistance, and reflocculation capacity of a precipitated calcium carbonate (PCC) suspension with cationic polyacrylamides (C-PAMs) varying in charge density and degree of branching were investigated in previous studies and correlated with retention and drainage performance in papermaking. In this study, the reflocculation performance of the PCC suspension was investigated using the same C-PAMs, in combination with microparticles, since microparticle retention systems have been widely used in papermaking to improve reflocculation of the suspension. Moreover, flocculation and reflocculation performance evaluated using the laser diffraction spectroscopy (LDS) technique was compared with that obtained using focused-beam reflectance microscopy (FBRM) to monitor the process. The coupling of these two techniques allows a detailed analysis of the reflocculation process, including evaluation of the flocs structure before and after the reflocculation stage.

Retention Performance of Nanocoated GCC with Positive Charge

In this study, we investigated retention characteristics of nanocoated GCC that was positively modified by Layer-by-Layer (LbL) multilayering process. Three layers were formed onto GCC particles with poly-DADMAC/PSS/poly-DADMAC (PD3) and C-starch/A-PAM/C-starch (CS3) systems, respectively. Untreated GCC, PD3 GCC (strongly positive charge) and CS3 GCC (weekly positive charge) were retained on pulp fibers under single retention system or microparticle retention system conditions. In single retention system, PD3 particles were not affected by cationic retention aid due to their strong positive charge, whereas CS3 particles reacted with cationic retention aid due to anionic sites on the surface of the weekly positive particles. In a microparticle retention system, positively modified GCC (PD3 and CS3) showed higher retention level than untreated GCC at the same dosage of retention aid. The cationic surface of GCC particles were more reacted with bentonite so the deposition onto pulp fibers was improved. In addition, the retention level of nanocoated GCC was increased with maintaining good formation.

Surface Modification of Nanocrystalline Cellulose and its Application in the Deinked Pulp

In this study, nanocrystalline cellulose (NCC), isolated from the bleached aspen kraft pulp, was surface modified using borate. The resultant nanocrystal suspensions, namely B-NCC, were characterized by conductometric titration and atomic force microscope (AFM). B-NCC was then applied as a retention aid in the bleached old newsprint deinked pulp. The results showed that the modification process led to a negative increase in surface charge density, while the particle size was not changed. The fines retention and pulp drainability were increased when the B-NCC was used either alone as the monocomponent retention aid, or together with cationic polyacrylamide (CPAM) to constitute a microparticle retention system. The microparticle retention system gave better retention and drainage rate, with the maximum values of 90.5% and 3.5 ml/s, respectively.

Nanocrystalline cellulose from aspen kraft pulp and its application in deinked pulp

Nanocrystalline cellulose (NCC) isolated from bleached aspen kraft pulp was characterized, and its application as pulp strengthening additive and retention aid was investigated. Results showed that NCC with high crystallinity of more than 80% can be obtained using 64wt% sulfuric acid. The structure of nanocrystalline cellulose is parallelepiped rod-like, and their cross-sectional dimension is in the nanometer range with a high aspect ratio. The formation of microparticle retention systems during the application of NCC together with cationic polyacrylamide and cationic starch in deinked pulp was able to further improve pulp retention and strength properties without negative influence on the drainage.

Application of PEO/Cofactor System on Papermaking Process for Recycled Fibers

Ionic trash in furnish decreases retention and drainage performance of the microparticle retention system using recycled fibers in closed papermaking system. Two retention systems, such as the microparticle system and the PEO/cofactor system, were compared and analyzed to improve retention. The PEO/cofactor system achieved similar retention performance at low addition level as the microparticle system. Optimum ratio of PEO/cofactor dual polymer system was 1:10. Ash retention was increased when using the fixing agent. As the TMP ratio increased, the PEO/cofactor system was more efficient in retention and drainage than the other system. The high molecular weight and non-ionic polymer retention system had less effect on flocculation hindrance than the traditional electrostatic retention system.

Application of Nano-Materials as Synergistic Retention Aid in Paper Making

Various negatively charged and positively charged inorganic nano-materials have been suggested to constitute the so-called microparticle retention systems with cationic or anionic polymers. Anionic microparticle retention systems consisted of cationic polymers and negatively charged inorganic nano-materials with various aspect ratios were reviewed while their working mechanism were analyzed. Cationic microparticle retention systems made up of either naturally or organo-modified cationic nano-materials were introduced.

Study on Preparation and Application as Organic Particulate Retention Agent of Chitosan-AM-DMDAAC Inverse Latex

Graft copolymerization of acrylamide (AM) and diallyl dimethyl ammonium chloride (DMDAAC) onto chitosan in inverse emulsion was studied. The effect on Zeta potential and average granularity of synthetic inverse latex of the main reaction conditions such as the proportion of cationic monomer in total monomers, concentration of potassium persulfate (KPS) used as initiating agent were investigated in detail. It was shown that when the weight ratio of chitosan, AM and DMDAAC was 1:6:2, KPS concentration was 4.0mmol/L, NaHSO3concentration was 2.0mmol/L, stable inverse latex which had optimal performance could be gained. Good retention effect was obtained when a novel organic microparticle retention system composed of the above-mentioned chitosan-AM-DMDAAC inverse latex and anicnic polyacryamide (APAM) was applied to the deink pulp. First Pass Retention retention percentage of deink pulp was improved from 83.2% to 95.0% with the organic microparticle retention system when the dosage of inverse latex was from 0 to 0.4% of absolute dry pulp.

Drainage and retention enhancement of a wheat straw-containing pulp furnish using microparticle retention aids

The usage of non-wood pulps in furnishes for the production of various paper grades is a real alternative for the substitution of wood pulp in papermaking. In terms of the papermaking process, the main limiting factor for non-wood pulp utilization is poor dewatering. This problem can be partially solved by means of retention aids, and the modern microparticle-based retention aids are very promising for this application. In this study the main aim was to characterize how the microparticle retention systems affect the retention, dewatering, and formation of a non-wood pulp furnish and how these effects and mechanisms differ when compared to normal wood pulp. The performance of several commercially available retention aids was studied by making dynamic sheet forming tests for reference and an organosolv wheat straw furnish. The emphasis in the experiments was on drainage enhancement. The maximum drainage gain obtained with the bentonite-CPAM retention aid system was about 5%. Despite the improved drainage, dewatering of the reference furnish was better than for the non-wood containing furnish.

Sodium titanate nanobelt as a microparticle to induce clay flocculation with CPAM

Sodium titanate nanobelt was synthesized by treating titanium dioxide hydrothermally in concentrated sodium hydroxide solution. The product was characterized by SEM analysis and zeta potential measurement. It served as a microparticle to constitute a microparticle retention system with cationic polyacrylamide (CPAM), while the microparticle system was employed to induce the flocculation of kaolin clay. The flocculation behavior of kaolin clay in such a system was investigated by using a photometric dispersion analyzer connected with a dynamic drainage jar. It was found that the sodium titanate nanobelt carried negative charges and had a lower zeta potential at higher pH. It gave a large synergistic flocculation effect with CPAM at a very low dosage, and showed higher flocculation effect with CPAM under neutral and weak alkaline conditions. A suitably high shear level was helpful for the re-flocculation of clay by sodium titanate nanobelt. The clay flocculation induced by CPAM/titanate nanobelt system demonstrated high shear resistance and also generated dense flocs.

Highly Substituted Cationic Starch as an Anionic Trash Catcher for High-Yield Pulp

High-yield pulp (HYP) and recycled fibers containing anionic trash are being used increasingly in the manufacture of various paper grades. Traditionally, anionic trash catchers (ATCs), such as PEI, CPAM, and poly-DADMAC, are used to minimize the anionic trash problem. In this work, we studied an alternative ATC, highly substi-tuted cationic starch (HS-CS). We determined the efficiency of HS-CS with different degrees of substitution of 0.57-0.97 in furnish containing dissolved colloidal substances (DCS). Flocculation behavior was also demonstrated in a dynamic drainage jar (DDJ). The results showed that HS-CS is a very good ATC. With the addition of HS-CS, the neg-ative effects of DCS on the microparticle retention system can be minimized and the effectiveness of retention aids can be improved. The results from the dynamic flocculation experiments support the same conclusion.

A deposition efficiency model for fiber–filler flocculation by microparticle retention system

A deposition efficiency model was developed in order to predict the effect of the dosage of retention aids (polymer and bentonite) on filler retention and validated with a pilot machine trial. The deposition efficiency is a function of the surface coverage of adsorbed and transferred polymer on solids (fiber and filler) and the surface coverage of microparticles on the polymer-adsorbed layer. The model includes the effect of bimodal particles (i.e., fiber and filler) and the polymer transfer from fiber to filler. In addition, the interaction between bare surfaces was included in the model and different bond strength of each interaction was considered. It was shown that an increase in the deposition efficiency leads to an increase in the filler retention. The dosage of CPAM is more predominant variable affecting deposition efficiency and thus filler retention than that of bentonite.

Microparticle Retention Aid Systems in Mechanical Pulp Suspensions

Todays papermakers face the ever-increasing challenge of producing good quality paper while keeping prices low. This is achieved by using cheaper raw materials such as mechanical pulps and mineral fillers. To increase productivity, machine speeds have also increased. To meet these challenges, it is crucial that the papermakers are able to effectively retain mineral fillers and fiber fines while simultaneously improving dewatering rate. Microparticle retention aid systems, typically utilizing anionic colloidal silica and/or clay-based particles in combination with cationic polymers, have been developed to help deal with these challenges. Generally, microparticle retention aid systems have shown better retention and dewatering performance compared to the classical single or dual polymer retention aid systems. In the past decade, many variations of the microparticle system have been developed to further improve its performance. With respect to the silica-based particles, these include modifications to their physical and chemical structures. In the case of the clay-based particles, various methods have been devised to keep the suspension dispersed, either by mixing the clay-based particles with silica-based particles or synthetic metal silicates. Cationic microparticle systems are also available. Examples include cationic bentonite and fibrous alumina, which are used in combination with cationic or non-ionic polymers. A patent literature search on microparticle retention systems was conducted. It covered the period from 1990 to 2005. The various inventions are described in this paper.

Microparticle retention aid systems in mechanical pulp suspensions

Today's papermakers face the ever-increasing challenge of producing good quality paper while keeping prices low. This is achieved by using cheaper raw materials such as mechanical pulps and mineral fillers. To increase productivity, machine speeds have also increased. To meet these challenges, it is crucial that the papermakers are able to effectively retain mineral fillers and fiber fines while simultaneously improving dewatering rate. Microparticle retention aid systems, typically utilizing anionic colloidal silica and/or clay-based particles in combination with cationic polymers, have been developed to help deal with these challenges. Generally, microparticle retention aid systems have shown better retention and dewatering performance compared to the classical single or dual polymer retention aid systems. In the past decade, many variations of the microparticle system have been developed to further improve its performance. With respect to the silica-based particles, these include modifications to their physical and chemical structures. In the case of the clay-based particles, various methods have been devised to keep the suspension dispersed, either by mixing the clay-based particles with silica-based particles or synthetic metal silicates. Cationic microparticle systems are also available. Examples include cationic bentonite and fibrous alumina, which are used in combination with cationic or non-ionic polymers. A patent literature search on microparticle retention systems was conducted. It covered the period from 1990 to 2005. The various inventions are described in this paper.

Effect of physico-chemical conditions on the properties of zeolite microparticles used in pulp and paper applications

Zeolites are framework aluminosilicates that have been proposed as a replacement for bentonite in microparticle retention systems. It has been claimed in many patents that zeolite can improve sheet formation in fine paper manufacturing. However, this improvement was not observed in mechanical grades. These experimental results, and also theoretical evidence, suggest that papermaking pH plays an important role in zeolite efficiency. In consequence, the effect of pH and temperature on the chemical properties of zeolite and bentonite microparticles was determined. Streaming potential, conductivity, and pH were measured while microparticle solutions were gradually acidified to pH 5. Samples were also taken at specific pH values to measure the cationic demand. Results showed that a gradual reduction of pH caused several modifications to zeolites. The first step was the neutralization of free hydroxyl ions in solution. The second step was an irreversible exchange of the charge-compensating sodium ions by hydrogen ions on the inner and outer surface of microparticles. Finally, dealumination of the zeolites occurred. It was determined that neutralization must be completed before ion-exchange can begin. However, ion-exchange and dealumination occurred simultaneously. Between pH 7.5 and 9, zeolites had more anionic sites than bentonite (around 0.8 meq/g vs. 0.5 meq/g). The higher surface charge of zeolites might partly explain their efficiency in microparticle systems. On the other hand, under pH 7.5, the anionic charge of zeolite samples rapidly decreased while that of bentonite was stable. The effect of temperature was also studied in the 25 to 55 °C range. Generally, a temperature rise promoted a greater dissociation of the surface hydroxyl groups and an acceleration of ion-exchange and dealumination processes.

Deposition of calcium carbonate particles on fiber surfaces induced by cationic polyelectrolyte and bentonite

The mechanism by which a two-component microparticle retention system, composed of cationic polyacrylamide (CPAM) and bentonite, operates was investigated by measuring the deposition of precipitated calcium carbonate (PCC) on fibers suspended in water. The results obtained by using varying amounts of polymer and bentonite indicate that CPAM by adsorbing on both the fiber and the PCC provides anchoring spots for bentonite. Thus, the bentonite acts as a bridge between fiber and PCC, and the tenacity of PCC attachment to fibers is stronger than a simple CPAM bridge. For optimum performance, a given ratio of CPAM and bentonite addition is required because in the presence of excess CPAM, the bridging ability of bentonite decreases.

ゼータ電位の理論と応用

A laboratory system has been developed to measure simultaneously the zeta potential, flocculation, and drainage of pulp and filler suspensions under hydrodynamic shear flow. The magnitude and trend of on-line streaming potential measurements correlated well with off-line electrophoresis measurements. The slight deviation between two measurements showed the absorptivity difference of cationic chemicals with furnish components. The instrument was used to optimize flocculation and drainage for single retention systems and microparticle retention systems in a laboratory. Flocculation and drainage were affected by the order of chemicals, and the type of furnish. Drainage increases that occurred with the addition of bentonite were strongly influenced by charge neutralization.

The chemistry of deposits in steam boilers

The mechanism by which a two-component microparticle retention system, composed of cationic polyacrylamide (CPAM) and bentonite, operates was investigated by measuring the deposition of precipitated calcium carbonate (PCC) on fibers suspended in water. The results obtained by using varying amounts of polymer and bentonite indicate that CPAM by adsorbing on both the fiber and the PCC provides anchoring spots for bentonite. Thus, the bentonite acts as a bridge between fiber and PCC, and the tenacity of PCC attachment to fibers is stronger than a simple CPAM bridge. For optimum performance, a given ratio of CPAM and bentonite addition is required because in the presence of excess CPAM, the bridging ability of bentonite decreases.