in Wet-End Chemistry
Research Areas in Papermaking Chemistry
This page summarizes research activities of Dr. Martin Hubbe and his associates at North Carolina State University. Additional information about research at the university related to papermaking chemistry can be found at the departmental website and at the website of Dr. Orlando Rojas.
Related information is available at the following links: Curriculum Vitae of Dr. Martin A. Hubbe; Abstracts of publications by the group; Mini-encyclopedia of papermaking chemistry; Online essays; description of Buckman Foundation endowment of research chair at NC State University.
Structure-Property Relations in Amphoteric Polymers for Papermaking and Non-Food Fiber Applications
With Orlando J. Rojas and Dimitris S. Argyropoulos. Post doctoral research associate: Xingwu Wang. Graduate students: Yan Wang and Junlong Song.
This research is aimed at increasing
the value of forest-based biomaterials by improving bonding between fibers.
This will be achieved by more effective use of a relatively new class of inter-fiber
bonding agents, the polyampholytes, which are long-chain molecules containing
both positive and negative ionic groups.
The composites to be obtained will be confirmed by nuclear magnetic resonance (NMR), gel permeation chromatography (GPC), and potentiometric titrations. Bulk solution characterization will include small-angle neutron scattering (SANS) and light scattering. The properties of adsorbed films of the same polymers will be evaluated by monitoring changes in the resonance frequency of the quartz crystal (QCM) and ellipsometry. Electrokinetic effects will be characterized by adsorption onto cellulose and silica, together with streaming potential (SPJ) and streaming current (SC) analyses.
Colloidal Properties of Nanoparticles Affecting their Interactions with Polyelectrolytes
With Joel J. Pawlak, Orlando J. Rojas, and Lucian A. Lucia. Graduate student: Sa Yong Lee
The goal of this project is to understand and develop the colloidal mechanisms related to the "Synthetic Mineral Microparticle" (SMM) additive system for promoting retention and dewatering improvements during the manufacture of paper. Important variables in the reseach include the ratio of aluminum-containing and silicate-containing solutions, as well as the pH and hydrodynamic shear conditions accompanying preparation of the microparticle suspensions. These factors are found to affect not only the retention and dewatering response of the treatment program, but also the charge characteristics of the solids. Research approaches include zeta potential analysis, polyelectrolyte titrations, filtration experiments, and AFM imaging.
Investigation of Paper Quality Factors Affecting Gypsum Wallboard Production
With Joel J. Pawlak and John A. Heitmann. Graduate students: Juan Bastidas and Kathy Austen.
The main goals of this work include elucidation of the bonding mechanisms between calcium sulfate dehydrate (gypsum) and paperboard during the production of gypsum wallboard. Test equipment for precise control and cycling of relative humidity has been developed. A chemical force method has been developed, using an atomic force microscope (AFM). It was shown that the adhesion between single gypsum crystals and cellulosic surfaces can be strongly dependent on which of the crystal faces contacts the substrate. Follow-up work will include an analysis of the relationship between gypsum-cellulose bond strength and the gypsum crystal face involved in bonding. The nature of the gypsum core material will be selectively changed by varying the ratio of water to stucco. Another set of experiments will be carried out to examine the effects of additives such as ball-mill accelerater or KOH. Morphologies will be characterized by SEM. Parallel experiments will examine the effects of these changes on the delamination of humidified board at different stages of setting.
Using Polyelectrolyte Complexation to Make Paper from Less Wood Fiber
With Stephanie M. Moore and Megan Lofton, summer undergraduate researchers sponsored by NSF's Green Processing Research Experience for Undergraduates (REU) program.
Dual-polymer treatments involving a high-charge cationic polymer followed by anionic carboxymethylcellulose (CMC) increased the strength of handsheets formed from the fiber fraction of recycled xerographic copy paper. The amount of the first additive, poly-diallyldimethylammonium chloride (poly-DADMAC), was varied, whereas the amount of CMC was held constant. Results contrasted with earlier work, in which maximum strength was obtained when the amount of poly-DADMAC was just sufficient to saturate the adsorption capacity of unbleached kraft fibers. Rather, in the case of recycled copy paper, significantly higher tensile strength was obtained when the poly-DADMAC addition exceeded the saturation level by a factor of ten. Tests were performed to evaluate a hypothesis that the strength increase was due to polyelectrolyte complex (PEC) formation in the bulk phase, followed by deposition of PECs onto the fibers. Pre-formed complexes were retained efficiently by the fibers, especially if their surfaces had been pretreated with a saturation level of poly-DADMAC. Surprisingly, such pretreatment increased the retention efficiency of all of the PEC mixtures tested, regardless of which sign of charge was in excess. The results suggested that PEC deposition yielded an additional increase of about 13% in dry strength, beyond what could be achieved by treatments not involving complexation.
Interfacial Properties of Biomaterials with Adsorbed Comb Copolymer
With Orlando J. Rojas
The focus of this project is the study of the boundary layer created by adsorbing comb copolymers on biomaterials such as cellulose. The main hypothesis is that the properties of composites built up by comb copolymers of high grafting density depend on the surface affinities, solvency and the architecture of the adsorbed layer. Adsorption dynamics, adhesion, repellency, and friction phenomena are some of the relevant properties to be investigated. Despite the current emphasis placed on the biobased economy of the 21st century our current knowledge on the interaction of cellulose with other polymers has lagged behind. This study is therefore aimed at providing a solid understanding of the performance of these composite materials. The final outcome of this initiative will be the development of macromolecular structures on renewable materials with enhanced biological, structural and functional properties.
Effect of Salinity on Polyelectrolyte Interactions with Solid Surfaces
With Orlando J. Rojas and Joel J. Pawlak
The ability of polyelectrolytes either to adsorb or to remain adsorbed on surfaces of opposite charge has important implications for industrial applications such as oil-well drilling, stabilization and flocculation of suspensions, and the retention of fine particles during the formation of paper. Despite theoretical and experimental progress in understanding such interactions, most past work has involved low levels of salinity. However, trends in water conservation favor increasing salt concentrations in many industrial environments. Though salts tend to make it more difficult to use conventional electrokinetic tests to sense the effects of polyelectrolyte adsorption, a new semi-automated device has been developed that has been found to give precise information even at electrical conductivity values as high as 20 mS/cm. It is proposed to use this device in a unique double-titration mode to sense the presence and extent of interaction between cationic acrylamide copolymers and silica surfaces. The forward titration will involve the addition of polymer to slurries of macroscopic particles, whereas the reverse titration will be carried out with silica nanoparticles. Supplementary tests will be carried out with a quartz crystal microbalance (QCM) and atomic force microscopy (AFM). Successful completion of the project will be important for (a) designing chemical treatment and formulation strategies that need to perform under varying conditions of salinity, and (b) as a check on some existing theories, and in order to stimulate further theoretical work related to adsorption of polyelectrolytes.
Fundamentals in Deposition Control
With Orlando J. Rojas
Contamination of equipment by deposition
of substances from industrial process streams results in billions of dollars
of annual losses in manufacturing productivity, losses in product quality, and
costs associated with cleanup. The proposed study addresses instances where
tacky, sticky, or waxy materials deposit from aqueous solution. Such deposit
problems are becoming increasingly critical for US industry, with particular
focus on the paper industry, partly as a result of efforts to address environmental
concerns. Systematic changes, which have been broadly defined as "green
processing", are affecting industrial processing environments. There is
an ongoing shift from solvent-based processes towards greater use of water-borne
or water-soluble additives for processing of raw materials. Industry also is
facing pressures to reduce water consumption, a trend that favors increased
concentrations of dispersed and dissolved organic substances in aqueous process
streams . Increased recycling of reclaimed materials also brings rising and
unpredictable levels of various contaminants .
Recently we have become interested in identifying and quantifying deposit problems at an early stage of their development. Colloid chemical methods offer huge potential advantages in terms of sensitivity, speed, and information content of the analyses. In our laboratories we have recent experience with the complementary methods of streaming potential (sensitive to electrical charges at surfaces exposed to water), dynamic contact angle (sensitive to the surface energies), and quartz crystal microbalance (QCM). We also use an atomic force microscopy (AFM), which is capable of imaging and sensing forces due to adsorbed molecules. Other ultra-sensitive tools for surface analysis are available for our use at the university. Because these tests can, in principle, detect sub-monolayer amounts of certain adsorbing species, there is potential to achieve order-of-magnitude advances in predicting the onset and accumulation of organic deposits, so as to be able to prevent or eliminate associated problems.
Factors Affecting Interactions of Polyelectrolytes During Charge Analysis by Streaming Current (SC) Titration
With John A. Heitmann, Houmin Chang, Dimitris S. Argyropoulos, D. S., and Orlando J. Rojas. Award of Ph.D. degree to Junhua Chen.
This thesis project investigated mechanisms related to the streaming current method, which is commonly used for analyses of colloidal charge in such applications as paper manufacture and water treatment. The working mechanism of this method is understood to involve polyelectrolyte complex (PEC) formation. Studies have found increasing deviations from 1:1 stoichiometry of complexation with increasing electrical conductivity, a quantity that tends to increase as papermakers work to increase the recirculation of water. With increased conductivities the need for accurate and reliable charge measurements has become more important. This research focused on experiments that define the range of sample types and electrical conductivity where it is possible to achieve accurate and reliable results from streaming current titrations.
Other studies related to the theories of polyelectrolyte complexation involved titrations carried out between solutions of a strong poly-acid and a strong poly-base over a range of salt concentrations. It was found that the stoichiometry of PEC complexation depended on the direction of the titration. An excess over the theoretical amount was required to achieve a streaming current reading of zero. Theoretical models based on non-equilibrium complexation were proposed to explain the current results. Other tests, such as turbidity and electrophoretic mobility also have been used to evaluate the theoretical models. The results are consistent with those from the streaming current analysis.
Factors that may influence the polyelectrolyte adsorption and PEC formation were also studied. No clear correlation was found between the charge densities of anionic polyelectrolytes and titration stoichiometry with the study of carboxymethylcelluloses. However, the shapes of the titration curves could indicate the strength of complexation between titrant and sample molecules.
The Interference of aluminum ion the stoichiometry of charge titrations was also found and consistent with previous works. Under certain conditions it is possible to consider the aluminum ion itself as a cationic sample. Turbidity and zeta potential tests indicated that there could be polynuclear species existing under the conditions in which the aluminum ions can be titrated as cationic samples. See "Publications" involving Junhua Chen. See online Ph.D. dissertation at http://www.lib.ncsu.edu/theses/available/etd-03312004-142137/unrestricted/etd.pdf .
Preventing Strength Loss Due to Drying and Recycling of Unbleached Kraft Fibers
With Richard A. Venditti and John A. Heitmann. Award of Ph.D. Degree in Min Zhang.
The purpose of this study was to
find out the mechanism of the paper strength loss that occurs when paper is
made from chemical pulps that have been recycled. In the case of unbleached
softwood kraft pulp, it was found that the paper strength (tensile strength
and compression strength) decreased with recycling. Traditional methods to increase
the strength of recycled paper involve either adding dry strength agents to
recycled fibers or refining the recycled fibers. These procedures increase the
cost and energy usage. Fibers are also shortened during refining and more fines
are produced, which leads to drainage problems and affects the productivity
of the paper machine.
It was found that due to drying, unbleached kraft pine fibers lost cellulose viscosity, water retention value, fiber flexibility and accessible surface area, as determined by their ability to adsorb poly-DADMAC. Handsheets made from dried fiber had lower strength and higher apparent density compared to the corresponding primary handsheets made from never-dried fibers. With the increase in drying temperature of virgin fibers, the above properties of dried fibers or strength of recycled handsheets experienced larger effects, especially for drying temperatures over 150 ºC.
In this research it was hypothesized that adding certain chemicals to virgin fibers before drying could prevent strength loss upon recycling. Results showed that relatively low molecular weight additives (such as sucrose and glucose) appeared to interfere with the mechanism of pore closure during drying and improved the strength of recycled paper. Higher molecular weight chemicals (such as starch) added to never dried virgin fibers also increased the strength of the recycled paper, but this was attributed to residual chemical being retained on the fiber surface during recycling. Although the effect of adding certain chemicals to virgin fibers before drying could significantly prevent strength loss in recycled paper, it was determined that improvements of recycled paper strength due to refining were of much larger magnitude.
It was found that recycled handsheets had lower strength compared with virgin handsheets within the pH range from 3 to 8, which encompasses the majority of papermaking applications. There was no significant effect of pH on paper strength within this range. The lack of effect of sheet forming pH on paper strength implies that under practical papermaking conditions, for the type of pulp considered in this research, adjusting sheet forming pH may be not an effective tool for increasing paper strength. The results from water retention value and cellulose viscosity measurements also supported this conclusion.
The fiber flexibility tests showed that the method is useful to determine the flexibility of individual fibers. In the case of sugar treatment, treated fibers had a higher flexibility than untreated fibers, and glucose had a larger effect than sucrose. Fibers were more flexible under alkaline conditions than those under acidic conditions, but fibers became less flexible with increasing salt concentration and hardness. See "Publications." See online Ph.D. dissertation at http://www.lib.ncsu.edu/theses/available/etd-10192003-214110/unrestricted/etd.pdf .
Colloidal Behavior and Adsorption Characteristics of Amphoteric Acrylamide Terpolymer Dry-Strength Additives
With John A. Heitmann, Dimitris S. Argyropoulos, and Orlando J. Rojas. Award of Master of Science degree to Takao Sezaki.
The colloidal and electrokinetic
behavior of several amphoteric acrylamide-based polyelectrolytes was elucidated
using potentiometric and colloidal titrations, as well as microelectrophoresis,
viscometry, and turbidity measurements. The independent variables were polymer
composition, pH, and the concentration of salt ions. Colloidal titrations revealed
a wide range of pH's over which most of the polyampholytes showed little tendency
to complex with highly charged, linear polyelectrolyte titrants. Specific viscosity
measurements, in the vicinity of the isoelectric point, were found to increase
with increasing salt concentration, which is a typical anti-polyelectrolyte
behavior. In a similar manner, salt addition suppressed the development of a
turbidity maximum at the isoelectric point. The overall data suggest that at
pH values relatively close to the isoelectric point, the outer segments of the
polyampholyte molecules tend to be enriched in the charge group present in excess
within the chain, with the interior groups being less available for interaction
Colloidal titrations of commercial amphoteric acrylamide-based polyelectrolytes were carried out at pH 3 and 11, using a streaming current technique. At these pH values the polyampholytes are considered to be in their respective cationic or anionic forms, acting as simple polyelectrolytes. The titration endpoint defined by zero streaming current (SC) output, deviated from a 1:1 stoichiometry, depending on the salt concentration. The endpoint was also dependent on the titration methods. This indicated that the rate of forming equilibrated poly-ion complexes between polyampholytes and titrants was relatively slow. The adsorption of the amphoteric polyacrylamide copolymers onto bleached hardwood fibers was significantly affected by pH. The adsorption of a polyampholyte was maximized near to its isoelectric point, such that the net charge of the polymer was relatively low, but opposite to that of the substrate. Neutral and negatively charged polyampholytes were found to be adsorbed onto negatively charged fibers. Addition of salt tended to increase the adsorption up to a conductivity value of 1000 ?S/cm. Adsorption was slightly increased with increasing time for adsorption, but this increase leveled off after a certain time. The stirring rate during adsorption was not an important factor for adsorption under the conditions used in the present work. See M.S. Thesis on line: http://www.lib.ncsu.edu/theses/available/etd-11242003-160324/unrestricted/etd.pdf
Effect of Different Forming Regimes on Retention Aid Programs (PPJ Studies)
With John A. Heitmann and Richard A. Venditti. Award of Master of Science degree to Taweewat Tripattharanan.
A new device, the Positive Pulse Jar (PPJ) was introduced in this study to compare the responses of different retention aid systems to hydrodynamic shear forces resulting from different idealized forming regimes. The major advantage of this equipment for this kind of study is the ability to simulate different forming regimes such as simple filtration, pulsation at different frequencies and amplitudes, uniform-shear forming, and a procedure corresponding to the Britt Jar method. Results showed that pulsations could increase the uniformity of paper, not only in the x-y direction, but also in some cases in the z direction as well. Under the conditions that were used for testing, a dual-polymer bridging system showed the greatest improvement in fine particle retention but this effect could be reduced by the application of hydrodynamic shear before dewatering. Following the application of high level of hydrodynamic shear, charge neutralization didn't show fully reversibility, and it was the least effective retention aid system compared with the other systems. Effects of new-designed cone rotor were also studied; making it possible to explore effects due to a well characterized average shear stress throughout the sample volume. For future studies, suggestions have been made to increase the usefulness of the PPJ as a tool in predicting the performance of new retention aid system under different forming conditions. See Publications involving Taweewat Tripattharanan. See M. S. Thesis online at http://www.lib.ncsu.edu/theses/available/etd-07092003-162828/unrestricted/etd.pdf .
The Adhesion of Paperboard to the Gypsum Core of Wallboard: An Investigation of Adhesive Bond Quality in Response to Paper Production Variables and Relative Humidity
With John A. Heitmann and Joel J. Pawlak. Award of Master of Science degree to Ryan Tomasiewicz.
Interactions between paperboard and the gypsum core during the manufacturing process of gypsum wallboard were investigated. The goal of this research was to understand the paper properties that can affect the quality of the adhesive bond under simulated test conditions. The categories of paper properties tested include strength properties, surface properties, and paper additives. This research showed that the current test methods in use did not provide enough sensitive and reproducibility data to gain crucial insight into the paper/core adhesive interaction. A new evaluation method must be secured. However, with the results obtained, it was believed that the three types of failure could be described. First, the adhesive bond may fail resulting in a clean peel during bond quality testing. Second, the paper bond network may fail resulting in complete paper coverage of the gypsum core. Third, a mixed failure of adhesive and paper bond resulting in incomplete and varied paper coverage of the gypsum core. See M. S. Thesis online at http://www.lib.ncsu.edu/theses/available/etd-06302003-135902/unrestricted/etd.pdf .
Development of Test Methods to Characterize Effects of Papermaking Additives on the Flocculation of Fiber Suspensions
Papermakers desire two seemingly
incompatible outcomes. On the one hand, strong agglomeration of fibers and fines
can help one to achieve rapid drainage and satisfactory fine-particle retention.
On the other hand, papermakers also want uniform distribution of fibers in the
sheet. Procedures have been developed in our lab to evaluate effect of different
retention and drainage chemical programs under stressed conditions of salt content,
fines content, or high levels of charged colloidal matter. In the work described
here the same tests were used to compare the reversibility of agglomerative
effects of some common classes of retention and drainage programs. Optical and
viscometric tests showed increased flocculation following treatment with increased
amounts of cationic polyacrylamide. Application of intense hydrodynamic shear
caused essentially complete reversal of flocculation. By contrast, treatment
with a highly charge density cationic polymer yielded a maximum in flocculation,
according to the optical test, at a treatment level corresponding to the point
of charge neutralization.
Divergent results were obtained when comparing fine-particle retention tests to drainage tests. In general, retention results were consistent with a model in which polymer bridges, i.e. "hard flocs," between fibers may be irreversibly broken by shear. Meanwhile, bonds formed between fibers and fine particles appeared to remain intact. In contrast, drainage results appeared to be more highly dependent on the electrokinetic properties of the furnish, i.e. factors related to "soft floc" formation.
Two types of chemical systems showed evidence that flocs formed again after the shear application were stronger or larger than those in an untreated slurry. An optical test showed that treatments that included poly-diallyldimethylammonium chloride (DADMAC) yielded a charge-dependent maximum in fiber flocculation that approximately corresponded to charge neutralization. By contrast, only a viscometric test showed a net increase in fiber flocs after treatments with cationic polyacrylamide (cPAM) following by nano-size anionic materials (microparticles) and intense shear. In certain cases the polyelectrolyte-induced bonds holding calcium carbonate filler particles to the fibers or to each other within the slurry appeared sufficient to withstand intense shear almost completely. Results support strategies in which hydrodynamic shear in a papermaking system helps to minimize fiber flocs, while leaving polymeric attachments to filler particles intact. See Publications involving "Reversibility."
Development and Applications of a Pressurized Streaming Potential Jar (SPJ) Device of Evaluation of Papermaking Fiber Suspensions
With post-doctoral research associate Fei Wang.
The streaming potential and other colloidal properties of aqueous suspensions of bleached kraft fibers were evaluated by a new laboratory instrument, the Streaming Potential Jar (SPJ). This device provides precise streaming potential data under moderately high electrical conductivity levels of 0.5 to 10 mS/cm. Features of the SPJ include automated operation, rapid acquisition and processing of data, continuous stirring, and applied pressures up to 276 kPa. The SPJ also provides data related to drainage rates and the turbidity of the filtrate. Test results showed a high degree of linearity of the streaming potential signals with applied pressure and little dependence of the results on the solids levels of the fiber slurries. These results, which are consistent with the Helmholtz-Smoluchowski equation, tend to justify the level of applied pressure used in this work. Changes in streaming potential with increasing pH were consistent with expected dissociation of surface-bound carboxyl groups on the fibers. The absolute magnitudes of the streaming potential values of bleached kraft pulps were strongly affected by increasing concentrations of Na2SO4. However, a high repeatability of measurements was obtained throughout the range of conductivities considered; relative standard deviations of streaming potentials were consistently below 3%. Titrations with poly-(diallyldimethylammonium chloride) yielded curves that had shapes similar to those of parallel tests by micro-electrophoresis; however, the amount of titrant needed to reach the endpoints was about three times higher in the case of the streaming potential tests. The disagreement between the endpoints determined by the two types of test is attributed to a diffusion process of the titrant into the porous fibers. See "Publications" involving Fei Wang.
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