Potentiometric back titration as a robust and simple method for specific surface area estimation of lignocellulosic fibers

The specific surface area (SSA) of cellulosic or lignocellulosic fibers is seldom reported in the recent literature on papermaking, despite its close relation with the degree of refining and other key pulp properties. Amidst outdated assays (Pulmac permeability test) and methods that, while accurate, are of doubtful usefulness for papermaking purposes (N₂ adsorption–desorption), we suggest a methodology based on the cationic demand. A commonly used cationic polyelectrolyte, poly(diallyldimethylammonium chloride) (PDADMAC), became adsorbed onto thermomechanical pulp samples. Then, a potentiometric back titration with an anionic polyelectrolyte measured the cationic demand, expressed as microequivalents of PDADMAC per gram of pulp. Multiplying this value by the surface area of a microequivalent of polymer, considering rod-like conformation in the case of minimum ionic strength, yielded the SSA of the lignocellulosic pulp. Our system assumes that the quaternary ammonium groups were anchored through electrostatic and ion–dipole interactions. Measuring the carboxyl content allowed for discriminating between both kinds of forces. Finally, the model could be validated by plotting the estimated SSA values against the Schopper-Riegler degree, attaining high correlation coefficients (R²?~?0.98). Owing to the high molecular weight of the polyelectrolyte of choice (107 kDa), and more particularly in the case of fine-free pulps, SSA values estimated from the cationic demand were consistently lower than those from dye (Congo red) sorption. Instead of being a drawback, the limited diffusion of PDADMAC through fibers can enable papermakers to attain a more helpful quantification of the available surfaces in operations with low residence times.

     

Lignin adsorption on cellulose fibre surfaces: Effect on surface chemistry, surface morphology and paper strength

The adsorption of lignin on cellulose fibres at neutral pH and the effects of calcium ions and a cationic polyelectrolyte (PDADMAC) on the adsorption have been studied. The surface coverage by lignin was determined by electron spectroscopy for chemical analysis (ESCA). The morphology of the lignin layer was studied by atomic force microscopy (AFM). The effect of adsorbed polyelectrolyte and lignin on the strength properties of the paper was also studied. The adsorbed amount of lignin increased monotonically with lignin concentration. Addition of calcium ions resulted in a very high surface coverage by lignin. PDADMAC did not enhance the adsorption of lignin, but without addition of polyelectrolyte the lignin was very weakly attached to the fibre surface. PDADMAC formed complexes with lignin in solution. At high polymer/lignin concentration ratios the charge of the complex was positive and it adsorbed irreversibly as large blobs. At low ratios the complex was easily washed away from the fibre surface. When PDADMAC was pre-adsorbed on the fibre surface the lignin adsorbed as small granules at all lignin concentrations. Neither PDADMAC nor lignin alone increased the strength of pulp sheets significantly. However, together they increased the bonding between fibres.     

Conformations of Alternating Partially Fluorinated Copolymers in Dilute Ethanol Solutions

Equimolar copolymers of N-vinyl pyrrolidone with 1,1,1-3,3,3-hexafluoroisopropyl-α-fluoroacrylate were obtained by reversible addition-fragmentation chain transfer radical (RAFT) polymerization and by conventional radical polymerization (RAD). The copolymer conformation and compositional heterogeneity were analyzed by dynamic and static light scattering. RAFT copolymers of 41,000 ≤ M _w  ≤ 68,000 g/mol were shown to adopt cylindrical all-trans conformation. RAD copolymer of higher molecular mass (M_w = 390,000 g/mol) exhibited less extended conformation, thus indicating that the statistical Kuhn segment is less than RAD copolymer length.     

Water Accessibilities of Man-made Cellulosic Fibers – Effects of Fiber Characteristics

The dynamic vapor water sorption and desorption experiments were performed on cellulosic fibers with different characteristics. The hysteresis between moisture sorption and desorption cycle at 10% relative humidity (RH) was independent on the total moisture regain and approximately 45% for all materials except for viscose fibers. Brunauer–Emmett–Teller surface volume (V_m) for moisture sorption and retention capacity of liquid water (WRV) were also measured. The V_m and WRV increase in proportion to the total amount of moisture sorption (M_inf(total)) in all specimen except in poplar fiber. The coefficients of parallel exponential kinetics (PEK) were estimated by the curve-fitting of experimental data of the moisture regain, and the influences of the fiber characteristics on the PEK coefficients, the moisture regain, the hysteresis, V_m and WRV are discussed. The total equilibrium moisture content in the viscose fibers was higher but the moisture uptake and release rate was slower than the lyocell and poplar fibers. The cationization and the modification of shape of cross section accelerated the total equilibrium moisture content in the viscose fiber. A drying process at low temperature enhanced both the equilibrium moisture content and the moisture uptake and release rate in lyocell fibers while a spin finish retarded them. The total equilibrium moisture content was heightened by the crosslinking of the fiber, however, no obvious effect of the crosslinking on the moisture uptake and release rate was found. Effects of the type of the specimen and linear density on the moisture accessibilities are also discussed.     

Flocculation and stabilization of colloidal silica by the adsorption of poly-diallyl-dimethyl-ammoniumchloride (PDADMAC) and of copolymers of DADMAC with N-methyl-N-vinyl- acetamide (NMVA)

 The stabilization and flocculation behavior of colloidal silica-particles with cationic polyelectrolytes (PE) is investigated. The zetapotentials, diffusion coefficients and flocculation rate constants of silica particles have been measured as a function of the adsorbed amount of cationic polyelectrolytes poly(diallyl-dimethyl-ammoniumchloride) (PDADMAC) of different molar masses and of statistic copolymers of DADMAC and N-methyl-N-vinyl-acetamide (NMVA) of various compositions at different salt concentrations and pH-values. Very fast flocculation due to van der Waals attraction occurs if the zetapotential is small. At low ionic strength this condition occurs just below the plateau of the adsorption isotherms where the surface charges are screened by adsorbed polycations. Additionally with high molecular polycations slow mosaic flocculation is observed at lower PE concentrations. At high ionic strength fast flocculation takes place at low macroion concentration due to the screening of the surface charges by adsorbed polycations and salt ions. At medium concentrations of polycations below plateau adorption slow bridging flocculation is observed. At plateau adsorption the suspensions become stabilized up to high ionic strength. At low salt concentration charge reversal at full coverage with polycations results in electrostatic repulsion. At high ionic strength the particles are stabilized sterically due to the osmotic repulsion of the long adsorbed PE tails. Therefore macroions of high molar mass are necessary to stabilize the suspension at high ionic strength. Received: 27 January 1998 Accepted: 23 March 1988     

Adsorption of polyelectrolytes on colloidal latex particles, electrostatic interactions and stability behaviour

The stabilization and flocculation behaviour of colloidal latex particles covered with cationic polyelectrolytes (PE) is studied with photon correlation spectroscopy and zetapotential measurements. Diffusion coefficients, flocculation rate constants and zetapotentials have been determined as a function of adsorbed amount of cationic poly-(diallyl-dimethyl-ammoniumchloride) (PDADMAC) of different molar masses and of statistic copolymers of DADMAC and N-methyl-N-vinyl-acetamide (NMVA) of various compositions in water and at high ionic strength. Flocculation by van der Waals attraction can be observed if the zetapotential is low. This occurs, if the surface charge is screened by the oppositely charged cations. Furthermore, in the case of adsorption of high molecular polycations mosaic flocculation occurs if the adsorbed amount is low. At high ionic strength, flocculation takes place if the adsorbed amount is below the adsorption plateau. If the adsorption plateau is reached the suspensions become stabilized. In water the charge reversal at full coverage leads to electrosteric stabilization both with low and high molar mass polycations. At high ionic strength only polycations with high molar mass are able to stabilize the suspension. If a certain molar mass of the polycation is exceeded, steric stabilization of the suspension occurs due to the formation of long adsorbed PE tails and their osmotic repulsion. The layer thicknesses are determined as a function of the molar mass. Received: 4 July 2000/Accepted: 18 August 2000     

Cellulose wet wiper sheets prepared with cationic polymer and carboxymethyl cellulose using a papermaking technique

Carboxymethyl cellulose (CMC)-rich cellulose sheets were prepared with a cationic retention aid, poly[N,N,N-trimethyl-N-(2-methacryloxyethyl)ammonium chloride] (PTMMAC), using a papermaking technique. When 5% PTMMAC and 5% CMC were added to cellulose slurries, approximately 94% of the polymers were retained in the sheets by formation of polyion complexes between the two polymers. When the PTMMAC/CMC/cellulose sheets were soaked in solutions consisting of ethanol, water and calcium chloride (EtOH/H₂O/CaCl₂) with a weight ratio of 75:24:1, almost all PTMMAC and CMC molecules remained in the sheets, forming the structures of PTMMAC-N⁺Cl⁻ and CMC-COO⁻Ca²⁺Cl⁻ without dissolution of these molecules in the soaking solution. Thus, PTMMAC, CMC and calcium contents in the sheets were able to be determined on the basis of these PTMMAC and CMC structures from analytical data such as nitrogen, calcium and chlorine contents. The trade-off properties between sufficient wet strength in use and water-disintegrability after use can be added to the PTMMAC/CMC/cellulose sheets by selecting weight ratios of the EtOH/H₂O/CaCl₂ solution used as the impregnation liquid.     

Controlled release of drug via tuning electrospun polymer carrier

Medicated‐fibers have been obtained through electrospinning after rifampin was dissolved in poly (lactic acid)/chloroform solution. The relationship between polymer variables [such as concentration, molecular weight (M_w), and introducing hydrophilic block] and drug release from the electrospun fibers is disclosed. The results show that polymeric concentration and M_w are crucial for producing the medicated fibers, which influence not only the morphology of the medicated‐fiber but also drug release rate from fiber. At the same M_w, the drug release rate decreases with the increase of spinning concentration. At two different M_w blends, drug release behaviors change. When the low M_w content is in a dominant position, drug release rate depends largely on mixing ratio of two M_w contents; on the other hand, drug release rate is also dependent on concentration of spinning fluid. In addition, the block copolymer [poly‐L ‐lactic acid (PLLA)‐polyethylene glycol‐PLLA] shows faster release rate as compared to homopolymer (PLLA). © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011     

Molecular weight distribution and mechanical behavior of PBI fibers

Two different polybenzimidazole (PBI) samples have been investigated in order to correlate the differences in molecular weight distribution (MWD) with changes in the elastic modulus and strength of undrawn and drawn fibers. It has been found that within the weight-average molecular weight range (7,000 ≤ M_w ≤ 13,000) there was no obvious correlation with M_w and M_n. However, one sample had a narrow unimodal molecular weight distribution and the other a wide bimodal molecular weight distribution. The small percentage of high molecular weight present in the latter sample gave its fibers better mechanical properties. X-ray diffraction studies showed that the orientation in both drawn fiber samples was equal. This isolated the effects of the molecular weight distribution on mechanical properties.     

Polyelectrolyte multilayers on wood fibers: influence of molecular weight on layer properties and mechanical properties of papers from treated fibers

This paper compares the influence of the molecular weight of polylelectrolytes forming polyelectrolyte multilayers (PEM) on wood fibers on adhesion and paper strength. Sheets were made from fibers treated with poly(allylamine hydrochloride) (PAH)/poly(acrylic acid) (PAA) of molecular mass 70,000 and 240,000, respectively, and of poly(dimethyldiallylammonium chloride) (PDADMAC)/poly(styrene sulfonate) (PSS) of molecular mass 30,000 and 80,000, respectively. The results were compared to what has recently been reported for PEM formation on fibers using a low-molecular-mass combination of PAH and PAA and a high-molecular-mass combination of PDADMAC/PSS. There was a less significant improvement in the case of the low-molecular-mass PDADMAC/PSS and the high-molecular-mass PAH/PAA. The adsorbed amounts of PAH and PDADMAC were also determined, showing a lower adsorbed amount of the low-molecular-mass PAH than of the high-molecular-mass PDADMAC. The amount of low-molecular-mass PDADMAC was similar to that found for high-molecular-mass PDADMAC/PSS. Individual fibers were partly treated and studied, showing a less significant decrease in wettability with low-molecular-mass PDADMAC/PSS than with the high-molecular-mass combination. The effect of the molecular weight on the adhesion was discussed in terms of the structure and wettability of the PEMs.     

Mechanical properties and enzymatic degradation of poly[(R)-3-hydroxybutyrate] fibers stretched after isothermal crystallization near Tg

Poly[(R)-3-hydroxybutyrate] (P(3HB)) fibers with high tensile strength were prepared by stretching the fibers after isothermal crystallization near the glass transition temperature. Two samples with different molecular weights (M_w = 0.7 × 10⁶ and 4.3 × 10⁶) were used to investigate the effect on tensile strength. Increasing the time for isothermal crystallization of P(3HB) fibers resulted in a decrease in the maximum draw ratio. But, the tensile strength of P(3HB) fibers increased remarkably when the isothermal crystallization time was prolonged to more than 24 h. The tensile strength of low-molecular-weight drawn fibers was higher than that of high-molecular-weight fibers. Therefore, it can be concluded that this procedure does not increase the tensile strength of the high-molecular-weight drawn fibers. This is because, in this drawing method, small crystal nuclei grow initially during the isothermal crystallization process. Then, the molecular chains between the small crystal nuclei that acted as the entanglement points are oriented by stretching. In the case of the high-molecular-weight fibers, because the molecular length between the entanglement points of the small crystal nuclei is too long, the molecular chains are not sufficiently oriented by the stretching process. However, in the case of the low-molecular-weight fibers, the molecular length is suitable for generating the extended chains. Based on the result of X-ray analysis of P(3HB) fibers stretched after isothermal crystallization, fibers have the oriented α-form crystal with 2₁ helix conformation and β-form with planar zigzag conformation. The enzymatic degradation of the stretched P(3HB) fibers was performed by using an extracellular PHB depolymerase purified from Ralstonia pickettii T1. The enzymatic erosion rate of β-form was faster than that of α-form in the P(3HB) fibers stretched after isothermal crystallization.     

Interactions of PEI (polyethylenimine)–silica particles with citric acid in dispersions

Adsorbed polyethylenimine (PEI) of M _w 1,800 and 70,000 on silica (SiO₂) dispersions produced flocculated slurry in the pH range of 5 to 12. Adsorbed citrate widens this flocculated pH regime. It also increases the strength of the interparticle attractive force or the yield stress over the pH range of between 3 and 8. The stronger attractive force is due to particle bridging by the citrate anions bonding with positively charge sites of the adsorbed PEI layer of the interacting particles at the closest point of interaction. The higher M _w PEI being more strongly attached to the silica particle produced a stronger attractive interparticle force with adsorbed citrate anions. Via charge balance calculation using contributions from SiO₂, PEI, and citrate, the pH of zero charge was found to correspond to the pH of zero zeta potential for PEI of M _w 70,000. This suggests 100% adsorption of PEI and citrate on SiO₂. The bridging interaction was confirmed by a linear relationship between yield stress and the square of the limiting citrate charge content. Adsorbed citrate was found for the first time to play the role of a bridging agent, a result of the positive charges being located on a more flexible adsorbed layer rather than being fixed to a rigid surface.     

Coagulation and flocculation measurements by photon correlation spectroscopy — colloidal SiO2 bare and covered by polyethylene oxide

With photon correlation spectrometry (PCS) the diffusion coefficients, average diameters and polydispersities of colloidal particles can be determined in dilute aqueous suspensions. In this study PCS is used to follow the coagulation and flocculation of silica particles. Electrolyte solution added to suspensions of bare particles and of particles covered with adsorbed polyethylene oxide layers induces aggregation. The rate constants of aggregation are evaluated by the second-order Smoluchowski theory with the assumptions of spherical aggregated particles and volume proportional light-scattering amplitude. Adsorbed PEO layers of molar mass lower thanM _w=160000 decrease the critical flocculation concentration and the flocculation states and rate constants for bare and covered particles are the same at high electrolyte concentrations. Polymer layers of high molar mass (M _w=325000, 900000) reducved at full coverage the rate constants and stabilize the suspensions even at high electrolyte concentrations. At low coverage adsorption of high molar mass polymers results in the same values as of low molar mass PEO. The correlation between rate constants and hydrodynamic PEO layer thicknesses demonstrates the steric influence of the tails of the adsorbed macromolecules on stability and flocculation.Dedicated to Prof. Dr. Joachim Klein on the occasion of his 60th birthday     

Polymer diffusion in high-M/low-M hard-soft latex blends

This paper describes experiments that investigate the use of low glass transition temperature (T _g) latex particles consisting of oligomer to promote polymer diffusion in films formed from high molar mass polymer latex. The chemical composition of both polymers was similar. Fluorescence resonance energy transfer (FRET) was used to follow the rate of polymer diffusion for samples in which the high molar mass polymer was labeled with appropriate donor and acceptor dyes. In these latex blends, the presence of the oligomer (with M _n = 24,000 g/mol, M _w/M _n = 2) was so effective at promoting the interdiffusion of the higher molar mass poly(butyl acrylate-co-methyl methacrylate; PBA/MMA = 1:1 by weight) polymer (with M _n = 43,00 g/mol, M _w/M _n = 3) that a significant amount of interdiffusion occurred during film drying. Additional polymer diffusion occurred during film aging and annealing, and this effect could be described quantitatively in terms of free-volume theory. This paper is dedicated to Professor Haruma Kawaguchi to honor his many contributions to the field of latex particles and their applications.     

Relationships of lignosulfonate adsorption onto the zinc sulfide surface

Low-molecular-mass lignosulfonates (M _w = 9250 amu) are adsorbed more strongly onto ZnS from neutral solutions (pH 4.5–4.8), and high-molecular-mass lignosulfonates (M _w = 46300 rpm), from acid solutions (pH 1.4–1.5). The sorption of the low-molecular-mass sample at pH 1.5 is affected by competing sorption of the solvent (Н₂SO₄). The lignosulfonate samples studied are adsorbed onto zinc sulfide by the chemisorption mechanism.     

SYNTHESIS OF POLYPROPYLENE-POLY(METH)ACRYLATE BLOCK COPOLYMERS USING METALLOCENE CATALYZED PROCESSES AND SUBSEQUENT ATOM TRANSFER RADICAL POLYMERIZATION

ABSTRACT

The synthesis of block copolymers containing low molar mass polypropylene and poly(meth)acrylates is reported. Vinyl-terminated polypropylene (M_n SEC=3,100; M_w/M_n=1.45) was used to prepare a macroinitiator for atom transfer radical polymerization (ATRP) via hydrosilation with 1-(2-bromoisobutyryloxy)propyl-tetramethyldisiloxane. Polar segments were then incorporated to polypropylene by chain extension using either methyl methacrylate, or n-butyl acrylate. While blocking efficiency was limited in this system, well-defined PP-b-PMMA (M_n=22,220; M_w/M_n=1.14) was obtained by extraction of unreacted polypropylene with diethyl ether.     

Precision synthesis of (1→6)-α-D-glucopyranan by cationic ring-opening polymerization of 1,6-anhydro-2,3,4-tri-O-allyl-β-D-glucopyranose

The ring-opening polymerization of 1,6-anhydro-2,3,4-tri-O-allyl-β-D-glucopyranose ( 2 ) has been carried out using various cationic initiators. For the condition of [ 2 ]/[BF₃·OEt₂] = 20 at −15°C for 90 h, the polymer yield, M_w and M_w/M_n of the polymer obtained were 79%, 215,600 and 3.45, respectively. In order to study the living characteristic of the polymerization of 2 , the cationic ring-opening bulk polymerization initiated by trimethylsilyl trifluoromethanesulfonate (TMSOTf) was carried out under the condition of [ 2 ]/[TMSOTf] = 1000 at −15 °C. The M_w value increased in proportion to conversion until c.a. 30% and below. The M_w/M_ns of resulting polymers were very narrow, e.g., the M_w/M_n value was 1.2 and below, which was smaller than that for the solution polymerization using BF₃·OEt₂. These results indicated that the ring-opening bulk polymerization of 2 using TMSOTf was living-like.     

Quartz crystal microbalance with dissipation monitoring and surface plasmon resonance studies of carboxymethyl cellulose adsorption onto regenerated cellulose surfaces

Adsorption of anionic polyelectrolytes, sodium salts of carboxymethyl celluloses (CMCs) with different degrees of substitution (DS = 0.9 and 1.2), from aqueous electrolyte solutions onto regenerated cellulose surfaces was studied using quartz crystal microbalance with dissipation monitoring (QCM-D) and surface plasmon resonance (SPR) experiments. The influence of both calcium chloride (CaCl(2)) and sodium chloride (NaCl) on CMC adsorption was examined. The QCM-D results demonstrated that CaCl(2) (divalent cation) caused significantly greater CMC adsorption onto regenerated cellulose surfaces than NaCl (monovalent cation) at the same ionic strength. The CMC layers adsorbed onto regenerated cellulose surfaces from CaCl(2) solutions exhibited greater stability upon exposure to flowing water than layers adsorbed from NaCl solutions. Both QCM-D and SPR results showed that CMC adsorption onto regenerated cellulose surfaces from CaCl(2) solutions increased with increasing CaCl(2) concentration up to the solubility limit (10 mM). Voigt-based viscoelastic modeling of the QCM-D data indicated that the CMC layers adsorbed onto regenerated cellulose surfaces had shear viscosities of η(f) ≈ 10(-3) N·s·m(-2) and elastic shear moduli of μ(f) ≈ 10(5) N·m(-2). Furthermore, the combination of SPR spectroscopy and QCM-D showed that the CMC layers contained 90-95% water. Adsorption isotherms for CMCs in CaCl(2) solutions were also obtained from QCM-D and were fit by Freundlich isotherms. This study demonstrated that CMC adsorption from CaCl(2) solutions is useful for the modification of cellulose surfaces.     

Highly reactive polyisobutylenes via AlCl3OBu2‐coinitiated cationic polymerization of isobutylene: Effect of solvent polarity,temperature, and initiator

The cationic polymerization of isobutylene using 2‐phenyl‐2‐propanol (CumOH)/AlCl₃OBu₂ and H₂O/AlCl₃OBu₂ initiating systems in nonpolar solvents (toluene, n‐hexane) at elevated temperatures (?20 to 30 °C) is reported. With CumOH/AlCl₃OBu₂ initiating system, the reaction proceeded by controlled initiation via CumOH, followed by β‐H abstraction and then irreversible termination, thus, affording polymers (M_n = 1000–2000 g mol^?1) with high content of vinylidene end groups (85–91%), although the monomer conversion was low (≤35%) and polymers exhibited relatively broad molecular weight distribution (MWD; M_w/M_n = 2.3–3.5). H₂O/AlCl₃OBu₂ initiating system induced chain‐transfer dominated cationic polymerization of isobutylene via a selective β‐H abstraction by free base (Bu₂O). Under these conditions, polymers with very high content of desired exo‐olefin terminal groups (89–94%) in high yield (>85%) were obtained in 10 min. It was shown that the molecular weight of polyisobutylenes obtained with H₂O/AlCl₃OBu₂ initiating system could be easily controlled in a range 1000–10,000 g mol^?1 by changing the reaction temperature from ?40 to 30 °C. The MWD was rather broad (M_w/M_n = 2.5–3.5) at low reaction temperatures (from ?40 to 10 °C), but became narrower (M_w/M_n ≤ 2.1) at temperatures higher than 10 °C. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Tensile strength of highly oriented polyethylene. II. Effect of molecular weight distribution

The tensile strength of oriented polyethylene filaments is discussed in relation to molecular weight. Short-term tensile properties at room temperature were obtained in our laboratory and from the literature for polymer samples covering the molecular weight (M _w) range from 54 × 10³ to 4 × 10⁶, and polydispersities ranging from 1.1 to 15.6, oriented by solid-state extrusion, melt spinning/drawing, solution spinning/drawing, and “surface growth.” It was found that both the molecular weight and its distribution markedly affected tensile strength. The breaking stress σ of highly oriented fibers varied with molecular weight roughly as σ ∝, M^0.4, at constant M _w/M _n over the entire range studied. Reduction of polydispersity from 8 to 1.1 by an increase of M _n with M _w approximately constant at 10⁵ increased tensile strength of oriented polyethylene filaments by a factor of nearly 2.