Characterization and properties of lignocellulosic fibers with thin-film deposited cationic precursor

https://doi.org/10.1016/S0927-7757(01)00815-9Get rights and content

Abstract

Cationic pulp has been prepared by depositing ultra-thin films of a cationic silane precursor on the pulp surface. The deposited thin film has been characterized by relative measurement of film thickness and also by determining the charge behavior of the modified fiber surface in an aqueous suspension by streaming current, ionic mobility and charge density measurements. Although the calculated film thickness was found to be less than 30 Å, a significant difference in the calculated thickness values between X-ray photoelectron spectroscopy and ellipsometry was observed. Streaming current measurements confirmed that the cationic charge carrying capacity of cellulosic fibers depends on the hydrophobicity of the fibers. The charge density of the cationic fibers was found to be lower than conventional polyelectrolytes that are used as flocculants in wet-end papermaking. Effect of pH on the ionic mobility of the precursor deposited fibers demonstrated the more pH tolerant character of the cationic fibers compared to the unmodified fibers. Effect of precursor concentration on cationic charge behavior of cellulose, stoned ground wood and thermomechanical pulp demonstrated that, for most of the cation modified fibers, there was a marginal increase in charge with higher precursor concentration. Temperature and pH have little effect on charge properties. A partial replacement of anionic fiber by silane deposited cationic fiber in a fiber slurry improved fines and filler retention properties. Microscopic analyses of floc structure suggested that the improved retention properties exhibited by the cationic fibers could be due to the formation of smaller but stronger flocs at higher shear rates.

Introduction

In practical applications of polyelectrolytes their charge densities are often of great importance. This is especially the case for polymeric flocculant in water treatment, effluent treatment, wet-end papermaking and elsewhere. Very often it is found that the optimum dosage of the polymeric flocculant is close to that required to neutralize the surface charge carried by the fibers, fines and colloidal particles, although there are many important exceptions [1]. Mechanical pulps, which contain a large quantity of fines, are highly anionic in nature. Moreover, many reaction products of wood and pulping chemicals are low molecular weight organic compounds and are negatively charged. Anionic fines and colloidal particles participate in the charge repulsion process during the wet-end papermaking operation and deteriorate the fines’ retention efficiency on the fiber mat. It also results in increased white-water consistency and a large accumulation of anionic charge in drained water. The most common way to deal with the negatively charged particles and dissolved components in pulp suspension is by adding cationic additives, such as hydrolysing metal salts and cationic polyelectrolytes. In the latter case, there is a close stoichiometric relationship between the anionic charge carried by the particles and dissolved components and the cationic charge of the additive. Therefore, optimum dosages can be predicted if the appropriate charge information is available. The charge density of polyelectrolytes is therefore of interest.

Again, the electrical properties of colloidal particles formed during the pulping process is not only important for charge neutralization but also important for the prediction of its colloidal stability. The electrical properties of colloidal and dissolved substances also influence the degree of interference with polyelectrolytes and fines in retaining them on the fiber mat. The electrophoretic mobility of a colloidal particle is often used to predict colloidal stability [1]. Surfactant adsorption onto particle surfaces and protein binding to surfaces have also been investigated [2], [3] by calculating (zeta) potential or shear plane potential. However, there are several other approaches to calculate a potential from a given mobility value [4]. Therefore, a thorough understanding of the factors governing the value of mobility (μe) is essential for interpreting experimental data for surface molecules.

It is presumed that one of the possible means to improve retention of anionically charged lignocellulosic fines is to promote hetero-flocculation by increasing interaction between oppositely charged fibers, fines and polyelectrolytes. Unfortunately, the high charge density of polyelectrolytes requires lowering of their molecular weight or increasing the number of primary cationic charges such as positively charge primary amines. The process has two disadvantages. First, low molecular weight polyelectrolytes develop weak ionic interaction and are shear sensitive. They develop weak flocs and are easily destroyed under high shear conditions, which is very often encountered in modern paper machines. Second, high molecular weight primary amine type cationic-polyelectrolytes have reduced ionic mobility. We have already demonstrated in one of our earlier reports [5] that deposition of an ultra-thin film of a cationic precursor on lignocellulosic fiber surfaces can change the surface charge density of the fibers. Moreover, addition of such a lignocellulosic polyelectrolyte in a pulp suspension resulted in a change in the flocculation behaviour of fines and fillers. Our previously published report [5] on the fluorosilane deposition verified some of these conclusions. Optimization of the polyelectrolyte behaviour of a cationic precursor deposited lignocellulose requires further understanding of the mechanism of polyelectrolyte development and their colloidal stability.

In this work, first, we have examined and validated the ultra-thin film forming property of a cationic silane precursor on supercalendered lignocellulosic fiber mat surfaces using ESCA and ellipsometry techniques. We have also studied the electrokinetic properties of the precursor deposited fibers as characterized by streaming current, ionic mobility and colloidal charge measurements. Emphasis is given to understanding the mechanism of colloidal stability by examining the effect of the hydrophobic–hydrophilic character of the impregnation solution on the thin-film deposition, since it is known that this apparently secondary effect seriously influences both colloidal stability of polyelectrolyte and electrophoretic mobility [6]. Finally, the electrokinetic behaviour of electrostatically stabilized lignocellulosic polyelectrolyte particles is examined by retention study.

Section snippets

Electrophoretic mobility

In a recent work, a simple model based on the White and O'Brian [7] theory was introduced that allowed the theoretical calculation of electrophoretic mobility (μe) versus zeta (ζ) potential curves [8]. A given value for the charge density (α) is converted into surface potential (ψo) under the assumption that only a diffuse double layer exists, i.e., the Gouy–Chapman theory was valid. Since the reciprocal of double layer extension (κa values) values larger than ten were considered, the equation

Chemicals

Amino trimethoxy silane (CatA) containing positive surface charge was obtained from Aldrich Chemicals and was used as supplied. Cotton cellulose, stoned groundwood (SGW) and thermomechanical pulps (TMP) were obtained from local mills and were used after being boiled in hot water for 15 min and vacuum dried. Anhydrous methanol and toluene were obtained from Aldrich. All the water was deionized to >17 MΩ/cm resistance.

We have performed some model experiments to determine the thickness of the

Cationic lignocellulosics of molecular thickness

Before sampling for XPS, surface charge and mechanical properties of fibers and handsheets made from treated and untreated substrates were determined in triplicate. The standard deviation of three separate runs did not exceed 8%. The CHx, CNx and, for the Si substrates, SiOx and Si signals were recorded at a perpendicular exit angle and used to calculate the thickness of the silane substrate layer based on Beer's law of attenuation. Specifically, it is assumed that the signals escaping through

Conclusions

ESCA and ellipsometric measurements revealed that an ultra-thin film of cationic silane can be deposited on a supercalendered lignocellulosic surface. The thickness of the deposited film of cationic silane as determined by ESCA and ellipsometry is higher than that predicted from self-assembled monolayer formation. Moreover, thickness measured by ellipsometry and ESCA also differed to some extent. This study also demonstrated a novel usage of cationic fibre in controlling electrical charge in a

Acknowledgements

Authors gratefully acknowledge the financial support of Natural Science and Engineering Research Council, Canada.

References (24)

  • M. Sain

    J. Appl. Surface Science

    (2000)
  • L. Vorwerg et al.

    Colloid & Surface A.

    (1999)
  • M.F. Toney et al.

    J. Colloid and Interface Sci.

    (2000)
  • S. Materazzi et al.

    Thermochimica Acta

    (1997)
  • J. Lahaye et al.

    Carbon

    (1999)
  • Y. Chong et al.

    J. Fluorine Chem.

    (1992)
  • A. Bismarck et al.

    J. Fluorine Chem.

    (1997)
  • D.F. Evans et al.

    The Colloidal Domain

    (1994)
  • J.M. Penla et al.

    Colloids Surf.

    (1994)
  • F.G. Gonzales et al.

    Colloid Polym. Sci.

    (1991)
  • R.H. Alvarez et al.

    Adv. Coll. Interf. Sci.

    (1996)
  • P.E. Laibinis et al.

    Science

    (1989)
  • Cited by (12)

    • Utilization of bio-polymeric additives for a sustainable production strategy in pulp and paper manufacturing: A comprehensive review

      2021, Carbohydrate Polymer Technologies and Applications
      Citation Excerpt :

      The degree of substitution of quaternary ammonium group on the cationic cellulose can be confirmed by determination of nitrogen content before and after modification (Moral et al., 2015). Since the cationic modification of cellulose makes its surface positively charged, the same when used as an additive while paper making results in high filler retention, surface homogeneity, improved drainage property, improved absorption of anionic fines and strength enhancement (Halab-Kessira& Ricard, 1999; Montplaisir, Chabot & Daneault, 2006; Sain & Boucher, 2002; W. Xie, Feng & Qian, 2008). Gao et al. (2016) have specifically emphasized on the production and utilization of cationized cellulose fibrils (CCF).

    • Cationic fibers from crop residues: Making waste more appealing for papermaking

      2018, Journal of Cleaner Production
      Citation Excerpt :

      Sang and Xiao (2009) produced cationic fibers by grafting, resulting in improved retention of china clay, a filler whose surface charge is negative. Sain and Boucher (2002), using amino trimethoxy silane to produce cationic fibers, clearly enhanced the retention of fines. In this paper, we report the functionalization of alkaline pulps from rapeseed stalks, orange tree trimmings and wheat straw, whose capability as raw materials for papermaking has been already studied (Aguado et al., 2015; Moral et al., 2016).

    • Image analysis of modified cellulose fibers from sugarcane bagasse by zirconium oxychloride

      2010, Carbohydrate Research
      Citation Excerpt :

      However, the polymer is relatively inert as the hydroxyl groups responsible for most of the reactions with organic and inorganic reagents are involved in extensive inter- and intramolecular hydrogen bonding.11–13 In order to make the cellulose more reactive, surface modification has been carried out with many metal oxides.14–19 Depending upon the metal oxide, the use has related to a specific application, such as TiO2 for bactericidal activities20 and retention and analysis of Cr(VI), Al2O3 for immobilization of an ion-exchange polymer21 and organofunctional groups for metal adsorption from ethanol solutions22, ZrO2 for adsorption sulfate ions,23 and Nb2O5 for cobalt(II) porphyrin immobilization and as oxygen sensor.24

    • Advances in Preparation and Application of Cationic Cellulose Nanofibril

      2022, Zhongguo Zaozhi Xuebao/Transactions of China Pulp and Paper
    View all citing articles on Scopus
    View full text