Elsevier

Carbohydrate Polymers

Volume 63, Issue 1, 18 January 2006, Pages 113-121
Carbohydrate Polymers

Mechanical and electrical properties of paper sheets treated with chitosan and its derivatives

https://doi.org/10.1016/j.carbpol.2005.08.028Get rights and content

Abstract

This work focused on studying the dependence of paper sheet strength properties on the composition of additives, namely chitosan, cyanoethyl and carboxymethyl chitosan. Chitosan and its derivatives enhanced the strength properties of unagged and aged paper sheets. Also, cyanoethyl chitosan improved the dielectric properties of the treated paper sheets. The dielectric study was carried out over a frequency range from 100 Hz to 100 kHz at temperature range from 20 to 140 °C. The variations of permittivity ε′ versus the cyanoethyl chitosan content at three different temperatures show the highest dielectric properties at cyanoethyl chitosan of 0.3%. The variation of ε″ versus the applied frequency was fitted by a superposition of Fröhlich and Havriliak–Negami functions in addition to the conductivity term. These functions could be ascribed by the Maxwell–Wagner effect and the orientation of the large aggregates formed by the addition of chitosan to the paper sheet.

Introduction

Paper fiber is held together by hydrogen bonds (Olsson & Salmen, 2004). These bonds affect the distance between the separate cross-linked fibers. Water molecules play an important role in the interfiber linkage. A large excess of free water, however, causes weakness of wet strength in paper sheets and paper board (Gardlund, Wagberg, & Gernandt, 2003). To improve the wet strength of the paper sheets, a number of resins and polymeric materials have been used such as urea, phenol- and melamine-formaldehyde resins (Gernandt, Wagberg, Gardlund, & Dautzenberg, 2003) in addition to polyacrylamide, polymethyl methacrylate (Nada et al., 1996, Nada and El-Saied, 1989), vinyl acetate–vinyl chloride copolymer (Nada & Ayoub, 1997). Moreover, some other polymers were used to increase the resistance of paper sheets toward water absorption such as perfluorated urethane mixture (Aboshosha, Ibrahim, & Nada, 1996).

On the other hand, some polymers were used for treatment of paper sheets to decrease its influence to the photo yellowing (Nada, El- Sakhawy, & Soliman, 1997). These polymers usefully used to treat the old paper documents (Nada, Kamel, & El-Sakhawy, 2000) and enable the interfiber bonding area to remain chemically linked in the presence of water. Otherwise, these polymeric materials can be used as additives during paper sheets formation or as solution to dip the paper sheet in it. The surface modification of cellulose fiber permits the direct formation of hydrogen bonds between the fiber surface areas (Mucha, 1998). The feature of good strength additives must be: (a) soluble in water based system, (b) substantive to cellulose so that its retention is efficient, (c) compatible with cellulose, (d) film forming to offer adhesive resistance, (e) contain a functional group capable of ionic or covalent bonding with paper fiber. Chitosan is known to be non-toxic and odorless, so much interest has been paid to its industrial applications in the past decade (Ikejima et al., 1999, Shignemasa and Minami, 1995). In addition, chitosan is expected to be useful in the development of composite materials such as blends or alloys with other polymers, since chitosan has many functional groups such as hydroxyls, amines and amides (Muzzarelli, 1997, Zong et al., 2000).

Dielectric measurements are considered to be powerful tools for studying the molecular behavior of polymeric materials, for such reason it attracts many authors to investigate the dynamics of cellulosic and polymer materials by using dielectric technique (Einfeldt et al., 2002, Einfeldt et al., 2003, Einfeldt et al., 2004, Nada et al., 2004).

In the present work, chitosan and its derivatives, cyanoethyl and carboxymethyl chitosan were used as additives to cellulose fiber during the formation of paper sheet or as solution for dipping the paper sheet in it. Infrared spectra of chitosan and its derivatives were detected. The dielectric properties as well as the mechanical properties of the produced paper sheets were also investigated.

Section snippets

Materials

Unbleached Kraft bagasse pulp, delivered by Edfo Paper Mill (Upper Egypt) was used in this work. Chitosan, commercial grade with 85% degree of deacetylation was used.

Acrylonitrile (AN) and monochloroacetic acid of analytical pure grades were used.

Cyanoethylation of chitosan

Five grams of chitosan were suspended in 250 ml 30% NaOH (w/v), then 150 ml AN were added to the chitosan solution and refluxed for 6 h. The produced cyanoethyl chitosan was precipitated by methanol, filtered by using a G2 sintered glass funnel and washed

Infrared spectra

Chitosan undergoes different reactions to produce derivatives used as additives in paper sheets. Cyanoethyl and carboxymethyl chitosan were prepared from chitosan. Infrared spectroscopy was used to follow the chemical structure of the produced derivatives. The infrared spectra (Fig. 1) of chitosan and its derivatives showed a band (shoulder) appeared at 3063 cm−1 due to NH2 stretching vibration (ElNashar, Abd-El-Messieh, & Basta, 2004). The relative absorbance of the band at 3400 cm−1 which is

Conclusions

Addition of chitosan or its derivatives achieve an improvement in the strength properties of paper sheets before/after aging. Additions of mixture of cyanoethyl and carboxymethyl chitosan improve the mechanical properties of the produced paper sheets. Values of breaking length of treated paper sheets, with chitosan or its derivatives, by the addition method during sheet formation are higher than those obtained with the dipping method. On the other hand, values of tear factor for treated paper

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