Elsevier

Carbohydrate Polymers

Volume 116, 13 February 2015, Pages 149-158
Carbohydrate Polymers

Antifouling coating of cellulose acetate thin films with polysaccharide multilayers

https://doi.org/10.1016/j.carbpol.2014.04.068Get rights and content

Highlights

  • Manufacturing of partially and fully deacetylated cellulose acetate thin films.

  • Tuning of film thickness, surface composition, wettability and morphology.

  • Correlation of alternating change in structural self-assembly, wettability and layer thickness.

  • Successful removal of the multilayer coatings using HCl/NaCl solutions.

Abstract

In this investigation, partially deacetylated cellulose acetate (DCA) thin films were prepared and modified with hydrophilic polysaccharides with the layer-by-layer (LbL) technique. As polysaccharides, chitosan (CHI) and carboxymethyl cellulose (CMC) were used. DCA thin films were manufactured by exposing spin coated cellulose acetate to potassium hydroxide solutions for various times. The deacetylation process was monitored by attenuated total reflectance-infrared spectroscopy, film thickness and static water contact angle measurements. A maximum of three bilayers was created from the alternating deposition of CHI and CMC on the DCA films under two different conditions namely constant ionic strengths and varying pH values of the CMC solutions. Precoatings of CMC at pH 2 were used as a base layer. The sequential deposition of CMC and CHI was investigated with a quartz crystal microbalance with dissipation, film thickness, static water contact angle and atomic force microscopy (AFM) measurements. The versatility and applicability of the developed functional coatings was shown by removing the multilayers by rinsing with mixtures containing HCl/NaCl. The developed LbL coatings are used for studying the fouling behavior of bovine serum albumin (BSA).

Introduction

Besides other materials, cellulose acetate (CA) was one of the first polymers used for filtration membranes in water purification (Kutowy & Sourirajan, 1975). CA is a renewable and bio-based material which exhibits several reliable properties such as moderate hydrophilicity, high biocompatibility, good desalting properties, and a high potential flux (Han et al., 2013, Hayama et al., 2004). Despites its advantages, CA has poor fouling resistance, which is caused by the accumulation of biological foulants (bacteria, cells, proteins, etc.,) on the membrane surface (Jones and O’Melia, 2001, Koseoglu-Imer et al., 2012). Fouling can lead to a drastic decline in permeate flux, filtration efficiency and lifetime of a membrane. To overcome this, surface functionalization of the CA substrate is an option. Among other techniques, available the layer-by-layer (LBL) technique is a simple and straightforward approach. This method is based on the alternate exposure of a substrate to positively and negatively charged components. It provides the possibility to introduce a large variety of functional materials into a coating (Findenig et al., 2012, Hadj Lajimi et al., 2011). This makes the technique a powerful tool to create customized anti-fouling surfaces. Polysaccharides (PS) are promising materials for creating such surfaces due to their diverse chemical composition (Bauer et al., 2013). Even though multilayer coatings from water soluble PS are known, (Hadj Lajimi et al., 2011, Radeva et al., 2006) their influence on the protein rejection behavior has not been studied extensively. Hadj Lajimi et al. (2011) investigated the LbL assembly of chitosan and alginic acid on CA membranes. The BSA coated surfaces were subsequently tested for their salt rejection properties (Hadj Lajimi et al., 2011). Keeping this fact in mind, we became interested if chitosan (CHI) and carboxymethyl cellulose (CMC) on CA can be used for reducing the fouling of BSA (Jeyachandran, Mielczarski, Rai, & Mielczarski, 2009).

Both, chitosan and CMC are renewable, biocompatible, non-toxic and biodegradable (Bulwan al., 2012). CMC is negatively charged in aqueous solution and can adsorb irreversibly on cellulose-based substrates (e.g. deacetylated cellulose acetate) via relatively selective cellulose-cellulose interactions (Kargl et al., 2012, Laine et al., 2002). CHI, a positively charged PS, has found application in the medical field (e.g. drug delivery), and is also able to bind CMC irreversibly via complex formation (Zhang et al., 2007, Zhang et al., 2013).

To obtain a better understanding and control on the growth of the multilayers under different pH (Schoeler et al., 2003, Shiratori and Rubner, 2000) and charge densities, (Glinel et al., 2002, Schoeler et al., 2001) it is advantageous to use thin CA model films (ca. 30 nm thickness) instead of membranes. Membranes exhibit great complexities in terms of composition, roughness, morphology, which often leads to results that are not directly comparable. However, model films consist of thin coatings on flat substrates and can be manufactured by a simple spin coating technique. In this case, a comprehensive characterization of the substrates can be carried out and modern surface analytical techniques can be utilized. One such technique for monitoring in situ self-assembly of charged PS on thin films is the quartz crystal microbalance with dissipation (QCM-D) (Dixon, 2008, Findenig et al., 2013). QCM-D allows studies on the interaction of dissolved polymers or proteins with thin solid films by measuring the frequency changes of an oscillating quartz crystal. Furthermore, QCM-D allows to probe polymer–polymer interaction, complex formation, surface hydration and viscoelastic properties of the adsorbates. The purpose of this study was therefore to prepare deacetylated cellulose acetate (DCA) model films, to explore their properties and to use them for the deposition of multilayers from CMC and CHI. To elaborate and develop the built up of thin LbL films from these polyelectrolytes two different methods were employed. In the first method, the same ionic strength and pH value was used for both polyelectrolyte solutions. In the second method, the pH value was varied for electrolyte free CMC solutions and kept constant for the CHI solutions. The potential application of the developed coatings is shown in the fouling behavior of BSA.

Section snippets

Material and methods

Cellulose acetate (CA, acetyl content: 39.8 wt.%, degree of substitution, DS: 2.5, molecular weight, Mw: 30 kDa), sodium salt of carboxymethyl cellulose, (CMC, DS: 0.7, Mw: 90 kDa), chitosan, CHI (deacetylation: 75–85%, low molecular weight, viscosity at 25° (1 wt.%, in 1 wt.% acetic acid) 20–300 mPa s, product Number: 448869), bovine serum albumin (fraction V, ≥96%), disodium phosphate heptahydrate (Na2HPO4·7H2O), sodium dihydrogen phosphate monohydrate (NaH2PO4·H2O) and glacial acetic acid (≥99.7%)

Cellulose acetate (CA) film characterization: Structure, thickness and wettability

The ATR-IR spectra of spin coated cellulose acetate (CA) films before and after deacetylation are shown in Fig. 1a. CA films, show characteristic peaks for single bondCdouble bondO, single bondCsingle bondO and single bondCsingle bondCH3 at 1749, 1251 and 1376 cm−1 (Kim, Nishiyama, & Kuga, 2002). In the case of deacetylated cellulose acetate (DCA) films (10 to 30 min), the emergence of hydroxyl groups (as indicated by a broad peak at ∼3244 cm−1) and the subsequent reduction of the C = O peak are observed (Kargl et al., 2012). This proves that CA films are

Conclusion

Simple LbL methods for creating antifouling coatings from the alternating deposition of hydrophilic polysaccharide multilayers of chitosan (CHI) and carboxymethyl cellulose (CMC) on partially deacetylated cellulose acetate (DCA) films were developed in this study. Deacetylation was necessary to increase the reactivity of cellulose acetate (CA) and irreversibly immobilize the multi-layers. Upon treatment of CA with potassium hydroxide, hydrophilicity is increased and film thickness is reduced as

Acknowledgment

The research leading to these results has received funding from the European Union Seventh Framework Programme (FP7/2007-2013) under grant agreement no. 214653. The authors acknowledge the financial support from the Ministry of Education, Science and Sport of the Republic of Slovenia through the program no. P2 0118.

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