Miscibility studies of the blends of chitosan with some cellulose ethers

Abstract

The polymeric films have been prepared based on blends of chitosan with two cellulose ethers—hydroxypropylmethylcellulose and methylcellulose by casting from acetic acid solutions. The films were transparent and brittle in a dry state but an immersion of the samples in deionized water for over 24 h leads to their disintegration or partial dissolution. The miscibility of the polymers in the blends has been assessed by infrared spectroscopy, wide-angle X-ray diffraction, scanning electron microscopy and thermal gravimetric analysis. It was shown that although weak hydrogen bonding exists between the polymer functional groups the blends are not fully miscible in a dry state.

Introduction

The blending of polymers, which results in preparation of new materials with improved physicochemical and mechanical properties, has received considerable attention of researchers in the past several decades. The final properties of the blends are determined by the miscibility of the polymers, which is greatly favored by formation of intermolecular hydrogen bonds between the component polymers (Coleman and Painter, 1995, He et al., 2004, Jiang et al., 1999).

Chitosan is a polyaminosaccharide, which is produced by partial N-deacetylation of chitin. Chitosan exhibits unique physicochemical properties and it is highly suitable for biomedical application due to its biocompatibility, non-toxicity, biodegradability, etc. In the past few years a number of publications appeared on the blending of chitosan with various polymers such as poly(vinyl alcohol) (Mucha and Pawlak, 2005, Pawlak and Mucha, 2003), poly(N-vinyl pyrrolidone) (Sakurai, Maegawa, & Takahashi, 2000), poly(ethylene oxide) (Amiji, 1995), starch (Pawlak & Mucha, 2003), cellulose (Twu et al., 2003, Wu et al., 2004) and its derivatives (Mucha and Pawlak, 2005, Pawlak and Mucha, 2003), etc.

Earlier Suto and Ui (1996) have reported on the chemical cross-linking of chitosan/hydroxypropylcellulose blends with glyoxal and glutaraldehyde. Based on the similarity of the backbones of chitosan (CHI) and hydroxypropylcellulose (HPC) they assumed that these polymers are miscible in the blend. The cross-linked films were shown to be amorphous, although the uncross-linked films retained cholesteric liquid crystalline order.

Pawlak and Mucha (2003) reported that the CHI/HPC blends form transparent homogeneous films at any polymer ratio, which is the result of strong hydrogen bonding interactions between the functional groups of the component polymers. Moreover, the presence of HPC in the blend was found to improve the thermal stability of CHI. The blends exhibited two stages of decomposition characteristic for both polymers. Later on the same authors (Mucha & Pawlak, 2005) have studied the CHI/HPC blending by dynamic mechanical thermal analysis and differential scanning calorimetry and found that this system undergoes phase separation, which occurs more drastically upon removal of water traces. The water molecules in this system were found to be an active compatibilizer, which works as a ‘glue’ acting by formation of additional hydrogen bonds.

In the present work, we have attempted to clarify the question on miscibility of chitosan with two cellulose ethers—hydroxypropylmethylcellulose (HPMC) and methylcellulose (MC) by infrared spectroscopy, wide-angle X-ray diffraction, scanning electron microscopy and thermal gravimetric analysis.