Thermochimica Acta 493 (2009) 42–48 Contents lists available at ScienceDirect Thermochimica Acta journal homepage: www.elsevier.com/locate/tca Miscibility and thermal stability of poly(vinyl alcohol)/chitosan mixtures Katarzyna Lewandowska Nicolaus Copernicus University, Faculty of Chemistry, Chair of Chemistry and Photochemistry of Polymers, 7 Gagarin Street, 87-100 Torun, Poland article info Article history: Received 29 December 2008 Received in revised form 16 March 2009 Accepted 6 April 2009 Available online 17 April 2009 Keywords: Poly(vinyl alcohol) Chitosan Miscibility Blends Thermal analysis abstract The miscibility and the thermal behaviour of chitosan acetate (ChA) with poly(vinyl alcohol) (PVA) have been investigated by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and dynamic mechanical analysis (DMA). Chitosan is blended with poly(vinyl alcohol) in acetic acid solution and this solution is cast to prepare the blend film. From thermal curves the thermal transitions: T g , T m and characteristic temperatures of decomposition: T di , T max have been determined and compared. The influence of the degree of PVA hydrolysis on the thermal properties of blend systems has been discussed. Based upon the observation on the DSC analysis, the melting point of PVA is decreased when the amount of ChA in the blend film is increased. Though some broadening of the transition curves could be noticed (DSC, TGA and DMA), the obtained results suggest that in the solid ChA/PVA blends the components are poorly miscible. Only PVA sample with relatively low DH = 88% and hence low degree of crystallinity shows partial miscibility with ChA of relatively low molecular weight. © 2009 Elsevier B.V. All rights reserved. 1. Introduction Techniques of thermal analysis have been used for many years for characterization of polymer materials. Thus, differential scan- ning calorimetry (DSC), thermogravimetric analysis (TGA), dynamic mechanical thermal analysis (DMA) are widely employed in both scientific and industrial sector. The thermal properties of polymers give valuable information regarding stiffness, toughness, stability and miscibility in blends [1–6]. Chitosan (ChA) is a linear polysaccharide which consists of 2-amino-2-deoxy--d-glucopyranose and 2-acetamido-2-deoxy- -d-glucopyranose. This biopolymer is obtained by the process of alkaline N-deacetylation of chitin. Chitosan is a weak polybase, showing a polyelectrolytic effect in aqueous dilute acidic solutions [7,8]. Unique properties of chitosan such as bioacitivity, biocompat- ibility and biodegradability have resulted in an increasing interest of its investigation and application e.g. in medicine, pharmacy and food and cosmetic industries. Poly(vinyl alcohol) (PVA) is a synthetic, non-ionic polymer solu- ble in water. PVA is recognized as a biodegradable polymer [9–11]. Its properties mainly depend on the degree of hydrolysis. Studies of physico-chemical properties of chitosan with poly(vinyl alcohol) in solid state have been reported [12–19]. Mechanical properties and FTIR characterization of ChA/PVA films have been studied by Miya et al. [12], Guthrie and co-workers [13], Marsh and co-workers [16] and Tharanathan and co-workers [17]. E-mail address: reol@chem.uni.torun.pl. Mucha et al. [14,18,19] has reported the results of thermal and rheo- logical properties. These studies have shown that ChA with PVA are poorly miscible. Moreover, FTIR analysis has revealed the existence of weak hydrogen bonding interactions between PVA and chitosan [12,16,17]. Young and co-workers [15] has studied the ChA/PVA blending by DSC, SEM and electron spectroscopy for chemical anal- ysis (ESCA) and found that this system undergoes phase separation. The SEM photographs shown the ChA/PVA blended membrane undergoes dramatic changes on the surface and bulk structure dur- ing the membrane formation [15]. However, the authors of these investigations did not frequently give full characteristics of the used polymer samples. Thus, some interesting aspects still remain to be elucidated such as the influence of the degree of hydrolysis of PVA and the molecular weight of the homopolymers (ChA) on the miscibility in the blend. The purpose of this work is the evaluation of the miscibility of chitosan acetate differing in molecular weight with poly(vinyl alco- hol) of different degrees of hydrolysis on the basis of differential scanning calorimetry (Hyper DSC), thermogravimetric analysis and dynamic mechanical thermal analysis (DMA). 2. Experimental 2.1. Materials The high molecular weight compounds used in this work were commercial products whose properties are given in Table 1. Dis- tilled water and 0.1M aqueous acetic acid were used as solvent. The viscosity average molecular weight M v of chitosan and PVA was measured with an Ubbelohde viscometer. The 0040-6031/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.tca.2009.04.003