RHEOLOGICAL PROPERTIES OF CHITOSAN ACETATE BLENDS
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RHEOLOGICAL PROPERTIES OF CHITOSAN ACETATE BLENDS
RHEOLOGICAL PROPERTIES OF CHITOSAN ACETATE BLENDS WITH VINYL POLYMERS Katarzyna Lewandowska Nicolaus Copernicus University, Faculty of Chemistry, Chair of Chemistry and Photochemistry of Polymers, ul. Gagarin 7, 87-100 Toruń, Poland Abstract In the present paper the rheological properties of solutions of chitosan acetate (ChA), poly(vinyl alcohol) (PVA), polyacrylamide (PAM) and of ChA/PVA or ChA/PAM mixtures were studied. The measurements were carried out under the change of sample properties such as degree of hydrolysis PVA, molecular weight, and under variable experimental conditions such as temperature, shear rate, and blend composition. The criterion of miscibility of solution blends, based on the additivity rule of apparent shear viscosity has been discussed. Moreover, for the all investigated samples, the mathematical interpretation of relationship between the apparent viscosity ha and shear rate g, according to the Ostwald de Waele model was established. Activation energy of viscous flow (Ea) has also been determined and discussed. The obtained results suggested that the miscibility of ChA with PVA or PAM depends on the blend composition and on the molecular weight of ChA. Key words: chitosan, poly(vinyl alcohol), poly(acrylamide), blends, rheology. Progress on Chemistry and Application of Chitin and Its ..., Volume XIV, 2009 41 K. Lewandowska 1. Introduction Blending is one of the often applied method in modification of high molecular weight compounds. This method is usually cheaper and less time-consuming for the creation of polymeric materials with new properties than the development of new monomers and/or new polymerization routes. An additional advantage of polymer blend is that the properties of the materials can be tailored by combining component polymers and changing the blend composition. It is known that specific properties of chitosan (ChA), particularly connected with its bioactivity, biocompatibility and biodegradability, results in many applications e.g. in medicine, pharmacy and food and cosmetic industries. Poly(vinyl alcohol) (PVA) and polyacrylamide (PAM) are synthetic, water-soluble polymers, showing unique shearthickening properties. Rheological properties of ChA/PVA blend solutions has been studied by Mucha [1]. The author [1] did not consider the influence of the hydrolysis degree of PVA on the rheological properties of chitosan with PVA. The purpose of this study was to evaluate the miscibility of blends of hydrophilic high molecular weight compounds. The influence of PVA degree of hydrolysis (DH) on the rheological properties of ChA/PVA blend was investigated. 2. Materials and methods Flow measurements were carried out using a rotary viscometer Bohlin Visco 88 with concentric cylinder over a range of temperature from 298 K to 318 K and with shear rates up to 1220 s-1. The investigated blend system contained: poly(vinyl alcohol): PVA(99) {degree of hydrolysis DH = 99%, Mv = 1.2×105 g/mol}, PVA(88) {DH = 88%, Mv = 1.1×105 g/mol} with chitosan acetate: ChA {degree of deacetylation DD = 78% Mv = 1.5×106 g/mol}, polyacrylamide: (PAM) {Mv= 3×106 g/mol} with ChA. Chitosan, PVA and PAM were solubilized separately in 1 M aqueous acetic acid. Ternary solutions for each system were prepared by mixing the appropriate quantity of polymer solutions in the weight rations wA : wB of 0.2 : 0.8, 0.5 : 0.5 etc. 3. Results and discussion The criterion of miscibility of solution blends [1, 2], based on the logarithmic additivity rule of apparent shear viscosity {ha} has been discussed in the present work. Moreover, for the all investigated samples, the mathematical interpretation of relationship between the apparent viscosity ha and shear rate g, according to the Ostwald de Waele model was carried out [1 - 4]. Activation energy of viscous flow {Ea} was calculated with Arrhenius equation [1, 4]. The obtained solutions were transparent and stable as the reproducibility of the flow curves was very high. 42 Progress on Chemistry and Application of Chitin and Its ..., Volume XIV, 2009 Rheological Properties of Chitosan Acetate Blends with Vinyl Polymers ChA/PVA blends 1 0. 00 B. 1. 00 0. 10 a (P a s ) 0. 01 C hA/PVA 1 00 :0 8 0:20 5 0:50 2 0:80 0 :100 0. 00 1 0. 00 A. 1. 00 0. 10 0. 01 0. 00 10 1 00 1 00 0 (s-1 ) Figure 1. Apparent shear viscosity ha versus shear rate g of 2% of ChA and PVA and their mixtures: ChA/PVA(99), B. ChA/PVA(88); T = 298 K. 400 1/s ChA/PVA(99) 400 1/s ChA/PVA(88) 30 Ea (kJ/m o l) 25 20 15 10 5 0 0 0.2 0.4 0.6 0.8 1 wChA Figure 2. Activation energy of viscous flow of ChA and PVA and their mixtures versus weight fraction of ChA (wChA) in the mixture. Dotted line – the values calculated according to the additivity rule. Progress on Chemistry and Application of Chitin and Its ..., Volume XIV, 2009 43 K. Lewandowska 0.2 A. 320 s-1 ; ChA/PVA(99) log a -0.3 -0.8 -1.3 -1.8 -2.3 0 0.2 0.4 wChA 0.6 0.8 1 0.8 1 0.2 B. 320 s-1 ; ChA/PVA(88) log a -0.3 -0.8 -1.3 -1.8 -2.3 0 0.2 0.4 wChA 0.6 n n Figure 3. Logarithm of apparent shear viscosity (log ha) of ChA and PVA and their mixtures versus weight fraction of ChA (wChA) in the mixture; T=298K. Solid line – the values calculated according to the additivity rule. 1.6 1.4 1.2 1 0.8 0.6 0.4 0.2 0 1.6 1.4 1.2 1 0.8 0.6 0.4 0.2 0 A. ChA/PVA(99) 0 0.2 0.4 w ChA 0.6 0.8 1 B. ChA/PVA(88) 0 0.2 0.4 w ChA 0.6 0.8 1 Figure 4. Rheological parameter n in two shear rate ranges: u 19 s-1 < g < 400 s-1 and o 400 s-1 < g < 800 s-1 versus weight fraction of ChA (wChA) in the mixture; T = 298 K. 44 Progress on Chemistry and Application of Chitin and Its ..., Volume XIV, 2009 Rheological Properties of Chitosan Acetate Blends with Vinyl Polymers ChA/PAM blends 10.00 ChA/PAM 100:0 80:20 50:50 20:80 0:100 a Pa s 1.00 0.10 0.01 10 100 1000 s-1 Figure 5. Apparent shear viscosity ha versus shear rate g of 1% of ChA and PAM and their mixtures: ChA/PAM; T = 298 K. 0.2 400 1/s ChA/PAM log ha -0.3 -0.8 -1.3 -1.8 -2.3 0 0.2 0.4 w 0.6 0.8 1 ChA Figure 6. Logarithm of apparent shear viscosity (log ha) of ChA and PAM and their mixtures versus weight fraction of ChA (wChA) in the mixture; T = 298 K. Solid line – the values calculated according to the additivity rule. Progress on Chemistry and Application of Chitin and Its ..., Volume XIV, 2009 45 K. Lewandowska 1.6 1.4 1.2 N 1 0.8 0.6 0.4 0.2 0 0 0.2 0.4 0.6 w 0.8 1 ChA Figure 7. Rheological parameter n in two shear rate ranges:t 200s-1 < g < 800s-1 and c 800 s-1 < g < 1220 s-1 versus weight fraction of ChA (wChA) in the mixture; T = 298 K. 40 200 1/s Ea (k J /mol) 35 1130 1/s 30 25 20 15 10 5 0 0 0.2 0.4 0.6 w 0.8 1 ChA Figure 8. Activation energy of viscous flow of ChA and PAM and their mixtures versus weight fraction of ChA (wChA) in the mixture. Dotted line – the values calculated according to the additivity rule. 46 Progress on Chemistry and Application of Chitin and Its ..., Volume XIV, 2009 Rheological Properties of Chitosan Acetate Blends with Vinyl Polymers The experimental results for homopolymers PVA(99), PVA(88), ChA, PAM and their blends are shown in Figure 1 and Figure 5. The solutions of chitosan, PVA and PAM samples used in the present investigation, as well as their solution blends behave as non-Newtonian fluids (Figure 1; Figure 5). Similar behaviour in the case of chitosan solutions has been observed e.g. by Mucha [1]. The viscosity curves for PVA and PAM solutions may be roughly divided into to parts: a region below the critical value of shear rate gc {PVA(99): 19 s-1 < g < 700 s-1; PVA(88): 19 s-1 < g < 400 s-1; PAM: 19 s-1 < g < 1045 s-1}, where a relatively large shearthinning effect is observed, and a second region above the critical value of shear rate, gc , in which the shear-thickening behaviour occurs [4, 5]. In the case of solution blends, the shearthickening behaviour in the investigated range of shear rate (n < 1) was not observed. The activation energy of viscous flow EA versus blend composition given in Figure 2 depicted the positive deviations from the additivity rule in all the investigated systems. In case of ChA/PAM blend solutions, the negative deviations are observed (Figure 8). Figure 3 and Figure 6 shows the logarithm of apparent shear viscosity (log ha) investigated blends versus weight fraction of ChA (wChA). As can be observed, the positive deviation of log ha from the additivity rule of ChA/PVA solution blends are observed. For ChA/PAM blends, the log ha values (Fig. 6) fulfilled the linear dependence drawn according to the additivity rule. Moreover, the value of rheological parameter n both for used chitosan solution as for solution blends (Figure 4; Figure 7) is lower than one, which indicates a non-Newtonian, shear-thinning flow pattern of the fluids [6]. 4. Conclusions 1. The solutions of homopolymers and their blends used in the present investigation behave as non-Newtonian fluids. 2. For ChA/PVA blend solutions, the positive deviation of log ha and Ea from the additivity rule of ChA/PVA solution blends are observed. The positive deviations of Ea mainly depend on the PVA degree of hydrolysis. 3. In case of ChA/PAM blend solutions, the activation energy of viscous flow (Ea) show negative deviations from the linearity. This behaviour suggest that ChA with PAM are poorly miscible. 4. The obtained results may indicate some degree of miscibility of ChA/PVA and ChA/ PAM blends of suitable composition. 5. References 1. Mucha M.; Rheological properties of chitosan blends with poly(ethylene oxide) and poly(vinyl alcohol) in solution. Reactive& Functional Polymers 38, (1998) pp. 19-25. 2. Lewandowska K., Staszewska D. U., Trzciński S.; Progress on Chemistry and Application of Chitin and Its Derivatives, Monograph, vol. IV, In: H. Struszczyk (ed), Łódz, (1998) pp. 17-35. 3. Zhang L. M.; Synergistic blends from aqueous solutions of two cellulose derivatives. Colloid Polym Sci 277, (1999) pp. 886-890. Progress on Chemistry and Application of Chitin and Its ..., Volume XIV, 2009 47 K. Lewandowska 4. Lewandowska K.; Comparative studies of rheological properties of polyacrylamide and partially hydrolyzed polyacrylamide solutions. J Appl Polym Sci 103, (2007) pp. 2235-2241. 5. Lewandowska K.; Modyfikacja Polimerów, Stan i Perspektywy w Roku 2007, In: Steller R, Żuchowska D (eds), Wrocław, (2007) pp. 490-495. 6. Skellard A. H. P.; Non-Newtonian Flow and Heat Transfer. Wiley, New York (1967). 48 Progress on Chemistry and Application of Chitin and Its ..., Volume XIV, 2009