Effects of spray drying on physicochemical properties of chitosan acid salts

Abstract

The effects of spray-drying process and acidic solvent system on physicochemical properties of chitosan salts were investigated. Chitosan used in spray dryings was obtained by deacetylation of chitin from lobster (Panulirus argus) origin. The chitosan acid salts were prepared in a laboratory-scale spray drier, and organic acetic acid, lactic acid, and citric acid were used as solvents in the process. The physicochemical properties of chitosan salts were investigated by means of solid-state CP-MAS (13)C nuclear magnetic resonance (NMR), X-ray powder diffraction (XRPD), differential scanning calorimetry, and Fourier transform infrared spectrometry (FTIR) and near-infrared spectroscopy. The morphology of spray-dried chitosan acid salts showed tendency toward higher sphericity when higher temperatures in a spray-drying process were applied. Analysis by XRPD indicated that all chitosan acid salts studied were amorphous solids. Solid-state (13)C NMR spectra revealed the evidence of the partial conversion of chitosan acetate to chitin and also conversion to acetyl amide form which appears to be dependent on the spray-drying process. The FTIR spectra suggested that the organic acids applied in spray drying may interact with chitosan at the position of amino groups to form chitosan salts. With all three chitosan acid salts, the FTIR bands at 1,597 and 1,615 cm(-1) were diminished suggesting that -NH groups are protonated. The FTIR spectra of all chitosan acid salts exhibited ammonium and carboxylate bands at 1,630 and 1,556 cm(-1), respectively. In conclusion, spray drying is a potential method of preparing acid salts from chitosan obtained by deacetylation of chitin from lobster (P. argus) origin.

Fig. 1

Scanning electron micrographs of a chitosan flakes, b chitosan acetate spray-dried at 120/80°C, c chitosan acetate spray-dried at 140/90°C, and d chitosan acetate spray-dried at 160/100°C

Fig. 2

Scanning electron micrographs of a chitosan lactate spray-dried at 120/80°C, b chitosan lactate spray-dried at 140/90°C, and c chitosan lactate spray-dried at 160/100°C

Fig. 3

Scanning electron micrographs of a chitosan citrate spray-dried at 120/80°C, b chitosan citrate spray-dried at 140/90°C, and c chitosan citrate spray-dried at 160/100°C

Fig. 4

X-ray powder diffraction patterns of chitosan powder (1) and spray-dried a chitosan acetate, b chitosan lactate, and c chitosan citrate samples at (2) 160/100°C, (3) 140/90°C, and (4) 120/80°C

Fig. 5

CP-MAS ¹³C NMR spectra of a chitosan acetate, b chitosan lactate, and c chitosan citrate samples spray-dried at a 160/100°C, b 140/90°C, and c 120/80°C

Fig. 6

FTIR spectra of a chitosan acetate, b chitosan lactate, and c chitosan citrate spray-dried at 120/80°C (the second curve from the top), 140/90°C (the third curve), and 160/100°C (the fourth curve). In each figure, a–c, the first curve (from the top) represents the FTIR spectrum of chitosan powder as a reference

Fig. 7

DSC thermograms of spray-dried a chitosan acetate, b chitosan lactate, and c chitosan citrate. In a, the DSC thermogram of chitosan powder is also shown as a reference (small figure)

Fig. 8

TGA thermograms of chitosan and spray-dried a chitosan acetate, b chitosan lactate, and c chitosan citrate

Fig. 9

Near-infrared reflectance spectra of spray-dried a chitosan acetate, b chitosan lactate, and c chitosan citrate. The second derivative of absorbance, log (1/R), at 1,800–2,060 nm