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Boletín de la Sociedad Chilena de Química

versión impresa ISSN 0366-1644

Bol. Soc. Chil. Quím. v.47 n.4 Concepción dic. 2002

http://dx.doi.org/10.4067/S0366-16442002000400025 

Synthesis and Characterization of
Chitosan-PHB Blends

GALO CÁRDENAS T. 1* and JOHANA SANZANA L1
2LUCIA H. INOCCENTINI MEI

1Departamento de Polímeros, Facultad Ciencias Químicas
Universidad de Concepción, Casilla 160-C, Concepción(Chile)
e-mail: gcardena@udec.cl
2Departamento Tecnologia Polimeros, Faculdade Engenharia
Unicamp, Brasil

(Received: March 21, 2001 - Accepted, September 8, 2002)

SUMMARY

Blends of chitosan, [poly( ß-1,4)-2-amino-2-deoxy-D-glucopyranose], CH, the desacetylated product of chitin, with poly(3-hydroxybutyrate), PHB, usingratios of 90/10, 75/25, 50/50, 25/75, and 10/90 of chitosan-PHB were
obtained.

The blends were obtained using trifluoracetic acid as co-solvent under continue stirring at room temperature. Chitosan was obtained from shrimps shells of `Mv = 81,430 Daltons and 91% deacetylation degree, DS, was used. The PHB comes from biological fermentation process (Copersucar, Sao Paulo, Brazil) and their `Mv = 183,200 Daltons. The elastomeric products were characterized by elemental analyses, thermogravimetry, FT-IR and SEM.

KEYWORDS: blends, chitosan, hydroxybutirate, deacetylation degree

RESUMEN

Se obtienen blendas de quitosano poli (b -1-4)-2-amino-2-deoxi-D-glucopiranosa, CH, el producto desacetilado de las quitina, con poli(3-hidroxibutirato), PHB, usando razones en peso de 90/10, 75/25, 50/50, 25/75 y 10/90 de quitosano con PHB.

Las blendas se preparan usando ácido trifluoracético como so-solvente bajo continua agitación a temperatura ambiente. El quitosano se obtiene desde quitina separada de caparazones de langostinos, `Mv = 81.430 Daltons y con una desacetilación de 91 % (DS). El PHB proviene de un proceso de fermentación biológica (Copersucar, Sao Paulo, Brazil) y su `Mv = 183.200 Daltons. Los productos elatoméricos fueron caracterizados por análisis elemental, termogravimetría, FT-IT y microscopía electrónica de barrido (SEM).

PALABRAS CLAVES: blendas, quitosano, hidroxibutirato, gas de desacetilación

INTRODUCTION

Blends, such as chitosan with cellulose have been reported (1,2). Some other blends using poly(hydroxybutyrate) and poly(hydroxyvaleryate) have been prepared (3,5). Chitosan has been crosslinked with glutaraldehyde (6,7) and with other reactants (8,9) to produce soluble polymers. Also, hydrogels by ionic or chemical cross-linking (10,11) have been reported.

Due to the great contamination problems provocated in municipal waste fields and tons due to the great amounts of synthetic polymers such PE, PP, PS, PAN, PVC and others, we are proposing the synthesis of blends using biopolymers which are degradable.

In order to prepare these blends a trifluoracetic acid was used as a co-solvent. In the case of chitosan and PHB a possible interaction between the ¾OH of butyrate and the ¾NH2 of the chitosan can be established.


The poly(hydroxyacids) are synthesized by microorganisms under good nutrient conditions in the presence of an excess of energy sources and oxygen using stainless steel reactors. The most important poly(hydroxyacids) PHA, is the poly[(R)-3-hydydroxybutyrate], a lineal homopolymer built in units of R-3-HBA (7).

The copolymers of [(R)-3-hydroxybutyrate and (R)-3-hydroxyvaleryate] are obtained with relative economic import due to their similar properties of the material with polypropylene and they are sold under the trade mark "biopol". Both poly (3-HB) and poly (3-HV) and their copolymers are biodegradable and their syntheses are based on renewable material (8,9).

EXPERIMENTAL

Blends. The chitosan (CH) and PHB were dissolved separatelyin trifluoroacetic acid under stirring. The polymer solutions were mixed unde stirring at room temperature with different weight ratios (10/90, 25/75, 50/50,75/25 and 90/10 for CH/PHB).Then the solutions were neutralized with NaOH 15%. The blends were dialyzed and lyophilized for purification.

Elemental Analysis. The carbon, hydrogen and nitrogen were determined in a Perkin-Elmer Model 2400, Serie II CHNS Analyzer.

FT-IR. The infrared spectra were recorded in a FT-IR Nicolet Magna 550 with detector 4 cm-1 resolution. The samples of the homopolymers were prepared using 100 mg of KBr and 2 mg of each polymer. However the blends were measured in NaCl cell due to the elastomeric behavior of the blends and unable to mix with KBr.

Scanning electron microscopy (SEM). The samples were coated with gold for 3’ to obtain a thickness of 150 A° on the polymers , an Edwards S 150 Sputter Coater was used. The electron micrographs were analyzed in an ETEC Austoscan Model U-1 for a morphological study of the blends.

Thermogravimetric studies. Thermogravimetric analysis were performed in a STA 625 combined TG-DSC equipment from Polymer Laboratories. The gas used was N2 at a heating rate of 10°C/min. From 25 to 450°C.

Molecular Weights. An Ostwald viscometer of 0.45 and 0.35 mm, was used for chitosan and PHB, respectively. A Thermostatic bath from Cole-Palmer Model was used. After getting the intrinsic viscosity from tables the K and a, were obtained for HAc/NaAc and CHCl3, respectively. From these data and the Kuhn ¾ Mark ¾ Houwinks equation the average viscosimetric molecular weight can be obtained. (Chitosan: K=0.076, a= 0.76; PHB: K= 0.01168, a= 0.78), respectively (12).

Deacetylation degree. A pH meter WTW pH 531, combined glass electrode WTW pH 531 was used. The percentage of the deacetylation in chitosan was determined using potentiometric titration (13).

RESULTS AND DISCUSSION

The blends of chitosan were prepared with trifluoroacetic acid as a co-solvent. The blends were obtained after liophilization. The blends composition is summarized in Table 1. Several ratios of chitosan /PHB were obtained 10/90, 25/75, 50/50, 75/25, and 90/10. The yield of the blends were almost quantitative.

Table 1. Blends composition


Blend
(g)

Chitosan
(g)

PHB

 


1 (50/50)

0.50

0.50

2 (75/25)

0.75

0.25

3 (25/75)

0.25

0.75

4 (90/10)

0.90

0.10

5 (10/90)

0.10

0.90



A dramatic decrease in the carbon and hydrogen is observed in most of the blends. Also the nitrogen contents decreases, most probably a decarbonylation and deamination process occurs during the reaction. The deamination and decarboxylation mosdt probably occurs by the reaction of chitosan with trifluoracetic acid due to the blends formation. It is interesting to observe that C/H ratio is constant in the blends with chitosan content.

Table 2. Elemental analysis of Homopolymers and Blends.


SAMPLE

CARBON
%

HYDROGEN
%

NITROGEN
%


Chitosan

42.62

7.73

7.98

PHB

54.45

7.57

0.18

Blend 1

17.38.

1.50

0.23

Blend 2

17.37

2.02

0.28

Blend 3

17.54

2.14

0.22

Blend 4

17.05

1.47

0.29

Blend 5

16.19

2.04

0.17



The infrared studies are indicative of the reaction between chitosan and PHB (see Fig. 3-5). Figure 3 shows the typical bands of chitosan, concerned with the n OH= and n NH centered at 3446 cm-1, Amide I band corresponding to n C=O vibration (1650 cm-1 ) of acetyl groups in chitosan. The band Amide III at 1332 cm-1 ,due to combination of NH deformation and the n CN stretching vibration and the band due to n C-O at 1089 cm-1.


Fig. 3. Chitosan Infrared spectrum.

Figure 4 shows typical bands of PHB, the hydroxyl group shows a band at nOH= 3440 cm-1, a carbonyl stretching a nC=O at 1726 cm-1, corresponding to carboxylate group and a nC-O at 1053 cm-1.


Fig. 4. PHB Infrared spectrum.

On the other hand, the spectrum of blend 1 shows bands of hydroxyl groups at nOH=3373 cm-1, the Amide I band corresponding to nC=O vibration at 1680 cm-1 and a nC-O at 806 cm-1 . This values are indicative of the blend formation due to the shift observed for several bands. The absorption bands at 1650 and 1591 cm-1 in pure chitosan showed significant changes in the spectra of the blends. The band at 1726 cm-1 from PHB disappear in the blends. Meanwhile, the addition of PHB implies that part of the hydrogen bonds in CH was broken and new interactions were formed.


Fig. 5. Blend 1 Infrared spectrum

The thermal stability of the blends was carried out by thermogravimetry (TGA). On table 3 we can see the date from the TGA. The chitosan exhibits a TD= 326.89°C and the PHB TD= 299.52°C. The blends loss weight is around 95% at 550ºC.

Table 3. Decomposition temperatures


Sample

TD (°C)


Chitosan

326.89

PHB

299.52

Blend 1

266.10

Blend 2

267.08

Blend 3

268.35

Blend 4

266.27

Blend 5

266.08



It is interesting to observe that most of the blends showed decomposition temperatures ranging between 266 and 268°C, independent of the composition ratios. Blend 3 (50/50) is the most stable with a TD =268.35°C. Another important feature is the presence of only one decomposition decay showing a different product to the homopolymers.

Also, a study of the morphology of the blends was carried out by scanning electron microscopy, we can observe that while the chitosan exhibit a surface with multilayers (figure 6 ), the poly(hydroxybutyrate) are beds with high porosity inside (figure 7 ), and interwined chains.


Fig. 6. CHITOSAN


Fig. 7. Sem of PHB

Blend 1 (50/50) shows an irregular surface with rugosities and interwined chains with some fractures (figure 8 ) but completely different from either the chitosan or PHB.


Fig. 8. BLEND 1

CONCLUSIONS

  • It was possible to obtain blends from two biopolymers such as chitosan and poly(3-hydroxybutyrate) using TFA as a co-solvent.

  • It was impossible to get blends in a extruder due to the absence of melting point chitosan.

  • The blends were prepared in different proportions of both polymers exhibiting different physical and morphological properties of those homopolymers.

  • The blends show great solubility in organic solvents such as acetone and 2-propanol.

  • The decomposition temperatures of an blends are similar, independent of the composition, which was around 266ºC. However, PHB has a TD= 299ºC and chitosan is 326ºC. Only, blend 3 shows the higher TD= 268ºC.

  • It is interesting to observe that the C/H ratio is constant in the blends with content of chitosan. However, the C/H ratio decreases as long as the chitosan content decreases.

  • Since the blends are a mixture of two biopolymers, they can be used as a support or carried for slow release drugs, pesticides and application in biomedical and artificial skin.

ACKNOWLEDGEMENTS

The authors would like to thank Copersucar for PHB donation. We also thanks Grant CORFO FIT B1-050 for financial support.

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*to whom correspondence should be addressed