Elsevier

Thermochimica Acta

Volume 396, Issues 1–2, 5 February 2003, Pages 153-166
Thermochimica Acta

Thermogravimetric and FTIR studies of chitosan blends

https://doi.org/10.1016/S0040-6031(02)00523-3Get rights and content

Abstract

Results of spectrophotometric and thermogravimetric studies of chitosan (CH) blends with polyvinyl alcohol (PVAL), starch (S) and hydroxypropylcellulose (HPC) obtained by casting from solutions in the form of transparent films containing 0–1.0 weight fraction of CH were discussed. Blends containing S are homogeneous only in the case of low-weight fraction of S (to 0.3).

On the basis of results of thermodegradation in dynamic and isothermal conditions, thermal stability of the tested systems was estimated. Thermogravimetric measurements in dynamic conditions were carried out in the temperature range of 100–450 °C at constant heating rate 15 °C/min. From thermogravimetry (TG) and DTG curves the activation energy and characteristic parameters of degradation of the tested blends were determined. The observed growth of activation energy and Tp—temperature of initial weight loss, Tmax—temperature of maximal rate and Ce—degree of conversion at the end of the measurement (at temperature 450 °C) along with the increase of polymer fraction (HPC and S) in the CH blend provides an evidence of improved thermal stability of the systems tested.

Investigations in isothermal conditions in air at temperature from 100 to 200 °C confirmed appreciable improvement of CH thermal stability in the blends being tested.

Infrared spectroscopic analysis of the blends showed a distinct stabilization of the process of chain scission. In the band at 1080 cm−1 associated with absorption in –C–O–C– group during degradation of the blends at temperature 200 °C much smaller decrease due to molecular scission were observed than in the case of pure CH.

Introduction

In view of a growing amount of wastes from man-made fibers, research projects are concentrated now on searching for polymer materials which would be man- and environment-friendly and characterized by a definite lifetime. Their degradation in various environmental conditions leads to a destruction of chains by breaking, splitting of fragments of the main chain or side constituents and release of volatile products.

For many years, chitosan (CH) being a deacetylated form of chitin which occurs in various ecosystems has aroused great interest of researchers. Because of its unique properties [1], [2], [3], [4], [5] such as bioactivity or biodegradability [6], [7], [8], it finds application in many areas of man’s life and health [9], [10], [11], [12]. The search for new applications calls for developments in the production methods, investigations of the structure [5], [13] and degradability of CH and blends that contain CH [14], [15], [16], [17], [18], [19].

The study aims at the estimation of thermal stability of biodegradable blends of CH with polyvinyl alcohol (PVAL), starch (S) and hydroxypropylcellulose (HPC) obtained from a solution in the form of transparent, homogeneous films. To record the process of thermal degradation of CH and its blends, the methods of thermogravimetry (TG) and infrared spectroscopy (FTIR) were used. The analysis of results was used to describe the degradation kinetics of CH and its blends. Important elements of the kinetic model of degradation are the values of activation energy and reaction order.

Section snippets

Materials used

CH (poly-2-aminoglucose) of deacetylation degree DD=78% and molecular weight M=2.1×105, was produced by the Sea Fishery Institute in Gdynia. It is a biodegradable natural copolymer obtained by chitin modification

DD=xx+ywhere x is the number of deacetylated monomeric units, and y is the number of chitin monomeric units.

S, potato starch was a commercial product. It is a recoverable biopolymer composed of amylopectin and amylose

PVAL of molecular weight M=7.2×104 (Polskie Odczynniki Chemiczne,

Interactions between components

Formation of homogeneous CH blends with PVAL, S and HPC is a result of strong interactions by hydrogen bonds between the functional groups of the blend components in which amino and amide groups present in CH take part. The analysis of FTIR spectra of the blends enables these interactions to be identified [22], [23].

On the basis of the harmonic oscillator model the reduction in force constant Δf can be represented by Eq. (1) [24]Δf=fnb−fb=μ(νnb2−νb2)2where μ=m1m2/(m1+m2) corresponds to the

Conclusions

  • 1.

    Both dynamic and isothermal thermogravimetric analysis of CH and its blends with HPC, PVAL and S revealed improving stability of CH in the blends.

  • 2.

    With an increase of the amount of S, PVAL and HPC in the blends an increase of Tp and Tmax is observed. It is most distinct for CH/HPC and CH/PVAL blends. These blends reveal two stages of fast decomposition characteristic of both components. A certain increase of the activation energy of CH degradation calculated on the basis of TG analysis is

Acknowledgements

The authors gratefully thank the Scientific Research Committee (KBN) in Poland for support under grant no. 3 T09C 028 19.

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