Biodegradable starch-based chitosan reinforced composite polymeric films were prepared by casting. The chitosan content in the films was varied from 20% to 80% (w/w). Tensile strength (TS) was improved significantly with the addition of chitosan but elongation at break (EB %) of the composites decreased. Tensile strength of the composites raised more with the addition of the acacia catechu content in the films varied from 0.05% to 0.2% (w/w). The better thermal stability of this prepared film was confirmed by thermo-gravimetric analysis. Structural characterization was done by Fourier transform infrared spectroscopy. Surface morphologies of the composites were examined by scanning electron microscope (SEM) which suggested sufficient homogenization of starch, chitosan and acacia catechu. Water uptake was found lower for final composites in comparison to starch/chitosan and chitosan films. The satisfactory rate of degradation in the soil is expected that the final composite film is within less than 6 months. The developed films intended to use as the alternative of synthetic non-biodegradable colored packaging films.
Generally, plastic products are derived from non-renewable fossil fuels and are non-biodegradable [
For coloring film a natural resin Khair (Acacia catechu) is used. Khair is a moderate size deciduous tree with rough dark gray brown bark. It belongs to family Leguminoseae-mimoseae. The most important product obtained from Acacia catechu var. catechu proper is Khair or catechu. This is obtained by boiling chips of heartwood with water in specially designed earthen pitchers and allowing the concentrate to cool and crystallize. As sold in local market, catechu is found in irregular pieces or small square blocks of grayish black color, which on breaking show a crystalline fracture [
Chitin is the second most abundant natural polymeric material. It is a linear polysaccharide composed of 2-ace-tamido-2-deoxy-D-glucosidic bonds. Conversely, chitosan is an amino polysaccharide comprising an unbranched chain of β (1 → 4)2-amino-2-deoxy-D glucopyranose residue. Chitosan has been extensively studied in pharmaceutical and medical fields for its biodegradability, biocompatibility, bioactivity, and interesting physicochemical properties partially acetylated chitosan having about 50% D-glucosamine unit which is only able to dissolve in water [
Starch, a natural renewable polysaccharide from a great variety of crops, is one of the promising raw materials for the production of biodegradable plastics because of its low cost, availability as a renewable resource, biodegradable and the innocuous degradation products. It has already been widely researched as an important raw material for environmental and biomedical applications. Starch is a carbohydrate consisting of a large number of glucose units joined together by glycosidic bonds. It consists of two types of molecules: the linear and helical amylose and the branched amylopectin [
The objective of the present research was developing colored films based on starch and chitosan by using acacia catechu. The mechanical properties of the prepared films were measured. Molecular interactions of components present in films were examined by Fourier Transform Infrared (FT-IR) spectroscopy. Thermal properties of the films were investigated by Differential Scanning Calorimetric (DSC) studies. Surface topography of the films was investigated by Scanning Electron Microscopy (SEM). The water uptake and the degradation test in soil were also performed.
Chitosan (powder, viscosity: 200 cP) and starch (potato starch) were purchased from Sigma-Aldrich Chemie GmbH, Germany. Acacia catechu bought from the local market of Bangladesh. The chemical formulas of chitosan, starch and acacia catechu,
Solution of 1% chitosan (w/w) was made using 2% (w/w) acetic acid solution. The chitosan films were prepared by casting onto flat silicon-coated Petri dishes and allowed to dry for 24 h at room temperature with 35% relative humidity. Dried films were peeled off manually using spatula and stored in the desiccators prior to characterization. Starch was dissolved in de-ionized hot (70˚C) water with constant stirring. Then starch and chitosan solutions were mixed together at different proportions. Composite films were prepared by solution casting at the same parameters (
Mechanical properties like TS, Tm (tensile modulus), and Eb of the films were investigated by the Universal Testing Machine (Hounsfield series S testing machine, UK, H50 KS-0404) with a crosshead speed of 1 mms−1 at
Formulation | Starch (%) | Chitosan (%) |
---|---|---|
1 | 80 | 20 |
2 | 70 | 30 |
3 | 60 | 40 |
4 | 50 | 50 |
5 | 20 | 80 |
Acacia catechu concentration in film formulation (wt%) | Concentration (wt%) of film components after casting (in dry film) | |||
---|---|---|---|---|
Starch | Chitosan | Acacia catechu | Total | |
0.05 | 47.62 | 47.62 | 4.76 | 100 |
0.1 | 45.46 | 45.46 | 9.08 | 100 |
0.15 | 43.48 | 43.48 | 13.04 | 100 |
0.2 | 41.67 | 41.67 | 16.66 | 100 |
a span distance of 25 mm. The dimensions of the test specimen were: 60 mm × 15 mm × 0.01 mm. The experiment was carried out according to the European standard (ISO/DIS 527-1:2010).
The thermo mechanical (TM) test of the films was taken using computer controlled Differential Scanning Calorimeter (Model: DSC-60 Supplier: Shimadzu Corp.). The temperature range was maintained at 30˚C to 500˚C and the temperature was increased at a rate of 10˚C/min. the flow rate of nitrogen gas was 20 ml/min. Sample weights were 7.82 mg.
FTIR spectra of the films were recorded using a Spectrum One spectrophotometer (Perkin-Elmer) equipped with an attenuated total reflectance (ATR) device for solids analysis and a high linearity lithium tantalate (HLLT) detector. Spectra were analyzed using the Spectrum 6.3.5 software. Films were stored at room temperature for 72 minutes in a desiccator containing saturated NaBr solution to ensure a stabilized atmosphere of 59.1% RH at 20˚C. Films were then placed onto a zinc selenide crystal, and the analysis was performed within the spectral region of 650 - 4000 cm−1 with 16 scans recorded at a 4 cm−1 10 resolution. After attenuation of total reflectance and baseline correction, spectra were normalized with a limit ordinate of 1.5 absorbance units. Resulting FTIR spectra were compared in order to evaluate the effects of starch filling in the chitosan-based films, based on the intensity and shift of vibrational bands.
Film samples (5 × 5 mm) were deposited on an aluminum holder and sputtered with gold-platinum (coating thickness, 150 - 180 Å) in a Hummer IV sputter coater. SEM photographs were taken with a Hitachi S-4700 FEG-SEM scanning electron microscope (Hitachi Canada Ltd., Mississauga, ON, Canada) at a magnification of 40,000´, at room temperature. The working distance was maintained between 15.4 and 16.4 mm, and the acceleration voltage used was 5 kV, with the electron beam directed to the surface at a 90˚ angle and a secondary electron imaging (SEI) detector.
Degradation tests of the monomer grafted film were performed under humid soil at ambient condition. Up to three weeks of the tests were carried out. Films ware placed inside 10 cm depth of humid soil and at set time points, samples were taken out cleaned and kept inside desiccators prior to weighting. The formula employed was:
where, Wb = weight before placement in soil;
Wa = weight after taken out and cleaned.
For each measurement, five samples in each replicate were tested. Analysis of variance and Duncan’s multiple-range tests were used to perform statistical analysis of all results, using PASW Statistics Base 18 software (SPSS Inc., Chicago, IL, USA). Differences between means were considered to be significant when p £ 0.05.
Chitosan (20% - 80% w/w) was added in starch-based films to investigate the effectiveness of chitosan as reinforcing filler. Tensile strength (TS) values of starch-based films was improved significantly (p ≤ 0.05) with the addition of chitosan.
With the rise of strength and modulus, the Eb values of the starch-based films decreased monotonously due to chitosan addition (
23%, 22%, 19%, 16%, and 12%, respectively. Chitosan acted as a reinforcing agent in starch-based biodegradable films. Thus, higher content of chitosan can render the films stiffer. As a result, decrease in Eb values was observed. Similar results were reported by Pinotti et al. [
Tensile strength (TS) values of chitosan/starch-based films were improved significantly with the addition of acacia catechu. Because Acacia Catechu is natural colored resin, like other natural resin it enhances mechanical properties of the film.
The thermo gravimetric analysis (TGA) for starch + chitosan + acacia catechu showed in
The absorption peaks of the pure chitosan film (
The FT-IR spectrum of pure starch film is represented in
The chitosan/starch-based film was investigated to find out the molecular interactions between chitosan and starch. The spectrum is represented in
peak (1099 cm−1) of starch (C-O stretching from C-O-C group) was not shifted. From this spectrum, this is clearly revealed that chitosan was not chemically reacted with starch, as expected. Here, a bio-blend was formed between chitosan and starch.
The chitosan + starch + acacia catechu-based film was investigated to find out the molecular interactions between chitosan, starch and acacia catechu. The spectrum is represented in
cm−1 Acacia catechu might be reacted with amide group of chitosan or may be hydrogen bond formed. The absorption peaks (3302 cm−1 and 2872 cm−1) of the starch + chitosan + acacia catechu film found broader than the absorption peaks of the pure chitosan film assignable to the stretching of intra and intermolecular O-H and -CH2OH vibrations at 3007 cm−1 overlapped with stretching -NH2 (2922 cm−1) and -NH secondary amides vibrations (2852 cm−1) because of O-H bond in acacia catechu. A major peak appeared in 1016 cm−1 which indicates C-O bond in acacia catechu.
The surfaces of the Acacia Catechu (0.15% by wt) containing chitosan/starch (50:50)-based films were investigated by scanning electron microscopy (SEM) from low to high magnification. The images are presented in Figures 13(a)-(i). In open eye, the surface of the films was very clear, homogeneous, and shiny. But at × 30 magnifications (a), phase separation is clearly shown which indicated that chitosan/starch (biopolymers) and acacia catechu (natural resin) did not react with each other, as expected. Natural resin was added to improve the mechanical strength and to make the film bioactive to protect the packaged food against bacteria. At medium magnification (×50, and ×100), represented by (b) and (c), phase separation is more clearly visible.
With the rise of magnification from ×250 to ×1000; Figures 13(d)-(f), few defects are found and surfaces look heterogeneous. Dramatic image is observed at ×3500 magnification (f). Here surface is cleaner and appearance is much better than other low magnification images.
At very high magnifications from ×7500 to ×40,000; Figures 13(g)-(i), surfaces of the films look much better. At ×40,000 magnifications (i) the SEM image of the film is fantastic and indicated more homogeneity. Films are clear from bubbles and irregularities. From this image, it is concluded that a homogeneous film surface appeared using three natural materials. Two biopolymers (chitosan and starch) and one natural resin (acacia catechu) mixed homogeneously and made a fantastic bio-blend for the preparation of biodegradable film for food packaging application.
The water uptake behavior of chitosan film and chitosan (50% by wt) reinforced starch-based composite films are shown in
showed 155% and 101% of water uptake. Chitosan is water soluble as the salts of various acids present in D-glucosamino unit. Partially acetylated chitosan has about 50% D-glucosamine unit that dissolves in water. The starch/chitosan film had better stability in water compared to native chitosan films. The reason could be due to the network formation between starches with chitosan, which prevented water molecules into the films. But both films showed strong affinity of water uptake that indicated strong hydrophilic nature. Both starch and chitosan had plenty of free hydroxyl groups and as a result within few min a significant quantity of water penetrated into the films. But the advantage is the reduction of water uptake due to the reinforcement of chitosan in starch-based films. For example, after 10 min of immersion in water the starch/chitosan film reduced to 34.83% of water uptake compared to native chitosan. So, chitosan improved the stability of the starch-based composite films in aqueous medium.
But films with acacia catechu were almost static. After 30 min, the water uptake of acacia catechu (0.15 wt%) + starch + chitosan based film, native chitosan and starch/chitosan films reached to 81%, 155%, and 101%.
Acacia catechu (0.15 wt%) + starch + chitosan based film had better stability in water compared to chitosan or chitosan/starch-based films. Acacia catechu might be create a network with the biopolymers (chitosan and starch) and formed network, which prevented water molecules penetration into the films.
In
weight loss is 0.5%, after three weeks, weight loss is 3%, after four weeks, weight loss is 5%. From this investigation, it was expected that this film will be biodegradable in soil in less than 6 months. Moreover, in the prepared films, Acacia catechu, starch and chitosan, all are natural fiber and totally biodegradable. So, the film did not lose its total inherent biodegradable character after mixing but withstand its stability for longer period.
Biodegradable film made of starch, chitosan and acacia catechu was successfully developed by solution casting. The key factor of the blend polymer is H-bonding with two polymers. Acacia catechu contributed to the improvement of tensile strength in starch/chitosan films. This film showed good thermal stability also. Structural characterization was done by FT-IR. The surface morphologies indicated better homogenization of the three biopolymers (starch, chitosan and acacia catechu). Water update was lower for acacia catechu incorporated film than starch/chitosan film. Finally, degradation rate in soil is satisfactory also. The prepared films can be used as the colored bio-degradable packaging films.
M. Z. I.Mollah,N.Akter,F. B.Quader,S.Sultana,R. A.Khan, (2016) Biodegradable Colour Polymeric Film (Starch-Chitosan) Development: Characterization for Packaging Materials. Open Journal of Organic Polymer Materials,06,11-24. doi: 10.4236/ojopm.2016.61002