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Effect of electron beam irradiation on the tensile properties of chitosan/corn cob biocomposite films.

INTRODUCTION

During recent years, there has been a growing interest in radiation modification on polymers. The radiation effects on polymers have been reported by many researchers over the past decades [11,1,12,6,10]. The radiation technology may not only for surface grafting to enhance surface, but also for reactive compatibilization [9,10]. The radiation technology offers several advantages including: (i) strong bridge between macromolecules can be formed; (ii) the compatibilization of polymer blend by high energy radiation; (iii) incorporation of multifunction monomers or ionomers in polymer blend to accelerate and increase the degree of crosslinking [9,10]. According to [1] and [11], they have reported that the high energy radiations may cause both crosslinking and degradation reactions in polymeric materials. Additionally, these high irradiation was also affected the tensile properties of polymeric materials [11]. Li and co-workers [6] have studied the irradiation modification on konjac glucomannan/chitosan blend films. They have reported the changes in tensile properties with irradiation doses.

Chitosan is a renewable and biodegradable polysaccharide. It is derivative of chitin. Chitosan is not soluble in water, but soluble in aqueous solutions of organic acid such as formic acid, lactic acid, and acetic acid [8, 13,14]. The amine groups of chitosan are protonated to NH3+, when the chitosan dissolving in organic acid. Chitosan forms viscous solutions in aqueous organic acid. These viscous solution have been used to produce chitosan film [7]. Numerous of researchers have focused on using biopolymer materials as an alternative for synthetic packaging materials. Additionally, chitosan possess immense potential as a packaging materials owing to its biodegradability, non-toxic, biocompatibility and renewable resources [5].

Many studies have described the use of natural filler in polymer matrix [14, 15, 2, 3, 4]. The natural filler give several advantages including cost effectiveness, being recyclable, biodegradability, low density, and being renewable. Corn (Zea Mays) is one of the arable crops worldwide. After harvesting of corn, the residues such as leaves, cob, stalk and husk are left in corn stover field. The corn cob can be utilize in low-value applications such as animal feed and charcoal. In this work, the corn cob was used as natural filler in chitosan matrix. Indeed, the utilization of corn cob gives economic advantage and reduces the environment impact.

The objective of this study was to develop corn cob (CC) filled chitosan (CS) biocomposite films. The influence of electron beam irradiation on the tensile properties and morphology study of CS/CC biocomposite films were studied.

Methodology:

Materials:

Chitosan (CS) was supplied by Hunza Nutriceutical Sdn, Bhd. (Malaysia) with degree of deacetylation (DD) of 90%. Corn cob (CC) was collected from Kodiang Plantations, Kedah, Malaysia. The CC was cleaned and ground manually into powder form with particle size of 38 pm. Acetic acid with grade 01730 was purchased from Fluka.

Preparation of CS/CC Biocomposite Films:

The CS/CC biocomposite films were prepared via solvent casting method. Firstly, the CS powder was dispersed in 1 v/v% of acetic acid and stirred for 30 minutes by using mechanical stirrer. Then, the CC powder was added in CS solution and stirred until homogenous solution was obtained. Next, the CS/CC biocomposites solution was poured into mould and dried at room temperature for 48 hours to produce CS/CC biocomposite films. Table 1 shows the formulations of CS/CC biocomposite films.

Tensile Properties:

The tensile test of CS/CC biocomposite films before and after irradiation were done at room temperature using an Instron Universal Testing System, Model 5569. A cross-head speed of 10 mm/min was employed according to ASTM D 882 standards.

Irradiation:

The CS/CC biocomposite films were irradiated using a 2 MeV electron beam acceleration at a dose of 10 kGy using an EPS-3000 electron beam machine. The acceleration energy, beam current and dose rate were 2 MeV, 2mA and 10 kGy/pass, respectively.

Morphology Study:

The tensile fracture surface of unirradiated and irradiated CS/CC biocomposite films was performed by a scanning electron microscope (SEM), Model JEOL JSM-6460 LA, at an accelerating voltage of 5 kV. A sputter coater was used to pre-coat palladium onto fracture surfaces before examining fracture surface.

RESULTS AND DISCUSSION

Tensile Properties:

Figure 1 shows the tensile strength of un-irradiated and irradiated CS/CC biocomposite films with different CC content. Both CS/CC biocomposite films exhibit decrease trend with increasing CC content. However, after irradiation, the tensile strength of irradiated CS/CC biocomposite films is higher than un-irradiated CS/CC biocomposite films. This is attributed to the formation of irradiation-induced crosslinking in CS matrix. According to Thomas et al., [11], they have reported that the crosslinked sample show higher tensile strength than the un-crosslinked sample at high radiation doses. Moreover, Akhtar et al., [1] reported the polymer undergoes brittle distortion at a certain degree of crosslinking and this phenomenon is increase the tensile strength after an absorbed irradiation dose. Figure 2 illustrates the proposed formation of crosslinking between CS and CS matrix.

The effect of irradiation on elongation at break of CS/CC biocomposite films is displayed in Figure 3. Obviously, it can be seen that the elongation at break of un-irradiated and irradiated CS/CC biocomposite films reduced with CC content. The addition of CC fller reduced the polymer matrix chain mobility as well as improved the rigidity of CS/CC biocomposite films. In contrast, the elongation at break of irradiated CS/CC biocomposite films was dramatically drop compared to un-irradiated CS/CC biocomposite films. The reduction of elongation at break could be corresponded to the reduction of polymer chain mobility, which results from the formation of crosslinkages between CS-CS matrix.

The modulus of elasticity of un-irradiated and irradiated CS/CC biocomposite films with different CC content is illustrated in Figure 4. Apparently, the modulus of elasticity of CS/CC biocomposite films increased as CC content increases. Such observation is associated with incorporation of CC filler reduced chain mobility and increased stiffness of biocomposite films. Once the CS/CC biocomposite films are exposed to electron beam irradiation, the modulus of elasticity of irradiated CS/CC biocomposite films was drastically increased compared to un-irradiated CS/CC biocomposite films. Hence, the CS/CC biocomposite films becomes brittleness. The modulus of elasticity of neat CS is the highest compared with un-irradiated and irradiated CS/CC biocomposite. This can explained that CS matrix formed crosslinking with itself without any restriction from CC filler, resulting in an improvement of modulus of elasticity.

Morphology study:

Figure 5 (a)-(c) display the SEM micrograph of un-irradiated neat CS, CS/CC biocomposite film at 20 wt % and 40 wt % of CC content, respectively. The un-irradiated neat CS showed a smooth homogeneous surface and matrix tearing. Both SEM micrograph of un-irradiated CS/CC biocomposite films at 20 and 40 wt % CC content exhibited rough surface and presences of fibrils on the fracture surface. Additionally, the presence of holes and cavities is indicated to the detachment of CC filler from CS matrix. This indicated a poor interfacial interaction between CC filler and CS matrix, which results in a reduction of tensile strength when CC content increases.

Figure 6 (a)-(c) illustrate the SEM micrograph of irradiated of neat CS, CS/CC biocomposite film at 20 wt % and 40 wt % of CC content, respectively. From SEM micrograph of irradiated neat CS, it can be observed that discontinuous fracture path on the fracture surface. This is attributed to the crosslinked state of the CS matrix between itself. After irradiation, the fracture surfaces as shown in Figure 6 show brittle type of failure with the absence of fibrils on the fracture surface and the amount of cavities also reduced. Furthermore, the irradiated fracture surface of both CS/CC biocomposite films show brittle crack. The presence of these cracks is assigned to the embrittlement of material.

Conclusion:

The effect of electron beam irradiation on tensile properties and morphology of CS/CC biocomposite films has been studied. The tensile strength and modulus of elasticity of irradiated neat CS and CS/CC biocomposite films is drastically increased as compared to un-irradiated biocomposite films. However, the elongation at break of irradiated neat CS and CS/CC biocomposite films is lower than un-irradiated biocomposite films. This is due to the formation of 3D-network between CS and itself after radiation. From morphology study, the SEM micrograph of both un-irradiated CS/CC biocomposite films showed the detachment of CC filler from CS matrix. On the other hand, both irradiated CS/CC biocomposite films exhibited brittle crack due to embrittlement.

ARTICLE INFO

Article history:

Received 28 February 2014

Received in revised form 25 May 2014

Accepted 6 June 2014

Available online 20 June 2014

ACKNOWLEDGEMENT

The authors would like to thank Ministry of Higher Educational (MOHE) for providing Fundamental Research Grant Schemes (FRGS) 2013 with the project number of 9003-00402.

REFERENCES

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(1) Chan Ming Yeng, (2) Salmah Hussiensyah, (3) Sam Sung Ting

(1, 2) Universiti Malaysia Perlis, Division of Polymer Engineering, School of Materials Engineering, 02600 Jejawi, Perlis, Malaysia.

(3) Universiti Malaysia Perlis, School of Bioprocess Engineering, 02600 Arau, Perlis, Malaysia.

Corresponding Author: Salmah Hussiensyah, Universiti Malaysia Perlis, Division of Polymer Engineering, School of Materials Engineering, 02600 Jejawi, Perlis, Malaysia.

Fax: 604-9798612. E-mail: irsalmah@unimap.edu.my

Table 1: Formulations of CS/CC biocomposite films

Materials                  Chitosan (wt%)        Corn Cob (wt%)

CS/CC                      100, 90, 80, 70, 60   0, 10, 20, 30, 40
biocomposite films
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Author:Yeng, Chan Ming; Hussiensyah, Salmah; Ting, Sam Sung
Publication:Advances in Environmental Biology
Article Type:Report
Date:Jun 5, 2014
Words:2015
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