Status of Bionanocomposite Research in Korea

Jong-Whan Rhim

Abstract

Nanotechnology in Korea has developed through a strong government-driven program and strategic investment in specialised fields. Although the food packaging sector represents a very small fraction of the nanotechnology investment program, bionanocomposites have great potential as a next generation of packaging materials. Bionanocomposites with various functionalities such as antimicrobial, self-cleaning, smart and intelligent packaging are expected to become a major driver in food packaging technology development.

Introduction

Nanotechnology has appeared as a core technology to lead the new industrial revolution of the 21st century through creating a new area in science and technology as well as improving the functionality of existing products or devices. Nanoscience and NT have already been applied in various fields such as computer electronics, communication, energy production, medicine and the food industry (Figure 1). Although application of nanotechnology in the food industry started later than other industries, the great potential of food nanotechnology, especially in the area of improving food quality and securing food safety, has been recognised by many nanoscientists and technologists (Tarver 2006). Nanotechnology is already applied to the food and food packaging industries (Nachay 2007, Brody 2007).

One of the potential applications of nanotechnology in food packaging is polymer/clay nanocomposites; they have recently emerged due to their potential for improving properties of packaging materials such as increased mechanical, barrier and chemical properties with a small amount (less than 5% by weight) of nanoclays reinforcement (Brody 2007). However, most work done on polymer/clay nanocomposites has focused mainly on synthetic polymers (Rhim and Ng 2007). Some important research on biopolymer-based nanocomposites (bionanocomposites) has been reported in Korea.

Bionanocomposite Research in Korea

Application of bionanocomposites in food packaging has been considered highly promising because they can improve the safety and quality of food products through improved barrier and mechanical properties as well as biodegradabilty. Bionanocomposite materials are among the most promising material for the production of environmentally-friendly biodegradable packaging materials. However, biodegradability of bionanocomposites is one of the most controversial issues in this research field. Early research workers reported improved biodegradability of nanocomposites. Tetto et al. (1999) first reported that polycaprolactone (PCL)-based

Figure 1: Application areas of nanotechnology in food science and food packaging

nanocomposites showed improved biodegradability over pure PCL. They suggested such an improvement in biodegradability may be attributed to a catalytic role of the organoclay. Sinha Ray et al. (2002, 2003) also demonstrated that biodegradability of polylactide (PLA)-based nanocomposites was significantly enhanced due to the presence of terminal hydroxylated edge groups in the clay layers. On the other hand, Lee et al. (2002) found biodegradation of aliphatic polyester composited with organoclay was retarded compared with the neat aliphatic polyester. They attributed the retardation of biodegradation to the improved barrier properties of the nanocomposites.

Rhim et al. (2006) prepared chitosan-based nanocomposite films and tested their antimicrobial activity against Gram-positive (Staphylococcus aureus and Listeria monocytogenes) and Gram-negative bacteria (Salmonella Typhimurium and Escherichia coli O157:H7). They found chitosan/organoclay (Cloisite 30B) nanocomposite films had strong bactericidal activity against Gram-positive bacteria with clear bacteriostatic activity against Gram-negative bacteria (Fig. 2). They

Figure 2: Antimicrobial activity of various chitosan-based nanocomposite films

suggested that the antimicrobial activity of chitosan/Cloisite 30B nanocomposite films might be attributed to the quarternary ammonium groups incorporated in the silicate layer of the organocaly. Recently Hong and Rhim (2008) demonstrated that the antimicrobial activity was caused by the quaternary ammonium salt by testing antimicrobial activity of the organoclay (Fig. 3). Microstructural observation using a TEM of L. monocytogenes cells treated with Cloisite 30B showed modification within the cell membrane with leakage of cytoplasm (Fig. 4). This result clearly explains the reason why the aliphatic polyester/Cloisite 30B nanocomposites showed retarded biodegradation (Lee et al. 2002).

Figure 3: Antimicrobial activity of three different nanoclays

Figure 4: Effect of organically modified nanoclay (Cloisite 30B) treatment on transmission electron micrographs of L. monocytogenes cells

Rhim et al. (2009) and Sothornvit et al. (2009, 2010) also tested antimicrobial activity of other bionanocomposite films prepared with other biopolymers such as PLA and whey protein and found that the antimicrobial activity of bionanocomposite films was greatly affected not only by type of the organoclay but also by the polymer matrix. Though the mechanism of nanocomposite biodegradation has not been explained clearly yet, it is very clear that biodegradability of bionanocomposite packaging materials completely depends on both the nature of pristine layered silicates and surfactants used for the modification of layered silicates. So it is possible to control the biodegradability of several biopolymers via judicious choice of organically-modified layered silicates with antimicrobial activity.

Future Perspectives

Bionanocomposites have great potential as the next generation of packaging materials with improved mechanical and barrier properties without sacrificing biodegradability. They have the potential to enhance both the quality and safety of packaged foods with longer shelf life. Nanotechnology including bionanocomposites will become a major driver in packaging technology development. Nanotechnology-based new materials with additional functionalities such as anti-counterfeit, anti-tamper, anti-microbial, sensors (temperature, moisture, light, decay), integrated power (intelligent tags, self-healing or cleaning containers) are emerging and will impact the packaging industry.

References

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Sothornvit, R, Hong, SI, An, DJ and Rhim, JW (2010) Effect of clay content on the physical and antimicrobial properties of whey protein isolate/organo-clay composite films. LWT-Food Sci. Technol. 43: 279-284.

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Dr Jong-Whan Rhim is a Professor in the Department of Food Engineering, Mokpo National University, Muangun, Jeonnam 533-729, Republic of Korea; E-mail: jwrhim@mokpo.ac.kr