The use of novel nanostructured materials has attracted considerable interest in the food industry for their utilization as highly functional ingredients, high-performance packaging materials, processing aids, and food quality and safety sensors. Most previous application interest has focused on the development of nanoparticles. However, more recently, the ability to produce non-woven mats composed of nanofibers that can be used in food applications is beginning to be investigated. Electrospinning is a novel fabrication technique that can be used to produce fibers with diameters below 100 nm from (bio-) polymer solutions. These nanofibers have been shown to possess unique properties that distinguish them from non-woven fibers produced by other methods, e.g., melt-blowing. This is because first the process involved results in a high orientation of polymers within the fibers that leads to mechanically superior properties, e.g., increased tensile strengths. Second, during the spinning of the fibers from polymer solutions, the solvent is rapidly evaporated allowing the production of fibers composed of polymer blends that would typically phase separate if spun with other processes. Third, the small dimensions of the fibers lead to very high specific surface areas. Because of this the fiber properties may be greatly influenced by surface properties giving rise to fiber functionalities not found in fibers of larger sizes. For food applications, the fibers may find uses as ingredients if they are composed solely of edible polymers and GRAS ingredients, (e.g., fibers could contain functional ingredients such as nutraceuticals, antioxidants, antimicrobials, and flavors), as active packaging materials or as processing aids (e.g., catalytic reactors, membranes, filters (Lala et al., 2007), and sensors (Manesh et al., 2007; Ren et al., 2006; Sawicka et al., 2005). This review is therefore intended to introduce interested food and agricultural scientists to the concept of nano-fiber manufacturing with a particular emphasis on the use of biopolymers. We will review typical fabrication set-ups, discuss the influence of process conditions on nanofiber properties, and then review previous studies that describe the production of biopolymer-based nanofibers. Finally we briefly discuss emerging methods to further functionalize fibers and discuss potential applications in the area of food science and technology.
Nonwoven fiber mats of chitosan with potential applications in air and water filtration were successfully made by electrospinning of chitosan and poly(ethyleneoxide) (PEO) blend solutions. Electrospinning of pure chitosan was hindered by its limited solubility in aqueous acids and high degree of inter- and intrachain hydrogen bonding. Nanometer-sized fibers with fiber diameter as low as 80 +/- 35 nm without bead defects were made by electrospinning high molecular weight chitosan/PEO (95:5) blends. Fiber formation was characterized by fiber shape and size and was found to be strongly governed by the polymer molecular weight, blend ratios, polymer concentration, choice of solvent, and degree of deacetylation of chitosan. Weight fractions of polymers in the electrospun nonwoven fibers mats were determined by thermal gravimetric analysis and were similar to ratio of polymers in the blend solution. Surface properties of fiber mats were determined by measuring the binding efficiency of toxic heavy metal ions like chromium, and they were found to be related with fiber composition and structure.
Films formed by blending of two polymers usually have modified physical and mechanical properties compared to films made of the individual components. Our preliminary studies indicated that incorporation of chitosan in polyethylene oxide (PEO) films may provide additional functionality to the PEO films and may decrease their tendency to spherulitic crystallization. The objective of this study was to determine the correlation between chitosan/PEO weight ratio and the physical, mechanical, and antibacterial properties of corresponding films. Films with chitosan/PEO weight ratios from 100/0 to 50/50 in 10% increments were characterized by measuring thickness, puncture strength (PS), tensile strength (TS), elongation at break (%E), water vapor permeability (WVP), and water solubility (WS). Additionally, the films were examined by polarized microscopy, wide-angle X-ray diffraction (WAXD), and Fourier transform infrared (FTIR) spectroscopy, and their antibacterial properties were tested against Escherichia coli. The chitosan fraction contributes to antimicrobial effect of the films, decreases tendency to spherulitic crystallization of PEO, and enhances puncture and tensile strength of the films, while addition of the PEO results in thinner films with lower water vapor permeability. Films with 90/10 blend ratio of chitosan/PEO showed the most satisfactory PS, TS, %E, and antibacterial properties of all tested ratios.
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