PVA-based electrospun nanofiber mats of potential use in active packaging
Abstract
The aim of this study has been devoted to the study of electrospun polymeric nanofiber mats that can be potentially used in active packaging. A previous characterization of the PVA solutions was carried out. Thus, density, electrical conductivity and viscosity have been measured as a function of PVA concentration (0, 4, 7 and 10% w/w). Subsequently, a standard electrospinning process was carried out. The fibber diameter was determined by analyzing high - resolution images from Scanning Electron Microscopy (SEM) using Image J software. Moreover, a characterization of tensile properties (by means of DMA) and vapour sorption capacity of PVA -based nanofiber mats was performed. In addition, water -soluble compounds were incorporated into electrospun nanofiber mats. Although they may induce marked changes in morphology, their incorporation may lead to marked improvements in techno -functional properties. Thus, addition of Sodium Carbonate (SC) involve s occurrence of beads, due to the increase in electrostatic charges, whereas Citric Acid (CA) induce an increase in fibber size, related to a loss of solvent evaporation efficiency. However, both compounds significantly enhance water vapour absorption capacity.
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Introduction
The use of proper packaging materials and methods to minimize food deterioration, while providing safe and wholesome food products has always been the focus of food packaging. Current trends in consumer preferences have stimulated research into novel packaging concepts that actively play a role in the preservation of foods, through either absorption or release of compounds, known as active packaging (Siripatrawan & Vitchayakitti, 2016). Active packaging technologies interact with the internal gas environment in order to improve the food preservation or sensory properties while maintaining the quality and safety of the packaged food. Such newly employed technologies use substances to continuously modify the gas environment (and may interact with the product surface) by removing or adding gases in the headspace inside the package (Janjarasskul, Tananuwong, Kongpensook, Tantratian, & Kokpol, 2016).
The internal atmosphere may be controlled by substances that absorb (scavenge) or release (emit). Polymers, due to their inherent ability to allow the passage of low molecular weight compounds, are the materials of choice for these novel packaging concepts. Some examples of active-packaging systems are O scavengers, CO emitters, ethylene absorbers, 2 2 moisture regulators, taint removal systems, ethanol emitters and antimicrobial-releasing systems (Bodbodak & Rafiee, 2016; Lucera, Conte, & Nobile, 2016; Siripatrawan & Vitchayakitti, 2016). O scavengers or CO emitters frequently associated 2 2 with Modified Atmosphere Packaging (MAP) systems, can be incorporated into polymer packaging by addition to the master batch via solution or dispersion, or they can be included in an inner layer in the case of multi-layer materials (Sandhya, 2010). Designing materials with scavengers or emitters requires the active polymer to be capable of being processed into packaging materials by conventional methods, while maintaining its properties as a container after the active agent has been exhausted. For meat preservation, CO emitters are commonly used because of their inhibitory activity against a range of 2 aerobic bacteria and fungi, being the only one displaying a direct antimicrobial effect, among the most frequently used gases in MAP systems. In fact, O scavengers/CO emitters are becoming increasingly attractive to food manufacturers and 2 2 retailers and the growth outlook for the global market is bullish (Arvanitoyannis & Oikonomou, 2012).
The fibres material, specifically electrospun fibber mat with submicron fibber diameters (100-300 nm) and exceptionally high surface area could readily overcome this problem. The electrospinning process has proven to be a facile approach for the fabrication of 3D fibber mats and recently functional nanofibers have been proposed, specifically through the immobilization/encapsulation of food ingredients or enzymes/proteins within the electrospun matrix (Fernandez, TorresGiner, & Lagaron, 2009; Tang, Liu, Hou, & You, 2011). The 3D structure of electrospun fibber mat acts as a passive barrier in food packaging and it can also exhibit higher antimicrobial activity. Therefore, electrospun fibres with incorporated enzymes (as antimicrobial agent) could be ideal as food packaging materials where they can act as killing agent and/or inhibit bacteria growth on surface of foods and allow or facilitate the development of new and healthier food products.
Additionally, fibber diameter and fibber mat architectures are tuneable by simply varying process and material parameters such as cospinning polymer, solution viscosity and conductivity, voltage, flow rate, nozzle-collector distance, and collection method (Bhardwaj & Kundu, 2010). Electrospun nanofibers offer many advantages over traditional fibres including high surface area to volume ratio, tuneable porosity, and ease of manipulating fibber chemical compositions and structures for desired properties and functionalities. While electrospinning serves as a technique with great potential for the delivery of ingredients for functional food products and active packaging, several challenges remain unresolved (Bhushani & Anandharamakrishnan, 2014).
The aim of this work has been to study new materials of potential use in active packaging. To achieve this objective, new electrospun mats, which exhibit novel properties related to food preservation such as CO release, have been evaluated. 2 Polyvinyl alcohol (PVA) aqueous solutions have been processed through electrospinning at different PVA concentrations. Electrospun PVA nanofiber mats have been characterized by means of Dynamic Mechanical Analysis (DMA), using both oscillatory dynamic and uniaxial tensile tests, and Scanning Electron microscopy (SEM). In addition, water vapour absorption capacity was determined. To improve this ability, the effect of addition of two different compounds was also evaluated: Sodium Carbonate (SC) and/or Citric Acid (CA)...
Conclusion
Electrospinning of PVA solutions at moderate concentrations leads to mats that consist of a network of randomly distributed non-woven fibres showing uniform sizes, in the order of 200 nm. Viscoelastic characterization from rheological measurements shows the typical response for a solid viscoelastic film. Moreover, parameters from stress -strain curves indicate that the mats obtained from the electrospun process are suitable for a commercial use.
In addition, it has been shown that water -soluble compounds may be incorporated into electrospun nanofiber mats, although they may induce marked changes in their morphological characteristics. Thus, addition of Sodium Carbonate involves occurrence of beads, due to the increase in electrostatic charges, whereas Sodium Citrate induce an increase in fibber size, related to a loss of solvent evaporation efficiency.
SC/PVA and CA/PVA electrospun nanofiber mats show higher vapour sorption capacity than those processed only wit h PVA, provided that the relative humidity exceeds a critical value. Interestingly, however, mats containing SC, CA and PVA show similar vapour sorption behaviour. This effect suggests that a chemical reaction between Sodium Carbonate and Citric Acid to re lease carbon dioxide takes place above 70% RH.
After these results, it may be concluded that electrospinning shows an apparent potential interest for its application as car bon dioxide emitter systems in active food packaging.