Effect of plasticiser on the morphology, mechanical properties and permeability of albumen-based nanobiocomposites☆
Graphical abstract
Introduction
The management of plastic waste has long been a matter of concern to the scientific community and industry. However, the magnitude of this problem affecting both public health and nature makes society more and more aware that this is one of the greatest challenges to be faced by humanity during the 21 st century. The need to find a truly sustainable alternative is imperative and in this the context, the option of using biodegradable bioplastics from renewable sources as an alternative to conventional plastics of fossil origin is gaining strength every day. Raw materials such as carbohydrates, lipids and proteins have been the main sources for obtaining biodegradable and renewable bioplastics for many years (Cuq, Gontard, & Guilbert, 1998; Song & Zheng, 2008). In particular, protein-based bioplastics turned out to be among the rates of fast-degrading polymers (Domenek, Feuilloley, Gratraud, Morel, & Guilbert, 2004). Moreover, proteins have been extensively used in the development of bioplastic materials because of their capability to form three-dimensional structures with different interactions and bindings that lead to a wide range of functional properties (Cuq et al., 1998). An example of this is egg white protein (albumen), which is composed mainly of ovalbumin. When this protein is heated, the free sulfhydryl sulphides located in its nucleus are exposed and oxidized to form disulphide bonds. Through covalent bonds such as these and other weak ones (ionic, hydrogen bonding and Van der Waals), the three-dimensional structure of the polymer matrix is created (Fernández-Espada, Bengoechea, Cordobés, & Guerrero, 2013; Jerez, Partal, Martínez, Gallegos, & Guerrero, 2007; Pommet, Redl, Morel, Domenek, & Guilbert, 2003). Albumen has been demonstrated to be a very interesting raw material for obtaining bioplastics focused on applications where transparency is important, without neglecting mechanical performance (Cuq et al., 1998; Diañez, Martínez, & Partal, 2016; Jerez, Partal, Martínez, Gallegos, & Guerrero, 2007). In addition, egg white protein can be easily processed by moulding and both the mixing and compression stages are carried out at temperatures lower than those required for processing most polymers and biopolymers (Jerez et al., 2007a).
However, despite the many advantages of these materials, they still have some deficiencies that prevent them from being competitive with conventional plastics in many of their applications. For this reason, the addition of certain types of nanoparticles to the polymer matrix for obtaining nanocomposites is a way of providing bioplastics with even more interesting and valuable features, without affecting their biodegradability and renewability.
It is already well known that the morphology obtained with the addition of nanoparticles is totally determinant in the mechanical (Lee & Kim, 2010), thermal (Mohanty & Nayak, 2012) and barrier properties (Sanchez-Garcia, Lopez-Rubio, & Lagaron, 2010) of the materials obtained. Specifically, in the case of laminar nanoparticles, the most significant improvements are observed when an exfoliated structure is achieved, in which the clay plates have been completely separated from each other and are uniformly dispersed through the polymeric matrix (Sharma, Malik, & Jain, 2018; Zhu et al., 2019).
In previous study (Diañez et al., 2016) we determined that the macromolecular structure of egg white-based materials was affected by the nature of the nanoclays added. Moreover, the molecular/macromolecular compatibility between the clay layers and the egg white matrix appeared as the key parameter governing the nanostructure, and therefore, the mechanical properties and the water absorption capacity of resultant nanobiocomposites.
Another indispensable component in the formulation of bioplastics and biocomposites are plasticisers, which have been proved to be a determining factor in the final properties of plastics, bioplastics and nanocomposites (Chivrac, Pollet, Dole, & Avérous, 2010; Hopkins, Stone, Wang, Korber, & Nickerson, 2019; Lara & Salcedo, 2016). Plasticisers are usually small molecules that are located between the polymer chains, facilitating their mobility, increasing free space and reducing interactions between them. This results in the material being easier to process, more flexible and less brittle, lowering its glass transition temperature and considerably increasing its elongation capacity (Athamneh, Griffin, Whaley, & Barone, 2008; Cuq, Gontard, Cuq, & Guilbert, 1997; Lee, Pranata, Ustunol, & Almenar, 2013; Song & Zheng, 2008; Vieira, Da Silva, Dos Santos, & Beppu, 2011). However, beyond all these well-known aforementioned effects, it is of great interest to evaluate the influence of plasticisers, on the dispersion of nanoparticles in the polymeric matrix. To create a packaging concept for optimal preservation of food, different parameters such as the thermal and mechanical properties, humidity uptake, and barrier properties must be taken into account in order to avoid loss of nutritional content, off‐flavors, color changes, oxidation processes, and spoilage. Knowing the influence of plasticizers on those parameters is very important to develop customized packaging materials (El Miri et al., 2018). Bio-based films could be a good alternative to prevent deterioration for many food products because they often possess excellent oxygen barrier properties. Unfortunately, plasticisers usually increase gases permeability. Previous studies have indicated that gas permeability increases proportionally with plasticiser content (Arvanitoyannis, Nakayama, & Aiba, 1998; Sothornvit & Krochta, 2000). However, although the use of plasticiser to modify the permeability of different films has been reported, the interaction of them and albumen-based nanobiocomposites requires additional elucidation, since the finding of a plasticiser that favours the correct dispersion of nanoparticles into this matrix could compensate for this negative effect and help to obtain materials with improved barrier properties.
Cuq et al. (1997) found that differences in plasticising ability of substances with similar chemical nature were actually due to different molar content when comparing on mass basis substances with different molecular weight. Previously, Donhowe and Fennema (1993)b) had stated that these effects of the chemical nature of plasticisers are only significant when the differences are substantial, such as when comparing glycerol with a much higher molecular weight PEG (Donhowe & Fennema, 1993).
The aim of this research was to find a plasticiser with the most suitable formulation to favour the dispersion of nanoclays in albumen bioplastic matrix and, consequently, to improve the mechanical behaviour and barrier properties of the obtained material. To accomplish this objective, two studies were performed. In the first one, the molar content of the plasticiser was varied, keeping the mass content constant. To this end, different proportions of two plasticisers of similar characteristics (and probably the most widely used) such as water and glycerol, were studied. Subsequently, in the second study, the plasticiser capacity of PEG 300, a large plasticiser that has already been successfully used in the plasticisation of other proteins, was evaluated.
Section snippets
Materials
The spray-dried egg white albumen (EW) used was provided by OVOSEC S.A. (Spain). Glycerol from Guinama (Spain), PEG 300 from Manuel Riesgo, S.A. (Spain) and distilled water were used as protein plasticisers. Regarding the nanoparticles, two selected montmorillonites from Southern Clay Products, Inc. (USA) were used: a) Cloisite® Na+ (MMT-Na) (natural sodium); and b) Cloisite® 30B (OMMT) (organo-modified).
Samples formulation
A plasticiser/protein mass ratio of 0.4/0.6 was always maintained (López-Castejón,
Results and discussion
The plasticisers investigated in this study represent different chemical composition and molar mass, thus providing the opportunity to explore the effects of these factors on dispersion of nanoclays and NBC final properties.
Conclusions
The effect of plasticiser composition and its molar concentration (glycerol and/or water and PEG 300) on albumen bioplastics/nanobiocomposites permeability and mechanical properties were compared. In general, for egg white-based-bioplastics and nanobiocomposites, the presence of glycerol favours the disorder or amorphous character of the structure. On the contrary, water gives a more ordered and compact material. Additionally, the best characteristics are obtained when the nanobiocomposites
CRediT authorship contribution statement
Isabel Diañez: Investigation, Visualization, Formal analysis, Writing - original draft, Writing - review & editing. Inmaculada Martínez: Supervision, Conceptualization, Methodology, Writing - original draft, Writing - review & editing. Perla A. Gómez: Investigation.
References (51)
- et al.
Edible films made from hydroxypropyl starch and gelatin and plasticized by polyols and water
Carbohydrate Polymers
(1998) - et al.
Hydrogen bonding analysis of glycerol aqueous solutions: A molecular dynamics simulation study
Journal of Molecular Liquids
(2009) - et al.
Starch-based nano-biocomposites: Plasticizer impact on the montmorillonite exfoliation process
Carbohydrate Polymers
(2010) - et al.
Synergistic effect of combined nanoparticles to elaborate exfoliated egg-white protein-based nanobiocomposites
Composites Part B Engineering
(2016) - et al.
Biodegradability of wheat gluten based bioplastics
Chemosphere
(2004) - et al.
Linear viscoelasticity characterization of egg albumen/glycerol blends with applications in material moulding processes
Food and Bioproducts Processing
(2013) Clay/polymer composites: The story
Materials Today
(2004)- et al.
Gluten-based bioplastics with modified controlled-release and hydrophilic properties
Industrial Crops and Products
(2013) - et al.
Effect of processing on the viscoelastic, tensile and optical properties of albumen/starch-based bioplastics
Carbohydrate Polymers
(2011) - et al.
Egg white-based bioplastics developed by thermomechanical processing
Journal of Food Engineering
(2007)
Gelatinization and retrogradation phenomena in starch/montmorillonite nanocomposites plasticized with different glycerol/water ratios
Carbohydrate Polymers
Polymer-layered silicate nanocomposites: An overview
Applied Clay Science
Influence of glycerol and water activity on the properties of compressed egg white-based bioplastics
Journal of Food Engineering
Effect of plasticizer and storage conditions on thermomechanical properties of albumen/tragacanth based bioplastics
Food and Bioproducts Processing
Influence of tragacanth gum in egg white based bioplastics: Thermomechanical and water uptake properties
Carbohydrate Polymers
Influence of plasticizers in pectin films: Microstructural changes
Materials Chemistry and Physics
Biopolymer reinforced nanocomposites: A comprehensive review
Materials Today Communications
Improved tensile strength of glycerol-plasticized gluten bioplastic containing hydrophobic liquids
Bioresource Technology
Natural-based plasticizers and biopolymer films: A review
European Polymer Journal
Efficiency of stress transfer between polymer matrix and nanoplatelets in clay/polymer nanocomposites
Applied Clay Science
Exfoliation of montmorillonite and related properties of clay/polymer nanocomposites
Applied Clay Science
Plasticized Starch/Tunicin Whiskers Nanocomposites. 1. Structural Analysis
Macromolecules
D1434-82 standard test method for determining gas permeability characteristics of plastic film and sheeting
Standard test method for tensile properties of plastics
ASTM International
Conformational changes and molecular mobility in plasticized proteins
Biomacromolecules
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This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.