Biodegradable poly(lactic acid)-based hybrid coating materials for food packaging films with gas barrier properties
Introduction
Packaging materials for food and medicine require high resistances to oxygen and water vapor permeation to ensure products do not deteriorate during storage and handling [1], [2]. Polymeric packaging materials with high barrier properties are usually produced with multilayered structures by coextrusion or lamination process [3], [4]. These multilayer films include various nondegradable polymer resins, such as polyolefin, polyamide, poly(ethylene terephthalate), and ethylene-vinyl alcohol copolymers.
Since nondegradable polymer resins synthesized from petrochemicals can cause environmental problems after their useful life, ecologically safe, biodegradable polymers have been used for the application of short-term storage packaging films [5], [6]. A variety of biodegradable polymer materials have been developed and commercialized to replace conventional nondegradable polymer resins. Biopolymers for use as biodegradable packaging synthesized from petrochemicals or renewable resources include aliphatic thermoplastic polyesters, such as poly(lactic acid) (PLA), poly(butylene succinate) (PBS), poly(ɛ-caprolactone) (PCL), and poly(hydroxyl butyrate) [7]. Among these, PLA synthesized from renewable resources has attracted much attention as it can achieve excellent mechanical properties, biodegradability, and biocompatibility, at competitive cost [8], [9], [10].
Despite its advantages, crystalline PLA shows a limitation for the application of gas barrier films to be used for the food or medical packaging materials, as it has relatively low resistance to oxygen and water vapor permeation compared with conventional nondegradable polymer resins [11]. Therefore, much work has been performed to improve the gas permeation resistance of biodegradable PLA resins by combining it with inorganic materials.
The most frequently used approach is the introduction of nanoscale, organically modified, layered silicates into polymer matrices to prepare biodegradable nanocomposites [12], [13], [14], [15]. Gas barrier, mechanical, and thermal properties can be improved upon the addition of small amounts of nanosized clay, due to the homogeneous dispersion of intercalated or exfoliated layered silicate platelets in the continuous matrix. However, clay loadings above a critical content can result in poor dispersion of silicate layers that exhibit intercalated clay tactoids with large domain size, which ultimately deteriorate the physical properties of the nanocomposites. Hence, this nanotechnology approach using nanoclay has a limitation in increasing the barrier properties to the level required as the high barrier packaging materials.
An alternative approach to improve gas barrier properties involves incorporating nanostructured silica components synthesized from inorganic precursors into organic polymer phases using sol–gel technology. Organic–inorganic hybrid coatings of various nondegradable polymer substrate films has been reported to improve gas barrier properties [16], [17], [18], [19]. In these hybrid coating materials, the nondegradable polymer resins such as poly(vinyl alcohol), poly(vinyl acetate), poly(vinylidene chloride), and poly(ethylene-co-vinyl alcohol) were applied as the organic components. However, such nondegradable polymer-based hybrid coatings would severely limit the environmental benefits of using biodegradable polymer substrates. Therefore the preparation of biodegradable polymer-based hybrid coatings that can be combined with biopolymer substrate films has been reported for less environmentally damaging biodegradable food packaging films [11].
This work reports the incorporation of biodegradable PLA resin as an organic polymer into inorganic silica networks to prepare biodegradable organic–inorganic hybrid materials with high gas barrier properties that could be coated onto PLA substrate films. The PLA/SiO2 hybrid materials were synthesized by sol–gel process using tetraethoxysilane (TEOS) as an inorganic precursor and 3-isocyanatopropyltriethoxysilane (IPTES) as a silane coupling agent. Phase microstructures, thermal properties, and crystallization behaviors of the resulting hybrid materials were investigated by SEM, DSC, and XRD. The gas barrier properties of the biodegradable hybrid-coated PLA films were assessed by measuring the permeabilities of oxygen and water vapor through the coated films.
Section snippets
Materials and preparation
Tetraethoxysilane (TEOS, Acros Organics, 98%) and 3-isocyanatopropyl-triethoxysilane (IPTES, Aldrich, 95%) were used as inorganic silicate precursor and silane coupling agent, respectively. Poly(lactic-acid) (PLA, 2002D, NatureWorks Co. Ltd.) was used as the organic polymer in the PLA/SiO2 hybrid materials. Hydrocholoric acid (HCl, Samchun Chemical, 37 wt%) was used as a catalyst. Tetrahydrofuran (THF, Ducsan, Korea) was used as a co-solvent to facilitate hydrolysis during the sol–gel reactions
FTIR analysis
In the organic–inorganic hybrid materials, the phase attraction between two phases has been considered as a crucial factor to the production of hybrid materials with high performance. Particularly, in nanostructured hybrid materials synthesized via sol–gel method using a polymer resin system as an organic component, the phase morphology in association with the physical properties of the hybrid materials is greatly influenced by phase interaction between the polymer chain segments and the
Conclusions
Environmentally less damaging hybrid coating materials with low gas permeability were prepared by incorporating biodegradable organic PLA resin into inorganic silicate with superior barrier characteristics via sol–gel process. The resulting PLA/SiO2 hybrids showed improved phase compatibility with addition of IPTES silane coupling agent capable of creating covalent bonds between the organic and the inorganic phases. This strong bonding resulted in homogeneous microstructures with silica
Acknowledgment
This work was supported by Kyonggi University Research Grant 2010.
References (25)
- et al.
Trends Food Sci. Technol.
(2007) - et al.
J. Membr. Sci.
(2009) - et al.
Biomaterials
(2003) - et al.
Polymer
(2006) Food Sci. Biotechnol.
(2007)- et al.
Polym. Eng. Sci.
(1993) J. Plast. Film Sheet.
(1996)- et al.
Mech. Compos. Mater.
(2008) - et al.
Polym. Int.
(1998)
J. Nanosci. Nanotechnol.
Polymer
Cited by (92)
Electrospun films incorporating humic substances of application interest in sustainable active food packaging
2024, International Journal of Biological MacromoleculesEffects of filler type and content on mechanical, thermal, and physical properties of carrageenan biocomposite films
2023, International Journal of Biological MacromoleculesElectrospun hybrid TiO<inf>2</inf>/humic substance PHBV films for active food packaging applications
2023, Journal of Industrial and Engineering ChemistryRecent progress in sustainable barrier paper coating for food packaging applications
2023, Progress in Organic CoatingsBio-based food packaging materials: A sustainable and Holistic approach for cleaner environment- a review
2023, Current Research in Green and Sustainable ChemistryPoly(L-lactic acid)/poly(ethylene oxide) based composite electrospun fibers loaded with magnesium-aluminum layered double hydroxide nanoparticles
2022, International Journal of Biological MacromoleculesCitation Excerpt :This polymer is mainly produced by natural materials fermentation such as corn, starch, sugarcane, etc., while partially produced by lactide and lactic acid polymerization [2]. PLA has been widely studied in various applications including food packaging [3], textile fibers, surgery sutures, and biomedicine such as stent and dialysis membrane preparations [4], tissue engineering, wound dressing, and drug delivery [5]. Despite favorable thermal, biological, and physical properties like easy processability, non-toxicity, high tensile strength, and satisfactory biodegradability, PLA has low flexibility, low crystallinity, and inadequate barrier properties [2].