Augmented barrier properties of poly (lactic acid) composite packaging film reinforced by antibacterial hybrid bio‐filler: Extending the shelf life of fruits

Biodegradable active films based on poly(lactic) acid (PLA) and starch were developed and characterized as to their functional and structural properties, using the bilayer film strategy, in order to obtain materials that better meet the food packaging requirements. Plasticization of semicrystalline PLA was analysed by using three different biodegradable compounds to enhance the PLA mechanical performance. Likewise, cinnamaldehyde was incorporated to PLA-starch bilayer films and their antimicrobial properties and release kinetics in food simulants were analysed. Semicrystalline and amorphous PLA and cassava starch (S) were used to obtain the films. Semicrystalline PLA and S were processed by melt blending and compression moulding, whereas amorphous PLA films were obtained by casting the ethyl acetate solution of the polymer, with and without cinnamaldehyde. Bilayer films were obtained by compression moulding of amorphous PLA layers with starch sheets, while semicrystalline PLA sheets were also used in bilayers for comparison purposes. The analyses of crystallization behaviour and glass transition of neat and plasticized semicrystalline PLA films revealed an increase in the crystallinity, along with a reduction in the glass transition temperature (Tg), in line with the rise in plasticizer concentration in every case. Despite the decrease in Tg, the tensile test did not reflect an enhancement of the film elongation capacity, in comparison to the non-plasticized polymer. Likewise, plasticizers did not reduce the film elastic modulus due to the greater induced crystallinity. On the basis of these results, a more extensible material, amorphous PLA, was considered to obtain PLA-starch bilayer films, taking advantage of the complementary barrier properties of both polymers and the high mechanical resistance of PLA. Despite the lower ratio of PLA sheet in the starch bilayer assembly (about 1/3 of the film thickness), a great improvement in tensile and water vapour barrier properties was achieved with respect to the neat starch films, the films maintaining high transparency and oxygen permeability as low as that of starch films. When cinnamaldehyde was included in the cast PLA sheet, films became thinner due to the losses of the volatile active during processing, but the improvement in barrier properties was maintained, with lower mechanical resistance. Thermal analyses revealed diffusion of cinnamaldehyde or low molecular weight compounds from the amorphous PLA layer to the adhered sheets (starch or semicrystalline PLA) which contributed to their plasticization and reduced the PLA crystallization. Antimicrobial activity of the cinnamaldehyde-loaded films against Gram- (Escherichia coli) and Gram+ (Listeria innocua) bacteria was tested through in vitro tests. Both amorphous PLA monolayers and starch-PLA bilayers were effective at controlling the bacterial growth, thus indicating that the active amount released into the growth medium exceeded the minimum inhibitory concentration (MIC) of both bacteria, despite the losses of the active compound during the film processing. In contrast, PLA-cinnamaldehyde loaded PLA bilayer films did not show antimicrobial activity. The analysis of the release kinetics of cinnamaldehyde from the films to the different food simulants revealed differing behaviours of the active compound delivery, depending on both films and food simulants. PLA bilayer films exhibited the slowest cinnamaldehyde release and the predicted amount delivered into the aqueous culture medium did not reach the MIC, explaining the lack of antimicrobial effect of these films. Therefore, the developed bilayer films based on amorphous PLA and starch represent an interesting strategy to obtain high barrier-highly resistant packaging films, with active properties when they include cinnamaldehyde as antimicrobial compound.

Coated polylactic acid (PLA) films consisting of crosslinked‐chitosan/beeswax layer were prepared to improve barrier properties and abrasion resistance of the base substrate. The effect of crosslinking the chitosan layer on durability and barrier properties of the coatings was investigated. Crosslinked samples exhibited lower degree of swelling compared to uncrosslinked samples and 50% reduction in water vapor transmission rate (WVTR) compared to neat PLA films. The beeswax coating decreased the WVTR of chitosan‐coated PLA films significantly (by 100%). However, it had a marginal effect on the oxygen transmission rate. Water vapor transmission was less affected by abrasion than oxygen transmission for both uncrosslinked and crosslinked samples. The WVTR of crosslinked samples were retained even after being subjected to abrasion, whereas WVTR of uncrosslinked samples dropped by 50%. Results obtained using the Taber test method also show that the weight loss of crosslinked coatings are about 75% less than that of uncrosslinked samples and can withstand a greater number of cycles before rupture. These translucent‐coated films retained good barrier and mechanical properties along with providing improved abrasion resistance after crosslinking. This approach provides exciting new possibilities for expanding the use of biodegradable polymers in packaging applications. POLYM. ENG. SCI., 59:1874–1881, 2019. © 2019 Society of Plastics Engineers

To improve the tensile properties of poly(lactic acid) (PLA) biodegradable packaging film, mango seed wax (MSW), an agro‐industrial waste from the mango fruit processing industry has been used as a plasticizing additive. Four different weight ratios of MSW (3, 5, 7, and 9 wt%) in pristine PLA were considered for optimization. The mechanical properties comprising tensile strength, elongation at break, and Young's modulus were studied. Characterizations such as Fourier transform infra‐red (FTIR) spectroscopy, and differential scanning calorimetry were studied. Oxidation induction time (OIT) analysis of samples was also conducted. Other studies such as thermal, barrier, and optical properties were also evaluated. The differential scanning calorimetry (DSC) analysis revealed better compatibility between MSW and PLA matrices. A small decrease in glass transition temperature (10%), and melting point (3%) was observed when increasing the percentage of MSW in PLA. Moreover, the visual transparency of MSW/PLA systems was intact when increasing the loading. The addition of 9% MSW results in a 700% enhancement in elongation at break than that of pristine PLA. The optimized sample (PLA with 5% MSW) showed a 26% improvement in the hydrophobicity of the PLA matrix. The barrier properties (55.6% in WVTR and 10% in oxygen transmission rate (OTR) were also improved by the presence of MSW. These are promising systems as a suitable material for biodegradable food packaging thermoplastic material.

Antimicrobial bionanocomposites of poly(lactic acid)/ZnO deposited halloysite nanotubes for potential food packaging applications

Electrospinning of gelatin/chitosan nanofibers incorporated with tannic acid and chitooligosaccharides on polylactic acid film: Characteristics and bioactivities

ABSTRACTThis study aimed to develop antimicrobial and biodegradable packaging films with excellent printability, designed to preserve the freshness of cherry tomatoes, using polylactic acid (PLA), polybutylene adipate terephthalate (PBAT), and natural thyme oil. Packaging films were prepared using the solvent casting method by incorporating 1%, 2.5%, and 5% (w/v) thyme oil into PBAT and PLA‐based polymer matrices. Fourier‐transform infrared (FTIR) spectroscopy confirmed the successful integration of thyme oil into PBAT, PLA, and PBAT/PLA polymeric matrices. When the concentration of thyme oil increased from 1% to 5%, the antibacterial properties against Staphylococcus aureus improved by 42% in films containing only PBAT, 46% in the films containing only PLA, and 28.5% in PBAT/PLA films. Similarly, for Escherichia coli, the improvements were 37.5%, 28.5%, and 45.5%, respectively. The water contact angle measurements revealed that the packaging films exhibited a certain degree of hydrophobicity. A packaging film incorporating 5% thyme oil (TO) (by total weight) into the PBAT and PLA polymeric matrix (PBAT/PLA‐5TO) exhibited effective antibacterial properties and extended storage stability. The PBAT/PLA‐5TO packaging film was found to extend the shelf life of cherry tomatoes sevenfold, significantly reducing spoilage rates and demonstrating remarkable effectiveness in prolonging shelf life. In conclusion, the packaging films prepared by incorporating thyme oil into the polymeric matrix present an innovative and biodegradable packaging material that offers a sustainable solution for the food packaging industry.

Polylactic acid (PLA) is a biopolymer that has potentialfor usein food packaging applications; however, its low crystallinity andpoor gas barrier properties limit its use. This study aimed to increasethe understanding of the structure property relation of biopolymerblends and their nanocomposites. The crystallinity of the final materialsand their effect on barrier properties was studied. Two strategieswere performed: first, different concentrations of poly(hydroxybutyrate)(PHB; 10, 25, and 50 wt %) were compounded with PLA to facilitatethe PHB spherulite development, and then, for further increase ofthe overall crystallinity, glycerol triacetate (GTA) functionalizedchitin nanocrystals (ChNCs) were added. The PLA:PHB blend with 25wt % PHB showed the formation of many very small PHB spherulites withthe highest PHB crystallinity among the examined compositions andwas selected as the matrix for the ChNC nanocomposites. Then, ChNCswith different concentrations (0.5, 1, and 2 wt %) were added to the75:25 PLA:PHB blend using the liquid-assisted extrusion process inthe presence of GTA. The addition of the ChNCs resulted in an improvementin the crystallization rate and degree of PHB crystallinity as wellas mechanical properties. The nanocomposite with the highest crystallinityresulted in greatly decreased oxygen (O) and carbondioxide (CO2) permeability and increased the overall mechanicalproperties compared to the blend with GTA. This study shows that theaddition ChNCs in PLA:PHB can be a possible way to reach suitablegas barrier properties for food packaging films.

UV protective poly(lactic acid)/rosin films for sustainable packaging

Polylactic acid (PLA) is a biodegradable polymer which has a wide range of applications; in this work, all PLA based composites formulations were compounded by twin screw extruder and testing specimens were produced. This article focuses on determinations of mechanical, antibacterial, thermal and barrier properties of PLA composites. It was found that only the tensile modulus of PLA composites increased while the others decreased when 10% wood was loaded. The effect of Triclosan and Cloisite® 30B compounding did not change the mechanical properties and glass transition temperature. However, by the presence of wood and Cloisite® 30B, Tm values of the composites exhibited double peak characteristic which was related to an increase in crystallinity level. Antibacterial activity of the PLA composites was improved with the Cloisite® 30B content, and this was attributed to cationic bactericide quaternary ammonium group between the silicates layers. Hydrophobic material Triclosan obviously changed water vapor permeability (WVP) of the PLA from 8.24 × 10−11 to at 7.26 × 10−11 g.mm/mm2.h.Pa for triclosan/PLA specimens. All PLA composites samples with 0.5% clay content showed a significant increase in oxygen barrier property.

This study aimed to enhance the oxygen barrier properties of polylactic acid (PLA) film, a biodegradable packaging material with high oxygen permeability (OP). Bi‐layer films were produced by coating thermoplastic starch (TPS) onto PLA films in various ratios while maintaining constant film thickness. The mechanical, optical, barrier, thermal, hydrophobicity, moisture sorption, and microstructural properties of the films were analyzed. Increasing the TPS ratio elevated moisture content (MC), water uptake, solubility, and opacity while enhancing UV barrier properties. TPS coating reduced tensile and burst strength but increased the burst deformation of the bi‐layer films. Bi‐layer film production resulted in a water vapor permeability increase of 59.26%–94.44% compared with neat PLA while decreasing OP by 2.52%–29.66%. The equilibrium moisture content (EMC) rose with higher TPS ratios, displaying type II isotherms. FTIR analysis indicated no chemical interactions between PLA and TPS. Increasing the TPS ratio decreased PLA crystallinity, supporting the mechanical and barrier properties of the bi‐layer films. Neat and bi‐layer films exhibited smooth, homogeneous surfaces, with a visible interface in the cross‐section of the bi‐layer films. In conclusion, TPS shows promise as an alternative to improve oxygen barrier properties in PLA films without adversely affecting other properties.

Polylactic acid (PLA) is a biodegradable and renewable polymer, which represents a valuable alternative to plastic packaging films, often associated with environmental problems. In this study, we tested the suitability of PLA as a biodegradable packaging film and assessed the antimicrobial activity of lemongrass oil (LO), incorporated into the PLA film in different concentrations. To obtain the optimal physical properties for PLA films, tensile strength, elongation at break, and water vapor permeability were measured under different preparation conditions. In addition, the antimicrobial activity of the LO contained in the PLA film against Listeria monocytogenes was investigated by disc diffusion and viable cell count. Among all concentrations tested, 2% LO was the most suitable in terms of antimicrobial activity and physical properties of the PLA film. Based on these results, we used the PLA film containing 2% LO to pack pork sausages; after 12 d of storage at 4℃, the population of inoculated L. monocytogenes in the sausage samples wrapped with the PLA film containing 2% LO was reduced by 1.47 Log CFU/g compared with the control samples. Our data indicate that PLA films containing 2% LO represent a valuable means for antimicrobial sausage packaging.

The usage of biopolymers in developing biodegradable food packaging films that are sustainable and safe towards environment has been restricted because of the poor mechanical and barrier properties of the biopolymers. This study aims to enhance the limited properties of biopolymers particularly polylactic acid (PLA) for food packaging applications by investigating the effects of incorporating different types (montmorillonite (MMT) and halloysite) and concentrations (0–9 wt.%) of nanoclays on the mechanical, oxygen barrier, and transparency properties of the films. PLA with 3 wt.% concentration of nanoclays resulted in the optimum mechanical and oxygen barrier properties due to the strong interaction between nanoclays and torturous path length created by nanoclays respectively. Nevertheless, these properties reduced as more nanoclays (≥5 wt.%) was added into the films due to agglomeration of nanoclays. PLA incorporated with MMT nanoclay exhibited better properties compared to halloysite nanoclay due to the nanoclay structure in nature. Addition of 3 wt.% nanoclays into virtually transparent PLA film have only small effects on the transparency of the film whereby the reduction in light transmittance was only around 10%. This study is crucial to improve the feasibility of biopolymers usage for food packaging applications.

Single-use plastics are a major source of pollution and biodegradable polymers could be the best substitute, as they possess similar barrier and functional properties. Aiming at improving barrier properties and providing antioxidant bioactivity, PLA (PolyLactic Acid) films were coated with a crosslinked suspension of plasticized gelatin incorporating phenolic compounds. The coating process induced weak modifications of PLA properties due to plasticization by moisture and glycerol from the coating suspension. Indeed, a double glass transition was displayed. The water vapor barrier properties of the PLA-coated films were not significantly affected. Phenolic compounds induced a crosslinking of the gelatin network, slightly decreasing the moisture sensitivity and surface hydrophilicity. Therefore, the mechanical properties of PLA were maintained after coating and their barrier properties were highly improved, with up to a 600-fold reduction of the oxygen transfer rate. These results make possible new applications for oxidation-sensitive foods, and even for semi-moist foods.

Morphological, thermo-mechanical, and barrier properties of coextruded multilayer polylactide composite films reinforced with graphene nanoplatelets and encapsulated thyme essential oil

This study aimed to prepare the nickel oxide supported on silica nanoparticles (NiO NPs) incorporated polylactic acid (PLA) bio nanocomposite films of various concentrations (0.25, 0.5. 0.75, 1 wt%) and study the resultant properties of NiO on the tensile, barrier, surface color, opacity and antibacterial properties for food packaging applications. The maximum tensile strength of 16.4 MPa was obtained at 1 wt% of the prepared biocomposite film. The barrier properties like oxygen transmission rate and water vapor transmission rate were significantly reduced and showed a better value of 841.20 (cc / (m2. day. atm)) and 3.96 (g/ m2 /day) on 1 wt% of NiO. The incorporation of NiO NPs increased the surface color (L*, a*, b*) and the opacity values were bio nanocomposite films. Also, the PLA / NiO bio nanocomposite films showed good antibacterial activity against gram-positive (L.monocytogenes) and gram-negative bacteria (Salmonella). Therefore, the prepared bio nanocomposite films could be used as an excellent packaging material for food packaging applications.