The research work in this thesis entitled "Synthesis and characterization of poly(lactic acid)-based antimicrobial bio-nanocomposites for potential food packaging applications" was carried out by me in the Department of Chemical Engineering at Indian Institute of Technology Guwahati, in partial fulfillment of the award of Doctorate in the Philosophy under the guidance of prof. The chapter also reviews the literature available on PLA-based nanocomposites for antimicrobial food packaging applications.
Sonochemical synthesis of poly(lactic acid) nanocomposites with ZnO nanoflowers: Effect of nanofiller morphology on physical properties
Chapter 3: Poly(lactic acid)/functionalized ZnO Nanocomposites for Antimicrobial Food Packaging Applications
Chapter 4: Antimicrobial bionanocomposites of poly(lactic acid)/ZnO deposited halloysite nanotubes for potential food packaging applications
Synthesis and characterization of poly(lactic acid)/clove essential oil/alkali-treated halloysite nanotubes composite films for food packaging
2.10 (a) TGA curves, (b) DTG curves, and (c) DSC patterns of regular PLA and PLA/ZnO nanocomposites with different loadings of ZnO nanoflowers. 4.8 (a) Water contact angle of nanocomposite films; (b) Dispersion of ZnO in a chloroform/water binary system; and (c) WVP of the nanocomposite films.
List of Tables
Introduction and Literature Review
Introduction
Among various biopolymers, poly(lactic acid) (PLA) is the most widely used material in food packaging applications (Shao et al., 2022). Additionally, PLA has been classified as a GRAS (Generally Recognized as Safe) material by the US FDA (United States Food and Drug Administration) (Mulla et al., 2021).
Bio-nanocomposites
Antimicrobial bio-nanocomposites are newly emerging food packaging materials that are very useful for inhibiting the growth of microorganisms on food surfaces and maintaining product quality, safety and extending shelf life. The antimicrobial agents as reinforcing fillers or additives are incorporated into the biopolymer matrix to synthesize antimicrobial bio-nanocomposites.
Biopolymers
- Poly (lactic acid)
- Structure and properties of poly(lactic acid)
- Synthesis of poly(lactic acid)
The formation of L-lactic acid, D-lactic acid or a mixture of L- and D- depends on the source and synthesis method. The final properties of poly(lactic acid), such as its crystallinity, thermal and mechanical properties, mainly depend on the ratio of L/D content (Ranakoti et al., 2022). The presence of L-lactic acid will produce semi-crystalline PLA (PLLA), while poly(DL-lactide) will produce an amorphous polymer (PDLLA).
Nanofillers/antimicrobial additives for PLA .1 Zinc oxide nanoparticles (ZnO-NPs)
- Surface modifications of ZnO nanoparticles
- Halloysite nanotubes (HNT)
- Essential oils
- Solvent casting method/solution technique
- In situ polymerization technique
These holes and free electrons generate reactive oxygen species (ROS) on the ZnO-NP surface from adsorbed oxygen and water molecules. In particular, it was found that the antimicrobial properties of ZnO-NPs depend on their size, morphology and specific surface area (Lallo da Silva et al., 2019).
PLA-based antimicrobial nanocomposites in food packaging applications
Properties of food packaging materials
- Barrier properties
- Mechanical properties
- Optical properties
- Antimicrobial properties
- Biodegradability
2021) reported a decrease in oxygen permeability (OP) value in chitosan film incorporated with gallic acid-loaded ZnO nanoparticles (Yadav et al., 2021). Here, the OP value was reduced by 46% in nanocomposite film compared to pure PLA (Jacob et al., 2022).
Literature review on antimicrobial bionanocomposites for food packaging applications
- Biopolymer/ZnO nanocomposites
- Biopolymer/halloysite nanotubes
- Biopolymer/essential oil/nanoparticles
- Biopolymer/functionalized ZnO nanocomposites
The refrigerator storage test showed that the BSG/CEO/ZnO nanorod nanocomposite film with 50% CEO (w/w protein) showed the highest antibacterial properties against Salmonella Typhimurium and L. The results clearly indicate the suitability of the nanocomposite films for active food packaging applications. 2019) have developed bionanocomposite films using carboxymethylcellulose (CMC), ZnO nanoparticles and different percentages of okra mucilage (OM) to extend the shelf life of chicken breast meat stored at 4°C (Mohammadi et al., 2019). The results revealed that the nanocomposite film showed excellent antimicrobial properties and could extend the shelf life.
Outcome of literature review/Research Gap
Objectives of the Thesis
Organization of the doctoral thesis This thesis has been organized into six chapters
The basic motivation behind this work is to obtain superior antimicrobial properties of PLA/ZnO nanocomposites with better compatibility of PLA functionalized. The synthesized PLA/ZnO@HNT films were characterized for physical, thermal, mechanical, UV shielding, barrier properties and antimicrobial activity for food packaging applications. In addition, a packaging test was performed on sliced apples over a 6-day storage period to evaluate the potential efficacy of nanocomposite films for food packaging applications.
In Chapter 3, the surface of ZnO nanoparticles was modified with the silane coupling agent 3-(aminopropyl)trimethoxysilane (APTMS). The effects of surface modified ZnO on the thermal, mechanical and antimicrobial properties of PLA were investigated.
Poly(hydroxybutyrate-co-hydroxyvalerate) based nanocomposites for antimicrobial active food packaging containing oregano essential oil. Influence of NiO-supported silicon nanoparticles on mechanical, barrier, optical and antibacterial properties of polylactic acid (PLA) bio-nanocomposite films for food packaging applications. Preparation and characterization of polylactic acid/fenugreek essential oil/curcumin composite films for food packaging applications.
Sonochemical synthesis of poly(lactic acid) nanocomposites with ZnO nanoflowers: Effect of nanofiller morphology on
Introduction
These bio-polymers have certain limitations such as poor mechanical, thermal, barrier properties etc. (Asgher et al., 2020). Guo et al. (Guo et al., 2020) investigated gas sensing ability of different morphologies of ZnO, including nanoparticles, nanoplates, and nanoflowers. 2016) also produced different shapes of ZnO nanoflowers, namely rod flowers, fusiform flowers and petals using hydrothermal process (Cai et al., 2016).
Materials and Methods .1 Materials
- Synthesis of ZnO nanoflowers
- Synthesis of PLA/ZnO nanocomposites
- Product characterizations
Both ZnO nanofillers and PLA/ZnO nanocomposites were characterized using standard techniques: (1) FTIR: FTIR was performed with an FTIR spectrometer (manufacturer: PerkinElmer, Singapore, model: Spectrum two) in the frequency range of 4000400 cm1 at room temperature in ATR (Atenuated Total Reflectance) mode. A drop of diluted PLA/ZnO nanocomposite was deposited on a carbon-coated grid for TEM analysis. The antimicrobial activity of PLA/ZnO nanocomposite films was quantitatively tested by the live colony count method against two pathogenic food-borne bacteria, Escherichia coli (Gram negative) and Listeria monocytogenes (Gram positive) using the colony count method (Rhim et al. , 2009). ).
Results and Discussion
- Characterization of ZnO nanoflowers
- Characterization of PLA/ZnO nanoflower nanocomposites
- UVVisible spectroscopy
- Thermal properties
- Mechanical properties
- Antimicrobial activity
The incorporation of ZnO significantly decreased the transmission of PLA/ZnO nanocomposite films (Hasan et al., 2021; Soylu & . Coskun, 2018). The result revealed that the incorporation of ZnO nanoflowers into PLA consistently lowers the thermal degradation temperatures of the final nanocomposite films. Moreover, the use of ultrasound during the synthesis process causes uniform distribution of ZnO nanoflowers in the nanocomposite films.
Conclusions
Properties improvement of ZnO nanorods using modified chemical bath deposition method: Effect of precursor concentration. New green synthesis route of ZnO nanoparticles using natural biodegradable polymer and its application as a catalyst for the oxidation of. Enhancing the photocatalytic activity of ZnO nanotubes: A comparison between thermal decomposition of zinc acetate under vacuum and in.
Poly(lactic acid)/functionalized ZnO Nanocomposites for Antimicrobial Food Packaging Applications
Introduction
This agglomeration would hinder the final properties (thermal, mechanical, barrier properties, etc.) of polymer nanocomposites (Maghsoudlou et al., 2019; Rong et al., 2006; Zare et al., 2017). Surface modification of nanofillers with a suitable coupling agent is one of them (Kango et al., 2013). Many studies have been carried out on the surface modification of nanoparticles using various modifiers such as carboxylic acids (Quiñones et al., 2014; Samavini et al., 2018), silanes (Ahangaran & Navarchian, 2020), organophosphorus (Kalska-Szostko et al. .). al., 2013; Mohapatra & Pramanik, 2009) etc.
Experimental .1 Materials
- Synthesis of ZnO nanoparticles
- Synthesis of PLA/f-ZnO nanocomposites
- Characterization techniques
Hunter color values, L* (lightness/darkness), a* (redness/greenness), b* (yellowness/blueness) were measured at five different locations of film samples. 11) Surface wettability: The surface wettability test of the nanocomposite films was performed using a contact angle goniometer and associated software (Holmarc, HO-IAD-CAM-01B). The film sample of dimension 20 mm×20 mm was placed on a sample holder and a water droplet of 3 μL was carefully placed on the film surface using microsyringe and contact angle (CA) was measured. Using film samples, the mouth of the bottle was covered and made airtight by wrapping with Teflon tape.
Results and discussion
- FTIR and XRD study of ZnO and f-ZnO
- Energy dispersive X-ray spectroscopy (EDX)
- FE-SEM analysis
- BET surface area analysis
- FE-TEM analysis of nanocomposites
- Thermal properties
- Mechanical properties
- UV-barrier properties and surface color of the nanocomposites
- Surface wettability and water vapour permeability
- Antimicrobial properties
FE-SEM micrograph of f-ZnO suggested non-aggregated and homogeneous distribution of f-ZnO nanoparticles compared to unmodified ZnO. Agglomeration was reduced due to surface modification of ZnO with silane coupling agent. FE-TEM analysis was done to study the distribution of ZnO and f-ZnO in the PLA matrix. The results revealed that the addition of ZnO and f-ZnO to PLA decreased the WVP of the nanocomposite films.
![Table 3.1. Intensity of index peak [101] and the crystallite size of ZnO and f-ZnO Sample 2Ө (degree) FWHM Crystallite size (nm) Intensity (%)](https://thumb-ap.123doks.com/thumbv2/azpdfnet/10343761.0/127.893.97.779.402.793/table-intensity-index-crystallite-sample-degree-crystallite-intensity.webp)
Conclusions
Strong electrostatic attraction between bacterial cells and ZnO nanoparticles causes accumulation of the ZnO nanoparticles on the outer surface of the plasma membrane. Enhancement of the UV barrier and antibacterial properties of crosslinked pectin/zinc oxide bionanocomposite films. Incorporation of zinc oxide nanoparticles improved the mechanical water vapor barrier, UV light barrier, and antibacterial properties of PLA-based nanocomposite films.
Antimicrobial bionanocomposites of poly(lactic acid)/ZnO deposited halloysite nanotubes for potential food packaging
Introduction
The improvement in functional properties of bionanocomposites can be achieved by the formation of good interfacial interaction and hydrogen bonding between nanofillers and matrix (Taherimehr et al., 2021). There are several types of nanoclays (montmorillonite, halloysite nanotubes etc.) available, among which halloysite nanotubes (HNT) are the most promising in the field of active food packaging due to their non-toxic, low cost and biocompatible nature (Risyon et al., 2020). Addition of HNT provides a tortuous path for the penetration of molecules through the film matrix, thereby reducing the permeability of gas and water molecules (Risyon et al., 2020).
Materials and methods .1 Materials
- Fabrication of ZnO deposited halloysite nanotubes (ZnO@HNT)
- Synthesis of PLA/ZnO@HNT nanocomposites
Schematic diagram of in situ synthesis of ZnO on HNT (ZnO@HNT) 4.3 Characterization of ZnO@HNT and its nanocomposite films. Where, 𝑇() = Spectral transmittance of the films, = bandwidth, = incident wavelength, a, b is the integral upper and lower limit which is basically the absorption range of UV-B and UV-A. The surface color of the nanocomposite films was measured using a colorimeter (Datacolor 550, Datacolor Technology Suzhou Co., Ltd., China).
Application of PLA/ZnO@HNT nanocomposites on fresh cut apples .1 Preparation of the packaged samples
- Weight loss
- Total soluble solids (TSS)
- Titratable acidity (TA) and pH
- Firmness
The weight loss of the sliced apples during storage was determined using a digital weighing balance. TSS value affects the taste as it indicates the level of sweetness of the fruit. The TSS of the filtered juice was measured three times with a hand refractometer (Bombay Scientific ERMA with ATC, range: 0 32 °Brix).
Results and discussion
- Characterization of ZnO@HNT
The results of X-ray diffraction (XRD) study of HNT and ZnO@HNT are shown in Fig. showed. Note: Degradation temperature for 5%, 10% and maximum weight loss (from DTG curve) is represented by- T5%, T10% and Tmax% respectively]. a) Nitrogen adsorption–desorption isotherms (inset: pore size curves), (b) XRD spectra, (c) TGA, and (d) DTG curves of HNT and ZnO@HNT. TGA and derived thermogravimetric (DTG) curves of HNT and ZnO@HNT are shown in Figs.
Characterization and properties evaluation of PLA/HNT and PLA/ZnO@HNT nanocomposites
- FE-SEM study
- XRD study
- Surface wettability and water vapor permeability (WVP)
- UV-barrier properties
- Thermal properties
- Mechanical Properties
- Antimicrobial properties
Incorporation of HNT and ZnO@HNT into PLA matrix results in significant improvement in tensile strength (Fig. 4.11b). Incorporation of HNT and ZnO@HNT also improves the elastic modulus of the PLA-based nanocomposites. At higher loading of ZnO@HNT (3 wt%), the antimicrobial activity of nanocomposite is more significant.
Study of the potential ability of the PLA based nanocomposite films for packaging of fresh cut apples
- Weight loss
- Total soluble solids (TSS)
- Fruit firmness
The TSS of sliced apples stored in PE, PLA, PLA/HNT and PLA/ZnO@HNT nanocomposites for days 0 to 6 at room temperature is shown in the figure. The results showed that sliced apples packaged in PLA/HNT and PLA/ZnO@HNT films retained relatively higher amounts of TSS compared to PE and PLA at the end of the 6th day of storage. This may be due to the lower respiration rate of cut apples packaged in PZH2, resulting in lower metabolic activities.
Safety issues and migrations of nanoparticles
The migration behavior of nanofillers is still not clear and more studies and investigations on the exposure, toxicity and effects of bionanocomposites are required for commercial and social acceptance.
Conclusions
Facile synthesis and characterization of ZnO nanoparticles grown on halosite nanotubes for enhanced photocatalytic properties. Alginate-based nanocomposite films reinforced with halloysite nanotubes functionalized by alkali treatment and zinc oxide. Synthesis and characterization of poly(lactic acid)/clove essential oil/alkali treated halloysite nanotubes composite.
Synthesis and characterization of poly(lactic acid)/clove essential oil/alkali-treated halloysite nanotubes composite
- Introduction
- Materials and Methods .1 Materials
- Synthesis of alkali treated halloysite nanotubes (NHNTs)
- Synthesis of PLA based nanocomposites with NHNT and clove essential oil (CEO) PLA based nanocomposites with NHNT and CEO were synthesized by using solvent casting
- Characterizations of nanoparticles and nanocomposite films
- Application of PLA based nanocomposites on fresh cut apples .1 Preparation of the packaged samples
- Weight loss
- Total soluble solids (TSS)
- Titratable acidity (TA) and pH
- Firmness
- Microbial analysis
- Statistical analysis
- Results and discussion
- Characterization of HNT, NHNT and PLA/CEO/NHNT
- Properties of nanocomposite films .1 Surface wettability
Halloysite nanotubes (HNTs) are a type of nanoclay with a hollow tubular structure with the chemical formula Al2Si2O5 (OH)4 (Saadat et al., 2020). Microbiological analysis of stored packaged cut apples was performed according to the number of aerobic mesophylls (Chi et al., 2019). The presence of hydrophobic clove essential oil increased the hydrophobicity of the film surface (Sharma et al., 2020).
