Nano-composites and food packaging
Food packaging needs to have a long shelf life and be inspected for quality and safety
in accordance with international standards. Polymer nanocomposites have become a
new type of food packaging materials in the last ten years due to their numerous
benefits, including improved mechanical, thermal, and barrier qualities. The fillermatrix interactions and performance of the resulting material are favored by the
higher surface area of nanoparticles compared to their microscale counterparts.
Today, micrometer-sized fillers are utilized to reinforce polymers to increase
strength and stiffness, improve solvency or fire resistance, or just to cut costs.
However, using these tiny fillers has several disadvantages, like brittleness and
opacity. It is best to highlight right away, nevertheless, that opacity is not a trivial
packing factor for foods that are sensitive to light, including vegetable oils and fruit
juices. Traditional fillers have limitations, whereas nanocomposites, where at least
one filler dimension is in the nanometer range, circumvent those restrictions.
Additionally, while microcomposites typically require significantly larger loadings
(25–40 wt%), the improvements in nanocomposite properties were achieved at
relatively low loading levels (5 wt%) of fillers. The finished product is less
expensive when nanoparticles are included in packaging materials in trace amounts,
which is acceptable to the end users. Due to their affordability and light weight,
polymeric materials are widely employed in food packaging. The three polymers
that are most frequently utilized in food packaging systems are polyethylene
terephthalate, polyethylene, and polystyrene.(Farhoodi,2016)
https://link.springer.com/article/10.1007/s12393-015-9114-2
There are several different types of nanostructures that perform additional tasks in
addition to reinforcing nanoparticles, whose main job is to improve the mechanical
and barrier properties of the packaging materials. These additional tasks can include
giving the packaging system active or "smart" qualities like antimicrobial activity,
enzyme immobilization, biosensing, etc. The most researched nanoparticles will be
arranged based on the main uses/applications they have in food packaging systems.
The uses of some particles can overlap at times, like with some immobilized
enzymes that can function as biosensors, oxygen scavengers, and/or antibacterial
components. (De,2009)
https://www.sciencedirect.com/science/article/abs/pii/S096399690900091X
Nano-composites and food safety
Antimicrobial substances being included into food packaging materials has drawn a
lot of interest. Antimicrobial films may aid in reducing the development of harmful
and spoilage microorganisms. Due to its appropriate structural integration and
barrier qualities provided by the nanocomposite matrix, an antimicrobial
nanocomposite film is particularly desired. The most popular silver-based
nanocomposites used as antimicrobial films for food packaging are widely known
for their potent toxicity to a variety of pathogens. Ag-NPs' aggregation stability and
antibacterial activity under the influence of surfactants and polymers, and found that
modified Ag-NPs had increased bactericidal impact. The stability of the aggregation
and antibacterial activity were found to be correlated. Ag-NPs have undergone
successful antibacterial testing. Smaller Ag-NPs have a better bactericidal effect than
bigger Ag particles because they have a larger surface area accessible for contact
with microbial cells. According to research comparing the effectiveness of polyamide 6/silver nano- and microcomposites, nano- composites with a modest silver
content demonstrated a superior enhanced efficacy against Escherichia coli than
microcomposites with a significantly larger silver concentration. Even after being
submerged in water for 100 days, polyamide 6 containing 2 weight percent Ag-NPs
was still effective against E. coli. Additionally, Ag-NPs absorbs and breaks down
ethylene. This could be a factor in how well it preserves fruits and vegetables. In
fact, a PE nanocomposite film containing Ag-NPs postponed the senescence of the
Chinese fruit jujube. The shelf life of asparagus was extended and microbiological
growth was reduced thanks to an Ag-NPs coating.(De,2009)
https://www.sciencedirect.com/science/article/abs/pii/S096399690900091X
• nano-based sensors for food safety (spoilage protector)
Nanoparticles can be used in packaging materials as reactive particles. The so-called
nanosensors can react to changes in the environment, degradation products, or
microbial contamination (for example, temperature or humidity variations in storage
rooms, levels of oxygen exposure). Industries determine the food's expiration date
by taking into account the distribution and storage conditions (particularly
temperature) to which the product is anticipated to be subjected. Foods are
frequently exposed to temperature abuse, and it is well recognized that these
circumstances are not always accurate. This is particularly concerning for goods that
need a cold chain. Furthermore, food goods may experience unexpectedly excessive
oxygen exposure due to micropores or sealing flaws in packing methods, which may
result in unfavorable effects. Nanosensors can detect specific chemical compounds,
pathogens, and poisons in food when they are integrated into food packaging. This
eliminates the need for inaccurate expiration dates and provides real-time status of
food freshness. Nano-based sensors are already being developed or are already on
the market to track components or products through the processing chain or to detect
diseases, spoilage, chemical pollutants, or product manipulation. Moreover, these
CNT-based sensors have a number of advantages over expensive and timeconsuming traditional detection techniques like HPLC. the lack of need for
exogenous chemicals or labels, the simplicity and cost-effectiveness, the quick and
high-throughput detection, the reduced power requirements, and the ease of
recycling. A multiwalled CNT-based biosensor being developed by Iyers may
identify microorganisms, hazardous proteins, and goods that have undergone
degradation in food and beverages.(De,2009)
https://www.sciencedirect.com/science/article/abs/pii/S096399690900091X
Safety Evaluation of Nanocomposite Food Packaging
Migration testing on packaging components were carried out to assure consumer
health protection and prevent food adulteration. A general migration limit (OML) of
60 mg (of substances)/ kg (of foodstuff or food simulants), which applies to all
substances that can migrate from food contact material to foodstuff, and a specific
migration limit (SML), which is fixed based on the toxicological evaluation of the
substance, have both been established in the area of plastic materials. The acceptable
daily intake (ADI) or tolerated daily intake (TDI) determined by the European Food
Safety Authority (EFSA) is typically used to determine the SML.
In order to determine the upper limit, it is assumed that a person weighing 60 kg
consumes 1 kg of food daily for the duration of his or her lifespan that is packaged
in plastic and contains the relevant substance in the maximum permissible amount
(as per European Union standards). However, testing new technology is necessary
to find any issues that might be related to the product. Numerous investigations on
the incorporation of monomers, plasticizers, and other additives into food/food
simulants. (Farhoodi,2016)
https://link.springer.com/article/10.1007/s12393-015-9114-2
Health Safety Aspects of Nanoparticles for the Consumer
Through cutaneous exposure, ingestion, or inhalation, nanoparticles can enter the
body. Nanoparticles will invariably come into touch with a wide range of
biomolecules once they have entered a biological environment, including proteins,
carbohydrates, and lipids that are dissolved in body fluids like the lymph, blood, or
interstitial fluid between cells. Smaller nanoparticles appear to be more harmful than
larger ones, according to observations. Small nanoparticles have a high surface area
compared to mass, which enhances the possibility that they will interact with nearby
biological molecules and, as a result, cause unfavorable reactions. However, toxicity
is not just caused by size; other variables, such as surface functionalization, also play
significant roles.(Farhoodi,2016)
It's possible that cationic nanoparticles' strong attraction for the negatively charged
plasma membrane explains why they are thought to be more harmful than neutral or
anionic counterparts. As a result, it is necessary to change each nanoparticle's
attributes one at a time in order to systematically test the toxicity of nanoparticles.
https://link.springer.com/article/10.1007/s12393-015-9114-2
nano-composites extending the shelf life of fruits and vegetables
Due to their vitamins, minerals, antioxidants, and fibre, fruits and vegetables are
high on consumer purchase lists and play a significant part in proper nutrition. But
the main issue with pre-serving fruits and vegetables is that they have a short shelf
life due to their high moisture content (75–95%), which causes quick deterioration
and decay of these items as well as an unattractive appearance. The use of suitable
packaging and preservation techniques could be used to increase the shelf life of
fruits and vegetables. Effective candidates include nanocomposite antimicrobial
packaging solutions because of their enhanced mechanical, barrier, thermal, and
antibacterial qualities. The implementation of suitable packaging and preservation
techniques could extend the shelf life of fruits and vegetables. Effective candidates
include nanocomposite antimicrobial packaging solutions because of their enhanced
mechanical, barrier, thermal, and antibacterial qualities. The presence of gases like
ethylene, CO2, and oxygen around fruits and vegetables has a negative effect on
both the respiratory rate and overall metabolic rate. In addition, the presence of
ethylene in the air raises questions about how to handle both climacteric and nonclimacteric fruits and vegetables after harvest because it speeds up ripening and
senescence. As a result, certain measures must be taken to restrict the presence of
ethylene in vegetables and fruits during storage and shipping, such as employing
ethylene absorbents and proper packing. Furthermore, bacterial and fungal growth
might be accelerated by high relative humidity (RH > 95%), leading to pathological
breakdown. Bio/polymeric nanocomposites are now being used more frequently in
the food packaging industry. High aspect ratio nanoparticles (NPs) are particularly
intriguing because they have a higher specific surface area, which improves the
matrix's reinforcing effects. There are many advantages of using NPs in
bio/polymers as opposed to alternative packaging methods. For the purpose of
enhancing the physicochemical qualities and extending the shelf life of fruits and
vegetables, Table ( ) lists several studies on bio-nanocomposite films and edible
coatings. (Jafarzadeh,2021)
https://www.sciencedirect.com/science/article/abs/pii/S0001868621000464
Table ( ) bio-nanocomposites films and edible coating improve physiochemical properties of
food (extending shelf-life)
Fruit /vegetable
Coating
Nanoparticles
Banana
Soy protein
isolate
ZnONP
Strawberry
Chitosan
Copper
Tomato
Chitosan
papaya
Chitosan
Advantage
Nanocomposite film could effectively delay ripening
rate and weight loss of bananas
effective control in reducing weight loss, firmness and
delayed changes in the respiration rate during 3 weeks.
The results showed that the chitosan/TiO2 film effected
Nano- titanium on delayed the ripening process of the tomatoes and
lower quality changes than those in the control film.
prevent microbial growth compared with the uncoated
ZnO
papaya during storage period.
• Prosperities of bio-nancomposite coating
By preventing moisture loss, the bio-nanocomposite films/coatings help further
reduce weight loss. Additionally, edible coatings improve the product's texture,
appearance, and shelf life by constructing semi-permeable barriers to gases and
moisture, such as carbon dioxide and oxygen. For instance, coating strawberry with
nano-ZnO and sodium alginate dramatically improved the moisture barrier of films,
reducing strawberry weight loss. Some packaged fruits and vegetables may suffer
severe negative effects from the presence of oxygen. Numerous degrading effects,
including nutrient loss and color changes, might result from it. The presence of
oxygen may have detrimental effects on some packed fruits and vegetables. It could
have a variety of deteriorating consequences, including as nutrient loss and color
changes. Active packaging, edible films, and coatings with oxygen scavengers and
humidity control systems all contribute significantly to lowering the gases that cause
fruits and vegetables to decay. Recently, it has been thought that the production of
polymeric films with the addition of nanoparticles (NPs) to boost gas barrier
qualities could decrease the rate of respiration, transpiration, and other metabolic
activities in fruit. The chitosan covering reduces oxygen transport, lowers
respiration, and delays the ascorbic acid reaction that causes strawberries to oxidize.
(Jafarzadeh,2021)
https://www.sciencedirect.com/science/article/abs/pii/S0001868621000464
Sources:
Farhoodi, Mehdi. "Nanocomposite materials for food packaging applications: characterization
and safety evaluation." Food engineering reviews 8.1 (2016): 35-51
De Azeredo, Henriette MC. "Nanocomposites for food packaging applications." Food research
international 42.9 (2009): 1240-1253.
Jafarzadeh, Shima, et al. "Application of bio-nanocomposite films and edible coatings for
extending the shelf life of fresh fruits and vegetables." Advances in Colloid and Interface
Science 291 (2021): 102405
SYNTHESIS OF NANOCOMPOSITES
1. Metal Nanocomposites
Metal matrix nanocomposites (MMNC) are made of a ductile metal or alloy matrix
with reinforcing elements implanted at the nanoscale. These materials combine the
toughness and ductility of metal and ceramic materials with high strength and
modulus. MMNC are therefore appropriate for the fabrication of materials with
high shear/compression strength and high service temperature characteristics.
Fig. ( ) Nanocomposite synthesis techniques.
1.1 Spray Pyrolysis
Spraying a solution onto a heated surface causes the contents to react and form a thin
film. The reactants are chosen so that any byproducts other than the target molecule
are volatile at the deposition temperature.The fabrication process includes the
following steps: (i) dissolving the inorganic precursors (starting materials) in an
appropriate solvent to produce a liquid source; (ii) creating a mist from this liquid
source using an ultrasonic atomizer; (iii) using a carrier gas to carry the mist into a
heated chamber; (iv) vaporizing the droplets in the chamber and trapping them with
a filter, promoting their decomposition to produce the corresponding oxide
1.2 infiltration
A prepared dispersion phase (ceramic particles, fibers, etc.) is soaked in a molten
matrix metal, which fills the space between the dispersed phase inclusions,
infiltration is a liquid state method of fabricating composite materials. The capillary
force of the dispersed phase (spontaneous infiltration) or an external pressure
(gaseous, mechanical, electromagnetic, centrifugal, or ultrasonics) applied to the
liquid matrix phase (forced infiltration) can act as the driving force in an infiltration
process.
1.3 rapid solidification
In the scientific literature, rapid solidification is broadly described as the quick
extraction of thermal energy, including super heat and latent heat, during the change
from a liquid state at high temperature to a solid at room temperature. Between the
matrix and the reinforcements, ultrasonics are utilized to mix and improve wetability.
1.4 high energy ball milling
A powder combination is placed in a ball mill and exposed to high-energy collisions
from the balls in a process known as high-energy ball milling. When creating nickelbase super alloys, high-energy ball milling, also known as mechanical alloying, is
able to successfully produce thin, homogenous dispersions of oxide particles that are
impossible to create using traditional powder metallurgy techniques. By altering the
reactivity of solids as they are being ground or by causing chemical reactions to
occur while they are being ground, high-energy ball milling can change the
circumstances under which chemical reactions typically occur.
1.5 chemical vapor deposition
A chemical procedure called chemical vapor deposition is utilized to create solid
materials with high performance standards. In order to create thin films, the
procedure is frequently employed in the semiconductor sector. The water (substrate)
is exposed to one or more volatile precursors in a conventional chemical vapor
deposition, which react and/or degrade on the substrate surface to form the desired
deposit. The removal of volatile byproducts, which occur often, is accomplished via
gas flow through the reaction chamber.
1.6 Physical vapor deposition
Vacuum deposition techniques that can be utilized to create thin films and coatings
are referred to as physical vapor deposition. The method by which the material
transitions from a condensed phase to a vapor phase and back to a thin film
condensed phase is what distinguishes physical vapor deposition. Sputtering and
evaporation are the two most common physical vapor deposition processes. The
following is the physical vapor deposition process: Three processes are used to
create a vapor phase: (i) sputtering/evap- oration of various components; (ii)
supersaturation of the vapor phase in an inert atmosphere to encourage the
condensation of metal nanoparticles; and (iii) thermal treatment under an inert
atmosphere to consolidate the nanocomposite.
1.7 Colloidal method
The colloidal method is a chemical procedure that produces metal particles by
chemically reducing inorganic salts in a solution. The dry material is then consolidated, dried, and thermally treated in a reducing atmosphere, such as hydrogen,
to promote selective oxide reduction and produce the metal component. Another
chemical method used to create metal matrix composites is the sol-gel procedure.
2. Ceramic Nanocomposites
2.1 powder process
One approach for creating ceramic nanocomposites is the powder process, which
involves the processing processes of compression, rolling, and extrusion. In a
straightforward compression procedure, powder is repeatedly squeezed vertically
by a horizontally stationary punch as it flows from a bin into a two-walled tube.
A sintering furnace is subsequently filled with the compacted mass. In order to
create sheets, powders are also rolled. The metal powder is fed into a two-high
rolling mill where it is compacted into strips. The strips are then sintered, given
another roll, and given another round of sintering. There are two different types
of powder extrusion: The powder is either extruded at high temperatures without
fortification in one type or is blended with a binder or plasticizer at room
temperature in the other. As long as the temperatures and pressures involved are
within the limits of the die materials, there is no restriction on the variety of
metals and alloys that can be extruded.
2.2 Polymer Precursor and Sol-Gel
The matrix material is combined with a polymeric precursor, and the mixture is then
pyrolyzed in a microwave oven to produce the reinforcing particles. Another method
for creating ceramic nanocomposites is called sol-gel, which involves (i) the
hydrolysis and polycondensation of a (in)organic molecular precursor dissolved in
organic media. These reactions result in the formation of three-dimensional
polymers with metal-oxygen bonds (sol or gel), (ii) further drying to produce a solid,
and (iii) at a later stage, thermal treatment to consolidate the material. Examples:
Al2O3/SiC, SiN/SiC, SiO2/Ni, ZnO/Co.
3. Polymer Nanocomposites
Nanostructured materials and nanophase/nanoparticle materials are two different
categories of nanomaterials. In contrast to nanophase materials, which are typically
dispersive nanoparticles, nanostructured materials are condensed bulk materials
consisting of aggregates with sizes in the nanometer size range. Polymer
nanocomposites with improved performance characteristics over conventional filled
polymer composites (reduced permeability, improved thermal resistance, flame
resistance, moisture resistance, charge dissipation, and chemical resistance) are
produced by adding inorganic nanoparticles to a polymer matrix. Nanofillers are
dispersed homogeneously and uniformly, resulting in an extremely broad inter-facial
area between the host polymer matrix and the nanoparticles for each volume.
Polymer nanocomposites are fundamentally different from traditional filled polymer
composites due to their enormous internal interfacial area and nanoscopic diameters
between nanoparticles.
3.1 melt building
The best method for creating clay/polymer nanocomposites with a thermoplastic and
elastomeric polymeric matrix is melt blendin. Usually, a banbury or an extruder is
used to melt the polymer and blend it with the necessary quantity of intercalated
clay. An inert gas, such as argon, nitrogen, or neon, is used during melt blending.
Alternately, the polymer and intercalant could be mixed dry, heated in a mixer, and
then sheared enough to create the required clay polymer nanocomposites. Compared
to in situ intercalative polymerization or polymer solution intercalation, melt
blending has many advantages. Melt blending doesn't use organic solvents, making
it environmentally friendly. Modern industrial techniques like extrusion and
injection molding are compatible with melt blending.
3.2 mixing solution
A method based on a solvent system in which the prepolymer or polymer is soluble
and the nanofillers (for layered nanofillers) are swellable is known as solution
mixing. First, a solvent—such as water, chloroform, or toluene—is used to swell the
nanofillers. When the polymer and nanofiller are combined in a solution, the
polymer chains intercalate and push the solvent out of the silicate's interlayer. The
intercalated/exfoliated structure is left behind once the solvent is removed,
producing polymer nanocomposites. Polymer composite solution mixing entails
intense agitation to disperse nanofiller in a polymer solution, careful solvent
management, and lastly composite film casting. Magnetic stirring, shear mixing,
reflux, or the most popular technique of sonication can all be employed to stir things
up.
3.3 In Situ Intercalative Polymerization
Polymer clay nanocomposites based on nylon 6 were originally created via in situ
intercalative polymerization. The layered silicate is inflated in the liquid monomer
solution using this technique so that polymerization can take place between the
intercalated sheets. The process of polymerization can be started by heat or
radiation, diffusion of an appropriate initiator, an organic initiator or catalyst fixed
through cation exchange inside the interlayer prior to the swelling step, or any
combination of these methods.
3.4 In Situ Formation and Sol-Gel
A layered structure of inorganic material can be created in situ, in an aqueous
solution that also contains the polymer. The polymer that dissolves in water serves
as a template for layer creation. Although less established for layered silicates, it is
frequently employed for the manufacture of layered double hydroxides (LDH)
nanocomposites. As part of the process, organic molecules and monomers are
embedded on sol-gel matrices, after which organic groups are added and chemical
bonds are formed, causing a sol-gel matrix to form in situ inside the polymer
and/or the simultaneous production of inorganic and organic networks. In the solgel method, silicate and polymer building blocks are dissolved in water to create an
aqueous solution that is used to synthesis clay minerals within the polymer matrix.
The polymer helps the inorganic host crystals develop during this process and
becomes trapped within layers as they expand.
https://www.sciencedirect.com/science/article/abs/pii/B9780081019757000051
source:
Rane, Ajay Vasudeo, et al. "Methods for synthesis of nanoparticles and fabrication of
nanocomposites." Synthesis of inorganic nanomaterials. Woodhead publishing, 2018. 121-139.