INTRODUCTION
Nanotechnology is an exciting and rapidly emerging technology allowing us
to manipulate and create materials and structures at the molecular level, often atom by
atom into functional structures having nanometer dimensions. This will make
products cheaper, production more efficient and more sustainable through using less
water and chemicals. Producing less waste and using less energy is a central concern
of food manufacturers, and the drive towards production efficiency is likely to
continue to boost nanotechnology funding. Nanoscale biotech and nano-bio-info will
have big impacts on the food and food-processing industries. The future belongs to
new products, new processes with the goal to customize and personalize the products.
More than 180 applications are in different developing stages and a few of them are
on the market already. The nanofood market is expected to surge from 2.6 bn. US
dollars today to 7.0 bn. US dollars in 2006 and to 20.4 bn. US dollars in 2010. More
than 200 Companies around the world are today active in research and development.
USA is the leader followed by Japan and China. By 2010 Asian with more than 50
percent of the world population will be the biggest market for Nanofood with the
leading of China.
Biobased nanocomposites are a new class of materials in food packaging
industry with improved barrier and mechanical properties as compared to those of
neat biopolymers. They are biodegradable and they are also produced from renewable
resources. So, these make them environment friendly. Unlike Edible films, they could
not have been consumed as a part of food. Biobased nanocomposites can be used to
extend the shelf-life of the fresh products such as fruits and vegetables by controlling
of respiratory exchange. Also it can improve the quality of fresh, frozen, and
processed meat, poultry, and seafood products by retarding moisture loss, reducing
lipid oxidation and discoloration, enhancing product appearance, and reducing oil
uptake by battered and breaded products during frying. Biobased nanocomposite is
interface between two important subjects in food packaging industry, namely Edible
films and nanocomposites. Therefore, this paper starts with short explanations about
Edible films and nanocomposites. Furthermore, a literature review about biobased
nanocomposites is presented. The last objective of this review is to explain a
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procedure for the replacement of biobased nanocomposites instead of Edible films in
food packaging industry.
To meet the increasing expectations of consumers, food must be safe, of
consistently good quality and sensory attributes, healthy and inexpensive and should
have a good shelf life. These considerations have led to ongoing extensive
investigation of suitable packaging materials for food products. In a recent era, a new
and an emerging class of clay filled polymers, called Polymer-Clay Nanocomposites
(PCN) has been developed. Properties such as superior mechanical strength, reduction
in weight, increased heat-resistance and flame retardancy, improved barrier properties
against oxygen, carbon dioxide, ultraviolet, moisture and volatiles, as well as
conservation of flavour in drinks and beverages are achievable with these novel
composites.
Applications of nanotechnology for food and beverage packaging
Nanocomposite sales volumes by packaging application (in tonnes),
2003-08
Main applications 2003 2008
Food Packaging
Carbonated soft drinks 136 3810
Beer 862 1542
Meats 181 726
Package foods and condiments 45 726
Cheese 91 227
Juices 45 91
Others
Pet Food 45 91
Electronics 45 91
Pharmaceuticals 45 23
Household appliances and
automotives
45 23
Total 1540 7350
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Today, food-packaging and monitoring are a major focus of food industry-
related nanotech R&D. Packaging that incorporates nanomaterials can be “smart,”
which means that it can respond to environmental conditions or repair itself or alert a
consumer to contamination and/or the presence of pathogens. According to industry
analysts, the current US market for “active, controlled and smart” packaging for foods
and beverages is an estimated $38 billion and will surpass $54 billion by 2008.
Chemical giant Bayer produces a transparent plastic film (called Durethan) containing
nanoparticles of clay. The nanoparticles are dispersed throughout the plastic and are
able to block oxygen, carbon dioxide and moisture from reaching fresh meats or other
foods. The nanoclay also makes the plastic lighter, stronger and more heat resistant.
Today, Nanocor, a subsidiary of Amcol International Corp., is producing
nanocomposites for use in plastic beer bottles that give the brew a six-month shelf-
life. By embedding nanocrystals in plastic, researchers have created a molecular
barrier that helps prevent the escape of oxygen. Nanocor and Southern Clay Products
are now working on a plastic beer bottle that may increase shelf-life to 18 months.
Kodak, best known for producing camera film, is using nanotech to develop
antimicrobial packaging for food products that will be commercially available in
2005.Kodak is also developing other ‘active packaging,’ which absorbs oxygen,
thereby keeping food fresh.
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World income generated by nanotechnologies (in billion Euros)
40
700
1000
0
200
400
600
800
1000
1200
2001 2008 2010-2015
Scientists at Kraft, as well as at Rutgers University are working on nano-
particle films concentration and other packaging with embedded sensors that will
detect food pathogens. Called “electronic tongue” technology, the sensors can detect
substances in parts per trillion and would trigger a color change in the packaging to
alert the consumer if a food has become contaminated or if it has begun to spoil.
Researchers in the Netherlands are going one further to develop intelligent
packaging that will release a preservative if the food within begins to spoil. This
“release on command” preservative packaging is operated by means of a bio switch
developed through nanotechnology.
Developing small sensors to detect food-borne pathogens will not just
extend the reach of industrial agriculture and large scale food processing. In the view
of the US military, it’s a national security priority. With present technologies, testing
for microbial food-contamination takes two to seven days and the sensors that have
been developed to-date are too big to be transported easily. Several groups of
researchers in the US are developing biosensors that can detect pathogens quickly and
easily, reasoning that “super sensors” would play a crucial role in the event of a
terrorist attack on the food supply.
RFid tags could be used on food packaging to perform relatively
straightforward tasks, such as allowing cashiers in supermarkets to tally all of a
customer’s purchases at once or alerting consumers if products have reached their
expiration dates. RFid tags are controversial because they can transmit information
even after a product leaves the supermarket. Privacy advocates are concerned that
marketers will have even greater access to data on consumer behaviour.
Wal-Mart in the US and TESCO in the UK have already tested RFid tagging
on some products in some stores. The tagging of food packages will mean that food
can be monitored from farm to fork during processing, while in transit, in restaurants
or on supermarket shelves and eventually, even after the consumer buys it. Coupled
with nanosensors, those same packages can be monitored for pathogens, temperature
changes, leakages, etc.
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WHAT CAN HAPPEN INSIDE A PACKAGE?
Fresh foods just after harvest or slaughter are still active biological systems.
The atmosphere inside a package constantly changes as gases and moisture are
produced during metabolic processes. The type of packaging used will also influence
the atmosphere around the food because some plastics have poor barrier properties to
gases and moisture.
The metabolism of fresh food continues to use up oxygen in the headspace
of a package and increases the carbon dioxide concentration. At the same time water
is produced and the humidity in the headspace of the package builds up. This
encourages the growth of spoilage microorganisms and damages the fruit and
vegetable tissue.
Many food plants produce ethylene as part of their normal metabolic cycle.
This simple organic compound triggers ripening and aging. This explains why fruit
such as bananas and avocados ripen quickly to optimise the composition of the
headspace in a package.
The shelf life of processed foods is also influenced by the atmosphere
surrounding the food. For some processed foods, a lowering of oxygen is beneficial,
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Distribution in % of the global economic impact of nanotechnologies in 2010
Transports (nanomaterials,
nanoelectronics); 7%
Others; 1%
Nanomaterials; 34%
Electronics;30%
P harmaceuticals;18% Chemistry (nanostructured
catalyst); 10%
slowing down discolouration of cured meats and powdered milk and preventing
rancidity in nuts and other high fat foods. High carbon dioxide and low oxygen levels
can pose a problem in fresh produce leading to anaerobic metabolism and rapid
rotting of the food. However, in fresh and processed meats, cheeses and baked goods,
carbon dioxide may have a beneficial antimicrobial effect. when kept in the presence
of ripe or damaged fruits in a container and broccoli turns yellow even when kept in
the refrigerator.
Extensive trials have shown that each fresh food has its own optimal gas
composition and humidity level for maximising its shelf life. Active packaging offers
promise in this area; it is difficult with conventional packaging.
ACTIVE PACKAGING SYSTEMS
Active packaging employs a packaging material that interacts with the
internal gas environment to extend the shelf-life of a food. Such new technologies
continuously modify the gas environment (and may interact with the surface of the
food) by removing gases from or adding gases to the headspace inside a package.
The table below sets out some areas of atmosphere control in which active
packaging is being successfully used.
USES OF ACTIVE PACKAGING
Active Packaging System Application
Oxygen scavenging Most food classes
Carbon dioxide production Most food affected by moulds
Water vapour removal Dried and mould-sensitive foods
Ethylene removal Horticultural produce
Ethanol release Baked foods (where permitted)
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Recent technological innovations for control of specific gases within a
package involve the use of chemical scavengers to absorb a gas or alternatively other
chemicals which may release a specific gas as required.
CSIRO is conducting research to develop the right package for each
commodity. The technology being developed by CSIRO incorporates chemical
scavengers in packaging films to control such gases as ethylene or oxygen.
Ethylene scavenging
A chemical reagent, incorporated into the packaging film, traps the ethylene
produced by ripening fruit or vegetables. The reaction is irreversible and only small
quantities of the scavenger are required to remove ethylene at the concentrations at
which it is produced. A feature of the CSIRO system is its pink colour which can be
used as an indicator of the extent of reaction and shows when the scavenger is used
up.
It is expected that the film will be produced in Australia and used as a
valuable means of extending the export life of fruit, vegetables and flowers.
Systems developed in other countries are already commercially available.
These usually involve the inclusion in the package of a small sachet which contains an
appropriate scavenger. The sachet material itself is highly permeable to ethylene and
diffusion through the sachet is not a serious limitation. The reacting chemical for
ethylene is usually potassium permanganate which oxidises and inactivates it.
Oxygen scavenging
The presence of oxygen in food packages accelerates the spoilage of many
foods. Oxygen can cause off-flavour development, colour change, nutrient loss and
microbial attack. Several different systems are being investigated by CSIRO to
scavenge oxygen at appropriate rates for the requirements of different foods.
One of the most promising applications of oxygen scavenging systems in
food packages is to control mould growth. Most moulds require oxygen to grow and
in standard packages it is frequently mould growth which limits the shelf life of
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packaged baked goods such as cakes and crumpets and of packaged cheese.
Laboratory trials have shown that mould growth on some baked products can be
stopped for at least 30 days with active packaging and significant improvements in the
mould-free life of packaged cheese have also been obtained.
Another promising application is the use of active packaging to delay
oxidation of and therefore rancidity development in vegetable oils.
Again the use of discrete sachets containing oxygen absorbents has already
found commercial application. In this instance the scavenging material is usually
finely divided iron oxide. These sachets have been used in some countries to protect
the colour of packaged cured meats from oxygen in the headspace and to slow down
staling and mould growth on baked products, e.g. pizza crusts.
This approach of inserting a sachet into the package is effective but meets
with resistance among food packers. The active ingredients in most systems consist of
a non-toxic brown/black powder or aggregate which is visually unappealing if the
sachet is broken. A much more attractive approach would be the use of a transparent
packaging plastic as the scavenging medium.
Humidity control
Condensation or 'sweating' is a problem in many kinds of packaged fruit and
vegetables. It is of particular concern in cartons of fresh flowers for which there is an
important export trade.
Unless the relative humidity around flowers is kept at about 98 per cent,
water will be lost from the bunches. Such high humidities mean there is a very real
risk of condensation occurring during transport as the temperature of the flowers may
fluctuate by several degrees. When one part of the package becomes cooler than
another, water is likely to condense in the cooler areas.
If the water can be kept away from the produce there may be little harm.
However when the condensation wets the produce, nutrients leak into the water
encouraging rapid mould growth.
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CSIRO has developed technology to control condensation inside packages.
This allows the food to remain dry without drying out the product itself. Therefore
sensitive products such as flowers and table grapes are protected from contact with
water. This helps to reduce growth of mould.
Carbon dioxide release
High carbon dioxide levels are desirable in some food packages because
they inhibit surface growth of microorganisms. Fresh meat, poultry, fish, cheeses and
strawberries are foods which can benefit from packaging in a high carbon dioxide
atmosphere.
However with the introduction of modified atmosphere packaging there is a
need to generate varying concentrations of carbon dioxide to suit specific food
requirements. Since carbon dioxide is more permeable through plastic films than is
oxygen, carbon dioxide will need to be actively produced in some applications to
maintain the desired atmosphere in the package.
So far the problems associated with diffusion of gases, especially carbon
dioxide, through the package, have not been resolved and this remains an important
research topic
Ethanol
Ethanol (or common alcohol) is not a permitted food preservative in
Australia. However its antimicrobial activity is well known and it is used in medical
and pharmaceutical applications. Ethanol has been shown to increase the shelf life of
bread and other baked products when sprayed onto product surfaces prior to
packaging.
A novel method of generating ethanol vapour, recently developed in Japan,
is through the use of an ethanol releasing system enclosed in a small sachet which is
included in a food package. Food grade ethanol is absorbed onto a fine inert powder
which is enclosed in a sachet that is permeable to water vapour. Moisture is absorbed
from the food by the inert powder and ethanol vapour is released and permeates the
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sachet into the food package headspace. This system is approved in Japan to extend
the mould-free shelf life of various cakes.
Sulphur dioxide
Sulphur dioxide is a permitted preservative in Australia for some processed
foods. It can also be used to control mould growth in some fruits. Serious loss of table
grapes can occur unless precautions are taken against mould growth. It is necessary to
refrigerate grapes in combination with fumigation using low levels of sulphur dioxide.
Fumigation can be conducted in the fruit cool stores as well as in the cartons. Carton
fumigation consists of a combination of quick release and slow release systems which
emit small amounts of sulphur dioxide.
When the temperature of the cartoned grapes rises due to inadequate
temperature control, the slow release system fails releasing all its sulphur dioxide
quickly. This can lead to illegal residues in the grapes and unsightly bleaching of the
fruit.
CSIRO is working on developing systems which gradually release sulphur
dioxide and are less sensitive to high temperature and moisture than those presently
used. These systems have potential use for fresh grapes and processed foods permitted
to contain sulphur dioxide such as dried tree fruits and wine.
An Overview of ‘Smart Packaging’ and ‘Active Packaging’
Using Clay Nanoparticles to Improve Plastic Packaging for Food Products
Chemical giant Bayer produces a transparent plastic film (called Durethan)
containing nanoparticles of clay. The nanoparticles are dispersed throughout the
plastic and are able to block oxygen, carbon dioxide and moisture from reaching fresh
meats or other foods. The nanoclay also makes the plastic lighter, stronger and more
heat-resistant.
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How Creating a Molecular Barrier by Embedding Nanocrystals in Plastic Can
Improve Packaging
Until recently, industry’s quest to package beer in plastic bottles (for cheaper
transport) was unsuccessful because of spoilage and flavour problems. Today,
Nanocor, a subsidiary of Amcol International Corp., is producing nanocomposites for
use in plastic beer bottles that give the brew a six-month shelf-life. By embedding
nanocrystals in plastic, researchers have created a molecular barrier that helps prevent
the escape of oxygen. Nanocor and Southern Clay Products are now working on a
plastic beer bottle that may increase shelf-life to 18 months.
Using Nanotechnology Methods to Develop Antimicrobial Packaging and ‘Active
Packaging’
Kodak, best known for producing camera film, is using nanotech to develop
antimicrobial packaging for food products that will be commercially available in
2005. Kodak is also developing other ‘active packaging,’ which absorbs oxygen,
thereby keeping food fresh.
Embedded Sensors in Food Packaging and ‘Electronic Tongue’ Technology
Scientists at Kraft, as well as at Rutgers University and the University of
Connecticut, are working on nano-particle films and other packaging with embedded
sensors that will detect food pathogens. Called “electronic tongue” technology, the
sensors can detect substances in parts per trillion and would trigger a colour change in
the packaging to alert the consumer if a food has become contaminated or if it has
begun to spoil.
Using a Nanotech Bioswitch in ‘Release on Command’ Food Packaging
Researchers in the Netherlands are going one further to develop intelligent
packaging that will release a preservative if the food within begins to spoil. This
“release on command” preservative packaging is operated by means of a bioswitch
developed through nanotechnology.
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Using Food Packaging Sensors in Defence and Security Applications
Developing small sensors to detect food-borne pathogens will not just
extend the reach of industrial agriculture and large-scale food processing. In the view
of the US military, it’s a national security priority. With present technologies, testing
for microbial food-contamination takes two to seven days and the sensors that have
been developed to date are too big to be transported easily. Several groups of
researchers in the US are developing biosensors that can detect pathogens quickly and
easily, reasoning that “super sensors” would play a crucial role in the event of a
terrorist attack on the food supply. With USDA and National Science Foundation
funding, researchers at Purdue University are working to produce a hand-held sensor
capable of detecting a specific bacteria instantaneously from any sample. They’ve
created a start-up company called BioVitesse.
Food Packaging Industry with Biobased Nanocomposites
EDIBLE FILMS
Edible films are defined as a thin layer of edible material formed on food as
a coating. Additionally, Edible films can carry antioxidants and antimicrobials, while
traditional packaging materials can not compete in these aspects. Edible films are
used to extend the shelf life of food and maintain its quality by inhibiting the
migration of moisture, oxygen, carbon dioxide, aromas and lipids. Other favourable
aspects of Edible films are: completely biodegradable can be a part of a food and can
reduce the consumption of naphtha-based polymeric films. The properties of the
edible films which have been mostly evaluated are mechanical properties and
specially gas permeability properties. A major component of Edible films is the
plasticizer. The addition of a plasticizer agent to Edible films is required to overcome
film brittleness, caused by high intermolecular forces. Plasticizers reduce these forces
and increase the mobility of polymer chains, thereby improving flexibility and
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extensibility of the film. On the other hand, plasticizers generally decrease gas, water
vapour and solute permeability of the film and can decrease elasticity and cohesion.
Type of degradation reactions in food systems determines optimum gases composition
in food packaging. For example, oxygen is involved in many degradation reactions in
foods, such as fat and oil rancidity, microorganism growth, enzymatic browning and
vitamin loss. Thus, many packaging strategies seek to exclude oxygen in packaging to
protect the food product. On the other hand, the permeability of Edible film to oxygen
and carbon dioxide is essential for respiration in living tissues such as fresh fruits and
vegetables. So, moderate barrier materials are more appropriate. If an Edible film with
the appropriate permeability is chosen, a controlled respiratory exchange can be
established and thus the preservation of fresh fruits and vegetables can be prolonged.
So the main characteristics to consider in the selection of Edible film are their oxygen,
carbon dioxide and water vapour permeability. The success of Edible films for fresh
products totally depends on the control of internal gas composition. Semi-permeable
coatings can create a modified atmosphere (MA) similar to controlled atmosphere
(CA) storage, with less expense incurred. However, the atmosphere created by
coatings can change in response to environmental conditions, such as temperature and
humidity, due to combined effects on fruit respiration and coating permeability. Types
of deteriorative reactions, required gas composition and some case study have been
summarized in Table for important areas of food industry.
Edible films have been prepared by casting solutions of proteins,
carbohydrates and lipids, in different combinations and compositions. Edible films
which are made of proteins are most attractive. Firstly, they are supposed to provide
nutritional value. Secondly, protein-based films have impressive gas barrier properties
compared with those from lipids and polysaccharides. For example, oxygen
permeability of soy protein-based films (when they are not moist) was 500, 260, 540
and 670 times lower than that of low-density polyethylene, methylcellulose, starch
and pectin, respectively. On the other hand, their mechanical properties are also better
than those of polysaccharide and fat based films because proteins have a specific
structure which confers a wider range of functional properties, especially high
intermolecular binding potential. In addition, Proteins, such as casein, whey proteins
and corn zein, have also been used in Edible film formulation as a moisture barrier
since these proteins are abundant, cheap and readily available.
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BIOBASED NANOCOMPOSITE FILM
Biobased nanocomposites are composed of biopolymer, nanoclay and
usually compatibilizing agents. Major component of biobased nanocomposites is
biopolymers. Biopolymers have great commercial potential for bioplastic and Edible
films, but some of the properties such as brittleness, low heat distortion temperature;
high gas permeability and low melt viscosity for further processing restrict their use in
a wide range of applications. Modification of biopolymers with nanotechnology is an
effective way to improve their properties. Biopolymers derived from renewable
resources are broadly classified according to method of production. This gives the
following three main categories:
1. Biopolymers directly extracted/removed from natural materials (mainly
plants) such as hydrocolloids (polysaccharides and proteins). The most frequently
utilized polysaccharides were cellulose and starch (and their derivatives), chitosan,
seaweed extracts (carrageenans and alginates), exudates (arabic gum), seed (guar
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gum), xanthan and gellan gum and pectin. Proteins include collagen, gelatin, casein,
whey proteins, corn zein, wheat gluten and soy proteins.
2. Biopolymers produced by classical chemical synthesis from renewable
bioderived monomers like polylactate (PLA).
3. Biopolymers produced by microorganisms or genetically transformed
bacteria like Polyhydroxyalkanoates. Hence, biopolymers which can be used in
biobased nanocomposites formulation are numerous.
The utilization of special compatibilizing agents (modifier) between the two
basic materials (biopolymer and nanoclay) for the preparation of biobased
nanocomposite is necessary. Layered silicates are characterized by a periodic stacking
of mineral sheets with a weak interaction between the layers and a strong interaction
within the layer. The space in-between the layers is occupied by cations. By cation
exchange reactions between the clay and organic cations (such as alkyl ammonium
salts), the layered silicate can be transformed into organically modified clay. The
inter-layer distance will increase by using voluminous modifiers. If this modifier is
compatible with biopolymer as well, a homogeneously and nanoscaled distribution
(exfoliation) of the clay sheets can be effected in the polymer matrix. The pure clay
shows an interlayer distance of 1.26 nm. It has been proven by XRD analysis that
most of the layers are indeed swollen after the modification reaction. The inter-layer
distance changes to 2.34 nm, an increase of nearly 100% compared to the pure clay.
A comprehensive review of biobased nanocomposite film applications in
food packaging industry is necessary. Therefore, continuing this section, several
studies which are concentrated on biobased nanocomposites have been presented.
Use of Polymer-Clay Nanocomposites in Food Packaging
The concept of PCN was developed in the late 1980s. Toyota was the first
company to commercialise these nanocomposites and to use nanocomposite parts in
one of its popular models for several years. PCN are a class of hybrid materials made
from nanoscale particles such as layered silicates, for example montmorillonite
(MMT), with layer thickness in nanometer dimension. Several potential applications
have been identified so far in various industrial sectors, for example automobiles
(gasoline tanks, bumpers, interior and exterior panels etc.), construction (building
sections, structural panels), aerospace (flame retardant panels, high performance
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components), electronics and electrical (printed circuit boards, electric components),
food packaging (containers, wrapping films), and coatings and pigments. The present
review will be restricted to food packaging applications only, including a brief outline
of preparation, characterisation, properties, recent developments and future prospects.
PREPARATION AND CHARACTERISATION OF POLYMER CLAY
NANOCOMPOSITE
Researches on the preparation and characterisation of PCN intended for food
packaging have been published only since the late 1990s. Most of the research that
has been published so far involved the use of montmorillonite (MMT) clay as the
nanocomponent. A wide range of synthetic polymers such as polyethylene (PE),
nylon and PVC, and biopolymers such as starch, have been investigated. Varying
amounts of nanoclay (usually 1 to 5 weight %) (Lange and Wyser, 2003) were used in
most of the published studies on PCN. Silicates used in the synthesis of PCN are
layered with a layer thickness of around 1 nm. The lateral dimensions of these layers
can vary up to several micrometres; consequently the aspect ratio of these fillers (ratio
of length to thickness) is particularly high with values greater than 1000. These layers
form stacks with a gap between them called the ‘interlayer’ or the ‘gallery’. The
inorganic cations within the interlayers can be substituted by other cations such as
lithium and sodium. A schematic presentation of the atom arrangements in a unit cell
for a three-layer clay such as MMT is shown in Figure.
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Figure. Structure of a layered silicate
There are usually three possible arrangements of these layered silicate clays,
which can be obtained when they are dispersed in a polymer matrix:
i) Non-intercalated: if the polymer cannot intercalate between the silicate sheets, a
non-intercalated microcomposite is obtained. Beyond this traditional class of
polymer-filler composites, two other types of composites can be obtained.
ii) Intercalated structure: the separation of clay layers by increasing the interlayer
spacing.
iii) Exfoliated or delaminated structure: the complete separation of clay platelets into
random arrangements. This is the ideal nanocomposite arrangement but is harder to
achieve during synthesis and/or processing.
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Figure. Schematic representation of intercalated and exfoliated nanocomposite from layered silicate clay filler and polymer.
Usually, the structure of nanocomposites can be characterised by two
complementary analytical techniques, namely, X-ray diffraction (XRD) and
transmission electron microscopy (TEM). XRD is used to identify intercalated
structures by determination of the interlayer spacing. Intercalation of the polymer
chains increases the interlayer spacing and according to Bragg’s law, it should cause a
shift of the diffraction peak towards lower angle. However, if the spacing between the
layers becomes too large, those diffraction peaks will disappear in the X-ray
diffractograms, which implies complete exfoliation of the layered silicates in the
polymer matrix. In this case, TEM is used to identify the exfoliated silicate layers.
The nanocomposites are generally prepared by i) solution method, ii) in situ/
interlamellar polymerisation technique and iii) melt processing.
i) In the solution method, the organoclay is swollen in a solvent. The
polymer, separately dissolved in that solvent is added to it so that the polymer
molecules can crawl between the silicate layers of the filler. The solvent is then
evaporated to obtain intercalated/exfoliated nanocomposite forms.
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ii) The in-situ method, also known as interlamellar polymerisation, involves
swelling of the layered silicates by absorption of a liquid monomer, or a monomer
solution. The monomer migrates into the galleries of the layered silicate, so that
polymerisation can occur within the intercalated sheets. Polymerisation can be
initiated either by heat or radiation, by diffusion of a suitable initiator, or by an
organic initiator.
iii) The melt intercalation method involves incorporation of clay filler in the
molten state of the polymer to form the nanocomposite material. The last method is
widely accepted in nanocomposite research due to its solvent-free process.
FUTURE PROSPECTS
Due to the excellent barrier properties, PCN has major applications in food
packaging industries for processed meats, cheese, confectionary and cereals as it
enhances the shelf life of food materials. Active projects are under way both in
industries as well as in academic research laboratories. Alcoa CSI has already applied
multilayer PCN as barrier liner materials for enclosure applications. Honeywell has
developed commercial Nylon- 6/clay nanocomposite products, AegisTM NC resin,
for drink packaging applications (Auto applications drive commercialization of
nanocomposites, 2002). Mitsubishi Gas Chemical and Nanocor have jointly
developed Nylon-MXD6 nanocomposites for multilayered PET bottle applications.
By 2009, it is estimated that the flexible and rigid packaging industry will use 5
million pounds of nanocomposites materials in the beverage and food industry. By
2011, consumption is estimated to be 100 million pounds. Beer bottles are expected to
be the biggest consumer by 2006 with 3 million pounds of nanocomposites, until
carbonated soft drinks bottles are projected to surpass that with use of 50 million
pounds of nanocomposites by 2011.
Nanocomposites can also be designed to incorporate and deliver active
substances into biological systems, at low cost and with limited environmental
impact. For example, creating “bacteria-repellent” surface in packaging film which
changes colour in the presence of harmful microorganism or toxins. Nanocomposites
with these types of unique characteristics could be used for a wide range of minimally
processed and processed food products such as meat and fish products, dairy foods,
cereals, confectionery, boil-in-bag food, fruit juices, beer and carbonated drinks.
Polymer nanocomposites are the future for the global packaging industry. Once
production and material costs are reduced, companies will be using this technology to
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increase their product’s stability and shelf life so that higher quality products can be
delivered to their customers while saving money. It seems that the advantages that
nanocomposites offer far outweigh the costs and concerns, and with time the
technology will be further refined and processes more highly developed. Research
continues into other types of nanofillers (i.e. carbon nanotubes), allowing new
nanocomposite structures with different improved properties that will further advance
the use of nanocomposite in many diverse packaging applications. On the other hand,
the safety and regulatory aspects toward the use of nanocomposites as food packaging
materials will be another topic of concern in near future (IFST, 2006).
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CONCLUSIONPackaging has developed into an essential technology in the handling and
commercialization of foodstuffs to provide, by maintaining or even increasing, the
required levels of quality and safety. There are high hopes in food and packaging:
longer shelf life, safer packaging, better traceability of products and healthier food is
only a few of the expected improvements. This paper gathers a number of significant
results where nanotechnology was satisfactorily applied to improve packaged food
quality and safety by increasing the barrier and mechanical properties of biopolymer
based nanocomposite. Also researches on biobased nanocomposites have been
published indicating that the science of biobased nanocomposites for food packaging
industry is still in its infancy. It appears that the momentum of PCN utilisation is
building slowly in the world possibly due to the cost and variability in the quality of
some of the products as well as popular resistance to accepting new technology. The
potential of nanocomposites as food packaging materials is largely due to the
enhanced gas and moisture barrier properties, increased stiffness with lighter weight,
strength and thermal stability. Novel biodegradable biopolymer/clay nanocomposite
films are also developed as environmentally friendly material to reduce plastic waste.
They too provide improved strength and barrier properties that are desirable for food
packaging. More understanding of the clay modification, dispersion and polymer-
filler interaction are needed to fill the gaps.
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REFERENCESAkkapeddi, K., Socci, E., Kraft, T., Facinelli, J., Worley, D. (2003) A new family of
barrier nylons based on nanocomposites and oxygen scavengers. 61st
Annual Technical Conference - Society of Plastics Engineers, 3, 3845-3848
Auto applications drive commercialization of nanocomposites (2002) Plastics
Additives and Compounding.
http://www.specialchem4polymers.com/resources/articles/article.aspx?id=579
(Accessed June 2006)
Avella, M., Vlieger, J.J.D., Errico, M.E., Fischer, S., Vacca, P., Volpe, M. (2005)
Biodegradable starch/clay nanocomposite films for food packaging
applications. Food
Chemistry, 93, 467-474
Brandsch, J., Piringer, O. (2000) Characterisatics of plastic materials. In: Plastic
Packaging Materials for Food. Piringer, O.G. and Baner, A.L. eds. Wiley-
Vch, Darmstadt, Germany
Butschli. (2004) Nanotechnology in packaging.
http://www.packworld.com/cds_print.html?rec_id=17883 (Accessed June 2006)
Chang J-H, Uk-An Y, Sur GS. (2003) Poly (lactic acid) nanocomposites with various
organoclays. thermomechanical properties, morphology, and gas permeability. J.
Polym. Sci. Part B: Polym. Phys., 41, 94–103
Chen, B., Evans, JRG. (2005) Thermoplastic starch–clay nanocomposites and their
characteristics. Carbohydrate Polymers, 61, 455–463
Collister, J. (2002) Commercialisation of polymer nanocomposites. In Polymer
nanocomposites synthesis, charcterisation and modelling. R. Krishnamoorti
& Vaia, R.A. eds. American Chemical Society, Washington, USA
Anonymous (2004).Down on the Farm: the Impact of Nano-Scale Technologies on
Food and Agriculture, ETC Group Report.
Donald, A.(2004).Food for thought. Nature Materials ,3,578-581
Moraru, C., Panchapakesan ,C,Huang Q.,Takhistov P.(2003).Nanotechnology: A new
frontier in food science. Food Technology ,57, 25-27
Scott, A.(2002).BASF takes big steps in small tech, focusing on nanomaterials.
Chemical Week.164,1-45
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