96 Handbook of herbs and spices
Coextruded films
Coextrusion is the simultaneous extrusion of two or more layers of different polymers
to form a single film. Coextruded films have the following advantages over other
types of film:
∑ They have very high barrier properties, similar to multi-layer laminates but are
produced at a lower cost.
∑ They are thinner than laminates and closer to mono-layer films and are therefore
easier to use on forming and filling equipment.
∑ The layers cannot separate.
The main types of compounds used in this application are:
∑ olefins (low-density and high-density polyethylene and polypropylene)
∑ styrenes (polystyrene and acrylonitrile-butadiene-styrene)
∑ polyvinyl chloride polymers
Edible and biodegradable films
There has been a paradigm shift imposed by growing environmental awareness to
look for packaging films and processes that are biodegradable and therefore compatible
with the environment. The concept of biodegradability enjoys both user-friendly and
ecofriendly attributes, and the raw materials are essentially derived from either
replenished agricultural feedstocks or marine food processing, and therefore capitalize
on natural resource conservation with an underpinning on environmentally friendly
and safe atmosphere.
Biopolymers from agricultural feed stocks and other resources have the ability
upon blending and/or processing to result in appropriate packaging materials. Their
functionality can be better expressed by using in combination with other ingredients
such as plasticizers and additives. The potential uses for such biopolymeric packaging
materials are:
∑ use and throw, disposable packaging materials
∑ routine consumer goods for day to day use
∑ disposable personal care
∑ lamination coating
∑ bags for agricultural uses.
Two types of biomolecules (hydrocolloids and lipids) are used in combination for
the preparation of biodegradable packaging films or composites. Individually they
lack structural integrity and characteristic functionality. Hydrocolloids, being hydrophilic
are poor moisture barriers, a property compensated by adding lipids, which are very
good moisture barriers. Composite films are a mixture of these and other ingredients
in varying proportions, which determine their barrier (to water, oxygen, carbon dioxide
and aroma compounds) and other mechanical properties.
Synthetic polymers are gradually being replaced by biodegradable materials
especially those derived from replenishable, natural resources. More than the origin,
the chemical structure of the biopolymer determines its biodegradability. Use of
biopackagings will open up potential economic benefits to farmers and agricultural
processors. Bilayer and multicomponent films resembling synthetic packaging materials
with excellent barrier and mechanical properties need to be developed. Cross-linking,
either chemically or enzymatically, of the various biomolecules is yet another approach
of value in composite biodegradable films. Innovative techniques for preserving food