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instrument. The film thickness (L) is measured using a micrometer.
The choice of detector determines which gas is being measured. Ther-
mal conductivity detectors are used for most gases—flame ionization
detectors for volatile organic vapors, coulometric sensors for oxygen,
2
and infrared detectors for water vapor. The permeability values of
some of the polymers are presented in Table 11.2.

11.4 Recent Advances in Packaging
Food packaging has become very sophisticated in today’s modern
society. Consumers and the packaging industry seek enhanced fea-
tures in packaging beyond its basic functions of containment, protec-
tion, convenience, and communication. Some recent advances in
food packaging have been in the area of active and intelligent pack-
aging. The former involves physical, chemical, or biological action
for altering the interactions between the package, the product, and
2
the package headspace to achieve a desired outcome. Examples of
active packaging are absorbing systems such as oxygen, carbon diox-
ide, moisture, ethylene, and releasing systems including carbon
dioxide, ethanol, antimicrobials, antioxidants, enzymes, flavors, and
nutraceuticals to protect and enhance food quality. Other packaging
systems are self-heating, self-cooling, microwave susceptors, and
selective permeable film. Intelligent packaging is defined as a pack-
aging system that is capable of carrying out functions such as detect-
ing, sensing, recording, tracing, communicating, and applying scien-
tific logic to facilitate decision making to extend shelf life, enhance
safety, improve quality, provide information, and warn of possible
problems.
Increased use of synthetic polymer bases has raised environmen-
tal concerns. Packaging constitutes approximately one-third of the
municipal solid waste stream by weight in many developed coun-
tries. Many different ways are being used to manage packaging
waster: reduce, reuse, recycle, compost, incinerate, and landfill. The
presence of some polymers such as PVC in incinerators may lead to
dioxins, a family of highly toxic chlorinated hydrocarbons. Due to
environmental concerns, PVC containers are being replaced by PET
or PE. Considerable efforts are being made to produce biodegradable
packaging from biobased materials such as polylactic acid, polyhy-
droxybutyrate valerate, and thermoplastic starch. The use of biobased
packaging for food application is limited due to the production cost
of biobased polymers and their weak mechanical and poor barrier
properties. Research is underway to improve the physical properties
of biodegradable plastic by incorporating nanoclay particles and
blending with other polymers. 11,12 Some innovative technologies such
as photoelectronic scanners and microprocessor-controlled video
cameras are being developed for online detection for seal defects or