Picture
Plastics in the Microwave
Oven
CE 435
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Presented by: Daniel Fulcher |
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Christopher Hunter |
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Martin Schaefer |
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April 17, 2001 |
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Introduction
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U.S. households owning a microwave oven
increased from 15% in 1980 to 78% by 1989 |
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Gorman’s New Product News reported the
number of new microwave product introductions increased from 278 in 1986 to
almost 1000 in 1988 |
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Microwave frequency of ~2.45 GHz
ensures effective penetration into the food and even food heating |
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Annual revenues of 3 billion dollars |
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Scope
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Max temperatures of 230oF
for microwave ovens and 400oF for dual oven applications |
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Containers should be sturdy, rigid in
shape and capable of supporting its contents |
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Limited migration of additives,
colorants, or fillers |
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Federal Food and Drug Administrative
approval |
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Home Meal Replacement
Packaging
HMR Packaging
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Crystallized polyethylene terephthalate
(CPET) |
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Polyphenylene oxide, high impact
polystyrene blend (PPO/HIPS) |
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CPET Morphology
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Heterochain, modified homopolymer with
~30% Crystallinity |
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Step growth condensation polymerization
reaction of terephthalic acid and ethylene glycol |
CPET Properties
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Crystallization of PET increases the
upper temperature resistance from 230°F to 400°F |
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Balance between strength properties and
temperature resistance |
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Crystallinity of 28%-32% and an
intrinsic viscosity of .85 to .95 |
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Two-layer structure of CPET and APET |
CPET Properties
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Good O2 and CO2
barrier properties |
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Acceptable water barrier properties |
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Easily colored with black carbon |
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CPET Processing
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In 2000, 84 million pounds produced at
~.52 $/lb |
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Eastman Chemical Company produces CPET
resin under the product name of VersaTray® |
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Thermoformed |
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Vacuum Snap-Back Thermoforming |
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CPET Processing
PPO/HIPS Morphology
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Fully miscible blended amorphous
polymer |
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Noryl® manufactured by General Electric Plastics |
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Noryl® PPO/HIPS blend is
approximately 25% PPO and 75% HIPS by weight |
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PPO Morphology
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Heterochain homopolymer |
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Created by a free-radical, step-growth,
oxidative-coupling polymerization |
HIPS Morphology
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Grafted copolymer of
cis-1,4-poly(1,3-butadiene) and styrene monomer |
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Polystyrene chains are atactic |
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2% to 15% by weight of polybutadiene |
HIPS Morphology
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Polystyrene (PS) and polybutadiene
phase separate creating compartmentalized regions |
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Polybutadiene forms small, dispersed
globules within the polymer structure |
PPO/HIPS Properties
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Improvements in final blend properties
are in direct proportion to the amount of PPO added |
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PPO is added to HIPS to increase
temperature resistance from approximately 180°F to 230°F |
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Blending with HIPS improves PPO’s low
resin flow characteristics |
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PPO/HIPS Properties
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Small, dispersed globules of
polybutadiene elastomer within the PS improves the blend impact strength |
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PPO improves the poor gaseous and water
vapor barrier properties of HIPS |
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Easily colored with black carbon |
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PPO/HIPS Processing
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High intensity mixer required to ensure
accurate blending during extrusion |
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Thermoforming on equipment designed for
PS |
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Thermoform-Fill-Seal process |
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HMR Covers
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Heat-seal the food containers |
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Most widely used film is multi-layer
polypropylene |
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Adhesives cause complications in
migration testing |
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PP is a low cost packaging film
~.53$/lb |
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Food Storage Containers
Polypropylene (PP)
Morphology
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Zieglar-Natta polymerization |
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Isotactic is crystalline, atactic is amorphous |
PP Chain Structure
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PP is a blend of atactic and isotactic |
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PP Properties
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Properties and processability
determined by isotacticity |
PP Processing
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1550 million pounds produced in 2000 at
~ .53 $/lb. |
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Injected or blow molded |
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INSPIRE® PP produced by Dow
Plastics |
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Regulations
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The code of federal regulations
provides guidance on polymers allowed in the direct contact of food. |
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Article 177 presents data specific to
each polymer |
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Composition specifications, allowable
coatings, modifiers, emulsifiers, and testing criteria |
CPET Regulations
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Article 177.1630 |
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Emulsifier < 2.0 percent of the dry
weight |
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Additional substances allowed must be
generally recognized as safe by the FDA |
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< 0.02 mg/in2 of
chloroform-soluble extractives for heptane and distilled water migration
tests |
PPO/HIPS Regulations
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Articles 177.1810 and 177.2460 |
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PS: molecular weight > 29,000 and
soluble in toluene |
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Maximum extractable fractions of
chloroform in distilled water and 50% ethanol are 0.0039 mg/cm2 |
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PPO: intrinsic viscosity > 0.30
deciliter/gram |
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< 0.02 weight percent extractable with n-heptane |
PP Regulations
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Article 177.1520 |
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Density of 0.880 -0.913 and m.p. 160 °C - 180 °C |
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Maximum extractable fraction of
n-hexane is 6.4% |
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Maximum soluble fraction of xylene is
9.8% |
Testing and Health Issues
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No specific requirements for microwave
food containers |
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FDA provides guidance for proper
microwave migration testing protocols |
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Migration tests using food simulants
(e.g. cooking oil) |
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Migration testing at the highest
cooking temperature |
Testing and Health Issues
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Size and type of food, cooking time,
and food geometry play part in the maximum temperature |
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Consult with FDA before deciding on a
migration testing protocol for microwave only containers |
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Plasticizers have been linked to
endocrine disorders |
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Further study needed to determine
possible health risks due to migration of polymer additives |
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Conclusion
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Primary polymer materials: CPET,
PPO/HIPS, PP |
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Applications ranging from single use
HMR to repeated use food storage containers |
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Essentially no health risks |
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Cost effective containers |
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Questions?
Slide 33