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Plastics in the Microwave Oven CE 435

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Plastics in the Microwave Oven CE 435. Presented by: Daniel Fulcher Christopher Hunter Martin Schaefer April 17, 2001. Introduction. U.S. households owning a microwave oven increased from 15% in 1980 to 78% by 1989

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plastics in the microwave oven ce 435

Plastics in the Microwave OvenCE 435

Presented by: Daniel Fulcher

Christopher Hunter

Martin Schaefer

April 17, 2001

  • U.S. households owning a microwave oven increased from 15% in 1980 to 78% by 1989
  • Gorman’s New Product News reported the number of new microwave product introductions increased from 278 in 1986 to almost 1000 in 1988
  • Microwave frequency of ~2.45 GHz ensures effective penetration into the food and even food heating
  • Annual revenues of 3 billion dollars
  • Max temperatures of 230oF for microwave ovens and 400oF for dual oven applications
  • Containers should be sturdy, rigid in shape and capable of supporting its contents
  • Limited migration of additives, colorants, or fillers
  • Federal Food and Drug Administrative approval
hmr packaging
HMR Packaging
  • Crystallized polyethylene terephthalate (CPET)
  • Polyphenylene oxide, high impact polystyrene blend (PPO/HIPS)
cpet morphology
CPET Morphology
  • Heterochain, modified homopolymer with ~30% Crystallinity
  • Step growth condensation polymerization reaction of terephthalic acid and ethylene glycol
cpet properties
CPET Properties
  • Crystallization of PET increases the upper temperature resistance from 230°F to 400°F
  • Balance between strength properties and temperature resistance
  • Crystallinity of 28%-32% and an intrinsic viscosity of .85 to .95
  • Two-layer structure of CPET and APET
cpet properties1
CPET Properties
  • Good O2 and CO2barrier properties
  • Acceptable water barrier properties
  • Easily colored with black carbon
cpet processing
CPET Processing
  • In 2000, 84 million pounds produced at ~.52 $/lb
  • Eastman Chemical Company produces CPET resin under the product name of VersaTray®
  • Thermoformed
  • Vacuum Snap-Back Thermoforming
ppo hips morphology
PPO/HIPS Morphology
  • Fully miscible blended amorphous polymer
  • Noryl® manufactured by General Electric Plastics
  • Noryl® PPO/HIPS blend is approximately 25% PPO and 75% HIPS by weight
ppo morphology
PPO Morphology
  • Heterochain homopolymer
  • Created by a free-radical, step-growth, oxidative-coupling polymerization
hips morphology
HIPS Morphology
  • Grafted copolymer of cis-1,4-poly(1,3-butadiene) and styrene monomer
  • Polystyrene chains are atactic
  • 2% to 15% by weight of polybutadiene
hips morphology1
HIPS Morphology
  • Polystyrene (PS) and polybutadiene phase separate creating compartmentalized regions
  • Polybutadiene forms small, dispersed globules within the polymer structure
ppo hips properties
PPO/HIPS Properties
  • Improvements in final blend properties are in direct proportion to the amount of PPO added
  • PPO is added to HIPS to increase temperature resistance from approximately 180°F to 230°F
  • Blending with HIPS improves PPO’s low resin flow characteristics
ppo hips properties1
PPO/HIPS Properties
  • Small, dispersed globules of polybutadiene elastomer within the PS improves the blend impact strength
  • PPO improves the poor gaseous and water vapor barrier properties of HIPS
  • Easily colored with black carbon
ppo hips processing
PPO/HIPS Processing
  • High intensity mixer required to ensure accurate blending during extrusion
  • Thermoforming on equipment designed for PS
  • Thermoform-Fill-Seal process
hmr covers
HMR Covers
  • Heat-seal the food containers
  • Most widely used film is multi-layer polypropylene
  • Adhesives cause complications in migration testing
  • PP is a low cost packaging film ~.53$/lb
polypropylene pp morphology
Polypropylene (PP) Morphology
  • Zieglar-Natta polymerization
  • Isotactic is crystalline, atactic is amorphous
pp chain structure
PP Chain Structure
  • PP is a blend of atactic and isotactic
pp properties
PP Properties
  • Properties and processability determined by isotacticity
pp processing
PP Processing
  • 1550 million pounds produced in 2000 at ~ .53 $/lb.
  • Injected or blow molded
  • INSPIRE® PP produced by Dow Plastics
  • The code of federal regulations provides guidance on polymers allowed in the direct contact of food.
  • Article 177 presents data specific to each polymer
  • Composition specifications, allowable coatings, modifiers, emulsifiers, and testing criteria
cpet regulations
CPET Regulations
  • Article 177.1630
  • Emulsifier < 2.0 percent of the dry weight
  • Additional substances allowed must be generally recognized as safe by the FDA
  • < 0.02 mg/in2 of chloroform-soluble extractives for heptane and distilled water migration tests
ppo hips regulations
PPO/HIPS Regulations
  • Articles 177.1810 and 177.2460
  • PS: molecular weight > 29,000 and soluble in toluene
  • Maximum extractable fractions of chloroform in distilled water and 50% ethanol are 0.0039 mg/cm2
  • PPO: intrinsic viscosity > 0.30 deciliter/gram
  • < 0.02 weight percent extractable with n-heptane
pp regulations
PP Regulations
  • Article 177.1520
  • Density of 0.880 -0.913 and m.p. 160 C - 180 C
  • Maximum extractable fraction of n-hexane is 6.4%
  • Maximum soluble fraction of xylene is 9.8%
testing and health issues
Testing and Health Issues
  • No specific requirements for microwave food containers
  • FDA provides guidance for proper microwave migration testing protocols
  • Migration tests using food simulants (e.g. cooking oil)
  • Migration testing at the highest cooking temperature
testing and health issues1
Testing and Health Issues
  • Size and type of food, cooking time, and food geometry play part in the maximum temperature
  • Consult with FDA before deciding on a migration testing protocol for microwave only containers
  • Plasticizers have been linked to endocrine disorders
  • Further study needed to determine possible health risks due to migration of polymer additives
  • Primary polymer materials: CPET, PPO/HIPS, PP
  • Applications ranging from single use HMR to repeated use food storage containers
  • Essentially no health risks
  • Cost effective containers

References annotated in the Polymers in the Microwave written report.

1.Rubbright, H.A., Davis N.O., The Microwave Decade, Packaging Strategies, West Chester, PA, 1989.

2.Becker, R. “As a Matter of Fact.” Chem Matters April 2000: Volume 18 Number 2. Online. Available HTTP:

3.Dow Plastics, Polypropylene Resins Molding Guide. The Dow Chemical Company, 1998.

4.Brady, A.L., Marsh, K.S., The Wiley Encyclopedia of Packaging Technology. New York: John Wiley and Sons, Inc., 1997.

5.Hanlon, J.F., Kelsey, R.J., Forcinio, H.E., Handbook of Package Engineering. Technomic Publishing Company, Inc., 1998.

6.Selke, S.E., Understanding Plastics Packaging Technology. Cincinnati: Hanser/Gardner Publications, Inc., 1997.

7.1999 CFR Title 21 Food and Drugs, Volume 3. Part 177 Indirect Food Additives: Polymers. Online. Available HTTP:

8.Eastman Chemical Company. Online. Available HTTP:

9.General Electric Company. Plastics Division. Online. Available HTTP:

10.Department of Polymer Science, University of Southern Mississippi, Macrogalleria, 1996. Online. Available HTTP:

11.Modern Plastics Encyclopedia. New York: McGraw-Hill Companies, Inc., 2001.

12.U.S. Food and Drug Administration. Online. Available HTTP:

13.U.S. Food and Drug Administration. FDA Consumer Magazine, Volume 97, Number 11. Maryland; FDA, 1998.