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 OvenCE 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

  • 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


Scope

  • 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


Home Meal Replacement Packaging


HMR Packaging

  • Crystallized polyethylene terephthalate (CPET)

  • Polyphenylene oxide, high impact polystyrene blend (PPO/HIPS)


CPET Morphology

  • Heterochain, modified homopolymer with ~30% Crystallinity

  • Step growth condensation polymerization reaction of terephthalic acid and ethylene glycol


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 Properties

  • Good O2 and CO2barrier properties

  • Acceptable water barrier properties

  • Easily colored with black carbon


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


CPET Processing


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

  • Heterochain homopolymer

  • Created by a free-radical, step-growth, oxidative-coupling polymerization


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 Morphology

  • Polystyrene (PS) and polybutadiene phase separate creating compartmentalized regions

  • Polybutadiene forms small, dispersed globules within the polymer structure


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 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

  • High intensity mixer required to ensure accurate blending during extrusion

  • Thermoforming on equipment designed for PS

  • Thermoform-Fill-Seal process


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


Food Storage Containers


Polypropylene (PP) Morphology

  • Zieglar-Natta polymerization

  • Isotactic is crystalline, atactic is amorphous


PP Chain Structure

  • PP is a blend of atactic and isotactic


PP Properties

  • Properties and processability determined by isotacticity


PP Processing

  • 1550 million pounds produced in 2000 at ~ .53 $/lb.

  • Injected or blow molded

  • INSPIRE® PP produced by Dow Plastics


Regulations

  • 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

  • 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

  • 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

  • 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

  • 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 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


Conclusion

  • 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


Questions?


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: www.acs.org/education/curriculum/chemmatt.html

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: www.access.gpo.gov/nara/cfr/waisidx_99/21cfr177_99.html

8.Eastman Chemical Company. Online. Available HTTP: www.eastman.com/productfiles/prod0018.html

9.General Electric Company. Plastics Division. Online. Available HTTP: www.geplastics.com/resins/techsolution/technifacts.html

10.Department of Polymer Science, University of Southern Mississippi, Macrogalleria, 1996. Online. Available HTTP: www.psrc.usm.edu/macrog/floor2.html

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

12.U.S. Food and Drug Administration. Online. Available HTTP: vm.cfsan.fda.gov/~dms/opa-pmnc.html

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


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