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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 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 CO2 barrier 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?

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