Grease Resistance Evaluation of Plastic Food Containers: Standards, Methods, and Compliance Requirem

Amorphous PET containers are generally limited to cold oily foods, while CPET trays designed for dual-oven use must demonstrate stability at elevated temperatures in the presence of fatty food simulants. Testing verifies resistance to hydrolytic and thermal stress combined with oil contact.

PLA and Other Biodegradable Containers

Polylactic acid and other biobased materials are increasingly used for eco-friendly packaging. These materials often exhibit lower heat deflection temperatures and sensitivity to hydrolysis, so grease resistance evaluation must verify performance under realistic serving temperatures, typically not exceeding 40–50°C for amorphous PLA.

Sample Preparation Requirements

Test specimens should be representative of regular production and handled to avoid surface contamination. Prior to testing, samples are conditioned in a controlled atmosphere of 23°C and 50% relative humidity in accordance with ISO 291. Sample areas exposed to food contact are calculated following GB 5009.156-2016 to allow migration results to be expressed per square decimeter of contact surface.

Testing Items

A comprehensive grease resistance evaluation typically includes the following test items:

• Overall migration (total migration limit) using fatty food simulants, with the acceptance criterion of no more than 10 mg/dm² as specified in GB 4806.7-2016 and Regulation (EU) No 10/2011.
• Specific migration of regulated substances that may be accelerated by oil contact, including antioxidants such as BHT and Irganox-type phenols, plasticizers if present in formulations, residual monomers, and oligomers.
• Hot oil immersion resistance, assessing appearance, deformation, warpage, and leakage after exposure to food-grade oil at defined temperatures such as 100°C or 121°C.
• Dimensional stability, measured as percentage change in length, width, and height after oil exposure.
• Mass change, expressed as the percentage of mass gain or loss following immersion, indicating absorption or extraction of formulation components.
• Mechanical property retention, including tensile strength and elongation at break measured before and after oil exposure per ISO 527 or ASTM D638.
• Surface quality assessment, covering oil staining, haze increase, softening, blistering, and stress crazing.
• Seal and leak integrity when filled with hot oily simulants, simulating actual transport and delivery conditions.
• Microwave suitability verification, combining oil contact with repeated reheating cycles to confirm performance under dual thermal and chemical stress.

Testing Methods

Selection of Food Simulants

Fatty foods are simulated using refined olive oil or another vegetable oil designated as simulant D2 under Regulation (EU) No 10/2011. Where analytical measurement in oil is impractical, volatile substitute simulants such as isooctane and 95% aqueous ethanol may be used with documented time-temperature conversion factors, in line with GB 31604.1-2015 and EN 1186-11.

Migration Test Conditions

The test time and temperature are selected to reflect the worst foreseeable use condition. Typical regimes include 2 hours at 70°C for hot-fill applications, 1 hour at 100°C or 2 hours at reflux for high-temperature use, and prolonged 10-day testing at 40°C for long-term room-temperature storage. Testing is performed on at least three replicate specimens per condition, and results are corrected for surface area and expressed in mg/dm².

Chemical Resistance Immersion Protocol

Following the general principles of ISO 175, ASTM D543, and GB/T 11547, immersion testing is conducted by fully submerging conditioned specimens in food-grade oil at the target temperature for a defined duration. After exposure, specimens are drained, blotted, and re-weighed, re-measured, and re-tested mechanically. Typical acceptance indicators include mass change within agreed limits, dimensional change below approximately 2%, and tensile property retention of at least 70% of original values, with no visible deformation, cracking, or delamination.

Overall Migration Determination

Overall migration is determined by exposing the food contact surface to the fatty simulant under the selected condition, followed by removal of the simulant and gravimetric determination of non-volatile residue, following GB 31604.8 or the relevant part of EN 1186. For substitute simulants, applied conversion factors must be reported. The result is compared against the 10 mg/dm² statutory limit.

Evaluation and Reporting

The final assessment combines compliance with migration limits, retention of physical and mechanical performance, and acceptable cosmetic condition. A complete test report should identify the material and product, sample dimensions and contact area, simulant and test conditions, methodology references, individual and mean results, and a clear conformity conclusion for the declared use conditions.

Applications

• Incoming material and batch release quality control for food container manufacturers producing PP, PET, PS, and PLA lunch boxes.
• New product development and formulation optimization, including trials of new resin grades, recycled content, or bio-based materials intended for oily food contact.
• Regulatory compliance demonstration for domestic market access under GB 4806.7 and for export to markets governed by EU and U.S. FDA requirements.
• Vendor qualification and periodic supplier audits conducted by food delivery platforms, supermarket chains, airline caterers, and central kitchens.
• Microwave and oven-use claim substantiation for products labeled as heat-resistant or dual-oven safe.
• Failure analysis and root cause investigation when containers deform, leak, or stain during commercial use with oily foods.

FAQ

What is grease resistance evaluation of plastic food containers?

It is a combined chemical and physical performance assessment that verifies whether a container can safely contact oily and fatty foods without excessive migration of substances into the food and without loss of structural integrity, dimensional stability, or surface quality.

Which standards govern this evaluation in China?

GB 4806.7-2016 defines the safety requirements for plastic food contact materials, while GB 31604.1-2015 establishes migration testing rules, GB 5009.156-2016 specifies pretreatment and sampling, and GB 31604.8 specifies overall migration determination. Chemical resistance immersion is guided by ISO 175, ASTM D543, and GB/T 11547.

Why is vegetable oil used as the food simulant?

Fatty foods represent the worst case for lipophilic migration from plastics, because many additives and oligomers are fat-soluble. Vegetable oil such as refined olive oil is designated as the reference fatty food simulant in both Chinese and European frameworks.

Does the test cover microwave reheating with oily food?

Yes. For containers intended for microwave use, testing is performed at temperatures corresponding to reheating conditions, often 100°C or higher for up to two hours, to simulate repeated or prolonged heating in the presence of oil.

What are the common causes of test failure?

Typical causes include use of resin grades with inadequate heat resistance, excessive additive loading, poor crystallinity in PP grades, insufficient wall thickness, mold-induced residual stress, and use of materials outside their declared temperature range.

How much sample is required for testing?

Depending on the scope, a full evaluation typically requires 30 to 60 complete containers plus material specimens for mechanical testing, allowing for replicates across multiple simulant and temperature conditions.

How often should grease resistance testing be repeated?

Testing is required for new products, after material or process changes, following regulatory updates, and as part of periodic compliance verification, typically annually or per contract with buyers and platforms, conducted by accredited third-party laboratories.