An article that outlines the compatibility testing methods for plastic/glass containers, bags with their contents

Introduction: In the cosmetics industry, the compatibility between packaging materials and contents (inner materials) is a key factor in ensuring product quality, safety and stability. Incompatibility may lead to product deterioration, reduced efficacy, sensory changes, and even safety hazards. The following will systematically introduce the compatibility between plastic containers, bags, and glass packaging materials and inner materials. The content of this article is only for reference by purchasing friends in the cosmetic industry.

ONE

Compatibility definition

Compatibility between packaging materials and contents refers to the ability of packaging materials to maintain the expected characteristics, quality, purity, safety and effectiveness of the contents without harmful interactions with the contents of the cosmetics during the entire life cycle of the product (production, filling, storage, transportation, use). Specifically, poor compatibility may manifest as:

1. Contents affect packaging materials: corrosion, dissolution, swelling, embrittlement, discoloration, cracking, seal failure, label falling off, etc.

2. Packaging materials affect contents:

Migration: Chemical substances in the packaging material (monomers, additives, catalyst residues, degradation products, ink solvents, etc.) dissolve into the contents.

Adsorption: The active ingredients (flavors, preservatives, active substances, etc.) or volatile components in the contents are adsorbed or absorbed by the packaging material, resulting in a decrease in content, a change in odor, or a decrease in efficacy.

Permeation: External environmental factors (oxygen, water vapor, odor) penetrate into the product through the packaging material, or volatile components/water in the contents escape through the packaging material, causing oxidation, water loss, deterioration, and odor transfer.

Physical and chemical changes: The surface properties of the packaging material lead to destruction of the emulsified system of the contents, crystallization, precipitation, viscosity changes, color changes, pH drift, etc.

3. Mutual influence: The superposition or synergistic effect of the above phenomena.

TWO

Compatibility requirements statement

The core requirements for compatibility are to ensure:

1. Safety: The level of migration substances complies with the limit requirements of relevant global regulations (such as China's "Technical Specifications for Cosmetic Safety", EU Cosmetic Regulation (EC) No 1223/2009, US FDA requirements, ISO standards, etc.), ensuring the safety of consumers. No toxic or harmful substances are dissolved.

2. Effectiveness: The content, activity, and stability of the product’s claimed ingredients meet the requirements within the shelf life. Key ingredients (such as preservatives, sunscreens, and active ingredients) are not excessively adsorbed or degraded.

3. Stability: The product maintains its physical form (such as no stratification of emulsions and no water/oil separation in pastes), chemical properties (such as stable pH value and no oxidation and rancidity), microbiological stability (the preservative effectiveness is not affected or weakened by the packaging materials), color, odor, viscosity and other key attributes during the shelf life.

4. Functionality: The physical properties of the packaging material (such as strength, barrier properties, sealing, opening and closing properties) will not be affected by the contents and become ineffective under the conditions of use. The contents will not deteriorate faster due to the degradation of the packaging material performance.

5. Sensory experience: The product’s appearance, smell, and skin feel will not undergo changes that are unacceptable to consumers (such as the generation of odor, discoloration of the packaging material affecting the appearance, and the contents being contaminated with odor from the packaging material).

6. Regulatory Compliance: Meet all applicable packaging material regulations and cosmetics regulatory requirements in the target market.

THREE

Compatibility test methods for different packaging material types

Compatibility testing usually needs to be conducted under simulated or accelerated conditions and combined with long-term stability testing. The test plan needs to be designed based on the specific packaging material, content formula, expected storage conditions and usage.

Plastic containers

Bottles, jars, tubes, pump heads, caps etc.

Common materials: PMMA, PE, PP, PET, PETG, MS, AS, PS, ABS, PC etc.

Test focus:

Migration test: Check whether plastic additives (such as antioxidants, light stabilizers, plasticizers - especially for soft PVC, special attention should be paid to phthalates), monomers (such as VCM, BPA - pay attention to PC material), catalyst residues, oligomers, etc. are dissolved in the contents.

Adsorption test: Detect changes in the content of key ingredients (such as preservatives, flavors, active ingredients, oils) in the contents and evaluate the degree of adsorption by plastic.

Chemical resistance/swelling: Observe whether the packaging material deforms, swells, stress cracks, becomes brittle, or changes color after coming into contact with the contents.

Sealing component compatibility: Test the compatibility of gaskets and O-rings (commonly used rubber, silicone, thermoplastic elastomer TPE) with the contents (swelling, dissolution, migration, leakage or functional failure).

Impact of barrier properties: Evaluate whether the contents (such as solvents, essential oils) affect the oxygen and moisture barrier properties of the packaging material.

Main test methods:

Accelerated aging/migration test: The packaging material and contents are stored under specific conditions (such as 40°C/75%RH, 50°C) for a certain period of time (such as 4 weeks, 8 weeks, 12 weeks), and then the content of the migrants (GC-MS, LC-MS/MS, etc.) and the content of key components (HPLC, GC, etc.) in the contents are tested. Simulated liquids (such as ethanol/water solution, isooctane, olive oil) or blank matrices are often used for control tests.

Long-term stability test: Test for up to 12-36 months under actual or simulated shelf conditions (such as 25°C/60%RH, 30°C/65%RH), with regular sampling and testing of various indicators.

Swelling/Weight Change Test: Measures the weight and dimensional changes of packaging components (especially seals) before and after immersion in contents or simulated fluids.

Mechanical property test: Test whether the tensile strength, impact strength, hardness, etc. of the packaging material changes after contact with the contents (which may affect the drop performance).

Sensory evaluation: Evaluate whether the contents have any peculiar smell, whether the peculiar smell of the packaging material has migrated into the contents, and whether the contents have changed color.

Specific component analysis: For example, if there is concern about BPA, the dissolution amount in PC products can be tested; the acetaldehyde content and its migration in PET can be tested.

Extractables and leachables studies: A more in-depth study that first extracts potential migrants from packaging materials under more stringent conditions (high temperature, strong solvents), and then evaluates the risk of leaching under actual use conditions.

Bags

Stand-up bags, stand-up bags, roll film, aluminum-plastic composite film, etc.

Common materials: PET/AL/PE, PET/PE, NY/PE, OPP/CPP, etc.

Test focus:

Barrier performance maintenance: Whether the contents affect the bonding strength of the composite layer, the integrity of the aluminum foil, or the barrier properties of the plastic layer (OTR oxygen transmission rate, WVTR water vapor transmission rate).

Interlayer delamination/delamination: Whether the contents (especially those containing oils, solvents or surfactants) cause delamination between the layers of the composite film.

Heat seal strength: Whether the contents contaminate the heat seal surface, causing a decrease in heat seal strength or leakage.

Migration and adsorption: As with plastic containers, pay attention to the adsorption of the contents by the inner layer PE/CPP and other materials, as well as the migration risk of inks and adhesives (especially solvent residues) into the inner layer contents (pay special attention to the use of direct contact with food-grade adhesives and inks).

Contents resistance: Whether the bag is corroded, swelled or caused to print fall off by the contents.

Physical strength: Whether the compression and puncture resistance of the bag are affected by the contents during filling and transportation.

Main test methods:

Accelerated aging/migration/adsorption testing: Same as plastic containers, special attention should be paid to the migration of the inner material and adhesive/ink.

Long-term stability test: Same as plastic containers, it is necessary to observe whether the bag collapses (oxygen barrier), leaks, or delamination.

Barrier Testing: Test the OTR and WVTR of the bag before and after aging (such as ASTM D3985, ASTM F1249).

Heat seal strength test: Test the peel strength of the heat seal before and after aging (ASTM F88).

Seal integrity testing: such as vacuum decay method, high pressure leak detection method, dye penetration method, etc. to detect micro leaks.

Peel strength test: Test the changes in the adhesion strength (ASTM D903, ASTM F904) between the layers of the composite film before and after aging.

Sensory evaluation: Same as plastic containers, pay special attention to odor migration.

Extractables and leachables research: Especially important for multi-layer composite bags.

Glass packaging materials

Categories: bottles, cans, jars

Test focus:

Chemical resistance: Whether the contents (especially strong acid and strong alkali products) corrode the glass surface, causing glass delamination (producing visible or invisible glass particles) or dissolving alkali metal ions (causing the pH to increase).

Internal surface treatment: Whether the release agent, siliconizing agent or other internal coating is compatible with the contents, whether it migrates or affects the stability of the contents.

Metal cap/pump head compatibility: Glass itself is inert, but the matching metal cap (tinplate, aluminum) and pump head (including various plastics and metal springs) must be compatible with the contents to prevent corrosion and rust that may cause contamination of the contents or functional failure.

Seal compatibility: Compatibility of bottle cap lining (such as PE foam pad, PVC pad, cork) or pump head seal with the contents.

Physical shock: Glass is fragile, but you need to ensure that the characteristics of the contents (such as viscosity, presence of solid particles) do not increase the risk of breakage during normal use and transportation (although not strictly a compatibility issue, but relevant).

Main test methods:

Glass particle/delamination test: Pour the contents or specific corrosive liquid (such as dilute acid or alkali) into a glass container, store it at high temperature (such as 121°C) or under accelerated conditions for a certain period of time, and assess the risk of delamination by visual inspection, light obscuration particle counting, and ICP-MS detection of the dissolved silicon, boron, sodium and other element contents (refer to USP <660> or similar methods).

Inner coating stability: Observe whether the inner coating has peeling, dissolution, blistering, etc.; check whether there is migration of coating components in the contents.

Metal parts corrosion test: Check whether the metal cover, pump head spring, etc. are rusted or discolored; detect whether the content of metal ions (such as Fe, Sn, Al, Cr, Ni) in the contents is abnormally increased (AAS, ICP-OES/MS).

Seal compatibility testing: Same as testing of closure components in plastic containers (swelling, migration, weight change).

pH Monitoring: Alkali dissolved from the glass may cause the pH to increase and needs to be closely monitored during stability testing.

Long term stability test: Same as plastic container.

Sensory evaluation: Same as plastic container.

FOUR

Things to note

1. “Formula + Packaging Material” Combination Test: Compatibility is highly dependent on the specific formula and specific packaging material. Changing the raw material supplier, fine-tuning the formula, or changing the packaging material/supplier/production process may affect compatibility and must be re-evaluated.

2. Comprehensiveness: The test must cover all packaging parts that come into contact with the contents (bottle body, bottle cap, inner plug, gasket, pump head, valve, nozzle, hose shoulder and head, etc.). For multi-layer composite packaging, each layer and adhesive/ink must be considered.

3. Representative samples: The packaging materials used for testing must be representative samples of mass production, including their production process (such as injection molding, blow molding, printing, and lamination), cleanliness, and sterilization method (if applicable).

4. Simulate the worst case scenario: The filling volume (headspace size), storage conditions (temperature, humidity, light), and product usage (such as whether it will be repeatedly squeezed or inverted) should simulate actual or more severe conditions.

5. Choose the appropriate analytical method and detection limit: The method needs to be able to detect the target migrant/adsorbent/change index sensitively and accurately. Pay attention to the limits of harmful substances required by regulations.

6. Pay attention to small changes: Even if there is no obvious change in the physical appearance, trace amounts of migration or adsorption may affect the stability, safety and efficacy of the product, and need to be detected by precision instruments.

7. Regulatory trends: Pay close attention to updates on regulations on banned/restricted substances in packaging materials (especially plastics, adhesives, and inks) in global target markets (such as phthalates, nitrosamines, primary aromatic amines, specific heavy metals, PFAS, etc.).

8. Supplier management: Require packaging material suppliers to provide Declaration of Conformity (CoC), Material Safety Data Sheet (MSDS), key ingredient information (such as additives, monomers, catalysts) and necessary migration test data (such as compliance testing). Establish strict supplier audits and quality agreements.

9. Integration of stability studies: Compatibility assessment is an important part of product stability studies, and the data from both need to be analyzed comprehensively.

10. Risk assessment: Conduct a preliminary compatibility risk assessment based on formulation characteristics (pH, polarity, solvent content, active ingredients, irritating ingredients), packaging material and structure, expected storage conditions and usage to guide the design of the test plan.

11. Cost and time: Comprehensive compatibility testing (especially E&L studies) is costly and time-consuming, but it is a key investment to ensure product safety and quality and avoid post-market recalls or complaints. Sufficient resources and time must be reserved in the project plan.

Summary:

The compatibility of cosmetic packaging materials and contents is a complex and critical topic. It requires a systematic and scientific testing process (including accelerated aging, long-term stability, physical and chemical analysis, sensory evaluation, etc.) based on an in-depth understanding of material science, chemistry, formulation technology and regulations. The focus and methods of testing are different for different packaging materials such as plastics, bags, and glass. Companies must maintain a rigorous attitude, invest the necessary resources, fully verify compatibility during the product development stage, and continuously monitor supply chain and regulatory changes to ensure the safety, effectiveness and consumer satisfaction of products throughout their life cycle.