Turnover Box Decolorization Testing: A Technical Guide to Color Fastness Evaluation of Plastic Crate

Turnover box decolorization testing is an essential quality control procedure that determines whether colorants in plastic distribution crates resist fading, bleeding, or transferring onto products, packaging, and food-contact surfaces. This technical guide explains the testing principles, applicable international standards, sample preparation requirements, and evaluation methods used by accredited third-party laboratories and in-house quality teams. It also covers practical applications in food logistics, cold-chain distribution, and supplier qualification for both virgin and recycled plastic crates.

Technical Overview

Turnover boxes are rigid, reusable plastic crates widely used in food distribution, cold-chain logistics, agriculture, pharmaceutical transport, and industrial material handling. They are typically manufactured from polypropylene (PP) or high-density polyethylene (HDPE) and colored with inorganic pigments, organic pigments, or dye dispersions. The decolorization test, also referred to as color fastness or color migration testing, evaluates whether these colorants remain permanently fixed within the polymer matrix when the crate is exposed to the friction, moisture, cleaning agents, oils, and temperature conditions encountered in real-world service.

The primary risk addressed by this test is pigment bleed. If colorants are poorly dispersed, inadequately bound, or incompatible with the base resin, they can migrate to the crate surface and transfer onto packaged goods, garments, labels, or food products. For crates used in direct food contact, color migration is both a contamination hazard and a regulatory compliance issue under food contact material frameworks such as GB 4806.7 and the GB 31604 series in China, and Regulation (EU) No 10/2011 in Europe.

Decolorization testing simulates contact stresses through rubbing, wiping, immersion in food simulants, and hot-contact loading. Results are graded against the grey scale for staining defined in ISO 105-A03 and GB/T 251, supplemented by visual assessment of simulant coloration and, where required, quantitative spectrophotometric analysis of extracts. Textile-derived rubbing methods such as ISO 105-X12, GB/T 3920, and JIS L 0849 are adapted for rigid plastic surfaces, making the test applicable across global supply chains.

Testing Samples

Standard Injection-Molded Polypropylene Crates

Polypropylene crates are the most common sample type. Test specimens are cut from flat regions of the side walls, base, and internal ribs, since pigment distribution can vary with wall thickness and flow patterns during injection molding. Both interior and exterior surfaces are evaluated because the interior typically contacts products or food directly.

High-Density Polyethylene Crates

HDPE crates, frequently used in cold-chain and outdoor applications, are tested with additional attention to stress-whitened areas and corners, where mechanical stress during demolding and handling can increase surface pigment exposure. Specimens from the base runners and stacking rims are included when these areas contact stacked contents.

Recycled-Content and Regrind Crates

Crates manufactured with recycled polypropylene or regrind streams carry a higher risk of color migration because reprocessed pigments and carrier resins may degrade during multiple processing cycles. Samples from different production lots are recommended to capture variability in incoming recycled feedstock.

Accessories and Secondary Components

Lids, hinged covers, divider inserts, sleeves, and label holders are tested as separate sample types, since they often use different color batches or resin grades than the crate body and may press directly against sensitive goods during stacking.

Sample Preparation and Conditioning

Specimens measuring at least 50 mm x 100 mm are cut with clean tools to avoid contamination or heat smearing of the surface. All samples are conditioned at 23 ± 2 °C and 50 ± 5% relative humidity for a minimum of 24 hours in accordance with ISO 291 and GB/T 2918. Surfaces are cleaned with deionized water and lint-free cloth, then dried before testing. A minimum of three replicates per surface and per color is standard practice to ensure statistical validity.

Testing Items

The decolorization test program for turnover boxes typically comprises the following evaluation items, selected according to the intended application and applicable regulatory scope:

• Dry rubbing color fastness: resistance to color transfer under dry friction against standard white cotton cloth.
• Wet rubbing color fastness: resistance to color transfer when the cotton cloth is wetted with deionized water, simulating damp handling and washing.
• Color migration into food simulants: tendency of colorants to bleed into water, 4% acetic acid, aqueous ethanol, and olive oil or an agreed substitute under use-representative time and temperature conditions.
• Solvent wipe resistance: color stability when wiped with sanitizing solutions such as dilute ethanol or isopropanol mixtures used in hygiene-critical logistics.
• Hot-contact color transfer: staining of white cotton or filter paper pressed against the crate surface under a defined static load at elevated temperature.
• Light fastness and weathering fade: optional assessment of color retention after xenon-arc or UV exposure for crates used in outdoor or sun-exposed service.
• Quantitative dye migration: spectrophotometric measurement of absorbance in simulant extracts where numerical migration data is required for compliance documentation.

Testing Methods

Rubbing Color Fastness Test

A motorized crockmeter rubs a standard white cotton cloth, mounted on a cylindrical finger applying a force of approximately 9 N, back and forth across the specimen for ten complete strokes over a 104 mm track. The test is performed with a dry cloth and, in a second run, with a cloth fully wetted with deionized water. The degree of staining on the cotton cloth is then graded using the grey scale for staining in accordance with ISO 105-A03 and GB/T 251, while any color change of the specimen itself is graded against ISO 105-A02 and GB/T 250. This approach follows the principles of ISO 105-X12, GB/T 3920, and JIS L 0849 as adapted for rigid plastic surfaces.

Food Simulant Immersion Test

Specimens are fully immersed in selected food simulants, typically water, 4% acetic acid, 10% or 20% ethanol, and olive oil or its designated substitute. Test conditions, such as 40 °C for 24 hours, 70 °C for 2 hours, or 100 °C for 1 hour, are chosen to represent the most severe foreseeable contact conditions based on the crate's intended use. After exposure, the simulants are examined for any visible coloration, turbidity, or surface film. Where quantitative results are required, the extracts are analyzed spectrophotometrically at the wavelength of maximum absorbance and reported as optical density or estimated colorant migration.

Contact Staining Test Under Load

White cotton fabric or filter paper is placed against the crate surface and subjected to a defined static load, commonly in the range of 2 to 5 kg, for approximately 30 minutes at temperatures between 60 °C and 80 °C. This method reproduces stacking and hot-filling scenarios in which loaded crates press against contents for extended periods. Staining is assessed using the grey scale for staining.

Solvent Wipe Test

A cotton pad saturated with a specified agent, such as 50% ethanol or a diluted acetic acid solution, is rubbed across the specimen for a fixed number of strokes under controlled pressure. The pad is inspected for picked-up color, and the specimen surface is evaluated for localized fading, gloss change, or pigment lift.

Grading and Acceptance Criteria

Results are reported on the grey scale for staining, where grade 5 indicates no visible transfer and grade 1 indicates severe staining. For food-contact and premium logistics applications, a minimum of grade 4 on both dry and wet rubbing, combined with no visible coloration of any food simulant, is the customary acceptance threshold. For industrial, non-food-contact crates, grade 3 may be acceptable when agreed between buyer and supplier. Any confirmed color migration into fatty or acidic simulants is generally treated as a failure regardless of rubbing grade, because it indicates mobile colorant within the polymer.

Applications

Decolorization testing supports quality, safety, and compliance decisions across the entire lifecycle of turnover boxes, from material development to field performance verification:

• Food distribution and cold chain: qualification of bakery trays, meat and poultry crates, seafood totes, and produce harvesting containers that contact food directly or indirectly.
• Pharmaceutical and healthcare logistics: verification that crates, totes, and sleeves used for medical supplies do not shed colorants onto packaging or cleanroom garments.
• Agriculture and horticulture: assessment of harvest crates exposed to moisture, plant acids, and outdoor sunlight during seasonal use.
• Automotive and electronics handling: confirmation that component trays and dunnage crates will not stain painted, coated, or textile surfaces during transit and storage.
• Regulatory compliance: generation of test evidence for food contact submissions under frameworks such as GB 4806.7 and the GB 31604 series, and conformity support for Regulation (EU) No 10/2011 on plastic food contact materials.
• Supplier qualification and incoming inspection: comparison of competing crate manufacturers, monitoring of production consistency, and validation of colorant changes or masterbatch substitutions.
• Recycled-content programs: demonstration that crates containing post-consumer or post-industrial regrind meet the same color fastness performance as virgin resin products.

FAQ

What is the purpose of the turnover box decolorization test?

The test determines whether colorants in a plastic crate will fade, bleed, or transfer to contacted surfaces under friction, moisture, solvents, oils, and heat. It protects packaged goods and food from contamination, preserves product presentation, and provides evidence of compliance with food contact material regulations.

What result is considered a pass?

For food-contact and high-specification logistics applications, dry and wet rubbing results of grade 4 or higher on the grey scale for staining, together with no visible coloration of any food simulant, are generally required. Lower thresholds, such as grade 3, may be agreed for industrial crates that never contact sensitive goods.

Which standards are commonly referenced?

Rubbing fastness is assessed using methods derived from ISO 105-X12, GB/T 3920, and JIS L 0849, with grading per ISO 105-A03 and GB/T 251. Food simulant migration testing follows GB 4806.7 and the GB 31604 series in China and aligns with Regulation (EU) No 10/2011 in Europe. Conditioning follows ISO 291 and GB/T 2918, and light fastness, when required, follows the ISO 105-B series.

Are recycled-content crates tested differently?

The test methods are identical, but recycled-content crates typically receive more extensive sampling across production lots, because reprocessed pigments and mixed-resin feedstock increase the likelihood of color migration. Quantitative simulant extraction is often added for recycled materials used in food-contact applications.

How long does testing take?

Standard rubbing, wipe, and contact staining tests are usually completed within three to five working days after sample conditioning. Full programs including food simulant immersion at multiple time and temperature conditions, and optional light fastness exposure, may require two to four weeks.

Can the test be performed in-house?

Yes. A calibrated crockmeter, standard cotton cloth, grey scales, and a controlled conditioning environment allow manufacturers to run routine screening in-house. For regulatory submissions, customer disputes, and export documentation, testing should be conducted by accredited third-party laboratories to ensure recognized reporting and traceability.