Evaluating colorfastness to laundering of Rayon Fibers with AATCC TM61

Evaluating colorfastness to laundering via AATCC TM61 is a standard industry practice for assessing how rayon fabrics  and their associated dyes hold up under the stresses of repeated washing. Because rayon is a regenerated cellulose fiber with unique physical properties when wet, this accelerated test provides a critical worst-case simulation of home or commercial laundering.

1. Core objectives of TM61

The primary goal of TM61 is to simulate five typical domestic launderings in a single 45-minute laboratory procedure. For rayon, this helps identify:

• Color change: How much the original shade fades or shifts.
• Staining: How much dye transfers to adjacent fibers (using a multifiber test fabric).
• Surface integrity: Whether the mechanical action causes pilling or fibrillation, which often occurs in certain rayon types like Lyocell.

2. Test conditions for Rayon

The test is conducted in a Launder-Ometer, which subjects the specimens to controlled temperature, chemistry, and mechanical friction. Depending on the intended end-use of the garment, one of several ‘Test Impacts’ is chosen:

Table: Laundering test parameters

Note: *WOB = Without Optical Brightener

3. The procedure for Rayon fiber

Specimen prep: A swatch (50 x 100 mm) is cut and backed with a Multifiber Adjacent Fabric (containing acetate, cotton, nylon, polyester, acrylic, and wool).

Mechanical action: The specimen is placed in a stainless steel canister with the specified volume of water, detergent, and stainless steel balls. These balls provide the ‘accelerated’ mechanical friction.

Rotation: The canisters rotate at 40 RPM within the Launder-Ometer.

Rinsing & drying: Specimens are rinsed in warm water (40±3°C) and dried either in a press or by air. Temperatures must be strictly controlled to prevent thermal degradation of the rayon fibers.

4. Why Rayon is a special case in TM61

Testing rayon requires specific attention to its chemical and physical behavior:

• Wet strength & swelling: Rayon can lose up to 50 per cent of its strength when wet and swells significantly. The mechanical impact of 50 to 100 steel balls in a 2A or 3A test can sometimes cause physical damage to delicate rayon weaves, which must be distinguished from actual color loss.
• Dye migration: Rayon is typically dyed with reactive or direct dyes. TM61 effectively tests the ‘wash-down’ of these dyes, especially in deep shades like navy or black, where unfixed dye might lead to heavy staining on the nylon or cotton portions of the multifiber strip.
• Fibrillation management: For high-tenacity rayon (Lyocell), the accelerated friction can create ‘frosting’ on the surface. While this is a physical change, it can cause the color to appear lighter, affecting the final Gray Scale rating.

5. Evaluation and grading

After conditioning, the results are assessed in a standard light booth (D65) using two primary scales:

• Gray scale for color change: Ranks the difference between the tested and untested specimen from Grade 5 (no change) to Grade 1 (severe change).

Gray scale for staining: Ranks the level of dye transfer to each of the fibers on the multifiber strip.