Measuring the dimensional stability of lyocell fibers with ISO 3759
In the competitive scenario of sustainable textiles, lyocell has emerged as a premium cellulose fiber, lauded for its exceptional strength and eco-friendly manufacturing. However, like all cellulosic materials, its dimensional stability - the ability of a fabric to retain its original shape and size after laundering, is a critical quality metric. To ensure global consistency in these measurements, the industry relies on ISO 3759. This standard serves as the essential preparatory blueprint for assessing dimensional change, providing the methodology for specimen preparation, marking, and final measurement.
The role of ISO 3759 in dimensional testing
ISO 3759 is not a washing procedure itself (that is typically handled by ISO 6330), but rather the mandatory protocol used before and after treatment. It ensures that any recorded shrinkage or growth is the result of the fiber's reaction to the treatment rather than inconsistent handling or measuring techniques.
For lyocell, which possesses a unique fibrillar structure, precise preparation is vital. While lyocell generally offers superior wet strength and lower contraction than viscose or cotton, its highly crystalline structure can lead to relaxation shrinkage if the fabric is not correctly set during finishing. ISO 3759 provides the rigorous groundwork needed to verify that a fabric meets international trade and quality control benchmarks.
Step-by-step procedure for lyocell fabrics
- Conditioning and preparation
The process begins by placing the fabric in a standard atmosphere (typically 20°C ± 2°C and 65 per cent ± 4 per cent relative humidity) as per ISO 139. Lyocell fibers are hygroscopic; therefore, the specimen must reach a state of equilibrium with the environment before any initial marks are made.
Standard specimens are cut to at least 500 mm x 500 mm, ensuring they are taken at least one meter away from the fabric ends. To prevent the edges from fraying during the mechanical stress of washing, a common issue with lyocell's smooth fiber surface edges should be overlocked with dimensionally stable thread.
- Marking reference points
Using a specialized template or a fine-point indelible marker, reference points (benchmarks) are applied. ISO 3759 requires at least three pairs of marks in both the warp (lengthwise) and weft (widthwise) directions.
- The distance between marks must be at least 350 mm.
- Marks must be at least 50 mm from the edge to avoid distortion from the fabric’s border.
- Treatment and final measurement
Once marked and measured (L0), the specimen undergoes the specified treatment. After treatment and a subsequent four-hour conditioning period, the fabric is laid flat on a smooth surface, and wrinkles are gently removed without stretching. The distance between the marks is measured again (L1) to the nearest 1 mm.
The dimensional change (DC) is calculated using the formula:
DC%=L0L1−L0×100
A negative result indicates shrinkage, while a positive result indicates elongation.
Why lyocell requires precision
Lyocell’s stability is often superior to other man-made cellulosics because of its high degree of fiber orientation. However, it exhibits a tendency towards fibrillation in wet environments, where micro-fibers peel away from the main fiber axis. By utilizing the rigorous marking and measurement protocols of ISO 3759, manufacturers can accurately predict how a lyocell garment will fit after repeated laundering, ensuring the premium ‘hand’ and ‘drape’ remain consistent for the consumer.