Analyzing lyocell flammability with ISO 6940 standard
Lyocell is celebrated for its soft texture, strength, and eco-friendly manufacturing process. However, because it is a regenerated cellulosic fiber, its chemical composition is nearly identical to cotton. For manufacturers and safety engineers, this creates a distinct flammability profile that necessitates rigorous testing under standards like ISO 6940.
Understanding lyocell’s flammability profile
Lyocell is composed of cellulose molecules, which are inherently combustible. Unlike certain synthetic fibers that may melt and shrink away from a flame (a behavior that can sometimes prevent ignition), lyocell maintains its structure, allowing the flame to propagate across the material.
When exposed to an ignition source, untreated lyocell burns steadily, produces a characteristic scent reminiscent of burning paper, and leaves behind a light, fine ash. Because it is highly breathable and often used in lightweight garments, its ease of ignition makes it a critical candidate for flammability testing, especially for items intended for children or workers in high-risk environments.
ISO 6940: Determining the ease of ignition
ISO 6940 (Textiles burning behavior; fabrics for apparel; dDetermination of ease of ignition of vertically oriented specimens) is the definitive international standard for measuring how quickly a fabric catches fire. The test is conducted using a vertical apparatus that holds a fabric specimen steady. A small, precise gas flame is then applied to the surface or the bottom edge of the fabric.
Testing parameters:
- Vertical orientation: By testing the fabric vertically, the standard simulates the most dangerous, real-world condition for apparel, how a garment hangs on the body.
- Ignition application: The flame is applied for varying, timed intervals. The goal is to determine the shortest exposure time required to cause the fabric to ignite.
- Metric of performance: The result is expressed as an ignition time. A lower time indicates a fabric that is highly susceptible to fire, while a higher time indicates a more ignition-resistant material.
How to reduce risks in lyocell textiles
Because lyocell is naturally prone to ignition, many manufacturers opt for secondary treatments to meet stringent safety requirements.
- Chemical flame retardants: Topical finishes can be applied to the fiber or fabric surface. These chemicals interfere with the combustion process, either by releasing gases that suppress the flame or by forming a ‘char’ layer that insulates the material from further heat.
- Fiber blending: In industrial applications, lyocell is often blended with inherently flame-resistant (FR) fibers, such as aramids or modacrylics. These blends leverage the comfort of lyocell while meeting the high ignition thresholds required by safety standards.
- Fabric construction: The density and weave of the fabric also play a role. Tighter, heavier weaves are generally slower to ignite than loose, sheer weaves, as they provide less oxygen access to the burning surface.
Thus for those utilizing lyocell in apparel or industrial workwear, ISO 6940 provides the objective data necessary to ensure compliance with global safety regulations. While lyocell’s cellulosic nature makes it naturally "easy to ignite" compared to engineered synthetic flame-resistant fibers, understanding this baseline allows manufacturers to apply the correct engineering controls, be it through chemical treatment or strategic blending to produce garments that are both sustainable and safe.