Viscose from bamboo is a type of rayon, a manufactured fiber derived from plant cellulose, but it is not a natural fiber like cotton or linen. The question of its toxicity arises from the highly chemical process required to transform the tough bamboo fibers into a soft textile. To determine the truth behind claims of toxicity, it is necessary to examine the manufacturing method, the chemicals involved, and the state of the final product. Toxicity concerns focus primarily on the production stage, impacting factory workers and the environment, rather than the consumer wearing the finished fabric.
How Viscose is Created from Bamboo Pulp
The vast majority of bamboo fabric is produced using the viscose method, a chemically intensive process often called the “xanthate” process. This method begins by harvesting and crushing raw bamboo stalks into a cellulose-containing pulp. The pulp is then steeped in a bath of strong alkali, typically a highly concentrated solution of sodium hydroxide (NaOH), also known as caustic soda.
The sodium hydroxide breaks down the bamboo structure to form alkali cellulose, which is then pressed, shredded, and aged. The next step introduces carbon disulfide (\(\text{CS}_2\)), a highly volatile and toxic chemical. This compound is mixed with the alkali cellulose to produce cellulose xanthate, a crumbly, orange-yellow substance.
The cellulose xanthate is dissolved in a milder solution of sodium hydroxide, creating a thick liquid known as viscose. This solution is forced through tiny nozzles, called spinnerets, directly into a bath of sulfuric acid (\(\text{H}_2\text{SO}_4\)). The acid instantly neutralizes the alkaline solution, regenerating the cellulose into solid filaments that are spun into yarn.
Health Risks Associated with Carbon Disulfide
The primary toxicity concern in viscose production centers on carbon disulfide (\(\text{CS}_2\)), a known neurotoxin. This chemical poses severe occupational hazards to factory workers who handle it during the xanthation step. Chronic exposure to \(\text{CS}_2\) is strongly linked to neurological damage, specifically peripheral neuropathy, which affects nerves outside the brain and spinal cord.
\(\text{CS}_2\) exposure can also lead to serious cardiovascular problems, including an increased risk of coronary heart disease. Chronic inhalation of the chemical may disrupt the endocrine system and cause reproductive harm. Female workers have been shown to experience a higher frequency of menstrual disorders and an earlier average age of menopause due to exposure.
The environmental impact is significant, as factories without stringent closed-loop systems release \(\text{CS}_2\) and other chemical byproducts into the air and waterways. Corrosive chemicals, including sodium hydroxide and sulfuric acid, also present risks of severe skin burns and eye damage upon direct contact with workers.
Safety of the Finished Fabric for Consumers
The finished bamboo viscose fabric is generally considered safe to wear under normal conditions. Although the production process is highly toxic, the final regenerated cellulose fibers go through extensive washing and finishing steps. This treatment is designed to remove chemical residues, resulting in a fabric that contains negligible amounts of the original toxic processing chemicals.
The safety of the final product depends highly on the quality control and regulations of the manufacturing facility. If production is not well-regulated, trace amounts of chemicals like carbon disulfide can potentially remain in the finished garment. While the risk to an adult wearer is low, micro-exposures to residual toxins could be more harmful to vulnerable populations, such as infants and toddlers.
Skin irritation from bamboo viscose is possible but is rarely due to residual \(\text{CS}_2\) or caustic soda. Adverse skin reactions are most often attributed to the dyes or other finishing agents applied to the fabric. Consumers can seek certifications like OEKO-TEX®, which verify that the final textile product is free from harmful chemical concentrations.
Lyocell Production as a Less Toxic Method
An alternative to the standard viscose method is the Lyocell process, a significantly less toxic way to convert bamboo pulp into a regenerated cellulose fiber. This method utilizes a different organic solvent, N-methylmorpholine N-oxide (NMMO), to directly dissolve the cellulose. Unlike the chemicals used in the viscose process, NMMO is considered non-toxic and is not associated with the severe health hazards linked to carbon disulfide.
The Lyocell process is characterized by its closed-loop system, which is a major environmental advantage. In this system, the NMMO solvent is captured, purified, and recycled for reuse, often with a recovery rate of up to 99.8 percent. This high recovery rate means virtually no harmful chemicals are released into the environment, making the process safer for workers and more sustainable.
While the final fabric is chemically the same regenerated cellulose fiber as bamboo viscose, the cleaner manufacturing process is the key difference. Lyocell-produced bamboo fabric, often branded as Tencel, provides a safer alternative to the standard viscose method. This process addresses core toxicity concerns by eliminating the need for highly volatile and corrosive chemicals.