Dyeing / Converting
Checklist for Environmental Finishing of Textiles
The impact on the environment by the process of dyeing textiles vary greatly around the world. Many developing countries have no regulations regarding the methods of dyeing, the types of dyes used, and the disposal of waste. In the United States, and especially California, environmental laws regulate the types of dyes and dyeing methods used by commercial dye houses.
There is a lot of confusion regarding the dyeing of textiles and what is to be considered "environmental". When determining the measure of harm done to the environment by the dyeing process, one must take into account three elements:
1. The actual dye used and whether or not it has toxic properties.
2. The method of dyeing and how much energy is required.
3. How much dye gets into the fabric and the method of disposal of excess dye and chemicals.
Many people mistakenly believe that fabrics dyed using natural dyes will be less harmful to the ecosystem than conventional dyeing methods, but this is not always the case. The process of extracting pigment molecules from nature may require more energy and harmful chemicals than synthesizing them in the lab. In some dyes, the actual pigment molecules are the same, whether they originated in nature or the lab.
Dyes are molecules that absorb and reflect light at specific wavelengths to give our eyes the sense of color. With natural dyes, the molecules are extracted from natural substances such as plants, animals, or minerals. Synthetic dyes are produced in a laboratory and synthesized from other chemicals. Some synthetic dyes contain heavy metals and other elements that react negatively if released in the environment. Newer synthetic dyes tend to have less harmful elements.
The method of dyeing also plays a factor. Harmful chemicals may be added to the dye bath to help the dye molecules bind to the fibers of the fabric. Also the amount of energy used to run the dye machine in the form of mechanical action and heat vary greatly from region to region.
The handling of waste is probably the biggest factor to determine how detrimental the process is to the environment. Is the excess waste filtered and neutralized before it is put down a drain? Or is it just dumped into a river? Once again, environmental laws play an important role with developing countries usually using the cheapest and most convenient method of disposal.
The following methods of finishing textiles generally refer to modern methods used in industrial dye houses. We have listed which methods do not cause harm to the environment and are used by Hemp Traders to convert their fabrics.
Prepare for Dyeing
No Chlorine bleached is used. Hydrogen Peroxide bleach is used on light or bright colors only.
Enzymes are used to desize natural sizing. Sizing is a generic term for compounds applied to fabrics to improve their smoothness, abrasion resistance, stiffness, strength, weight, or luster. (Starch is generally used to achieve this effect.)
Non-biodegradable synthetic sizing is reclaimed after the desizing process.
Scouring (cleaning) agents used are biodegradable. No solvent scouring.
No Mercerization, which is a treatment on fabric that swells the fibers of the yarns in a strong alkali. Piece goods, normally under tension, are immersed in sodium hydroxide (caustic soda) and then are neutralized in acid. This process causes a permanent swelling of the fiber which increases luster, strength and an affinity for dyes.
Low impact dyes or dye stuff is:
Natural components are water soluble
Fixation is 70% or more
No heavy metal content
Low impact dye process follows these methods:
Heat reclamation on site.
Water filtration on site.
No salt added to dye bath.
Additional auxiliaries and additives in the dye bath are biodegradable.
The following mechanical finishes are acceptable:
Tentering: Process for holding a fabric to desired width during drying. A tenter frame machine holds the fabric firmly at the edges by pins or clips as it advances through a heated chamber. This is generally the final step in finishing, giving the fabric its finished appearance.
Sanforized: A trademarked control standard of shrinkage performance. A method of compressive shrinkage involving feeding the fabric between a stretched blanket and a heated shoe. When the blanket is allowed to retract, the cloth is physically forced to comply. Leaves fabrics with a residual shrinkage of not more than one percent.
Compacting: A permanent treatment by which heat and pressure shrink a fabric so that resulting texture is crepey/crinkled and bulky.
The following heat finishes are acceptable:
Calendering: Fabric is passed between heated cylinders under pressure to produce a flat, glossy, smooth, high luster surface.
Steam Chamber: Stabilizes the colors of dyes after printing and dyeing processes. Process where steam is passed through fabric. This partially shrinks and conditions the fabrics when applied, especially on wovens.
Heat Shrinkage: Improves shrinkage resistance and shape retention of fabric and often other desirable properties, such as wrinkle resistance by means of either dry or moist heat.
Singeing: Burning off protruding fibers from fabric by passing over flame or heated plates. Imparts the smooth surface necessary for printing and clear finishes.
The following aesthetic mechanical finishes are acceptable:
Brushing: Utilizes multiple brushes or other abrading elements to raise fiber ends thus producing a nap on surface of fabric.
Sanding/Sueding: Process by which fabric passes over rapidly revolving rollers covered with abrasive paper.
Napping: Raising the surface fibers of fabric by means of passage over rapidly revolving cylinders covered with metal points/fine wire brushes or teasel (plant) burrs.
The following chemical finishes are acceptable:
Enzyme Washing: The use of an enzyme (organic catalyst used to speed up a chemical reaction) to produce stone washed effects on fabrics. This process id less damaging to fabrics than actual stone washing and produces a highly desirable soft hand.
Biopolishing: Where cellulose (any group of enzymes that degrade cellulose) enzymes hydrolyze the fiber surfaces. This treatment improves hand, reduces fuzz and pilling and gives clearer finish. Biopolishing agents should adhere to the following requirements to be considered environmental.
Softeners used are biodegradable.
No Formaldehyde based resins.
No undisclosed chemical finishes.
No acid wash/No stone wash.