Dyeing and Finishing Hemp

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:

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.

Hemp garments can be dyed or  natural color. Natural is not really a color; it is simply the absence of dyes and is basically the natural beige color of the hemp fibers after processing. This is why hemp garments that are a  natural color can vary greatly in color.

Chemical Methods.

Chlorine is often used to clean and prepare the garments for dyeing and then synthetic dyes are used. 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 used in U.S. and Europe 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 company to company and country to country.

Mercerization is sometimes used to prepare garments for dyeing because it increases luster, strength and an affinity to accept dyes. Mercerization is a treatment that swells the fibers of yarns by immersing the yarns in sodium hydroxide, which is a caustic soda, and then neutralizing them with acid.

Organic Methods.

For hemp to be considered organic, the finishing of the fabrics is done largely without the use of synthetic chemicals. If their use becomes necessary only those chemicals which meet strict ecological criteria are employed. New ecologically safe technologies in dyeing and finishing have been developed such as air finishing technology that uses strong blasts of compressed air to soften hemp fabric in the finishing stage.

Sometimes a starch sizing might be used before dyeing and finishing. Sizing is a generic term for compounds applied to fabrics to improve their smoothness, abrasion resistance, stiffness, strength, weight of luster. Starch is generally used in organic processing and enzymes are often used to desize natural sizing. Hydrogen peroxide bleach is used to prepare the fabric for light or bright color dyes.

Natural dyes can be made from plants, earth clays, and even insects. 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.

Low impact and fiber-reactive dyes are made from natural components that are water soluble with a fixation ratio of at least 70%. They have no heavy metal content. The low impact dye process reclaims heat used in the dyeing process and has on-site water filtration to cleanup waste waters used in the dyeing process. Any additives used in the dye bath must be biodegradable.

The following eco-friendly process might be used to finish the hemp fabric. Note: these processes might also be used on other natural fabrics.

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.

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.

Brushing: Utilizes multiple brushes or other abrading elements to raise fiber ends thus producing a nap on surface of fabric.

Sanding or 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.

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.