Denim Enzyme Washing: Achieving a Worn Look Sustainably

Enzyme Wash

Denim Enzyme Washing: Achieving a Worn Look Sustainably

Denim enzyme washing, also known as "bio-stoning," is a textile finishing technique that uses enzymes to give denim a unique look and feel. This process can achieve effects similar to traditional stone washing, resulting in a softer feel or a popular vintage, weathered appearance. The weathered effect is primarily produced by using cellulase enzymes, often combined with mechanical agitation like steel balls. These enzymes work by breaking down fabric fibers and releasing dye, leading to a faded look and a softer texture. Enzyme washing is particularly effective for indigo denim, often yielding better and more consistent results, including a whiter and bluer color contrast, compared to traditional stone washing. This technique relies on biotechnology, specifically bioprocessing or bio-finishing. While enzyme washing can be more costly than stone washing, its benefits often outweigh the expense.

In today's world, there's a growing emphasis on sustainable and eco-friendly practices. Enzymes used in this process are fully biodegradable and non-toxic, making them an increasingly important solution. This enzyme treatment has successfully replaced various chemical and mechanical treatments, leading to improved fabric quality and comfort.

A Brief History of Enzyme Washing

The environmental impact of traditional stone washing in the early 1980s spurred the search for more sustainable alternatives. The first enzyme wash method was introduced in Europe in 1989, with its adoption spreading to the United States in subsequent years. Notably, Novozymes developed a spray technique that applies enzymes directly to denim fabric, significantly reducing water consumption in the enzyme washing process. This innovation highlights why enzyme washing is now an integral part of the textile industry.

Advantages of Enzyme Washing

Using cellulase enzymes offers numerous benefits:

Sustainability: Cellulase enzymes are a more sustainable alternative to stone washing (which uses pumice stones) and acid washing (which requires excessive water). Traditional methods produce more wastewater and residual pumice stones that need to be eliminated.
Reduced Fabric Damage: Enzyme treatment minimizes damage to the denim fabric.
Water Conservation: The process requires less water as it doesn't necessitate multiple washes, leading to less waste and reduced wear on machinery. In short, it's a highly sustainable and eco-friendly process.
Recyclability: Enzymes can be recycled and reused, further enhancing sustainability.
Improved Aesthetics and Feel: Enzymatic treatment results in denim and garments with a softer feel and a better overall appearance.
Increased Productivity: Eliminating pumice stones boosts the washing load capacity.
Efficiency: Cellulase enzymatic treatment is more efficient because it removes the time-consuming step of cleaning stone fragments from denim jeans.
Fewer After-Washes: The number of subsequent washes needed is significantly reduced.

Disadvantages of Enzyme Washing

One primary disadvantage of enzyme washing is back-staining, where dye released during enzymatic activity can redeposit on the denim fabric. While some denim wash specialists argue that this effect is often undetectable to the average user, garments may require rigorous washing to remove back-staining.

The Enzyme Washing Process in Detail

Temperature is a critical factor in the enzyme treatment process, as enzyme activity is highly sensitive to temperature ranges. Enzymes become significantly less active below $1 5^{\circ} C$ and above $6 0^{\circ} C$ . Within the optimal range, increasing temperature can enhance color fading by hydrolyzing more fibers, which are then removed through abrasion.

Mechanical action also contributes to the color fading effect in enzyme washing. Fabric treated without agitation may result in better color fading and a softer feel, as weakened fibers are not removed, leading to a more hairy or fuzzy surface. Conversely, strong mechanical agitation leads to an effect called biopolishing, where weakened fibers are thoroughly removed, producing a smoother and cleaner surface. This also results in a more faded shade as dye particles are removed along with the fibers.

Prolonged treatment time is necessary for further cellulose degradation and increased color fading. Weak dye particles desorb and are weakly absorbed into the fabric or garments. Longer treatment with cellulase heavily hydrolyzes cotton fibrils, producing fabric that is less fuzzy than the original.

Flow Chart of Enzyme Wash Process

The enzyme treatment process involves the hydrolysis of cellulase enzymes, which catalyzes the loosening of surface fibers. These loosened fibers are then removed through abrasion, either fabric-to-fabric or fabric-to-stone, during the washing process. Temperature and pH are crucial and must be specific to the enzyme used. Typically, a pH of $6 - 7$ is maintained for neutral enzymes and $4.5 - 5.5$ for acidic enzymes, often by adding acetic acid ( $C H_{3} COO H$ ). An enzyme dose of $2 - 4$ grams per liter is generally sufficient. Denim treated with enzymes often exhibits a more uniform color when no stones are added.

Here's a step-by-step breakdown of the enzyme wash treatment:

Denim fabric or garment loading
Desizing or starch-washing removal
Rinse two times
Insertion of enzyme for washing
Adjusting enzyme pH
Setting temperature according to enzyme type
Tumbling wash time (depends on desired shade/effects)
Rinse two times
Softening agent application
Unloading
Drying process

The enzyme wash process generally consists of four basic steps: Desizing, Bio-abrasion, Back wash, and optional Additional Bleaching.

1. Desizing

This initial step removes dust and other impurities from garments or denim fabric and acts as a wetting agent.

Water L:R (Liquor Ratio) = $1 : 5$
Temperature: $5 0^{\circ} C$ to $7 0^{\circ} C$
Desizing agent: $0.5$ to $2$ mg/liter
Wetting agent: $0.2$ to $0.5$ mg/liter
Duration: $10$ to $15$ minutes
Follow with a second wash with cold water.

2. Bio-abrasion

In this step, enzymes are added to remove color and achieve faded denim. If more fading is desired, stones can be added at half the volume of the garments.

Water L:R = $1 : 5$
Enzyme: $0.6%$ to $2%$ (depending on desired results)
Maintain pH: $4.5$ to $5.5$
Anti-back staining agent: $2$ to $2$ mg/liter
Temperature: $5 0^{\circ} C$ to $5 5^{\circ} C$
Time: $50$ to $95$ minutes
Follow with a second wash with cold water.

3. Back Wash

This step removes all deactivated enzymes and released coloring material from the denim or garments. The fabric is then dyed again through a rinse wash.

Water: $1 : 5$
Anti-back staining agent: $1$ to $3$ mg/liter
Soda ash: $0.3$ mg/liter
Temperature: $7 5^{\circ} C$ to $8 5^{\circ} C$
Duration: $5$ to $10$ minutes
Normal rinse.

4. Additional Bleaching (Optional)

This step is performed if extra fading is needed. Chemicals are used to prevent a yellowing effect on the denim.

Water: $1 : 5$
Sodium metabisulfite (meta): $1$ to $2$ mg/liter
Sodium hypochlorite: $5$ to $5$ mg/liter
Temperature: $4 5^{\circ} C$ to $5 5^{\circ} C$
Duration: $10$ to $20$ minutes
Normal rinse.

Finally, the garment is loaded into a hydro extractor and then to a dryer.

Frequently Asked Questions

How are enzymes used in the jeans industry? Enzymes break down cellulose fiber ends on the jeans' surface and loosen dye particles, creating a vintage or weathered appearance. These enzymes are used in water at specific temperatures and pH levels to achieve the desired faded effects.
What chemicals are used in denim washing? Common chemicals used in denim washing include anti-back staining agents, detergents or soaping agents, soda ash, hydrogen peroxide, bleaching agents, laundry enzymes, sodium metabisulfite (meta), and sodium thiosulfate (hypo).
How is enzyme washing done? Enzymes degrade cellulose surface fibers, causing them to loosen along with dye particles. These loose particles and fibers are then removed by abrasion between the fabric itself or between the fabric and stones during the enzymatic washing process. This treatment relies on the hydrolysis of cellulase enzymes, which catalyzes the loosening and removal of surface fibers through further abrasion. Temperature and pH are precisely controlled for the specific enzyme used.
Why is acetic acid used in enzyme baths? Acetic acid ( $C H_{3} COO H$ ) is used to neutralize the pH of the garments or fabric, controlling the pH value during the wash process. The temperature and pH are kept specific to the enzyme's requirements.