Silk has long been regarded as the “queen of fibers,” admired for its unmatched beauty, smoothness, and shine. From royal garments to contemporary couture, silk remains one of the most elegant natural fibers on Earth. But before this precious material reaches the loom, it undergoes a vital stage known as the degumming process, which reveals silk’s true softness and luster.
In this article, we’ll explore what silk is, its structure and composition, and dive deep into how silk degumming works, including modern eco-friendly methods that make silk production more sustainable.
What is Silk?
Silk is a natural protein fiber produced by the Bombyx mori silkworm. During its cocoon stage, the larva secretes a liquid protein that solidifies into continuous filaments when exposed to air. These filaments are later unwound to produce raw silk threads.
The art of silk production, called sericulture, originated in ancient China over 5,000 years ago. Today, silk is produced in many parts of the world, but Asian countries—especially China and India—remain leading producers.
Chemical Composition of Silk
Silk fibers are primarily made up of two proteins:
- Fibroin: The inner structural protein, responsible for silk’s strength and sheen.
- Sericin: The outer gummy substance that holds the filaments together within the cocoon.
Typical Composition of Raw Silk:
- Fibroin – 70–75%
- Sericin – 20–25%
- Wax, pigments, and mineral salts – 1–5%
The fibroin core gives silk its tensile strength and glossy finish, while sericin provides protection to the worm during metamorphosis. However, sericin also makes the silk stiff and dull—hence, it must be removed through degumming.
Why the Degumming Process is Essential
When raw silk is produced from cocoons, it appears coarse, yellowish, and somewhat rigid. This is because the sericin coating prevents light reflection and flexibility. The purpose of silk degumming is to remove this sericin layer while keeping fibroin intact.
Objectives of Degumming:
- Eliminate sericin and impurities.
- Enhance luster, softness, and elasticity.
- Improve dye absorption for vibrant colors.
- Prepare silk for weaving, finishing, and garment production.
A well-degummed silk fiber is smooth, glossy, and flexible, showcasing the luxurious texture we associate with fine silk.
How the Silk Degumming Process Works
The degumming process involves treating silk with water, soap, mild alkalis, enzymes, or acids to dissolve the sericin layer. The challenge is to remove sericin completely without damaging the fibroin core.
Main Steps in Silk Degumming:
- Soaking:
Raw silk is soaked in warm water to soften sericin and remove dirt or oil. - Boiling or Scouring:
The silk is boiled in a soap or enzyme bath under controlled temperature and pH. Sericin dissolves gradually, freeing the fibroin. - Rinsing:
The silk is washed thoroughly to remove residual sericin and chemicals. - Neutralization:
If alkalis are used, a mild acid rinse (like acetic acid) restores the natural pH. - Drying:
Silk is carefully dried at low temperatures to preserve shine and texture.
Main Methods of Degumming Silk
Different degumming methods are used depending on the quality required and environmental considerations.
1. Soap and Alkali Degumming (Traditional Method)
This is the oldest and most common process. Raw silk is boiled in a solution of olive oil soap and a weak alkali such as sodium carbonate (Na₂CO₃).
Typical Conditions:
- Soap: 1–2% on weight of fabric (owf)
- Sodium carbonate: 0.1–0.5% owf
- Temperature: 95–100°C
- Duration: 30–60 minutes
The soap emulsifies the sericin, while alkali helps break it down. Repeating the treatment ensures full removal.
Pros: Effective, simple, produces bright silk.
Cons: Can cause yellowing and high wastewater load if not controlled.
2. Enzymatic Degumming (Eco-Friendly Process)
Enzymatic degumming uses biological enzymes such as proteases or sericinases to selectively break down sericin without damaging fibroin. It’s one of the most sustainable methods today.
Typical Conditions:
- Enzyme: 0.5–2% owf
- Temperature: 45–60°C
- pH: 8–9
- Duration: 30–90 minutes
Pros:
- Biodegradable and non-toxic.
- Maintains fiber strength and whiteness.
- Reduces pollution and water consumption.
Cons:
- Enzyme cost is higher.
- Requires precise control for complete degumming.
3. Acid Degumming
Acids such as citric or formic acid are sometimes used to hydrolyze sericin.
Typical Conditions:
- Acid concentration: 1–3%
- Temperature: 60–80°C
- Duration: 30–45 minutes
This method is effective for partial degumming or specialty silk finishes. Overexposure can weaken fibroin, so timing is crucial.
4. High-Temperature Water Degumming (Autoclave Method)
This modern process uses pressurized hot water at 120–130°C. The high temperature dissolves sericin without chemicals, making it a clean and rapid option, though it requires specialized autoclave equipment.
5. Ultrasonic and Microwave-Assisted Degumming
Advanced technologies like ultrasound and microwaves enhance degumming by improving water penetration and molecular vibration. They accelerate sericin removal even at lower temperatures.
Advantages:
- Energy-efficient and fast.
- Reduces chemical usage.
- Retains silk’s natural properties.
Factors Influencing Degumming Quality
- Temperature: Too high can damage fibroin; too low leaves sericin residues.
- pH Level: Strong alkalinity removes sericin faster but risks silk weakening.
- Duration: Extended boiling may lead to weight loss or fiber breakage.
- Agitation: Ensures uniform exposure and prevents patchy degumming.
- Type of Silk: Mulberry, tussar, or eri silks vary in sericin content, so conditions must be adjusted.
Properties of Silk After Degumming
Once the sericin layer is removed, silk transforms remarkably:
- Soft and smooth touch.
- High luster and light reflection.
- Better dyeability due to exposed amino groups in fibroin.
- Improved flexibility and drape.
- Enhanced comfort through better moisture and air permeability.
These features make degummed silk ideal for fine clothing, upholstery, and high-end accessories.
Sustainability and Environmental Impact
Traditional degumming methods, especially soap-alkali, generate large volumes of organic wastewater containing dissolved sericin. To make silk production greener, the industry is adopting eco-innovations:
- Enzyme-based and low-temperature degumming for lower pollution.
- Water recycling systems to reduce waste.
- Ultrasonic or microwave degumming to save energy.
- Sericin recovery for reuse in cosmetics, pharmaceuticals, and biopolymers — turning waste into value.
Conclusion
The beauty of silk doesn’t come naturally — it’s crafted through precise science and artistry. The degumming process plays a pivotal role in revealing the silk’s natural sheen, softness, and brilliance.
From traditional soap-alkali boiling to cutting-edge enzyme and ultrasonic methods, degumming continues to evolve with technology and sustainability. As the world moves toward greener textile practices, silk remains a shining example of how ancient craftsmanship can harmonize with modern innovation.
Silk, after all, is not just a fiber — it’s a story of transformation, refinement, and timeless elegance.