Waterproofing Finishing in Textile
Md. Jasimuddin Mandal
Govt. College of Engineering and Textile Technology,
Serampore, India.
Email ID: jasimmandal@gmail.com
What is Waterproofing?
The water repellency of textile fabrics may be broadly classified into two types, waterproof and water resistant. Often, the word ‘rain’ or ‘shower’ is used commercially instead of ‘water’ (e.g., shower-resistant, rainproof, etc.). The term ‘water repellent’ is actually a relative term because there is always some attraction between a solid and a liquid in contact, though the force of attraction may be small.
The term ‘waterproof’ is normally taken to represent the conditions in which a textile can prevent the absorption of water and also the penetration of water into its structure. Waterproofing is nothing but preventing the passage of both air and water through a fabric. Fabrics for waterproofing by application of coating materials must generally be prepared in a similar manner as for water repellent finishing. It is important that the fabric surface is smooth and hence most fabrics are singed to remove protruding surface fibers that could either become detached by the action of the doctor knife in coating, or subsequently penetrate through the coating surface to give an uneven coated surface and provide sites in the fabric surface that could promote wicking of liquids.
Waterproof materials are currently used in the three major textile areas (clothing, home and outdoor products and technical textiles). There are a large number of possible applications, from rain garments to medical and military equipment. Regardless of the applications for which waterproofness is the determinant function, the complexity of the conditions during use requires the multicriterial design of the fabric structure and its testing to ensure a high number of functional characteristics such as: vapour permeability, tensile strength, abrasion resistance, flexural strength (repeated cycles), resistance to low and high temperatures, resistance to light, chemical resistance and more. Waterproofness is measured as the hydrostatic pressure needed to penetrate the waterproof fabrics.
Purpose of Waterproofing:
For certain uses such as Tarpaulin, Umbrella cloth, Rain coat fabrics etc., it is required to give this type of finish as these types of fabric are generally used against the air and water in the normal life. So they should have some property to prevent both air and water passing through them.
This finish makes the wearer feel uneasy and uncomfortable as the air circulation is not there.
Principle of Waterproofing:
A film on the surface of the fabric should be formed for the prevention of air and water.
When a uniform coating of suitable substances such as rubber is produced on the surface of a fabric, the interstices between the warp and weft yarns are blocked by the continuous film or substance and both water and air not pass through the treated fabrics.
It is a chemical and property giving finish.
Requirements:
The fabric should not become unnecessarily stiff and the fabric should have soil release or soil repellent property.
The finish should not alter the fastness properties or dyed material, feel, strength etc., of the fabric.
Method:
By two methods it can be carried out:
- Methods by which hydrophobic substances are deposited on the cloth.
- Methods by which the fabric itself becomes hydrophobic.
Chemicals Used:
- Vulcanized natural rubber.
- Oxidised oils of varnishes.
- Polyvinyl chloro acetate.
- Polyvinylidine chloride.
- Cellulose acetate.
- Cupprammonium hydroxide solution.
Process:
A. The simplest method of waterproofing is the coating of fabric with rubber as a thin film.
Disadvantages:
- Unwanted stiffness and harshness.
- Fabric becomes harsh and brittle.
B. The application of natural oil will also produce this finish.
Advantage:
- No cracks or brittleness.
Disadvantage:
- It is not permanent.
C. Coating of water impermeable substances like pitch, asphalt and molten waxes produce waterproofing.
Advantage:
- It will give excellent proofing.
Disadvantage:
Many desirable properties of the fabric will be destroyed.
D. Using synthetic resins we can produce this finish.
Example: Polyvinyl chloro acetate, Cellulose acetate, Polyvinylidine chloride.
E. Water proofing with wax emulsion.
- It can be applied on cotton, linen, wool, silk fabrics.
- Aluminium acetate is used along with the wax emulsion.
There are two steps involved in producing this finish.
1st step:
Wax emulsion: 1-3 kg
Water: 50 litres
Pad the material with wax emulsion solution.
2nd step:
In wet condition,
Aluminium acetate: 1- 3 kg (12˚ Tw)
Water: 50 litres
Impregnate the fabric and squeeze thoroughly.
Then dry the fabric in a stenter or on a drying range at 110˚C to 120˚C.
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Founder & Editor of Textile Learner. He is a Textile Consultant, Blogger & Entrepreneur. He is working as a textile consultant in several local and international companies. He is also a contributor of Wikipedia.
