Water Repellent Finish
Course name: Wet processing II
Course Code: WPE 311
of water
# Mechanism
repellency.
# How due action fluorocarbon release soil and repel water
can
simultaneously ?
Water Repellent:
Water repellency is a quality of textile materials that prevents water droplets from spreading on the surface.
This is achieved by applying hydrophobic substances onto the fabric, creating a surface that resists water
absorption. Unlike creating a solid film, the process of making fabrics water repellent involves depositing
hydrophobic materials without forming a continuous layer.
Properties of Water Repellent fabric:
• Water repellent fabrics maintain their breathability due to their open pores, allowing water vapor and air to pass
through. However, under sufficiently high hydrostatic pressure, such as during heavy rain, water can still
penetrate the fabric. Importantly, the weave structure of the fabric, particularly the interstices (gaps) between
warp and weft threads, remains mostly unchanged or only slightly modified.
• This property makes water repellent finishes suitable for apparel applications, particularly for summer dress
materials. Despite repelling water, these fabrics are comfortable to wear in warmer weather as they allow air
circulation and moisture vapor to escape. This balance between water resistance and breathability makes water
repellent textiles a practical choice for creating clothing that offers protection without sacrificing comfort.
Application of Water Repellent fabric:
• Outdoor Apparel: Rain jackets, hiking pants etc.
• Outerwear: Coats, parkas, and winter jackets etc.
• Active Wear: Athletic clothing, workout gear, and sportswear.
• Footwear: Hiking boots, sneakers etc.
• Umbrellas, Backpacks and Bags.
• Camping Gear: Tents, sleeping bags, and camping equipment.
• Medical and Protective Clothing: Medical gowns, protective gear etc.
• Home Textiles: Tablecloths, cushions, and outdoor furniture covers etc.
• Car Upholstery, luggage and travel gear.
Difference between Waterproof and water Repellent finish ⑬
. Water Proof Water Repellent
. 1. Pores of interstices filled. 1. Pores of interstices open.
2. Completely impervious to water. 2. Water permeability is small.
3. Completely impervious to air. 3. Air permeable
4. Impervious even at high hydrostatic pressure. 4. Permeable by its own property.
5. Fabric stiff, not pliable 5. Fabric pliable.
6. Permanent finish. 6. Durable and renewable finish.
7. A uniform coating is applied on the surface of 7. Some hydrophobic material is deposited on the
material by using rubber, PU, PVC etc. surface, no continuous film is produced.
Physical Chemistry of Wetting:
• Wetting refers to a liquid's ability to maintain contact with a solid surface due to intermolecular interactions.
It's determined by the balance between adhesive forces (liquid to solid) and cohesive forces (within the
liquid). Adhesive forces cause liquid drops to spread on a surface, while cohesive forces make them ball up.
• The wetting of a solid by a liquid is explained by the contact angle (θ) formed between the solid's surface and
the tangent to the liquid-air interface.
• A liquid drop's contact angle signifies its wetting behavior. A contact angle of 0° indicates complete
spreading, while 180° indicates a spherical shape with no contact. When considering the formation of water
droplets, various forces at the interfaces of water, fiber, and air come into play. The equilibrium shape of the
water layer on the fiber is influenced by three main forces:
Physical Chemistry of Wetting (cont..)
• Surface tension between water and air vapor (γLV): This force reflects the attraction between the water drop and
the surrounding air vapor.
• Surface tension between the textile and the liquid (γTL): This force describes the interaction between the textile
material and the liquid.
• Surface tension between the textile and air vapor (γTV): This force represents the interaction between the textile
surface and the air vapor.
Physical Chemistry of Wetting (cont..)
• In the case of a liquid drop on a smooth solid surface, equilibrium forces are considered, excluding the
influence of gravity. This equilibrium is described by the Young equation, which relates the contact angle
(θ), the surface tensions (γ), and the forces acting at the interfaces. The Young equation helps explain how
the interplay of these forces determines whether a liquid drop spreads or forms a spherical shape on a solid
surface.
• Mathematically, the Young equation is given by:
γTV = γTL + γLV * cos(θ), where, 0˚ ≤ θ ≤ 180 ˚
• If the adhesive forces are stronger, the liquid will spread more and have a smaller contact angle.
• If the cohesive forces are stronger, the liquid will bead up and have a larger contact angle.
Relation between contact angle and wettability
Mechanism of Repellency:
• Repellent finishes operate by reducing the free energy at fiber surfaces, influencing the interaction between
liquids and fibers. If adhesive forces between a fiber and a liquid drop are stronger than the cohesive forces
within the liquid, the drop will spread. Conversely, if adhesive forces are weaker, the drop won't spread.
• Surfaces with weak interactions with liquids are termed low energy surfaces. For effective repellency, the critical
surface energy (or tension) of such surfaces must be lower than the surface tension of the liquid being repelled.
• Water has higher surface tension (73 mN m–1) compared to oils (20–35 mN m–1). Oil repellency finishes using
substances like fluorocarbons (with low surface energy, γC = 10–20 mN m–1) can achieve water repellency due
to their strong repellent action against liquids with lower surface tensions. However, products like silicones (with
higher surface energy, γC = 24–30 mN m–1) may repel water but not oils.
Different methods to introduce low energy surfaces to textiles:
• Mechanical Incorporation: One approach involves mechanically introducing water-repellent products into or
onto the fiber and fabric surfaces. For instance, paraffin emulsions can be used for this purpose.
• Chemical Reaction: Another method is chemically reacting the repellent material with the surface of the fibers.
Fatty acid resins can be chemically bonded to the fiber surface to confer water repellency.
• Formation of Repellent Films: This can be achieved using substances like silicone and fluorocarbon products,
which form a protective layer to repel water and other liquids.
• Special Fabric Constructions: Specific fabric constructions designed for repellency include stretched
polytetrafluoroethylene films (such as Goretex), films made from hydrophilic polyester (like Sympatex), and
microporous coatings using hydrophilic modified polyurethanes.
Classifications of water repellent chemicals:
Water repellent chemicals can be categorized into three main groups:
• Non-Durable: These repellents provide temporary water resistance and are often made from substances like
paraffin wax-aluminium acetate emulsion. They offer a short-term effect.
• Semi-Durable: Semi-durable repellents offer intermediate water resistance and are typically composed of
wax or salt solutions. They provide a moderate level of protection against water.
• Durable: Durable repellents offer long-lasting water resistance. They include compounds like pyridinium
compounds, Melamine resins, stearamide compounds, and Silicone compounds. These chemicals provide a
strong and lasting shield against water.
Each category offers different levels of water repellency and durability, allowing for various applications
based on the desired level of protection and longevity.
Problems associated with repellent finishes:
Repellent finishes can bring about certain issues in fabric properties, including:
1. Static Electricity: Repellent finishes might lead to static buildup in fabrics.
2. Poor Soil Removal: Aqueous laundering (washing with water) may become less effective at removing
dirt and stains from fabrics treated with repellent finishes.
3. Greying: Soil redeposition, known as greying, can occur during aqueous laundering, causing fabrics to
look less clean.
4. Stiffer Fabric Feel: The texture of the fabric can become stiffer or less comfortable to the touch.
5. Increased Flammability: Repellent finishes might contribute to higher flammability in fabrics.
However, repellent finishes can also have positive effects on fabric properties, such as:
Better Durable Press: Improved resistance to wrinkles and creases in the fabric.
Faster Drying and Ironing: Treated fabrics may dry more quickly and require less effort when
ironing.
Enhanced Chemical Resistance: Increased protection against acids, bases, and other chemicals.
# Comparative officiency of silicone and paraffin water repellents with mechanism
.
Repellent Chemistry
Paraffin repellents:
• It is the earliest types of water repellents which lack oil repellency.
They are commonly formulated as emulsions containing aluminum or
zirconium salts of fatty acids, often stearic acid.
• These additives enhance the adhesion of the finish to polar fiber
surfaces by creating junctions between polar and non-polar regions, as
depicted in Figure. In this arrangement, the paraffin component of the
repellent is drawn to hydrophobic areas, while the polar segments of
the fatty acid are attracted to the metal salts present on the fiber
surface. Fig: Fatty acid metal salt. A, hydrophobic
interactions; B, polar interactions ; C, Fiber
surface.
Advantages of Paraffin Repellents:
1. Application Versatility: They can be applied using both exhaustion and padding methods.
2. Compatibility: Paraffin repellents work well with various types of finishes.
Disadvantages of Paraffin Repellents:
3. Reduced Permeability: These repellents lead to lower air and vapor permeability in treated fabrics.
4. Limited Durability: They are not highly durable, especially when subjected to laundering and dry
cleaning processes
Silicone water repellents:
• Silicone water repellents, specifically polydimethylsiloxane products, can create a hydrophobic layer around
fibers, as shown in Figure 1. Their unique structure allows them to establish hydrogen bond with fibers while
exhibiting a water-repelling outer surface.
• To enhance durability, water-repellent silicones often consist of silanol, silane, and a catalyst like tin octoate,
as depicted in Figure 2. The outward-facing methyl groups are responsible for water repellency. When applied
and dried on fibers, the silanol and silane components can react (Figure 3) to form a protective three-
dimensional crosslinked sheath around the fiber.
Fig 1: Polydimethylsiloxane on fiber surface; A, hydrophobic surface; B,
hydrogen bond to polar surface; C, fiber surface.
Silicone water repellents:
Fig 2: Components of silicone repellent Fig 3: Silanol-Silane reaction; A is removal of H2; B is
Si-O-Si crosslinked polymer; tin octoate is the catalyst
AB
Advantages of Silicone Water Repellents:
• High Water Repellency: Silicone water repellents offer a high level of water resistance even at low
concentrations (0.5–1% of fabric weight).
• Soft Fabric Feel: Treated fabrics maintain a very soft and comfortable texture, enhancing wearability.
• Enhanced Properties: Silicone-treated fabrics exhibit improved sewability, shape retention, and an enhanced
appearance and feel, particularly in the case of pile fabrics.
• Application Versatility: Some modified silicone repellents can be exhaustively applied, making them suitable
for pressure-sensitive fabrics.
AB Disadvantages of Silicone Water Repellents:
• Increased pilling and seam slippage, reduced repellency if excessive amounts are applied (for example silicone
double layer with polar outside, Fig. 4).
Fig 4: Silicone double layer on fiber; A polar surface; B hydrophobic attraction to the methyl
group; C hydrogen bonds to polar fiber surface; D fiber surface.
• Moderate durability to laundering (through hydrolysis of siloxane and rupture of the film by strong cellulose fiber
swelling) and dry cleaning (adsorption of surfactants).
• No oil and soil repellency.
• The silicone finish may enhance the attraction of hydrophobic dirt.
• The waste water, especially the residual baths, from these finish application processes are toxic to fish.
Fluorocarbon-Based Repellents:
• Fluorocarbon-based repellents offer the lowest surface energies for fiber surfaces among all repellent
finishes, allowing for both oil and water repellency. These repellents are created by introducing perfluoro
alkyl groups into acrylic or urethane monomers, which are then polymerized to form finishes on fabrics.
Fig: Fluorocarbon repellent on fiber surface. m=8-10; X and Y are co-monomers
,mainly stearylacrylates, R= H or CH3 (polyacrylic or methacrylic acid esters).
A is the fiber surface
Fluorocarbon-Based Repellents: (cont..)
• The application process for most fluorocarbon products involves padding, drying, and curing.
• During heat treatment, the perfluoro side chains orient themselves into nearly crystalline structures, a
crucial factor for achieving optimal repellency.
• This orientation, however, can be disrupted by washing and dry cleaning, leading to a reduction in finish
performance.
• To restore the orientation and maintain repellency, a new heat treatment such as ironing, pressing, or
tumble drying is necessary.
Advantages of Fluorocarbon-Based Repellent Finishes:
• General advantages of fluorocarbon-repellent finishes include low active add on (< 1 % owf) and more rapid
drying of treated fabrics.
• Special FCs allow improved soil release during household laundering or stain resistance on nylon, which is
especially useful for carpets.
Disadvantages of Fluorocarbon-Based Repellent Finishes:
• Disadvantages of fluorocarbon repellents include high cost, greying during laundering, potentially hazardous
aerosols.
• Specialized wastewater treatment is often needed to handle waste water generated during the application of
these finishes.
• They usually cannot be applied effectively by exhaustion (but there are some new FC products that are
exceptions to this rule)
Test methods
The water repellency of fabrics is evaluated by one of the three main types of test methods:
1. Spray tests to simulate exposure to rain.
2. Hydrostatic pressure tests, which measure the water penetration as a function of pressure exerted by water
standing on the fabric.
3. Sorption of water by the fabric immersed in water being evaluated, which should be suitably
preconditioned prior to testing.
Thank You
