Application of Solvent in Textile

Chapter-1: Introduction

1.1 Definition of solvents

Solvent able to dissolve other substances. It is the liquid in which a solute is dissolved to form a solution, a liquid, typically one other than water, used for dissolving other substances, something that acts to weaken or dispel a particular attitude or situation.

The substance in which the solute is dissolved is called a solvent. "Solvents dissolve the reactants and provide the medium in which reactions take place." Solvents work under the general rule of like dissolves like. The term "like" refers to the overall polarity of the solvent molecule and the overall polarity of the solute. Based on the dielectric constant which refers to polarity, solvents are typically broadly classified as polar, semi polar and non-polar solvents.

A solvent is a molecule that has the ability to dissolve other molecules, known as solutes. A solvent can be solid, liquid or gas. The molecules of the solvent work to put the solute molecules apart. Eventually, the molecules of solute become evenly distributed in throughout the solvent. This homogenous mixture is perfectly even, and cannot be separated physically. Heat or another chemical process must be applied to the solution to separate the solvent and solute.

1.2 Examples of solvents

There are many solvents but universal solvent is water. It is least expensive, most commonly used and helps dissolve many substances. Besides water based on need one can opt for ethanol, oils and petroleum oils like kerosene and petrol.

But for research and industry the list of solvents used include:

a)      Water

b)      Ethanol

c)      Methanolexamples of solvents

d)      N-propanal

e)      Butanol

f)       Ether

g)      Dicholoromethane

h)      Carbon disulphide

i)       glycerol Acetone

j)       Carbon tetrachloride

k)      Cyclohexane

l)       Formic acid

m)   Tolune

n)      Anisole

o)      Pyridine

p)      Acetic Acid

q)      Hexane

r)       Xylene

s)      Trifluoroacetic acid

t)       Dimethyl sulfoxide

u)      benzene

v)      Nitrobenzene

w)    Quinoline

x)      Dibutyl pthalate

y)      Dimethylformamide

z)      Cyclohexane

aa)  Anisole

bb)  Tetrahydrofuran

1.3 Different types of solvents

            Solvents can be briefly classified based on their chemical nature and behavior.

A.    Based upon Polarity:

In general, most solvents have polarity due to their internal chemistry. This polarity is due to concentration of charges on one of the element inside a solvent molecule. It imparts changes on the molecule such that they can dissolve solutes having polarity or able to ionize them. When a solute is mixed in a solvent, the solvent molecules dissolve the solute by separating apart the solute molecules using forces like hydrogen bonding, vanderwals forces etc.

1.      Polar solvents: These are solvents having dielectric constant more than 15. They can dissolve salts and other ionizable solutes. Ex: Water, alcohol. Polar solutes like salts dissolve in polar solvents.

2.      Non-polar solvents: These solvents are non-polar and have dielectric constants less than 15. They cannot form inter-molecular bonds by use of hydrogen bonding, vanderval forces etc. Hence, they cannot dissolve polar compounds. Ex: Benzene, CCl4.

Fats and oils are soluble in non-polar solvents. Hence to remove lipids from an extract, petroleum ether is used in industry.

B.     Based on Chemical nature:

1.       Aprotic solvents: (No protons). These solvents are non-reactive and chemically inert. They neither take protons nor give protons. Ex: benzene (C6H6). chloroform (CHCl3).

2.       Amphiprotic solvents: Theses solvents which can give and take up protons on reaction. They have neutral pH. Ex: Water, alcohol.

3.      Protogenic solvents (proton+genesis = give): These are the solvents acidic in nature. They can donate a proton and hence called “protogenic”. Ex: HCL, H2SO4, perchloric acid.

4.      Protophyllic solvents: These are the solvents which take up protons. They are basic in nature and are mostly alkalies. Ex: NaOH, KOH etc.

These photogenic and propylic solvents can be again classified as leveling agents and differentiating agents. A strong acid or base is levelling agents as it can donate or accept protons to even weak base or acid respectively. While weak acids and weak bases cannot do so and can only give proton to strong base or take up proton from strong acid respectively.  Hence due to this differentiation they are called differentiating agents.

C.    Based on chemistry:

Solvents are also classified based on their center of chemistry due to presence of some special elements. These special elements bring total change in their physical and chemical properties. Inorganic solvents: Solvents without carbon are called inorganic solvents. Ex: water, NaOH, HCl Organic solvents. Solvents having carbon are called organic solvents. Ex: Alcohols (CH3OH), hydrocarbons solvents like Benzene. Halogenated solvents: Solvents having halogens are called halogenated solvents. Halogens are elements found in 17th group of periodic tables. Based on their behavior and properties, solvents are selected for purposes like acid base titration, complementary, extraction procedures, solubilization, chromatography, spectrophotometry etc. The above nature seems highly specific. Because sugars (C12H22O12) molecules appear to be organic in nature due to presence of carbon in it. But interestingly sugar is insoluble in organic solvents like benzene. This is because sugar molecules have polarity and require polar solvents to dissolve. Hence, we see sugar dissolves well in plain water which is inorganic but having polarity. So, among the types of solvents available, to dissolve a solute, one should consider both chemistry and also polarity.

Chapter-2: Description

2.1 Characteristics of Solvents:

An ideal solvent for Textile processing should have the following characteristics –

1. Non- toxic.

2. Non-flammable.

3. Non-corrosive.

4. Inert to textile materials.

5. Stable to repeated distillation.

6. Low Specific heat.

7. Low heat of evaporation.

8. Readily available.

9. Economic feasibility.

2.2 Application of Solvent in Textile Areas:

a)      Solvent Scouring,

b)      Solvent Dyeing,

c)      Other Areas.

a)      Solvent Scouring:

Solvent scouring is the treatment of fabrics in organic solvent medium to remove impurities such as lubricating oils and spin finishes.

Advantages:

a.  When a temperature is 700-750C, it remains solvent. But at 900-950C, the solvent rapidly flashes-off and recovered. Here, maximum 90% solvent recovery is possible.

b. Immersion for 30 seconds in solvent, the fat and wax content is reduced 0.15% which is

commercially acceptable.

Disadvantages:

a. 100% solvent recovery is not possible at least 5-10% solvent go to waste.

b. Process is very expensive.

c. Machines are not easily available.

Reasons of using solvents in processing:

Solvent is introduced in place of water in processing, dyeing and finishing for the following reasons-

1. Unacceptable environmental hazards due to more or less untreated waste.

2. Shortage of cheap and plentiful pure water.

3. Realization and concurrent pressure from lawmakers and public opinion to treat waste to an acceptable pollutant levels.

4. To reduce cost through advanced technology.

5. Solvent can be recycled easily and inexpensively.

6. Energy efficient process.

b) Solvent Dyeing:

            Solvent dyeing is a dyeing process carried out from a continuous non-acqueous phase. Here solvent is used as dyeing media. But water may be added to assist dyeing process. Since the introduction of hydrophobic fibers like cellulose acetate in 1920’s solvent has been considered for dyeing because it was not possible to dye such fibers with ionic dyes and water.

Advantages of Solvent Dyeing:

1. High wettability and dyeability.

2. Rapid dyeing with minimum energy requirements.

3. Better levelness and dye yield compared with better fabric aesthetics.

4. Solvent is being recycled, so the effluent control problem is eliminated.

5.Less time required.

Disadvantages of Solvent Dyeing:

1. Solvents are expensive, so higher production cost

2. Problem in equipment’s availability.

3. Existing dye cannot be used in full range.

c) Other Areas.

                        In all textile areas use solvent like printing, finishing. Solvent must need in all textile process.

2.3 Conclusion:

            Solvent able to dissolve other substances. Solvents can be broadly classified into two categories: polar and non-polar. In textile sector solvent is used for scouring, dyeing, printing, and other areas. Most of solvent is useful and good for textile but some of solvent not use in this time for their disadvantages. But solvents are use in all areas of textile.