Softeners-Cationic softening agents in textile processing

Excerpt:

SOFTENING agents are applied to textile to improve their hand, drape and cutting and sewing qualities of textile. Effective softeners must be readily dispersible in water and rapidly absorbed so that uniform deposition on the fabric can occur within a relatively short treatment time and generally exhaustion should take place in almost 5 mins for the softener to be effective and economically usable. It must impart softness, fluffiness and lubricity to the treated cloth and reduce static build up especially in case of hydrophobic fibres like cellulose acetate, nylon, polyester and acrylic fibres. These effects should be obtained without the loss of fabric whiteness or brightness and then the treated fabric should retain its ability to absorb water in subsequent use for drying the body or other surfaces.

The origin of cationic softeners

The origin of cationic softeners may be traced to the attempts made during the early 1930 in improving the washing fastness of direct and acid dyeing by complex formation between the dye anions and the quarternary ammonium cation of the dye fixing agent on the fibre. While short chain cationics were ineffective, long chain compounds were found to be better in both aspects of softening and dye fixing.

In the preparation in the Sap amines, asymmetric diethyl ethylene diamine was used instead of ethylene diamine, because of the ease with which the former could be quaternised to give a cationic compound. Thus the treatment to the reaction product of Oleyl Chloride and asymmetric diethylene diamine with dimethyl sulphate a quaternary compound having high substantivity for textile fibres, is formed.

Fabric Softeners are used to modify the hand and to restore the lost properties to the laundered fabric.

Oleyl chloride + Asymetric diethylene diamine

C2H5

C17H33-COCL + H2N - CH2 - CH2 -N

C2H5

NaOH

Asymetric diethyl diamine with two C2H5 groups attached

C2H5

C17H33-CONH + CH2 - CH2 - N

C2H5

HcL

Combines to form a CO-NH

C2H5

C17H33-CONH + CH2 - CH2 -N

C2H5

CL

CH3CONH

Attached a CL to N with HCL addition

C2H5

C17H33-CONH + CH2 - CH2 -N

C2H5

OOC CH OH CH2

Attached to OOC CH OH CH2

C2H5

C17H33-CONH + CH2 - CH2 -N

C2H5

OOCH3

From an Aliphatic Compound

C2H5

C17H33-CONH + CH2 - CH2 -N

C2H5

CH2

Froms an Aromatic Compound

These mainly belong to the cationic type and are made from quaternising ammonium salts, imidazolium salfts and amido amines salts. The hydrophobic portion of the quaternary ammonium salts is usually a fatty hydro carbon which causes the cationic softener to lubricate the fibres in the fabric. The principle effect of lubrication is believed to have a bearing in the wear life or abrasion resistance of the fabric.

Most of the cationic softeners show strong germicidal properties. Shorter alkyl chains or those having instauration are better bactericides than those which are usually preferred as textile softeners. The long saturated alkyl group (C10 H33 - C10 H39) are preferred for softening but they reduced water solubility. However when the amine is quaternised increased solubility and greater pH stability results.

Hydrophilicity and Hydrophobicity

The cationic molecules usually balance hydrophilicity and hydrophobicity. When the cationic product is held on the fabric, the primary effect is one of lubrication or increase yarn to yarn or filament slippage.

The substantivity of cationic softeners for synthetics hydrophobic fibres is limited, the order of increasing absorption being acrylic, polyester, amide, acetate, cotton viscose rayon and wool. Softening however is a function not only of the softeners, but also of the fabric used, method of application, softener concentration pH and subsequent treatment etc.

Chemistry of Cationic softeners

The simplest cationic softeners are primary, secondary and tertiary mono amines and their salts, formed by neutralization of the amines usually with acetic acid. The primary and secondary amines have little importance in textile field since the hydrogen on the nitrogen atom leads to yellowing. But they serve as raw materials for making quaternary ammonium compounds. Reaction with alkylating agents like methyl chloride, benzyl chloride dimethyl sulphate etc. converts the insoluble amines into water soluble salts which are more active than original amines. These quaternary compounds have excellent thermal stability especially on the acidic side. Strearyl or disteayl dimethyl ammonium chloride or methosulphate, cetyl dimethyl benzyl ammonium chloride or methosulphate etc. belong to this group.

The next group of commercial importance are amido amines which are formed by reaction of fatty acids or glycride and a substituted or unsubstituted short chain polyamine. Generally the reaction occurs at only one of the amine functions giving an amide leaving one or more unreacted amino fraction group. The amine may be diethyl triamine N, N–diethylene diamine etc. Derivatives of ethylene diamine have high melting points and exhibit poor solubility.

Fatty acid + ethylene dhamine

C2H5

R- COOH + H2N - CH2 - N

C2H5

-H2O

With Acetic acid or HCL

C2H5

R- CONH - CH2 - CH2 - N

C2H5

Cationic Softeners

This amide is quaternised with glacial acetic acid or hydrochloric acid to give cationic fabric softeners.

Imidazolines are the next group of cationic softeners. These are formed from fatty acid and poly ethylene poly amines.

Imidazolines

R - COOH + H2N - CH2 - CH2 - NH - CH2 - CH2 - NH2

  • H2O

With Acetic acid or HCL

R- CONH - CH2 - CH2 - NH - CH2 - CH2 - NH2

Heating - H2O

Gives a CH2-NH-CH2 group by combination

N - CH2

R-C

N - CH2

CH2 - CH2 - NH2

Cyclic compounds are formed

The cyclic compound (imidozoline) has a lower melting point and higher solubility than the parent amido amine. These cyclic products include amino esters prepared by reaction of fatty acid or acid chloride with amino alcohols like diethanol amine or hydroxyl ethyl ethylene diamine.

R - COOH + HOCH2 - CH2 - NH - CH2 - CH2 - OH

R - COOCH2 - CH2 - NH - CH2 - CH2OH

Cationic Softeners

R - COOH + HOCH2 - CH2 - NH - CH2 - CH2 - NH2

R - COOCH2 - CH2 - NH - CH2 - CH2 NH2

Cationic Softeners

These are quite water soluble, give good softening properties and are easy to make but being esters have definite disadvantage of being easily hydrolysable. After quaternisation also the ease of hydrolysis is retained by them.

Stearamides is a soft paste. The colour of saturated amide is lighter than that of the unsaturated amides. They are soluble in Ketones, ester, alcohols, fats and fatty acids. Their solubility increased with temp. In the saturated series the longer the chain the lower is the solubility. In case of solvents, the higher the molecular weight of the solvent, the higher is the solubility of an amide.

Reaction of the amides with formaldehyde may give methylol stearamide or methyilene bis stearamide depending on the conditions.

Amide + Formaldehyde

R- CONH2 + CH2 O

R- CONHCH2 OH

  • H2O

Gives a CONH linkage with Acetic acid or HCL

R - CONHNH - CO - R

Cationic Softeners

A mixture of acetic acid and stearamide (CH3COOH + C17H33CONH2) acts as a cationic active slightly acidic water soluble softening agent for cotton materials.

Method of Application

The two principal methods of application of cationic softeners

  1. By exhaustion from dilute baths and

  2. Padding from relative concentrated solutions and drying the material.

Industry has two type of cationic softeners to offer:

  1. Cation Softener in gel form or cationic softener in paste form both giving luxuriant supple feel.

  2. Non yellowing cationic softeners imparting rich dull cottonish look with luxurious soft feel. Stearic Acid & Oleic Acid based:

They are chemically made up of:

  1. RB Fatty Acid based

  2. Oleic Acid, Stearic Acid based