CD – PET

ðð  CD-PET is a Cationic Dyeable Polyester.

ð  It is also known as Basic Dyeable Polyester.

ð  It is modified polyester.

ð  In normal polyester, there are no sites for ionic dyes. So, it can only be dyed by disperse dyes.

ð  Compared to ionic dyes, disperse dyes have smaller molecular extinction coefficients and lower build-up property.

ð  So these dyes cannot give bright and deep colours.

ð  Moreover, fastness to sublimation and wet treatments of disperse dyes are relatively poor compared to other classes of dyes.

ð  In order to avoid these problems, cationic dyeable polyester(CD-PET) was developed.

Modification Process (Manufacturing of CD-PET)

ð  Co-polymerisation of an isophthalic acid component containing a sulfonic acid group makes it possible to use cationic dyestuffs for polyester staple fibres and filaments.

ð  Generally, the sodium salt of 5-sulfo-isophthalic acid (Na-SIPA) is used as CD co-monomer.

ð  A cationic or basic dyestuff contains amines or ammonium groups or quaternary nitrogen-heterocyclic.

ð  Dyeing of CD-PET is an ion exchange process.

ð  The sodium cations (Na+) from CD-PET are substituted by the bigger dye cations, whereas the sodium ions enter into the dye bath.

ð  Thus, PET is chemically modified in a manner that cationic dyestuffs can form a chemical complex with the fibre.

ð  The chemistry of producing CD-PET is complicated.

ð  The reason for difficulty is the acidic character of Na-SIPA, especially in connection with hydrolytic or glycolytic conversion.

ð  Therefore, after direct addition of this salt into the PET esterification stage, the diethylene glycol (DEG) would reach a high level because ether formation is acid-catalysed.

ð  Additionally, the acidic character enhances the TiO₂ agglomeration.

ð  The result is difficulty in the spinning process, and an excessively low melting point of CD-PET

      

Chemical Structure 

 Physical Properties

Density (g/cc)		1.45 – 1.49
Tenacity (g/d)	Dry	3.8 – 4.2
	Wet	3.8 – 4.2
Breaking Elongation (%)	Dry	21 – 40
	Wet	21 – 40
Elastic Recovery (%)	At 2%	90 – 92
	At 5 %	75 – 85
	At 10 %	45 – 60
Stiffness (g/d)		15 – 35
Moisture Regain (%)	65 % RH	0.8
	90 % RH	1.1
Melting Point (ºC)		210 – 220
Softens at (ºC)		175 – 190

Chemical Properties

(1)   Effect of Acid:-

·         CD-PET fibre shows good resistance to organic acids.

·         The fibre also exhibits good resistance to inorganic acids at room temperature.

·         Only with concentrated sulphuric acid, the fibre partially degrades.

(2)   Effect of Alkalis:-

·         The fibre is quite resistance to weak alkalis at room temperature.

·         At 97ºC, 1 N NaOH solution, fibre surface degrades due to saponification.

·         Ammonia will causes aminolysis and loss in strength.

(3)   Effect of Bleaching agents and Solvents:-

·         The fibre has excellent resistance to bleaching agents and organic solvents.

·         The fibre is swollen or dissolved by phenols, chloroacetic acid, chlorophenols.

(4)   Effect of Sunlight:-

·         The fibre, on direct exposure to sunlight, loses its strength and weakness.

(5)   Dyeability:-

·         This fibre is specially modified for dyeing with cationic dye.

·         So basic (cationic) dyes are mostly used to dye CD-PET.

Applications

ð  Knitting: suede-imitation, plush fabric for home textile , sportswear

Woven: peach skin velvet