PHYSICAL STRUCTURE OF TEXTILE FIBRES

 

PHYSICAL STRUCTURE OF TEXTILE FIBRES

Requirements of a fibre forming polymer or fibre formation

v  Polymers must have straight and long chain molecules.

v  The molecular chains must be more parallel to each other.

v  Polymers must have the attractions.

v  Polymers should be chemically resistant.

v  They should be hydrophilic.

v  Molecules must have same measures of freedom for easy movement in order to give required extensibility.

v  They should have higher melting point.

Methods for investigation of fibre structures

v  X-ray diffraction method

v  Infra-red radiation absorption method

v  Optical microscopic method

v  Electron microscopic method

v  Nuclear magnetic resonance method (NMR)

v  Thermal analysis

v  Density measurement

v  Chemical test

v  General physical properties

Uses of X-ray diffraction method

v  This method helps to determine chemical formula (chemical group, chemical   bonding) of fibres.

v  By this method amount of water or moisture present in the fibres can be known.

v  It gives idea about crystalline & amorphous regions of a fibre.

v  It gives idea about molecular configuration (molecular spacing) of fibres.

Uses of Infra-red radiation absorption method

v  By this method spiral angle of cotton fibres can be measured.

v  It gives idea about crystalline & amorphous regions of a fibre.

v  It may show the information about the size, shape and arrangements of the crystals

v  It gives idea about molecular packing of polymer.

v  It gives idea about crystal orientation of a polymer.

v  Spacing among the molecular chains can be measured.

v  The length of repeating unit that forms fibre forming polymer can be determined.

v  It helps to identify the fibres.

v  It helps to determine the cross-sectional shape of fibres.

Uses of Electron microscopic method

v  This is very much suitable method for watching crystalline region of fibres.

v  Specimen size can be enlarging from 6000-200000 times by this method.

v  It gives idea about atomic structure from fibre image.

Effects of structural factors on fibre properties

1) Chemical bonding arrangement

       a) Single bonds (-c-c-c-c-)

i) Less strength

ii) More flexibility

iii) Easy moveable polymer system

     

       b) Double bonds (-c=c-c-c=c-)                            

            i) More strength

ii) Less flexibility

iii) No moveable polymer system

2) Crystallinity

           

Crystallinity is the arrangement of fibre molecules in the polymer chain. Crystallinity can be classified as a) crystalline region and b) non crystalline region.

a) Crystalline region: In crystalline region the molecules are arranged parallel. So they contain-

v More strength

v More density 

v Elastic property lower

v More stiffness and more rigid.  

v A crystalline region does not permit easy entry of moisture and dye molecule (less   absorbent)

b) Non crystalline region: Here the fibre molecules are arranged randomly without following any particular arrangement. So they contain-

v Lower strength 

v More elastic    

v Permits easy entry of moisture              

v More flexible

v For example, cotton fibre contains 65% crystalline and 35% non crystalline region. Generally man made fibres are of greater strength due to its higher crystallinity.

3) Orientation

Orientation is the arrangement of molecular chains in fibre. Orientation property shows the arrangement of molecule and molecular chain. Fibre molecule can be arranged parallely or randomly presenting high or low oriented fibre. In a highly oriented fibre molecules are aligned in parallel order with compactness while low oriented polymer yield random arrangement of molecules.

Properties of a highly oriented fibre:

v  Higher strength

v  Higher crystalline

v  Less absorbent

v  Less elastic due to less extensibility

v  Good shininess.

     

4) Chain character

a)      Long chain (-CH₂-CH₂-CH₂-CH₂-)_n: More strength and less flexibility

b)      Short chain (-CH₂-CH₂-)_n: Less strength and more flexibility

c)      Long side chain: More strength and less flexibility

d)      Short side chain: Less strength and more flexibility

5) Nature of repeating unit

       a)  Same monomers (homo-polymer): More strength and less flexibility

       b)  Different monomers (co-polymer): Less strength and more flexibility

6) Molecular packing

       a)  Regular packing: More strength and less flexibility

       b)  Irregular packing: Less strength and more flexibility

            -CH₂-CH₂-HCCH₃-CH₂-CH₂- HCCH₃-CH₂-CH₂ -   

                                    Regular packing

            -CH₂-CH₂- CH₃CCH₃-CH₂-CH₂- HCCH₃-CH₂-CH₂ -   

                                    Irregular packing

8) Degree of Polymerization

Degree of polymerization is the no. of total monomer present in a polymeric chain. Length, strength, fineness, elongation depends on it. In the case of nylon fibre, if DP is 10000 to 20000 then strength of the fibre increases, also cotton and acrylic are of higher strength due to their higher DP. Acetate and wool are weak as their DP is low.

9) Cross link effect

If cross link is present in fibre the main chain can not sliding, as result fiber strength is increased, crystallinity will increase and does not create crease.