properties of polyster
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Explanation: hey mate..........
Polyesters can be formed from the reaction of a diacid or acid anhydride and a diol with the elimination of water, or by ring-opening polymerization of cyclic (di-)esters.
According to the composition of their main chain, polyesters are classified as aliphatic, semi-aromatic and aromatic (see table below).
Aromatic reactants improve the hardness, rigidity, and heat resistance, whereas aliphatic acids and diols increase the flexibility, lower the melting or softening point and improve the processability.
Common aliphatic diols are ethylene glycol, 1,4-butanediol, and 1,3-propanediol. They are often reacted with aromatic diacids, such as terephthalic acid, phthalic acid, phthalic anhydride and naphthalene dicarboxylic acid.
Glycerol and unsaturated acids (anhydrides) like maleic anhydride, are sometimes added to crosslink the polyesters.
In the case of unsaturated acids (anhydrides), crosslinking is achieved in a subsequent free radical chain polymerization.
Double bonds in the backbone of the polyesters also improve the resistance to softening and deformation at elevated temperatures.
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Answer:
The answer is-
Explanation:
Physical properties
Moisture regains
The moisture regain of polyester is low, ranges between 0.2 to 0.8 per cent. Although polyesters are non-absorbent, they do not have wicking ability. In wicking, moisture can be carried on the surface of the fibre without absorption.
Specific gravity
The specific gravity 1.38 or 1.22 depending on the type of polyester fibres is moderate. Polyester fibres have a density greater than polyamide fibres and lower than rayon. Fabrics made from polyester fibres are medium in weight.
Heat effect
The melting point of polyester is close to that of polyamide, ranging from 250 to 300°C. Polyester fibres shrink from flame and melt, leaving a hard black residue. The fabric burns with a strong, pungent odour. Heat setting of polyester fibres, not only stabilizes size and shape but also enhances wrinkle resistance of the fibres.
Mechanical properties
A wide of polyester fibres properties is possible depending on the method of manufacture. Generally, as the degree of stretch is increased, which yields higher crystallinity and greater molecular orientation, so are the properties, e.g., tensile strength and initial Young’s modulus. At the same time elongation normally decreases. An increase in molecular weight further increases tensile strength, modulus, and extensibility.
Shrinkage of the fibres also varies with the mode of treatment. If relaxation of stress and strain in the oriented fibre occurs, shrinkage decreases but the initial modulus may be also reduced. Yarns maintained at a fixed length and constant tension during heat setting are less affected with respect to changes in modulus, and reduced shrinkage values are still obtained.
Poly (ethylene terephthalate) shows nonlinear and time-dependent elastic behaviour. Creep occurs under load with a subsequent delay in recovery on the removal of the load, but compared to that of other melt-spun fibres, creep is small.
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