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Heading 3908 : Polyamides in primary forms.
This heading covers polyamides and copolymers thereof. Linear polyamides are known as nylons.
Polyamides are obtained by condensation polymerisation of dibasic organic acids (for example, adipic acid, sebacic acid) with diamines or of certain amino-acids (e.g., 11-aminoundecanoic acid) or by rearrangement polymerisation of lactams (e.g., epsilon-caprolactam).
Some of the important nylon type polyamides are polyamide-6, polyamide-11, polyamide-12, polyamide-6,6, polyamide-6,9, polyamide-6,10 and polyamide-6,12. Examples of non-linear polyamides are the condensation products of dimerised vegetable oil acids with amines.
Polyamides have a high tensile strength and resistance to shock. They also have excellent chemical resistance, especially to aromatic and aliphatic hydrocarbons, ketones and esters.
Apart from their use as textiles, polyamides have a wide application as thermoplastics in moulding. They are also used as coatings, adhesives, packaging films. In solvents, they have a specialised use as lacquers.
For the classification of polymers (including copolymers), chemically modified polymers and polymer blends, see the General Explanatory Note to this Chapter.
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