The Physical Properties of Nylon 66

Written by john brennan
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The Physical Properties of Nylon 66
Many ropes are made from nylon 6,6. (Jupiterimages/ Images)

Nylon 6,6 is a polyamide fibre synthesised by combining adipic acid with hexamethylene diamine. The 6,6 notation indicates that both reactants donate six carbons each to the polymer they form, unlike nylon 6, which is produced through a different process. Nylon 6,6 is one of the most versatile man-made fibres and finds a host of applications -- everything from carpet material to parachute cords. Its distinctive physical properties are responsible for its success.

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In nylon 6,6, there are six carbons intervening between two amide groups. (An amide group involves an oxygen double-bonded to a carbon directly next to a nitrogen bonded to a hydrogen and another carbon.) Nitrogen and oxygen are both very electronegative elements, meaning they are "selfish" when sharing electrons with another atom and the electrons tend to spend more time around the nitrogen/oxygen atoms. Consequently, hydrogen bonds form where the partially positively-charged hydrogen atom bonded to a nitrogen interacts with the oxygen atom in an amide group on a neighbouring chain. This feature accounts for many of nylon 6,6's remarkable properties.

Strength and Density

One of nylon 6,6's most valuable properties is its high tensile strength -- greater than that of wool, silk or cotton. Its strength derives from hydrogen bonds between neighbouring chains, which enable the nylon to form tough, durable fibres that hold together under stress. The specific gravity of nylon 6,6 ranges from 1.02 grams per cubic centimetre to 1.49 grams per cubic centimetre, depending on its amount of crystallinity -- which in turn depends on how it is formed.

Heat Capacity and Conductivity

Nylon 6,6's heat capacity -- the amount of heat energy needed to raise its temperature by 1 degree Celsius -- is 1.67 joules per grams Celsius, only about 40 per cent of the heat capacity of water. Its thermal conductivity (the rate at which it conducts heat) ranges from 0.200 to 0.290 watts per meter Kelvins; although this value is much higher than many insulating materials, it is lower than glass and far lower than good conductors like metals. Nylon 6,6 is also a poor conductor of electricity.

Other Properties

Nylon 6,6 is abrasion-resistant and resistant to attack by many chemicals; it is easy to wash and can be dyed during preparation, making it even more valuable for use in clothing and accessories. Its melting point is 263 degrees Celsius. The melting point for nylon 6,6 is much higher than the melting point for nylon 6, which is otherwise fairly similar to nylon 6,6 in terms of its physical properties. The lower melting point of nylon 6 is a disadvantage since garments made from nylon 6 poorly tolerate ironing.

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