This heading covers polymers of all olefins (i.e. acyclic hydrocarbons having one or more double bonds) except ethylene. The important polymers of this heading are polypropylene, polyisobutylene and propylene copolymers. For the classification of polymers (including copolymers), chemically modified polymers and polymer blends, see the General Explanatory Note to this Chapter.
The general physical properties of polypropylene are similar to those of high‑density polyethylene. Polypropylene and propylene copolymers also have a very wide range of applications, for example, packaging film, moulded parts for automobiles, appliances, housewares, etc., wire and cable coating, food container closures, coated and laminated products, bottles, trays and containers for storing precision equipment, ducting, tank linings, piping for chemical plant, tufted carpet backing. Polyisobutylene when sufficiently polymerised resembles rubber but is not classified in Chapter 40 as it does not conform to the definition of synthetic rubber. It is used for waterproof coatings and for modifying other plastics. Polyisobutylene, slightly polymerised and meeting the requirements of Note 3 (a) to this Chapter, is also included in this heading. It is a viscous liquid used to modify the properties of lubricating oils. The heading, however, does not cover liquid synthetic polyisobutylene or other liquid synthetic polyolefins not meeting the requirements of Note 3 (a) to this Chapter (heading 27.10).
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