Division 4 In note 1 to this chapter and in heading No 4002, the expression ‘synthetic rubber’ applies to:

unsaturated synthetic substances which can be irreversibly transformed by vulcanization with sulphur into non-thermoplastic substances which, at a temperature between 18 and 29 ^oC, will not break on being extended to three times their original length and will return, after being extended to twice their original length, within a period of five minutes, to a length not greater than one-and-a-half times their original length. For the purposes of this test, substances necessary for the cross-linking, such as vulcanizing activators or accelerators, may be added; the presence of substances as provided for by note 5 (b) (ii) and (iii) is also permitted. However, the presence of any substances not necessary for the cross-linking, such as extenders, plasticizers and fillers, is not permitted;

thioplasts (TM); and

natural rubber modified by grafting or mixing with plastics, depolymerized natural rubber, mixtures of unsaturated synthetic substances with saturated synthetic high polymers provided that all the abovementioned products comply with the requirements concerning vulcanization, elongation and recovery in (a).