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1.1 This part of ISO 9988 establishes a system of designation for polyoxymethylene (POM) thermoplastic materials, which may be used as the basis for specifications. Polyoxymethylene materials are thermoplastic materials composed principally of long-chain synthetic homopolymers and copolymers of formaldehyde. The repeating unit in the molecular chain is – CH2O – as an integral part of the main polymer chain resulting from polymerization of formaldehyde. 1.2 The types of polyoxymethylene plastic are differentiated from each other by a classification system based on appropriate levels of the following designatory properties: a) melt mass-flow rate or melt volume-flow rate, b) tensile modulus, and on information about basic polymer parameters, intended application, method of processing, important properties, additives, colorants, fillers and reinforcing materials. 1.3 This part of ISO 9988 is applicable to all polyoxymethylene homopolymers and to copolymers of polyoxymethylene and blends of polymers containing polyoxymethylene. It applies to materials ready for normal use in the form of powder, granules or pellets and to materials unmodified and modified by colorants, additives, fillers, etc. 1.4 It is not intended to imply that materials having the same designation necessarily give the same performance. This part of ISO 9988 does not provide engineering data, performance data or data on processing conditions which may be required to specify materials for particular end-use applications. If such additional properties are required, they shall be determined in accordance with the test methods specified in part 2 of this International Standard. 1.5 In order to specify a thermoplastic material for a particular application or to ensure reproducible processing, additional requirements may be given in data block 5 (see 3.1).