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Polyethylene types: HDPE, LDPE, LLDPE and mLLDPE
Polyethylene is classed by density and chain structure. HDPE (0.941–0.965 g/cm³) is rigid and chemical-resistant, used for pipe (PE100), jerrycans, bottles and crates. LDPE (0.910–0.930) has a branched structure that makes it flexible and clear, used for extrusion coating, shrink and food film. LLDPE is a linear low-density copolymer with butene (C4), hexene (C6) or octene (C8) comonomer; with high puncture and tear resistance it is the main raw material for stretch and packaging film. mLLDPE, made with metallocene catalysts, offers even higher toughness and clarity.
Prime, wide-spec and off-grade polymer
Prime material is original product sold under the producer’s brand and grade number, meeting every value in the TDS. Wide-spec is production in which one or more values – e.g. MFI or colour – fall outside the narrow range but remain usable; off-grade may be transition production, sweepings or contaminated material and is usually sold unbranded and without a COA. Off-grade is cheaper but varies from lot to lot, so samples must be tested and “as is” terms and claim rights made clear.