Plastics & polymers
Bioplastic: bio-based vs. compostable
The term covers two different properties. Bio-based plastics take their carbon from renewable sources such as sugar cane, corn or vegetable oil (e.g. bio-PE, bio-PET); they may be chemically identical to fossil versions and need not biodegrade. Compostable plastics – PLA, PBAT, PHA, starch blends – break down within a set time under industrial composting according to EN 13432 or ASTM D6400, and some are fossil-based. When buying, ask separately for the bio-based content (ASTM D6866) and the compostability certificate (TÜV OK compost, BPI).
Food-contact compliance (EU 10/2011, FDA)
Evidence that plastics used for food packaging and equipment do not transfer substances into food above permitted limits. In the EU the framework Regulation 1935/2004 and, for plastics, Regulation 10/2011 apply – a positive list of substances plus overall and specific migration limits; in the USA, FDA 21 CFR Part 177. Buyers should request the supplier’s declaration of compliance (DoC) covering additives and, where needed, migration test reports; recycled plastics are also subject to Regulation (EU) 2022/1616.
Homopolymer, random copolymer and block (impact) copolymer
A homopolymer is made from one monomer (e.g. propylene only); it is hard, stiff and cheap, used for raffia, BOPP film and general injection moulding. A random copolymer has a little ethylene randomly built into the chain, making it clearer and more flexible – preferred for transparent containers and hot-water pipe (PP-R). A block or impact copolymer contains a rubbery phase giving high impact strength at low temperatures, used for automotive parts, pails and crates. Because the wrong type causes cracking or clarity problems, the order must state the type clearly.
Masterbatch vs. compound
A masterbatch is a pigment, filler or additive – UV stabiliser, antistatic, flame retardant, slip – dispersed at high concentration in a carrier polymer and let down into the base resin, typically at 1–5 %. A compound is a ready-to-use product containing the final formulation: for example 30 % glass-fibre-reinforced PA6, talc-filled PP or HFFR cable compound, processed directly. Masterbatch gives flexibility and low inventory; a compound guarantees consistent quality and technical properties.
Melt flow index (MFI / MFR)
The mass of molten polymer that flows through a die in 10 minutes at a set temperature and load – 230 °C/2.16 kg for PP, 190 °C/2.16 kg or 5 kg for PE – expressed in g/10 min (ISO 1133, ASTM D1238). A low MFI means high molecular weight and strength, a high MFI easy flow: pipe and blow-moulding grades are about 0.1–1, film 1–4, injection 10–60, and fibre and meltblown 25–1,500 g/10 min. When comparing offers, always check the test conditions.
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.
Recycled content (PCR / PIR)
PCR (post-consumer recycled) material comes from packaging and products that have reached consumers and become waste; PIR (post-industrial recycled) comes from production scrap and trimmings. Rules such as the EU Packaging and Packaging Waste Regulation (PPWR) and brand pledges are setting minimum PCR shares in packaging. Recycled-content claims should be verified with certification such as GRS, RecyClass, EuCertPlast or ISCC PLUS (mass balance); food-contact rPET additionally needs an approved super-clean process.