Carbon Footprint

Continuous recirculation is the practice of continuously feeding reclaimed material back into the production stream — reintroducing in-house scrap (and sometimes recycled content) into the feed so resources are used to the fullest and waste is minimized. It is the circular-economy principle that the regrinding cycle puts into practice on the molding floor. ## How it works in a molding cell - In-house loop: runners, sprues and rejected parts are ground into regrind and metered straight back into virgin resin at a controlled ratio, shot after shot — the regrinding cycle. - Closed-loop, near real time: with beside-the-press granulating, the reclaimed flakes return to the same machine's feed continuously, not in separate batches. - Steady-state balance: the recycled fraction settles to an equilibrium set by how much scrap each shot makes versus the dosing ratio. ## Why it matters - Resource efficiency & cost: less virgin resin bought and less waste hauled away for the same number of good parts. - Lower carbon footprint: keeping carbon circulating in the process beats landfill/incineration plus new fossil feedstock. - Lean & sustainability: continuous recirculation is a pillar of lean manufacturing (eliminating material waste) and of a plant's sustainability goals. ## The control caveat Recirculation must be managed, not unlimited: every pass adds a regrind generation of heat history that degrades the polymer, so molders cap the blend ratio, limit generations and cascade higher-generation material to lower-spec parts. Where properties or regulations forbid recyclate, the loop runs on pure virgin resin and chemical recycling (depolymerization) becomes the circular route instead. ## Related terms - See also: regrinding cycle, regrind, regrind generation, carbon footprint, depolymerization ## What is continuous recirculation in injection molding? Continuously feeding reclaimed in-house material (regrind) back into the production stream at a controlled ratio so resources are maximized and waste minimized — the circular-economy principle behind the regrinding cycle. ## How is continuous recirculation different from the regrinding cycle? Continuous recirculation is the broad principle of always feeding reclaimed material back into production; the regrinding cycle is the concrete closed loop — grind scrap, blend with virgin, re-mold — that carries it out on the floor. ## What limits continuous recirculation? Polymer degradation: each reprocessing pass adds a regrind generation that lowers properties, so the blend ratio and number of generations are capped, and regulated or high-spec parts may require virgin resin or chemical recycling instead.

Depolymerization is the chemical breakdown of a polymer back into its building-block monomers (or short oligomers) — essentially reversing polymerization. In plastics it is the basis of chemical recycling: instead of grinding and re-melting plastic (mechanical recycling, which only yields regrind), the long chains are split apart so the recovered monomers can be purified and re-polymerized into virgin resin-quality material. ## How it works Heat, chemistry or both attack the bonds in the polymer chain: - Thermal / pyrolysis: heat without oxygen cracks chains into monomers, oils or gas. - Solvolysis (glycolysis, methanolysis, hydrolysis): a reactant chemically cleaves the chain — widely used for PET, which depolymerizes cleanly back to its monomers. - Catalytic / enzymatic: catalysts or engineered enzymes break specific bonds at lower temperatures. It works best on step-growth/condensation polymers (PET, PA, PU); pure addition polymers like PE and PP are harder and usually go to pyrolysis. ## Why it matters for molders - True circularity: depolymerized-and-rebuilt resin can match virgin resin properties, unlike regrind, which degrades each regrind generation. It can be used in regulated, food-contact or high-spec parts that won't accept mechanical recyclate. - Lower carbon footprint: keeping carbon in the plastic loop (vs landfill/incineration + new fossil feedstock) is a key lever in a part's footprint. - Handles mixed/contaminated waste: chemical recycling can process streams mechanical recycling can't. The trade-off is energy and cost; depolymerization is more energy-intensive than mechanical recycling, so it complements rather than replaces regrind. ## Related terms - See also: polymer, monomer, regrind, virgin resin, carbon footprint ## What is depolymerization in plastics? The chemical reversal of polymerization — breaking a polymer back into its monomers so they can be purified and re-polymerized into new, virgin-quality resin; it is the core of chemical recycling. ## What is the difference between depolymerization and mechanical recycling? Mechanical recycling grinds and re-melts plastic into regrind, which degrades with each cycle; depolymerization chemically breaks the polymer back to monomers that rebuild into virgin-quality resin, enabling true closed-loop recycling. ## Which plastics can be depolymerized? Condensation polymers like PET, polyamides (PA) and polyurethanes depolymerize cleanly (e.g. PET via glycolysis/methanolysis); addition polymers like PE and PP are harder and usually processed by pyrolysis into oils and feedstock.

Lean Manufacturing is the systematic methodology to reduce the seven classic wastes (overproduction, waiting, transport, over-processing, inventory, motion, defects) in any production system. In injection molding it attacks press idle time, start-up scrap and long changeovers. ## Pillars of Lean in molding - Continuous flow: minimize inventory between press, secondary ops and packaging - Pull (kanban): produce only what the next customer requests - Jidoka (built-in quality): automatic scrap detection by vision or sensors - Standardization: start-up checklists, master parameters and SMED - Continuous improvement (kaizen): small daily improvements by the operator ## Common Lean tools in molding plants - 5S for orderly workstations and tool cribs - SMED to slash mold-change times (target <10 min) - Total Productive Maintenance (TPM) for machine availability - OEE (Availability × Performance × Quality) as the headline KPI - Andon: visible alerts for stops, scrap or changeovers ## Typical indicators - World-class OEE in injection molding: 85 % - Target mold-change time: <10 min (SMED) - Acceptable scrap: <1 % in stable production - Order-to-ship lead time cut by 40 – 70 % after implementation ## Common pitfalls Rolling out tools without changing culture, copying Toyota without adapting, chasing metrics (OEE) without attacking root cause, and abandoning 5S discipline at the first demand spike.

Regrind is plastic material recovered by grinding runners, sprues, defective parts or purges, then blended with virgin resin and reintroduced into the process. It is a key sustainability and cost-reduction tool in injection molding. ## Why use regrind Recovers the ~20 – 30 % unavoidable scrap from cold runners and cuts raw-material cost by 5 – 25 %, with a lower carbon footprint. On non-critical parts, pure or near-pure regrind is fully viable. ## Typical proportions (regrind/virgin blend) - Cosmetic / engineering parts: 10 – 20 % - Non-visible structural parts: 20 – 50 % - Internal / non-critical: 50 – 100 % - Some resins (PVC, PE): up to 100 % in approved applications ## Regrind system equipment - Granulator: rotating blades, sizing screen - Pellet size: 3 – 8 mm for homogeneous mix with virgin - Beside-the-press: granulator next to the machine, regrind returns to the hopper via blower - Magnet + metal detector: mandatory to avoid screw damage - Volumetric or gravimetric blender: meters regrind and virgin in a defined ratio ## Limitations and issues - Cumulative thermal degradation each pass (lowers viscosity, properties) - Cross-contamination with another resin causes delamination or breakage - Yellowing or graying on unpigmented resins - Property loss in multi-generation regrind - FDA / medical / automotive restrictions forbid uncertified regrind ## Disallowed applications FDA food-contact, class II/III medical devices, structural crash parts in automotive, and certain children's toys under specific regulation.