Acrylonitrile Butadiene Styrene (ABS) is a two-phase terpolymer in which polybutadiene rubber domains are dispersed in a styrene-acrylonitrile copolymer matrix, commonly with 15–35 wt% acrylonitrile, 5–30 wt% butadiene, and 40–60 wt% styrene. The practical metric often summarized as ABS Yield per Kg: Scrap Rate, Regrind Recovery and the Real Unit Cost is not the purchased mass of resin, but the mass of dimensionally conforming parts or extrudate produced per kilogram of compounded material consumed after scrap generation, regrind recovery, and reject losses are allocated. A cold-runner injection molding operation producing thin-wall parts can show total scrap rates of 25–40 wt%; if no regrind is reused, 1 kg of conforming product may require 1.33–1.67 kg of virgin ABS. Regrind recovery changes that mass balance by assigning a recovered material value, but moisture uptake, fines, molecular degradation, color drift, and measurement variability impose processing limits. The following sections address process-specific yield drains, regrind validation methods, and a normalized cost model.

What Makes Cold Runner Scrap the Primary Drain on ABS Yield per Kilogram?

In two-plate cold-runner tooling used for multi-cavity ABS moldings, sprue and runner mass frequently equals 15–40 wt% of total shot mass for components below 10 g. Family molds with unbalanced flow can exceed 50 wt% runner scrap because larger runner diameters are required to balance fill pressure across dissimilar cavities. Hot-runner valve-gate systems reduce runner scrap to below 5 wt%, but they increase melt residence time and impose additional shear history on the polybutadiene phase. General-purpose ABS is typically processed at melt temperatures of 230–260 °C, mold temperatures of 40–80 °C, and screw back pressures of 0.5–1.0 MPa, with molding protocols aligned to ISO 294-1 or ASTM D3641. Startup purges and color changes add non-recoverable scrap; clearing a previous color on a 120-t injection molding machine may require 50–100 kg of purge resin. Scrap rate must be measured as total non-conforming mass—runners, sprues, purgings, edge trim, and rejected parts—divided by total mass throughput, not as rejected part count. Underreported purge and start-up losses are a common distortion in yield-per-kg accounting.

Regrind recovery from sprues, runners, edge trim, and purgings imposes a separate mass-balance constraint. Granulators handling ABS should be fitted with screen sizes of 4–6 mm; fines below 0.5 mm should remain below 5 wt% of the regrind fraction because excessive fines lower bulk density and create feed bridging in gravimetric blenders. Ground ABS bulk density commonly ranges from 0.55–0.65 g/cm³, compared with 0.62–0.72 g/cm³ for virgin pellets, so volumetric feeders require recalibration when regrind ratios change. Because ABS is hygroscopic, regrind must be dried with the same discipline as virgin resin: desiccant dryers with a dew point of −40 °C or lower, 2–4 h residence at 80 °C, and moisture content by ISO 15512 held at or below 0.1 wt%. Moisture above that threshold produces splay, surface silver streaks, and reduced impact strength. Contamination from polycarbonate, PVC, or flame-retardant ABS grades creates incompatible phases and can degrade at ABS processing temperatures; even small cross-contamination of 1–2 wt% can produce delamination or brittle failure.

When Regrind Content Moves Beyond 30 wt%, Which Property Measurements Govern the Substitution Cap?

At 10–20 wt% regrind, general-purpose ABS typically shows tensile stress at yield within ±5% of virgin values when measured under ISO 527-2. The more sensitive indicator is notched Izod impact under ISO 180/A or ASTM D256, because the polybutadiene phase can undergo crosslinking, particle agglomeration, or interfacial debonding after repeated heat histories. A regrind fraction of 20–30 wt% often preserves 85–95% of virgin notched Izod impact, but at 50 wt% regrind retention can fall below 80% in high-impact ABS grades. Melt flow rate measured at 220 °C/10 kg under ISO 1133-1 may increase by 10–30% after multiple passes, altering fill pressure, cushion control, and pack/hold response. The following checklist defines the minimum data set for regrind substitution at process changeover or when the recovered fraction exceeds 20 wt%.

Cost Allocation Without a Conforming Product Mass Balance

A normalized mass balance makes the real unit cost explicit. For 100 kg of conforming product, a 25 wt% scrap rate implies 133.3 kg total throughput. At 90% recovery efficiency, 30.0 kg of regrind is returned to the process and 3.3 kg is lost as fines, purge, or contaminated material. If virgin resin index is 100 per kg and regrind is assigned a value of 70 per kg, the raw material cost is 103.3 × 100 + 30.0 × 70 = 12,430 index units per 100 kg conforming product, or 124.3 index per kg. Grinding, conveying, and drying may add 2–5 index per kg of scrap handled; for 33.3 kg scrap, this adds 67–167 index units. The resulting real unit cost is approximately 125.0–126.0 index per kg. Without regrind recovery, the same mass balance requires 133.3 kg of virgin resin at 100 per kg plus disposal cost, yielding 133.3–134.0 index per kg. The gap between these two unit costs is determined by recovery efficiency, by regrind handling cost, and by whether the regrind can be returned to the same part without exceeding impact, color, or melt-flow specifications. If the recovered material cannot be reused in the original part because of custom color or high-impact requirements, it may be downgauged to black utility components or lower-stress parts at a lower opportunity value.

Sheet extrusion of ABS introduces a different yield structure. Cut-sheet thermoforming of ABS produces skeletal trim, edge trim, and reject formed parts that often total 30–50 wt% of starting sheet mass. A sheet line with a 120 mm single-screw extruder, L/D 32:1, and gravimetric feeding can return ground sheet trim to the extrusion process if the trim is free of release agents, inks, and adhesive contamination. Melt temperature for ABS sheet is typically 220–250 °C, with chill roll temperatures maintained at 60–90 °C. In thermoforming, regrind levels above 30 wt% can reduce hot-sheet extensibility and increase wall-thickness variance; this is evaluated by area draw ratio and formed-part thickness grids rather than Izod impact alone. Published data for high-rubber ABS at >50 wt% post-industrial regrind combined with hot-runner residence times above 10 min remains limited; processor qualification should use lot-specific rheology, impact testing, and purge-frequency records to establish the actual regrind tolerance of the production line.