Recycled ABS Grades in the Catalogue: Black, Grey and Natural Compared. This article examines three recompounded Acrylonitrile Butadiene Styrene (ABS) colour streams differentiated less by base resin chemistry than by pigment loading, contaminant burden, and the visual tolerance each colour provides on a production moulding line. Natural grade is unpigmented or lightly stabilised reclaim from white goods, appliance trim, and light-coloured sheet edge material. Grey grade contains a titanium dioxide/carbon black blend that yields a mid-luminosity industrial grey. Black grade is mass-pigmented with carbon black at sufficient loading to mask dark specks, oxidative yellowing, and minor polycarbonate haze. The comparisons below address melt rheology, mechanical response, colour stability, drying behaviour, and regulatory screening. Values cited as representative production-lot windows are not guaranteed specifications unless a lot certificate states otherwise. Published data for this specific configuration is limited; therefore, the ranges reflect commonly observed industrial spreads rather than single-point design values.

How Do Melt-Volume Rate and Pigment Agglomeration Shift Rheology Across the Three Streams?

Melt-volume rate (MVR) is measured at 220 °C under 10 kg load according to ISO 1133-1:2022. In a recompounding line using a 40 L/D co-rotating twin-screw extruder, natural ABS exhibits the highest MVR window at 18–24 cm³/10 min, grey ABS falls at 16–22 cm³/10 min, and black ABS at 14–19 cm³/10 min. The reduction in the black stream is attributed to carbon black secondary aggregation; the pigment forms a particle network that raises low-shear viscosity and can increase melt pressure at the screen changer by 8–15% relative to natural at the same screw speed. Grey material is less rheologically offset because the mixed pigment system has lower specific surface area and less particle-to-particle structure than furnace carbon black. Capillary rheometry at 230 °C and shear rates between 100 s⁻¹ and 1000 s⁻¹ indicates shear-thinning power-law exponents near 0.32–0.41 for black and 0.28–0.36 for natural. The precise exponent is lot-dependent because recycled feedstock contains dispersed polycarbonate, SAN oligomers, and rubber-domain crosslink fragments. Raising barrel temperature alone does not correct these differences. A moulding operation switching from natural to black without adjusting decompression stroke may observe screw recovery time elongation of 0.5–1.2 s on a 1200 kN injection machine. Published data for spiral-flow normalisation is limited; however, the MVR offset is repeatable when feedstock is held constant. The dominant source of lot-to-lot shift is not the pigment but the rubber fraction and residual impact modifier in post-consumer reclaim.

Tensile yield stress measured to ISO 527-2:2012 at 5 mm/min is only marginally separated among the streams; natural ABS trends toward 39–45 MPa, while black ABS is 36–42 MPa because carbon black agglomerates act as stress concentrations and reduce yield elongation. Notched Izod impact at 23 °C under ISO 180/A shows a larger penalty: natural reclaim may reach 18–28 kJ/m², grey 15–25 kJ/m², and black 12–20 kJ/m². Batch-to-batch impact scatter on a 40 L/D compounding line is typically ±5 kJ/m² for natural ABS from mixed appliance waste; grey and black can vary by ±4 kJ/m² when a single feedstock source is used. Melt-filtration at 150–250 µm reduces the number of hard particles that initiate brittle failure but cannot restore original rubber morphology. In weld-line-critical parts, the black stream can appear more consistent because the dark surface hides flow-front convergence lines, but weld-line tensile strength measured on a double-gated tensile bar is typically 15–25% lower than the base material strength for all three streams. When a grey appearance part is moulded from a blend of black and natural regrind, the operator must control the let-down ratio to within ±1.5 wt%; otherwise the grey lightness shift exceeds ΔE 1.0 under D65/10° viewing.

When Carbon Black Masks Contamination but Raises Regulatory Screening Risk

Black ABS can tolerate a higher burden of dark paint flakes, trace rubber, and polycarbonate haze because carbon black at low luminance reduces the visual response. At 0.5–1.0 wt% carbon black on total compound, CIELAB lightness L* measured to ISO 11664-4:2008 falls below 30, and surface mottling from mixed feedstock is no longer visually objectionable. Natural ABS rejects this feedstock: residual polycarbonate domains create visible haze bands at loadings as low as 0.3–0.8 wt%, and yellowing from butadiene oxidation increases b* to 8–14 in older reclaim. Grey occupies the middle tier; it can hide light-coloured contamination but cannot mask severe rust stains, carbon black streaks, or bromine-rich flame-retardant residues. The trade-off is regulatory rather than visual: black streams derived from mixed electronics can carry brominated flame retardants that require screening to IEC 62321-3-1:2014. Homogeneous grey and natural white-goods reclaim generally shows lower halogen screening risk, but a RoHS compliance statement under 2011/65/EU must still be lot-specific.

Pre-drying of recompounded ABS in a desiccant wheel dryer with a dew point ≤ -40 °C is required before injection moulding or sheet extrusion. Drying at 80 °C for 2–4 h reduces residual moisture below 0.02 wt%; moisture content is verified with ISO 15512:2019 Karl Fischer or weight-loss methods. Natural grade exhibits visible splay at moisture levels above 0.03 wt% more readily than black or grey because unpigmented resin offers no hiding capacity for hydrolysis-generated voiding. Black carbon black raises equilibrium moisture uptake by approximately 0.02–0.05 wt% at 50% RH and can extend required dryer residence time by 20–40 minutes in humid plants. Grey stream with titanium dioxide is intermediate. Melt temperature should be held between 230 °C and 250 °C, and mould surface temperature at 40–80 °C. When mould temperature drops below 40 °C, all three grades exhibit reduced weld-line strength, but black parts hide the aesthetic defect while natural parts show delamination and flow haze. Amine-based mould release agents should be avoided with natural and grey ABS because amine residues can accelerate surface yellowing and interfere with subsequent adhesion or painting.

Vicat Softening, UV Ageing Response, and Gloss Recession in Outdoor-Exposed Housings

Vicat softening temperature under ISO 306/B50 places natural ABS at 99–104 °C, grey at 98–103 °C, and black at 96–102 °C. The dark stream absorbs more infrared energy and can develop higher surface temperature during continuous service, but black carbon black also provides ultraviolet screening that slows photo-oxidation of the butadiene phase. After 500 h of xenon-arc exposure to ISO 4892-2:2013 cycle 1, black ABS typically shows lower gloss recession and lower yellowness shift than natural ABS of the same rubber content. Natural ABS under the same exposure shifts from a starting yellowness index of 3–8 to 12–20, while black changes by less than 2 CIELAB units; grey shows intermediate drift. These ageing differences do not imply superior thermal stability in black moulding. If a black part is processed above 260 °C or held at melt temperature longer than 10 minutes, carbon black absorbs frictional and conductive heat, accelerating chain scission and generating acrid volatiles. Barrel residence time should therefore be kept below 5 minutes for all streams, but black grade is less forgiving of hot-runner dead spots because degradation stains are hidden until part failure.

For load-case assignment, black ABS is typically applied to internal brackets, fan shrouds, and electrical enclosures where dimensional stability and hiding power outweigh impact ductility. Grey ABS is selected for office machine housings and point-of-sale frames where a mid-lightness surface is required and minor flow lines are acceptable. Natural ABS is reserved for parts that are later painted, plated, or used in light-coloured appliance trim, provided the feedstock is sorted to remove polycarbonate, aluminium flakes, and oxidised fines. Injection moulding of natural ABS on a machine previously running black compound requires purging with a high-viscosity ABS or SAN carrier until the melt-manifold temperature stabilises; otherwise black streaks reappear for up to 50 shots in a 1200 kN machine. The purge requirement is less severe when switching from natural to black. Screw design preference differs with colour stream: black grades benefit from distributive mixing elements and fine-screen filtration at 200–400 µm mesh to break carbon black agglomerates; natural grades require vacuum venting at ≤ 50 mbar to strip volatiles and avoid silver streaking. Grey material tolerates a broader control envelope but responds poorly to low backpressure; a backpressure setting below 5 bar can produce colour striations in a shot-to-shot study. Contamination with polyvinyl chloride above 0.5 wt% is detrimental to all three streams; hydrochloric acid cleavage accelerates depolymerisation and causes brown streaks in natural and grey parts, while black parts may hide the visual symptom but not the loss of impact strength. Polyoxymethylene contamination should also be excluded because of formaldehyde release at ABS melt temperatures.