Acrylonitrile butadiene styrene (ABS) is a two-phase thermoplastic composed of grafted polybutadiene rubber domains dispersed in a continuous styrene-acrylonitrile (SAN) copolymer matrix. Commercial injection-molding grades typically contain 15–25% polybutadiene by mass, 22–28% acrylonitrile, and the balance styrene, with rubber particle diameter controlled by emulsion polymerization at 0.1–0.5 μm or continuous mass polymerization at 0.5–2.0 μm. Under ISO 527-2, unfilled ABS grades exhibit tensile yield stress from 38 MPa to 45 MPa and tensile modulus from 2100 MPa to 2500 MPa. Notched Izod impact measured to ISO 180/A at 23 °C typically falls between 15 kJ/m² and 35 kJ/m²; at -30 °C the same test frequently drops below 15 kJ/m². Heat deflection temperature measured to ISO 75-2 at 1.8 MPa is commonly 90–100 °C, while Vicat B50 under ISO 306 is 95–105 °C. Melt volume-flow rate under ISO 1133 at 220 °C and 10 kg load is typically 5–25 cm³/10 min. The material is dried at 80 °C for 2–4 h in a desiccant dryer to reduce residual moisture below 0.05% before melt processing.

The simultaneous specification of notched impact above 30 kJ/m² at -30 °C and heat deflection above 110 °C at 1.8 MPa exceeds the ordinary property envelope of unmodified ABS. Raising butadiene content increases low-temperature toughness but lowers modulus and heat resistance. Raising acrylonitrile content improves heat resistance and chemical resistance but reduces ductility and processability. Blending with bisphenol-A polycarbonate introduces a higher-glass-transition amorphous phase and a ductile secondary polymer network, forming the basis of PC/ABS compounds for applications requiring both impact and thermal stability.

When ABS Alone Is Not Enough: PC/ABS for Impact and Heat Together

PC/ABS compounds containing 40–65% polycarbonate by mass are formulated to shift the property balance beyond the ABS ceiling. Notched Izod values under ISO 180/A at 23 °C are generally 40–65 kJ/m², and at -30 °C the same test commonly retains 20–45 kJ/m². Tensile yield stress under ISO 527-2 is typically 50–60 MPa, and heat deflection temperature under ISO 75-2 at 1.8 MPa reaches 110–125 °C. Instrumented puncture impact under ISO 6603-2 at 23 °C increases from approximately 10–20 J for general-purpose ABS to 40–70 J for unfilled PC/ABS. Automotive interior retainers, power-tool housings, and electrical equipment enclosures use PC/ABS where ABS alone fails in low-temperature drop tests, heat-soak tests, or structural loading after exposure to interior solar loads.

Compounding of PC/ABS on a co-rotating intermeshing twin-screw extruder with 40:1 L/D is run at melt temperatures of 240–280 °C, vacuum venting at -0.08 MPa, and screw speed in the range 400–600 rpm. Polycarbonate domains are developed through high-shear dispersion and elongation into lamellar or co-continuous morphologies. Melt temperature above 300 °C initiates polycarbonate chain scission, while residence time above 10 min can oxidize polybutadiene and generate black specks. Production-scale compounding lines monitor specific mechanical energy input and melt pressure at the die plate; torque variation above ±10% indicates feeding instability, viscosity inhomogeneity, or incorrect polycarbonate dispersion. Batch-to-batch melt viscosity is checked by ISO 1133 to keep lot-to-lot variation within control limits for injection molding.

What Injection Molding Parameters Shift When Polycarbonate Content Rises Above 40 Percent?

PC/ABS injection molding requires higher barrel temperatures and higher mold temperatures than ABS. Barrel profiles are set from 240 °C near the feed zone to 270–280 °C at the nozzle, with mold temperature maintained between 60 °C and 100 °C. ABS molds are commonly run at 40–80 °C. The elevated mold temperature for PC/ABS reduces frozen-in orientation and improves weld-line strength; it is not solely a surface-gloss adjustment. Back pressure is held at 0.5–1.5 MPa, cushion size at 3–6 mm, and injection speed is set moderate to high depending on flow length. Hydraulic injection molding machines with clamp force from 6,000 kN to 12,000 kN are used for large housings. Drying before molding uses desiccant wheel dryers with supply-air dew point below -30 °C, drying temperature 100–110 °C, drying time 4 h, and residual moisture below 0.02%. Insufficient drying produces silver streaks, splay, and hydrolysis-induced molecular weight loss in the polycarbonate phase.

Weld-line strength in PC/ABS moldings is sensitive to mold temperature and gas counterpressure. Notched Izod specimens cut across a weld line retain 50–70% of unwelded impact when mold temperature is kept above 80 °C; at mold temperatures below 60 °C, retention can fall below 40%, producing brittle failures in drop tests. Chemical resistance follows polycarbonate limitations: standard PC/ABS stress-cracks in contact with aromatic hydrocarbons, ketones, esters, and concentrated mineral acids under tensile strain. Cleaning with chlorinated solvents should be avoided; isopropanol or mild soap solution is acceptable for surface cleaning. ABS has wider resistance to dilute aqueous acids and bases but is attacked by glacial acetic acid, concentrated nitric acid, and aromatic solvents. Neither material should be exposed to methyl ethyl ketone or toluene in stressed applications.

Flame-Retardant Grades, Paintability, and Regulatory Compliance

Halogen-free flame-retardant PC/ABS grades compounded with phosphate ester additives achieve UL 94 V-0 at 1.5 mm and 5VA at 2.5 mm in many supplier listings. General-purpose ABS often requires 2.0–3.2 mm sections for V-0 unless brominated or mineral synergists are used. The phosphate ester additive reduces heat deflection temperature by 5–15 °C and increases water uptake; higher mold temperatures are required to reduce deposit formation on tool surfaces. Paintability of PC/ABS is tested by ASTM D3359 crosshatch adhesion after flame or plasma pretreatment; ABS generally requires an adhesion promoter for solvent-borne coatings. Medical housing grades are assessed under ISO 10993-5 for cytotoxicity and ISO 10993-10 for skin sensitization. Electrical enclosures are evaluated under IEC 60695-2-11 glow-wire endpoints where end-product standards require. Compliance documentation includes REACH and RoHS 2011/65/EU as amended by (EU) 2015/863. Standard PC/ABS grades are not recommended for repeated steam autoclave exposure above 121 °C because hydrolysis reduces molecular weight; cyclic autoclave testing is required for reusable medical device housings.