CHIMEI (Chi Mei) ABS PA-726 is a high-flow acrylonitrile-butadiene-styrene terpolymer within the Polylac ABS series. The grade is specified for injection-moulded components that require a measurable combination of melt flow, surface gloss, and moderate mechanical strength. Product conformity is evaluated under ISO 1183-1:2019 for density, ISO 1133-1:2022 or ASTM D1238-20 for melt flow index, ISO 527-2:2012 for tensile properties, ISO 178:2019 for flexural properties, ISO 180:2023 for notched Izod impact, and ISO 75-2:2013 for heat deflection temperature. Density of unfilled ABS PA-726 generally falls within 1.04–1.06 g/cm³. Exact lot-dependent values are reported on the manufacturer’s certificate of analysis; therefore, processing parameters must be validated against the supplied data rather than nominal grade sheets.

When high-gloss thin-wall moulding dictates a melt flow-oriented ABS selection

In injection moulding of thin-wall enclosures below 1.5 mm nominal thickness, PA-726 is selected because its high-flow classification permits reduced injection pressure and improved filling of long flow paths compared with general-purpose medium-impact ABS grades. On reciprocating-screw machines with a shot size of 30–70% of barrel capacity, the resin is processed at a melt temperature of 210–240 °C and a mould temperature of 40–70 °C. Surface gloss is retained only when the cavity surface finish is maintained below Ra 0.05 µm and when gas venting is adequate. Vent depth must not exceed 0.03 mm to avoid flash while preventing burn marks. High-gloss appearance is not an intrinsic material property alone; the mould surface must be polished, and the cooling regime must avoid sink marks at section changes. PA-726 is often specified for appliance control panels, vacuum cleaner housings, and computer peripheral enclosures where wall thickness below 2.0 mm and visual appearance are critical. The high-flow formulation reduces shear heating but may reduce melt strength; therefore, thin-wall parts with abrupt changes in wall thickness require radii of at least 0.5 mm to avoid jetting and internal stress concentrations.

Moisture control is a critical first processing boundary for PA-726. The resin must be dried to a moisture content below 0.05% by weight before injection moulding. Desiccant-bed dryers with a closed-loop hopper and dew point at or below -30 °C are recommended; conventional hot-air ovens are not sufficient under relative humidity above 60%. Drying at 80–85 °C for 3–4 hours is typical, and holding the dried resin at 80 °C in the hopper prevents re-adsorption. When ambient storage exceeds 8 hours from drying, re-drying is mandatory. Processing undried PA-726 results in surface splay, silver streaking, and a reduction in notched Izod impact values due to hydrolysis and void formation at the rubber phase. Batch-to-batch variations in moisture uptake are observed on production lines when silo-to-machine transfer lines are not purged with dry air; therefore, moisture analysers should be installed at the hopper inlet rather than at the silo outlet.

What Are the Relevant Test Methods and Specification Limits for PA-726?

Specification compliance for PA-726 is assessed according to the following test method matrix. The exact measured values vary by production lot, colour, and post-processing condition; the table identifies the test methods that must be cited on a certificate of analysis.

PA-726 is not classified as a flame-retardant ABS under IEC 60695-11-10; the typical rating is at or below HB at 1.5 mm unless a specific compound with flame-retardant additives is selected. The grade is not intended for continuous service above 85 °C under load. It is also not inherently UV-stable; long-term outdoor exposure results in yellowing and loss of surface gloss. Where UV resistance is required, the moulded part must be painted, coated, or co-extruded with a UV-stabilised cap layer. These boundaries are not process defects; they define the selection limits of the resin matrix.

In masterbatch or dry-blend operations, PA-726 is compounded with carbon black, titanium dioxide, or polymer-compatible colour masterbatch. The addition level must be limited to 2.0–5.0 wt% for pelletised masterbatch because higher levels reduce melt flow and increase the risk of pigment inhomogeneity on curved surfaces. Halogenated flame retardant additions, if required, are not recommended without a complete revalidation of flow performance and surface gloss, because these additives shift the melt viscosity curve and may generate plate-out on mould surfaces. When high-gloss black parts are specified, the use of carbon black with primary particle size below 20 nm improves jet black depth but may increase static surface dust attraction. Twin-screw compounding of PA-726 with 15.0 wt% short glass fibre increases flexural modulus but sacrifices surface gloss and Izod impact; therefore, glass-filled PA-726 is not a direct drop-in substitution for unfilled PA-726 in appearance-critical mouldings.

Comparative position among high-flow ABS, high-heat ABS, and electroplating ABS

PA-726 is differentiated from other ABS grades by its flow-to-impact balance. General-purpose high-impact ABS maintains higher notched Izod values but requires higher injection pressure and is less suited to thin-wall filling. High-heat ABS grades, characterised by higher heat deflection temperature above 100 °C, exhibit lower melt flow and may require hot-oil mould temperature control above 100 °C; PA-726 is processed with water-cooled moulds at 40–70 °C, which reduces energy input and cycle time. Electroplating ABS grades are formulated with controlled butadiene domain size for acid etching adhesion; PA-726 is not a direct substitute for electroplating ABS because the etched surface may not provide sufficient Pd-Sn colloidal adsorption. Flame-retardant ABS grades deliver UL 94 V-0 at 1.5 mm but often reduce flow and gloss. Selection of PA-726 is therefore appropriate when visual gloss, mould filling, and moderate mechanical performance are the dominant requirements, and when service temperature does not exceed 85 °C.

Flow behaviour in PA-726 follows shear-thinning pseudoplastic behaviour. Melt flow index measured per ISO 1133-1:2022 is a single-point parameter and does not capture the full shear-viscosity curve; therefore, mould filling analysis should be based on capillary or slit rheometry data. In high-shear regions such as gates and thin-wall sections above 1000 s⁻¹, the melt viscosity decreases, which permits thin-wall filling. However, in thick sections where shear rate falls below 100 s⁻¹, orientation recovery and mould shrinkage become more pronounced. For a nominal wall thickness of 2.0 mm, the linear mould shrinkage is typically 0.4–0.7%; design tolerances should account for this range. Shrinkage anisotropy is lower when the mould temperature is maintained at the upper end of the recommended range and when the holding pressure profile is optimised with a pressure transducer at the gate.

PA-726 has limited chemical resistance to ketones, esters, and aromatic hydrocarbons. Exposure to acetone, methyl ethyl ketone, or toluene causes surface attack and stress cracking in moulded parts. For applications requiring occasional contact with household cleaning agents, the resin performs acceptably with diluted aqueous solutions, but compatibility testing per ISO 22088-3:2020 or ASTM D543-21 is required. Environmental stress cracking resistance is influenced by moulded-in stress; annealing at 70–80 °C for 2–4 hours reduces residual stress and improves resistance to certain oils and detergent solutions. However, annealing above the heat deflection temperature of the grade causes dimensional distortion and is not recommended.

Regulatory conformity for PA-726 may include RoHS Directive 2011/65/EU Annex II restriction of lead, mercury, cadmium, hexavalent chromium, PBB, and PBDE; REACH Regulation (EC) No 1907/2006 SVHC screening; and FDA 21 CFR 177.1520 for food contact if the specific grade and colourant are covered. The presence of processing aids or colourants may alter compliance; therefore, the end-use manufacturer must obtain a product-specific declaration. PA-726 is not intended for medical implant use under ISO 10993-1:2018 unless specific biocompatibility data has been generated for the finished device.

PA-726 is occasionally compared with polycarbonate/ABS blends. PA-726 has a lower heat deflection temperature and lower impact strength than most PC/ABS blends, but it offers easier flow, lower melt temperature, and lower material density. When an application requires notched Izod values above 50 kJ/m² or heat deflection temperature above 100 °C, PA-726 is not the correct selection. Conversely, for multi-point hot-runner tools with small gates, the high flow of PA-726 reduces gate pressure drop and improves cavity balance compared with medium-flow PC/ABS. This distinction is critical in tools with more than 8 cavities.

Production-scale injection moulding of PA-726 requires matching the machine and tool design to the grade’s melt flow. The following processing window is a representative starting point for a 2.0 mm wall thickness appliance housing; it must be adjusted for actual part geometry and gating.

On production lines, the most commonly observed defect in PA-726 moulding is splay due to incomplete drying or condensation in feed lines. The second is jetting in long, thin-wall sections when the gate is smaller than 0.8 mm diameter. A third failure mode is mould deposit from pigment masterbatch where the screw L/D ratio is below 18:1 and plasticating is incomplete. These process failures are not product defects; they indicate that the machine configuration or drying protocol is outside the grade’s processing envelope. Published data for the exact setting correlation on every moulding machine is limited; therefore, process validation using short-shot studies and pressure-drop measurements is required.