Specifying Automotive PC/ABS: Hardness, Heat Deflection and Odour

Heat deflection decides feasibility

Interior parts must survive summer sun load; upper instrument panel surfaces reach 90-100 °C in still air. That is why upper door panels and centre console trim typically specify HDT (1.82 MPa) of at least 100 °C, and above 110 °C for areas in direct sunlight.

Watch the test load: values at 0.45 MPa run 10-15 °C higher than at 1.82 MPa, and data from different loads cannot be compared directly.

Hardness versus surface durability

Rockwell R110-R120 is a common requirement for gloss interior trim, essentially resistance to fingernail scratching and wipe-down abrasion. The usual lever is raising PC content or adding mineral filler, paid for with lower impact and a narrower processing window.

Matte grained parts are more forgiving on hardness and instead emphasise colour uniformity at weld lines and grain replication.

Odour and VOC are hidden gates

Interior materials must meet OEM odour grades — typically 3.0 or better on the 10-point scale — and VOC limits, tested to VDA 270 and VDA 278. Residual low-molecular additives from compounding are the main odour source.

This constrains formulation: low-odour antioxidants, low-volatility flame retardants and thorough vacuum devolatilisation during compounding are requirements, not nice-to-haves.