PPA (Polyphthalamide): High-Temperature Nylon — HDT 280°C for Automotive Under-Hood Applications

Polyphthalamide (PPA) is a semi-aromatic high-temperature nylon that bridges the gap between standard aliphatic nylons (PA66, PA6 — HDT ~65-85°C) and ultra-high-performance thermoplastics (PEEK, PEI — cost 5-10× PPA). The aromatic diacid...

Polyphthalamide (PPA) is a semi-aromatic high-temperature nylon that bridges the gap between standard aliphatic nylons (PA66, PA6 — HDT ~65-85°C) and ultra-high-performance thermoplastics (PEEK, PEI — cost 5-10× PPA). The aromatic diacid component (typically terephthalic acid and/or isophthalic acid comprising >55% of the diacid content — this is what makes it a 'polyphthalamide') raises the glass transition temperature to 125-135°C (vs 50-65°C for PA66) and the melting point to 310-325°C (vs 255-265°C for PA66). With 30-50% glass fiber, PPA achieves an HDT of 270-285°C at 1.82 MPa — approaching PEEK territory at one-third to one-fifth the material cost.

PPA's dominant application is automotive under-hood components: thermostat housings, coolant pump impellers, charge-air cooler end caps, and EGR valve components exposed to 130-180°C coolant/glycol and hot engine air. PPA resists long-term glycol/water aging significantly better than PA66 (which hydrolyzes and embrittles above 130°C in coolant). It also provides excellent resistance to road salt (CaCl₂, NaCl solutions — which cause stress-corrosion cracking in PA66), automotive fluids (oil, transmission fluid, power steering fluid), and biodiesel exposure.

Processing Warning: PPA requires mold temperatures of 120-170°C (oil-heated molds — water-heated max 95°C is too cold). Inadequate mold temperature produces an amorphous skin layer that post-crystallizes in service, causing dimensional change, warpage, and loss of mechanical properties. PPA absorbs moisture MORE SLOWLY than PA66 (aromatic backbone reduces water affinity) — but still requires drying to <0.05% moisture (80°C for 4-8 hours, desiccant dryer) before processing. Wet PPA hydrolyzes at melt temperature, same failure mode as all nylons.

Technical Properties

Equivalents & Cross-References

Related Diagnostics & Materials

References & Industry Standards

• ASTM International. Standard Specifications for Engineering Plastics & Thermoplastics. astm.org
• UL Prospector. Plastics & Elastomers Material Database. ulprospector.com
• MatWeb. Material Property Data for Engineering Thermoplastics. matweb.com
• ISO 1043. Plastics — Symbols and Abbreviated Terms. iso.org