Accelerated weathering parameters for some aromatic engineering thermoplastics. Part 2: Polycarbonate copolymers,...

Area of Science:

• Materials Science
• Polymer Science
• Photochemistry

Background:

• Understanding material responses to environmental factors is crucial for accurate accelerated weathering and service life prediction.
• Polymers like polycarbonate-b-resorcinol polyarylate copolymer (RPA), poly(acrylonitrile-co-butadiene-styrene) (ABS), and polycarbonate copolymers are susceptible to photodegradation.

Purpose of the Study:

• To investigate the effects of UV intensity, temperature, relative humidity (RH), and UV wavelength on the yellowing and gloss loss of RPA, ABS, and polycarbonate copolymers.
• To compare the photodegradation behavior of these polymers with other aromatic polymers.

Main Methods:

• Exposure of polymer samples to controlled environmental variables using the NIST SPHERE (Simulated Photodegradation via High Energy Radiant Exposure).
• Quantification of yellowing and gloss loss as indicators of degradation.
• Analysis of degradation kinetics, including activation energy and response to varying RH and UV wavelengths.

Main Results:

• Most polymers showed a proportional response to UV irradiance (reciprocity), with ABS deviating at elevated temperatures.
• ABS exhibited a higher activation energy for yellowing (31 kJ mol⁻¹ ± 2 kJ mol⁻¹) compared to other aromatic polymers.
• RPA showed a negative activation energy (-5 kJ mol⁻¹ ± 3 kJ mol⁻¹), indicating distinct photodegradation mechanisms. Both ABS and RPA degraded faster at RH ≤ 10% compared to RH ≥ 50%.

Conclusions:

• Accelerated weathering protocols should utilize UV sources that accurately mimic sunlight.
• Testing temperatures should approximate in-use conditions to ensure reliable service life predictions.
• Maintaining relative humidity above 10% is recommended for more accurate accelerated weathering studies.