Time‐temperature superposition principle application to the hygrothermal discoloration of colored high‐density polypropylene/wood composites

Discoloration kinetics of wood plastic composites (WPCs) made of recycled high density polyethylene (HDPE) during accelerated hygrothermal aging test at 45–65°C was conducted by means of time‐temperature superposition principle (TTSP). Color parameters measured with a spectrophotometer by CIELAB color system showed that L* and Δ E* increased while a* and b* decreased with aging time and temperature. A single horizontal shift was adequate for the superposition of color parameter master curves, indicating temperature can be used as accelerating factor to the discoloration of the studied WPCs. The regression line for Arrhenius plot showed a linearity for color parameters ( R ² = 0.9996), suggesting TTSP concept can be used to analyze and predict the discoloration kinetics of WPCs at low aging temperature. The prediction of color parameters at ambient aging temperature (21°C) can be extended to 7.2 years. The activation energy calculated from color parameters using TTSP method was 85.5 kJ/mol and similar to the reported values of HDPE thermal relaxation reactions calculated from other methods in the open literature. POLYM. COMPOS. 37:1016–1020, 2016. © 2014 Society of Plastics Engineers