Color and physico-mechanical properties change from 10 months of natural outdoor weathering for injection molded bamboo flour (BF)/polypropylene (PP) foamed composites were investigated. The composite surface morphology, before and after exposure, was observed by using environmental scanning electron microscopy (ESEM). Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) were used to characterize the chemical structures. Natural weathering was shown to cause more discoloration and surface deterioration, while the physicomechanical properties, rheological behavior, and thermal stability were less negatively affected for composites with higher BF amount ranging from 0 to 35 wt%. The rheological behavior results indicated decreases in the storage and loss moduli and the complex viscosity of weathered composites. Crossover frequency was found to increase and the average molecular weight decreased. The initial thermal decomposition temperature declined in foamed PP by 25 C and in 35% BF/PP foamed composite by 6 C, indicating a slight decline in thermal stability, as shown by thermogravimetric (TG) analysis. Photodegradation, photooxidation, and matrices chain scission in the composites were confirmed by FTIR and XPS analyses.

The effect of outdoor natural weathering on the properties of injection molded 33 wt% bamboo powder (BP)=polypropylene (PP) foamed composites with and without the antioxidant and hindered amine light stabilizers (HALS) were investigated. The composites containing the antiaging agents had higher color stability, slightly greater retentions of flexural modulus, tensile and notched impact strengths, higher creep resistance, and better rheological stability than the reference composite. The antiaging agents of pentaerythritol tetrakis(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate) and poly-(n-hydroxyethyl-2,2,6,6-tetramethyl-4-hydroxy-piperidyl succinate) had more beneficial effect than n-octadecyl-b-(4-hydroxy-3,5-ditert-butyl-phenyl)-propionate and bis(2,2,6,6-tetramethyl-4-piperidinyl)sebacate. After 12 months of exposure, ᭝E* decreased from 22.8 of the reference composite to 9.9 of the composite with the antiaging agents. Rheological behavior results indicated that the storage modulus, complex viscosity, and non-Newtonian fluid index of composites containing the antiaging agents were slightly increased. Natural weathering caused less decreases in the storage and loss moduli, crossover modulus, relaxation time, and average molecular weight for composites containing the antiaging agents than those for the reference composite. Environmental scanning electron microscopy (ESEM) observation confirmed the improved surface durability for composites containing the antiaging agents.