Morphological, physical, chemical, and thermal decomposition properties of air-heat-treated balsa fruit fibers at different temperatures

This study was conducted to investigate the effect of air heat treatment on the morphological, physical, chemical, and thermal decomposition properties of balsa fruit fibers (BFF). BFF were heat-treated in air at 100 ℃, 200 ℃, 240 ℃, 280 ℃, 300 ℃, 320 ℃, and 340 ℃. Color changes, weight loss, and moisture adsorption were also examined. The color of BFF was light brown below 200 ℃, brown at 240 ℃, dark brown at 280 ℃, and black from 320 ℃. The total color change (ΔE*) of BFF increased rapidly until 280 ℃ and became from 280 ℃ constant until 400 ℃. The microfibrils in the fibers were observed below 240 ℃ and disappeared at 280 ℃, and the fibers heat-treated above 280 ℃ showed an amorphous-like cell wall. The fibers below 240 ℃ showed a straight form with a smooth surface, whereas the fibers at 240 and 280 ℃ showed an uneven form with lumps on their surface due to melted wax. With increasing temperature, the weight and width of the fibers decreased. The vapor adsorption property of the BFF increased with increasing treatment temperatures. X-ray diffractograms of BFF showed cellulose I crystalline structure until 320 ℃, which changed to amorphous at 340 ℃. Holocellulose, α-cellulose, and hemicellulose were detected in fibers below 240 ℃ but not in samples treated at 280 ℃. The wax content of the BFF decreased as temperatures increased. FT-IR spectra showed the peaks of plant wax and carbohydrate compounds in BFF until 320 ℃ and the peaks of lignin at all temperatures. The thermal decomposition properties of BFF noticeably changed after heat treatment above 240 ℃.