Effects of Blend Ratio and Heating Rate on the Thermal Decomposition of Coffee Husk and Disposable Face-Mask Waste

Coffee husk and disposable surgical masks are contrasting feedstocks for thermochemical co-processing. This study examined how blend ratio and heating rate affect non-additive mass-loss behavior during co-pyrolysis under nitrogen. Thermogravimetric analysis used a nominal sample mass of 5 mg for coffee husk (CH100), unused three-ply surgical-mask material (M100), and coffee-husk-to-mask mass ratios of 75/25 (CH75M25), 50/50 (CH50M50), and 25/75 (CH25M75). Samples were heated from ambient temperature to 800 °C at 10, 20, and 30 °C min−1 under a nitrogen flow of 25 mL min−1. Blend curves were compared with mass-weighted pure-feedstock predictions at the matching heating rate over 50–750 °C. This common evaluation interval included moisture release, principal devolatilization, and subsequent slower mass loss, with residual mass compared at 750 °C. The primary derivative thermogravimetric (DTG) peak shifted from 314.4 to 336.3 °C for CH100 and from 403.7 to 432.7 °C for M100 between 10 and 30 °C min−1. CH50M50 had the most negative mean mass deviation among the tested blends: −14.31, −13.43, and −12.93 percentage points at the respective rates. The results identify blend-dependent departures from the additive reference and CH50M50 as a candidate for further controlled co-pyrolysis studies. The observed mass deviations alone do not establish a chemical mechanism or improved product yield.