Physico-mechanical properties and decay fungi resistance of Dendrocalamus asper and Bambusa spinosa thermally modified in spent engine oil medium

This study examined the effects of thermal modification (TM) using spent engine oil as the heat transfer medium on the physico-mechanical properties and decay resistance of Bambusa spinosa Roxb. and Dendrocalamus asper (Schult. & Schult.f.) Backer. The TM process was conducted at three temperatures (140, 160 and 180 °C) and three durations (30, 60 and 90 minutes), coded as T1 to T9. The tests followed ASTM D 143–94 and ASTM D 2017–05 standards. The results revealed that thermally modified bamboo samples exhibited noticeable aesthetic colour changes, with a gradual darkening towards brown, and significantly improved dimensional stability, demonstrated by reductions in water absorption (27–75 %), thickness swelling (25–89 %), and equilibrium moisture content (31–64 %) compared with control samples. However, a decrease in flexural strength was observed at the highest temperature and longest duration (T9: 180 °C for 90 min), with reductions of 54–56 %. Despite this decrease in mechanical strength, the decay resistance of the T9-treated samples was comparable to chemically preserved bamboo, classifying them as highly resistant to decay fungi. Overall, the study demonstrated that spent engine oil is an effective medium for the thermal modification of bamboo when conducted in a controlled temperature setting.