Dimensional stability and mechanical strength of thermally modified giant bamboo [Dendrocalamus asper (Schult.) Backer] using steam and oil

Various thermal modification (TM) treatments using different media have been commercialized, including the commonly practiced TM via steam and hot oil using vegetable or mineral oils. To expand the range of oil treatment mediums, this study explored the use of spent cooking oil (used oil from food frying in restaurants), which was centrally collected by a certified hauler and treater of this waste liquid. The effects on the dimensional stability and mechanical strength of giant bamboo [Dendrocalamus asper (Schult.) Backer] poles subjected to 175°C and 200°C for 30 min and 60 min in steam and oil, respectively were determined. The data were analyzed using a factorial experiment in a completely randomized design with TM treatments, temperature, duration, and presence of nodes as factors.

Results revealed significantly improved dimensional stability in modified bamboo as indicated by reduced moisture content, dimensional shrinkage/swelling, and water loss/absorption at higher temperatures. While treatment duration moderately affected dimensional stability, oil-treated samples exhibited greater enhancement.

In terms of mechanical strength, bamboo treated at 175°C exhibited enhanced flexural (modulus of rupture or MOR, and modulus of elasticity or MOE) and compressive strength (CS). However, treatments at 200°C led to marked reductions in these properties. Node presence generally weakened bamboo, except for CS. Oil-treated samples demonstrated superior mechanical strength, although there was a slight reduction in MOR with extended exposure.

In conclusion, steam and oil-based TM improve the dimensional stability and mechanical strength of giant bamboo at 175°C. For optimal properties, a 30-min treatment is recommended. This research underscores the viability of spent cooking oil in enhancing bamboo's physico-mechanical attributes, contributing to sustainable applications.