Internal Structure, Thermal Decomposition, and Combustion Behavior of Inorganic-Bonded Bamboo Composite with Modified Magnesium Oxysulfate Binder

Inorganic-bonded bamboo composite (InorgBam) replaces conventional organic resins with a modified magnesium oxysulfate (MOS) binder, creating a distinct bamboo-bundle-reinforced inorganic matrix. This study investigated its mechanical failure characteristics, internal structure, thermal decomposition, and combustion behavior using mechanical tests, X-ray computed tomography (CT), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and cone calorimetry. CT results showed that the bamboo bundles remained longitudinally continuous, while the hardened MOS phase occupied most inter-bundle spaces; localized voids, underfilled regions, and interfacial discontinuities were also observed. Thermal analysis indicated that InorgBam exhibited a broader DTG response at approximately 390–400 °C than the bamboo fiber bundles, which showed a sharper peak near 340 °C. At 800 °C, the residual mass of InorgBam was about 60%, compared with 24–25% for the bamboo fibers. Under a heat flux of 50 kW/m2, InorgBam showed no sustained flaming during 1800 s of exposure, and its pHRR was 17.9 kW/m2, 93.2% lower than that of bamboo scrimber. These results indicate that MOS dehydration and the formation of an inorganic-rich residue contribute to the improved thermal stability and reduced heat-release intensity of InorgBam.