The splitting of bamboo in response to changes in humidity and temperature.

Hone, Timothy; Cahill, Luke; Robinson, Anthony; Korde, Chaaruchandra; Taylor, David

Bamboo culms are extensively used for structural and decorative purposes. Under certain atmospheric conditions culms can split longitudinally with detrimental effects on their appearance and structural integrity. Here we describe the first ever systematic study of this phenomenon. We tested culms of Moso bamboo (Phyllostachys Pubescens), which had been commercially dried to a moisture content of 12.5%. Using a purpose-built environmental chamber, we measured the rate of splitting for ten different test conditions, varying temperature and humidity and testing samples with and without nodes. A 50% probability of splitting after one week was found to be associated with a reduction in moisture content to 8%. We found that splitting was mainly determined by a change in relative humidity, as opposed to absolute humidity. We hypothesised that splitting occurs owing to an incompatibility in shrinkage in the tangential direction during drying, creating tensile residual stress near the outer surface of the culm. Using data from the published literature we developed a simple theoretical model capable of predicting splitting. Higher residual stress was predicted near nodes, which was consistent with our finding that splitting rarely occurs in samples having no nodes. These findings will be useful in the prevention of splitting, through control of the environment or other protective measures.