The relationship between moisture content and shrinkage strain in the process of bamboo air seasoning and cracking

Abstract

The industrial utilization of natural bamboo has been plagued by cracking that are closely related to the relationship between the moisture content (MC) and drying shrinkage. To reveal the cracking mechanism, three relationships between environmental factors and drying rate (DR), MC and shrinkage strain, strain variation and cracking were investigated during the air seasoning (AS) of the 6-meter-long bamboo in free state. The DR decreased significantly affected by hygroscopicity, and a model considering hygroscopicity and environmental factors was proposed for estimating the DR. Natural bamboos were prone to cracking between 42% and 12% MC. The top cracking was earlier and more than other parts, which is caused by initial lower MC and absence of end diaphragm. There were significant differences in shrinkage strain between different tissues and sites. This work reveals the drying characteristics, the law of strain variation, and cracking mechanism in bamboo AS process, which is vital to the prevention and control of drying defects.

Keywords:

• Bamboo air seasoning
• moisture content model
• shrinkage strain
• cracking

Additional information

Funding

This work was supported by Fundamental Research Funds of ICBR (No. 1632019030 and No. 1632018025) and the sub-task of the national “13th Five-Year” key research and development plan on the Properties of Round Bamboo and Design and Manufacture of Modular Spliced Furniture (No. 2016YFD060090502)