Swelling of Phyllostachys edulis with different treatments

To determine the degree of swelling for bamboo (Phyllostachys edulis) in different aqueous solutions, bamboo samples were soaked in different concentrations of Na2CO3, NaOH, ZnCl2 (combined with HNO3 hydrothermal treatment), and deionized water. Changes in macro-and micro-structure were observed with the volume and area expansion rates used as evaluation indexes for the degree of swelling. Results indicated that NaOH and Na2CO3 both showed a good effect on the swelling of bamboo, meanwhile, the swelling effect of bamboo was proportional to concentration of Na2CO3, but inversely proportional to concentration of NaOH. Among the treatments, optimal volume increase rate were found with 0.5 mol·L-1 NaOH (9.69%) and with 1.0 mol·L-1 Na2CO3 (10.57%). Unsatisfactory swelling effect for swelling occurred when ZnCl2 was used alone, but pretreatment with a low concentration of HNO3 solution (500 g·L-1 ZnCl2 with 100 g·L-1 HNO3) improved swelling effect. Meanwhile, area of the bamboo in transverse sections before and after swelling showed that the area of fiber sheath distribution increased, but the area for parenchyma cell distribution after swelling was increased relatively small. Thus, changes in volume of bamboo after swelling was mainly due to changes in the fiber sheath distribution area.