Differences in the viscoelastic properties between earlywood and latewood in the growth rings of Chinese fir as analyzed by dynamic mechanical analysis (DMA) in the temperature range between-120 degrees C and 120 degrees C

作者：Li, Anxin; Jiang, Jiali^*; Lu, Jianxiong

来源：Holzforschung, 2019, 73(3): 241-250.

DOI：10.1515/hf-2018-0054

• Chinese fir
• density
• earlywood
• growth ring
• latewood
• microfibril angle
• percentage of tracheid cell wall
• viscoelasticity

To clarify the viscoelasticity of earlywood (EW) and latewood (LW) within different growth rings of Chinese fir, the following data were determined: absolute dry density, percentage of tracheid cell wall, microfibril angle (MFA), modulus of elasticity (MOE), storage modulus (E') and loss modulus (E '') within the 3rd and 6th growth rings (in heartwood, hW) and the 14th and 18th growth rings (in sapwood, sW). The E' and E '' data were obtained by dynamic mechanical analysis (DMA) between -120 degrees C and 120 degrees C, at a heating rate of 1 degrees C min (-1) at the frequencies of 1, 2, 5 and 10 Hz under a dynamic load amplitude of 10 mu m. All measured data were different between EW and LW. In the same growth ring, LW had a greater MOE and larger E' than those of EW due to the higher density of LW. The MOE and E' increased for both EW and LW with increasing tree age. The variation of MFA in different growth rings of EW influenced the MOE and E'. Both density and the MFA affected the MOE and E' in LW. The profiles of E '' plots vs. DMA temperature reveal two maxima around -12 degrees C (beta 13 mechanical relaxation process, alpha MRP) and 12 degrees C (alpha MRP). The LW-MRP maxima are higher than those of EW, but in both cases increased with tree age. No frequency dependence was seen for the alpha MRP, whereas the loss peak temperature (LPT) of the beta MRP increased with increasing frequency of DMA. Almost no difference in alpha LPT was observed between the four EW growth rings, and their beta LPTs were similar. The LW-alpha LPT was almost the same in the four growth rings, but the hW-beta LPT was higher than that of sW. In addition, the apparent activation energy (Delta H) of the hW-beta MRP was greater than that of sW in both EW and LW, and the EW data > LW data in individual growth rings. These differences can be explained tentatively that hW and EW contain more extractives than sW and LW, and the deposited of extractives limit the motion of molecular segments within the cell walls.

• 出版日期2019-3
• 单位中国林业科学研究院