The Effect Of Micro-explosion Treatment On The Permeability And Softening Effects Of Poplar Sheets

Fast-growing Poplar plantation is one of important plantation timber species in our country with its high growth speed and large volume. But fast-growing Poplar has low surface hardness, small density, qualitative soft material and poor mechanical performances, which make its use is restricted. Modification of fast-growing Poplar is an effective approach to adding its value. Micro-explosion treatment can improve its permeability and softening effects, which will lay the theoretical foundation and supporting data for the modification of fast-growing Poplar. It has great theoretical significance and practical value.Fast-growing Poplar sheets with the thickness of 1 mm,2 mm,3 mm,4 mm,5 mm are the research object in this paper. The effect of micro-explosion treatment on the permeability, microscopic structure, softening effects and dynamic thermal mechanical properties of Poplar sheets are studied in this paper. The results showed that:(1) Micro-explosion treatment has significant influence on fast-growing Poplar’s tangential permeability, while no significant influence on fast-growing Poplar’s radial permeability. After micro-explosion treatment, tangential penetration depth increased by 28.2%-184.2% while maximum radial penetration depth has an increase of less than 30%. The impact order:thickness>initial moisture content> micro-explosion pressure> micro-explosion times.(2) After micro-explosion treatment, the pit membrane of Poplar sheets occurred varying degrees of damage, while other structures were not observed significant changes. Main failure modes of pit membrane are diameter split, ring split and completely broken. From the surface to the core of specimen’s thickness direction, the number of the damaged pit membrane and its damage extent has decreased with the increase of depth. The greater the thickness is, the more obvious the decline is.(3) Micro-explosion treatment can improve the softening effects of Poplar sheets, which will reduce the thickness rebound rate when it is compressed. After the treatment, the maximum decrease of tangential and radial thickness rebound rate is 46.3% and 31.2%, respectively. Impact order:thickness> initial moisture content> micro-explosion pressure> micro-explosion times.(4) The storage modulus of micro-explosion treated specimen is lower than that of untreated ones. Compared with untreated specimen, the loss modulus peaks of treated ones move to lower temperature region. The glass transition temperature decreased by 4℃-15℃ and softening effect increased.