Microwave Drying of Scots Pine Lumber:Structure Changes,Its Effect on Liquid Permeability

Microwave(MW)drying method was adopted to enhance the liquid permeability of Scots pine lumber.Structure changes were characterized by stereoscope microscope,scanned electron microscope(SEM)and transmission electron microscope(TEM)examination.Pore parameters before and after MW treatment were detected by mercury intrusion porosimetry(MIP)method,and the effect of structure changes on liquid permeability were analyzed.As stereoscope microscope,SEM and TEM examination results showed,macro and micro checks mainly developed at intercellcular of tracheids,intercellular of ray parenchyma and tracheid,while these checks extend main along the radial-longitudinal plane.Pit border destruction,aspirated pits’orus translocation and micro-checks in tracheid cell wall were also observed.MIP test shown that pore volume and pore area increased as macro and micro checks generated to form new cavities.Microstructure changes would increase the quantity of pores or enlarge the pore diameter.Liquid flow pathways increased as macro and micro checks generated,aspirated pits reopened to form new pathways;liquid flow efficiency improved as porosity,pore volume and pore diameter increased which facilitated the liquid flow.

Spectroscopic/Microscopic Elucid

The Arundo donax is a typical fast-growing species from the family Gramineae,which is widely cultivated in China.With a huge yield of A.donax in China,this plant offers great potential for biofuels production.The different types of organization of cell and the tissue in the A.donax could influence the efficiency of enzymatic hydrolysis.In this study,A.donax was subjected to 0.5%(w/w)sulfuric acid(H2SO4)for pretreatment at 140℃for 10 min,20 min,40 min,and 60 min,respectively.The changes in microstructure,chemical composition,topochemical properties were comprehensively analyzed.Using a series of spectroscopic and microscopic techniques including Fourier transform infrared spectroscopy(FT-IR),X-Ray diffraction(XRD),polarized light microscopy(PLM),and confocal Raman microscopy(CRM)to obtain the correlative structural and chemical information.Analysis results of chemical composition,FT-IR spectra and XRD indicated that with increasing reaction time,more hemicellulose and lignin would be removed.Correspondingly,there was an obvious increase of the cellulose relative crystallinity via extending reaction time.Results of the PLM observations showed that the birefringence gradually dimmed due to the diminishing of the cellulose component.Furthermore,the CRM mapping images showed the lignin component in compound middle lamellar(CML)was difficult to remove relatively as compared with that in secondary walls.These results indicated that the combination of spectroscopic and microscopic elucidation could give an insightful understanding of chemical changes in cellular level during pretreatment.