The Influence Of White Rot On The Properties Of Larch Wood At Meso And Micro-mechanicial Level

In this study, Larix olgensis samples were decayed using white rot fungi (Coriolusversicolor) in different stages of decay. To evaluate the impact of white rot fungi on woodmesomechanics and miromechanics, longitudinal tensile strength and nanoindentationproperties of decadent specimens were tested before we got the data of mass loss rate. Thegrowth of hyphae in the wood was observed by optical microscope and scanning electronmicroscope, and wood chemical compositions in different decadent stages were tested usingFTIR and NMR. All these methods can help us analyse the reasons for the change of woodmechanical strength after rot erosion.The main research results were summarized as follows:(1) The color of wood surface changed significantly in the white fungi condition. Thecolor of untreated wood was faint yellow and it changed to dark reddish-brown after fungierosion. Wood mass loss rate also showed an increasing trend with the extension of thedecadent time. The mass loss rate are6.99%,10.26%,12.38%and13.63%respectively whensamples decayed for3weeks,6weeks,9weeks and12weeks. This indicates that incipientdecay in wood is around6weeks and mass loss rate is greater before that time.（2）There are different fracture modes during tensile test of larch wood flakes. Untreatedsamples did not broke completely at maximum load, but decayed samples broke completely intwo forms, tidy fracture and layered fracture, this is because different proportions of earlywood and late wood in different samples. The first part of load-displacement curve meetHooke’s law linearly which can be called elastic deformation, second part of the curve presentsthe characteristics of plastic materials. Tensile strength decreased significantly in incipientdecay. White rot fungi has smaller impact on MOE compared with brown rot fungi.(3)Nanoindentation MOE of different decadent times show that MOE had not declinedgreatly before9weeks, but hardness dropped significantly. After9weeks, MOE decreased greatly while hardness did not change a lot. This is because chemical compositions havechanged a lot during decadent period, white rot fungi mainly erode lignin in the wood cell wallbefore9weeks, but after that, they destroyed cellulose and hemicellulose which play a role ofskeleton in the wood cell wall.(4)It can be seen from the pictures of optical microscope and environmental scanningelectron microscope that mycelium appeared in lumen after the decadent, and hardnessdecreased small because mycelium reduced in12weeks. Content of lignin, cellulose andhemicellulose decreased after decadent, and lignin content varied little between9weeks and12weeks which explains the reason of small decline of nanoindentation hardness in12weeks.The NMR spectra shows the white rot fungi damage lateral chain of lignin, which is theimportant reason to affect the wood discoloration.