Study On Mechanism Of Extrusion Bonding And Pretreatment Of Eucalyptus Wood Fiber

As Eucalyptus growing fast and having short rotation,the output of the unit area of land under intensive farming conditions can be doubled.In addition Eucalyptus is widely distributed.Based on these advantages,fast-growing Eucalyptus can be widely used in the field of manufactuing wood-based panels,Wood based composite materials and pulp ande paper industries.The critical process of fiber combination is that the fiber bond with each other effectively and form a bond with sufficient mtensity.However,the existing technology adopts bonding process like urea resin whose products are more likely to emit toxic gases like formaldehyde and free phenol,causing severe environmental pollutions.Nuclear magnetic resonance(NMR),fourier transform infrared spectrometer(FT-IR),canning lectronmechanismcope(SEM)had been employed in order to study the mechanism of extrusion bonding and pretreatment of Eucalyptus wood fiber,many beneficial results were obtained after nearly two-year pilot study,as follows:(1)Both extrusion temperature and extrusion duration had a significant influence on the internal bond strength of boards.The comparatively ideal extrusion condition was extrusion temperature 160?,surface pressure 15MPa with 20-minute extrusion duration.There were chemical bonds produced in the process of extrusion,such as ether bond and ester bond.Extruded eucalyptus fiber samples had more lignin than untreated ones.(2)As for alkali pretreatment,strong alkali could eliminate the hemicellulose while weak alkali could partly reduce the cellulose in the eucalyptus fiber,and alkali solution could degrade hgnin.The duration of alkali pretreatment had a relevantly big effect on the internal bond strength and 10 hours was comparatively suitable.(3)As for acid pretreatment,part cellulose and hemicellulose were degraded;part lignin was dissolved but benzene ring structure was not opened.The duration of alkali pretreatment had a relevantly big effect on the internal bond strength.The comparatively suitable duration for acetic acid pretreatment and oxalic acid pretreatment was 10 hours and 15 hours respectively.(4)As for alkaline oxidation pretreatment,part hemicellulose in the eucalyptus fiber presented deacetylation;the benzene ring of lignin was not opened during the oxidation but aromatic nucleus side chain was oxidized;reducing groups like hydroxyl and olefin were oxidized by H2O2,increasing the number of carbonyl.As for acid oxidation pretreatment,the benzene ring of lignin had ring-opening reaction after oxidized;the number of active group on the aromatic ring increased;H2O2 dissolved and produced free hydroxyl,making the aromatic ring of lignin hydroxylate.Acid oxidation pretreatment was more effective than the alkaline one,and oxidation pretreatment had a significant effect on internal bond strength and 10?hour of duration was more suitable.(5)The results of infrared spectroscopy and nuclear magnetic resonance showed that after acid oxidation pretreatment,the benzene ring of lignin had ring-opening reaction,demethoxy reaction occurred,aromatic ring hydroxylation.As for Na2SiO3 pretreatment,the high concentration of solution almost eliminated all hemicellulose in the eucalyptus fiber,and low concentration only degraded part of the hemicellulose.During the extrusion process,such characteristic groups of eucalyptus fiber as hydroxyl,methyl,methylene,benzene ring had significant change,confirming that cellulose,hemicellulose and lignin had bridged chemical reactions such as esterification and etherification,producing bonding effect so that eucalyptus fiber released self-bonding.During the extrusion of eucalyptus fiber,hydroxyl reacted with each other and formed hydrogen-bonding and reduced the number of free hydroxyl,which endowed the panel with good water resistance and strengthened the fiber self-bonding.