| The scrimber comprised of fibrotic veneers and PF resin is a novel enhanced composite,which is compressed and formed in parallel direction.CoMPared with traditionalwood-based panel,the scrimber has higher raw material utilization rate,available design and high mechanical strength and so on.Currently,the scrimber has become one of the main ways to utilize the fast-growing wood efficienty,and used as outdoor exterior materials in outdoor field e.g.wood structure building and landscape facilities.The scrimber which experiences long term of sun light irradiation gives rise to surface broken and cracks,surface discoloration and dimensional shrinkage.Light aging is the major factor to constrict the scrimber application.Therefore,the study of the mechanism dimensional shrinkage and the exploring of anti light aging technique are helpful for outdoor applications.Therefore,in this paper,the scrimbers are made from heat-treated and untreated fibrotic veneers.The mechanical properties,physical properties,surface properties and endurance quality of the scrimbers were studied.In addition,several analytical techniques such as fourier transform infrared spectrometer?FTIR?,X-ray photoelectron spectrometer?XPS?,Solid-state nuclear magnetic resonance technology?NMR?,scanning electron microscopy?SEM?,and Gas chromatography and mass select-detector?GC-MS?are employed to investigate the cell structural changes as well as chemical,physical and mechanical properties,crystalline and Photodegradation product of scrimbers irradiated by UV 313 light,and then to explore the influence of heat treatment on light aging process and photodegradation mechanism of scrimbers.Several conclusions were drawn from these experiments:?1?After heat treatment with the condition of 160?/0.3 MPa and 180?/0.3 MPa,polysaccharide degraded and the quality of veneer decreased,on the contrary,the extract increased.The mass loss rate of fibrosis veneer were 2.22%and 4.13%respectively.The color changed to coffee and then to black brown.Lightness parameters L*reduced by 23.61%and 51.39%,red-green parameter a*increased by 62.5%and 75.1%,yellow-blue parameter b*increased and then decreased obviously;the equilibrium moisture content,water absorption rate and glue amount all showed a downward trend,with the equilibrium moisture content reducing by 40.94%and 42.98%respectively,and the water absorption rate and glue absorption rate decreasing by 21.14%?49.51%and 8.64%?15.89%respectively;Similarly,the PH decreased by 4.27%and 5.78%respectively.The content of holocellulose reduced by4.90%and 15.15%separately,hemicellulose decreased by 10.17%and 35.54%,?-cellulose reduced by 2.14%and 4.67%respectively.?2?The FITR spectrum of fibrotic veneers showed several main absorption peaks,after heat treatment,the peaks that related to hemicellulose all decreased apparently,especially,1730 cm-1,1370 cm-11 and 1163 cm-11 weakened sharply.XPS results showed that the O/C of fibrotic veneers by defibering process decreased from 0.34 to 0.31,because veneer squeezed by mechanical force leading to extract penetrating to the surface.The value of O/C decreased from 0.31 to 0.29 after the treatment with the different conditions.XRD results showed that the crystallinity of cellulose increased by 6.67%and 20.67%respectively.?3?After heat treatment at 160°C/0.3MPa and 180°C/0.3MPa,the MOR of the scrimber decreased by 13.33%and 36.67%,the MOE of the scrimber decreased by 4.76%and 9.52%,and the HSS of the recombined wood decreased by 5.56%and 30.56%,respectively.CS of th e scrimber decreased by 12.38%and 21.90%,respectively.After heat treatment,the hemicell ulose was degraded,which resulted in the separation of cellulose and lignin and the weakness of mechanical strength of cell wall.The macroscopic manifestation were as follows:the decr ease in the mechanical properties of the material;the thickness expansion ratio?TSR?of the h eat-treated scrimber is less than that of the untreated one after testing at 63°C blistering for 24h and 100°C for 28h.The TSR of the scrimber was reduced by 23.16%and 57.92%,and the WAR was decreased by 8.29%and 28.0%,respectively,after the heat treatment at 160°C/0.3MPa and 180°C/0.3MPa for 63 hours at 63°C.The TSR decreased by 26.02%and 45.38%,an d the WAR decreased by 5.0%and 29.88%,respectively,under the condition of 100°C boiled for 28 h.The profile density analysis showed that the cross-section density of the plate after heat treatment was more uniform than that of the control group.There is no significant differe nce in the cross-section density of the scrimber between 160°C/0.3MPa and 180°C/0.3MPa;the corrosion resistance,chemical resistance and photo-aging resistance after heat trea tment were improved,and the mass loss rate was reduced from 40.25%to 35.11%and 20.15%;but the mildew resistance of the scrimber was not improved after the heat treatment.?4?Lignin is the main degradation material in photoaging process.Before lignin is aged,4-hydroxybenzaldehyde,acetaldehyde,3,5-dimethoxy-4-hydroxybenzaldehyde,are mainly identified,5-Heptacyclotriene and other 11 major products.after lignin photoaging,the photodegradation products are mainly-hydroxy-4-methoxy benzoic acid,undecaaldehyde,methyl naphthalene,3,4'-dihydroxy-3'-methoxypropiophenone,4-hydroxybenzoic acid,1,2-epoxy-3-phenoxypropane,furfural,etc.These products include ketones,aldehydes,acids,etc.,most of which degradation products and lignin basic unit composition similar structure,indicating that photo-aging aging process of chemical degradation of lignin macromolecules.?5?Phenolic resins react with partially reactive groups in hemicellulose,cellulose,and lignin in cell walls,reducing the number of hydroxyl,carboxyl,etc.groups and forming new stable chemical crosslinks;most adhesives are distributed in cracks in fibrinated wood veneers due to crushing and spalling,as well as in broken duct cells,part of the adhesive penetrates through the pits into the cell and intercellular layers of parenchyma cells and adheres to the inner surface of the cell cavity.The adhesive adheres to the surface of the wood and forms a layer of film to protect the wood.After photoaging,the adhesive degrades first,and the degradability is similar to that of wood.Therefore,the scrimber has better aging resistance than the poplar wood. |
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