Philip Evans Wood Surface Science Laboratory University of British Columbia Vancouver, Canada

Transcription

1 Philip Evans Wood Surface Science Laboratory University of British Columbia Vancouver, Canada 1. Surface science 2. FTIR & photo-degradation 3. FTIR & phot0-protection 4. Profilometry & plasma etching 5. X-ray micro-ct of adhesive interfaces 6. Concluding remarks

2 Surface science seeks to characterise, understand and engineer the material that occurs at the interface of two phases, solid-gas, solidliquid etc The development of high vacuum devices was a key milestone in the development of surface science XPS device, University of British TOF-SIMS Columbia (UBC) Atomic Force Microscopy Laser Photodiode Tip Surface Cantilever Meincken M, Evans PD International Wood Products Journal, 1 (2):

3 IR spectroscopy exploits the fact that bonds in molecules absorb heat (IR) at specific wavelengths The absorption of IR radiation depends on the strength of the bonds and the mass of the atoms bonded together These feature allow us to characterise the structure of organic molecules Absorbance Infra-red vibrations of water Symmetric stretch Scissors bend Asymmetric stretch Wavenumber (cm-1) FTIR Spectroscopy & Photodegradation of Wood Surfaces

4 Photodegradation of Lignin at Wood Surfaces FTIR-internal reflectance spectroscopy was used to probe the surface (depth of 1.4 m) of wood exposed outdoors FTIR-IRS revealed delignification of wood surfaces within hours and complete delignification within one week Cellulose degradation Evans PD, Thay PD, Schmalzl KJ Wood Sci & Tech. 30, Paint Adhesion to Weathered Wood Exposure of wood outdoors for as little as 5 days (before painting) can reduce the adhesion of acrylic primers to pine 0d 5d 10d 15d 20d 25d Evans PD, Thay PD, Schmalzl KJ Wood Sci & Tech. 30, d

5 Condenser & Reflector 341 nm (UV) Xenon lamp carbonyl (1730cm -1 ) Diffraction aromatic grating (1510cm -1 ) 372 nm (UV) longer 403 nm (violet) wavelength shorter wavelength Depth (µm) 0 Irradiation chamber Wood samples 300 Spectro-irradiator 400 was used to expose Japanese cedar wood samples to monochromatic radiation at various 1800 wavelengths (246 to nm, 1600 band 1400 pass = nm 1600 ) 1400 Wavenumber (cm -1 ) Kataoka Y, Kiguchi M, Williams RS, Evans PD Holzforschung 61, We concluded that violet light is the component of the visible spectrum that photodegrades lignin & extends photodegradation into wood beyond the zone affected by UV radiation Yutaka Kataoka receiving the Japan Wood Research Society Prize Kataoka Y, Kiguchi M, Williams RS, Evans PD Holzforschung 61, 23-27

6 FTIR Spectroscopy & Surface Protection of Wood Photodegradation of Acetylated Wood Evans PD, Wallis AFA, Owen NL (2000). Wood Sci & Tech 34(2):

7 Chromic acid Absorbance Unweathered Weathered Wavenumber cm-1 Evans PD, Michell AJ, Schmalzl K Wood Sci & Tech 26, O O Cl O Wood Wood O H HCl Absorbance Benzoylated, Unweathered Wavenumber Benzoylated 67% WG 50 d weathering Benzoylated, Weathered Evans PD, Owen N, Schmid S, Webster R Polymer Deg & Stab 76,

8 0.698 mm QUV 100 h Alpha = 320 Beta = 30 Xenon arc mm 250 h Alpha = 320 Beta = mm Alpha = 320 Beta = h Alpha = 320 Beta = mm Alpha = 320 Beta = h Alpha = 320 Beta = 30 Confocal Profilometer mm 3.19 mm 30.6 mm Confocal Profilometry & Plasma Modification of Wood

9 Enthalpy of the system Gas Solid Energy Plasma Energy Sources An excited gas which consists of a mixture of electrons, negatively and positively charged particles, and neutral atoms and molecules Electrical (e.g. DC and RF discharges) Thermal (electrically Liquid heated furnaces) Chemical (exothermic reactions, Energy e.g. flames) + = + = Nuclear (controlled nuclear reactions) + Combination of energies (e.g. explosions) Molecule Free radicals Subatomic particles 17 Man-made Natural Plasma Lightning cutting torch Dielectric Northern lights barrier discharge (Laroussi, M. 2002)

10 Untreated Strength (MPa) Plasma treated 7 year old Eucalyptus tereticornis growing in plantation in India (part of ~20 million hectares of eucalyptus plantations in the world; 10% of total plantation area) Etching of Bordered Pits Tracheid Tracheid Pit Pit Double cell wall Double cell wall 50 µm Radial Radial longitudinal longitudinal surface surface of redwood: of redwood: plasma Untreated for 667 s

11 Y λl λm λn Objective surface Y x x 100 µm Quantification of Cell Wall Etching Using Confocal Profilometry Untreated 333 s plasma 667 s plasma Jamali, A., Evans, P.D. (2011). Wood Science & Technology 45:

12 Effect of Plasma Treatment Time on Etching of Wood Cell Walls Ratio of cell wall volume removed to the initial volume p< Treatments time (s) Jamali, A., Evans, P.D. (2011). Wood Science & Technology 45: Plasma preferentially etches cellulose at wood surfaces creating a surface that is rich in lignin Plasma etching can be used to probe the spatial distribution of lignin in the wood cell wall Ratio of area under peak to control Control Treatment time (s) 1600 cm cm cm cm-1

13 X-Ray Micro-CT of Adhesive Interfaces The properties of adhesive interfaces between the elements in wood composites may hold the key to developing stronger, more durable and cost effective biocomposites We are exploring the properties of these interfaces using X-ray - CT Blending with an x-ray opaque resin and hot pressing of mat

14 Sample was placed on rotation stage and a series of radiographs were obtained by rotating specimen through 360 degrees. It took 14 hours to collect the projection data Projection data (radiographs) were processed on supercomputer using a reconstruction algorithm to generate a tomogram (3-D variation in density of treated sample) Segmentation was performed using intensity histograms to delineate different phases in sample (air, wood and adhesive)

15 Both adhesive and wax are applied to flakes used to make wood composites Our research suggests that modification of surface energy of flakes by wax favours redistribution of adhesive during pressing

16 Phase V Top of board Bottom of board Evans et al Int. J. Adhesion Adhesives 30: Our research has focussed on discovery of novel phenomena at wood surfaces The process of discovery has been greatly aided by early application of new (appropriate) technologies, persistence and luck It was worth the effort! Thanks for inviting me to talk at this meeting. Q s?