Title page for ETD etd-11172010-213121

Type of Document Master's Thesis
Author Church, William Travis
Author's Email Address wchurch@vt.edu
URN etd-11172010-213121
Title Laser Activated Bonding of Wood
Degree Master of Science
Department Wood Science and Forest Products
Advisory Committee
Advisor Name Title
Renneckar, Scott H. Committee Chair
Barone, Justin Robert Committee Member
Quesada-Pineda, Henry Jose Committee Member
  • differential scanning calorimetry
  • photo acoustic fourier transform infrared spectros
  • scanning electron microscopy
  • light-activated
  • wood
  • bonding
  • carbon dioxide laser
  • Design of Experiment
  • x-ray photoelectron spectroscopy
Date of Defense 2010-11-11
Availability unrestricted
It was found that laser modified wood surfaces can be bonded together to create a wood composite without the need of any additive. This bonding method removes the need of applying adhesive, potentially lowers cost, and eliminates off gassing of petroleum resins, creating a wood product with many eco-friendly attributes. This body of work outlines a) initial chemical analysis of the laser modified surface b) its bond strength and c) the optimization of factors that control the strength of the bond.

Surface chemical analysis on laser modified wood was conducted using photo acoustic Fourier transform infrared spectroscopy (PA-FTIR) and X-Ray photoelectron spectroscopy (XPS). Light microscopy and scanning electron microscopy were utilized for surface topology analysis. Differential scanning calorimetry (DSC) quantified the thermal properties of the modified wood surface. Screening of multiple factors that would contribute to surface modification and adhesion was performed utilizing mechanical testing. Optimization of significant factors that affect bond strength was determined statistically utilizing a design of experiment approach.

Chemical analysis of the laser modified surface revealed changes in the carbonyl and aromatic regions indicating modification of the hemicellulose and lignin components, intensifying with increasing laser modification. The C1/C2 ratios found via XPS revealed that one or more of the following is occurring: more extractives have moved to the surface, condensation reactions among lignin units, and the loss of methoxy and breakage of aryl ether linkages occurred. Microscopy images showed color changes to a darker caramel color with a smoothing of surface topology, suggesting the occurrence of the softening and/or melting of wood polymers. DSC verified chemical and/or physical changes in the wood with the modified material now having a glass transition temperature between 130-150°C. DOE found that laser parameters (power and focus) as well as hot press parameters (temperature and pressure) were significant in optimizing the bond.

The impact of the study is the first documentation of the ability to laser modifies wood surfaces and subsequently bond them together. The ability of the wood polymers at the surface to undergo flow at elevated temperature is implicated in the adhesion mechanism of the laser modified wood.

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