Aspects of Wood Adhesion: Applications of 13C CP/MAS NMR and Fracture Testing

Type of Document Dissertation
Author Schmidt, Robert G.
Author's Email Address Rob.Schmidt@neste.com
URN etd-22798-141819
Title Aspects of Wood Adhesion: Applications of 13C CP/MAS NMR and Fracture Testing
Degree Doctor of Philosophy
Department Wood Science and Forest Products
Advisory Committee
Advisor Name Title
Dr. C.E. Frazier Committee Chair
Frederick A. Kamke Committee Member
James P. Wightman Committee Member
Thomas C. Ward Committee Member
Wolfgang G. Glasser Committee Member
Keywords

* interpenetrating network formation
* IPN
* pMDI
* isocyanate
* phenol formaldehyde
* PF
* mechanisms of adhesion

Date of Defense 1998-01-28
Availability unrestricted
Abstract

Phenol Formaldehyde (PF) and polymeric isocyanate (pMDI) are the two main types of adhesives used in the production of structural wood-based composites. Much is unknown about various aspects of adhesion between these two types of resins and wood. The present research describes the development of techniques which will permit an enhanced understanding of 1.) the extent of cure of PF within a wood based composite, 2.) the scale of molecular level interactions between PF and pMDI and wood, 3.) mechanical performance and durability of wood-adhesive bonds.

Correlations were established between conventional methods of characterization of neat PF (thermomechanical analysis, swelling studies) and measurements made using 13C CP/MAS NMR. These correlations were then utilized to characterize PF cured in the presence of wood. The use of 13C labeled PF allowed estimates of relative degrees of resin conversion to be made. The use of 13C and deuterium labeled PF allowed qualitative estimates of resin molecular rigidity to be made. The scale of molecular level interactions between PF and pMDI and wood was probed using NMR relaxation experiments. Evidence was shown to suggest the formation of an interpenetrating polymer network (IPN) morphology existing at both types of wood-resin interphases. The formation of the IPN morphology was strongly influenced by resin molecular weight, cure temperature and the presence of solvent.

A new test geometry for the evaluation of the fracture toughness of wood-adhesive bonds was developed. Consistent and reliable results were obtained. It was found that low molecular weight PF possessed enhanced durability over high molecular weight.

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