The weathering of wood composites is caused by a complex combination of chemical and mechanical effects. Wood composites such as glulam beams are increasingly being used outdoors where their service life depends to some extent on the durability of the adhesive used in the composite. Increases in the durability of adhesives used in such composite materials would prolong their service life and enable them to compete more effectively with other structural materials such as concrete and steel. This study attempted to improve our understanding of the photodegradation of adhesives and the relationship between wood and adhesive photodegradation. The effectiveness of a UV light absorber and hindered amine light stabilizer (UVA and HALS) at protecting adhesives from photodegradation was also investigated. First, the effect of adhesive type (melamine formaldehyde, epoxide, and emulsion polymer isocyanate), stabilizer and adhesive stabilizer interaction on tensile strength, weight loss and discoloration of adhesive dog-bone samples exposed in two different weatherometer devices (QUV and Xenon-arc) was examined. Structural and chemical changes of the adhesive specimens were examined using Fourier Transform Infrared (FTIR) spectroscopy and Scanning Electron Microscopy (SEM). Secondly, the effects of adhesive type (melamine formaldehyde, epoxide), stabilizer and adhesive stabilizer interaction on surface roughness and discoloration of wood-adhesive-dowel samples exposed to solar radiation was examined. Profileometry and SEM was used to examine the surface of dowels in the region where they were exposed to both wood and sunlight. An epoxide adhesive (butyl glycidyl ether of bisphenol-A with polyamide) used in the aircraft industry showed outstanding resistance to weathering. The other adhesives were not as resistant to weathering, but the addition of a UVA/HALS photostabilizer to the adhesives generally increased their photostability (particularly color changes of the epoxy adhesives and weight loss of the MF adhesive). Greater degradation of adhesive samples occurred when they were exposed in a QUV weatherometer than in a Xenon-arc weatherometer. The synergistic effect of moisture and UV radiation on the degradation of adhesives may account for this observation. Adhesive dowels embedded in wood did not show greater degradation (erosion) in the region where they were exposed to both wood and sunlight. Therefore the hypotheses that wood photosensitizes adhesives could not be supported by experimental findings. Further refinement of the experimental methodology developed in this thesis would be desirable to retest this hypothesis. All of the four adhesives that were tested possessed some interesting characteristics that might make them suitable for use in glulam exposed outdoors, but out of the four the two epoxy adhesives appeared to have the greatest potential.

The weathering of wood composites is caused by a complex combination of chemical and mechanical effects. Wood composites such as glulam beams are increasingly being used outdoors where their service life depends to some extent on the durability of the adhesive used in the composite. Increases in the durability of adhesives used in such composite materials would prolong their service life and enable them to compete more effectively with other structural materials such as concrete and steel. This study attempted to improve our understanding of the photodegradation of adhesives and the relationship between wood and adhesive photodegradation. The effectiveness of a UV light absorber and hindered amine light stabilizer (UVA and HALS) at protecting adhesives from photodegradation was also investigated. First, the effect of adhesive type (melamine formaldehyde, epoxide, and emulsion polymer isocyanate), stabilizer and adhesive stabilizer interaction on tensile strength, weight loss and discoloration of adhesive dog-bone samples exposed in two different weatherometer devices (QUV and Xenon-arc) was examined. Structural and chemical changes of the adhesive specimens were examined using Fourier Transform Infrared (FTIR) spectroscopy and Scanning Electron Microscopy (SEM). Secondly, the effects of adhesive type (melamine formaldehyde, epoxide), stabilizer and adhesive stabilizer interaction on surface roughness and discoloration of wood-adhesive-dowel samples exposed to solar radiation was examined. Profileometry and SEM was used to examine the surface of dowels in the region where they were exposed to both wood and sunlight. An epoxide adhesive (butyl glycidyl ether of bisphenol-A with polyamide) used in the aircraft industry showed outstanding resistance to weathering. The other adhesives were not as resistant to weathering, but the addition of a UVA/HALS photostabilizer to the adhesives generally increased their photostability (particularly color changes of the epoxy adhesives and weight loss of the MF adhesive). Greater degradation of adhesive samples occurred when they were exposed in a QUV weatherometer than in a Xenon-arc weatherometer. The synergistic effect of moisture and UV radiation on the degradation of adhesives may account for this observation. Adhesive dowels embedded in wood did not show greater degradation (erosion) in the region where they were exposed to both wood and sunlight. Therefore the hypotheses that wood photosensitizes adhesives could not be supported by experimental findings. Further refinement of the experimental methodology developed in this thesis would be desirable to retest this hypothesis. All of the four adhesives that were tested possessed some interesting characteristics that might make them suitable for use in glulam exposed outdoors, but out of the four the two epoxy adhesives appeared to have the greatest potential.

The weathering of wood composites is caused by a complex combination of chemical and mechanical effects. Wood composites such as glulam beams are increasingly being used outdoors where their service life depends to some extent on the durability of the adhesive used in the composite. Increases in the durability of adhesives used in such composite materials would prolong their service life and enable them to compete more effectively with other structural materials such as concrete and steel. This study attempted to improve our understanding of the photodegradation of adhesives and the relationship between wood and adhesive photodegradation. The effectiveness of a UV light absorber and hindered amine light stabilizer (UVA and HALS) at protecting adhesives from photodegradation was also investigated. First, the effect of adhesive type (melamine formaldehyde, epoxide, and emulsion polymer isocyanate), stabilizer and adhesive stabilizer interaction on tensile strength, weight loss and discoloration of adhesive dog-bone samples exposed in two different weatherometer devices (QUV and Xenon-arc) was examined. Structural and chemical changes of the adhesive specimens were examined using Fourier Transform Infrared (FTIR) spectroscopy and Scanning Electron Microscopy (SEM). Secondly, the effects of adhesive type (melamine formaldehyde, epoxide), stabilizer and adhesive stabilizer interaction on surface roughness and discoloration of wood-adhesive-dowel samples exposed to solar radiation was examined. Profileometry and SEM was used to examine the surface of dowels in the region where they were exposed to both wood and sunlight. An epoxide adhesive (butyl glycidyl ether of bisphenol-A with polyamide) used in the aircraft industry showed outstanding resistance to weathering. The other adhesives were not as resistant to weathering, but the addition of a UVA/HALS photostabilizer to the adhesives generally increased their photostability (particularly color changes of the epoxy adhesives and weight loss of the MF adhesive). Greater degradation of adhesive samples occurred when they were exposed in a QUV weatherometer than in a Xenon-arc weatherometer. The synergistic effect of moisture and UV radiation on the degradation of adhesives may account for this observation. Adhesive dowels embedded in wood did not show greater degradation (erosion) in the region where they were exposed to both wood and sunlight. Therefore the hypotheses that wood photosensitizes adhesives could not be supported by experimental findings. Further refinement of the experimental methodology developed in this thesis would be desirable to retest this hypothesis. All of the four adhesives that were tested possessed some interesting characteristics that might make them suitable for use in glulam exposed outdoors, but out of the four the two epoxy adhesives appeared to have the greatest potential. / Forestry, Faculty of / Graduate

No description available.

No description available.

No description available.

Photocatalysis has received increasing attention in recent years as an effective technology in wastewater treatment applications. In this project, bismuth molybdate (Bi2MoO6), which is a popular visible-light-driven photocatalyst, was prepared by solvothermal and hydrothermal methods. The synthesis conditions, including thermal reaction temperature, synthesis duration, and precursor stirring time of the solvothermal method were optimized based on the photodegradation of Rhodamine B (RhB) under visible light irradiation. Furthermore, the CeO2/Bi2MoO6 composites with different CeO2 loading content were successfully prepared by the wet impregnation route and characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM), energy dispersive spectroscopy (EDS) and diffuse-reflection spectroscopy (DRS). The photodecomposition of RhB aqueous solution under visible light irradiation indicated that composites showed enhancements in degradation activity and 20 wt% CeO2/Bi2MoO6 exhibited the highest photocatalytic activity which was 24.13% and 83.33% higher than those of Bi2MoO6 and CeO2, respectively. This enhancement could be attributed to the formation of heterojunctions that effectively suppressed the recombination of holes and electrons. Quenching experiments revealed that photo-induced holes and superoxide radicals (O2•-) were the main active species during the degradation process. Reusability was assessed by a set of 5 cycling degradation experiments and the results indicated that the composite could be applied long-term. Moreover, the effect of some operating parameters including temperature, initial pH, catalyst dosage and initial substrate concentration were investigated.

Thesis (Ph. D.)--Washington State University, December 2007. / Includes bibliographical references.

No description available.

Synthesis and physical characterizations of a novel class of zwitterionic organic chromophores were carried out. A series of tetracyanoquinodimethane (TCNQ) derivatives was prepared from reactions with primary and secondary amines. By modifications of the structure it was hoped to optimize their nonlinear properties. The newly synthesized organic chromophores were highly polar, zwitterionic and transparent at wavelengths above 600nm, which is a requirement for waveguide devices at 650nm. The molecular dipole moments were determined experimentally and theoretically. The experimental dipole moments and the theoretical dipole moments were found to be in agreement. The nonlinear optical properties of the new compounds were studied using the Kurtz powder technique. Large second harmonic generation was observed from 7-(2,6, dimethylmorpholino)-7-(4-methylpiperidine)- 8,8-dicyanoquinomethane (25 times urea) as a result of the noncentrosymmetric crystal lattice (P2(_1)2(_1)2(_1)). A large twist between the donor moieties and the benzene ring was found from the crystallographic data, and compared with a theoretical model using an ab initio calculation. Strong fluorescence was observed in the solid states and glass forming solvents at low temperatures. An increase of the quantum yields as a function of viscosity was observed due to the constraining effect of the environment. Variations in the quantum yields from chromophore doped polymeric matrices such as PMMA at room temperature and at low temperature are attributed to the different "free volume" of the polymeric matrices. Possible mechanisms for the emission process in either viscous or non-viscous media are proposed. Photodegradation in solution was observed for illumination by a white light source. In parallel studies photodegradation in PMMA films was observed both in air and under vacuum. A possible photodegradation mechanism via free radicals, compatible with these experimental observations is suggested.