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dc.contributor.authorRiedlinger, Darren Andrewen_US
dc.description.abstractWater-based resol phenol formaldehyde, PF, and organic polymeric methylenebis(phenylisocyanate), pMDI, are the two primary choices for the manufacture of exterior grade wood-based composites. This work addresses simple physical blends of pMDI dispersed in PF as a possible hybrid wood adhesive. Part one of this study examined the morphology of hybrid blends prepared using commercially available PF and pMDI. It was found that the blend components rapidly reacted such that the dispersed pMDI droplets became encased in a polymeric membrane. The phase separation created during liquid/liquid blending appeared to have been preserved in the cured, solid-state. However, substantial interdiffusion and copolymerization between blend components also appeared to have occurred according to measured cure rates, dynamic mechanical analysis, and atomic force microscopy. In the second part of this study a series of PF resins was synthesized employing the so-called â split-cookâ method, and by using a range of formaldehyde/phenol and NaOH/phenol mole ratios. These neat PF resins were subjected to the following analyses: 1) steady-state flow viscometry, 2) free formaldehyde titration, 3) non-volatile solids determination, 4) size exclusion chromatography, 5) quantitative solution-state 13C nuclear magnetic resonance, NMR, 6) differential scanning calorimetry, 7) parallel-plate oscillatory cure rheology, and 8) dielectric spectroscopy. The neat PF analytical results were unremarkable with one exception; NMR revealed that the formaldehyde/phenol mole ratio in one resin substantially differed from the target mole ratio. The neat PF resins were subsequently used to prepare of series of PF/pMDI blends in a ratio of 75 parts PF solids to 25 parts pMDI solids. The resulting PF/pMDI blends were subjected to the following analyses: 1) differential scanning calorimetry, 2) parallel-plate oscillatory cure rheology, and 3) dielectric spectroscopy. Similar to what was inferred in part one of this study, both differential scanning calorimetry (DSC) and oscillation cure rheology demonstrated that cure of the PF continuous phase was substantially altered and accelerated by pMDI. However within actual wood bondlines, dielectric analysis detected little variation in cure speed between any of the formulations, both hybrid and neat PF. Furthermore, the modulated DSC curing experiments detected some latent reactivity in the hybrid system, both during initial isothermal curing and subsequent thermal scanning. The latent reactivity may suggest that a significant diffusion barrier existed between blend components, preventing complete reaction of hybrid blends even after thermal scanning up to 200 °C. Part three of this work examined the bonded wood mode-I fracture performance of hybrid resins as a function of the resol formaldehyde/phenol ratio and also the alkali content. A moderate increase in unweathered fracture toughness was observed for hybrid formulations relative to neat PF. Following accelerated weathering, the durability of the hybrid blends was promising: weathered hybrid toughness was equivalent to that of weathered neat PF. While the resol F/P ratio and alkali content both influenced hybrid fracture toughness, statistical modeling revealed interaction between these variables that complicated result interpretation: the influence of hybrid alkali content depended heavily on each formulationâ s specific F/P ratio, and vice versa.en_US
dc.publisherVirginia Techen_US
dc.rightsI hereby certify that, if appropriate, I have obtained and attached hereto a written permission statement from the owner(s) of each third party copyrighted matter to be included in my thesis, dissertation, or project report, allowing distribution as specified below. I certify that the version I submitted is the same as that approved by my advisory committee. I hereby grant to Virginia Tech or its agents the non-exclusive license to archive and make accessible, under the conditions specified below, my thesis, dissertation, or project report in whole or in part in all forms of media, now or hereafter known. I retain all other ownership rights to the copyright of the thesis, dissertation or project report. I also retain the right to use in future works (such as articles or books) all or part of this thesis, dissertation, or project report.en_US
dc.subject13C NMRen_US
dc.subjectfracture testingen_US
dc.subjectwood adhesionen_US
dc.titleCharacterization of PF Resol/Isocyanate Hybrid Adhesivesen_US
dc.contributor.departmentMacromolecular Science and Engineeringen_US
thesis.degree.nameMaster of Scienceen_US
thesis.degree.grantorVirginia Polytechnic Institute and State Universityen_US
dc.contributor.committeechairFrazier, Charles E.en_US
dc.contributor.committeememberRoman, Marenen_US
dc.contributor.committeememberRiffle, Judy S.en_US

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