Cure studies of network-forming polyurethanes

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dc.contributor.authorToffey, Ackahen
dc.contributor.departmentForest Productsen
dc.date.accessioned2014-03-14T21:31:22Zen
dc.date.adate2009-03-12en
dc.date.available2014-03-14T21:31:22Zen
dc.date.issued1993en
dc.date.rdate2009-03-12en
dc.date.sdate2009-03-12en
dc.description.abstractThe polyhydroxy character of lignocellulosics and their natural abundance make them good candidates for the manufacture of polyurethanes. The cure characteristics of hydroxypropyl-cellulose and hydroxypropyl lignin (HPC and HPL, respectively) with polymeric methylene diphenyl diisocyanate (MDI) was studied via dynamic mechanical thermal analysis (DMTA). HPC/MDI and HPL/MDI resins flow at 30°C and proceed to cure at 50°C. The latter has excellent thermal stability over the former. Crosslinking of HPL and HPC with MDI follow an nth order kinetics, with an order of reaction of 2 and an apparent activation energy in the range of 12.9 kcal/mol - 14.7 kcal/mol. The rate of cure with time is higher in HPL-based polymers than HPC-based ones at the initial stage of cure; the difference vanishes at later stages. This demonstrates that the hydroxyl groups in HPC are less accessible to the NCO groups, and that cure rate might be dependent on diffusion limitations at later stages. Degree of cure, under all cure schedules, follows a parallel trend, and has to do with the fact that the hydroxyl groups of HPC are less accessible to isocyanate. Both HPL and HPC react with MDI at a reduced rate in comparison to a synthetic polyol: caprolactone triol. Time-glass transition temperature superposition was used to calculate times to vitrification of the HPL-based polymers, and is presented in a TTT cure diagram. This bio-based polymer displays the s-shaped vitrification pattern characteristics of thermosets. A similar approach did not work with HPC-based polymers. HPC- and HPL-based polymers did not display damping transitions, in isothermal cure, typical of gelation and vitrification. As the isocyanate to hydroxyl ratio (NCO:OH) increased, the glass transition temperature of the polymers increased, and the transition amplitude and width decreased and increased, respectively. In practical terms, this study illustrates that it is advantageous to use a) to use high isocyanate to hydroxyl ratios in order to produce polyurethanes which retain desirable damping behavior over a wider range of temperature. b) to use HPC/MDI resins in those situations where retention of stiffness at temperatures below 230° is required. c) to use HPL where rapid cure is desired. The study also reveals that the relative reactivity of water, HPL and HPC with isocyanate takes the form water > HPL > HPC.en
dc.description.degreeMaster of Scienceen
dc.format.extentxii, 104 leavesen
dc.format.mediumBTDen
dc.format.mimetypeapplication/pdfen
dc.identifier.otheretd-03122009-041354en
dc.identifier.sourceurlhttp://scholar.lib.vt.edu/theses/available/etd-03122009-041354/en
dc.identifier.urihttp://hdl.handle.net/10919/41509en
dc.language.isoenen
dc.publisherVirginia Techen
dc.relation.haspartLD5655.V855_1993.T633.pdfen
dc.relation.isformatofOCLC# 29741633en
dc.rightsIn Copyrighten
dc.rights.urihttp://rightsstatements.org/vocab/InC/1.0/en
dc.subject.lccLD5655.V855 1993.T633en
dc.subject.lcshLignocelluloseen
dc.subject.lcshPolyurethanesen
dc.titleCure studies of network-forming polyurethanesen
dc.typeThesisen
dc.type.dcmitypeTexten
thesis.degree.disciplineForest Productsen
thesis.degree.grantorVirginia Polytechnic Institute and State Universityen
thesis.degree.levelmastersen
thesis.degree.nameMaster of Scienceen

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