Progress 12/01/00 to 05/31/05
Outputs
The wood-species dependent performance of polymeric isocyanate resin (PMDI) was investigated by fracture analysis and solid-state NMR. The fracture energy of two different woods (yellow-poplar and southern yellow pine) bonded with PMDI was evaluated using mode-I cleavage. The fracture toughness of pine samples was significantly greater than the corresponding yellow-poplar samples. Separately, the cure chemistry of wood/PMDI bondlines was investigated by solid-state NMR with nitrogen-labeled (N15) PMDI resin. A small but statistically significant species effect was found on both the cure chemistry and the proton rotating-frame relaxation times in samples cured at lower temperatures. These differences were not found at higher cure temperatures. This lead to a hypothesis in which species effects might arise in the cores of commercial wood-based composite panels, where lower cure temperatures are found. Wood acetylation was found to alter the wood-PMDI cure chemistry as
expected, and illustrated the possible influence of urethane formation on PMDI performance.
Impacts
This work will assist other scientists to better understand why adhesive performance changes with different wood types. This will help with the future production of better and more durable wood-based composite materials which are important to almost all North American homeowners.
Publications
- Das, S., 2005, Wood/Polymeric Isocyanate Resin Interactions: Species Dependence, Ph.D. Dissertation, Virginia Tech
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Progress 10/01/03 to 09/30/04
Outputs
We have determined that the cure chemistry of isocyanate resins displays a slight wood species dependence. We are studying isocyanate resin cure chemistry with two woods: yellow-poplar and southern pine. Solid-state nuclear magnetic resonance indicates that the cure chemistries differ slightly but in a statistically significant fashion. However, we are somewhat skeptical about the statistical significance because there are only a few experimental replications. This is common with nuclear magnetic resonance because the experiments are very expensive and time-consuming and so few replications are possible. So, while our data indicates that slight differences exist we are of the opinion that cure chemistry is not responsible for the large differences in adhesive performance between these two woods. Consequently we suspect that cure chemistry is less important than differences in the adhesive interphase morphology; this is simply the 3-D arrangement of adhesive and wood
molecules. In deed, using dynamic mechanical analysis, we have shown that the isocyanate resin interacts more dramatically with pine wood, than wish poplar wood. This reinforces our notion that cure chemistry is less important than interphase morphology.
Impacts
This work will provide insight about how different wood species interact with isocyanate resins. This should help us understand why the performance of wood-based composites changes as the wood species mixture changes within these materials.
Publications
- No publications reported this period
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Progress 10/01/02 to 09/30/03
Outputs
Current efforts are directed towards the use of dynamic mechanical analysis (DMA) of wood samples treated with isocyanate resins. This involves the impregnation of the samples with resin, followed by heat treatment (resin curing), and finally the dynamic mechanical analysis. DMA reveals information about wood polymer relaxations for the primary softening transition in wood, and how the isocyanate resin changes these relaxations. At this interim stage our accomplishments have been the establishment of the DMA parameters as follows: determination of the most suitable sample grain orientation, determination of the linear viscoelastic boundary, and determination of the optimum hygrothermal sample history.
Impacts
This work will provide insight about how different wood species interact with isocyanate resins. This should help us understand why the performance of wood-based composites changes as the wood species mixture changes within these materials.
Publications
- Das, S., and C.E. Frazier. Characterization of wood-pMDI bondline by solid state NMR. Proceedings 26th Annual Meeting of the Adhesion Society, Myrtle Beach, 209 - 211, 2003.
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Progress 10/01/01 to 09/30/02
Outputs
The cure chemistry of polymeric MDI resins has been clarified through the development of a double isotopic labeling technique. This technique relies on the insertion of carbon and nitrogen magnetic isotopes in the functional groups of polymeric MDI resins. This method has been used to learn why polymeric MDI performs differently with different woods, in this case southern pine and yellow-poplar. It was determined that the cure chemistry of polymeric MDI was slightly, but significantly different with these two woods. At this point, we believe that the basis for the species dependence of the resin performance is partly due to differences in this cure chemistry, and partly due to differences in the interphase morphology.
Impacts
It is expected that researchers will adopt this new methodology to learn more about the behavior of polymeric MDI resins. The capabilities of this new method far exceed previous methods. Consequently, a new tool is available to help manufacture improved wood-based composites.
Publications
- No publications reported this period
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Progress 10/01/00 to 09/30/01
Outputs
The cure chemistry of polymeric MDI resins has been clarified through the development of a double isotopic labeling technique. This technique relies on the insertion of carbon and nitrogen magnetic isotopes in the functional groups of polymeric MDI resins. The method allows one to evaluate the covalent bonding that occurs between the resin and the wood substrate. To date, the method has been established, but recent results have focused on the optimization of the technique. For example, the efficiency and yield of the organic syntheses has been improved. Experiments are under way to use the method as a means of comparing how polymeric MDI resins function with different woods.
Impacts
It is expected that researchers will adopt this new methodology to learn more about the behavior of polymeric MDI resins. The capabilities of this new method far exceed previous methods. Consequently, a new tool is available to help manufacture improved wood-based composites.
Publications
- Zhou, Xiaobing and C.E. Frazier. Double Labeled Isocyanate Resins for the Solid-State NMR Detection of Urethane Linkages to Wood. Int. J. Adh. & Adhesives (21) 259 - 264, 2001
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