Progress 03/01/03 to 08/31/05
Outputs
Urea-formaldehyde (UF) resins are prone to hydrolytic degradation, which limits their use to indoor applications. This study examined the modification of urea formaldehyde (UF) resin with various thermoplastics as a means to increase the moisture resistance and toughness of the adhesive. UF adhesives were modified in-situ with various hydrophobic and hydrophilic thermoplastic formulations via a semi-interpenetrating polymer network or S-IPN method, using either polar or non-polar initiators. Unmodified and modified UF resins were characterized in terms of viscosity, pH and gel time in their prepolymer suspension state. The properties were measured in order to document differences in thermoplastic formulations and to assess whether the modified resins could be used in typical particleboard manufacturing equipment. In addition, gel times were measured at four different temperatures and activation energy was derived from the gel time data. Cured solid UF resin plaques
were prepared in order to isolate moisture sorption effects of the cured UF resin from that of the wood component in composites, which dominates their moisture uptake. Relative crosslink density and moisture sorption tests were run on cured UF resin plaques. Relative crosslink density was determined to correlate moisture resistance to increased bond density in the cured UF resin formulations. Viscosity was found to increase in most cases after modification with thermoplastics, with higher viscosities resulting from formulations using an acidic (polar) initiator. This was likely due to a separate thermoplastic polymer phase forming within the UF network. One formulation, however, had lower viscosity after the modification, likely because of the different mechanism of reaction and the likelihood that the reaction had not yet occurred under the low temperatures used in modification. Solids content of modified UF resins was slightly higher than that of the unmodified UF. However, solids
content did not affect the viscosity of modified UF resins. Decreased pH values were observed in thermoplastic-modified UF resins, regardless of initiator. With the same thermoplastic formulation, pH was lower with polar initiator than when non-polar initiator was used. Viscosity of all modified resins was below 500cP, which would allow their use in conventional industrial spraying equipment. For all thermoplastic-modified UF resins, activation energy was decreased compared to the unmodified UF. Polar thermoplastic modified UF with acidic initiator was found to have both the highest relative crosslink density and the lowest moisture sorption of the formulations tested, which suggested that crosslink density was a factor in the lower moisture sorption of cured thermoplastic-modified UF resin. Modification of UF with thermoplastic did not increase its toughness.
Impacts
Urea formaldehyde (UF) is the least expensive of the commercial adhesives used in wood composite products, and thus is desirable for wood bonding. However, UF resin also has the lowest moisture resistance of the major wood adhesives, which limits its practical use to indoor products only. An effective modification of UF resin in order to improve moisture resistance while retaining a cost advantage over other wood adhesives would greatly increase the market for these adhesives. This study has demonstrated that thermoplastic modification of UF adhesive with polar or non-polar initiator could be an effective method to enhance its moisture resistance while maintaining its processing properties.
Publications
- Kim, J.W., Carlborn, K., Matuana, L.M., and Heiden, P.A. 2005. Thermoplastic Modification of Urea-Formaldehyde Wood Adhesives to Improve Moisture Resistance. Journal of Applied Polymer Science (Submitted, September 2005).
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Progress 01/01/04 to 12/31/04
Outputs
This project is still on-going. We have generated some conclusive results and two manuscripts are in preparation. An Associate Researcher (Post-Doc) is in charge of this project.
Impacts
Urea formaldehyde (UF) resin in an inexpensive thermosetting adhesive that is widely used in the wood composites industry. However, there are two disadvantages to UF resins, lower moisture resistance and higher brittleness compared to other expensive wood adhesives. The purpose of this work is to improve the moisture resistance and toughness of UF adhesives by modification with thermoplastics. Therefore, the outcome of this project will yield an industrially viable, low-cost modified UF adhesive with significantly improved moisture resistance, mechanical properties, and reduced dimensional swell.
Publications
- None as of January 2005. However, 2 manuscripts are in preparation
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Progress 01/01/03 to 12/31/03
Outputs
This project was tranferred from Michigan Technological University in March 2003. Research is on-going at Michigan State University since September 2003.
Impacts
Urea formaldehyde (UF) resin in an inexpensive thermosetting adhesive that is widely used in the wood composites industry. However, there are two disadvantages to UF resins, lower moisture resistance and higher brittleness compared to other expensive wood adhesives. The purpose of this work is to improve the moisture resistance and toughness of UF adhesives by modification with thermoplastics. Therefore, the outcome of this project will yield an industrially viable, low-cost modified UF adhesive with significantly improved moisture resistance, mechanical properties, and reduced dimensional swell.
Publications
- No publications reported this period
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