Wood Composites Production with Epoxy Resin Substituted Liquefied Lignocellulosic Biomass, and Polymeric Diphenylmethane Diisocyanate Substituted Defatted Soy Flour as Wood Adhesives

Abstract

Wood composites such as oriented strand board (OSB), particleboard and medium density fiberboard (MDF) have contributed significantly towards efficient wood utilization Wood composites are engineered wood products from reconstituted wood materials bonded with thermosetting adhesives under heat and pressure. Currently, synthetic adhesives dominate the wood composites industry. Recent environmental health concerns, sustainability, and price uncertainties of these synthetic adhesives, which are petroleum derived, have engendered efforts to more environmentally friendly, sustainable, and cost-effective bio-based adhesive alternatives. In this study, synthetic adhesives were modified with renewable components to form composite panels taking advantage of the individual binder components. The first section of this work, chapters 3 and 4, focused on the utilization of bio-oil in epoxy resin modification for binding wood composites. In chapters 3, bio-oil was obtained from fast pyrolysis (FP), and hydrothermal liquefaction (HTL) of loblolly pine biomass. Water/ethanol mixture (1/1, wt/wt) was used as the solvent. The FTIR results revealed that the FP and HTL bio-oils had similar chemical functional groups. However, the gas chromatography–mass spectrometry (GC-MS) analysis indicated variations in the composition of the bio-oils. The study found low ash content of 0.01 wt % and pH of 2.3 ± 0.5 for both FP and HTL bio-oils. The 31P-NMR spectroscopy analysis revealed that the FP and HTL bio-oils were rich in phenolic OH and aliphatic OH functionalities, which could serve as a potential bio-polyol. OSB was manufactured utilizing epoxy, and epoxy modified pyrolysis bio-oil as an adhesive binder in Chapter 4. The results showed that epoxy resin with bio-oil content of 20% showed comparable bonding properties to that of polymeric diphenylmethane diisocyanate (PMDI). Bio-oil substitution of 20% improved the hydrophobicity of the OSB. The TGA and DSC analysis of the epoxy resins showed improved thermal stability at lower bio-oil substitution levels. It was concluded that epoxy resin amended bio-oil could be a potential adhesive to produce OSB. The second section delved into the utilization of PMDI and defatted soy flour. In chapter 5 the chemical functionalities of PMDI amended soy was studied via FTIR and the acceptable range of soy flour substitution in PMDI for OSB applications was discussed. Heating PMDI to approximately 40 ºC eliminate soy aggregation and reduces viscosity. The production of particle boards to ascertain the contribution of soy flour in increasing the Cold Tack of pMDI resin was discussed in chapter 6. PDMI resin has low tack which limits its application. The soy flour increases the tack of pMDI resin, which increases the surface coverage and the relative bonded area at the glue line. 20% substitution level of soy is a practical maximum because higher levels could lead to excessive cold tack as well as to higher resin viscosity. In chapter 7, CO2 evolution was used to understand the kinetics of the soy and PMDI during mixing and how different mixing techniques affect the resulting wood composites. It was found that soy chemically interacts with the isocyanate groups of PMDI during mixing. As a result, CO2 is evolved. Results of partial substitution of pMDI resin by 10-15% soy flour for the manufacture of OSB, improved board properties. For MDF the soy-substituted resin performed as well as the control pMDI. The reaction of soy flour with pMDI occurs over several hours as tracked by CO2 evolution. Uniform mixing of soy flour with pMDI is critical because unreacted soy flour tends to retain water, which degrades the wet properties of the board.