This report describes the development of a binder for wood-based composite products that uses depolymerized lignin as the major component in the binder system. The key feature of this new binder system is that it does not employ formaldehyde, a known carcinogen, where there is significant regulatory pressure to remove formaldehyde from all composite products used in the home. Depolymerized lignin was used just as it comes out of the bioreactor, where both the clean cellulose and majority of the methanol solvent were removed which are easy separation process. However, the remaining reaction mass that contains lignin monomers, residual solvent and sugars was used as received, without any additional purification.

 

The current wood composite market landscape is dominated by four binder systems: urea formaldehyde (UF), phenol formaldehyde (PF), melamine formaldehyde (MF) and polymeric methylene diphenyl diisocyanate (pMDI). Note that three of the four mentioned binder systems involve formaldehyde.

 

A variety of cure packages for the uncleaned, depolymerized lignin monomer were studied. The properties were compared to the physical properties for binder systems that are the industry standard for wood-based composite products. Screening studies were performed to prune the possible composition space for the binder system. Additional high-fidelity studies were performed with (i) more focused composition variations, (ii) additional components of the complex additive package and (iii) additional physical property tests.

 

Formulations using glyoxal, glutaraldehyde, and azetidnium complex proved the best crosslinkers when used with depolymerized lignin from (1.) rice, (2.) wood, (3.) corn stover, and (4.) kraft lignin

 

processes. Other supplemental components such as starch fillers, waxes, urea, and acid and base catalysts were used. Sample boards and laminates were hand-made in the lab. In screw hold tests, the boards samples performed well when compared to hand-made lab boards using the current industry binder systems. Density of the depolymerized lignin boards were met by changing press conditions and masses. Water absorption and thickness swell recovery meet industry standards of less than 15%. Laminate resins passed flow studies with acceptable XY-Flow and Z-Flow. In boil testing, samples performed well in moisture absorption and thickness swell and show no warp or blisters.

 

This study was able to show that a properly formulated binder package that employs the depolymerized lignin (with other reaction products) can produce wood composite products with physical properties that are equal to, or better, than the current binder systems used in the industry, but without formaldehyde.