Tailoring of oxidized starch's adhesion using crosslinker and adhesion promotor for the recycling of fiberboards

The growing interest in recycling waste medium density fiberboards (MDFs) is driving the development of new adhesives that provide sufficient adhesion, and allow disintegration of the waste MDFs. Described in here is the preparation of adhesives based on oxidized starch (OS) in combination with blocked-polymeric 4-4 diphenylmethane diisocyanate (B-pMDI) as a crosslinker and poly(vinyl alcohol) (PVA) as an adhesion promotor for the recycling of waste MDFs. The COOH groups of OS were reacted with NCO groups of B-pMDI to form amide linkages, and the CHO groups were reacted with OH groups of PVA through hydrogen bonding. Further, when applied as an adhesive, the OS formed ester linkages with OH of MDF fibers. As the results, MDF bonded with 1% B-pMDI/15% PVA/OS adhesive had an internal bonding strength of 0.13 MPa, 0.01 mg L⁻¹ of formaldehyde emission (FE), and 12% of degree of fiber disintegration. These results demonstrate that the B-pMDI/PVA/OS adhesive is a possible alternative to the current urea–formaldehyde resins for the recycling of waste MDFs into recycled MDFs without FE.