Formaldehyde emission behavior of plywood with phenol-formaldehyde resin modified by bio-oil under radiant floor heating condition

Bio-oil was added as a substitute of phenol for phenol-formaldehyde (PF) resin to reduce the cost and formaldehyde emission (FE) in radiant floor heating system. The effects of substitute rate of bio-oil to phenol, temperature and heating time of radiant floor heating system on the FE of plywood with bio-oil phenol-formaldehyde (BPF) resin were examined using desiccator method. The variations on chemical structure of cured BPF resin were analyzed by the Fourier transform infrared spectroscopy (FT-IR) and solid-state nuclear magnetic resonance (NMR) to understand the FE behavior of plywood. Results showed that the FE of plywood was increased at prolonged heating time and the temperature significantly affected FE of plywood; the initial FE value at 50 °C was 20-30 times as higher as that at 20 °C. Elevated temperature increased the final equilibrium FE value and shortened the time to reach the balance. However, adding bio-oil reduced the initial and final equilibrium FE values, decreasing by 12-49% and 25-51%, respectively. Analytical results revealed that the initial FE was mainly from the residual formaldehyde from the manufacturing of plywood and the subsequent FE released owing to the breakage of C-O-C and CH2 bonds in resin.