Mechanical model and changed chemical structure of phenol-formaldehyde adhesive on plywood with different hot press process

ABSTRACT

In the study, the bonding strength of phenol-formaldehyde (PF) adhesive on plywood under different hot press temperature and time was evaluated. A mechanical mathematical model was established to analyze the curing process of PF adhesive, in which the parameters of model could be used to predict the bonding strength and change rate of plywood. The thermal curing degree of the adhesive was determined by differential scanning calorimetry (DSC), Fourier transform infrared (FTIR) as well as Nuclear magnetic resonance (NMR) were used to analyze the chemical structure of adhesives with different curing degree. The results show that higher of hot press temperature, the shorter of time to reach the target temperature. The changed rate constant of bonding strength and the maximum bonding strength of plywood could be calculated by the mechanical mathematical model accurately, and the temperature at 130°C was the optimal temperature for plywood manufacture in the study. FTIR analysis indicated that the primary reaction of PF adhesive in the alkaline medium was the condensation occurring between hydroxymethyl groups and residual active position of other phenolic rings. NMR data presented that the ratio of -CH₂- (34.5–35.1 ppm)/CH₂-OH (62.4–63.1 ppm) could be used to evaluate the curing degree of PF adhesive.

KEYWORDS:

• Phenol-formaldehyde adhesive
• hot press process
• bonding strength
• mechanical model
• chemical structure

Additional information

Funding

This work was supported by the Fundamental Research Funds for the National Natural Science Foundation of China [Project 31790188]; Innovation-Driven Project Funds of Guangxi [AA17204087-15].