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Abstract
The aging properties of phenol-formaldehyde resin modified by bio-oil (BPF) were analyzed using ultraviolet (UV) weathering. The variations on bonding strength of BPF were measured, and the changes on microstructure, atomic composition and chemical structure of BPF were characterized by using a scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS) and nuclear magnetic resonance (NMR), respectively. With the increase of aging time, the bonding strength decreased gradually, the resin surface became rougher and the O/C radio of resin surface increased. However, the loss rate of bonding strength of BPFs was 9.6–23.0% lower than that of phenol-formaldehyde resin (PF) after aging 960 h. The aging degree of BPF surfaces was smaller in comparison to PF at the same aging time. These results showed that the bio-oil had a positive effect on the anti-aging property. Analytical results revealed that with increasing the aging time, the XPS peak area of C–C/C–H decreased, while that of C=O and O–C=O increased. The intensity of methylene and ether bridges in NMR analysis decreased along with increasing the intensity of aldehydes, ketones, acids and esters. These results indicated that the aging mechanism of BPF was a process of the breakage of molecular chains and formation of oxygen-containing compounds.
Highlights
Phenol-formaldehyde resin (PF) has been widely used in outdoor wooden products because of its excellent mechanical properties, thermal stability and electrical insulation [1,2,3]
A number of studies found that the introduction of inorganic element like boron [9,10] and titanium [11] in the synthesis of resin effectively improved the stability and water resistance of the resin
The changes of bonding strength could be divided into three stages prolonged aging time: initial stage (0–120 h), middle stage (120–480 h) and last stage
Summary
Phenol-formaldehyde resin (PF) has been widely used in outdoor wooden products because of its excellent mechanical properties, thermal stability and electrical insulation [1,2,3]. A number of studies found that the introduction of inorganic element like boron [9,10] and titanium [11] in the synthesis of resin effectively improved the stability and water resistance of the resin. These inorganic compounds tend to form covalent bond with phenolic hydroxyl or hydroxymethyl groups of PF and the bond energy of B–O and Ti–O is much higher than that of C–C bond, improving the thermal stability.
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