Aging Performance And Mechanism Of Phenol-Formaldehyde Resin Modified By Bio-oil For Engineered Wood Flooring In Floor Heating Systerm

Radiant floor heating is recognized internationally as the most advocated heating system in the word.Engineered wood flooring is the commonly-used wood flooring material of radiant floor heating system.In the radiant floor heating system,however,the adhesives in engineered wood flooring will degrade more quickly and more formaldehyde will release.These restricte the extensive application of engineered wood flooring in radiant floor heating industry.Thus,it has important theoretical significance and practical application value to seek for an environmentally friendly adhesive with nice aging resistant.In this paper,the phenol-formaldehyde resin modified by bio-oil(BPF resin)was used as the adhesive for wood heating floors.The aging performance of BPF resin and the formaldehyde emission of plywood with BPF resin were analyzed.The aging behaviors of BPF resins with different synthetic processes and under different aging conditions were confirmed.The influencing mechanism of bio-oil and its components on the aging performance of BPF resin was investigated.The main conclusions of this paper are as follows:(1)After boiling-dring cycle accelerated aging treatment,the bonding strength of plywood with BPF resin changed significantly in the aging 1-4 periods.With the increase of aging period,the surface roughness of BPF resin film increased,meanwhile,the particles and holes gradually appeared.The methylene bridge and ether bridge in molecular structure of BPF resin decreased,while the aldehyde and acid structures increased with increasing aging period.Compared with phenol-formaldehyde(PF)resin,the loss rate of bonding strength of plywood with BPF resin was smaller after aging.Besides,after aging 7 periods,the surface roughness and the decreasing degree of methylene bridge of BPF resin were lower than those of PF resin.(2)As rising temperature of radiant floor heating system,the initial formaldehyde emission,the growth rate of formaldehyde emission,and the final equilibrium formaldehyde emission of plywood with BPF resin increased significantly.The addition of bio-oil could weaken the effect of temperature on the increase of formaldehyde emission from plywood,and the weaken effect enhanced with the increase of substitute rate of bio-oil to phenol.Structural analysis results showed that the initial formaldehude emission of plywood mainly came from the residual formaldehyde,and the subsequent formaldehyde emission was due to the aging of resin.(3)After aging 960 h in accelerating aging tester,the loss rate on bonding strength of plywood decreased with the increasing substitute rate of bio-oil to phenol.Meanwhile,the surface aging degree and O/C radio of BPF resin film decreased.With the increase of NaOH addition,the loss rate on bonding strength of plywood with BPF resin was almost unchanged,and the surface aging degree of resin film decreased first and then increased after aging.As rising reaction temperature,the loss rate on bonding strength of plywood with BPF resin and the surface aging degree of BPF resin film both decreased after 960 h of aging.The softing based the influencing degree of different synthetic peocess parameters on the aging performance of BPF resin was the substitute rate of bio-oil to phenol,NaOH addition and reaction temperature.(4)Compare with the five aging conditions,the mass loss of plywood and film with BPF resin changed largest under the hygrothermal environment.The most obvious changes on the bonding strength of plywood,the apparent morphology and surface O/C radio of BPF resin film were under the accelerating aging tester.Compare with the single aging,the influence on the aging performance of BPF resin from the comprehensive aging like aging under hygrothermal environment and accelerating aging tester was larger.The effect of water on the aging performance of BPF resin was greater than that of heat and ultraviolet light.(5)Compare with the BPF resins prepared by five bio-oil model compounds,the loss rate on the bonding strength of plywood prepared by the phenol free bio-oil model compound was the highest,and the apparent morphology of resin film prepared by the ketone free bio-oil model compound changed largest after aging 960 h.Structural analysis results showed that the phenols and ketones of bio-oil had positive effects on the synthesis of BPF resin,while the aldehydes and acids had negative effects.After aging 960 h,all kinds of bio-oil compounds could improve the aging performance of BPF resin.