Poplar/PF Adhesive Interphase Characterized At Multi-scales

This paper studies the interphase of LVLs made from Poplar. Raw materialsinclude phenol formaldehyde resins manufactured under3different reaction time:PF1(80min), PF2(120min) and PF3(160min);3different sealants for lathe checks:gelatinized starch/wood flour compound, soybean adhesive and gelatinized starch. Weuse fluorescence microscope, digital image correlation(DIC) and bonding strength testto characterize the interphase at different scales. These characterization’s results areused to explore the influences of resin reaction time, existence of lathe checks andchecks’ sealing treatments on the interphase properties of LVLs. Results from thisresearch are listed below:For LVLs made by planing, the data from fluorescence microscope observationindicate that the depth of PF penetrating into wood is PF3＞PF1＞PF2, with no linercorrelation to reaction time. DIC analysis results veil that the strain value at bulkadhesive layer of materials made from3different resins is PF1＞PF2＞PF3, so theadhesive layer strain decreases as the reaction time increases. As a result of bondingstrength test, dry strength of materials manufactured with different resins is PF1≥PF2＞PF3, while wet strength is PF2＞PF1＞PF3. Because wet strength is the criticalindex for LVLs, thus reaction time of120min is preferred in this study to optimize thebonding quality.Results from the fluorescence microscope observation show that the resin willover penetrate into wood along lathe checks and distributes at vessels. DIC test’sanalysis indicate that strain of LVLs made from peeling veneers is larger than thatfrom planing veneers. Bonding strength test veil that the strength of LVLs made frompeeling veneers is lower than that from planing veneersThe data from fluorescence microscope observation indicate that sealants canblock the over-penetration of PF resin into wood effectively, and the order of treatingeffect is gelatinized starch/wood flour compound＞soybean adhesive＞gelatinizedstarch. As a result of DIC test, the strain value at bulk adhesive layer of treatedsamples is gelatinized starch/wood flour compound≤soybean adhesive＜gelatinizedstarch. The data from bonding strength test indicate that the dry strength of samplestreated with different sealants is gelatinized starch/wood flour compound＜soybeanadhesive＜gelatinized starch, while wet strength is gelatinized starch/wood flourcompound≥soybean adhesive＞gelatinized starch. Take wet strength as main indexand dry strength as auxiliary index, soybean adhesive is a better sealant in bondingtest.