Preparation And Properties Of Phenol-formaldehyde Resins Modified With Larch Thanaka And Urea

In the 21 st century, with the dwindling of oil and other non-renewable resources, the use of biomass resources is very important. Because of the increment in the price of oil derivatives of phenol, the cost of phenol resin adhesive preparation with phenol increases. To further reduce the cost of modified phenolic resin adhesive, biomass larch thanaka and urea modified phenolic resin adhesive(PTUF) was adopted. Through the research on the composition of larch thanaka analysis, the activated process of PT activation solution and copolymerization process, the low cost PTUF adhesive was prepared, whose bonding strength reached the national Ⅰ plywood requirement and formaldehyde emission reached E0 level. Through the analysis of PTUF adhesive with FT-IR, DSC and TGA-DTG, the structure of PTUF adhesive was determined. This paper discovered the best hot-pressing technology by studying the influence of different glue mixing viscosity of PTUF, pressing time, temperatures of pressing andtypes of veneer on plywood performance. Cycle time of torage of PTUF adhesive was assessed. SEM was adopted to analyze the relationship of microscopic layer and bonding strength of PTUF adhesive. Conclusions are as follows:(1).In the prepared process of PT activation solution, the best recipe of activator was Na2SO3/PT of 2.13%, CaSO3/PT of1.60%, 40% NaOH/PT of 34.25%. When the PT activation time was 2.5h, the best effect was achieved and could also be energy-saving.(2) The best option was F/PT equivalent of 0.8. The bonding strength of PTUF adhesive prepared with U/PT 20% and 40% reached national Ⅰ plywood requirements and formaldehyde emission reached E0 level.(3) Through FT-IR analysis of larch thanaka and PTUF adhesive, it was found that the thanaka’s partial C—H bond ruptured and became phenolic hydroxyl and methoxy group content reduced during adhesive preparation. C=O stretching vibration conjugated aldehyde or acid and C≡C absorption disappeared after the synthesis reaction of adhesive, which proved the bond rupture.(4) DSC and TGA-DTG were applied to analyze PTUF and PUF, the conclusion demonstrated that the heat stability of PTUF adhesive was inferior to that of PUF adhesive. Since PTUF contained a small amount of thanaka impurities(undissolved cellulose), decomposition peak appears in the TGA heating process at 510 ℃.(5) The bonding strength performed best when glue mixing viscosity ranged from 20000 to 60000 mPa ? S and pressing time was 1.5min/mm and hot-pressing tempreture. This process could be applied to produce plywood with eucalyptus and poplar, eucalyptus plywood, which could meet national requirements. It was safer to press plywood with PTUF adhesive in 1 week.(6) Through SEM analysis of microscopic structure of PTUF adhesive, it was discovered that the crack of eucalyptus veneer was greater than that of poplar veneer and eucalyptus veneers existed throughout cracks. The interface between adhesive and poplar was denser than than that between adhesive and eucalyptus So the bonding strength of poplar plywood was better than that of eucalyptus plywood and eucalyptus poplar combined plywood.