Research On Container Flooring Manufactured By Strengthened Poplar Veneer

With the vigorous development of modern transportation industry, C hina has already become the biggest country producing container flooring production at present. As traditional container flooring material like tropical hardwood including Apitong reduces sharply recently, which restricted the development of container flooring industry in C hina severely. As one of the fast-growing timber species, poplar is widely bred and cultivatedd in our country. Poplar is relatively cheap and abundant, but it also has many defects such as loose structure and low strength, which seriously hinders the scope of its use. Therefore, this paper aims to improve the properties of poplar through strengthened modification, thus developing a new kind material to replace traditional hardwood and extend the useage of poplar. Poplar veneer was taken as raw material, which was impregnated with low molecular weight phenol formaldehyde to improve its physical and mechanical properties. Three structures of the container flooring including thin shell structure, inner strengthened structure and homogeneous structure were manufactured and their physical and mechanical properties were also analyzed in detail. Conclusions of the research are as follows:(1) The single factor test method was adopted to study the effect of solid content of low molecular weight phenol formaldehyde, dipping time and veneer thickness on weight gain rate. The results showed that poplar veneer weight gain rate varied with the solid content of low molecular weight phenol formaldehyde and increased with the increment of dipping time, but when the dipping time increased to 90 min, the extension of dipping time had little impact on he weight gain rate of poplar veneer; at the same time, the weight gain rate of thin veneer was greater than that of thick veneer significantly.(2) Contact angle of conventional phenol formaldehyde(PF), ethylene glycol, methylene iodine and distilled water on poplar venee were measured. Results showed that the equilibrium contact angle of conventional phenol formaldehyde(PF) on poplar veneer increased with the veneer thickness, impregnation time and solid content of low molecular weight phenol formaldehyde. Solid content of low molecular weight phenol formaldehyde had the maximum impact on the surface free energy and the surface free energy decreased with the increase of solid content of low molecular weight phenol formaldehyde. Veneer thickness and dipping time had little effect on the veneer surface free energy. In the whole, PF equilibrium contact angle of the impregnated veneer is less than that of the untreated poplar veneer while the surface free energy was greater than that of the untreated ones. In this way, the impregnation of poplar veneer improved the veneer surface wettability to some extent.(3) Orthogonal experiment method was applied to research the hot-pressing process and 5 layers of plywood were produced by impregnated veneers. Results showed that the best hot-pressing process parameters were as follows: unit extrusion pressure of 2.1 MPa, hot-pressing temperature of 140 ℃, hot pressing time of 1.5 min/mm, two-sided glue quantity of 250 g/m2. Based on this hot pressing process, the main mechanical properties of 5 layers plyboard were drawned as followed : rapture modulus of 162 MPa, elastic modulus of 15018 MPa and bonding strength of 2.59 MPa.(4) X ray method was introduced to measure section density distribution of three structures of container flooring. The results showed that density on the surface layer of thin shell structure was around 0.85g/cm3, density on the middle layer was near 0.80g/cm3, density on core layer was about 0.75g/cm3; density on the surface layer of inner strengthened structure was around 0.85g/cm3, density on the middle layer was near 0.80g/cm3, density on core layer was about 0.95g/cm3; density of three layers of homogeneous structure was relatively close with the value of about 0.83g/cm3.The section density distribution of three structures of container flooring were relatively consistent as designed.(5) Physical and mechanical properties of three structures of container flooring were tested and results showed that they all met the requirements of national standard. Homogeneous structure owned the best dimensional stability and inner strengthened structure achieved the highest rapture of modulus(MO R) and elasticity of modulus(MOE). MO R and MOE of thin shell structure and homogeneous structure were relative close to each other. The bonding strength of secondary bonding inte rface of three different structures of the container flooring ranged from 1.74 MPa to 2.48 MPa. The sequence were as follows: core laye of homogeneous structure(D/D), core layer of thin shell structure(C/D), core layer of inner strengthen structure(D/E), surface layer of thin shell(inner strengthened) structure(B/D), surface layer of homogeneous structure(A/D).(6) The influence of aging treatment on the performance of the three structures of container flooring varied. The results showed that after aging, homogeneous structure got the maximum reduction rate of 24 h absorbing water thickness expansion rate and the minimum growth multiple of 24 h water absorption rate. MOR and MO E of three different structures of container flooring decreased to different degrees. Homogeneous structure acquired the highest retention rate of MOR and MOE; thin shell structure earned the lowest retention rate of MOR and MO E⊥; inner strengthened structure obtained the minimum retention rate of MO E∥. The retention rate of bonding strength of three different structures was high and relatively close, the value of which ranged from 85.6% to 85.6%. Therefore, mechanical properties of inner strengthened structure and homogeneous structure container floor ing performanced better than that of thin shell structure after aging.(7) Through DIC analysis, strain distribution on different density gradient layer bonding interface was observed. Results showed that under the load of 450 N, the maximum shear strain occurred near the notches at both ends of the density gradient layer bonding interface that is stress concention. Shear strain on the low density layer of the specimens was greater than that on the high density layer of the specimens. After aging, shear strain of the specimen was less than that of the untreated specimen and the aera of stain distribution became larger while the continuity decreased and the strain distribution became more clutter.