Study On The Preparation And Properties Of Poplar-Derived Sealed Materials By The Method Of Hot-Pressing

To achieve satisfying greenness and sealing properties for special goods transportation and storage,sealed packaging materials in this work were fabricated by method of hot-pressing from fast-growing poplar,and the influence of hot-pressing process conditions on the sealing and mechanical properties was studied.A mathematical model about the relationship between density and sealing properties of the as-prepared materials was established.This work provides a reference for the further development and utilization of high-practice sealed packing materials from fast-growing poplar.The main research work and conclusions obtained are as follows:?1?The as-prepared sealed materials after hot-pressing exhibited high average densities of 0.458-0.709 g/cm3compared with 0.366 g/cm3of raw material.The extent of hot-pressing conditions to affect the average density was in the follows:hot-pressing pressure>hot-pressing temperature>hot-pressing time,and the most significant factor is the hot-pressing pressure.The maximum profile density increased from0.402 g/cm3of raw material to 0.526-0.933 g/cm3of the obtained sealed materials.The influencing degree of hot-pressing conditions on the maximum profile density was in the order of hot-pressing pressure,hot-pressing temperature and hot-pressing time,and hot-pressing pressure is the most remarkable one.?2?After treatment,the leakage rate of the sealed materials was only 0.0017-0.0096 h^-1 much less than the above 0.01 h^-1 of raw poplar.The sealing level increased from level 4 to level 3 even level 2.Hot-pressing pressure was the most significant factor affecting the leakage rate followed by hot-pressing temperature ans hot-pressing time.The optimal hot-pressing conditions were 180°C,2.0 MPa,20 min.?3?Based on mass and energy conservation,a mathematical model illustrating the relationship between the maximum profile density and leakage rate of the obtained sealed materials was established with the pressure gradient as the main penetration force.The verification results showed that the theoretical values of the leakage rate of poplar sealed materials ranged from 0.0056 to 0.0096 h^-1,and 72%as-prepared fast-growing poplar sealed materials exhibited small differences of leakage rate between the measured value and theoretical value,indicating that the model was pretty practical.?4?The bending elastic modulus parallel to grain of sealed materials ranged from 9734.62 to16092.80 MPa higher than that of raw material.The extent of influencing parameters determining the bending elastic modulus parallel to grain was in the order of hot-pressing pressure>hot-pressing time>hot pressing temperature,and hot-pressing pressure exhibited the most significantly conclusive effect.?5?The as-obtained sealed materials showed a hygroscopic resilient rate ranging from 37%to 89%and a water-adsorption resilient rate from 105%to 169%.The determination of hot-pressing conditions on hygroscopic resilient rate and water-adsorption resilient rate was in the sequence of hot-pressing pressure,hot-pressing time and hot-pressing temperature,and hot-pressing pressure is the most remarkable influencing factor.?6?The contour arithmetic average deviation of the obtained sealed material after hot pressing treatment was from 0.797 to 2.222 um,which is lower than the 2.343 um of raw material.The ten-point height of the micro unevenness is between 5.262 and 13.566 um lower than that of raw material.The roughness grade of the obtained materials was reduced from N9 to N6.?7?The brightness of the sealed materials was 73.19-86.50.The red-green product index was 5.53-9.49,and the yellow-blue product index ranged from 16.75 to 20.39.The extent of hot-pressing conditions to affect the surface color was in the follows:hot-pressing temperature>hot-pressing time>hot-pressing pressure,and the most significant influencing factor affecting the yellow-blue product index was the hot-pressing temperature.