Preparation And Characterization Of Wood Fibers Based Thermal Insulation Packaging Materials

Traditional thermal insulation packaging materials are environmentally unfriendly materials from petroleum based plastics such as expanded polystyrene（EPS）and expanded polyethylene（EPE）.Because of the increasing energy demand and fossil energy shortage in human society,it is of great significance to develop renewable biomass based insulation materials that can replace the above foam plastics.In this paper,the light and porous natural balsa wood was selected as the raw material,and lignin and hemicellulose crosslinked with each other in wood structure were removed by chemical method,making layered structure of fiber bundles formed by cellulose molecules retain in the wood,thus a more loose and porous delignified wood fibers material was obtained.Then,according to the anisotropic characteristics of wood fiber,the better structural strength of wood can be realized through the stacking combination of different fiber directions.Finally,in order to meet the requirements of cold chain logistics transportation,the surface of delignified wood was coated with environmentally friendly（ethylene-vinyl-acetate copolymer）,thus meeting the requirements of waterproof and anti-condensation,achieving lower thermal conductivity and reducing the temperature loss caused by material failure in logistics.The cushioning and thermal insulation effect of the material is verified through experimental design and characterization test.The conclusions are as follows:（1）The weight loss rate of balsa wood before and after delignification is 45.61%,and the density of ultimate material is 0.073 g/cm~3;In wood,honeycomb pore structure can be observed by scanning electron microscope.The results of N₂adsorption showed that the porosity increased after delignification treatment;Fourier transform infrared spectroscopy showed that hemicellulose and lignin can obviously be removed under the action of chemical reagents;The maximum tensile force that delignified wood can bear is 63N,which is 10N higher than that of natural wood（53N）,indicating that the axial tensile property of fiber is improved;The thermal decomposition of delignified wood occurs at250-350℃;The thermal conductivity of delignified wood is near 0.07661 W/m·K,which can be used as excellent thermal insulation material.（2）After 50 cycle under pressure-release,the recovery rate of wood block can still reach 70-80%,indicating delignified wood has excellent elasticity and recoverability;When the fibers are vertically staggered and stacked at 90°,the maximum stress of delignified wood is 4 MPa and the maximum strain is 90%;Whenσ_m=1.10 MPa,the delignified wood with density of 0.165 g/cm~3has the minimum buffer coefficient,C=1.27;The resonance frequency of delignified wood is 77 Hz,the Tr value above 100 Hz is less than 1,the response acceleration value is less than the excitation acceleration,the cushioning effect of buffer pad is good,and the packaging system has good damping effect;The delignified wood buffer liner can effectively protect the internal product such as repeater when it falls within the height of 40 cm.（3）The material coated with EVA is waterproof and can effectively solve denaturation of the material due to absorbing water during condensation.Coating surface treatment makes the material become a closed cell structure,which blocks the exchange between the air inside the wood and the outside world,and effectively reduces heat transfer;The compressive stress and strain of delignified wood coated with EVA increased whenσ_mit was near 0.5 MPa,the buffer coefficient C of the material placed in the same fiber direction after coating is similar to that of foamed polyethylene（EPE）,polyvinyl chloride（PVC）and foamed polystyrene（EPS）;With the increase of heating time,the heat transfer rate of natural wood is higher than that of delignified wood,and the heat diffuses along the fiber axis;The thermal conductivity of delignified wood coated with EVA decreased from0.07661 W/m·K to 0.01862 W/m·K;After temperature monitoring within 48 hours,the average insulation temperature can be lower than 1℃of polystyrene,showing better insulation performance than expanded polystyrene（EPS）.In a word,through delignification and modification of natural wood,a bio-based thermal insulation material substituting plastic with cushioning and thermal insulation properties can be fabricated,which can be used as a reference for the green development of packaging industry in the future.