Research On Continuous Extrusion Technology And Properties Of Re-combined Eucalyptus Fiber Profiles

The integrated utilization efficiency of plant fiber renewable sources,such as wood and straw,was significantly limited due to complicated components and microstructure as well as the properties of insoluble and non-melting.In this paper,a new method is proposed for the reconstruction of plant fiber into re-combined composite profiles with high fiber content based on the efficient dissociation of plant fiber by Continuous Screw Extrusion Steam Explosion(SESE).The Eucalyptus fibers after SESE pretreatment,a certain amount of water and polyvinyl alcohol(PVA)were mixed evenly first.Then the composites were added into the counter-rotating twin screw extruder designed by ourselves.The cellulose acted as reinforcement,PVA and lignin as well as hemicellulose acted as thermoplasticity matrix or binder in the composites while being processed.The re-combined composite profiles with plant fiber content up to 65%~85% were made by continuous extrusion moulding.This paper systemically studies the processibility and product properties of 20 mesh Eucalyptus powder and SESE pretreated Eucalyptus fiber,and processing characteristic and moulding mechanism of all composite systems,which possessed great theoretical significance and application values.The formula and process parameters with preferable deformability and briquettability were firstly exploded by off-line compression tests.And then,the hot pressing molding process parameters,properties and bonding mechanisms of hot pressed board were further studied based on the off-line tests results.Conveying extrusion system was designed based on the compression characteristic and molding characteristic of Eucalyptus powder and Eucalyptus fiber pretreated by SESE,in which plant fiber was continuously prepared into profiles under certain temperature,pressure and time.The processability of continuous extrusion,mechanical properties,micromorphology,and thermal properties with different formulations were investigated.In addition,the continuous extrusion molding mechanism was also explored.Eucalyptus powder and Eucalyptus fiber used in experiment have different granularity and morphology but identical components.The bulk density of Eucalyptus fiber composite systems were lower than that of Eucalyptus wood composite systems.The deformability of these two systems are poor.The compression molding characteristics of two formula were studies at room temperature,160 ?,180 ?and 200 ? by compression test device designed by ourselves.Researches show that compression pressure increased exponentially with the increase of material density.However,the increase of pressure has a less obvious improvement on material density when the density is relatively high.On the other hand,compression density gradually increased with the increase of temperature and/or PVA content.The relaxation coefficient of Eucalyptus fiber composite systems were significantly lower than that of Eucalyptus wood.The initial bulk modulus(K0)and experimental coefficient A of eucalyptus wood compound system reduce with the increase of temperature and/or PVA content.However,the K0 and A of Eucalyptus fiber composite systems are lower,the increase of PVA content and temperature has little effect on the deformability of them but significantly improved the filling extent and binding between fibers.Materials deformed and regularly arranged when compressed in low temperature.On the other hand,water promoted deformability and briquettability of materials,and melting of plasticization component in plant fiber and PVA,might even formed thin layer covered or wrapped plant fiber with high PVA content at high temperature.The compression deformability and briquettability of Eucalyptus fiber composite systems perform better than Eucalyptus powder in the same process and formula conditions.The density and mechanical properties of hot pressed board prepared from Eucalyptus fiber composite systems are higher than that of Eucalyptus powder in the same process and formula conditions,especially in the formula without or less PVA content.The flexural properties of hot pressed board of Eucalyptus powder composite systems and Eucalyptus fiber composite systems present out the same change trend.In detail,flexural strength significantly increase and flexural modulus firstly increase and then decrease with the increase of PVA content.The thermal degradation properties of materials no significant change before and after hot pressed although little bound water still exist in hot pressed board.The addition of PVA can significantly improve binding performance between materials and surface quality.However,excess PVA will cause a decrease in flexural strength and increase costs.The results indicated that the optimum content of PVA is 15%.Hot pressed board presented more compact structure and better binding comparing to transient compression tests.The actual feeder yield of Eucalyptus powder composite systems and Eucalyptus fiber composite systems were lower than theoretical feeder yield based on measuring volume feeding.Feeder yield is the extrusion yield when the counter-rotating twin screw extruder work well.The feeder yield is related to the bulk density of materials.The extrusion yield of both composite systems are equal when extrude processing by adjusting the screw speed of feeder.The density of re-combined profiles made by Eucalyptus fiber composite systems are higher than re-combined profiles made by Eucalyptus powder.The operating load is more light and stable for processing Eucalyptus fiber composite systems.The compression strength on the axial and radial and flexural properties of Eucalyptus fiber re-combined profiles were also higher than corresponding Eucalyptus powder re-combined profiles.The moisture content of materials decreased after extruded,and the thermal degradation change not obviously before and after extrud processed.For Eucalyptus powder composite systems,the excess or insufficient PVA content is not good to extrusion molding,resulting poor re-combined profiles comprehensive properties.The Eucalyptus powder composite systems with 15% PVA content has better processability and performance.Different from this,there are wide formula range(10%-20% PVA)for extrusion process for Eucalyptus fiber composite systems,and the extruded re-combined profiles have better performance.The compression strength on the axial and radial of Eucalyptus fiber re-combined profiles were 29.4% and 13.6% higher than Eucalyptus powder re-combined profiles with 15% PVA,respectively.Eucalyptus fiber has better formula range,process range and process stability compared to Eucalyptus powder.Re-combined profiles have better performance can be made at lower PVA content for Eucalyptus fiber.