Preparation And Deformation Of Thin Bamboo Bundle Veneer Laminated Composites

Currently,recombinant bamboo is widely used in the field of construction and engineering due to its high raw material utilization rate,high strength,good durability and its ease of adaptability,etc.Restructured bamboo is another bamboo product that is used in the field of architectural decoration(such as cladding panels,curtain wall panels,decorative panels,door panels),however,it suffers from applications issues which include excessive weight,excessive strength,uneven stress resistance,easily deformed,and expensive.Restructured bamboo has huge market prospects due to its unique advantages which include that it can be developed into thin,light,and stable bamboo bundle fiber composite materials that have the possibility to replace conventional recombinant bamboo products.However,due to the large variability of the bamboo bundle fiber raw material and the uneven density of the slab,resulting in residual stress being present after the thinning of the bamboo bundle fiber composite material.These stresses cause warpage occur in the reconstructed bamboo plate.Therefore,it is of scientific value and practical significance to improve the uniformity of bamboo bundle raw materials.For this study,the deformation mechanism of thin bamboo composites was done by carrying out the evaluation and classification of bamboo bundle veneers,based on the wet deformation characteristics of bamboo vascular bundle-parenchyma cells gradient structure,the effect of fine brooming on the bamboo bundle fiber morphology,resin penetration distribution characteristics,and orthogonally symmetrical preformance of the structure.In order to achieve the thinning of the bamboo bundle composite materials for construction,bamboo bundle veneers were the primary object.The light transmittance and mechanical stiffness were used as indicators to conduct real-time quality control evaluation of bamboo bundle veneer;in order to obtain uniform density and stable performance,wchich will be able to provide raw materials for the subsequent manufacturing of thin bamboo bundle veneer laminates composites.The whole bamboo bundle veneers(with or without wood veneer)were used as the raw material to produce thin bamboo bundle veveer laminated composites(TBLC).TBLC is produced when whole bamboo bundle veneers were laminated in a forward direction or in a crisscross manner to form a composite with a thickness of less than 6.0 mm.The influence of different process parameters on its physical and mechanical properties of TBLC was studied,and the internal relationship between the quality of bamboo bundle veneer and the performance of the board was established.The basic characteristics of the raw materials-bamboo/bamboo veneer of thin plates,process parameters,structural characteristics,hydrothermal deformation and external load deformation were systematically studied for the warpage deformation of thin plates.The warpage deformation mechanism of TBLC was revealed and the deformation law under the synergy of moisture and temperature was illuminated.With this information it was possible to provid the scientific basis for improving the uniformity of bamboo bundle composite materials and developing new,thin bamboo bundle composite materials with designable structure and controllable properties.The main research contents and main conclusions of this paper are as follows:(1)The light transmittance and mechanical stiffness were the main evaluation indicators.A self-developed real-time online monitoring evaluation system was used to perform quantitative characterization of the density,uniformity and mechanical properties of bamboo bundle veneers,thus establishing the quality evaluation system for bamboo bundle veneers.The quality classification rule of bamboo bundle veneer was obtained.The effects of factors such as the evaluation pressure and the number of connecting lines on the quality of the bamboo bundle veneer were studied.The light transmittance and the mechanical rigidity of the bamboo bundle veneer were fluctuated between 0?60% and 700 ? 1200 N/mm,respectively.Then the bamboo bundle veneer was divided into three grades: A,B and C.The mechanical stiffness of bamboo beam veneer was greatly affected by the pressure and the more accurate results can be obtained at the pressure of 50 N.Compared with one brooming,the light transmittance and mechanical stiffness of the bamboo bundle veneer after two brooming were reduced by 62.58 % and 4.03 %,respectively.(2)The influence of the bamboo bundle veneer quality,density,gluing amount and slab pavement on the physical-mechanical properties and uniformity of the thin bamboo bundle veneer laminated composite was studied.The relationship among the grade of bamboo bundle veneer,the density uniformity and warpage deformation of TBLC was established.When the glue amount increased from 7.4 % to 18.9 %,the water absorption thickness expansion rate and water absorption rate of TBLC decreased by 79.67 % and 63.92 %,respectively.The density distribution variability of Type? recombined bamboo with hybrid pavement was1.55 times and 2.26 times of the Type? and Type? TBLC with the laminated structure,respectively.While the density variability of type I prepared by class B bamboo veneer was1.46 times of type II TBLC prepared by class A bamboo veneer.(3)The relationship between the gradient structure of bamboo and its wet deformation was studied.The effect of the preform method on the warpage of the thin bamboo bundle veneer laminated composite was analyzed.And the mechanism of warpage for TBLC was revealed.The gradient structure of bamboo vascular bundle made the thickness direction of TBLC asymmetric.The stress inside the TBLC was caused by the difference in the sensitivity of bamboo fibers and parenchyma cells to moisture and the structural heterogeneity,which were the main reason for the warpage of TBLC.The longitudinal deformation of TBLC was smaller than the transverse deformation due to the difference of the longitudinal and radial wet expansion and mechanical properties.The deformation rules of the three-layer TBLC and the single-layer board prepared by different bamboo radial unit were similar,that is,a plate made of bamboo bundle veneer with green side has the largest deformation,and that made of bamboo bundle veneer with yellow side has the smallest deformation.The diagonal warpage of the single-layer board prepared from bamboo bundle veneer with green side was 48.15%higher than that prepared from bamboo bundle veneer with yellow side.The deformation of the plate was reduced effectively by increasing the number of pavement layers.The diagonal warpage of the three-layer structure TBLC was 85% lower than that of the single-layer board.The deformation of TBLC can be reduced by adjusting the layup angle of the bamboo bundle veneer.The diagonal warpage of TypeD with the fully consequent group billet was 25% and60% higher than TypeE and TypeF with transverse structure respectively.(4)The deformation law of TBLC in a hot and humid environment was clarified,and a prediction model of warping deformation was established.In the hot and humid environment,the water-absorbing expansion and thermal expansion in the width direction of the plate were greater than the length direction,and the transverse warping deformation of the plate was greater than the longitudinal warping deformation.In the thickness direction of the board,water molecules diffused from the surface layer of the board to the core layer according to Fick's second law.Due to the high density of the surface layer and the blocking effect of the resin,compared with the subsurface layer and the core layer,the surface layer of the board should first absorb water to expand and the expansion rate per unit thickness was higher.The humidity gradient formed caused stress inside the plate.The damage at interface was produced because of the penetration of water molecules and the thermal expansion of temperature,accelerating the release of residual stresses inside the plates,which caused an increase of warpage for TBLC.As the temperature increased,the warpage in the width and diagonal direction of TBLC both increased.When the temperature ranged from 25 ? to 100 ?,TypeE's transverse warpage and diagonal warpage were respectively increased by 155.88 % and66.67 %.TBLC with odd layer 0/90 ° symmetrical pavement structure had better moisture and heat stability.