Study On Preparation And Properties Of Transparent Wood Made From China-fir(Cunninghamia Lanceolata)and Poplar(Populus Deltoides)

Wood contains a large amount of cellulose,which has high strength and excellent optical transmittance.Based on the properties of wood,this paper selected China-fir sapwood,China-fir heartwood,and poplar as the main research object.The optical and mechanical properties of transparent wood were studied,and the influence factors of the initial wood on the transparent wood were analyzed.Combined with the research conclusions,transparent wood with better performance was prepared to meet the application requirements.The main contents of this paper include selection and performance analysis of natural wood,preparation and performance analysis of delignification template,preparation and performance analysis of transparent wood,preparation and performance analysis of transparent fiber wood.The main conclusions are as follows:(1)In terms of material density,the densities of delignification templates of China-fir sapwood,China-fir heartwood and poplar have been greatly increased by about 1g/cm~3 after impregnation with polymethyl methacrylate(PMMA),of which the density increase of the poplar template is up to 1.051 g/cm~3.The density increase of the delignification template of softwood China-fir was lower than that of hardwood poplar,and that of the heartwood of China-fir was lower than that of the sapwood.Moreover,the densities of delignification templates and untreated China-fir heartwood were higher than those of sapwood before transparent wood preparation.However,the density of transparent wood prepared from China-fir sapwood is higher than that of transparent wood prepared from China-fir heartwood.The direct reason that the density of transparent wood prepared from China-fir heartwood is lower than that of sapwood was the uneven distribution of PMMA inside the transparent wood.One of the reasons for the uneven distribution of PMMA in China-fir heartwood is that China-fir heartwood itself contains more extracts,and its permeability is lower than that of China-fir sapwood.Secondly,after delignification,the lignin content of sapwood is lower than that of heartwood.The removal of lignin provides a lot of pore structure and enhances the permeability of wood,thus facilitating the impregnation of PMMA.On the contrary,the delignification template of China-fir heartwood with high lignin content is more difficult to be completely impregnated by PMMA.(2)In terms of optical properties,the original opaque wood was endowed with transparent properties after impregnation with PMMA.Because the delignification template of China-fir heartwood still contained high lignin content,the transparent wood prepared from China-fir heartwood was yellowish compared with poplar and China-fir sapwood.The texture of transparent wood prepared from poplar was not obvious,but the texture of transparent wood prepared from China-fir was still visible.The transparent wood texture of China-fir was most obvious at the junction of early wood and late wood.From the electron microscopic observation of China-fir,it can be found that the junction of cell walls and PMMA was obvious in latewood of China-fir.However,the junction of cell walls and PMMA in early wood is closer,and the contour was not obvious.Therefore,the PMMA impregnation of China-fir latewood was less uniform than that of its early wood.The inhomogeneous combination of PMMA and the cell walls of latewood means that the possibility of light refraction and reflection is greater.Because the light refraction in early and latewood is inconsistent,the transparent wood prepared by China-fir has obvious texture characteristics.The transparent wood prepared from poplar and China-fir sapwood had similar transmittance,but the transmittance of China-fir heartwood was lower than the former two.The direct reason for affecting transparent wood transparency is the lignin residue of delignification template and the uniformity of PMMA distribution in wood.However,the reasons for these two factors can be attributed to the permeability of untreated wood,so the permeability of untreated wood is the fundamental reason to determine the transparency of transparent wood.(3)In terms of mechanical properties,the transparent wood made from poplar had the highest fracture strength.The fracture strength of transparent wood was proportional to the density of transparent wood.The fracture strength of delignification templates did not determine the strength of transparent wood.The ultimate strength of transparent wood was directly affected by the density of transparent wood,while the density of transparent wood is mainly affected by the permeability of delignification templates.(4)In summary,the key factor affecting the performance of transparent wood was the permeability of the untreated wood.Therefore,based on the traditional preparation process of transparent wood,this paper dispersed the wood fibers to improve permeability.As the lignin of dispersed wood fibers was easier to remove and PMMA could easily penetrate wood fibers,transparent wood based on wood fibers can be easily made into any thickness or size,and the preparation efficiency was higher than that of traditional transparent wood.Due to the high permeability of the untreated wood fibers,transparent fiber wood had good mechanical properties and favorable transmittance.The simulated thermal characteristic test in a real environment showed that transparent fibre wood also provided excellent thermal insulation effect.