Effects Of Different Pretreatment On Properties Of Compressed Chinese Fir And Poplar

As an environment-friendly material,wood has been widely concerned by academia and industry.However,the contradiction between supply and demand of wood resources in China is prominent.It is urgent to modify fast-growing wood with rich resources to replace natural wood.Compression modification technology can make good use of fast-growing wood resources,improve the performance of fast-growing wood,and greatly solve the problem of supply and demand of wood resources.Compressed wood technology generally includes three stages:pretreatment,hot compaction and later fixation.Different pretreatment processes have different effects on the properties of compressed wood.Therefore,it is of great significance to explore the mechanism of different pretreatment methods(the effect on wood structure)for the preparation of compressed wood.In addition,it is very important to develop a low energy consumption and environment-friendly pretreatment method for the preparation of compacted wood.Compared with the traditional pretreatment(physical and chemical method),the biodegradation method-white rot fungus pretreatment was proposed in this study,and compared with physical and chemical methods.The paper takes Chinese fir and Poplar as experimental materials,and selects three methods of hydrothermal,alkaline sulfite and white rot fungus to conduct pretreatment.The micromorphology,mass loss,chemical composition content,chemical and crystal structure are characterized for study mechanism of different pretreatment methods,And compared density,compression rate,micromorphology,dimensional stability and mechanical property by different pretreatment.The main conclusions are as follows:(1)The mechanism of the three pretreatment methods is different.Hydrothermal pretreatment has the least damage to the cell wall structure of wood,almost does not degrade the components of wood,its mass loss rate and chemical composition content change little,the characteristic peak value of infrared spectrum related to hemicellulose and lignin weakens slightly,and the crystallinity showing an slowly upward trend.The results showed that the alkaline sulfite and white rot fungus treatment mechanism was similar,the cell wall was damaged obviously,the porosity of cell wall increased,the mass loss rate and chemical composition content changed greatly,the infrared spectrum characteristic peaks related to cellulose,hemicellulose and lignin decreased obviously,the alkaline sulfite pretreatment mainly destroyed the amorphous area of cellulose,and the crystallinity showed an upward trend.The pretreatment of white rot fungi caused damage to the crystalline area of cellulose,and the crystallinity was increased.(2)The properties of compressed Chinese fir wood by three pretreatment methods are as follows:For hydrothermal,the density(0.97g/cm~3),compression ratio(69.44%),compressive strength(54.5MPa)and hardness(2252.5N)of pretreated for 3h were the highest,and the increase rate of thickness(19.31%)was the lowest;For alkaline sulfite,the density(1.25g/cm~3),compression ratio(81.58%),compressive strength(105.6MPa)and hardness(4822.4N)of pretreated for 5h were the highest,and the increase rate of thickness(6.89%)was the lowest;For white rot fungus,the density(1.16g/cm~3),compressive strength(85.7MPa)and hardness(3443.7N)of pretreated for 120d were the highest,and the increase rate of thickness(9.93%)was the lowest;but the compression ratio(81.24%)for 150d was the lowest.(3)The properties of compressed Poplar wood by three pretreatment methods are as follows:For hydrothermal,the density(1.06g/cm~3),compression ratio(64.21%),compressive strength(62.3MPa)and hardness(2981.5N)of pretreated for 2h were the highest,and the increase rate of thickness(21.83%)was the lowest;For alkaline sulfite,the density(1.28g/cm~3),compressive strength(112.9MPa)and hardness(5614.3N)of pretreated for 3h were the highest,and the increase rate of thickness(9.54%)was the lowest;but the compression ratio(78.22%)for 5h was the lowest.For white rot fungus,the density(1.22g/cm~3),compressive strength(101.4MPa)and hardness(4462.4N)of pretreated for 90d were the highest,and the increase rate of thickness(11.06%)was the lowest;but the compression ratio(79.77%)for 150d was the lowest.(4)The three pretreatment methods used in this study can improve the properties of compressed wood.Hydrothermal pretreatment process is easy to operate,environmental protection,almost no damage to wood,but the low compression rate cause a small performance improvement.Alkaline sulfite and white rot fungus pretreatment process are similar,the performance of the prepared compressed wood is significantly improved,and the performance is higher than that of hydrothermal pretreatment compressed wood,but the alkaline sulfite pretreatment process is will be used a large number of chemicalsin,which will pollute the environment,while the white rot fungus pretreatment process is eco-friendly and sustainable.