Research On The Preparation And Performance Optimization Of Bio-based Building Insulation Materials

With the development of the social economy,building energy consumption is increasing.Meanwhile,the construction industry also leads to a large amount of greenhouse gas emissions,which seriously affects the realization of carbon peak and carbon neutralization goals.To reduce building energy consumption and greenhouse gas emissions,building thermal insulation is considered as one of the most effective strategies.China is an agricultural country in the world,and biomass is rich and distributed widely.However,the traditional energy utilization mode of biomass combustion power generation has a large scale,high cost of biomass collection in front-end and low price of products in terminal,resulting in poor economy and difficult to promote in practical applications.Therefore,this study recycled agricultural and forestry waste to prepare environment-friendly and high-performance bio-insulation for high-value resource applications.It can not only meet the needs of building thermal insulation,but also save resources,fix carbon and protect the environment,which is conducive to energy conservation and emission reduction.Based on the experimental study and theoretical analysis,the ratio of each component was optimized,and effective preparation processes and performance improvement methods were proposed to improve the comprehensive performance of bio-insulation.In addition,the evaluation framework of the whole life cycle of the external wall thermal insulation system was established by the entropy method.The main contents of this dissertation are as follows:Firstly,bio-insulation was prepared by using rice husk as raw material,geopolymer as the binder,and hydrogen peroxide as the foaming agent.The effects of mass ratio of rice husk to geopolymer（R/S）,foaming agent to geopolymer（F/S）and prewetting water to biomass（Wp/R）on the density,thermal conductivity,high-temperature resistance,compressive strength,and water and moisture absorption properties were discussed.The experimental results showed that when the R/S,F/S and Wp/R are 0.16,0.009 and 0.5,the optimal performance is obtained with a density of 295 kg/m³,the thermal conductivity of 0.107 W/（m·K）,compressive strength of1.92 MPa,water absorption of 64%and moisture absorption of 11.3%.Secondly,to analyze the durability of bio-insulation under changing climatic conditions,this work investigated the effect of freeze-thaw,wet-dry and cool-heat cycles on the appearance,compressive strength and thermal conductivity of wheat straw-based（WG）,rice husk-based（RG）and sawdust-based（SG）insulation materials.Moreover,the acoustics performance of bio-insulation was studied and compared with other insulation materials.The results showed that,after the three cycle modes,there is no obvious crack or disaggregation on the macro-level of the bio-insulation,indicating that it has a good skeleton structure.In addition,the changes in compressive strength and thermal conductivity of bio-insulation are less affected by the cool-heat cycle.By contrast,WG shows better durability with compressive strength losses of 19.4%,1.3%and 2.6%in the three modes,respectively,while it has no obvious negative impact on thermal performance.Moreover,WG has a high sound absorption coefficient of 0.71（at 1028 Hz）.Next,due to the porous structure of bio-insulation,its water absorption and moisture absorption rates are large,which will affect the insulation performance.Three waterproof treatment solutions were proposed.Among them,the preparation process of a self-waterproof structure was given for the first time.And several key parameters were analyzed in detail by experiments,namely the effect of precuring time of the substrate on the geopolymer coating appearance;the effect of different coating thicknesses on the microstructure,water and moisture absorption;the effect of different waterproofing forms on the static water contact angle,water and moisture absorption.The results showed that,the optimum precuring time and coating thickness are 9～24 h and 2 mm,respectively,and the interface between the coating and the substrate possesses a high bonding strength.For different waterproof forms,the static water contact angles of Multi-S₉G₂W,SW and Multi-S₉G₂samples are 92?,77?and 33?respectively,which indicate that the surface of Multi-S₉G₂W is hydrophobic.Moreover,Multi-S₉G₂W has low water absorption and moisture absorption,with values of 3.3%（after 96 h）and 1.5%（after 168 h）respectively.Therefore,the best method is to first add the geopolymer coating on the surface of the bio-insulation substrate and then brush the waterproofing agent.Finally,taking Changsha in Hunan province as an example,the optimal insulation thickness,life cycle cost,payback period,annual power consumption and CO₂emissions of different types of insulation materials under different external wall systems（reinforced concrete,sintered shale hollow brick or aerated concrete block）were analyzed by the method of LCC.And overall evaluation of different external wall insulation systems was carried out from three aspects of economy,energy and environment.The results showed that,RG has the lowest life cycle cost,which can save 15 CNY/m²every year compared with foam cement（FC）.In addition,the investment payback period of the seven insulation materials is in descending order:FC>WG>SG>RG≈PU>XPS>EPS.During heating and cooling,the annual power consumption of bio-insulation is relatively high,but its total CO₂emissions are lower than that of traditional building insulation materials.Based on the entropy method,RG obtains the highest score among the three bio-insulation materials.When the external wall is made of aerated concrete blocks,the score of RG is lower than EPS and XPS,but higher than PU and FC.To sum up,compared with inorganic insulation materials,bio-insulation materials have a lower investment payback period,considerable economic and environmental benefits,and higher comprehensive scores,which has a good application perspective in the field of building thermal insulation.The research of this topic,from the perspective of high-value utilization of agricultural and forestry wastes,improvement of thermal insulation for rural buildings and energy utilization efficiency,is of great significance to achieve energy conservation and emission reduction.In addition,it also provides a new idea for the development of renewable multi-functional building insulation materials,which helps to promote the sustainable development of low-carbon buildings.