Optimization The Performance On Wood Fiber Based Vacuum Insulation Panel By Producing Of Dry-process

With the continuous advancement of science and technology,the applications of thermal insulation materials were more and more widely.As not only in refrigeration cold chain,aerospace and other fields,but also in the field of traditional building thermal insulation and household appliances.Vacuum Insulation Panel(VIP)is a new generation of high-performance thermal insulation materials developed rapidly in recent years.It is designed based on insulation structure and vacuum insulation mechanism.It has very low thermal conductivity,which has3-8 times lower thermal insulation compared with traditional thermal insulation materials.The heat insulation performance of VIP is mainly depending on the core material.However,the traditional VIP core material,such as fumed silica,polyurethane foam and glass fiber,etc.,is difficult for using popularizing due to its high cost,complex preparation process and environmental pollution.In this paper,wood fibers used for medial density fiber-board(MDF)manufacture were used to produce core materials by dry forming method.The effects of processing parameters,content and ratios of core materials on the thermal insulation properties of VIP were investigated.The thermal conductivity mechanism of VIP was systematically analyzed.The propose of this work is to develop a high-performance,low-cost,green and environmentally friendly wood fibre-based VIP.The main results are as follows:(1)The effects of preparation parameters on the thermal conductivity of wood fiber VIP were studied,and the optimum preparation process was obtained.The results showed that with the density of wood fiber core material 200 kg/m~3,the vacuum holding time30 min,and the drying temperature 140℃,the core material has good formability.The prepared VIP has good thermal insulation performance.The thermal conductivity as low as 9.6 mW/(m·K)was obtained at room temperature.The thermal conductivity increased to 14.0 mW/(m·K)when the ambient temperature increased to 55℃.The thermal conductivity of VIP also increased with storage time,which were 10.2 mW/(m·K)and22.3 mW/(m·K)after 30 days at 25℃and 80℃,respectively.(2)According to the problem of relatively high thermal conductivity and short service life of wood fiber VIP,the fumed silica was added to improve the thermal insulation performance of wood fiber VIP.The results showed that when the addition of fumed silica was 30%,the thermal conductivity of the prepared fumed silica/wood fiber VIP was decreased to 7.2 mW/(m·K),which has gone down by 25percent compared with pure wood fiber VIP.The durability have the same tendency as above,the thermal conductivity of VIP increased to 7.3mW/(m·K)and 12.7 mW/(m·K)after 30 days of storage at 25℃and80℃,respectively.Compared with wood fiber VIP,the addition of fumed silica can significant improve the thermal insulation and service life.(3)Furthermore,the thermal insulation performance of fumed silica/wood fiber VIP was optimized by adding carbon black.When the weight ratio of carbon black,wood fiber and fumed silica is 5:65:30,the thermal conductivity decreased to 6.8 mW/(m·K).When the ambient temperature rises to 55℃,the thermal conductivity of VIP is only 7.9mW/(m·K).The durability properties was also improved by carbon black addition,which is 6.85 mW/(m·K)and 9.8 mW/(m·K)after 30 days of storage at 25℃and 80℃,respectively.(4)Combining with the change of pore structure and transmittance of wood fiber based core material,the gas thermal conductivity,radiative thermal conductivity and solid thermal conductivity of wood fiber based VIP were calculated systematically.The results show that the thermal conductivity of wood fiber VIP is mainly composed of solid thermal conductivity and radiative thermal conductivity under vacuum condition,which are 7.3 mW/(m·K)and 2.3 mW/(m·K),respectively.The gas thermal conductivity is almost neglected.Adding fumed silica and carbon black can effectively reduce the solid thermal conductivity and radiative thermal conductivity of wood fiber VIP.When the weight ratio of carbon black,wood fiber and fumed silica is 5:65:30,the solid thermal conductivity and radiative thermal conductivity of VIP are 6.4 mW/(m·K)and 0.4 mW/(m·K),respectively.