Exploration On Humidity Control Properties Of Two Kinds Of New Palygorskite Based Composites

The dehumidification energy consumption of air conditioning system is high.The appearance of humidity control materials makes the passive humidity control of buildings studied and applied.It uses its porous structure to absorb and desorb water vapor in wet air,which can narrow the fluctuation range of indoor relative humidity.However,in order to study the effect of temperature and humidity regulation and energy saving achieved by indoor application of a certain type of hygroscopic material,the comprehensive thermal and humidity physical property parameters of hygroscopic material are often required in the mathematical model.However,the previous research on the thermal and wet physical properties of materials is not systematic,which is not easy to use in the theoretical simulation application research.Therefore,this study selected palygorskite with good humidity control performance as the base material and gypsum as the binder.Biomass additives such as flax fibers and wood fibers were added to enhance its humidity control performance,and two new types of pumice-based humidity control materials were developed: flax fiber-palygorskite(FP)and wood fiber-palygorskite(WFP).Their thermal and moisture properties were comprehensively tested.Firstly,scanning electron microscopy,high-performance specific surface area,and micropore analyzer were used to determine the microstructure characteristics,pore size distribution,particle size distribution,and porosity of the four raw materials.Then,the vapor permeability coefficient,isothermal adsorption curve,moisture diffusion rate,vapor resistance factor,thermal diffusivity,and specific heat at constant pressure of the two composite humidity control materials were measured.Samples with four thicknesses of the two materials were prepared,and their moisture buffering values were measured.Based on the measured thermal and moisture properties,numerical simulation was further used to study the moisture response behavior of the two composite humidity control materials under different thicknesses,temperatures(10,18,and 23℃),relative humidity waveforms(square wave and harmonic wave),and ranges(54%-75%,75%-95%),and the maximum moisture penetration depth was analyzed.Finally,the mold growth of the two materials was predicted to evaluate their durability.The main conclusions are as follows:(1)The microstructure of Palyaxite is loose and porous,and flax fibers and wood fibers have long and narrow tubular structures.The porosity of FP and WFP is 0.42 and0.45,respectively.(2)The moisture physical parameters of FP and WFP were similar,but the isothermal adsorption curve,vapor permeability coefficient and moisture diffusion rate of WFP were slightly higher than those of FP.When the relative humidity is low(for FP,RH≤42%;For WFP,RH≤31%),the moisture diffusivity increased with the increase of relative humidity.When relative humidity is high(RH >42% for FP;For WFP,RH >31%),the moisture diffusivity decreased with increasing relative humidity.(3)For both FP and WFP,the practice moisture buffer value increases with the increase of sample thickness.In the relative humidity range of 75%-95%RH,the practice moisture buffer value of FP sample with a thickness of 2.5cm is 1.15 times that of 1.5cm thick,1.43 times that of 1cm thick,and 1.83 times that of 0.5cm thick.The WFP shows a similar incremental pattern.(4)The higher the temperature,the higher the relative humidity interval,the larger the wet buffer value of the material,and in the same range of heat and humidity,the relative humidity square wave is larger than the wet buffer value of the material under the action of harmonics.The maximum practice penetration depth for FP and WFP is3-4cm and 4-5cm.(5)When relative humidity was low(RH≤55%),no mold was found on FP and WFP surfaces.When relative humidity was higher(RH>75%),mildew growth was observed on all surfaces,and mildew growth on WFP surface was more serious than FP surface.