Preparation And Performance Of Composite Humidity-control Materials Based On Porous Minerals

Humidity-control material is to adjust the air relative humidity on its own adsorption-desorption properties. The research and application of humidity-control materials is quite important for improving living environment, advancing the preservation quality of goods and reducing energy consumption.This paper prepares porous mineral-based composite by the way of inorganic salts modifying and compounding PAA based on the natural porous minerals namely diatomite, zeolite and sepiolite to improve the humidity-control performance. Desiccator method is used to evaluate the maximum equilibrium moisture content under different relative humidity and adsorption-desorption kinetic curves of the composite samples. BET method, SEM, XRD and IR are used to characterize the pore structure, microscopic appearances, the crystal structure and functional groups of porous materials to discuss the modification and humidity-control mechanism of porous minerals.Three inorganic chloride salts namely calcium chloride, magnesium chloride and sodium chloride are chosen to modify diatomite, zeolite and sepiolite, and the effects of concentration, kinds of inorganic salts and kinds of minerals on composite’s humidity-control performance are investigated. It can be seen that the adsorption-desorption content and speed of porous minerals are obviously improved for inorganic salts modification. The best humidity-control performance is achieved when calcium chloride is chosen to modify the minerals, in which modified sepiolite gets the optimal performance. The moisture content is increased with more calcium chloride in composite under the same relative humidity. The maximum equilibrium moisture contents under75%RH of diatomite, zeolite and sepiolite before modification are0.32%,3.51%,0.39%, respectively. And that of minerals modified by calcium chloride with mass concentration of20%are88.59%、82.96%、98.12%. The saturation desorption contents under33%RH of modified minerals are29.12%、27.68%、30.46%. The modified sample’s surface is covered with a layer of continuous uniform particles and the modification decreases the specific suface area and pore volume, while increases the average pore size. The changes in the structure lead to the improvement in the humidity-control performance. Physical adsorption of porous mineral and chemical adsorption of inorganic salt occur in the process of moisture adsorption of porous minerals modified by inorganic salts and promote each other to result in an increase of adsorption quantity. Porous minerals modified by inorganic salts combine the wide humidity range adjustment of inorganic salts and good desorption property of porous minerals.Modified porous minerals and acrylic acid are selected as raw materials to prepare porous mineral/sodium polyacrylate composite by reversed phase suspension polymerization method. Effects of mineral content, dispersant concentration and neutralization degree on adsorption-desorption speed and capacity are investigated. It is clear that moisture capacity and adsorption-desorption speed has been promoted after the composition between PAA and diatomite, zeolite and sepiolite, Through the study of composition of PAA, the optimal formula for diatomite/sodium polyacrylate composite is diatomite40wt%, Span15wt%and neutralization degree90%, that for zeolite/sodium polyacrylate composite is zeolite10wt%, Span10wt%and neutralization degree80%, and that for sepiolite/sodium polyacrylate composite is sepiolite10wt%, Span5wt%and neutralization degree90%. The saturation adsorption contents under75%RH of the three formula are50.12%、51.55%、58.91%, and the saturation desorption contents under33%RH of the three formula are29.14%、32.38%、38.69%. Pit shape exists on the surface and the surface is covered with polymer, mineral’s crystal structure has not been destroyed after composition and polymerization reaction indeed occurs between organic polymer and porous minerals. The composition of porous minerals and polyacrylate combine the excellent desorption ability of porous minerals and high hygroscopic property of polyacrylate. Minerals coated with polymer plays an important role in water vapor channel, which is advantageous for water molecules in and out and leads to improve the moisture capacity and adsorption-desorption speed.The article also preliminarily study the application of porous minerals in cement mortar. Dry-mixed mortar with zeolite content of0,10%,20%and30%are prepared to test its workability, mechanical properties and humidity-control performance. Experimental results show that the addition of zeolite to mortar increases the water consumption and the consistency loss in2h, however not affects the water retention. The optimum mechanical properties are achieved when the zeolite content increases to20%. Simulated indoor humidity-control test is conducted by mortar with zeolite content of0and20%compared with paint. Results show that paint doesn’t have humidity-control effect, but cement mortar could play an excellent humidity-control part by absorbing and releasing water vapor on its own when the relative humidity changes rapidly, and achieves better effect with zeolite.Natural porous materials such as diatomite, zeolite and sepiolite could be modified by the way of inorganic salts modifying and organic composition, which is an effective way to improve the humidity-control performance. Humidity-control materials based on porous minerals are expected to apply in the cement mortar fields and play an excellent part to adjust the indoor humidity in interior wall decoration.