| Calcium chloride is cheap and certain hygroscopic inorganic desiccant, but it has not good hygroscopic capacity and pollutes things for easy extravasation after the moisture absorption, which result in the application in many areas being restricted. Acrylamide cross-link polymer is water absorpting material and can absorb amount of water and lock it due to its strong hydrophilic polyacrylamide groups in polymer chain and three-dimensional network structure, which display better bibulous water-retaining capacity. In this study, we attempted to prepare CaCl2/PAM novel hybrid gel desiccant using polyacrylamide as the matrix and calcium chloride as the hygroscopic additive by free radical polymerization in aqueous solution from ameliorating CaCl2's deliquesce and raising its hygroscopic rate. This gel desiccant kept low cost,high regeneration and well hygroscopic performance of calcium chloride and effectively prevented calcium chloride from deliquescing for the water CaCl2 adsorb will being absorbed by polyacrylamide polymer super absorbent bibulous water-retaining resin, as well as raised the hygroscopic rate greatly for calcium chloride and polyacrylamide synergistic effect.This research mainly investigated several important factors that affected gel desiccant's hygroscopic performance, such as calcium chloride mass, calcium chloride's solubility temperature, crosslinking mass, initiator mass, polymerization temperature, hygroscopic environmental temperature, and so on. We discussed the influence law of various factors deeply by single factor experiment; we discussed reuse performance by the hygroscopic rate change of composite material after regeneration; This paper also analyzed the cost of gel desiccant. In the study, we discussed complex structure of composite material by series of characterization, such as Fourier infrared (IR) and X-ray diffraction (XRD), Scanning electron microscopy (SEM) and Thermogravimetric -differential scanning calorimeter (TG-DSC); We discussed hygroscopic swelling process of composite material by material's surface adsorption characteristics, action ways between polymer network and water, as well as the complex structure of CaCl2/PAM; We discussed hygroscopic rate change trend with environment humidity and hygroscopic swelling velocity of composite material by analysing hygroscopic swelling dynamic in different relative humidity (RH), at the same time, we investigated the impact of calcium chloride on hygroscopic swelling velocity rate using swelling dynamic.We got the following results from the study: 1,We attempted to prepare CaCl2/PAM novel hybrid gel desiccant using polyacrylamide as matrix, calcium chloride as hygroscopic additive, ammonium persulfate as initiator and N, N'-and methyl double acrylamide as cross linker by free radical polymerization in aqueous solution in nitrogen protection. Through the single factor experiment, it was found that the satisfactory experimental conditions of composite gel was following:CaCl2 mass is 80%, solubility temperature was 50℃, cross linker N, N-and methyl double acrylamide (MBA) mass was 0.9%, initiator ammonium persulfate (APS) mass was 0.8%, and polymerization temperature was 60℃; The maximum hygroscopic rate that was 2.5 times than CaCl2 and 5.3 times than PAM was 196.6%, which due to composite material synergistic effect for CaCl2 and cross-link PAM compouding; The satisfaction environment temperature of gel desiccant that was 30℃had certain little influence on its hygroscopic rate, the composite material consisting 80% CaCl2 mass still displayed higher hygroscopic rate in all environment temperature, which showed that it had good thermal stability and could be applied to real life. Through the hygroscopic rate change of composite material after regeneration in 80℃oven, it was found that gel desiccant displayed better reuse performance in different environmental temperature and humidity. Through the cost analysis, it was found that gel desiccant retained cheap advantage of calcium chloride.2,It was found from IR characterization that all charateristic function group's stretching vibrational peaks of PAM existed, and stretching vibrational peaks of primary amine salt (?)NH2 appeared because for the complexation with calcium ion and amino group in CaCl2/ PAM composite material. It was found from XRD characterization that the crystalline structure of CaCl2 was not obvious damage after CaCl2 and PAM compouding, but its diffraction peak become weak for being capsuled in polymerization network. The results of XRD characterization as follws:the surface of CaCl2 / PAM protruded large calcium chloride, which increased the contact area with gas phase and benefited for calcium chloride absorbing water from gas phase; most of calcium chloride dissolved out after composite material dipping in water and only a few retained in polymer network for complexation, also, polymerization resin matrix structure became loose after calcium chloride dissloution, while the whole structure was not obvious changes. It was found from TG-DSC characterization that the free water in polymerization network raised greatly for the addition of calcium chloride. We came to some conclusion from series of structure characterization of composite material, it as follows:calcium chloride that was free state was physically wrapped in polymer network when compouding with polyacrylamide, and only a handful of calcium chloride chemically crosslinked with polymer for complexation with polymer chain; The free water in polymerization network raised greatly for the addition of calcium chloride that provided polyacrylamide with preferable absorbing water environment.3,From the surface adsorption characteristic and action ways between polymer network and water, coupled with the structure characteristics of hybrid gel dessicant, we concluded hygroscopic swelling process of gel dessicant, it as follows:first, bulge of calcium chloride, lots of drape and microporous molecular on surface of composite material physically adsorbed water molecules from wet air and made water condense in its surface; Secondly, water molecular diffused in composite material particle internal surface and was chemically adsorbed by calcium chloride, meanwhile calcium chloride became water solution for adsorbing water and water became free state again, which provided polyacrylamide with preferable absorbing water environment; Then, free water diffused into the polymer network and been locked in resulted from being combined with polymer chain and forming hydrogen bonding, which prevented calcium chloride from deliquescing, at the same time polymer form a gel for absorbing water and highly swelling. The hygroscopic swelling process above explained synergy effect of composite material well and provided better theory basis to great performance of composite material.4,Through the hygroscopic swelling mode in different relative humidity, we could conclude that the Schott second dynamic equation may be employed to discuss hygroscopic swelling processes of gel dessicant; Through the dynamic equation and dynamic curve, we could get dynamic related parameters, maximum hygroscopic rate Smax and hygroscopic swelling velocity constant k, and Smax increased along with increase of environment relative humidity, while the rate constant K decreased, hygroscopic swelling velocity was decided by k, this result demonstrates that it takes more time for gel dessicant to reach swelling balance at relatively higher relative humidity; Hygroscopic swelling dynamic also may be employed to discuss the effect of calcium chloride on hygroscopic swelling velocity, the higher calcium chloride mass, the lower hygroscopic swelling velocity. |
PDF Full Text Request