| Organic moisture absorbent is a new type of functional hygroscopic material due to their excellent moisture absorption and retention property. The resins, modified by chemical and physical modification, have a water-absorbent property by hydrophilic groups. Besides organic moisture absorbent has no corrosion or pollution, and markedly it is renewable. Due to the diversity of products such as powder, granular or film, they could be applied into different applications. For example, moisture absorbency of product made in film could be greatly increased. In this paper, sodium polyacrylate, poly [acrylate-co-methacrylate] and sodium polyacrylate/urea with acrylic acid as the main raw materials. The factors such as monomer concentration, dosage of initiator, reaction temperature and so on influencing on the properties of moisture absorption were systematically investigated. The best reaction condition and the sequence of the factors influencing on hygroscopicity were based on the orthogonal experiment design. The mathematical correlation on various factors and moisture absorbency was obtained based on the multiple regression analysis. Composition, heat properties and microstructurewere studied by means of DTA analysis, infrared spectrum analysis, and SEM analysis.Sodium polyacrylate was synthesized with acrylic acid as monomer by means of aqueous solution polymerization. The factors such as monomer concentration, dosage of initiator, crossing-linking agent concentration, neutralization degree, reaction temperature and alkali influencing on the properties of moisture absorption were systematically investigated. The best reaction condition was based on the orthogonal experiment design. The optimal synthesis conditions were as following:the concentrations of initiator, monomer and cross-linking agent were respectively 0.2%,30% and 0.1%; the reaction temperature was 40℃;and the neutralization degree was 80%. The highest moisture absorption amount is 0.98g/g . The moisture content intuitive analysis table indicated the sequence of the factors influencing on hygroscopicity was shown as follows: neutralization degree> temperature>initiator amount>monomer>crosslinker amount. The mathematical correlation on various factors and moisture absorbency was obtained based on the multiple regression analysis:Y =36.001 +0.918ln[M] -3.297 [I]3-0.544sin[C] -22.050 lg[T]-0.000963[N]2The results showed that the moisture absorption capacity of sodium polyacrylate was higher than the molecular sieve's and silica gel's under the condition of T=25℃and RH=90%.However, the moisture absorption speed of sodium polyacrylate was slower than silica gel's. The saturated moisture absorbency of sodium polyacrylate was 98% after five regeneration experiments were carried out. Visible, hygroscopic ability of sodium polyacrylate was still stable after regeneration.The desorption rate of sodium polyacrylate was lower than silica gel, but its moisture retention property was good.The surface cross-linking was carried out by post-processing. The -COOH groups on the surface layer of sodium polyacrylate particles contacted the cross-linker uniformly and had cross-linking reaction, forming high crosslinking density layer on the surface, which had induced greater capacity and faster moisture absorption rate. The results of DTA showed that the temperature pyrolysis of sodium polyacrylate was 430℃, which can satisfy the need of special hygroscopic environment.Poly[acrylate-co-methacrylate] was synthesized with acrylic acid and methylacrylic acid as monomer by means of aqueous solution polymerization. The factors such as monomer ratio, monomer concentration, dosage of initiator, crossing-linking agent concentration, reaction temperature and alkali influencing on the properties of moisture absorption were systematically investigated. The best moisture absorbency of poly[acrylate-co-methacrylate] reaches to 0.86g/g. The results showed that under low humidity the moisture-absorbing rate is very slow under low humidity. The moisture absorbency under relative humidity of 90% is ten times of that under relative humidity of 40%. By comparing this copolymer with silica gel and molecular sieve under the condition of T=20℃, RH=90%, the results indicated that the moisture-absorption rate and moisture-absorption capacity of poly[acrylate-co-methacrylate] copolymer were obviously better than silica gel's and molecular sieve's.The SEM photograph showed the poly[acrylate-co-methacrylate] copolymer had a dense three-dimensional network structure. The copolymer formed into compact porous structure, which benefited for its moisture absorption. Finally, the result of TGA indicated that poly[acrylate-co-methacrylate] has got an improvement in the thermal stability.Sodium polyacrylate/urea was synthesized with acrylic acid and urea as monomer. The factors such as monomer concentration, dosage of initiator, rossing-linking agent concentration, neutralization degree, urea content influencing on the properties of moisture absorption were systematically investigated. The best reaction condition was based on the orthogonal experiment design. When mu/mAA was 0.2, its moisture absorption property was best ,on which surface formed uniform holes.The optimal synthesis conditions were as following: the concentrations of initiator, monomer and cross-linking agent were respectively 0.2%,20% and 0.2%.The highest moisture absorption amount is 0.98g/g . The Moisture Content Intuitive Analysis Table indicated the sequence of the factors influencing on hygroscopicity was shown as follows: monomer concentration>reaction temperature>reaction time>initiator amount >crosslinker amount. The mathematical correlation on various factors and moisture absorbency was obtained based on the multiple regression analysis:Y = -0.987-0.0047 [M] +0.476[I] 3 +0.0406ln [C] +0.311 ln[N] +0.566 [U] 0.0907 The results of SEM showed that sodium polyacrylate/urea had a lot of micropore structure, which was produced by decomposition of urea. NH3 and CO2 were originated from the decomposed urea, played a role in pore making agent. Hygroscopic properties comparison between sodium polyacrylate/urea and sodium polyacrylate showed that the moisture absorption capacity and absorption rate of sodium polyacrylate/urea were superior to sodium polyacrylate, but moisturizing and regenerative properties of sodium polyacrylate were bad.There were two main reasons why moisture absorption property of sodium polyacrylate/urea were higher than sodium polyacrylate.Firstly, decomposition of urea produced holes, which increased the effective surface area and improved the moisture absorption rate. Secondly , urea was not only pore making agent,but participated in reaction. A new group (N=C=O)was generated.A variety of hydrophilic groups were more conducive to its moisture absorption capacity than a single hydrophilic group.
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