| The property of some coating materials used in the surface modification of ammonium nitrate was studied preliminarily.The coating materials included surfactants:the parts of C12-22 aliphatic alcohols,acids,amines,amides;polymer materials:homopolymers and copolymers of methacrylic acid and its esters,acrylic acid and its esters.Firstly,the coating materials should be not hygroscopic in certain conditions,so the hygroscopic test method for the two grams of coating materials was established and the hydroscopieity of these materials was measured for the time of 72h,at 25?,relative humidity of 52%,and at 35?,relative humidity of 68%and 92%respectively.The results showed under three test conditions,the hygroscopeity of C16-22 alcohols,C12-22 acids and C16-22 amides was less than 0.01%,C12-18 amines had a little of hygroscopicity.On the base of these results,the hygroscopicity regulations of these surfactants were summarized.For the surfactants with same polaric group head,the longer of the nonpolar carbon chain,the stronger its anti-hygroscopicity.As a same carbon chain length but different polaric group head,the hydroscopicity order was amines>alcohols>amides>acids.Also in the above three test conditions,polyacrylic acid and polymethacrylic acid were hygroscopic,but the hydroscopicity of their corresponding polymers was less than 0.01%within 72h.The measured hygroscopicity data could provide judgments in the selection for the experimental conditions.Secondly,in order to compare the anti-hygroscopicity of the coating materials,the Washburn method was used,the solid surfactants were pressed and the polymer films were made for the measurments of these materials contact angles at 20?.The results showed that the contact angles of choosen surfactants were between 60°and 80°.straight chain C22 amide with highest one was 77.61-77.64°;for the elastic films of copolymers formed with the monomer ratio 1:1 of MMA:BA or MMA M A,and the ratio 2:1 of MM A:BA or EA:EMA,the contact angles were 86.92?86.95°,84.31?84.33°,92.84?92.87°,84.71?84.73°,respectively.The anti-hygroscopicity of the polymers were better than the surfactants.The measured contact angle data could reflect the hygroscopicity of the coating materials,the larger of the value,the stronger of the anti-hygroscopicity.Thirdly,besed on the using conditions of solvent,coating material and ammonium nitrate in the surface modification processes of ammonium nitrate,a simplified experimental method named dynamic method was used for the measurement of solubility at 20? to ammonium nitrate in the solvents,and the solubility to the coating materials in the solvents was investigated.The results were as follows:ammonium nitrate was insoluble in the 7 kinds of the solvents such as cyclohexane,chloroform and acetonitrile which were selected from 14 kinds of solvents with the polar range from 0.01 to 6.6.The solubility of surfactants in these non-solvents of ammonium nitrate was as follows:in the same solvent,with the carbon chain increased,the dissolved amount of surfactants decreased gradually except stearic acid.In the different solvents,the polarity and the structure similarity were also important for a good solubility.For the homopolymers and partial copolymers of both methacrylates and acrylates,they were easily soluble in chloroform with a dose of more than 10 g/L.Their solubility were consistent with the principle of solubility parameters,when the difference values of solubility parameters of polymers and solvents were within the range of 1.3?1.8,these polymers could be soluble,otherwise insoluble.The experimental results of solubility of the coating materials could provide a kind of jugement for the collection of surfactants and solvents,and also some explanation for the results in the coating process.Finally,in order to offer some assistance in the coating process design,the surface tension of the straight aliphatic alcohols and acids with C16-22 atoms in chloroform,cyclohexane,toluene,petroleum ether,ethyl acetate at 20?,25? and 30? were determined by hanging-piece method based on the national standard "GB/T 22237-2008" respectively.The results indicated:in the same solvent,with the carbon chain increased,the surfactants critical micelle concentration decreased except stearic acid.In the different solvents,these surfactants reduced significantly the surface tension of organic solvents with larger polarities,but weakely that with less polarity.The relationship between the obtained surfactants and the solvents surface tension could provide for the optimization of dosages and conditions in the coating process of ammonium nitrate... |
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