| Whisker-like calcium sulphate has the characteristics of high strength,high modulus and high toughness,which makes it a new material worthy of development.However,there are problems with its dispersity and application when used as filler,due to its strong polarity and containing crystal water.In this paper,we developed a new process for high performance calcium sulfate whiskers that is in-situ modified by stearic acid or styrene-acrylic emulsion or cellulose sulfonate.The experiment was carried out in alcohol-water mixed solvent system,and the modifier mentioned above worked as template,too.The synthesis process conditions were optimized.Besides we evaluated the application effects in polypropylene resin(PP)and adhesive.We explored and summarized effect of different conditions on the performance of the composite during the synthesis process,such as he type and amount of modifier,the influence of post-treatment temperature and developed an in-situ modified calcium sulfate whisker series which is superior to other inorganic nanomaterials.The optimum conditions for the synthesis of calcium sulfate whiskers in the alcohol-water solvent are ethanol-water volume ratio of 1:1,initial reaction concentration of 1 mol/L,reaction at room temperature(about 30 C)for 2 h to obtain calcium sulfate whiskers with a diameter of about 1?m and an aspect ratio of about 80.The optimum pH of the reaction is 10,and the optimum molar ratio of Mg2+/Ca2+ ions is 0.1.The average diameter and aspect ratio of calcium sulfate whiskers are about 500 nm and 120 relevantly.Further studies have found that we can obtain calcium sulfate hemihydrate with stable morphology and small grain size at about 36 nm and better dispersity when dries at 140 0C for 4 h.We use stearic acid,styrene-acrylic emulsion and cellulose sulfonate to in situ modify calcium sulfate whisker and get its product.When the amount of stearic acid is 2 wt%,the activation degree of calcium sulfate is almost 100%,the oil absorption value is about 25 g.The aspect ratio reaches a maximum about 31 when the amount of styrene-acrylic emulsion is 6%,and the average diameter is 880 nm.The diameter and aspect ratio of calcium sulfate whiskers modified by calcium cellulose sulfonate are 700 nm and 43,respectively.Modified calcium sulfate was applied to PP and adhesive.Stearic acid in-situ modified calcium sulfate was used in PP.When using 3%of modifier and adding 20 wt%,the impact toughness increased by 59.25%compared to pure PP,and the tensile strength remained basically unchanged.When addition amount is 50 wt%or 60%,the impact toughness of the composite material can still be substantially maintained.Considering the price of stearic acid,3%stearic acid is the optimum modifier dosage from the perspective of cost savings and enhanced composite properties.The styrene-acrylic emulsion modified calcium sulfate was added to PP.When adding 4%of the modifier and adding 20 wt%,the impact toughness was increased by 49.33%compared with pure PP.When the amount was increased to 40%.the impact toughness was increased by 34.32%;The tensile strength increased 10%.Using as a filler in the adhesive,bonding strength increased by 28.46%when the amount of modified calcium sulfate whisker is 50%.and it can pass the water resistance test.We also applied calcium cellulose sulfonate modified calcium sulfate to PP.when the addition amount was 10 wt%,the impact toughness increased by 74.97%.Even the added amount was increased to 40 wt%,the impact toughness was still slightly improved compared with pure PP.Using as a filler in adhesive,when addition amount is 30 wt%,the bonding strength of the composite adhesive increased by 86.5%.When the addition amount is 50 wt%,the adhesive strength of the composite adhesive still has a 54%increase.This paper puts forward a new process for in-situ preparation method for synthesizing high-performance modified calcium sulfate in a mixed solvent,which produces a series of products with excellent toughening and strengthening effects.It has opened up a new way for recycling waste to synthesize high-performance calcium sulfate whiskers.The results and rules of this paper have important guiding significance for the subsequent development and application of calcium sulfate whisker products. |
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