| Calcium carbonate is an important functional powder material,which is widely used in plastics,daily chemical products,paper industry,coating industry,rubber,chemical building materials and other fields.At present,the main raw materials are natural ores and marine shells.In this paper,eggshell,which is safe,non-toxic,cheap and widely sourced,is used as the raw material of calcium carbonate.The precipitation method is used to prepare light calcium carbonate and fine calcium carbonate with high whiteness,high purity and good dispersion.The effects of inorganic acid concentration,shell acid ratio and carbonization agent concentration on the properties of light calcium carbonate were investigated;Then,the quality of eggshell derived light calcium carbonate was compared with that of commercial calcium carbonate,so as to provide a theoretical basis for the application of eggshell derived light calcium carbonate;Then the light calcium carbonate was further processed,and the light calcium carbonate was micronized by ball milling method.The effects of ball milling time,ball mill speed and ball milling medium size on the particle size of micronized calcium carbonate were studied;Finally,the prepared light calcium carbonate and fine calcium carbonate are applied to degradable starch film in order to obtain food grade packaging film with better mechanical properties.The main research contents and results are as follows:(1)Light calcium carbonate was prepared by precipitation method.The optimum process conditions were hydrochloric acid concentration of 8 mol / L,chitosan acid of 1:2g / ml and 0.6 mol / L sodium carbonate solution.The yield of light calcium carbonate was 73.6%,the purity was more than 98%,the sedimentation volume was 2.57 ± 0.18 ml/ g and the particle size was 3-15 μ In the range of M,the distribution is narrow,and the morphology is mainly spherical calcite calcium carbonate formed by stacking flake particles.(2)Comparing the self-made eggshell source light calcium carbonate with commercial limestone calcium carbonate and oyster calcium carbonate,the results are as follows: the purity of eggshell calcium carbonate and limestone calcium carbonate meets the requirements of high-quality calcium carbonate(more than 98%),there are many magazines in oyster shell calcium carbonate,with low purity,dark color and low whiteness;The content of heavy metal cadmium in bio based eggshell calcium carbonate and oyster calcium carbonate was significantly lower than that in limestone calcium carbonate;The types of calcium carbonate of the three are calcite calcium carbonate,but the light calcium carbonate from eggshell is spherical,the two commercially available calcium carbonate are flake,and the dispersion of calcium carbonate from eggshell is better than the two commercially available calcium carbonate,and the agglomeration of limestone calcium carbonate and oyster calcium carbonate is obvious.(3)Through wet ball milling,the light calcium carbonate from eggshell is micro refined.The best process is that the ball milling speed is 3000 r / min,the particle size of the ball is 0.5 mm,the ball milling time is 2 h,the sedimentation volume of the prepared fine calcium carbonate is 2.86 ± 0.27 ml / g,the oil absorption value is 21.76 ± 1.79 g,the particle size is in the range of 120 nm-140 nm,the distribution is narrow,the particles are uniform,and the morphology is mainly flake calcite calcium carbonate.(4)The composite film was prepared by adding different amounts of eggshell derived fine calcium carbonate into the starch based film.The optimum addition amount was 4%(accounting for the amount of starch).It was heated and stirred at 80 ℃ for 1 h,and then heated to 90 ℃ for blending for 2 h.at this time,the tensile strength of the film was 3.78 ± 0.41 MPa,the tensile rate of fracture was 17.74±1.41%,and the elastic modulus was 365.31±15.49 MPa,which were 182.61%,93.32% and 168.73% of that of pure starch film respectively.The whiteness and opacity of the composite film increased,the addition of calcium carbonate enhanced the heat resistance of the starch based composite film,and the surface microstructure was smoother than that of the pure starch film. |
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