Study On Preparation And Properties Of Vermiculite Nanosheets

Vermiculite has rich natural resources,unique structure,surface chemistry,adsorption properties,thermal/mechanical properties and environmental friendliness,which attracts many scholars in basic research and commercial applications.There are few direct applications of raw vermiculite（RVMT）,most of which tend to be applied in the form of expanded vermiculite（EVMT）.Compared with EVMT,vermiculite nanosheets（VMT nanosheets）have more excellent properties.Many scholars have studied the multifunctional application of VMT nanosheets,but there is few research on how to improve the large-scale production of VMT nanosheets,resulting in the low scale production of VMT nanosheets,which limits the application of vermiculite nanosheets in the multifunctional field.In this paper,the stripping of vermiculite（expansion stripping,chemical stripping and mechanical stripping）is the main body.The yield of VMT nanosheets prepared under different technological conditions was studied to solve the above problems.The main research contents and results of this paper are as follows:（1）The effects of calcination temperature,time,ion modification,hydrothermal compression assisted ion modification and synergistic effect with H₂O₂ on expansion ratio,bulk density and structure of vermiculite were investigated.To improve the interlayer ionic hydration of vermiculite,the effects of different ions on the modification of RVMT were studied.The results show that KNO₃ modified RVMT can obtain a higher expansion rate（13.1 times）of EVMT.To improve the content of water molecules between layers of vermiculite,the RVMT modified by hydrothermal pressing assisted chemistry（KNO₃）is proposed.When the concentration of KNO₃ is 0.8 mol·L^-1,the hot-pressing temperature is 220℃,the hot-pressing temperature is 30 h,and the thermal expansion treatment（temperature was 800℃for 100 s）,the expansion ratio of vermiculite can reach 15.8 times.The packing density was reduced to 0.040 g·m L^-1.Using the high decomposition capacity of H₂O₂,the expansion ratio of vermiculite increased to 28 times and the bulk density decreased to 0.0082 g·m L^-1 under the synergistic action of the RVMT modified by hot pressing assisted KNO₃ and H₂O₂（30%volume concentration）.The preparation of EVMT with high expansion rate provides the premise for mass production of vermiculite nanosheets with high yield.（2）Using shear/collision（transverse/longitudinal）peeling principle,a narrow gap liquid phase peeling method different from ball mill was constructed.Nano gap was constructed by adjusting the proportion of pellets（0.2-2.0 mm balls accounted for about 80%）,and high yield and scale production of VMT nanosheets was achieved at low speed（1000-5000 rpm）.The yield of VMT nanosheets is up to more than80%).This method achieves scalable production of batch VMT nanosheets.The simple and economical strategy provides a promising method for obtaining many nanosheets from two-dimensional layered materials.Using a narrow gap stripping device to achieve liquid glycerin-modified VMT nanosheet（G-VMT）,and applied in PVC to construct VMT-based organic and inorganic PVC composites with good thermal stability performance（aging thermal stability time:390 min,thermal decomposition time:38 min）,and the combination of calcium stearate（Ca St₂）has a synergistic effect to effectively improve the thermal stability of PVC（aging thermal stability time:420 min,thermal decomposition time:48 min）.In situ preparation of VMT-based organic and inorganic PVC nanocomposites using a narrow gap stripping device as a coupling reactor is realized,which provides a novel strategy for in-situ preparation of composites.（3）The liquid phase stripping of VMT was realized by using the synergistic effects of shear force,shock wave,microjet and collision provided by the adjustable rotor and stator high-speed shearing machine.The content of VMT nanosheet was 14.3%after the liquid phase stripping for 6 h at 12000 rpm.Under ultrasonic assisted peeling,the content of VMT nanoparticle reaches 15.8%,and the content of VMT nanoparticle less than 10μm reaches 96.1%.The crystal structure of the prepared VMT nanoparticle is complete.A self-supporting flexible VMT film with controllable macro size and ordered microstructure was assembled by vacuum filtration.The study showed that when the diameter of the main piece of VMT dispersion solution was less than 3.7μm and the content of VMT nanosheets was more than 54%,the VMT films could not be assembled into self-supporting flexible VMT films.Wrap VMT film on fruit or attach VMT film on the surface of fruit by dipping method to form"fruit fresh-keeping clothes",effectively improve the fruit fresh-keeping effect,and realize the application of vermiculite nanosheets in macro field.（4）Using the hole,impact and shear effect generated by high pressure homogenization,high-pressure liquid phase stripping was used to prepare low-layer VMT nanosheets,the size of which can reach 50-100nm and the thickness of which is about 2-4 nm.The influences of high-pressure homogenization time,pressure and ultrasonic assistance on the VMT stripping efficiency were investigated:the content of VMT nanosheets was 85.7%when the high-pressure homogenization was performed for 80 min at 1250 bar,and the content of VMT nanosheets was increased by 3.3%when the high-pressure homogenization was performed for 40 min alternating with ultrasonic assistance at 1000 bar.High pressure homogenization is a clean and easy method to produce nanosheets,which provides a good direction for large-scale production of nanomaterials.