The 2021 Green Mine Science and Technology Award (non-metallic ore, mineral material related fields) application work is organized and reviewed by the Zhongguancun Green Mine Industry Alliance Non-metallic Mine Special Committee, please pay attention to the V letter public number "Powder Technology Network".
Various silicate minerals such as kaolinite, talc, pyrophyllite and wollastonite, as well as minerals such as dolomite and duralumite monohydrate, are widely used as fillers in ceramics, plastics, rubber, coatings and other fields to improve the climatic stability of products, reduce shrinkage, oil absorption and so on.
However, as a typical inorganic substance, all kinds of natural minerals have good hydrophilicity and are very different from the surface interface properties of the organic polymer matrix, resulting in their difficulty in being effectively wetting and coating during the mixing process, and are prone to agglomeration. Therefore, it is necessary to use various types of modifiers such as coupling agents to modify the surface of minerals organically, so that the surface of the particles is hydrophobic and lipophilic, so as to improve their compatibility with organic matter.
Compared with the traditional wet modification technology, the dry modification technology based on mechanical force chemistry has a short reaction time, simple operation and easy industrialization, which has become the development trend of mineral surface modification in recent years.
1. Silicate minerals
Silicate minerals such as Eliite, Montmorillonite, Kaolinite and Wollastonite can also be mixed with silane and stearic acid modifiers to improve their surface pro-organic solvent properties, increase sedimentation rate, and optimize hydrophobic effect.
Wu Weiduan et al. used the supersonic air flow generated by high-speed airflow milling as a mechanical force, using stearic acid modifiers, respectively, ultra-fine crushing and surface modification of layered silicate minerals such as talc, sericite and kaolinite, and systematically studied the surface properties of minerals before and after modification and the changes in rubber mechanical properties such as tensile strength, tear strength and elongation, and the results showed that the supersonic airflow mechanical force generated by airflow milling can induce the existence of layered silicate minerals that have been crushed and broken. Free radicals or active spots on the stearic acid surface produce mechanical chemical adsorption for the purpose of modification.
After mechanical chemical modification, various types of silicate mineral powder can replace silica as a reinforcing agent and filler in rubber products, and its overall material mechanical properties are better than that of unmodified layered silicate mineral powder/rubber composites.
2. Carbonate minerals
In addition to silicate minerals, mechanical chemical technology is also suitable for modifying various other types of mineral fillers in rubber and plastics. For carbonate minerals, Gai Guosheng et al. through vertical stirring grinding heavy calcium carbonate and coupling agent modification, its X-ray diffraction spectroscopy, infrared spectroscopy, differential heat and other test results proved that grinding is from other complex energy into mechanical chemical processes, and while grinding can achieve surface hydrophobic modification of minerals, resulting in good system effect.
Xu Liqiang et al. adopted the mechanical force chemical method, respectively, with titanium ester, aluminate and stearic acid 3 different modifiers to modify the surface of the dolomite powder surface, infrared spectroscopy confirmed that the functional group of the surface of the modified particles has changed, the activation index of the modified powder, hydrophobicity have been improved, so that the dolomite powder as a functional filler can be better applied to coatings, rubber and plastics and other industrial fields.
3. Mica minerals
Mica-based minerals have now become a new type of industrial filler, which is widely added to composite materials to give new functions to the surface of the material, improve the adhesion strength, hydrophobicity, oxidation resistance and so on. However, natural mica minerals have fewer active points, low surface activity, and poor compatibility with polymer components in composite materials, and need to add coupling agents and use mechanical chemical methods for surface modification, thereby improving their use value.
Zhang Jingyang took a certain amount of sericite powder and phthalate coupling agent mixed with supersonic air flow pulverizer for crushing and surface modification, and the surface area of sericite mineral after modification was greatly improved, and the surface energy was greatly reduced, which proved that it achieved super-refinement and surface modification simultaneously, achieved the purpose of combining mechanical chemical modification and mineral surface modification, and improved the role of mica mineral filler in the development of new technologies and new products of composite materials.
Lin Hai et al. used wet stirring mill to mechanically chemically modify the two-dimensional nanosheets of sericite, and also added a phthalate coupling agent to modify the two-dimensional nanomaterials of polypropylene and sericite, and investigated the influence of elongation, yield strength, pH value, modification temperature, modification time and other factors on the modification effect, and found that the modified minerals and organisms had good compatibility, so that their ultraviolet resistance was strengthened.
Feng Gang et al. used a high-energy ball mill to modify the muscovite by using silane coupling agent/paraffin wax and silane coupling agent/sebacic acid, and blended the modified muscovite with polypropylene, and the results showed that the lipophilic and dispersive properties of muscovite after modification were improved, and the mechanical properties such as impact strength, elongation at break and tensile strength of polypropylene/muscovite composites were improved, and the preparation cost was effectively reduced.
4. Pyrophyllite
Kong Deyu et al. used phthalate coupling agents and polymethylsilane coupling agents to mechanically modify the chemical surface of the chlorophyllite, and determined the dispersion, particle size distribution and water absorption rate of the modified powder, and found that the coupling agent can play a role in dispersion and grinding, improve the fineness and efficiency of grinding; while the chlorophyllite crystal Under the mechanical chemical action, a large number of active centers appear in the neonatal cleavage surface and the nascent section, so that the surface is hydroxylized, and the coupling reaction is prone to adsorb to the surface of the solid particles, so that the mineral surface is completely hydrophobic.
Based on the study of the former, Fang Wei et al. co-ground calcium stearate, sodium stearate and methyl silicone oil with the mechanistic chemical co-grinding of chlorophyllite, and tested the contact angle, oil absorption and infrared spectra of the modified sample, the results showed that the mechanical chemical action excluded the hydroxyl groups in the chlorophyllite, and the surfactant molecules achieved hydrophobicization of the pyrophyllite surface through physical adsorption and chemical interaction with the hydroxylation surface of the pyrophyllite, of which methyl silicone oil had the best effect.
5. Tailings
Yuan Liangming et al. have confirmed that mechanical force chemical methods to modify bauxite tailings are feasible in the process, and the use of mechanical grinding can activate the tailings surface to generate new functional groups, so that the phthalate coupling agent and the tailings are interconnected in the form of covalent bond binding and hydrogen bond binding, so as to achieve the purpose of modification, and the research results have guiding significance for improving the level of reuse of tailings resources.
Source: Liu Chunqi, Ma Tian, Li Zhao, et al. Research Progress on Mechanical Chemical Activation and Modification of Natural Minerals[J].Metal Mine: 2021", edited and sorted by [Powder Technology Network], please indicate the source when reprinting!