Studying the Influence of Mica Particle Size on ...

The incorporation of layered silicate into polymer matrices has resulted in significant improvements in tensile strength, barrier protection, and thermal stability [ 9 15 ]. Mica is widespread in the natural environment. As an easily obtained layered silicate mineral, mica has attracted great attention because of its unique electric insulation, chemical durability, thermal stability, and lack of toxicity [ 16 17 ]. Many studies have been reported for mica applications in different polymer matrixes due to its superior performance in enhancing the properties of coatings [ 18 20 ]. Combined with polymer coatings, mica can strengthen corrosion resistance as an anticorrosive component, improve mechanical properties including compressive strength and yield strength, and enhance electrical insulation and thermal stability of composite materials [ 21 26 ]. Wang et al. [ 20 ] prepared a hydrophobic coating of mica particles and polypropylene by copolymerization and the result indicated that the composites had great quality compatibilities and mechanical properties. Xia et al. [ 26 ] synthesized low density polyethylene (LDPE)/mica composite coatings with enhanced sound insulation and improved mechanical properties compared to the conventional composites. Most of the polymer/mica composite coatings are synthesized by the heat curing method. A distinct disadvantage of heat curing is the production of volatile organic compounds. In contrast, the polymer/mica composite coatings prepared by the environmentally-friendly UV curing method can be fast cured and have no emission of volatile organic compounds. To our knowledge, there are few investigations on mica as a filler in UV curable coating systems. Gao et al. [ 27 ] prepared a series of UV curable coatings containing different content of mica, and the results showed that mica provided positive effects on the mechanical properties and thermal stability of coatings. Cheong et al. [ 28 ] synthesized and characterized the delaminated muscovite mica/UV coating and obtained coatings with advanced anticorrosive properties. However, the influence of mica as filler on coatings was not studied in detail, and the effect of mica size on coating was not considered.

In this work, a series of UV curable EA/mica composite coatings was synthesized and the effect of mica particle size on the coatings was investigated. The mica powders were ball-milled to obtain different particle size mica and the effect of ball-milling time on mica powders was investigated. The influence of mica particle size on the stability of liquid mixtures was explored. The morphologies, particle size, and structures of mica powders were characterized by scanning electron microscopy (SEM), laser particle size analysis, and X-ray diffraction (XRD). The morphologies, chemical structures, and electrochemical performance of the coatings were investigated by SEM, Fourier transform infrared spectroscopy (FTIR), and electrochemical impedance spectroscopy (EIS). The mechanical properties of the coating were measured in accordance with the corresponding standard test methods.

Depending on the production process, mica powder can be produced by wet grinding and dry grinding.

Dry Ground Mica Powder

Dry ground mica powder is made by crushing, grinding, and classifying scrap and flake mica.

Characteristics of Dry Ground Mica Powder

• Dry ground mica powder is low in purity and aspect ratio. The dry grinding method will easily damage the mica crystal form and lamellar.
• The quality of dry-milled mica powder is greatly affected by the raw mica ores and climate, so the quality is difficult to control.

Application of Dry Ground Mica Powder

Dry-milled mica powder is mainly used for cattle felt, electric welding rod, drilling mud, etc. Generally, it is not used as a functional filler.

Dry Ground Mica Powder Processing Flow (for reference only)

Advantages of Dry Mica Grinding

1. 1

   Simple production process without too much equipment;

2. 2

   No need for water and heat, less energy demand;

3. 3

   Compared with wet ground mica powder, the dry-milled mica products are more cost-effective, especially for less demanding flier grade mica powde.

Disadvantages of Dry Mica Grinding

1. 1

   The dry ground powder with a low aspect ratio, rough and less shiny surface can’t be used in high-end applications;

2. 2

   Dry ground mica products have high impurity content;

3. 3

   The dust pollution of the mica dry milling plant is serious.

Wet ground mica powder

Wet mica powder is processed through multiple processes with water as the medium.

Characteristics of Wet Ground Powder

• Wet ground mica powder has higher purity, higher aspect ratio, smoother surface, better cementation, better dispersion, and better adhesion;
• Wet ground mica products are less affected by raw ore and climate, and the quality is easier to control;
• It has wider applications.

Application of Wet Ground Mica Powder

Wet ground mica powder is mainly used in mica pearlescent pigments, high-grade coatings, engineering plastics, and composite materials. It is also used in daily chemicals, new building materials, decorations, and medicine.

Wet Ground Mica Powder Processing Flow (for reference only)

Advantages of Wet Mica Grinding