Classification and types of fillers

There are many types and varieties of fillers, mainly the following categories:
(1) Calcium carbonate: Calcium carbonate is the most common and cheapest filler. Calcium carbonates of different origins and properties are as follows:
A Ordinary calcium carbonate (chalk): white crystals or powders, specific gravity 2.70-2.95, soluble in acid but difficult to dissolve in water. Heated to 825℃ decomposes into calcium oxide and carbon dioxide.
Natural calcium carbonate minerals include limestone, calcite, calcite, datian stone, etc., which are ground into powder and called ordinary calcium carbonate. They are divided into dry grinding and wet grinding, with a particle size between 1.5-44 microns, dry grinding has a particle size greater than 20 microns and wet grinding has a particle size less than 20 microns.
B Precipitated calcium carbonate: Powdered calcium carbonate generated by the precipitation of lime water or sodium carbonate solution with lime water by carbon dioxide, generally divided into:
Light precipitated calcium carbonate: specific gravity 2.50-2.60
Heavy precipitated calcium carbonate: specific gravity 2.70-2.80
The particle size of precipitated calcium carbonate is 1.0-16 microns, the specific surface area is 5-25 m/g, the refractive index is 1.49, the pH value is about 10, it is insoluble in water and alcohol, and releases carbon dioxide when it encounters acid; it has slight hygroscopicity.
C Active light calcium carbonate: This is a light calcium carbonate with a layer of fatty acid soap adsorbed on the surface of the particles. It is a tasteless and odorless white powder with a specific gravity of 1.99-2.01. The moisture content is below 0.5%, the stearic acid content is 2-5%, the particle size is less than 0.1 microns, the specific surface area is 25-28m/g, and the refractive index is 1.49. It is insoluble in water and alcohol, decomposes and releases carbon dioxide when it encounters acid, and has no chemical changes when placed in the air, and has only slight hygroscopicity. The activity is greater than that of ordinary calcium carbonate, and it has a slight reinforcing effect.
(2) Carbon black: This type of filler includes various carbon blacks. Carbon black is a product produced by partial combustion or thermal decomposition of liquid or gaseous hydrocarbons in the absence of air. The elemental composition of carbon black is mainly carbon, with only a small amount of hydrogen and oxygen. It is a black powdery substance with a "quasi-graphite crystal" structure and a colloidal particle size range. Due to different production technologies, carbon black can be divided into many grades, but the following two are commonly used in the plastics industry:
A Natural gas tank black: a black powdery substance with a relatively rough surface that easily absorbs moisture in the air. The average particle size is 23-30 micrometers, and the specific surface area is 130-160m/g.
B Mixed gas tank black: This is a type of carbon black made from anthracene oil, naphthalene oil, etc. in coal tar that is gasified and mixed with natural gas as raw materials.
The so-called "structure" of carbon black refers to the tendency of carbon black to aggregate and arrange in strings. This "structure" plays an important role in the rheological properties of the carbon black-polymer system. "High structure" carbon black promotes high viscosity, high elastic modulus, low flow rate and smooth low swelling extrusion of polymers. Carbon black added to polymers can not only protect against light degradation and thermal oxidation, but also improve the rigidity of plastic products.
(3) Cellulose
A Shredded paper: Kraft paper, white paper, colored paper and other paper can be used as fillers. Generally, the paper is soaked in resin, sliced ​​after drying, and then pressed into boards.
B Wood powder: Widely used in thermosetting resins, it has high impact strength, low shrinkage, good electrical properties and low price. Wood powder particles should be uniform in size, and large particles such as wood chips and bark should be removed.
C Cotton scraps: Cotton scraps are obtained by cutting cotton cloth or purifying cotton spinning. Plastic products filled with cotton scraps have improved impact resistance and large volume.
D α-cellulose: α-cellulose is a colorless cellulose product obtained by alkali treatment of wood pulp. It is mainly used in light-colored urea-formaldehyde and melamine formaldehyde resin formulations. The impact strength of products filled with α-cellulose is not as good as that of products filled with wood powder. They have higher hardness, do not affect specific gravity, and have low molding shrinkage.
E Peanut shell: Peanut shell is a cheap filler with high phenol content and abundant sources. Peanut shell powder can appropriately improve the performance of HDPE, PS, and PP and reduce costs. The surface of peanut shell powder is generally non-polar. Its water absorption is also lower than that of wood powder.
F Walnut shell: Walnut powder is a waste produced when processing walnuts. Because it contains a large amount of wood resin and keratin wax, it does not absorb water.
G Glass fiber; mainly used for plastic reinforcement.