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About extrusion machine

2022-11-02 Page view : 51 views

Six points of interest! Calcium carbonate whiskers have promising potential
About extrusion machine
Calcium carbonate is familiar, but what are calcium carbonate whiskers?

Whiskers are naturally occurring or synthetic short fibres with a single crystal structure, which are very small in diameter by an order of magnitude (microns), have a large aspect ratio and are generally regarded as one-dimensional crystalline materials.

Hundreds of whiskers have been developed, including many metal whiskers such as nickel and iron, oxide whiskers such as MgO and ZnO, ceramic whiskers such as SiC, boride whiskers such as TiB2 and ZrB2, and many other inorganic and organic whiskers.

Calcium carbonate whisker is a synthetic single crystal material, the chemical formula is CaCO3, the relative molecular weight is 100.09, of which CaO and CO2 accounted for 56.03%, 43.97%, its melting point is 759 ℃, the density is 2.86g/cm3. calcium carbonate whisker macroscopically usually white loose powder, in the scanning electron microscope is needle-like or fibrous crystals, length of 20-60μm, short diameter of 0.5-1.0μm, length to diameter ratio of 20-30, belong to the aragonite phase.

The properties of calcium carbonate whiskers are better than those of other materials in terms of whiteness, heat resistance and wear resistance, so they have good prospects for application in many fields.

Application in plastics

Calcium carbonate whiskers have a large aspect ratio and small crystal size, almost no internal dislocations, grain boundaries and other defects in the general crystal, mechanical properties close to the intact crystal, so it will be added to the plastic strengthening effect is very obvious, can effectively improve the strength, elastic modulus and other mechanical properties.

Experiments have shown that for polyethylene, the mechanical properties of filled calcium carbonate whiskers are better than those of filled talc, glass fibre and ordinary light calcium carbonate. Calcium carbonate whiskers have a significant impact strength enhancement on polyethylene and have less impact on the surface smoothness of the product compared to glass fibre.

When calcium carbonate whiskers are substituted for glass fibres in the nylon material, the resulting product has a better surface finish and the composite can be used in the manufacture of precision plastic products.

In addition, unlike other materials, the composition of calcium carbonate whiskers is found in abundance in nature and is also very widely distributed. Calcium carbonate can also react chemically with strong acids to produce carbon dioxide and inorganic salts. If the body inhales small amounts of calcium carbonate, it will be decomposed by the body’s natural reaction and will not cause any harm. Therefore, the use of calcium carbonate whiskers as a reinforcing material for biodegradable plastics does not cause secondary pollution to the natural environment and can effectively reduce white pollution and protect the environment.

Applications in rubber

Calcium carbonate whiskers can be added to natural rubber as a filler, but because of the poor combination of filler and natural rubber, a surface vacancy effect is created. Therefore, calcium carbonate whiskers need to be improved. Chen Tao et al. used Si-69, sodium stearate and titanate coupling agent to improve the calcium carbonate whiskers. The experiments showed that the treated calcium carbonate whiskers had higher surface energy and enhanced interfacial interaction with natural rubber, which could play a significant role in the reinforcement of natural rubber.

Applications in friction materials

Calcium carbonate whiskers have good temperature resistance and can be used in friction materials to significantly improve wear resistance.

Li Litao used calcium carbonate whiskers in automotive brake linings and investigated the friction increasing and reducing properties of calcium carbonate whiskers and the comparison of asbestos, heavy calcium carbonate and calcium carbonate whiskers. The experimental results show that the friction coefficient, wear rate and mechanical properties in the automotive brake linings are optimised when calcium carbonate whisker is added at 15%; moreover, its overall performance is superior to the other two.

Applications in coatings

In the coatings industry, calcium carbonate whiskers are widely used in aqueous coatings. In aqueous coatings, calcium carbonate whiskers can act as a backbone in the coating due to their good morphology and good dispersion, giving full play to the excellent mechanical properties of calcium carbonate whiskers. Coatings filled with calcium carbonate whiskers have improved gloss, better dispersion and reduced sinkability. When calcium carbonate whiskers are used in coatings, the viscosity of the coating increases significantly, as does the thixotropy, bond strength and storage stability. In addition, due to the properties of calcium carbonate whiskers, they can be evenly distributed in silica sols and emulsion solutions, thus reducing the discontinuity of the coating, which is very effective.

Applications in paper production

In the paper industry, the use of granular calcium carbonate as a filling material has already greatly improved the performance and printing speed of paper, while the use of calcium carbonate whiskers as a filling material provides the former with even better printability and can be used as an additive to produce paper with high whiteness and better flatness. Due to its specific morphology and properties, paper made from calcium carbonate whiskers has better printability, higher strength and better retention than paper made from calcite. Therefore, due to this advantage, calcium carbonate whiskers have a very promising future in the paper industry, especially for the production of paper with different applications and needs.

Applications in medical materials

In addition to industrial applications, calcium carbonate whiskers are also commonly used in medical materials. Calcium is an essential element in the human body, usually in the form of calcium phosphate, which is the main component of bones. Artificial bone composites can be prepared by filling with calcium carbonate whiskers and improving the mechanical properties of the material. The artificial bone composites were prepared by Xu Duyang et al. using a mixed solution method. The experimental results show that the artificial bone material does not cause damage to human cells and is of great medical value. In addition, calcium carbonate whiskers are considered to be a green, non-toxic biomedical stimulant. Calcium carbonate whiskers are also used in the medical field as an active material to make culture media. It can be said that calcium carbonate whiskers can also make a difference in the medical field.

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