What are the indicators of rubber carbon black?
The indicators to be tested for rubber carbon black include impurities, specific surface area, DBP absorption value and compressed sample DBP absorption value, coloring strength, heating loss, pouring density, 300% modulus stress, 45μm, 150μm, 500μm sieve residue content, ash content , fine powder content, PH value, acetone extract, etc.
Significance of various detection indicators of carbon black for rubber
1. Carbon black impurities
The impurity of carbon black is generally determined by different specifications of the sample sieve. The oversized particles that cannot pass through 20 mesh (840um sieve diameter) are called impurities. The granular impurities in carbon black include hard carbon, iron filings, furnace charge debris, and foreign matter mixed in during packaging and transportation. Hard carbon is a coke granular substance formed by direct carbonization of raw oil droplets without gasification during the carbon black formation reaction. Normal carbon black products are not allowed to have excessively large particle impurities (sieve hole diameter > 840um).
2. Carbon black particle size
The specific surface area of carbon black can be tested by four methods, mainly including iodine absorption method, CTAB adsorption specific surface area measurement method, nitrogen adsorption specific surface area measurement method, and STSA measurement method. The specific surface area refers to the sum of the surface areas of carbon black particles per unit mass or unit volume. The specific surface integral of carbon black is the external specific surface area, the internal specific surface area and the total specific surface area. In recent years, the specific surface area has replaced the particle size as the main basis for the classification of carbon black varieties.
3. DBP absorption value and compressed sample DBP absorption value
The two indicators of carbon black DBP absorption value and compressed sample DBP absorption value reflect the structure and structure of carbon black, and the compression sample DBP absorption value has a stronger correlation with the rubber compound performance. The oil absorption value of carbon black also has a certain relationship with the specific surface area. In the case of the same structure, carbon black with a large specific surface area (small particles) has a higher oil absorption value. In other words, only when the specific surface area is the same, the oil absorption value can Objectively reflect the structure of carbon black.
4. Heating loss
The moisture content of rubber carbon black can be determined by testing the carbon black heating loss; the moisture content not exceeding the standard has no effect on rubber products and vulcanization process, but when the moisture content is too high, bubbles will appear in the vulcanized rubber, which will reduce the adhesion of cloth layer products And affect the product quality.
5. Carbon black pour density
Pour density is the main indicator of granular carbon black. The apparent density (also known as fine powder content) of ungranulated powdered carbon black is very small, only between 80-190Kg/㎡. Its large volume is easy to fly, which makes the packaging, transportation, storage, mixing, processing and dispersion of carbon black difficult. Therefore, except for a small amount of pigment carbon black, which requires powder, almost all industrially produced commercial carbon black must be wetted. or dry granulation or compression (acetylene black). The densification effect of the granulation process effectively reduces the apparent volume per unit mass of carbon black. The pouring density of granulated granular carbon black is about 300-500Kg/㎡.
6. Tinting strength
The tinting strength of carbon black is a measure of the ability of carbon black to dye black and white raw materials. Generally, rubber carbon black does not have high requirements for this index, and this index is more important in pigment carbon black.
7.300% modulus stress
The modulus stress essentially reflects the ability of the vulcanized rubber network structure to resist deformation under external force. The modulus stress at 300% stretch is often used as a measure of the reinforcing properties of vulcanizates. The modulus stress is greatly affected by the structure of carbon black, and the modulus stress increases with the increase of the structure. In addition, the modulus stress has a certain relationship with the specific surface area and surface activity of carbon black. The higher the 300% modulus stress and the smaller the elongation at break, the better the toughness of the compound.
8.45μm, 150μm, 500μm sieve residue content:
The impurity of carbon black is generally determined by different specifications of the sample sieve. The residual part that cannot pass through 35 mesh (500um sieve diameter) is called 35 mesh sieve residue, and the residue that cannot pass 325 mesh (45um sieve diameter) is called 325 mesh sieve residue. These three indicators are very important for thermal cracking carbon black, especially the value of the 45μm sieve residue content, which directly affects the brightness of the appearance of the finished product and subsequent processing. The lower the content of 45μm sieve residue, the brighter the product and the more beautiful the appearance. The fierce competition in the market now makes everyone pursue excellence in the internal and external quality of high-end products, so the extremely low 45μm sieve residue content can attract the attention of buyers.
9. pH value
The PH value reflects the acidity and alkalinity of the carbon black surface, and the PH value is one of the factors affecting the scorch time (T35) of the rubber compound. The lower the PH value, the longer the T35. In fact, the scorch time is positively related to the self-vulcanization time of the semi-finished rubber material. If the T35 is shorter, the rubber material will be self-vulcanized before it is transferred to the finished product processing, and the rubber material will become difficult to process. This is what we do not want to happen. and if the T35 is longer, it will take a while for the rubber to start vulcanizing after it is transferred to the finished product, which wastes time and energy, which we don't want to happen, so T35 is more acceptable in the actual production process In about 10 minutes.
10. Ash content:
The ash content of carbon black can be defined as the amount that remains after burning in a high temperature furnace. The ash in carbon black is mainly derived from inorganic substances and dissolved inorganic salts in raw oil and process water (quick cooling, wet granulation). Usually the ash content of carbon black is less than 0.5%, which will not affect the application of carbon black.
11. Fine powder content
Granular carbon black also contains a small amount of ungranulated or broken carbon black powder, which is called fine powder content. The less fine powder content, the better, and it is usually not expected to exceed a few percent.
12. Acetone extract
The index of acetone extract reflects the complete degree of conversion of carbon black production (organic polymers remaining on the surface of carbon black that are not completely cracked during carbon black production). Carbon black is produced from raw materials such as ethylene tar, coal tar, and natural gas through different processing processes. There must be some residual raw materials mixed in the generated carbon black, and the size of the acetone extract reflects the amount of residue. However, many rubber carbon black manufacturers do not provide this indicator.
Significance of three physical indicators of carbon black for rubber
The three physical indicators of rubber carbon black mainly refer to tensile strength MPa, elongation at break %, and 300% modulus stress MPa. The significance of these three carbon black physical indicators lies in the corresponding physical properties of the produced rubber products. Of course, different rubber products have different requirements for such indicators.