Carbon black in rubber Determination

Carbon black rubber industry is an indispensable raw materials, second only to the amount of rubber, is one of the most effective and widely used in reinforcing agent. Black vulcanized rubber to improve performance, increase the hardness of rubber, modulus, fracture energy, tensile strength, tear, fatigue and wear resistant properties. Carbon Black additional role of a big to be effective to reduce the cost of rubber, especially in the use of silicone rubber, acrylic rubber and fluorine rubber, rubber products in the special. The latter, the amount of carbon black, the better, but not an excessive amount of carbon black increased, reinforcing effect, but the impact of the products finish and tensile properties to increase the difficulty of processing products, so a reasonable amount of carbon black The rubber industry is the research topic. How accurate determination of the content of carbon black products in it? In this paper, rubber products, introduced in the determination of the content of carbon black.

Carbon black rubber in the determination of the basic principles of solvent extraction by small organic molecules, or break through the degradation of rubber polymer removal by thermal oxidation of inorganic compounds and carbon black separation. There are currently nitric acid oxidation, high temperature tube furnace pyrolysis, thermal analysis method, microwave cracking and degradation metathesis method. The main difference between the ways on how to break down or degradation of polymer in the process. Removal of small molecules and inorganic compounds isolated in this two basic types. The difference is that different rubber require different operating conditions, such as extraction time, extraction solvent used in the selection, rinse the remnants of solvent and temperature, and so on. Both see the process of GB 7766-87 standard and GB 3515-83. The following highlights the different ways in or degradation of polymer decomposition process.

First, the determination of carbon black

1. Nitric acid oxidation

The basic principle: the heat concentrated nitric oxide by solvent extraction over the sample, and then isolated from inorganic compounds such as carbon black and insoluble materials, with a particular solvent until clear liquid rinse-insoluble transparent, dry weight after the end Insoluble-burning, burning, after the loss of quality is the quality of carbon black. The methods belong to the classical method has become the national standard GB7766-87, it mainly applies to double bond with the type of unsaturated butadiene rubber; saturation of the rubber needs to be done accordingly change, or nitric acid oxidation degradation of polymer can not. In addition to the methods of post-oxidation degradation products were part of the low molecular weight, and thus carbon black residue, such as the separation more difficult, rubber specific needs of specific procedures for washing and cleaning solvents, or more errors. In addition to test a long time.

2. High-temperature tube furnace pyrolysis

The basic principles: First of all, with a corresponding number of solvent extraction-hour sample, and then drying, said replay burning boat people, and then under nitrogen in the polymer pyrolysis, cooling out after weighing combustion boat, and then in the air in the combustion removal Carbon black, and then weighing, the quality of the content of carbon black is lost. The methods belong to the classical method has been included as the national standard GB3515-83, refer to the specific operating standards. It is suitable for a variety of saturated and unsaturated vulcanized rubber, but because of its heat through and remove the polymer solution, so as acrylonitrile-butadiene rubber and neoprene pyrolysis produce carbon-containing residue of rubber is not suitable to use this method, It requires the same rubber products do not contain the pyrolysis will have a residual points with the agent. Thermal decomposition method to avoid the choice of solvent washing and tedious process of cleaning, nitric acid oxidation time.

3. TG analysis

The basic principles: to learn that after the solvent extraction of the sample put in a number of TG within the micro-scale heat, then the sample containing polymers, carbon black and inorganic compounds. To do with nitrogen carrier gas, nitrogen gas to control temperature and flow rate of speed, after warming up to a certain temperature (configured with the temperature about the type of rubber), the polymer temperature until no longer weight loss, this time for the residue of carbon black and inorganic compounds . And then switch for the air carrier gas, so that the occurrence of black oxide and volatile until the samples are no longer weight loss, this time the only remnants of inorganic compounds.

This method has the advantage of the largest weight loss, automatically recorded by the apparatus and draw weight loss curve, according to the weight loss curves can be calculated polymer, inorganic compounds and carbon content. Therefore, the method is less sample (only a few dozen mg), and precision time-saving advantages. However, TGA expensive, and operators need to have experience, be able to identify skilled TG curve at different stages of the starting point. Its scope of application of the tube with high-temperature furnace pyrolysis.

4. Microwave cracking method

Similar to the basic principles of weight loss analyzer, the main difference is the thermal decomposition of the energy needed by the occurrence of microwave devices, first, because of microwave heat quickly, reduce test time; Second, the results close to the classic method. J K Sekinger introduced a law cracking microwave test the content of carbon black in the SBR method does not require the use of inert gases do not have to vacuum, cracking only 7min, and TG also need to test lh. Sekinger studied temperature cracking, splitting time, the content of styrene and carbon black surface area and other factors, the experiments show that the method for styrene with different content, filled with oil content of carbon black and styrene butadiene rubber.

5. Metathesis degradation

That take 100 ~ 200mg by the solvent extraction after the samples kept in centrifuge tubes, and then adding a certain concentration of (CH) Sn and WCIJ6 degradation as a catalyst for the solution, while adding appropriate amount of n-decene, the aim is to dilute the reaction system, to accelerate the degradation reaction Speed, reducing adsorption in the small molecule on the surface of carbon black. Canada finished reactants, sealed glass tube, after a certain number of hours after the reaction by adding ethanol to terminate reaction, ethanol can also dilute the reaction system, carbon black in favor of the centrifugal settlement. The centrifuge tube release centrifuges, high-speed centrifuge settlement of carbon black, used solvents to clean completely colorless clear liquid, with the final concentration of ammonia and ethanol mixed cleaning solution residue, a catalyst to remove the residual elements, then residues Mainly carbon and inorganic compounds. Separation of inorganic compounds and other similar methods. The method is suitable for carbon-carbon double bonds of fatty type of rubber, cross-linked to the degree of impact test results. F Stelzer and others use this method to test butadiene rubber content of carbon black, and electron microscopy, analysis of the surface area of carbon black, that the method does not damage the structure of carbon black. However, the determination of the existence of methods for a long time and too much trouble to clean shortcomings.

Second, the analysis of the factors

Different methods of decomposition or degradation mechanism is different, different test conditions, so there are different ways to different factors. In this paper, but only to introduce a number of common factors. First, the measured concentration of carbon black, to understand the main rubber composition and structure of the different needs of different rubber polymer degradation methods and operating conditions, nitric acid oxidation degradation can not butyl rubber, ethylene-propylene rubber and neoprene, The high-temperature tube furnace heat is not suitable solution NBR. Second, to understand the rubber vulcanization system. Yu Songlin pointed out that the sulfur vulcanization of rubber, of which 30% of the sulfur and carbon black, therefore, measured in carbon content, the need for a Ceco-Sc-Bl2-determination of sulfur in the carbon content of sulfur, carbon black to improve The accuracy of the determination. F Stelzer using metathesis method degradation of butadiene rubber content of carbon black, sulfur and peroxide vulcanization of rubber curing systems used by large differences in operating conditions. The former degradation need to be 5 ~ 10h, which needs 16 ~ 20h. According to the curing system should determine the different operating conditions. Thirdly, there must be a preliminary analysis of the samples contained in plastic inorganic compounds, which affect the analysis of the results of a variety of factors, which can be used X-ray diffraction analysis and other methods, such as Waddell, such as using PA-FTIR Analysis of PIXE and rubber composition and Inorganic compounds.