China's black talc is rich in resources. In the era of increasingly scarce white talc resources, it is necessary to study the characteristics of black talc and its application in modified plastics. The preliminary trial results show that in the field where whiteness is not required, the effect of black talc is remarkable, and the application prospect is good.
1 The resource situation, characteristics of black talc in China and the necessity of its application in modified plastics
The talc ore is divided into white, green, pink, gray and black. The color depends mainly on the type of other ingredients that are symbiotic with talc. When a certain amount of organic matter is contained, the talc ore is gray or black.
Talc is an important industrial raw material. China is a major talc resource in the world and a major consumer and exporter. White talc has been developed and widely used because of its good appearance, high purity of talc and perfect sheet structure. The talc in Liaoning Haicheng, Shandong Qixia, Guangxi Longsheng and other places is especially famous, and is exported to Europe, America, Japan and other countries. Due to long-term high intensity and over-exploitation, the resources of superior talc have been relatively scarce and prices have been rising. The price of the superior talc ore (white talc mine) in Haicheng, Liaoning has reached more than 1,000 yuan / ton, and the ground powder has reached several thousand yuan / ton.
Black talc
Talc is one of the important raw materials for important modified plastics. The unique flaky (layered) structure of talc powder significantly increases the rigidity of the filled plastic, ie the bending strength and modulus are significantly higher than the unfilled base, and the heat distortion temperature of the filled modified plastic is obvious. Improvement, which is feasible for the processing and manufacturing of plastic materials and products requiring high rigidity (such as automobile bumpers, industrial parts such as washing machine casings, and plastic pipes with high ring rigidity), and so far, in addition to higher-priced mica There are no other mineral materials that are more cost-effective to replace.
The biggest impact of the rising price of white talc with good color and high purity is the increase in the cost of modified plastic raw materials. This is indispensable for the plastic products with high color appearance, but it does not require color or requirements. Plastic products, such as automobile bumpers, double-wall corrugated pipes and other plastic products, as long as the layered structure is good, the effect of increasing the rigidity is significant, other colors of talc can also be used reasonably and effectively. This is not only the modified raw material that makes the plastics processing industry cost-effective, but also the best use of the colored talc resources that were not valued or even abandoned, and made a great contribution to society!
2 Basic characteristics of black talc
The mineral composition of the main black talc reservoirs and black talc in China is shown in Table 1.
Table 1 China's main black talc reservoir and black talc mineral composition (by oxide) (%)
Origin SiO2al2O3Fe2O3TiO2CaOMgOK2ONa2OLOI Jiangxi Guangfeng 55.840.340.13
4.3427.86
11.14 Hunan Cathouse 61.592.881.570.101.8323.370.280.127.37Jiangxi Jiujiang 61.565.862.580.192.3217.160.570.148.89 Sichuan Fengdu 61.522.131.06
2.8922.80
9.58 Guangdong Pingyuan 53.100.490.480.077.1827.170.020.1210.92 Guangxi Luchuan 57.561.030.42
1.1828.21
10.86
The proven reserves of black talc in China are 600-800 million tons. The main minerals are talc, quartz, calcite, sepiolite, etc. Although the mineral composition of black talc varies significantly from the mineral composition, they are Similar to white talc, it appears black, mainly containing 3~5% carbon, which can be burned out when calcined at high temperature.
The origin and mineral composition (in terms of oxides) of several conventional white talc used are shown in Table 2.
Table 2 Four white talc origins and mineral composition (based on oxides)
SiO2MgOTiO2al2O3Fe2O3CaONa2OK2OLOI Shanxi 157.9032.950.030.960.181.180.250.016.84 Shanxi 252.9232.590.110.440.260.110.780.7211.48 Shandong 61.4431.31/0.500.101.300.010.015.52 Haicheng 61.3731.00.030.170.060.220.040.095.44
Black talc can be converted into ore with high whiteness by high temperature calcination. Jiangxi Guangfeng's black talc calcination temperature is about 1250 °C. At 1200 °C, the ore is instantly whitened, its density is about 2.7g/cm3, and many bright crystals can be seen on the surface under strong light, mainly CaO. reason. The whiteness after grinding can reach more than 93%.
3 Application status of black talc and its application in plastics
At present, the black talc ore is mainly used as a general ceramic body, and can be used for high-grade ceramics such as polished tiles and glazes after calcination. As a filling material, it can be used in the fields of paint coating, paper making, textiles and the like. In plastics, due to the traditional concept of white talc as the standard, it is considered to be used after calcination to achieve higher whiteness, and the calcination cost is high, and the process equipment is complicated. The performance and efficacy of the talcum powder after calcination are not Can be systematically studied, so the application in modified plastics has not received the attention and input it deserves.
Under the arrangement and organization of the China Plastics Association's Modified Plastics Professional Committee, the experiment was carried out in the application of the black talc in the HDPE double-wall corrugation, which is more urgent and cost-effective. A gratifying research result.
3.1 Types and characteristics of talcum powder (see Table 3)
Table 3 Characteristics of different types of talc
Code color whiteness (%) particle size (μm) 325 mesh sieve residue (%) LOI with oxide to make mineral composition D50D98SiO2MgOCaOFe2O3al2O3H01 white 71.598.4732.770.077.1353.9326.721.220.972.13H02 pan green 74.449.9932.520.019.6940.3617.041.432.4930. 32H06 black 20.997.3440.960.3010.7654.1625.293.620.060.13H08 gray 46.3310.4249.360.0511.4236.8023.961.912.1720.95
3.2 Test procedure
3.2.1 talcum powder masterbatch and pipe production, performance test
The amount of the surface treatment agent used for the four kinds of talc powders was the same, the amount of the auxiliary agent of the master batch was slightly different, and the amount of the carrier resin was the same. The masterbatch production and bellows extrusion equipment are the same, and the process operating conditions are basically the same.
3.2.2 talc powder filled HDPE material performance test spline production and performance test
3.1 Test results (see Table 4, Table 5)
Table 4 Performance of talc-filled HDPE double-wall corrugated pipe
Pipe number Adding masterbatch melt flow rate (g/10min) (190°C, 5kg) Pipe weight (kg/m) Pipe ring stiffness (kN/m2) Species density (g/cm3) G01MH011.670.151.99.45G02MH021. 6221.11.98.67G06MH061.515.01.758.00G08MH081.503.01.78.00
The base material of the four-wall corrugated pipe made of four kinds of talc masterbatch is the new resin HDPE 2480, which has a ratio of 2:1 to the masterbatch.
Table 5 Physical and mechanical properties of talc-filled HDPE materials
Sample No. Masterbatch Type Filled HDPE Material Physical and Mechanical Properties Tensile Strength (MPa) Elongation at Break (%) Flexural Modulus (MPa) Impact Strength (kJ/m2) Vicat Softening Temperature (°C) No Gaps and Notches ZS01MH0124 .8263.590025.08.4123ZS02MH0222.7172.175025.08.3117ZS06MH0623.6972.190023.87.5116ZS08MH0822.4459.460024.27.5121
3.2 Discussion
(1) H01 talcum powder is the best talcum powder in the classical sense. The talc content is high (calculated as SiO2), and the sheet structure is remarkable. Therefore, the double-wall corrugated tube has the most significant effect of increasing the rigidity, which is also expected. . Although the meter weight of the pipe using this talcum powder is high, it means that the wall thickness is favorable for the ring stiffness, but it is 18% higher than the ring stiffness of the G06 and G08 pipes, and it is impossible to increase the wall thickness alone.
(2) H06 is a typical black talc. H08 is a tailings that are discarded by talc due to color depth. It is ground into powder without calcination. The stiffness of the double-wall corrugated pipe produced by it is 8kN/m2. Significant increase in stiffness.
(3) The double-wall corrugated pipe is produced by using the powder (H06, H08) ground by colored talc, and the processing fluidity is better than that of the H01 talc powder.
(4) From the physical and mechanical properties of HDPE materials filled with different kinds of masterbatch, the best talc powder (H01) filled with HDPE has the best mechanical properties, tensile strength, flexural modulus and impact strength. The highest, Vicat softening temperature is also relatively high, which is a good indication that the flaky structure of talc is advantageous for the rigidity of HDPE. At the same time, it should be noted that the performance of other kinds of mineral powder-filled HDPE materials is worse than H01, but overall the performance is also good, especially the black talc (H06) filled HDPE material has the same flexural modulus as H01. It shows that if the appearance color of the filling material is not high, the effect of increasing the black talc is remarkable. Compared with the data in Table 4, the modification results of the mechanical properties test results of the filler materials are consistent.
4 Outlook
The preliminary research results show that the black talc is directly calcined without being calcined, and has a significant effect of increasing the rigidity and good processing fluidity. Because of its relatively low price, it has a good performance and price ratio in the use of plastic materials and products that are not demanding color, and its promotion and application prospects are good. If it is due to the presence of free carbon (3~5%), it can contribute to the aging resistance of plastics (to be confirmed).
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