Inorganic particle-filled composite materials are increasingly used in construction, automotive, electronics and other fields. However, these hydrophilic inorganic particles generally have high surface energy, poor compatibility with non-polar resins, difficult to uniformly disperse when the filling amount is high, and weak interaction with the matrix, which usually leads to system processing fluidity and poor performance. Mechanical properties, especially impact strength, drop sharply [1,2]. However, the use of filler surface treatment agents with excellent performance can realize the simultaneous reinforcement and toughening of inorganic particles, which has become an effective modification method for high performance of general plastics [3]. At the same time, as a material generally needs to be used under exposure conditions for a long time, the aging resistance is very important, and there are few systematic research reports in this regard. In this study, self-prepared coupling agents based on rare earth organic complexes were used to study the aging properties, mechanical and flow properties of three typical and practical systems. For example: PP/CaCO3 is a more commonly used filling and toughening system, PP/Mg(OH)2 is a typical halogen-free flame retardant system, and ABS/BaSO4 is a composite material with good surface properties. This work has certain guiding significance for the application of inorganic particle-filled composite materials.
1 Experimental part
1.1 Raw material polypropylene (PP): product of Guangzhou Petrochemical General Plant, brand F401, melt flow rate 2.5g/10min, density 0.91g/cm3; CaCO3: product of Guangzhou Huangpu Tiantai Co., Ltd., 400 mesh; BaSO4: Guangxi precipitated sulfuric acid Barium factory product, 400 mesh; Mg(OH)2: Zhejiang chemical factory product, particle size 1000 mesh; rare earth coupling agent REC: a mixture of rare earth metal organic complexes, self-made.
1.2 Surface treatment of fillers Various fillers dried at 120°C for 10h, add rare earth coupling agent REC in a high-speed mixer, and stir at a high speed at 60°C for 10min. The filler without REC also undergoes the same drying and stirring process.
1.3 Compound sample preparation and performance test The base resin was plasticized on a two-roll open mill (XKR-160A, Zhanjiang Machinery Factory), then added with fillers, mixed evenly, and then unloaded, and placed in a flat vulcanizer (QLB-D, Huzhou). Rubber Machinery Factory) pressed into 1mm, 4mm thick sheets, of which the 1mm thick sheet was punched into a specified spline according to GB1040-83, and the breaking strength was measured by DXLL-2500 electronic tension meter (Shanghai Chemical Machinery No. GB1043-83 was mechanically cut into Izod notched impact strips, and the impact properties were measured with a WPM impact tester (Germany). Determination of GB3682-83; photo-oxidative aging performance is evaluated by natural exposure aging test according to GB3631-83. Tensile specimens are used to measure the retention rate of breaking strength at different aging times (the ratio of the breaking strength of samples with different aging times to the initial value). The thermo-oxidative aging performance was carried out in a 120 ℃ thermo-oxidative aging box according to GB7141-86, and the change of carbonyl absorption peak was measured by RFX-65AFTIR infrared spectrometer (USA). For the PP system, the carbonyl index (CI) was calculated according to the following formula [4] ]: CI=1713cm-1 absorption strength 1465cm-1 absorption strength where 1713cm-1 corresponds to the stretching vibration of C=0, 1465cm-1 corresponds to the deformation vibration of -C-H on the polypropylene carbon chain, CI represents The relative content of carbonyl can characterize the aging degree of the material. For the ABS system, the aging process is mainly caused by the easy oxidative degradation of the double-chain contained in butadiene, so the thermal-oxidative aging degree uses the change of the double-chain absorption peak intensity at 970cm-1, 1635cm-1, etc., that is, the absorption intensity after aging. It is characterized by the ratio of the initial intensity of the peak [5].
2 Results and discussion
2.1 Mechanical properties and flow properties Table 1, Table 2 and Table 3 list the mechanical properties and melt flow rate (MFR) of PP/CaCO3 system, PP/Mg(OH)2 system and ABS/BaSO4 system with different components, respectively. ), in which the oxygen index (OI) of the PP/Mg(OH)2 system with different components is also listed in Table 2.
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It can be seen that after the untreated filler is added, the mechanical properties and fluidity of the system deteriorate sharply with the increase of the addition amount. The notched impact strength of the filled system treated with REC is significantly higher than that of the untreated system, especially the PP composite system. Toughening of inorganic particles. At the same time, in the case of high filling, the yield strength does not decrease significantly, and the fluidity also increases greatly. For the PP/Mg(OH)2 system, REC treatment has no obvious adverse effect on the flame retardant properties. It can be seen that REC is an ideal modifier in terms of mechanical properties and processing properties.
2.2 Aging performance
2.2.1 PP/Mg(OH)2 system and PP/CaCO3 system The ratio of time breaking strength to initial breaking strength (ie, breaking strength retention rate) varies with aging time. It can be seen that with the prolongation of aging time, the fracture strength of the system decreases. Compared with pure PP, the strength of the system containing Mg(OH)2 decreases faster. After being exposed to the atmosphere for 150 days, the fracture strength retention rate of the former can reach 56%, while the latter is only 23%, Mg(OH)2 accelerates the photo-oxidation process of the material and makes the photo-oxidative aging resistance of the system worse. Compared with the untreated Mg(OH)2, the photo-oxidative aging resistance of the system treated with REC has a tendency of further deterioration, but this trend is not obvious and does not affect its application in this system.
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Table 4 lists the carbonyl index CI of each system after thermal-oxidative aging for 350h. The greater the value of CI, the higher the degree of aging. It can be seen from the table that the thermal oxygen aging performance of the system is completely different from that of photo-oxidative aging: compared with pure PP, the thermal oxygen aging performance of the system containing Mg(OH)2 is improved, that is, the resistance to PP is improved. The thermal oxidation process has a retarding effect; the thermal oxidation aging performance of the system treated with REC has no obvious change, indicating that it has no obvious effect on the thermal oxidation process; the situation of the PP/CaCO3 system is basically the same as that of the PP/Mg(OH)2 system. .
2.2.2 Aging properties of ABS/BaSO4 system Figure 2 is the curve of the fracture yield strength of ABS/BaSO4 system filled with 0, 10% and 30% (weight) respectively in the natural aging process as a function of aging time, it can be seen that , After adding BaSO4, compared with pure PP, the natural aging resistance of the system is improved. Figure 3 shows the change of the fracture strength retention rate during the aging process with the aging time of the untreated BaSO4, the BaSO4 filled system treated by REC and the titanate coupling agent during the natural exposure process. It can be seen that after adding various surface treatment agents, the photo-oxidative aging resistance of the system is deteriorated, but in terms of the degree of deterioration, the REC is slightly lower than that of the titanate coupling agent.
The aging process of ABS is mainly caused by the easy oxidative degradation of the double bonds contained in butadiene [5]. The absorption peak intensities at 970cm-1 and 1635cm-1 changed significantly. The ratio of the absorption intensity after aging to the initial absorption intensity of the sample is listed in Table 5. As can be seen from the table, it is proved that BaSO4 can improve the anti-thermal oxidation aging process of ABS. REC has no obvious change in the thermal oxidation aging performance of the system, while the thermal oxidation resistance of the system is obviously deteriorated by the titanate coupling agent treatment.
3 Conclusions (1) The coupling agent REC has a good modification effect on these fillers, such as the mechanical properties are significantly improved, and the fluidity is significantly improved. (2) The addition of CaCO3 and Mg(OH)2 can accelerate the photo-oxidative aging process of PP, and have no obvious retardation on the thermal-oxidative aging process; while BaSO4 has an effect on the photo-oxidative and thermal-oxidative aging process of ABS system. All have blocking effect. (3) The photo-oxidative aging process of the new coupling agent REC, PP and ABS system has a slight promotion effect, but has no obvious effect on the thermal-oxidative aging process, and the aging performance is better than that of the titanate coupling agent.
