Research on Cell Structure of NBR and PVC Blend Foaming Materials in Modern Plastics Processing Cao Pei Liu Li + Liu Guangyu (Engineering Research Center of High Performance Polymers and Molding Technology of Qingdao University of Science and Technology, Qingdao, Shandong 266042). The results show that when the effective vulcanization system is adopted, the cell has a uniform cell distribution and a high closed cell ratio; when the NBR/PVC mass ratio is 50/50, the foamed product has a high closed cell ratio, a large cell, and a relatively low cost. Low; compression vulcanization foaming is compared with free foaming, and compression foaming is more conducive to the production of lower density articles; when molding foaming, the density of the foamed articles decreases as the amount of blowing agent increases.
Although the nitrile rubber (NBR) foamed article has good elasticity, its shrinkage rate is large. Insulation materials on the market mostly use NBR and polyvinyl chloride (PVC) blend materials as the matrix of the foaming material, because NBR has good compatibility with PVC. With the blend as the matrix of the foamed material, the corresponding article can have the elasticity of the rubber foamed article and the good stiffness of the plastic foamed article and a small shrinkage ratio.
1 test part 1.1 raw materials NBR, 2907, PetroChina Lanzhou Petrochemical Company; foaming agent AC, Weifang Yaxing Co., Ltd.; foaming agent H, Jiangsu Taicang Xinxin Auxiliary Factory; dioctyl phthalate (DOP) ), Zibo Plasticizer Factory; PVC, S1000, Qilu Petrochemical Company Chlor-alkali Plant; Ca/Zn Heat Stabilizer, Sulfur (S), Zinc Oxide (ZnO), Stearic Acid (SA), Zinc Stearate Sale; accelerator 2-thiol benzothiazole (M), tetramethylthiuram disulfide (TT or TMTD), N-cyclohexyl-2-benzothiazole sulfenamide (CZ or CBS), N - tert-Butyl-2-benzothiazole sulfenamide (TBBS), all commercially available; Alkaline 4010NA, RD, commercially available.
1.2 Sample preparation 5 parts, 2 parts of stearic acid, 3 parts of antioxidant, 20 parts of carbon black, 20 parts of calcium carbonate, 10 parts of DOP, 5 parts of heat stabilizer, vulcanization system variables, foaming system variables.
Mixing process: After the MBR three-stage mastication, the foaming agent, anti-aging agent, filler, carbon black, activator, accelerator, softener, vulcanization system, etc. are added in sequence, and the mixture is thinned several times. When mixing 24h.NBR and PVC, first mastic PVC, then add plastic NBR, and finally add human foaming agent, anti-aging agent, filler, carbon black, activator, accelerator, softener, vulcanization The system is evenly mixed. After a few passes, the lower piece is parked for 24 hours. The vulcanization foaming process: the rubber compound is re-refined during the molding foaming, and a certain amount of rubber is weighed and preheated after the film is placed. In the mold, pressurization and heat vulcanization are performed on the flat vulcanizing machine, and the foam is ejected from the mold after the pressure is removed; the vulcanization-foaming condition is 170/180 ° C, 79 MPa, 10 min. at a certain temperature during free foaming. Heat radiation vulcanization in the oven for a certain period of time; sulfur 1.3 instrument SK-160B double roll mill, Shanghai Rubber Machinery Factory; PLE-331 internal mixer, Kechuang Rubber & Plastic Machinery Co., Ltd.; QLfr3 503502 flat vulcanizing machine, Jinan test Machine factory; EK-2000P vulcanization foaming machine, Youken Industrial Co., Ltd.; electric heating Dry box, DHG202 type, Shandong Weifang Medical Instrument Factory; SM-6700F field emission scanning electron microscope (SEM), Japan Electronics Corporation.
1.4 Test method 6343-2009 determination; SEM observation of the cell structure.
2 Results and discussion 2.1 Vulcanization system The selection of vulcanization system in the preparation of sponge rubber is extremely important, which directly determines whether the foaming process can proceed smoothly. 2. In this test, first fix the amount of foaming agent, and change the type of vulcanization system. To study the matching relationship between vulcanization system and foaming system foaming speed. Three vulcanization systems, namely a common vulcanization system, a semi-effective and an effective vulcanization system, are employed. The basic formula is used, the foaming agent AC is used as the main foaming agent, and ZnO is used as the auxiliary foaming agent, and the amount thereof is fixed. The test results are shown in Table 1. The NBR vulcanization curve and the thermal weight loss curve of the foaming agent. The difference between the three vulcanization systems can be clearly seen. The polysulfide ordinary vulcanization system has a short scorch period, which is favorable for foaming; the semi-effective vulcanization system has a long scorch period, which is not conducive to the formation of bubbles, cannot prevent the bubbles from approaching each other, forms open pores and stringhole structures, and is vulcanized. The efficiency is low; the effective vulcanization system integrates the advantages of both, shorter scorch time, higher vulcanization efficiency, and therefore better cell structure and uniform distribution. The cell structure is as shown, and the result just verifies the conclusion.
Table 1 NBR foaming test formula No. sulfur / mass part accelerator / mass part vulcanization system ordinary semi-effective effective is 1.0 part CZ and 1.0 part TT composite accelerator, the same below.
NBR vulcanization and foaming agent weight loss analysis 1 - foaming agent; a common vulcanization system; 3 - effective vulcanization system; half of the effective vulcanization system according to the test basic formula, signed in the effective vulcanization system vulcanization speed is fast, so the use of semi-effective vulcanization system, The amount of blowing agent is constant.
The SEM photograph of the foamed product, and the comparison, it can be clearly seen that the addition of PVC has a great influence on the cell structure. The cell diameter is obviously larger, and the opening structure is more. When the PVC is 30 parts, the cells are relatively uniform and the cell size is small; when the PVC is 40 parts, the foaming effect is not very good, the cell distribution is uneven, and the cell size difference is large; when the PVC is 50 parts, except NBR In addition to the reason for the phase structure of PVC, the diameter of the cells of the other materials is larger on average, so the article has a lower density. However, the wall of the hole is thin and the structure of the opening is large, so that the external force that can be withstood becomes small. Comparing the density data in Table 2, it is found that the two are consistent. It can be concluded that the NBR/PVC mass ratio can be selected to be 50/50 when higher mechanical properties are not required, which can significantly reduce the cost.
The SEM analysis of different PVC proportioning products is the mass ratio of NBR/PVC, the same as below.
Table 2: Different mass ratio NBR/PVC foaming sample density No. mass ratio 170C free foaming density / (g 2.3 foaming agent dosage fixed vulcanization system and D0P dosage, NBR / PVC mass ratio is 50/50, inspection change The effect of the amount of blowing agent on the density and cell structure of the foamed product.
Table 3 NBR / PVC foaming test formula dosage / mass parts density 1; 7 density 2) / 1) 170C free foaming density; 2) 170C molded foaming density.
It can be seen from Table 3 that, with the increase of the amount of the foaming agent, the molded foaming density exhibits an expected decreasing tendency. When the amount of the foaming agent is 18 parts, the density is up to 0.045 g/cm3, and the density of the foamed product is the smallest. . SEM photographs of NBR/PVC foaming materials for different blowing agent dosages. It can be seen that the bubble appears as a deformed circular or elliptical shape with a complete bubble wall, indicating that the prepared rubber foaming material is mainly a closed cell structure, which is obviously different from the difference between the two formulations. The plasticizer is added, so the effect of plasticizer is also obvious, and it is not discussed for data reasons. It can be seen that with the increase of the amount of foaming agent, the number and diameter of the cells in the foaming material increase, the wall of the bubble becomes thinner, and the pressure inside the pores becomes larger. Therefore, when the sample is prepared by scissors, the bubble is blasted and the wall wall is self-supporting. Poor.
SEM analysis of different foaming agent content products In the free foaming process, the density of the foamed product did not decrease with the increase of the amount of the foaming agent, and on the contrary, it showed an upward trend. Therefore, if the density of free-foamed articles is to be reduced, the vulcanization system should be further adjusted.
3 Conclusions It can be seen from the comparison of the three vulcanization systems that the foamed product has better cell structure when the effective vulcanization system is used, and the cell distribution is high and the cell closed rate is high.
The bubble diameter of the foam product is larger, the density is the smallest, and the cell structure is better.
Compared with free foaming, molded foaming is more conducive to making lower density products. This is because the vulcanization rate is much lower than the foaming speed, and the molding foaming can provide an external pressure, which has a certain binding effect on the gas decomposed by the foaming agent. At the time of compression foaming, the density of the foamed article decreases as the amount of the foaming agent increases.
(Finish)
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