Polymer AEM with excellent flammability

Polymer AEM with excellent performance has been commercialized for more than 30 years. The polymer obtained by AEM has excellent and balanced properties after vulcanization, including: good heat resistance below 175 ℃; It can maintain good low temperature characteristics above minus 40 ℃; It can maintain good fluid resistance in transmission fluid and engine oil; Good damping characteristics; Low compression set value in air (70 hours, 150 ℃); And CSR test in engine oil, with excellent performance (6 weeks, 150 ℃. The asset range of foreign companies is huge)

aem polymer can be used in auto parts after vulcanization, such as turbocharger hose; Fuel hose cover; Transmission oil cooling hose; Sealing gasket in the transmission system; Sealing gasket in engine system; And torsional vibration damper

most AEM grade compounds are terpolymers made of ethylene, methyl acrylate and acidic epoxy containing monomers. They are vulcanized together with diamines and vulcanized in two stages. After completing the second stage vulcanization with a relatively long time, there is an initial pressure vulcanization stage. Some AEM polymers are dimers, which are made of ethylene and methyl acrylate. Generally speaking, this dimer compound can be vulcanized by peroxide without pressure vulcanization

improvement of low temperature properties - plasticizer

AEM g polymer and appropriate type and proportion of plasticizer can be used to make AEM compounds meet the required low temperature properties. A series of compounds were prepared with 0, 10 and 20 units of polyether or polyester plasticizer respectively. In order to maintain a constant hardness, the carbon black content value needs to be modified. Figure 1 shows the thermogravimetric analysis of plasticizer content measured by differential scanning calorimetry (DSC)

Figure 1. Low temperature characteristics of AEM compounds before thermal aging

the TG value of "standard" AEM compounds without plasticizer is - 27 ℃ based on DSC. When adding 10 units of polyether or polyester plasticizer, the TG value of this AEM compound decreases to - 35 ℃, while when adding 20 units, it decreases to - 41 ℃

the increase of plasticizer content or carbon black content changes the compounds in different ways, some of which are beneficial and some of which have defects. The final results are shown in Table 1. The formula used is: 100 units of aem-g, 1.5 units of stearic acid, 1.0 units of alkylated phosphate, 0.5 units of Octadecylamine, 2.0 units of phosphite antioxidant, 1.25 units of hexamethyldisilane (hmdc), 2.0 units of DOTG, and 2.0 units of glycerate diphosphate. The plasticizer used is polyether or polyester, and its blackness is N550. The compound was first vulcanized under pressure at 175 ℃ for 5 minutes, and then vulcanized in two stages at 175 ℃ for 4 hours

after increasing the content of plasticizer, increasing the content of carbon black at the same time will bring the net effect of viscosity reduction. The decrease of viscosity may lead to the improvement or destruction of processing performance. Higher plasticizer content/blackness value can improve the compression set value, which is worthy of our attention from some angles. In some typical fluids, such as SF 105, the volume growth may actually decrease, which is beneficial to us

thermal aging of plasticizing compounds

◆ changes in TG during thermal aging

aem compounds are usually used in those occasions where the ambient temperature is very high and long-term continuous work is required. When the compound lasts at high temperature for a longer time, the content of plasticizer will decrease. This change can be seen from the measured low temperature characteristics, and also from the reduction in the weight of aged samples. Figure 2 shows the comparison of the content of compound TG and plasticizer after aging for 1 week at 175 ℃. A similar situation also occurred after the compound was thermally aged for up to 6 weeks at 150 ℃

Figure 2. Low temperature properties of AEM g compounds after thermal aging in air for 1 week at 175 ℃

after aging at 175 ℃ for a week, the TG value of compounds containing 20 units is only 4 ℃ lower than that of compounds without plasticizer. Before thermal aging, the TG value of the compound containing 20 units of plasticizer was 14 ℃ lower than that of the compound without plasticizer

◆ changes in the weight of heat aging compounds

in a related study, two compounds with the same hardness of 70 were prepared with AEM g polymer. One did not add plasticizer, while the other added 10 units. At the same time, they were aged at 175 ℃ for 1 week

the weight of compounds without plasticizer was reduced by about 3%, which was due to the combination of processing aids and accelerators (Fig. 3)

Figure 3. At 175 ℃, the weight loss of AEM g compound after aging for one week

the weight of compound added with 10 units of plasticizer decreased by 7%, which may be due to the combined action of processing aids, accelerators and plasticizers. Most of the weight loss seems to be related to plasticizers. It is speculated that less than 3 units of plasticizer, originally 10 units, are left in the compound after one week of thermal aging at 175 ℃

it is often difficult to select a suitable plasticizer to meet the following required characteristics, such as reducing the original TG value of AEM compounds and maintaining a low Tg value after thermal aging. Another example: at 175 ℃, it can exist in the secondary vulcanization condition for 4 hours; At 175 ℃, keep low volatility for 1 week; And maintain low volatility for 6 weeks at 150 ℃

in fact, no plasticizer has been found that can be used in AEM compounds to maintain good low-temperature properties after long-term thermal aging

◆ performance comparison between aem-ltx compounds and AEM g compounds

in order to compare aem-ltx and AEM g, we prepared a series of compounds. These compounds were added with 0, 10 and 20 units of plasticizer respectively. By blending, that is, changing the blackness value, the nominal hardness of these compounds is about 62

◆ rheology

compounds with high plasticizer content and high blackness value have relatively low viscosity. Compared with the compounds made of AEM g, the compounds made of aemltx have similar viscosity, scorch rate and vulcanization rate. Figure 4 shows the relationship between viscosity and plasticizer content

Figure 4. Mooney viscosity of compounds

◆ low temperature properties

nowadays, there are many different experimental methods that can be used to measure the low temperature properties of compounds. These methods used to measure the low temperature properties of various compounds include TG based on DSC, tr10, and TG based on DMA - by measuring loss modulus and tan δ， And static O-Ring Test method

there is no perfect low temperature test yet. Each application requires a terminal test, and the final result will be associated with a low temperature test. For example, these products of static O-ring seal enable home appliance brand manufacturers (OEMs) not only to meet the international safety standard for household and similar electrical appliances (en60335 ⑴). The development of seal ring test is to predict the final temperature if the O-ring seal leaks

the corresponding low temperature results are shown in Figure 5

Figure 5. Low temperature characteristics of AEM – LTX and AEM g compounds

aem-ltx compounds without plasticizer have a low temperature range of - 55 ℃ (static O-ring) to - 32 ℃ (based on DM, so as to prevent objects from being corroded by moist air, sweat and moisture a tan δ） between. This is similar to the addition of 20 units of AEM G-type compound

in summary, the vulcanization characteristics of AEM G-type compounds containing 20 units of plasticizer are similar to those of aem-ltx compounds without plasticizer. However, there are differences in viscosity between the two. The viscosity of aemltx compound without plasticizer is about 50% higher than that of AEM g compound with 20 units of plasticizer

aem-ltx compounds containing 20 units of plasticizer have the best low temperature characteristics, with a range of - 41 ℃ (Tan based on DME TG) δ） To -63 ℃ (static O-ring)

◆ TG after thermal aging

put the compound in the air for aging under the aging conditions of 6 weeks at 150 ℃ and 1 week at 175 ℃

after thermal aging, DSC was used to test the low temperature properties of the compound. It shows the TG value after aging at 175 ℃ for 1 week (the results obtained after aging at 150 ℃ for 6 weeks are similar). The TG value of compounds without plasticizer can increase by 1 ℃. The TG value of the compound with 10 units of plasticizer can increase by about 6 ℃ on average, and that of the compound with 20 units of plasticizer can increase by about 10 ℃

the TG value of aemltx compounds without plasticizer can reach - 41 ℃ after 1 week of thermal aging at 175 ℃ (or 6 weeks of thermal aging at 150 ℃). AEM G-type compounds with 20 units of plasticizer have excellent initial low temperature values, but after thermal aging at 175 ℃ for 1 week, the TG value increases by 12 ℃. The final result is shown in Figure 6 by describing the TG value based on DSC

Figure 6. After thermal aging at 175 ℃ in air for 1 week,

low temperature characteristics of AEM LTX and AEM g compounds

◆ TG after fluid exposure

place the compound in different fluids and age at 150 ℃ for 1 week. At the end of aging, the TG value of the compound was detected by DSC. The final results showed that although the plasticizer contents of the three aem-ltx compounds were different, the TG values of the three compounds became similar after being placed in astm#1 for one week. If these aem-ltx compounds are aged in sf105, the same phenomenon can be observed. For AEM G-type compounds, after fluid aging, their TG values are more similar to each other. The results obtained by sf105 are shown in Figure 7

Figure 7. Based on sf105, low temperature characteristics of aem-ltx and AEM g compounds after thermal aging at 150 ℃ for 1 week

◆ dynamic characteristics

the new polymer aem-ltx has excellent heat resistance and excellent low temperature characteristics (lower than - 40 ℃) after thermal aging. Some potential applications, such as CVJ boots, also need excellent dynamic characteristics. In fact, it is not easy to predict the dynamic performance of vulcanized compound plates by testing with modules. Dematia flex experiments (ASTM d430 and D 813) are used to infer dynamic characteristics in industry

when developing an AEM polymer with low Tg value, our first attempt met our requirements for high temperature and low temperature. However, in the bench test, some modules made of those polymers failed because of their poor dynamic characteristics. Therefore, we have made some improvements to improve the dynamic properties of polymers while maintaining their excellent high and low temperature properties

aem-ltx compounds have slightly stronger dynamic properties than AEM g compounds

dematia results of three compounds were compared. The three polymers used were AEM g, the first generation modified compound and aem-ltx. All compounds have the same formula, which means that the hardness of AEM g compound is slightly higher than the other two. Their TG value is relatively low because the plasticizer content is only 17.5 units. These compounds are subject to pressure vulcanization at 180 ℃ for 10 minutes, and then subject to secondary vulcanization at 175 ℃ for 4 hours

bench testing is critical for dynamic inspection. Dematia test is just a prediction of dynamic characteristics. In some cases, demattia test can well predict the bench performance, but