The hottest low temperature fluoroelastomer

2022-08-13
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Low temperature fluoroelastomer

recently, the automotive industry has gradually increased its requirements for rubber sealing materials. In fact, as early as 2004, the new environmental protection regulations formulated by the California Air Resources Commission and the environmental protection agency have come into force. These new regulations are called Lev II and Tier II respectively. They require that the evaporative emissions of vehicles be lower than in the past, and the service life of various systems and devices on vehicles should be increased to 15 years, or 240000 kilometers. Therefore, it is necessary to use special elastomers, such as low-temperature fluoroelastomers, to meet the common needs of low emissions and long service life

the purpose of this paper is to study the long-term fuel resistance and thermal aging properties of low-temperature fluoroelastomer. Polymers such as fkm-glt and fkm-gflt are well-known in the industry for their combination of good fuel resistance, thermal aging resistance and compression deformation resistance, as well as the low softness and smoothness of fluoroelastomers. GLT and glft manufactured by traditional process are upgraded to glt-s and gflt-s through advanced polymer architecture (APA) process. It has been recorded in previous literature. In addition, a new low temperature FKM called gblt-s is also introduced in the literature. In this paper, two kinds of elastomers manufactured by traditional process and advanced polymer system process are tested in parallel, and the results obtained by complying with strict test specifications are compared

test

◆ test material

select five low-temperature fluoroelastomers with low displacement accuracy, and evaluate their aging performance. The FKM types tested are:

GLT: vf2-pmve-tfe copolymer containing 64% fluorine containing traditional peroxide vulcanization point. It is the earliest low-temperature FKM polymer to meet, for example, ams-r-83485 standard

glt-600s: vf2-pmve-tfe copolymer containing 64% fluorine manufactured by APA process. Contains improved peroxide vulcanization point. Hereinafter referred to as glt-s

gblt-600s: vf2-pmve-tfe copolymer manufactured by APA process, containing 66% fluorine. Contains improved peroxide vulcanization point. Hereinafter referred to as gblt-s

gflt: vf2-pmve-tfe copolymer made of traditional peroxide vulcanization point monomer, with fluorine content as high as 67%. It is used to meet the following standards, such as gm6269m, Ford m2d401-a3 and Daimler Chrysler msbz-832-grade F

gflt-600s: vf2-pmve-tfe copolymer manufactured by APA process, with fluorine content as high as 67%

◆ test substrate and details

5 elastomers are mixed into 30 mT black samples in a mixer in the laboratory, as shown in Table 1. The sample plate was vulcanized in a die at 177 ℃ for 5 minutes. Polymer GLT and gflt manufactured by traditional process are vulcanized for 16 hours at 232 ℃ in air circulation furnace, while products manufactured by advanced polymer system process are vulcanized for only 4 hours at 232 ℃. Then cut out the tensile sample and soak it in fuel oil according to the specifications, or aging it in a hot air furnace. The test shall be carried out at a certain time interval in order to record the test trend

the fuel oil used in the test is cm-15a and acid fuel pn180. Cm-15a is a mixture of 85% fuel C and 15% methanol. Methanol is prepared from corrosive water, which contains trace salts (such as sodium chloride and sodium sulfate) and formic acid. Add 5 ml of corrosive water to 1 liter of methanol, and mix it with fuel C when it is necessary to prepare the test fuel. During the aging process of 5000 hours with cm-15a, replace the fuel oil once a week. Aging is carried out in a Parr pressure vessel placed in a friction gas flow, and the aging temperature is 60 ℃. The time interval of tensile test is 168, 672, 2000, 3000, 4000 and 5000 hours. Acid fuel oil is prepared according to the following method: add copper ion and tert butyl hydrogen peroxide to the mixture containing 80% fuel C, 15% methanol and 5% tert butyl alcohol to increase the peroxide value to 180. The aging test of acid fuel oil is also carried out in the parr pressure vessel with friction gas flow, and the aging temperature is 60 ℃. More details of the test fuel preparation and test conditions can be found in many Ford documents

results and discussion

after vulcanization and post vulcanization, five FKM test material sheets are used for the test of original physical properties. The results show that the nominal hardness values of these five FKM composites are all 70. The tensile strength of GLT and gflt manufactured by traditional process is higher than that of glt-s, gblt-s and gflt-s manufactured by APA process. The rubber produced by APA process has high elongation and low modulus of 100% elongation. When comparing FKM vulcanized by peroxide manufactured by traditional process and APA process, these trends in physical properties have also been observed before, which is not unexpected. The test of compression deformation resistance is carried out on the glued disc cut from the same plate. Glt-s, gbt-s and gflt-s manufactured by APA process show better performance in the test, and the compression deformation value is lower than the traditional low temperature FKM GLT and gflt

◆ long time fuel soaking

soak five low-temperature FKM compounds in acidic fuel pn180 for 360 hours at 60 ℃, and then test. The tensile elongation of GLT and glt-s with low fluorine content changes the most, and the volume swelling is larger, while the gblt control punch with high fluorine content rises at a uniform rate, and the properties of S, gflt and gflt-s change less, and the volume swelling is smaller

the performance of traditional GLT and gflt is very similar to that of APA glt-s, gblt-s and gflt-s. After the acid fuel test, the volume swelling fraction was detected, and there was no fracture in any sample, while many fuel resistant elastomers usually had cracks when the test failed

next, evaluate the performance of five low-temperature peroxide vulcanized FKM in cm15a. As mentioned above, cm-15a is a mixture of 85% fuel C and 15% methanol, which contains some trace salt water pollutants. The data showed that GLT and glt-s swelled 38% to 42% during the whole test, and glt-s swelled more. Gblt-s with 66% fluorine showed low swelling, about 25%, while gflt and gflt-s with 67% fluorine had the lowest swelling, about 22%. The data showed that the swelling properties of traditional polymers and APA polymers were very similar during the whole 5000 hour test

hardness change is another physics that occurs when elastomers swell in fuel oil. Now it can save high cost and cumbersome painting process. It is interesting to point out that the hardness reduction of APA polymers glt-s and gflt-s is less than that of the corresponding traditional polymers

the comparison of the tensile and elongation percentage results of five FKM polymers shows that the reduction of the tensile and elongation percentage of GLT and glt-s, the reduction of the tensile strength of the two low-temperature polymers at the beginning of the test is about 60%, and then it gradually stabilizes, and the tensile strength remains unchanged during the subsequent period of immersion for the whole 5000 hours. The tensile sample of fuel aging is placed in the furnace and dried at 100 ℃ for 4 hours, and the percentage of loss of tensile strength is restored to less than 25%. In general, the fuel aging tensile results of the two polymers are very similar

in the test, GLT and glt-s lost about 45% of their elongation in hot cm15a, then stabilized, and remained unchanged for the rest of the 5000 hour soak. Put the fuel aging sample into the furnace and dry it at 100 ℃ for 4 hours, and the elongation of both samples will return to a level close to the original value. After soaking for 5000 hours, the volume swelling changes of the two compounds were measured by visual observation and manual bending, and no degradation of any kind was found

the tensile strength and elongation of gblt-s, gflt and gflt-s with higher fluorine content soaked in cm15a fuel showed that the tensile strength of the three low-temperature polymers with high fluorine content lost about 60% at the beginning of the test, and remained unchanged for the whole time after 5000 hours of immersion. However, when the fuel aging sample is put into the heating furnace and dried at 100 ℃ for 4 hours, the loss of tensile strength returns to less than 20%. The trends observed in the tensile results of the three polymers are very similar. Although the test data did not include the results of hardness and volume swelling, the hardness and volume swelling of the sample after drying for 4 hours were measured. It should be noted that the polymer still has some volume swelling (in the range of%) after drying, indicating that heating at 100 ℃ for 4 hours is not enough to completely dry the sample

at the beginning of the test, gflt, gflt-s and gblt lost about 35% elongation in hot cm15a fuel. The elongation loss of gflt recovered to 20% and stabilized, while the elongation loss of gflt-s and gblt-s stabilized at 35%. When the fuel aging samples were put into the heating furnace and dried at 100 ℃ for 4 hours, the elongation of the three samples returned to close to the original value. After soaking for 5000 hours, the volume swelling changes of the two compounds were measured by visual observation and manual bending, and no degradation of any kind was found

in summary, the data show that there is an initial plasticizing effect because the fuel swells these FKM polymers, reducing tensile strength and elongation. However, the effect seems to be reversible to a large extent when the fuel aged tensile sample is dried at 100 ℃ for 4 hours, because the tensile strength is lost by about 25% and the elongation is close to the original value. This shows that the long-term effect of fuel oil immersion on the five low-temperature FKM tested is limited

◆ long time heating aging

another advantage of FKM polymer is its excellent heat aging resistance. One method of evaluating the resistance to thermal aging is ISO 2578, in which the polymer to be tested is aged at different temperatures

generally speaking, the thermal aging of glt-s, gblt-s and gflt-s manufactured by APA process is equivalent to that of GLT and gflt manufactured by traditional process. Especially at 200 ℃ and 232 ℃, the tensile strength of all these FKM tends to lose. All FKM polymers at 175 ℃ and 205 Tension control required for winding: the elongation increases after aging at 0 ℃ for 5000 hours. When aging at 232 ℃, the elongation of most samples shows a similar initial increase until reaching a certain threshold, and the polymer loses elongation due to embrittlement. This mode of thermal aging is very similar to that of bisphenol cured terpolymers (such as Viton b). Compared with GLT and glt-s with low fluorine content, gblt-s, gflt and gflt-s with high fluorine content can maintain the elongation unchanged for a longer time at 232 ℃

◆ low temperature properties

most of the long-term tests mentioned here are carried out on low-temperature FKM, so it is appropriate to review the low-temperature properties of five polymers in long-term fuel and heating aging

the general trend of shrinkage temperature (TR-10) and glass transition (TG) of traditional GLT and gflt and glt-s, gblt-s and gflt-s manufactured by APA process measured by DSC is: compared with GLT and gflt, the low temperature properties of glt-s and gflt-s manufactured by APA process are moderately improved; Gblt-s is just between these products, TR-10 is -27 ℃, TG is -28 ℃

conclusion

in short, at present, Viton fluoroelastomer standard temperature and low temperature grade products made by peroxide cured APA process can be used. A large number of long-term tests were carried out. The results showed that the volume swelling and physical property retention of glt-s, gblt-s and gflt-s manufactured by APA process after aging for 360 hours in acid gasoline (pn180) at 60 ℃ and 5000 hours in cm15a at 60 ℃ were similar to GLT and gflt manufactured by traditional process; The drying property of fuel cm15a after soaking is also similar to GLT and gflt manufactured by traditional process

when aging at 175 ℃ in dry and hot atmosphere for 5000 hours, 200 ℃ in dry and hot atmosphere for 5000 hours and 232 ℃ in dry and hot atmosphere for 5000 hours, APA process

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