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Application of BIPB/S/DTDM/CZ composite vulcanization system in EPDM rubber hose compounds

vulcanization hose applications

Abstract: The effects of sulfur vulcanization system, peroxide vulcanization system, and composite vulcanization system on the performance of EPDM rubber hose compounds were compared, and the performance of EPDM rubber hose compounds using the BIPB/S/DTDM/CZ composite vulcanization system was studied by orthogonal experimental method. The results show that the comprehensive performance of EPDM rubber hose compounds using the BIPB/S/DTDM/CZ composite vulcanization system is better than that of the sulfur vulcanization system and peroxide vulcanization system. The amount of BIPB is the main factor affecting the scorch time T10, and the amount of S is the main factor affecting the compression set. The optimal ratio of BIPB/S/DTDM/CZ composite vulcanization system is BIPB 2.5, S 0.3, DTDM 1.2, and CZ 0.9.

Keywords: EPDM rubber hose compounds; sulfur vulcanization system; peroxide vulcanization system; composite vulcanization system.

The main chain of the ethylene propylene diene monomer (EPDM) polymer is completely saturated, which gives it excellent heat aging resistance, weather resistance, ozone resistance, chemical resistance, and electrical insulation properties, making it widely used in products such as rubber hoses and seals for automotive components. EPDM rubber can be vulcanized using conventional sulfur vulcanization systems, sulfur donor vulcanization systems, peroxide vulcanization systems, and reactive resin vulcanization systems. Different vulcanization systems directly affect the vulcanization characteristics and physical mechanical properties, as well as heat aging resistance, of the rubber material. Experimental results have shown that EPDM sulfur vulcanizates using conventional sulfur vulcanization systems have good comprehensive mechanical properties, but poor heat aging resistance and resistance to compression set deformation, while EPDM peroxide vulcanizates have good heat aging resistance and resistance to compression set deformation, but poor tear strength and other properties. Therefore, this article compares the effects of sulfur vulcanization systems, peroxide vulcanization systems, and composite vulcanization systems on the properties of EPDM rubber hose compounds, and uses the BIPB/S/DTDM/CZ composite vulcanization system to study the scorch time, tensile strength, elongation at break, and compression set deformation performance of EPDM rubber hose compounds using the orthogonal experimental method. The formulation of this vulcanization system was optimized, resulting in EPDM rubber hose compounds with excellent properties.

Experiment

1.1 Main raw materials

EPDM, grade 5890F, Korean SK product, carbon black from Shanghai Cabot Chemical Co., Ltd., modified calcined clay from Zhejiang Tongfu Nanomaterials Co., Ltd., BIPB (odorless DCP) from Hunan Yixiang Chemical Co., Ltd., anti-aging agent, nano calcium carbonate, paraffin oil, sulfur, accelerator DTDM, accelerator CZ are all commercially available products.

1.2 Main equipment and instruments

Mixing mill XSM-2 from Shanghai Kechuang Rubber and Plastic Machinery Equipment Co., Ltd., open mill XK-160 from Qingdao Xincheng Yiming Rubber Machinery Co., Ltd., 100t electric heating plate vulcanizing machine from Shenzhen Xinjinli Machinery Co., Ltd., rubber rotorless vulcanizer, universal material tensile testing machine, thickness gauge, Shore hardness tester, rubber aging tester, all from Taiwan Songshu Testing Instruments Co., Ltd., compression permanent deformation device from Yangzhou Jiangdu Kaide Testing Machinery Co., Ltd.

1.3 Test formula

Basic formula (unit: parts): EPDM 100, zinc oxide 5, stearic acid 1.5, anti-aging agent 1.5, nano calcium carbonate 25, paraffin oil 30, carbon black 50, modified calcined clay 20, vulcanization system see Table 1:

Table 1: Sulfur curing system

SampleNo.BIPBSDTDMCZ
Sulfur vulcanization system1#/20.91.2
Peroxide vulcanization system2#2.5///
Composite vulcanization system3#2.50.30.90.9

1.4 Preparation process

EPDM is added to the mixer for plasticizing for 3 minutes, then active agents and anti-aging agents are added and mixed for 2 minutes. After that, half of the reinforcement filling system (carbon black, modified calcined clay, and nano-calcium carbonate) is added and mixed for 3 minutes, followed by adding the remaining half of the reinforcement filling system and plasticizers for further mixing. The mixture is then cured at 125℃. Vulcanization accelerator is added on the open mill, and after milling, the material is cut with a knife three times and rolled into triangular packages six times before being rolled into large rolls five times. Finally, the material is cut into sheets and stored for more than 16 hours. The vulcanization curve is measured using a vulcanization tester, and samples are taken for related tests. The curing condition is 170℃ x t90.

1.5 Performance testing

The mixing rubber vulcanization characteristics are tested according to GB/T16584-1996, with a test condition of 170℃ x 30min. The Shore A hardness is tested according to GB/T531.1-2008, and the tensile performance is tested according to GB/T528-2009. The heat resistance and air aging properties are tested according to GB/T3512-2014, with a test condition of 110℃ x 72h. The compression permanent deformation performance is tested according to GB/T7759.1-2015, with a test condition of 110℃ x 24h.

 

2.Results and Discussion

2.1 The influence of different vulcanization systems on the properties of EPDM rubber hose compounds.

Table 2 shows the properties of EPDM rubber hose compounds using three different vulcanization systems: sulfur vulcanization system, peroxide vulcanization system, and composite vulcanization system. The sulfur vulcanization system generates polysulfide crosslinks, which can break under long-term aging at high temperature. The breaking of crosslinks leads to stress relaxation and molecular chain displacement, and the newly generated crosslinks from the broken crosslinks encounter active points, thereby hindering molecular chain recovery and causing an increase in compression permanent deformation. The peroxide vulcanization system and the composite vulcanization system mainly generate C-C crosslinks with high bonding energy, which are not easily damaged under stress and heat, resulting in small changes in compression and aging after the test. At the same time, from Table 2, it can be seen that the use of the composite vulcanization system has a delay effect on the scorch time T10, improving operational safety. The vulcanization time T90 reflects the effect of the composite vulcanization system on the vulcanization flatness. The sulfur vulcanization system has the highest tensile strength, followed by the composite vulcanization system, and the peroxide vulcanization system has the lowest. The composite vulcanization system has the highest elongation at break, the smallest compression permanent deformation, and the best heat resistance and air aging properties, followed by the peroxide vulcanization system, and the sulfur vulcanization system has the third best performance. Overall, for EPDM rubber hose compounds, the composite vulcanization system should be prioritized.

Table 2: Effects of Three Different Vulcanization Systems on the Properties of EPDM Rubber Hose Compound

Sample NO.1#2#3#
T10/min2.5331.2672.293
T90/min12.7516.03317.625
Tensile strength/MPA15.912.314.6
Elongation at break/%397449485
Shore A hardness/ degree706568
Compression set/%262118
Heat aging resistance(110℃x72h)
Tensile strength change rate/%+5+10+8
Elongation at break change rate%-8+6+2
Shore A hardness change/ degree+8+4+5

2.2 Design of Orthogonal Experiment

2.2.1 Characteristics and Selection of Orthogonal Tables

When conducting multi-factor and multi-level experiments, the advantage of using orthogonal experimental design is that:

(1) Uniform dispersion, that is, experimental conditions are evenly dispersed among completely combinatorial levels, with strong representativeness;

(2) Overall comparability, that is, for each column of factors, the occurrence frequency of other factors at each level in the sum of all levels is the same, which maximally eliminates the interference of other factors and facilitates the derivation of reasonable conclusions.

2.2.2 Determination of Experimental Factors and Levels

In this paper, BIPB, S, DTDM, and CZ are selected as four factors, each with three suitable levels, for the design of orthogonal experiments. The design of experimental factors and levels is shown in Table 3.

Table 3: Experimental factors and levels.

LevelABCD
BIPBSDTDMCZ
12.00.90.61.2
22.50.60.90.9
33.00.31.20.6

2.2.3 Orthogonal Experimental Table and Experimental Data

Since there are four factors to be examined, each with three corresponding levels, ignoring the interactions between the factors, the orthogonal table obtained should be 4 factors and 3 levels, with a corresponding orthogonal table header of L9(34). A total of 9 experiments were conducted in three batches. The L9(34) orthogonal table and its corresponding experimental data are shown in Table 4, and the experimental result analysis is shown in Tables 5 to 8.

 

Table 4: L9(34) Orthogonal experimental table and results.

NO.Factor columnFactor columnMechanical performancepermanent compression deformation rate/%
ABCDT10/minTensile strength/MPAElongation at break/%
L111113.14812.748545
L212223.09213.252036
L313332.87813.554524
L421232.31212.853635
L522312.72513.548430
L623122.4814.150024
L731322.57214.850926
L832132.0614.248222
L933211.8921343516

Table 5: Analysis of the extreme difference in results of T10 scorch time

FactorT10/Min
ABCD
Mean13.0392.6622.5632.588
Mean22.5062.6262.4322.700
Mean32.1602.4172.7102.417
R0.8790.2450.2780.283

Table 6: Analysis of the extreme difference in results of tensile strength

Factortensile strength/MPa
ABCD
Mean113.13313.43313.66713.067
Mean213.46713.63313.00014.033
Mean314.00013.53313.93313.500
R0.8670.2000.9330.966

Table 7: Analysis of the extreme difference in results of Elongation at break

FactorElongation at break/%
ABCD
Mean1516.667510.000489.000468.000
Mean2506.667495.333497.000509.667
Mean3475.333493.333512.667521.000
R41.33416.66723.66753.000

Table 8: Analysis of the extreme difference in results of permanent compression deformation

Factorpermanent compression deformation rate/%
ABCD
Mean135.00035.33330.33330.333
Mean229.66729.33329.00028.667
Mean321.33321.33326.66727.000
R13.66714.0003.6663.333

2.2.4 Orthogonal Experiment Results Analysis

This article mainly studied four properties of EPDM rubber hose material, including T10 scorch time, tensile strength, elongation at break, and compression permanent deformation. The four properties can be arranged in order of importance based on their range from Table 5 to Table 8. For T10 scorch time, the order is A>D>C>B. For tensile strength, the order is D>C>A>B. For elongation at break, the order is D>A>C>B. For compression permanent deformation, the order is B>A>C>D.

In the orthogonal experimental design of EPDM rubber hose material, tensile strength is the most important property, with factor A ranked third. A2 or A3 can be chosen for tensile strength, and A1 or A2 can be chosen for T10 scorch time, which is the most important property. For elongation at break and compression permanent deformation, factor A is ranked second, so A1 or A2 can be chosen for elongation at break, and A2 or A3 can be chosen for compression permanent deformation. Considering all factors, factor A should be chosen as A2. Factor B is ranked least important for T10 scorch time, tensile strength, and elongation at break, but is the most important for compression permanent deformation. Therefore, B3 should be chosen. Factor C is ranked second for tensile strength and third for T10 scorch time, elongation at break, and compression permanent deformation. Therefore, C2 or C3 can be chosen for tensile strength and C3 for the other properties. Factor D is ranked most important for both tensile strength and elongation at break. D2 or D3 can be chosen for both properties, while D1 or D2 can be chosen for T10 scorch time. Factor D is ranked least important for compression permanent deformation, so D2 should be chosen.

In summary, the optimal ratio of EPDM rubber hose material with a composite vulcanization system is A2B3C3D2, which means that the basic formula includes 2.5 parts BIPB, 0.3 parts S, 1.2 parts DTDM, and 0.9 parts CZ.

3 Conclusion

(1) The comprehensive performance of EPDM rubber hose material using the composite vulcanization system of BIPB/S/DTDM/CZ is better than that of sulfur vulcanization and peroxide vulcanization systems.

(2) The orthogonal experimental results and analysis show that the amount of BIPB is the main factor affecting T10 scorch time, and the amount of S is the main factor affecting compression permanent deformation.

(3) Based on the orthogonal experimental results and analysis within the range of each factor level, the best ratio for EPDM rubber hose material using a composite vulcanization system is 2.5 parts BIPB, 0.3 parts S, 1.2 parts DTDM, and 0.9 parts CZ.

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