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Post cure thermo-oxidative effects on HNBR.

HNBR is widely recognized as a high-performance elastomer due to its superior mechanical properties and resistance to chemicals, ozone and heat. One of the primary applications of HNBR is seals in which both heat resistance and low compression set are major requirements. Generally, high crosslink density is necessary in order to develop low compression set. As HNBR is highly saturated, peroxide is typically used for curing. With ongoing pressures to reduce costs, manufacturers may reduce press cure times. In an effort to compensate for the short press cure, a post cure typically is done at an elevated temperature. It is theorized that the post cure contributes to premature aging of the product. Peroxide manufacturers recommend excluding oxygen in order to prevent polymer degradation when peroxide curing (ref. 1). Typically, only 1-2% oxygen reacted is sufficient to deteriorate an elastomer product severely.

To address concerns regarding the post cure oxidation effects, this investigative study was initiated for evaluation of state of cure, effects of cure temperatures, cure times and post cures. States of cure as measured by an oscillating disc rheometer (ODR) include optimum (measured by t'90 x 1.5) and 80% cure (measured by t'80); this simulates cure conditions that can occur in production. Post cures in air were evaluated at 150 and 175 [degrees] C at varying times. Cure temperatures ranging from 170 to 200 [degrees] C were assessed. To evaluate the oxidative effects, post cure in nitrogen was also evaluated at varying cure times and temperatures. Physical properties were measured, including rheological, viscosity, tensile and compression set. Compression set was used as an indicator of crosslink density. Air oven aging was performed at 150 [degrees] C for 168 and 504 hours. As HNBR hardens during air aging, it was not surprising that nitrogen aging slowed the aging process while air aging showed greater deleterious effects on physical properties.

Experimental

Two HNBR recipes using Z-21, a 36% ACN, 95% hydrogenated acrylonitrile butadiene copolymer, were mixed employing two commonly used peroxides: Peroxide 40C (40% active, dicumyl peroxide) and Peroxide 40KE (40%, active ([alpha],[alpha] -bis (t-butylperoxyl) diisopropyl-benzene). The level of peroxide was based on a milli-molar equivalent of 8 phr of 40KE. The formulations are listed in table 1. Multiple cure times and temperatures with and without post cure in air and nitrogen were evaluated, as well as two different states of cure: Optimum (measured by t'90 x 1.5) and 80% cure (measured by t'80).

Phase 1 of this investigation was initiated to determine the effects of high temperature cures relative to optimum cure. Based on these results, Phase 2 was designed to evaluate both optimum and short press cures (t'80) with varying post cures. Finally, Phase 3 was designed to determine the effects of an inert environment for post curing and high-temperature aging. By eliminating oxygen, only the thermal effects would be seen. The experimental design for the three phases follows.

Phase 1

* A range of cure temperatures was evaluated - 170 [degrees] C, 180 [degrees] C, 190 [degrees] C and 200 [degrees] C. Samples were cured at two conditions: Optimum cure and 80% cure with a four hour air post cure at 150 [degrees] C. Physical property results were compared.

* Compression set, using plied disk, cured as noted above, was measured after 168 hours at 150 [degrees] C.

Phase 2

* Compression set was determined using an optimum cure and 80% cure molded at 190 [degrees] C with a variable air post cure using the following conditions: 1, 2, 3, 4, 6 and 8 hours at 150 [degrees] C and 1, 2, 4 and 6 hours at 175 [degrees] C.

Phase 3

* The optimum cure and 80% cure were aged in air at 150 [degrees] C for 168 and 504 hours.

* The optimum cure and 80% cure were post cured in a nitrogen atmosphere based on the following schedule:

i. Post cure temperature of 150 [degrees] C for 2, 4 and 8 hours; and

ii. Post cure temperature of 175 [degrees] C for 2, 4 and 8 hours.

* All post cure specimens were air and nitrogen aged at 150 [degrees] C for 168 and 504 hours. Results of first and third were compared.

* Compression set was determined using the same cure schedule as in the first two. Compression set results were compared.

Mixing

All compound masterbatches were prepared in a 1,600cc internal mixer. After incorporation of fillers, roughly four minutes, the masterbatch was discharged at a temperature of approximately 140 [degrees] C. This masterbatch was then transferred to a cool 20-cm two-roll mill, sheeted to approximately three millimeters thickness and allowed to rest for about one hour. After the rest period, the compound masterbatch was then placed back onto the mill, allowed to form a smooth rolling bank and curatives added.

Cure and rheological properties

Mooney viscosity and Mooney scorch measurements were conducted according to ASTM D1646 at 100 [degrees] and 125 [degress] C, respectively. Cure characteristics were determined using a moving die rheometer and an oscillating disc rheometer, per ASTM D 5289 and ASTM D 2084, respectively. Based on rheological data as. listed in tables 2-4 for the various studies, the t'90 and t'80 were used respectively to obtain the optimum and 80% cure. The t'80 represents the short press cure, which can occur in production.

Physical properties evaluation

Tensile strength, elongation and modulus values were obtained according to ASTM D412. The data collected used a six-station tensile test instrument. Air oven aged physical properties were obtained according to ASTM D573 and were evaluated on the tensile tester. Tests in this study have been carried out according to ASTM standards. Tensile properties were determined after the initial press cure and post cure. Aging properties, changes in tensile, elongation and hardness were determined after 168 hours and 504 hours at 150 [degrees] in air and nitrogen. Compression set was determined using the plied disk method per ASTM D395. Physical properties for the three main phases are located in tables 1-6.

Results and discussion

Peroxides (ref. 2) work by decomposing to form free radicals upon heating. The basic reactions are:

POOH + PH [right arrow] PO * + P * + [H.sub.2] 0 1

The radicals are then free to react with the abstractable hydrogens forming a new polymer radical which can then combine to form a crosslink bond. All radicals are susceptible to other damaging reactions. In the presence of oxygen, radicals may form hydroperoxides. The hydroperoxide will thermally decompose leading to polymer degradation.

P * + [0.sub.2] [right arrow] or [vector] POO * and POO * + P [right arrow] or [vector] POOH + P * 2

In this scheme, crosslinks are formed by recombination according to equation 2.

P * + P * [right arrow] or [vector] P-P, P * + PO * [right arrow] or [vector] P - O - P , P * + POO * [right arrow] or [vector] POOP 3

Approximately 1-2% reacted oxygen is required to deteriorate an elastomer product severely. Coupling of diffusion and chemical reaction is frequently encountered in chemical engineering problems. Oxidation of rubber parts not only involves a chemical reaction, but also diffusion. During oven aging, the polymer structure is changed due to complicating thermal and oxidation degradation and crosslinking. HNBR generally becomes stiffer, while tensile strength remains somewhat constant initially and then falls off. The percent elongation changes systematically with time and temperature rise. Modulus increases linearly with time during air aging (ref. 3). In a previous study (ref. 4), a correlation between modulus and percent elongation has been established. It has been shown that an increase in crosslink density is proportional to an increase in modulus during air aging. Compounds with higher crosslink density show less relative modulus change and, therefore, better heat resistance.

Results

Figures 1 and 2 show that as the cure temperature increased, the compression set improved in the first phase of study, regardless of peroxide type. The improved compression set translates to greater crosslink density, as shown in table 1. Across the cure temperature range, the air post cure (four hours at 150 [degrees] C) increased the modulus, reduced the percent elongation and increased the compression set, regardless of peroxide type, as seen in figures 1 and 2. Based on this set of results, the second phase was initiated with the cure temperature established at 190 [degrees] C.

[FIGURE 1 AND 2 OMITTED]

In the second phase of testing, the effects of an optimum cure and an 80% cure (t'80) with higher post cure temperatures (150 [degrees] C and 175 [degrees] C) and cure times (one hour to eight hours) were evaluated. Results are tabulated in table 2. Regardless of the post cure temperature and time, the best compression set results were obtained on the optimally cured specimen without a post cure (figures 3 and 4). The peroxide type had no effect. The least square method (ref. 5) was used to establish the best fitting line to this set of data. "[R.sup.2]" is a measure of "fit" and an indication of variation in the data; the larger the value (up to 100), the better the fit. As shown in figures 1-4, the [R.sup.2] values are relatively high, ranging from 0.88 to 0.98. Exposure to air post cure did result in some deterioration, as illustrated in figures 3 and 4.

[FIGURE 3 AND 4 OMITTED]

At this point of the investigation, it was apparent that additional post cure in air increased compression set and modulus. Increasing cure temperature improved these properties. Phase 3 was initiated to determine the effects of oxygen or the lack thereof in the optimum and short cure (80% cure) with and without a post cure.

The third phase of testing began with a comparison of the original properties at optimum cure and 80% cure. Further, the comparison was extended to include results after nitrogen post cure. The same trend occurred regardless of peroxide type; results were graphed using the Peroxide 40KE. Results were:

* As shown in table 3, the original properties of the optimum cure and the 80% cure show very little difference in the physical properties.

* Regardless of the different nitrogen post cure times and temperatures, as shown in table 4, the optimum and 80% cure physical properties were comparable, being within two sigma of the post cure properties, as illustrated in figures 5 and 6.

[FIGURE 5 AND 6 OMITTED]

The optimum and 80% cure samples, without post cure, were then air aged. The remaining nitrogen post cure samples were also air aged. The results are as follows:

* The press cure samples with no post cure showed the greatest change in percent elongation when compared to the nitrogen post cure samples after aging in air, as shown in table 5.

All nitrogen post cure samples were aged in nitrogen and air. Compression set results were obtained after an optimum cure with post cure at 150 and 175 [degrees] C at varying times; compression set was not determined using an 80% cure. The results were:

* The best compression set results were obtained after a nitrogen post cure of eight hours at 150 [degrees] C, as depicted in figure 7.

[FIGURE 7 OMITTED]

* After 504 hours in nitrogen, the property changes were minimal and substantially less than the changes incurred in air after 168 hours. As expected, aging in air gave the greater changes in physical properties, as shown in table 6.

* Disregarding the influence of cure time (whether optimum or 80%) and post cure, it appears that the nitrogen aged compounds have much greater retention of modulus and percent elongation than the air aged, as shown in figures 8 and 9.

[FIGURE 8 AND 9 OMITTED]

Regardless of peroxide type used, this study demonstrates the reduction of degradation in an inert atmosphere.

Overall, in this phase of study, the post cure samples aged in nitrogen showed very few signs of aging after 504 hours at 150 [degrees] C. Thus, it is clearly shown that oxidation is the primary degradation mechanism under these conditions. The air aging of the press cure and the post cure samples gave comparable results. There was a decline in percent elongation and increase in modulus as would be expected.

Conclusions

In summary, based on this body of investigative work, we have concluded the following:

* Higher temperature cure will develop greater crosslink density, as evidenced by the increased modulus and reduced compression set. Thus, utilizing a higher temperature cure with reduced cure time can decrease production molding costs.

* Best compression set results were obtained using an optimum press cure without air post cure.

* If elastomer seals are short cure (80%), a post cure in an inert atmosphere (non-air or fluid bath), will produce similar results comparable to the optimum cure.

* Aging in a nitrogen environment dramatically improved the retention of mechanical properties. The compound is subjected only to the thermal effects; the oxidation effects are eliminated.

Future work

Future work will evaluate a designed experiment, which will assess a 40%, 60%, 80% and 100% cure state to better understand the state of cure effects. Post cure in air and nitrogen followed by aging in both air and nitrogen for 1,008 hours will be conducted on the various states of cure. Crosslink density will also be determined using DSC and compression set using both plied disk and buttons. The DSC will provide a crosslinked density reference point. Evaluation of any differences with plied disk and button will be performed.
Table 1 - high temperature cure with post cure

Recipe(s) 1 2
Z-21 100 100
N-774 50 50
Zinc oxide 5 5
AO-445 1.5 1.5
AO-ZMTI 1 1
Peroxide 40KE 8 ---
Peroxide 40C --- 12.78

Total 165.5 170.28
Table 2 - phase 2 post curing effects

Recipe 1 2

Mooney viscosity: ML(1+4) @
 100 [degrees] C 109.4 105.5
Mooney scorch' ML (1+30) @
 125 [degrees] C
 Viscosity Minutes 66.4 65.4
 t5 Minutes 27.6 15.7
 t35 Minutes >30 >30
ODR: 3.0 arc at 190
 [degrees] C
 ML dNm 18.5 18.9
 ts2 Minutes 0.9 0.7
 t'90 Minutes 3.6 2.6
 MH dNm 111.2 108.2
Vulcanized properties
Originals: Cured @ 190
 [degrees] C
 Hardness (A) Pts. 67 67
 Stress 50% MPa 2 2
 Stress 100% MPa 4 4
 Stress 200% MPa 16 17
 Tensile MPa 24 24
 Elongation % 272 269
 Tear strength, Die C kN/m 52 52
Compression set: Method
 B - plied discs:
Aging in air for 168 hrs./150
 [degrees] C
 Optimum % set 21.0 22.0
 T'80 + Post Cure 1 hr./150
 [degrees] C % set 22.1 24.4
 T'80 + Post Cure 2 hr./150
 [degrees] C % set 23.7 24.1
 T'80 + Post Cure 3 hr./150
 [degrees] C % set 24.1 25.2
 T'80 + Post Cure 4 hr./150
 [degrees] C % set 24.3 26.4
 T'80 + Post Cure 6 hr./150
 [degrees] C % set 26.9 26.1
 T'80 + Post Cure 8 hr./150
 [degrees] C % set 27.4 28.2
 T'80 + Post Cure 1 hr./175
 [degrees] C % set 22.9 24.4
 T'80 + Post Cure 2 hr./175
 [degrees] C % set 26.0 26.7
 T'80 + Post Cure 4 hr./175
 [degrees] C % set 26.9 26.7
 T'80 + Post Cure 8 hr./175
 [degrees] C % set 28.5 28.8
H-16-61- 1 1
Stress/strain: Cured @ 170
 [degrees] C
Vulcanized properties
Press cure time, minutes 18.9 10.8
 Hardness (A) Pts. 69 69
 Stress 50% MPa 2 2
 Stress 100% MPa 6 6
 Stress 200% MPa 19 19
 Elongation % 250 299
 Stress/strain: Cured @ 200
 [degrees] C
 Press cure time, minutes 3.15 1.9
 Hardness (A) Pts. 68 70
 Stress 50% MPa 2 2
 Stress 100% MPa 5 6
 Stress 200% MPa 18 21
 Tensile MPa 26 26
 Elongation % 267 288
Specific gravity 1.2 1.2
Compression set: Method
 B - plied discs
Aged 168 hrs./150 [degrees] C 40KE 40KE
Cure temperature Optimum cure T'80+PC
 170 [degrees] C 22.4 34.6
 180 [degrees] C 22 32
 190 [degrees] C 21.3 31.5
 200 [degrees] C 17.6 25.9

Recipe 1 2

Mooney viscosity: ML(1+4) @
 100 [degrees] C
Mooney scorch' ML (1+30) @
 125 [degrees] C
 Viscosity Minutes
 t5 Minutes
 t35 Minutes
ODR: 3.0 arc at 190
 [degrees] C MDR: 0.5 arc at 190
 [degrees] C
 ML dNm 1.3 1.4
 ts2 Minutes 0.4 0.4
 t'90 Minutes 2.0 1.2
 MH dNm 21.3 21.7
Vulcanized properties
Originals: Cured @ 190
 [degrees] C
 Hardness (A) Pts.
 Stress 50% MPa
 Stress 100% MPa
 Stress 200% MPa
 Tensile MPa
 Elongation %
 Tear strength, Die C kN/m
Compression set: Method
 B - plied discs:
Aging in air for 168 hrs./150
 [degrees] C
 Optimum % set
 T'80 + Post Cure 1 hr./150
 [degrees] C % set
 T'80 + Post Cure 2 hr./150
 [degrees] C % set
 T'80 + Post Cure 3 hr./150
 [degrees] C % set
 T'80 + Post Cure 4 hr./150
 [degrees] C % set
 T'80 + Post Cure 6 hr./150
 [degrees] C % set
 T'80 + Post Cure 8 hr./150
 [degrees] C % set
 T'80 + Post Cure 1 hr./175
 [degrees] C % set
 T'80 + Post Cure 2 hr./175

 [degrees] C % set
 T'80 + Post Cure 4 hr./175
 [degrees] C % set
 T'80 + Post Cure 8 hr./175
 [degrees] C % set
H-16-61- 2 2
Stress/strain: Cured @ 170
 [degrees] C
Vulcanized properties
Press cure time, minutes 10.5 5.8
 Hardness (A) Pts. 68 70
 Stress 50% MPa 2 2
 Stress 100% MPa 5 5
 Stress 200% MPa 17 19
 Elongation % 267 258
 Stress/strain: Cured @ 200
 [degrees] C
 Press cure time, minutes 2.55 1.6
 Hardness (A) Pts. 66 67
 Stress 50% MPa 2 2
 Stress 100% MPa 4 5
 Stress 200% MPa 15 17
 Tensile MPa 25 25
 Elongation % 307 272
Specific gravity 1.2 1.2
Compression set: Method
 B - plied discs
Aged 168 hrs./150 [degrees] C 40C 40C
Cure temperature Optimum cure T'80+PC
 170 [degrees] C 24.7 32.2
 180 [degrees] C 23.3 30.9
 190 [degrees] C 22.6 28
 200 [degrees] C 19.8 26.3
Table 3

Recipe 1 2
Mooney viscosity: ML(1+4) @
 100 [degrees] C 107.5 105.0
Mooney scorch: ML (1+30) @
 125 [degrees] C 64.5 63.3
Viscosity Minutes 0.0 17.5
t5 Minutes
ODR: 3.0 [degrees] arc at 190
 [degrees] C
 ML dNm 14.0 15.1
 ts2 Minutes 0.8 0.6
 t'90 Minutes 3.2 2.23
 MH dNm 105.8 109.6
Vulcanized properties
Cure @ 190 [degrees] C (T90 x 1.5)
 Hardness (A) Pts. 69 70
 Stress 50% MPa 1.9 1.9
 Stress 100% MPa 4.4 4.5
 Stress 200% MPa 17.6 17.3
 Tensile MPa 26.5 28.6
 Elongation % 264 308
Specific gravity 1.18 1.19
Compression set: Method B
Aged: 168 hrs./150 [degrees] C
H24-39
 Original cure (t90 x 2.5) 28.1 23.0
 Post cure 2 hrs./150 [degrees] C 26.2 23.2
 Post cure 4 hrs./150 [degrees] C 24.2 19.6
 Post cure 8 hrs./150 [degrees] C 20.6 21.3
 Post cure 2 hrs./175 [degrees] C 26.1 24.5
 Post cure 4 hrs./175 [degrees] C 27.4 23.9
 Post cure 8 hrs./175 [degrees] C 35.0 31.4

Recipe 1 2
Mooney viscosity: ML(I+4) @
 100 [degrees] C
Mooney scorch: ML (1+30) @
 125 [degrees] C
Viscosity Minutes
t5 Minutes
ODR: 3.0 [degrees] arc at 190
 [degrees] C MDR:0.5 arc at 190 [degrees] C
 ML dNm 1.2 1.4
 ts2 Mnutes 0.4 0.3
 t'90 Minutes 1.9 1.16
 MH dNm 18.1 20.9
Vulcanized properties
Cure @ 190 [degrees] C (T90 x 1.5) Cure at 190 [degrees] C (T80)
 Hardness (A) Pts. 70 70
 Stress 50% MPa 1.9 2.0
 Stress 100% MPa 4.7 4.9
 Stress 200% MPa 17.1 18.5
 Tensile MPa 26.9 26.5
 Elongation % 292 267
Specific gravity
Compression set: Method B
Aged: 168 hrs./150 [degrees] C Aged 504 hrs./150 [degrees] C
H24-39
 Original cure (t90 x 2.5) 39.8 36.5
 Post cure 2 hrs./150 [degrees] C 35.6 34.4
 Post cure 4 hrs./150 [degrees] C 34.6 32.9
 Post cure 8 hrs./150 [degrees] C 33.3 29.2
 Post cure 2 hrs./175 [degrees] C 34.6 34.4
 Post cure 4 hrs./175 [degrees] C 35.1 37.6
 Post cure 8 hrs./175 [degrees] C 47.3 49.6
Table 4 - a comparison of optimum and 80%
cure versus post cure

40KE: Optimum cure 50% 100% 200% Tensile % Elong.
Original T90 278 641 2,552 3,847 264
PC 2hrs./150 [degrees] C 267 651 2,481 4,086 329
PC 4hrs./150 [degrees] C 258 610 2,410 3,975 317
PC 8hrs./150 [degrees] C 272 672 2,447 3,956 327
PC 2hrs./175 [degrees] C 261 599 2,347 4,059 333
PC 4hrs./175 [degrees] C 261 603 2,411 3,882 319
PC 8hrs./175 [degrees] C 276 638 2,413 3,912 294
Post cure average 266 629 2,418 3,978 320
Post cure std. deviation 7.1 29.5 44.7 80.4 14.0

40KE: 80% cure
Original T80 279 679 2,475 3,905 292
PC 2hrs./150 [degrees] C 262 606 2,367 4,137 333
PC 4hrs./150 [degrees] C 266 636 2,343 4,007 292
PC 8hrs./150 [degrees] C 276 675 2,513 4,111 319
PC 2hrs./175 [degrees] C 261 610 2,373 4,020 319
PC 4hrs./175 [degrees] C 273 658 2,396 3,933 329
PC 8hrs./175 [degrees] C 273 643 2,451 3,869 292
Post cure average 269 638 2,407 4,013 314
Post cure std. deviation 6.3 26.9 63.5 102.2 17.9

40C: Optimum cure
Original T90 274 650 2,504 4,141 308
PC 2hrs./150 [degrees] C 266 625 2,521 3,902 292
PC 4hrs./150 [degrees] C 273 650 2,555 3,871 281
PC 8hrs./150 [degrees] C 278 657 2,535 4,065 292
PC 2hrs./175 [degrees] C 257 572 2,421 4,043 292
PC 4hrs./175 [degrees] C 258 577 2,367 3,932 293
PC 8hrs./175 [degrees] C 271 613 2,444 3,789 278
Post cure average 267 616 2,474 3,934 288
Post cure std. deviation 8.4 35.7 74.4 1,04.9 6.7

40C: 80% cure
Original T80 295 709 2,685 3,843 267
PC 2hrs./150 [degrees] C 269 657 2,621 3,991 285
PC 4hrs./150 [degrees] C 270 661 2,591 3,651 268
PC 8hrs./150 [degrees] C 291 704 2,637 3,865 273
PC 2hrs./175 [degrees] C 274 658 2,557 3,922 290
PC 4hrs./175 [degrees] C 268 624 2,482 4,272 328
PC 8hrs./175 [degrees] C 289 691 2,552 3,890 292
Post cure average 277 666 2,573 3,932 289
Post cure std. deviation 10.4 28.3 56.0 202.2 21.2
Table 5 - nitrogen and air aging on post cured Z-21

Recipe 1 2 1 2

Aged in oven: Cured t90 Cured t80
168 hrs./150 [degrees] C PC 2 hrs./150 PC 2 hrs./150
 [degrees] C [degrees] C

Hardness change, pts. 6 7 6 8
50% mod. change, % 63 71 68 80
100% mod. change, % 75 86 91 82
Tensile change, % -1 3 -2 -4
Elong. change, % -11 6 -14 -7

 Cured t90 Cured t80
 PC 8 hrs./150 PC 8 hrs./150
 [degrees] C [degrees] C

Hardness change, pts. 7 8 8 8
50% mod. change, % 57 68 59 55
100% mod. change, % 66 82 70 67
Tensile change, % 3 -3 -3 7
Bong. change, % -11 -1 -10 -2

168 hrs./175 [degrees] C Cured t90 Cured t80
 PC 2 hrs./175 PC 2 hrs./175
 [degrees] C [degrees] C

Hardness change, pts. 8 9 7 8
50% mod. change, % 72 90 66 76
100% mod. change, % 98 112 88 86
Tensile change, % -1 -3 2 1
Elong. change, % -15 -7 -9 -4

 Cured t90 Cured t80
 PC 8 hrs./175 PC 8 hrs./175
 [degrees] C [degrees] C

Hardness change, pts. 7 8 7 8
50% mod. change, % 38 56 53 56
100% mod. change, % 54 75 68 67
Tensile change, % 10 5 15 6
Elong. change, % 2 0 1 -1

504 hrs./150 [degrees] C Cured t90 Cured t80
 PC 2 hrs./150 PC 2 hrs./150
 [degrees] C [degrees] C

Hardness change, pts. 9 10 9 10
50% mod. change, % 115 136 119 106
100% mod. change, % 140 169 166 140
Tensile change, % -4 -4 -6 -3
Elong. change, % -22 -15 -26 -12

 Cured t90 Cured t80
 PC 8 hrs./150 PC 8 hrs./150
 [degrees] C [degrees] C

Hardness change, pts. 11 10 10 10
50% mod. change, % 126 134 122 132
100% mod. change, % 145 156 139 143
Tensile change, % -4 -3 8 -2
Elong. change, % -28 -19 -29 -22

504 hrs./175 [degrees] C Cured t90 Cured t80
 PC 2 hrs./175 PC 2 hrs./175
 [degrees] C [degrees] C

Hardness change, pts. 11 12 10 10
50% mod. change, % 154 152 120 128
100% mod. change, % 189 201 152 145
Tensile change, % -6 -3 -2 -2
Elong. change, % -101 -23 -23 -23

 Cured t90 Cured t80
 PC 8 hrs./175 PC 8 hrs./175
 [degrees] C [degrees] C

Hardness change, pts. 10 11 10 11
50% mod. change, % 125 141 116 121
100% mod. change, % 167 178 150 138
Tensile change, % 4 -5 3 0
Elong. change, % -24 -26 -24 -18

Recipe 1 2 1 2

Aged in nitorgen: Cured t90 Cured t80
168 hrs./150 [degrees] C PC 2 hrs./150 PC 2 hrs./150
 [degrees] C [degrees] C

Hardness change, pts. -2 -2 -2 -2
50% mod. change, % 9 8 8 10
100% mod. change, % 10 7 13 8
Tensile change, % 3 6 0 8
Elong. change, % -8 3 -3 4

 Cured t90 Cured t80
 PC 8 hrs./150 PC 8 hrs./150
 [degrees] C [degrees] C

Hardness change, pts. -1 -1 0 -1
50% mod. change, % 7 0 13 4
100% mod. change, % -1 -5 13 2
Tensile change, % 10 1 4 7
Elong. change, % 9 1 11 9

168 hrs./175 [degrees] C Cured t90 Cured t80
 PC 2 hrs./175 PC 2 hrs./175
 [degrees] C [degrees] C

Hardness change, pts. 1 0 0 0
50% mod. change, % 8 10 3 6
100% mod. change, % 10 11 1 1
Tensile change, % 4 4 6 1
Elong. change, % -2 0 10 -5

 Cured t90 Cured t80
 PC 8 hrs./175 PC 8 hrs./175
 [degrees] C [degrees] C

Hardness change, pts. -1 -1 0 -1
50% mod. change, % 12 9 14 32
100% mod. change, % 14 14 17 57
Tensile change, % 6 6 14 -9
Elong. change, % -10 5 -12 -13

504 hrs./150 [degrees] C Cured t90 Cured t80
 PC 2 hrs./150 PC 2 hrs./150
 [degrees] C [degrees] C

Hardness change, pts. 1 2 0 1
50% mod. change, % 8 12 13 -3
100% mod. change, % 9 16 29 1
Tensile change, % 8 4 3 6
Elong. change, % 2 4 -8 9

 Cured t90 Cured t80
 PC 8 hrs./150 PC 8 hrs./150
 [degrees] C [degrees] C

Hardness change, pts. 2 1 1 1
50% mod. change, % 8 2 -1 8
100% mod. change, % 6 -1 -6 21
Tensile change, % 9 3 3 8
Elong. change, % -3 5 5 -1

504 hrs./175 [degrees] C Cured t90 Cured t80
 PC 2 hrs./175 PC 2 hrs./175
 [degrees] C [degrees] C

Hardness change, pts. 3 3 2 1
50% mod. change, % 17 15 18 10
100% mod. change, % 25 20 25 9
Tensile change, % -1 5 4 4
Elong. change, % -10 3 4 -2

 Cured t90 Cured t80
 PC 8 hrs./175 PC 8 hrs./175
 [degrees] C [degrees] C

Hardness change, pts. 3 2 3 2
50% mod. change, % 31 25 35 18
100% mod. change, % 48 39 55 25
Tensile change, % 0 8 9 5
Elong. change, % -18 -8 -13 -10
Table 6

Original cures aged in air for 168 hrs./150 [degrees] C

 Optimum cure T'80 cure
 at 190 [degrees] C at 190 [degrees] C

 1 2 1 2
Hardness change 7 8 6 8
50% mod. change 51 79 47 63
100% mod. change 73.2 89.8 59.5 70.7
200% mod. change 18.8 22.6 22.3 13.3
Tensile change 6.4 -7.1 7.3 0.6
Elongation change 18.2 -14 9.9 0

Original cures aged in air for 504 hrs./150 [degrees] C

Hardness change 11 12 10 12
50% mod. change 115 132 103 101
100% mod. change 139 136 117 102
Tensile change 2.6 -13.6 -4.6 -5.1
Elongation change -23 -36.7 -31.8 25.5


References

(1.) Class, Jay B., "A review of the fundamentals of crosslinking with peroxides," Rubber World, Aug. 1999, pp. 35-39.

(2.) Purakel, Thomas L. and Purper, Robert L., "Peroxide curing of rubber," Elastomerics, July 1977, pp. 19-26.

(3.) S. Hayashi et al, 140th ACS Meeting, Detroit, MI, Oct. 8-11 (1991), paper no. 29.

(4.) Kube, Olaf, et al, "Aging behavior of HNBR," ACS Rubber Division Meeting, Dallas, TX 2000.

(5.) Hamburg, Morris, "Statistical analysis for decision making, "Harcourt, Brace & World, Inc., 1970, pp. 468-470.
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Title Annotation:rubber production
Comment:Post cure thermo-oxidative effects on HNBR.(rubber production)
Author:Wood, Michael E.
Publication:Rubber World
Article Type:Statistical Data Included
Geographic Code:1USA
Date:Dec 1, 2001
Words:4939
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