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Re-refined oil in dynamic NR compounds.

The use of renewed raw materials (such as re-refined oil) in rubber compounds is becoming a growing trend. It is cost effective as well as environmentally friendly. Total world consumption of lube oil in the automobile and non-automobile industries, amounting to about 30 million tons (ref. 1), is eventually converted to waste oil. This waste oil is re-refined by vacuum, or vacuum/china or the thin film distillation method (refs. 4-6) to produce useful re-refined oil. Some early studies were reported to use re-refined oil as a process oil in cheap natural rubber compounds, like mats, etc. Early this year, the author published a study of its use in EPDM hose compounds (refs. 2 and 3). Here, we are presenting our study on replacing existing rubber process oil (naphthenic type) with re-refined oil in different engine mount recipes.

Experimental

The re-refined oil used was produced by the clay/vacuum process (refs. 4 and 5) where the waste oil and 33% w/w clay were charged in a reactor. The vacuum was started at around 110[degrees]C, and gradually brought to 760 mm of Hg. The first fraction, called light oil, was collected between 110[degrees]C-200[degrees]C, while the final oil fraction was collected between 200[degrees]C-350[degrees]C. The temperature of the reactor was maintained between 300[degrees]C-350[degrees]C for about four hours. Re-refined oil was recovered by pressing cooled slurry residue of the reactor in a filter press. The properties of this re-refined oil vis-a-vis the properties of various oils from a refinery are presented in table 1. Some properties of re-refined oil, such as specific gravity, VGC, etc., were between naphthenic and paraffinic oil, while flash point, aniline point, paraffinic hydrocarbon content (CP %), etc., were closer to paraffinic oil values. Heavy metal contaminations were also very low. So we studied the effect of this oil, without further modification, in natural rubber engine mount recipes repineing an equal quantity of naphthenic oil.

Masterbatches without any plasticizer were mixed in a 75 liter dispersion kneader. Different portions of the masterbatch were weighed and mixed with plasticizers on a 16" x 42" mixing mill. Accelerators were added on the next day. Slabs and buttons were molded on a standard lab press at 160[degrees]C for 15 and 20 minutes, respectively. All tests reported here were done as per ASTM procedures.

Results and discussion

Recipes at 20 phr oil level are presented in table 2. While 100 phr natural rubber was used in recipes EM1 and EM2. a blend of 70/30 phr natural rubber/PBR was used in EM3 and EM4. Most aged or unaged tensile strengths and elongations (table 3) of re-refined oil compounds (EM2 and EM4) were lower than naphthenic oil compounds (EM1 and EM3) by about 5-10%; though, hardness and the rheometer properties such as Mh-MI, T10% and T90% were almost equal (so not presented). An increase in N330 level in the re-refined oil compound was needed to increase initial tensile strength.

In addition to the above physical properties, the following dynamic properties are more important in engine mounts:

* High static spring constant (Ks); providing stability and bearing;

* low dynamic spring constant (Kd); lowering natural frequency (fnd); and

* high damping ratio (C/Cc); lowering amplitude at resonance frequency.

The right balance of these three properties is required for efficient function of an engine mount. Also, properties should not change after creep and standard fatigue tests.

To study the dynamic properties of compounds, the buttons were aged per the flowchart of table 4, and the results of DMA tests after aging are presented in table 5. Here we observed that all Ks and Kd values before or after aging at 70[degrees]C for 168 hours were the same in both oils, except for higher values of re-refined oil in the 100% NR compound before aging. Also, both stiffness values had decreased by about 10-15% after heat aging at 70[degrees]C for 168 hours under 25% compression as per the flowchart in table 4.

[TABLE 4 OMITTED]

This study was further extended to a 30 phr oil level, as presented in table 6 with recipes EM 5, EM 6 and EM 7. In EM 7, 6 phr of re-refined oil was substituted with aromatic oil because it reduced its aniline point to ~95[degrees]C, i.e., near the naphthenic oil range.

From tables 7 and 8 it may be observed that the tensile strengths and elongations of re-refined and naphthenic oil compounds (EM 5 and EM 6) were almost equal, both before and after heat aging. Mixed oil compound (EM 7) had slightly better results. Similarly, the compression set values (table 9) of EM 5 and EM 6 were almost equal, though those of the mixed oil compound (EM 7) were surprisingly lower than both oils, even after 500 hours heat aging; however, hardness remained the same for all three oils.

To study the dynamic properties, buttons were molded from these three compounds (EM 5-EM 7) at 165[degrees]C for 20 minutes and heat aged under 25% compression for varying times up to 500 hours as per the table 4 flowchart. DMA results of these buttons, unaged and aged, are presented in tables 10-12. All Ks and Kd values (table 10) of re-refined oil (EM 6) were slightly higher than naphthenic oil (EM 5), while those values of mixed oil (EM 7) were mostly intermediate. However, more interesting was the decrease of both Ks and Kd values with aging up to 168 hours with all three compounds (EM5-EM7), and thereafter both stiffness values had started increasing again so that the Ks and Kd values of 500 hours aged buttons were almost equal to the unaged buttons. This was in spite of an almost 53-59% compression set (table 9) and a 5-6[degrees] durometer hardness increase, after 500 hours aging. A similar reduction in Kd and Ks values with 20 phr oil compound (EM1 and EM2) was earlier discussed in connection with table 5. However, the Kd/Ks ratio (table 11) remained almost unchanged during aging. Possibly, the modification of crosslink chains during aging under severe compression had created a more resilient, stress-free network which had reduced both static and dynamic spring constants through better distribution of stress. A similar trend in Ks and Kd was also observed in products made from these compounds. The damping coefficient values (table 12) of naphthenic and re-refined oil compounds (EM5 and EM6) were almost equal; while values of EM 7 with 6 phr aromatic oil were higher than both oils. Possibly, the aromatic oil had increased the K", i.e., loss modulus of the compound, which had increased the damping coefficient (C).

In order to validate the above findings, resilient mounts (figure 1) were molded from three compounds, EM 5, EM 6 and EM7. All mounts, after initial testing, were bolted after 25% compression and then aged at 70[degrees]C in an oven for 168 hours. After cooling and subsequent static and dynamic testing, the mounts were subjected to a dynamic load of 150 300 kgs for half million and one million cycles, respectively. Dynamic test results at each stage are reported in tables 13-15. Hardly any difference was observed in Ks and Kd (table 13), damping coefficient (table 14) or tan [delta] (table 15) values of resilient mounts from EM5, EM6 and EM 7 compounds. However, both stiffness values (table 3) of all three compounds, EM 5, EM 6 and EM 7 had clearly fallen after seven days of aging. Thereafter, during fatigue, all Ks values had fallen further, while Kd values had increased slowly. Compression set values were observed between 23-28% after 168 hours aging, while hardness had increased by 2-3[degrees] durometer in all three compounds. Field failures of mounts are said to be influenced by an increase in damping coefficient and tan g values during use in actual fitment in automobiles. The trends of button tests and product tests seemed to be within reasonable limits. Further hysteresis studies of individual models, both before and after aging would more clearly reflect the micro structure changes responsible for such abnormal behaviors.

[FIGURE 1 OMITTED]

Summary

* Tensile strength and elongation of re-refined oil was slightly lower than naphthenic oil. The effect was higher in NR than NR+PBR blends. Differences had decreased after long aging. A minor correction in carbon black type/level is needed.

* Static and dynamic stiffness values (Ks and Kd) of re-refined oil compounds were marginally higher than those of naphthenic oil compounds at all frequencies tested (10, 20 and 80 Hz), both before and after aging at 70[degrees]C, 0-500 hours, under 25% compression. However, Kd/Ks ratio, damping coefficient (N-sec/mm) and tan [delta] remained almost flat during aging and subsequent fatigue testing of products.

* Replacing a small part (6 phr) of re-refined oil with aromatic oil had

--Improved tensile strength and elongation.

--Lowered initial and aged Ks and Kd values of re-refined oil.

--Reduced both aged and unaged compression set.

--Increased damping coefficient.

* All Ks and Kd values decreased during aging (under 25% compression) for all types of oils at both the 20 and 30 phr level. After 168 hours of aging, values had started increasing so that the Kd and Ks values at 500 hours were almost equal to the initial values, though compression set was above 50% after 500 hours aging and hardness had also increased by 5-6[degrees] durometer. Rearrangement of crosslink networks might have distributed the stress more evenly, reducing both stiffness values.

References

(1.) Brian Handwerk, National Geographic News, published in June 2011.

(2.) "Cost-effective plasticizers in hose compounds," presented by Bhattacharya, P.S., at the Hose Conference, Aug, s5, 2010, Cleveland, OH.

(3.) "Re-refined oil as effective plasticizer in EPDM compounds," Bhattaeharya, P.S., Rubber World, March 2012.

(4.) "The engineering aspect of a used oil recycling project," Harrison, C. Waste Management, Vol. 14, No. 3-4, pp. 231-235, 1994.

(5.) "Technical guidelines on used oil re-refining or other re-uses of used oil," Basel Convention, Nov. 2002 (reprint).

(6.) Used Oil Re-Refining Study. to Address Energy Policy Act of 2005, Section 1838, July 2006, Office of Fossil Energy, U.S. Department of Energy.
Table 1--comparison of properties and compatibility
with various rubbers

Particulars Paraffinic oil Naphthenic oil
 spec. spec.

Sp. gravity 0.850-0.890 0.885-0.900
VGC region 0.790-0.819 0.820-0.850
C A% <10 0-30
C P% 60-75 35-55
C N% 20-35 30-45
Aniline point ([degrees]C) 100-125 85-100
Flash point ([degrees]C) 200 190
Heat loss % 0.5 max. 0.5 max.
 (150[degrees]C, 3 hrs.)
Heat loss % 0.5 max. 0.1
 (120[degrees]C, 72 hrs.)
Compatibility:
Natural rubber Good Good
SBR Good Good
SBS Good Good
Polybutadiene Good Good
EPDM Good Good
Chloroprene rubber Not Good
Polyisoprene rubber Good Good
Butyl rubber Good Good
NBR

Particulars Aromatic oil Re-refined oil
 spec. result

Sp. gravity 0.90-1.00 0.86-0.865
VGC region 0.950-0.999 0.810-0.815
C A% 35-50 6.9
C P% 20-35 64.5
C N% 25-40 25.6
Aniline point ([degrees]C) RT 80 110
Flash point ([degrees]C) 180 205-210
Heat loss % 1% max. 0.12
 (150[degrees]C, 3 hrs.)
Heat loss % 1.0 max 0.3
 (120[degrees]C, 72 hrs.)
Compatibility:
Natural rubber Good Good
SBR Good Good
SBS Good Good
Polybutadiene Good Good
EPDM Good Good
Chloroprene rubber Not Good Not Good
Polyisoprene rubber Good Good
Butyl rubber Good Good
NBR Not Good Not Good

Table 2--formulations of engine mount

Ingredients EM 1 EM 2 EM 3 EM 4
 in phr in phr in phr in phr

TSR 20 100 100 70 70
PBR 1220 -- -- 30 30
R7 0.2 0.2 0.2 0.2
VN3 7.2 7.2 7.2 7.2
N 774 24 24 24 24
N 330 30 30 30 --
Elasto 541 20 -- 20 --
Re-refined oil -- 20 -- 20

Table 3--comparison of tensile strength
(kg/[cm.sup.2]) and elongation (%) of napthenic
and re-refined oil compounds, before and
after aging (70[degrees]C, 168 hrs.)

 EM 1 EM 2-NR/ EM 3 EM 4
 NR/ re-refined NR+PBR/ NR+PBRl
 naphthenic oil naphthenic re-refined
 oil (20 phr) oil oil
 (20 phr) (20 phr) (20 phr)

Tensile 225 216 191 201
 strength
 Kg/[cm.sup.2]
Aged tensile 214 201 174 171
 strength,
 168 hours
Elongation % 622 596 570 530
Aged 526 506 540 500
 Eb, 168 h.

Table 5--unaged and aged (70[degrees]C, 168 hrs.)
stiffness (Ks and Kd), N/mm; freq. 0-80 Hz; amplitude
[+ or -] 120.1 mm

 Ks Kd Kd Kd Ks
 (10 Hz) (20 Hz) (80 Hz) 168 h.

E M 1-NR/ 337 425 475 563 276
 Naphthenic oil
 (20 phr)
EM 2-NR/ 358 465 538 626 295
 re-refined
 oil (20 phr)
EM 3 NR+PBR/ 336 429 496 580 309
 naphthenic oil
 (20 phr)
EM 4 333 430 498 571 292
 N R+PBR/
 re-refined
 oil (20 phr)

 Kd (10 Kd (20 Hz, Kd (80 Hz,
 Hz, 168 h.) 168 h.) 168 h.)

E M 1-NR/ 360 421 483
 Naphthenic oil
 (20 phr)
EM 2-NR/ 380 432 474
 re-refined
 oil (20 phr)
EM 3 NR+PBR/ 387 448 500
 naphthenic oil
 (20 phr)
EM 4 377 431 474
 N R+PBR/
 re-refined
 oil (20 phr)

Table 6--engine mount recipes studied
at 30 phr oil level

Ingredients EM 1 EM 2 EM 5 EM 6 EM 7
 in phr in phr in phr in phr in phr

CV 60 100 100 100 100 100
Silica VN3 7.5 7.5 7.5 7.5 7.5
N 774 24 24 24 24 16
N 330 30 30 30 30 40
Elasto 541 20 0 30 0 0
Re-refined oil 0 20 0 30 24
Elasto 710 0 0 0 0 6

Table 7--effect of aging at 70[degrees]C for 0-500
hours on tensile strength (Kg/cm2)

 EM 1 EM 2 EM 5 EM 6 EM 7
 (20 phr (20 phr (30 phr (30 phr (24+6) phr
 N. oil) RR oil) N oil) RR oil) RR+E710

Ts (0 hrs.) 225 216 204 198 212
Ts (168 hrs.) 214 201 198 192 196
Ts (250 hrs.) 190 188 198
Ts (500 hrs.) 185 180 188

Tablee 8--effect of aging at 70[degrees]C for
0-500 hours on elongation (%)

 Eb Eb Eb Eb
 (0 hrs.) (168 hrs.) (250 hrs.) (500 hrs.)

EM 5 (30 phr) 630 545 510 472
 N. oil
EM 6 (RR oil 30 620 535 520 500
 phr)
EM 7 (24+6) 655 585 500 484
 phr RR+E710

Table 9--effect of aging at 70[degrees]C for 0~500
hours on compression set (%)

 Compression set (%) at:

 70 hrs. 168 hrs. 250 hrs. 500 hrs.

EM 5: naphthenic 37 46 53 58
 oil (30 phr)
EM 6: re-refined 37 47 54 59
 oil-30 phr
Em 7: RR + 37 38 47 53
 aromatic
 (24+6 phr)

Table 10--effect of aging at 70[degrees]C @ 25% compression (as
per table table 4), up to 500 hrs., on Ks and Kd (N/mm) of test
buttons(frequency: 10 Hz and amplitude: 1 [+ or -] 0.1 mm)

 Ks Ks Ks Ks
 (0 hr.) 168 hrs. 250 hrs. 500 hrs.

EM1 (20 phr 337 276
 N. oil)
EM2 (20 phr 358 296
 RR oil)
EM 5 (30 phr) 239 190 200 229
 N. oil
EM 6 (RR 246 206 220 233
 oil--30 phr)
EM 7 (24+6) 236 202 193 226
 phr RR+E710

 Kd Kd Kd Kd
 (10 Hz) (10 Hz) (10 Hz) (10 Hz)
 168 hrs. 250 hrs. 500 hrs.

EM1 (20 phr 425 360
 N. oil)
EM2 (20 phr 465 380
 RR oil)
EM 5 (30 phr) 415 338 377 422
 N. oil
EM 6 (RR 431 356 386 441
 oil--30 phr)
EM 7 (24+6) 419 328 362 431
 phr RR+E710

Table 11--change in Kd/Ks ratio with aging
at 70[degrees]C (freq: 10 Hz, amplitude: 1 [+ or -] 0.1 mm)

 10 Hz 10 Hz 10 Hz 10 Hz
 (0 hrs.) (168 hrs.) (250 hrs.) (500 hrs.)

EM 1 (20 phr 1.26 1.3
 N. oil)
EM 2 (20 phr 1.29 1.28
 RR oil)
EM 5 (30 phr) 1.74 1.78 1.88 1.84
 N. oil
EM 6 (RR oil-- 1.75 1.73 1.75 1.89
 30 phr)
Em 7 (24+6) 1.77 1.61 1.87 1.9
 phr RR+E710

Table 12--effect of long term aging at 70[degrees]C,
25% compression (table 4) on damping coef
ficient (N-sec/mm) of test buttons (frequen
cy: 10 Hz and amplitude: 1 [+ or -] 0.1 mm)

 Damping coefficient (10 Hz)

 0 hrs. 70 hrs. 168 hrs. 250 hrs. 500 hrs.

EM 5: nahpthenic 0.68 0.74 0.55 0.51 0.7
 oil (30 phr)
EM 6: re-refined 0.67 0.59 0.597 0.59 0.78
 oil--30 phr
EM 7: 0.88 0.63 0.7 0.64 1
 RR + aromatic
 (24+6 phr)

Table 13--Kd and Ks at (1) initial, (2) aging @ 25% elastic compression
at 70[degrees]C x 7 days and (3) thereafter fatigue at 150 = 300 Kgs x 2
Hz for half and one million cycles

 Kd Kd (7d) Kd (7d+ Kd (7d+
 (initial) creep 500,000c) 1 million)

EM 5 968 856 873 876
 (Naphthenic
 oil--30 phr)
EM 6 988 861 859 870
 (re-refined
 oil--30 phr)
EM 7 997 866 898 882
 (24+6)
 mixed

 Ks, Ks (7d) Ks (7d+ Ks (7d+ 1
 (initial) creep 500,000c) million)

EM 5 565 476 479 433
 (Naphthenic
 oil--30 phr)
EM 6 586 467 446 428
 (re-refined
 oil--30 phr)
EM 7 578 478 477 430
 (24+6)
 mixed

Table 14--damping coefficient (N-sec/mm)
change during aging and fatigue of mounts

 Initial C(7d) C(7d+ C (7d+1
 creep 500,000 million
 cycles) cycles)

EM 5 (naphthenic 4.66 4.5 4.5 4.5
 oil--30 phr)
EM 6 (re-refined 4.7 4.3 4.4 4.52
 oil--30 phr)
EM 7 (mixed) 5.5 5 4.8 4.9
 24+6 phr

Table 15--tan [delta] change during aging and
fatigue of resilient mounts

 Initial C (7d) C (7d+ C (7d+1
 creep 500,000 million
 cycles) cycles)

EM 5 (naphthenic 0.146 0.149 0.138 0.142
 oil--30 phr)
EM6 (re-refined 0.151 0.141 0.146 0.14
 oil--30 phr)
EM7 (mixed) 0.163 0.161 0.172 0.147
 24+6 phr
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Author:Bhattacharya, P.S.; Polymers, Bony
Publication:Rubber World
Date:Nov 1, 2012
Words:3091
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