Effect of recycled dust stop lubricating oil in rubber compounds.
When a tire and tube assembly is mounted on a rim, the flap, which is a cured rubber product, is placed in between the tube and the rim. The flap protects the tube from any damage due to friction against the rim. It also supports the tire bead area to firmly seat with the rim. In the case of tubeless tires, the flap also supports to prevent air leakage from the juncture of the bead and the rim. In order to meet all the above requirements, the flap compound needs good tear resistance, resistance to compression set and retention of high temperature aging properties.
The rubber industry has implemented a considerable number of arrangements to save the raw and other materials of natural origin and to protect the environment. Even then, the production wastes continue to be a serious threat that demands more and more engineering and scientific forces to resolve (ref. 1). Since the disposal of waste materials is a worldwide environmental problem, immense public and political pressure has been raised to recycle waste materials. This has resulted in the evolution of legislation at the local, state and national level. Currently in the global market, the usage level of the recycled material in tires is about 5%. In India, the level is much less and insignificant. The government of India has not yet decided the future usage target level of recycle materials. As per the legal authority in the U.S. and Europe, the goal is to use around 25% of recycle material in an automotive non-tire component and 10% recycled content in tires (ref. 2).
Aromatic oil, which also comes from nature, is a petroleum product containing a higher percentage of aromatics. It is extensively used for carbon black mixing in most of the general purpose unsaturated rubbers (such as natural rubber (NR), polybutadiene rubber (BR) and styrene butadiene rubber (SBR). The tire industry (producing about 190 metric tons of product per day) reports that approximately 30,000 liters of dust stop lubricating oil is liberated from dust stops of the mixers in a year. The handling of such a huge amount of oil is a great problem. Throwing this oil away will cause immense environmental pollution. Since the oil contains metallic impurity, using it, as such, in a rubber compound will cause severe degradation of the rubber product (refs. 3-9).
A number of reports is available regarding the use of tire recycled material, namely reclaim rubbers and crumb rubbers for the development of different rubber compounds (refs. 10-34). However, no such study is so far available regarding the use of the dust stop lubricating oil in a rubber compound. In the present study, the dust stop lubricating oil was collected as a liberated material from the dust stops of an internal mixer from a tire industry shop floor. The information was received from the shop floor that the initial oil used for dust stop lubrication was an aromatic processing oil type. The collected oil was centrifuged and physico-chemical characterization was carried out. The characterization of the centrifuged oil was also carried out in a natural rubber based flap compound.
After collection of the dust stop lubricating oil, it was centrifuged in a laboratory centrifuge machine using 3,000 rpm for 30 minutes. The oil was decanted and characterized for the following parameters:
* The specific gravity of the dust stop oil was determined in accordance with ASTM D1298 using a hydrometer.
* The Saybolt viscosity (SUS) at 100[degrees]C of the oil was determined as per ASTM D88. The flash point and fire point were determined in accordance with ASTM D92. The pour point was determined as per ASTM D1513.
* The aniline point was estimated in accordance with ASTM D611. Clay gel analysis was carried out as per ASTM D2007 in order to determine the percentage of saturates, polar and asphaltene. Fourier transform infrared spectroscopic (FTIR) analysis was carried out in accordance with IS 13155 using an FTIR 2000, in order to determine the aromatic carbon ([C.sub.A]) content.
The ash content of the oil both before and after centrifuging was determined using a muffle furnace. The ash determination was performed using a slow heating rate up to 550[degrees]C until a constant weight was obtained. The analysis of the ash was performed to estimate the metals present in the oil using an atomic absorption spectrophotometer (AAS 3300) in accordance with ASTM D4004.
A side-by-side characterization of a known aromatic oil sample was also performed for all the above tests. The aromatic oil was not centrifuged since it was received from a standard source.
Compound mixing and characterization
The mixing of rubber compounds was carried out using a two-wing rotor laboratory internal mixer of 1.5 liter capacity in two stages (master batch and final batch), and the formulation is given in table 1.
Master batch mixing was done keeping the temperature control unit (TCU) at 90[degrees]C and rotor speed at 60 rpm. First, the natural rubber was masticated along with the peptizer (PCTP) for 30 seconds, followed by the addition of SBR 1502. After about 20 seconds, the black, oil, zinc oxide, stearic acid and the antidegradants (6PPD and TMQ) were added. The ram was scraped in between and the masterbatch was dumped after an attainment of the power integrator (PI) at 0.32 kWh. The dump temperature of the masterbatches was found to be within 140-150[degrees]C. The masterbatches were sheeted out on a laboratory two-roll mill. The masterbatches were further mixed after a maturation period of eight hours.
For final batch mixing, the TCU was kept at 60[degrees]C and rotor speed at 30 rpm. The masterbatch along with the curatives (sulfur, accelerators and scorch inhibitor) were added in the internal mixer, and after an attainment of PI of 0.12 kWh, the batch was dumped. The dump temperature of the batches was maintained within 100 +/- 5[degrees]C. The final batches were also sheeted out on a laboratory two-roll mill.
Rheometric properties were determined at 141[degrees]C over a period of 45 minutes using a 0.5[degrees] arc in a MDR 2000E instrument, in accordance with ASTM D5289. The Mooney viscosity, ML (1+4) at 100[degrees]C and Mooney scorch at 135[degrees]C was determined in a MV 2000E, as per ASTM D1646.
The rubber compounds were cured in accordance with ASTM D 3182 in an electrically heated hydraulic curing press using a compression molding technique. The molding conditions followed to prepare different samples are given in table 2.
The tensile and tear properties were measured using a Zwick UTM 1445 instrument in accordance with ASTM D412 and ASTM D624. The hardness was measured with a dead load IRHD tester in accordance with ASTM D1415. The fatigue to failure properties (FTFT) at 100% extension ratio were measured in a Monsanto FTFT machine as per ASTM D4482. The fatigue life was calculated using the Japanese Industrial Standard (JIS) number average method. DeMattia cut initiation and cut propagation were tested as per ASTM D 430 and ASTM D813 using a DeMattia Flexon tester. The compression set was determined in accordance with ASTM D395.
The tensile specimens were air-aged in a multi-cell aging oven at 100[degrees]C for one, two, three and five days in order to amplify the deterioration of compound properties due to the metals present in the dust seal oil.
The swelling index of the cured and air aged tensile samples was measured using the following formula in accordance with ASTM D3616.
Swelling index = Swollen weight/Initial eight
Results and discussions
The physico-chemical characterization of dust stop oil, as well as the aromatic oil, is shown in tables 3 and 4.
From the data of table 3, it was clear that the dust stop oil has shown similar characteristics to that of the aromatic oil taken as a reference. This also confirms the fact that, even after use in the mixer dust stop and centrifuging, the oil did not change its own characteristics.
It was evident from the table 4 data that the dust stop lubricating oil had higher metal content before it was centrifuged. After the centrifugation, the metal content was reduced to a large extent. The above result also fulfilled the objective of centrifuging the oil.
The rheological properties, including Mooney viscosity and Mooney scorch data, are shown in table 5.
The experimental compound has shown similar rheometric properties to that of the control compound. The Mooney viscosity and Mooney scorch data were also found comparable.
The results of tensile, hardness and swelling index in original, as well as after air aging and tear strength, compression set and FTFT properties are reported in table 6a. The DeMattia cut initiation and cut growth values are reported in table 6b.
The original stress-strain properties, tear strength and FTFT values of both the compounds were found comparable. The compression set and swell index of both compounds was similar, and any deviation in the observed values was within experimental error limit. The retention of properties after aging was also found to be similar. The metals present in the recycled dust stop oil did not have much impact on aging. This may be due to centrifugation of the oil taken in to use.
In the case of the experimental compound, the cut initiation occurred earlier than the control compound; however, the cut growth properties of both compounds were found comparable.
The recent rise in raw material prices, particularly crude oil and its derivatives, and the rising environmental issues have forced the rubber industry, especially the tire industry, to explore the possibilities of using recycled material along with the virgin compound or as a replacement of the virgin material. In the present experiment, the experimental compound showed comparable properties with respect to the control compound. This clearly indicates that the centrifuged dust stop oil can be used as a replacement for the aromatic oil in a flap compound. This will give rise to a substantial cost benefit, as well as the evolution of an environmentally friendly technology.
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Table 1--flap compound formulations (phr) Mix Id. > Control Experimental Ingredients Centrifuged dust stop -- 10 lubricating oil Aromatic oil (RPO 701) 10.0 -- Other ingredients used in the above formulation kept constant were: NR (EBC # 3X)--90.0; SBR 1502--10.0; N330 black--45.0; PCTP (Peptizol 7) - 0.10; zinc oxide--4.0; stearic acid--2.0; 6PPD (Pilflex 13) --0.5; TMQ (Pilnox TDQ)--2.0; P. wax--1.5; CaC[O.sub.3]--10.0; soluble sulfur--2.0; NOBS (Pilcure MOR)--0.50; and PVI 100 (Accitard RE) --0.10. Table 2--molding conditions for test sample preparation Sample Temperature Time Pressure ([degrees]C) (min.) (kg/[cm.sup.2]) Tensile slab having 2.0 mm 141 30 150 thickness Compression set sample 170 7 150 Fatigue to failure test 141 30 150 (FTFT) sample DeMattia fatigue test sample 141 60 150 Table 3--physico-chemical characterization Test parameter Centrifuged Aromatic dust stop oil oil Specific gravity @ 25[degrees]C 0.988 0.993 Saybolt viscosity @ 100[degrees]C 97 105 (SUS) Flash point ([degrees]C) 235 220 Fire point ([degrees]C) 260 245 Pour point ([degrees]C) +16 +14 Aniline point ([degrees]C) 46 45 Clay gel analysis Saturates (%) 15.23 16.12 Polar (%) 19.0 19.23 Asphaltene (%) 0.09 -- Aromatic carbon, [C.sub.A] (%) 37.9 37.4 Table 4--ash content and ash analysis Test parameter Aromatic Dust stop Dust stop oil oil before oil after centrifuging centrifuging Ash content (%) 0.005 0.043 0.007 Copper content (ppm) 2.26 95.98 9.82 Iron content (ppm) 2.69 9.68 1.54 Manganese content (ppm) 0.08 1.03 0.87 Chromium content (ppm) 0.13 Table 5--rheometric properties at 141 [degrees]C/30 min. Sample Minimum Maximum torque, torque, ML, MH, (dN-m) (dN-m) Control 1.55 12.04 Experimental 1.59 11.94 Sample Scorch Optimum time, cure time, [ts.sub.2], [tc.sub.90], (min) (min.) Control 6.97 11.25 Experimental 7.12 11.21 Sample Viscosity Mooney ML (1+4) scorch, Q 100[degrees]C MS at (MU) 135[degrees]C (min.) Control 34 13.39 Experimental 36 14.31 Table 6a--physical properties of compounds Test M100% M300% Parameter (MPa) (MPa) Sample Id. Control--original 1.6 7.4 (1 day/100[degrees]C) (119) (111) (3 days/100[degrees]C) (113) (-) (5 days/100[degrees]C) (126) (-) Experimental-- original 1.5 6.8 (1 day/100[degrees]C) (127) (125) (3 days/100[degrees]C) (113) (-) (5 days/100[degrees]C) (120) (-) Test TS EB Parameter (MPa) (%) Sample Id. Control--original 20.2 555 (1 day/100[degrees]C) (76) (84) (3 days/100[degrees]C) (31) (47) (5 days/100[degrees]C) (16) (30) Experimental-- original 21.7 617 (1 day/100[degrees]C) (83) (82) (3 days/100[degrees]C) (31) (48) (5 days/100[degrees]C) (15) (27) Test Hardness Swell Parameter (IRHD) Index Sample Id. Control--original 56 3.07 (1 day/100[degrees]C) (+5) (105) (3 days/100[degrees]C) (-4) (106) (5 days/100[degrees]C) (-8) (99) Experimental-- original 55 3.14 (1 day/100[degrees]C) (+7) (100) (3 days/100[degrees]C) (-3) (99) (5 days/100[degrees]C) (-8) (94) Test Tear Compression Parameter (Nlmm) set (%) Sample Id. Control--original 62 60.9 (1 day/100[degrees]C) (3 days/100[degrees]C) (5 days/100[degrees]C) Experimental-- original 62 57.9 (1 day/100[degrees]C) (3 days/100[degrees]C) (5 days/100[degrees]C) Test FTFT Parameter (Kc) Sample Id. Control--original 35 (1 day/100[degrees]C) (3 days/100[degrees]C) (5 days/100[degrees]C) Experimental-- original 36 (1 day/100[degrees]C) (3 days/100[degrees]C) (5 days/100[degrees]C) (Note: Results in the parenthesis () are the percentage retention of physical properties after air aging at 100[degrees]C for one, three and five days. In the case of hardness, the '+' values indicate an increase in hardness after aging and '-'. Table 6b--DeMattia cut initiation and cut growth properties Test Cut Parameter initiation After (kc) 5 kc Sample flexing Id. Control 70 3.1 Experimental 60 2.9 Test Crack growth (mm) Parameter After After 10 kc 15 kc Sample flexing flexing Id. Control 4.2 5.0 Experimental 4.9 Test Parameter After After 20 kc 30 kc Sample flexing flexing Id. Control 5.3 7.9 Experimental 5.6 7.9 Test Parameter After After 50 kc 70 kc Sample flexing flexing Id. Control 10.4 11.8 Experimental 9.3 11.5 Test Parameter After 100 kc Sample flexing Id. Control 15.0 Experimental 16.3
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|Title Annotation:||Tech Service|
|Author:||Ameta, Suresh C.|
|Date:||Mar 1, 2006|
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