EPDM Green EPDM Compounds[1] Compounding€¦ · isotridecyl stearate Loxiol G40 EmeryOleo 466 0.86...

ROHSTOFFE UND ANWENDUNGEN RAW MATERIALS AND APPLICATIONS

26 KGK · 01-2 2018 www.kgk-rubberpoint.de

Green bio-based sustainable EPDM Compounding

Keltan® Eco is the world’s first commer-cial EP(D)M rubber partly produced from bio-based feedstock. The ethylene used for this rubber is produced from ethanol, derived from sugar cane. To in-crease the sustainability of EPDM rub-ber products the potential of greener alternatives for traditional plasticiser oils and fillers have been explored. A variety of (trans-esterified) natural oils and fat, factice and squalane has been studied as replacement for traditional, mineral extender oil. Modified natural oils and squalane give the best perfor-mance. Carbon black, obtained from py-rolysis of waste tires, rice husk ash and micro-cellulose have been investigated as replacements for standard fillers. This study has resulted in sulphur-vul-canised, Keltan® Eco EPDM with more than 85% of sustainable ingredients for automotive sealing applications

Grüne EPDM-Gummi-mischungen Grün biobasiert nachwachsend nachhaltig EPDM Compounding

Keltan® Eco ist der erste kommerzielle EP(D)M Kautschuk der Welt, der teilwei-se aus natürlichem Ausgangsmaterial hergestellt wird. Das eingesetzte Ethy-len wird über Ethanol aus Zuckerrohr er-zeugt. Zur Erhöhung der Nachhaltigkeit von EP(D)M-Produkten wurde das Po-tential von grünen Alternativen für tra-ditionelle Weichmacheröle und Füllstof-fe untersucht. Variationen von (trans-veresterten) natürlichen Ölen und Fet-ten, Faktisse und Squalan wurden als Ersatzstoffe für traditionelle minerali-sche Verstreckungsöle eingesetzt. Modi-fizierte natürliche Öle und Squalan erge-ben die besten Eigenschaften. Ruß aus Pyrolyseprozessen von Altreifen, Reis-schaleassche und Microcellulose sind als Ersatzstoffe für Standardfüllstoffe unter-sucht worden. Die Studie hat resultiert in Schwefel-vulkanisierten „Keltan® Eco“-EPDM basierende Compounds mit mehr als 85 % nachhaltigen Komponen-ten für Dichtungsanwendungen.

Figures and Tables:By a kind approval of the authors.

IntroductionThe reduction of greenhouse gas emis-sions and addressing the limited availa-bility of fossil fuels are two great chal-lenges of our generation [2,3]. Keltan® Eco is Arlanxeo’s response to an urgent call to increase the eco-friendliness of synthetic rubber. Keltan Eco is the world’s first commercial EP(D)M rubber, partly produced from bio-based feedstock (Fig-ure 1). The ethylene used in this rubber is produced from ethanol, which in its turn is derived from sugar cane [4,5]. Conse-quently, the carbon footprint of EPDM products is significantly reduced (up to 7 times lower for an EPDM polymer with 70 wt% ethylene) and Keltan Eco is truly sustainable, according to a Life Cycle As-sessment [6]. If all EPDM rubber in auto-motive sealing systems in all cars glob-ally produced today would be made from Keltan Eco, < 3% of the land currently used for sugar cane production for etha-nol in Brazil would be required, which amounts to < 0.04% of all arable land in Brazil. If second generation feedstock technology becomes available, this will be an interesting option to further in-crease land use efficiency. Currently, five different Keltan Eco products are com-mercially available with varying ethylene and ENB contents and Mooney viscosity. These products are identical to regular Keltan EPDM products in terms of techni-cal performance and as such are true technical drop-ins. The 14C content of Keltan Eco EPDM determined via the ASTM D6866 test confirms the bio-origin of the ethylene used.

Typically, rubber products not only consist of elastomer(s), but also of (rein-forcing) filler(s), plasticiser, crosslinking agents and other additives. Actually, EPDM products may easily contain up to 400 phr of compounding ingredients in-corporated into 100 phr of rubber. Car-bon black is produced via the incomplete combustion of a hydrocarbon feed with natural gas. Silica is produced via the precipitation from a silicate salt solution. Inert white fillers, such as clay, talc and chalk are extracted from the ground in open mines and milled to fine powders. Traditional extender oils for EPDM are refinery fractions of crude oil. All of these ingredients typically used for EPDM com-pounding lack sustainability. Numerous studies have been performed on more

sustainable rubber compound ingredi-ents [7,8]. With respect to fillers one may consider all sorts of natural fibers ( jute, palm, sisal, hemp etc.) and natural flours and powders (wood, cork, soy etc.) [9-12] as well as recycle carbon black, produced via pyrolysis of waste tires [13]. The for-mer should be viewed as inert, white fillers which only dilute the compound but do not contribute to the perfor-mance, whereas the latter has a promis-ing performance close to that of tradi-tional carbon black. Natural oils, such as palm oil, rice bran oil, ground nut oil, soybean oil, mustard oil and sunflower oil, have all been explored as green plas-ticiser in rubber products, but with lim-ited success due to the inferior proper-ties of the final compounds [14-21].

In further efforts to increase the sus-tainability of EPDM rubber products based on Keltan Eco, we have explored the tech-nical potential of green alternatives for traditional plasticiser oils and (reinforcing) fillers. The emphasis in this study is on the technical aspects, such as the compound mixing, processing, vulcanisation and properties (after ageing) of the final vul-canisates. There will be no further discus-sions on the level of sustainability nor on the costs of the alternatives ingredients and the final compounds.

In a first screening a variety of bio-based oils has been studied as replace-ments for traditional mineral oil. The na-tural oils studied, e.g. linseed oil, tung (or wood) oil, coconut oil and olive oil, are all triglycerides with fatty acid chains varying in length and unsaturation. These four natural oils were selected, because they provide a nice spread in the level of unsa-turation (as witnessed by the iodine num-ber) and the melting point. Butter fat is a

Green EPDM Compounds[1]

AuthorsMartin van Duin, Philip Hough, Geleen, The Netherlands Corresponding Author: Martin van DuinKeltan R&DARLANXEO Elastomers B.V.P.O. Box 1856160AD Geleen, The NetherlandsE-Mail: [email protected]. +31(0)467020853


27KGK · 01-2 2018www.kgk-rubberpoint.de

triglyceride obtained from cow milk and was included, because it has a rather low iodine number, though a relatively high melting point. Modified natural oils, such as hydrogenated coconut oil (almost no unsaturation) and mono-esters produced via trans-esterification of natural oils, i.e. ethylhexyl oleate (reaction product of high-oleate sunflower oil with ethylhexyl alcohol) and isotridecyl stearate (satura-ted mono-ester), were included in a se-cond phase of the oil screening study to overcome some of the compatibility and vulcanisation issues experienced with the natural oils and butter fat. Factice, which is a highly vulcanised vegetable oil, was originally introduced to the rubber indus-try around 1850 as a partial economic substitute for natural rubber [22,23], but is used today as special processing agent. Factice was tested as a full oil replace-ment, because it consists of highly cross-linked natural oil and, thus, could over-come some of the issues encountered with the natural oils, but was also tested in combination with natural oils with the idea that it could act as a sort of sponge to permit higher loadings of the natural oil. Finally, 2,6,10,15,19,23-hexamethyltetra-cosane (squalane) was evaluated. Squala-ne is a fully saturated C30 hydrocarbon, which resembles an EPM hexamer and is sometimes used as a high-boiling solvent for EPDM in academic studies [24]. Squalane is traditionally obtained via hyd-rogenation of the triterpene squalene from shark liver, but more recently a pro-cess was developed where plant sugar is converted via genetically engineered yeast into trans-β-farnesene [25], which is dimerised and subsequently hydrogena-ted to squalane [26].

In a second screening sustainable fill-ers have been investigated as replace-ments for standard carbon black and in-ert, mineral fillers. Pyrolysis black is eval-uated versus standard furnace black. This pyrolysis black consists of both the origi-nal carbon black, used in the production of tires, and additional black, formed upon pyrolysis of the rubber and plasti-ciser in the end-of-life tire waste. While one can argue that pyrolysis black is not derived from a bio-based source, a pro-portion is in fact derived from natural rubber. In addition, (tire) rubber end-of-life waste is a major environmental issue and pyrolysis seems to be a preferred re-cycling technology, which in the end re-

duces the CO2 production by 5 ton per ton of rubber compound [13]. In the context of this study we choose to use the term sustainable ingredient. Rice husk ash is basically silica, recovered via burning off the organic fraction of rice husk which is obtained during the rice cleaning process [27]. Micro-cellulose is a natural fiber, produced through a process of chemical disintegration of different woods.

In the final study we combined the leads from the first two screening studies and explored EPDM compounds with the highest level of sustainable ingredients, while still maintaining the performance of high-quality EPDM compounds.

Fig. 1: Production of Keltan® Eco EPDM, enabling EPDM rubber products with up to 90% sustainable ingredients.

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1 Characteristics of Keltan® (Eco) EPDM polymers from ARLANXEOKeltan bio-based ethylene (wt%) ENB (wt%) ML 1+4 @ 125°C oil (phr)5470 - 70 4.6 55 06471 - 67 4.7 65 158550 - 55 5.5 80 0

Eco 5470 + 70 4.6 55 0Eco 8550 + 50 5.5 80 0

2 Characteristics of (bio-based) oil plasticisers.chemical composition

product supplier molar mass(g/mol)

density(g/cm3)

melting point(°C)

solubility parameter(J/cm3)0.5

iodine number(g/100 g)

paraphinic mineral oil

Sunpar 2280 Sunoco ~ 700 0.89 15.9 0

refined linseed oil Rutteman ~ 880 0.93 -20 17.2 193Chinese tung oil Rutteman ~ 870 0.94 4 17.2 168

olive oil Albert Heyn ~ 880 0.92 -1 17.2 84butter fat Friesland Campina ~ 840 0.91 36 17.0 34refined coconut oil Rutteman ~ 720 0.92 25 17.2 11hydrogenated coconut oil

Agri-pure AP-620 Cargill ~ 720 0.92 32 17.2 2

isotridecyl stearate Loxiol G40 EmeryOleo 466 0.86 -5 16.6 1ethylhexyl oleate Tudalen TP 130B Hansen+Rosenthal 394 0.87 0 16.6 0.64squalane Neossance Amyris 422 0.81 -38 15.3 0.13factice Rhenopren EPS Rhein Chemie/

LANXESS~ 1.0

5.5%ENB-EPDM Keltan 8550 ARLANXEO 300.000 0.86 15.7 11.6



Experimental

MaterialsFor a brief description and the charac-teristics of the EPDM polymers, the oil plasticisers and the fillers used in this study, see Tables 1, 2 and 3, resp. The details have been provided by the sup-pliers. The solubility parameters of the oils have been calculated using a group contribution method [28]. First, the oil plasticisers were screened in sulphur-vulcanised EPDM compounds with vary-ing oil and carbon black contents (33/50, 33/150, 67/100, 100/50 and 100/150 phr/phr) based on an amor-phous, high Mooney EPDM (Keltan 8550) (Table 4). Next, pyrolysis black was evaluated in a sulfur-vulcanised, automotive, solid seal compound based on a crystalline EPDM (Keltan 5470) (Ta-ble 5). Rice husk ash and micro-cellulose were evaluated in a white bull-eye com-pound based on a 15 phr oil-containing, crystalline EPDM (Keltan 6471) (Table 6). Finally, the best leads for bio-based plasticisers and sustainable fillers from the two screening studies were com-bined in two highly filled, automotive, solid seal compounds (Table 7). The first has low-temperature flexibility for dy-namic sealing applications and, thus, is based on an amorphous, high Mooney EPDM (Keltan [Eco] 8550). The second is typical of a static seal, where low-tem-perature flexibility is not required and, thus, is based on a crystalline, medium Mooney EPDM (Keltan [Eco] 5470). All sulphur accelerators were from the Rhe-nogran family, supplied by Lanxess Rhein Chemie Additives, and the TMQ and ZMMBI heat stabilisers were from

the Vulkanox family, supplied by Lanxess Advanced Industrial Intermediates.

CompoundingThe rubber compounds have been pre-pared on an internal mixer (1.5 liter) from Harburg & Freudenberger. The mix-er is equipped with PES5 rotors with a thermostatically temperature-controlled body using circulating water. Mixing was carried out according to ISO 2393 follow-ing an upside-down mixing protocol with 72% fill factor, 45 °C mixer body temperature, 8 bar ram pressure and 50 rpm rotor speed. In the first 30 sec. the rubber polymer was crumbled; next the compounding ingredients with the ex-ception of the curatives were added and mixed for 210 sec., giving a total mixing time of 240 sec. Thereafter, the vulcani-sation system was added on a tempered two-roll mill (20 cm diameter, 50°C and 20 rpm speed) and final dispersion was accomplished by cutting, rolling up and rotating the rolled rubber sheet by 90° through the mill nip three times, respec-tively. For the comparison of the alterna-tive, white fillers with silica, the starting mixer body temperature was 70 or 130 °C. After mixing for 240 sec. the rotor speed was increased to achieve a batch temperature of 150 °C and then mixing was continued for 180 sec. at 150 °C to complete silanisation.

TestingThe compound Mooney viscosity (1+4) was measured at 100 °C (ML) (DIN 53523 part 3) and the Mooney scorch character-istics, such as t2 at 125 °C (DIN 53523 part 4) were measured on a Monsanto MDR 2000E Rheometer. The cure charac-

teristics of the compounds, such as scorch time ts2, vulcanisation time tc90 and maximum torque difference ∆S = MH – ML were determined with a Mon-santo MDR 2000E Rheometer at 180 °C (DIN 53529 part 3).

Test plates (2 and 6 mm thick) were compression moulded at 180 bar and 180 °C. The 2 mm test plates used for tensile and tear measurements were ob-tained after curing for tc90 plus 10%, whereas the 6 mm press plates, used for hardness and compression set measure-ments, were cured for tc90 plus 25%. Evaluation of the cured compounds fo-cused on the following properties: hard-ness Shore A or IRHD (DIN 53505), tensile properties, such as tensile strength (TS), elongation at break (eab) and modulus at 100 (M100%) and 300% elongation (M300%) using a dumbbell #2 (DIN 53504), tear resistance Delft (tear) (ISO 34) and compression set (CS) for 24 or 72 hours at -25 °C, 23 °C, 70 °C, 100 °C and/or 125 °C (DIN ISO 7743). Hardness, tensile properties and tear resistance were also measured at room tempera-ture after hot-air ageing for 7 days at 70, 100 and/or 125 °C or for 7 and 14 days at 135 °C (DIN 53508). Oil volume swell was determined for IRM901 and 903 oils for 48 hours at 70 °C (DIN 53521). All test specimens were prepared according to DIN ISO 23529 and data evaluation was done in accordance with DIN 53598.

The level of oil bleeding of the sam-ples was estimated by manually touch-ing the surface of the samples and sub-jectively ranking the surface feel after storing samples of unvulcanised, milled compounds for 1 week and test sheets, compression moulded at 180 °C for 4

3 Characteristics of (sustainable) fillers.chemical composition

product supplier particle/fibre size (µm)

surface area

density (g/cm3)

comments

carbon black Corax N550 Orion Engineered Carbons 0.039-0.055 40 1) 1.8 Fast Extrusion Furnace (FEF) black

carbon black BBC 500 Black Bear 0.005 - 0.1 77 1) 1.75 pyrolysis products of waste tires; also contains 5% ZnO/S and 1-27% silica

aluminosilicate Polestar 200R Imerys Performance Minerals ~ 2 8.5 2) 2.6 soft calcined clay

silica Ultrasil VN 3 Evonik Industries ~ 0.015 180 1) 2 precipitated silicacalcium carbonate Superfine S whiting ~ 2 2.8 2) 2.7 superfine calcium

carbonate amorphous silica Silica Verde do Arroz (formerly

Geradora de Energia Eletrica Alegrete)



Fig. 2: Bleeding of oil from samples with varying (bio-based) oil types and oil/black com-positions: top: milled sheets of unvulcanised compounds and bottom: vulcanised com-pounds, assessed after one and four weeks, resp., of storage at room temperature (subjec-tive ranking on a scale of 5: no oil bleeding; 4: surface slightly slippery: 3: greasy surface; 2: grease transfers to finger tips; 1: oil deposited in trays).

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weeks, at room temperature in alu-minum trays. Samples were ranked on a scale of 5 (no oil bleeding), 4 (surface slightly slippery), 3 (greasy surface), 2 (grease transfers to finger tips) and 1 (oil deposited in trays).

Results and discussion

Bio-based oilsThe results of the screening study for re-placing mineral oil by bio-based oils in EPDM compounds (Table 4) will not be presented or discussed in detail. They will be presented in terms of general trends and issues that were encountered, focusing on lack of compatibility and re-duced vulcanisation. A type of go/no-go elimination approach will be followed, eventually resulting in a selection of bio-based oils that seem to offer a feasible, technical alternative for mineral oil.

CompoundingIn the screening study of bio-based oils to replace mineral oil, compounds with varying oil/black ratios were evaluated (Table 4). All compounds based on bio-based oils with 33/50, 33/150, 67/100 and 100/150 (phr/phr) oil/black compo-sitions could be mixed well with mixing characteristics quite similar to the min-eral oil references. The compounds based on butter fat smelled like French fries, which could be considered objectiona-ble. However, mixing of the 100/50 (phr/phr) compounds based on the natural oils, i.e. linseed oil, tung oil, coconut oil and olive oil, and butter fat showed low power development and required very long mixing times compared to the min-eral oil reference. The resulting com-pounds appeared to be of relatively poor quality with varying degrees of sticki-ness/greasiness and a lack of coherence, probably because there was too little carbon black filler compared to the high level of relatively polar natural oils. The more polar, natural oils and butter fat have a lower compatibility with the apo-lar EPDM (compare solubility parameters in Table 2), which makes them quite sen-sitive for these kind of mixing issues. These incoherent/sticky 100/50 (phr/phr) oil/filler compounds can obviously not be used for practical purposes.

The Mooney viscosities (ML) of the compounds with natural oils and butter fat were quite similar to those with equi-valent levels of mineral oil, ranging bet-ween 35 and 75 MU, though mineral oil usually gave the highest compound ML.

The compound ML correlates quite nicely with the reciprocal of the oil/black ratio, as expected. ML of all the compounds with 33 phr oil and 150 phr black, inclu-ding that based on mineral oil, was ext-remely high (>150 MU), due to the very low oil/filler ratio, preventing any practi-cal application. The ML values of com-pounds with factice fully replacing mine-ral oil were also very high (>100 MU). Particularly, factice levels of 67 and 100 phr in combination with 100 and 150 phr

carbon black resulted in extremely vis-cous compounds, for which compound ML could no longer be measured. This is because factice behaves like an elastic solid rather than a liquid plasticiser. Using factice as a 50/50 (w/w) mixture with butter fat resulted in a reduction of the compound ML. However, only in the presence of 50 phr carbon black accepta-ble values of compound ML (< 100 MU) are obtained. The ML values of com-pounds with factice/butter fat having 67 and 100 phr carbon black were still too high. In summary, factice can not be used in large quantities in these natural oil containing compounds. The ML results of the compounds where isotridecyl steare-ate, ethylhexyl oleate and squalane were used, are typically ~20 MU below that of mineral oil, probably because these three bio-based oils have much lower molecu-lar weight than mineral oil (Table 2: ~400 vs. ~700 g/mol).

Compression moulded plaques of the EPDM compounds with 33/50, 67/100 and 100/150 (phr/phr) oil/filler based on isotridecyl stearate, ethylhexyl oleate and squalane felt completely dry, show-ing no signs of bleeding after storage for 1 week at room-temperature (5 on the scale of 1 to 5), and were comparable to

4 EPDM compound compositions with varying oil and black contents used for screening of the bio-based oils.K8550 EPDM 100N550 carbon black 50/50/100/150/150bio-based or mineral oil

33/100/67/33/100

TMQ 1ZMMBI 1ZnO active 5stearic acid 1sulfur-80 1.25MBTS-80 1.31ZBEC-70 0.7ZDBP-50 3.5Vulkalent E/C 0.5total 198/265/282/298/365



the respective reference compounds based on mineral oil (Figure 2: top). The compounds based on linseed oil, coconut oil and hydrogenated coconut oil with 33/50 and 67/100 (phr/phr) composi-tions were also dry, but the 100/150 (phr/phr) compositions showed slight greasiness when touched by fingers, achieving a rating of 4.5 on the scale of 1 to 5. For butter fat, only the 33/50 (phr/phr) compound was dry; the other butter fat compounds were greasy (2 and 3 on the 1 to 5 scale). Obviously, the occur-rence of bleeding of the natural oils and butter fat out of the compounds, espe-cially at high oil levels (100 phr), is the result of a lack of compatibility of the polar oils for the apolar EPDM. Combina-tions of factice with butter fat (50/50 w/w) and with hydrogenated coconut oil (33/67 w/w) did not prevent the blee-ding of the oil out off the compounds.

In summary, the more polar nature of the natural oils and butter fat compared to the apolar EPDM, as witnessed by the relatively high solubility parameters (Ta-ble 2: 17.0 – 17.2 vs. 15.7 {J/cm3}0.5), leads to reduced compatibility, resulting in poor compound quality and bleeding of the oil out of the compounds. This is es-pecially the case in those compounds with high oil/black ratios. For butter fat

there seems to be an extra effect related to its melting point being above room temperature. The use of factice results in very high compound viscosities (ML) and, when used in combination with natural oils, does not reduce the bleeding. The good compatibility of isotridecyl stea-rate, ethylhexyl oleate and squalane is because these oils have somewhat lower polarities more close to that of EPDM, as witnessed by their solubility parameters (Table 2: 16.6, 16.6 and 15.3, resp. vs. 15.7 {J/cm3}0.5).

VulcanisationRheometry of the EPDM compounds showed that the various natural oils and butter fat have a detrimental effect on the vulcanisation compared to the min-eral oil references (Figure 3). For a given compound composition the rheometer torque difference ∆S (= MH-ML) decreas-es in the order: mineral oil > coconut oil >> butter fat > tung oil >> olive oil > lin-seed oil. ∆S also decreases with increas-ing levels of natural oil or butter fat. The compounds with hydrogenated coconut oil, isotridecyl stearate, ethylhexyl oleate and squalane have rather similar ∆S val-ues as the mineral oil reference com-pounds. The presence of high levels of unsaturation in the bio-based oils easily

explains these results. Natural oils and fats are triglycerides of C12 – C18 fatty acids, both saturated (stearic, palmitic, myristic and lauric acid) and unsaturated (mono-unsaturated: oleic and palmit-oleic acid; di-unsaturated: linoleic acid; tri-unsaturated: linolenic and eleostearic acid). The unsaturation in these oils will compete with the EPDM unsaturation for sulphur vulcanisation, resulting in a de-crease of the rubber vulcanisation effi-ciency. Indeed, the rheometer ∆S se-quence observed parallels the level of unsaturation of the natural oils, as wit-nessed by their iodine numbers: mineral oil < coconut oil < butter fat < olive oil < tung oil < linseed oil (Table 2), with the exception of tung oil, as will be explained below. Obviously, higher levels of natural oil will also result in more competition for sulphur vulcanisation. Hydrogenated coconut oil, isotridecyl stearate, ethyl-hexyl oleate and squalane are virtually without unsaturation (Table 2) and, therefore, do not compete with EPDM for sulphur vulcanisation, resulting in ∆S values comparable to the mineral oil ref-erences. The rheometer scorch times ts2 follow the same trend as ∆S, both as a function of the oil type and oil content, probably for the same reasons. In view of the previous discussion it is difficult to explain why the rheometer vulcanisation time tc90 decreases in the series olive oil > butter fat > mineral oil > linseed oil > tung oil ~ coconut oil.

Figure 4 shows a plot comparing the experimental, normalised rheometer ∆S versus the calculated, normalised ∆S. The experimental, normalised ∆S is defined as ∆S of an EPDM compound with a par-ticular natural oil, divided by ∆S of the corresponding compound with mineral oil and ranges from zero (no vulcanisati-on of compound with natural oil) to unity (vulcanisation identical to mineral oil re-ference). The calculated, normalised ∆S is calculated as the molar ratio of the unsa-turation in EPDM vs. the total amount of unsaturation in both EPDM and the oil, and, therefore, combines the effects of the level of unsaturation in the oil and the amount of oil used in the compound. This parameter also ranges from zero (infinite unsaturation in oil and/or infini-te amount of oil) to unity (no unsaturati-on in oil and/or no unsaturated oil). The data in Figure 4 show an excellent, linear correlation with a slope close to unity with the exception of the tung oil data. This shows that the decrease in the rheo-meter ∆S for the natural oil based com-

Fig. 4: Experi-mental, norma-lised rheometer torque difference ∆S of EPDM compounds with varying oil types and varying oil/black levels ver-sus calculated, normalised ∆S.

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Fig. 3: Overlay of MDR 2000E rheometer cur-ves at 180 °C for sulphur vulcani-sation of 33/50 (phr/phr) oil/black EPDM compounds with varying oil plas-ticisers.

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Fig. 5: Plots of some physical properties (top left: modulus at 300% elongation; top right: tensile strength; bottom left: compression set at 125°C and bottom right: oil swell in IRM 901 oil at 70°C) versus crosslink density (rheometer ∆S) for compounds with varying (bio-based) oil/carbon black compositions (33/50, 33/150, 67/100, 100/50 and 100/150 phr/phr); lines are just to guide the eye.

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pounds is fully explained by the competi-tion for sulphur vulcanisation with EPDM and that the unsaturation in the natural oils has the same molar reactivity to-wards sulphur vulcanisation as ENB in EPDM rubber. The tung oil exception is probably related to the fact that tung oil consists for ~80% of oleostearic acid, which is a conjugated triene, whereas the unsaturated fatty acids in the other natu-ral oils and butter fat are monoenes (oleic and palmitoleic acid), non-conjugated diene (linoleic acid) or non-conjugated triene (linolenic acid). Assuming a 30% efficiency for tung oil brings the tung oil data in Figure 4 to the same line as for the other (bio-based) oils.

Unfortunately, vulcanised plaques of the compounds with natural oils, hydro-genated coconut oil and mixtures of fac-tice with natural oils showed much more bleeding after storage for 4 weeks at room temperature than the correspond-ing unvulcanised compounds (Figure 2: compare top with bottom). Bleeding was especially high for the compounds with low carbon black levels, because of insuf-ficient porous black to absorb all the natural oil. Of the 33/50 (phr/phr) natu-ral oil/black compounds only the butter fat sample was considered to be just ac-ceptable (4.5 on scale from 1 to 5). All 67/100 (phr/phr) vulcanisates with natu-ral oils were (very) greasy (2 to 4) and of the 100/150 (phr/phr) vulcanisates only the linseed oil and tung oil samples

showed no bleeding. Again bleeding is the result of poor compatibility between the apolar ERPDM rubber and the rela-tively polar, natural oils. There seems to be no clear explanation for the differenc-es in bleeding between the various natu-ral oils; in addition there seems to be no correlation with the crosslink density. The vulcanisates with mineral oil and squalane were completely dry (5 on the 1 to 5 scale). For ethylhexyl oleate a dry sample was obtained for the 33/50 (phr/phr) composition and slightly greasy samples for the 67/100 and 100/150 (phr/phr) compositions (5 and 4.5 ratings, resp.). For isotridecyl stearate dry vulcani-sates were obtained for the 33/50 and 67/100 (phr/phr) compounds. These im-provements in compatibility are related to the smaller mismatch in polarity

In summary, the unsaturation present in natural oils competes with EPDM for sulphur vulcanisation. Higher levels of unsaturation in the oil and and higher levels of unsaturated oil result in lower crosslink densities. Because squalane, isotridecyl stearate, ethylhexyl oleate and hydrogenated coconut oil have very low levels of unsaturation, the com-pounds based on these oils have crosslink densities very close to the mineral oil references. It could be argued that sul-phur vulcanisation might reduce bleed-ing of polar oils out off the EPDM com-pounds by linking the unsaturated oil molecules to the rubber network. How-

ever, calculations on a molar basis show that, although the level of unsaturation in the natural oils is sufficiently high to compete with EPDM for sulphur vulcani-sation, the fraction of the relatively small oil molecules thus linked to the network is negligible. Indeed, extractions with tetrahydrofuran for 2 days at room tem-perature performed on the 33/50 (phr/phr) oil/black vulcanisates yielded resi-due weights for the natural oil com-pounds (80 – 83%), which were similar within experimental error to the mineral oil reference (80%) and also to the theo-retical residue weight (81%). Only for linseed oil a much lower residue weight was determined (63%), which shows that the EPDM in the compound with the natural oil with the highest unsaturation level was so poorly crosslinked that it partly dissolved.

Properties (after ageing)In general, excellent correlations were found between the physical properties of the vulcanised compounds before ageing and the rheometer ∆S as a measure for the crosslink density, which are in full agreement with trends commonly ob-served in rubber chemistry and technol-ogy studies [23, 29, 30]. Some illustrative examples are shown in Figure 5. For vul-canisates with a given oil/carbon black composition but with varying oil type, the hardness and the moduli at 100 and 300% increase with the rheometer ∆S,



whereas the elongation at break (eab), the compression sets (CS) at 70, 100 and 125°C and the volume swell in IRM 901 and 903 oils decrease with the rheometer ∆S typically in the sequence of linseed oil < olive oil < tung oil < butter fat < coconut oil < hydrogenated coconut oil ~ isotride-cyl stearate ~ ethylhexyl oleate < squalane < mineral oil. For the 33/150 (phr/phr) oil/black vulcanisates the tensile strength (TS) increases with ∆S. For the 33/50 (phr/phr) oil/black vulcanisates TS goes through a maximum versus ∆S. For the other compound compositions TS shows signs of peaking at a higher ∆S. The tear resistance (tear) shows an optimum vs. ∆S for all compositions. CS at -25°C is an exception as it hardly correlates with ∆S. It is close to 100% for the compounds based on the natural oils. For the refer-ence mineral oil compounds values below 70% are observed. Solidification of the oils at -25°C is the most probable expla-nation (cf. melting points in Table 2). In-deed, a DSC experiment showed that the 33/50 (phr/phr) butter fat compound dis-played an extra melting point at +6 °C as well as the typical EPDM glass transition temperature at -59°C. In summary, all physical properties correlate with the rheometer ∆S as a measure for crosslink density in a well-known and expected way, and, thus, correlate with the levels of unsaturation in the (bio-based) oils as discussed in the previous section.

For a given oil the physical properties are usually found to correlate with the oil and carbon black levels (compare various lines in Figure 5), again in a way that is commonly observed in rubber technolo-gy studies [23,29,30]. Higher oil levels result in lower hardness, moduli and TS and in higher eab, CS at various test tem-peratures and oil swell. It is noted that the unsaturated bio-based oils not only act as plasticisers, but also reduce the crosslink density. Therefore, for a given

oil type the level used affects the me-chanical properties in two ways, by coin-cidence in a parallel fashion. Higher lev-els of carbon black result in higher hard-ness, moduli, TS and tear, in somewhat higher CS at various temperatures and in lower oil swells. For some reasons the correlations between oil content and tear resistance and between carbon black content and eab (not shown) are not easy to explain.

In a small side study with the 33/50 (phr/phr) butter fat/black compound at-tempts were made to compensate for the decrease of the crosslink density, due to the competition for sulphur between EPDM and the unsaturated, bio-based oils. Countermeasures included increas-ing the ENB content of the EPDM from 5.5 to 9.0 wt%, increasing the sulphur content in the compound from 1.25 to 2.5 phr and increasing the amount of the sulphur curative package, i.e. doubling the amount of sulphur plus accelerators. Each measure resulted indeed in an in-creased crosslink density, as witnessed by the higher rheometer torque difference ∆S, and in corresponding improvements of the physical properties with higher TS, lower high-temperature CS’s and lower oil swells. Although these measures did result in the desired changes, the abso-lute effects were too small to be useful, since the final vulcanisate properties did not reach those of the mineral oil refer-ence compound. However, combining an increase of the ENB content from 5.5 to 9.0 wt% with either increasing just the sulphur content or doubling the sulphur curative package did result in a butter fat compound with properties quite similar to those of the mineral oil reference. Only CS at -25°C could not be repaired by these (combined) measures, which confirms that the low-temperature CS of these EPDM compounds is not only limited by the crosslink density, but also by the so-

lidification of the bio-based plasticisers (see above).

The effects of the type and the amount of bio-based oils on the vulcani-sate properties are fully explained in terms of their effects on the crosslink density and, thus, are not that exciting. Even the beneficial effects of increasing the ENB content of the EPDM and/or adding more sulphur (and accelerators) on the vulcanisate properties are simply the result of increased crosslink density. Some properties after ageing show a dif-ferent behavior though and, especially, the tensile and tear strengths results af-ter ageing are actually quite confusing on first sight. The properties of the min-eral oil reference vulcanisates change upon ageing and change more with harsher ageing conditions (original un-aged → 70°C → 100°C → 125°C), leading to a higher hardness and higher modulus at 100% and a lower TS, eab and tear. The compounds based on (hydrogenated) co-conut oil, isotridecyl stearate, ethylhexyl oleate and squalane show similar trends, but not as strong. The compounds based on squalane have properties after ageing that are closest to the mineral oil refer-ence. Interestingly, for the squalane com-pounds the hardness change upon age-ing decreases with increasing ageing temperature, showing virtually no hard-ness change at 125°C. Surprisingly, TS and tear of the olive oil vulcanisates ac-tually increase upon ageing. TS and tear of the aged vulcanisates based on butter fat and tung oil seem only to show some scatter around the starting values of the non-aged samples, almost suggesting some sort of heat stabilising effect of these two bio-based plasticisers.

These seemingly confusing ageing re-sults for TS and tear can be rationalised again in terms of the crosslink density. Obviously, the rheometer torque differ-ence can not be used as a measure for the crosslink density of aged vulcani-sates, so the modulus at 100% elonga-tion (M100%) is used for that purpose. Figure 6 shows a plot of TS versus the corresponding M100% for the 33/50 (phr/phr) oil/black vulcanisates both be-fore and after ageing at various condi-tions. All data fall on one curve with the exception of the tung oil data, which is probably again explained by the high content of oleostearic acid (see previous section). Such a maximum of TS vs. crosslink density is well-known from oth-er rubber technology studies [29 and 30] and is explained by a balance between

Fig. 6: Plot of tensile strength versus modulus at 100% elonga-tion as measure for crosslink den-sity for 33/50 (phr/phr) oil/black vulcanisa-tes before and after ageing for 1 week at 70, 100 and 125°C.

6



5 Automotive, solid seal EPDM compound composition used for evaluating pyrolysis carbon black versus standard furnace black.compound formulation FEF black pyrolysis blackKeltan Eco 5470 EPDM 100 100N550 carbon black 120BBC 500 carbon black 135

Superfine S whiting 85 85Flexon 876 paraffinic oil 80 80PEG 4000 2 2CaO-80 10 10ZnO active 5 5stearic acid 1 1sulfur-80 1,8 1,8CBS-80 2,1 2,1TMTD-80 0,5 0,5ZDMC-80 1,2 1,2ZDBC-80 2,5 2,5total 411,1 426,1MDR rheometry @ 180°CML (dNm) 1,1 1,6MH-ML = ∆S (dNm) 18 17ts2 (min) 0,6 0,7tc90 (min) 1,7 3,7vulcanisate propertieshardness (IRHD) 68 68modulus @ 100% (MPa) 2,8 2,0modulus @ 300% (MPa) 8 6tensile strength (MPa) 11 10elongation at break (%) 440 501rebound resilience (Schob) (%) 35 34compression set 24 hr @ 100°C (%) 63 59after ageing for 168 hr @ 100°Chardness (IRHD) 78 78modulus @ 100% (MPa) 6,8 5,4tensile strength (MPa) 11 11elongation at break (%) 183 207

an increased number of network chains that are bearing the stress vs. the net-work chains becoming less extensible and, thus, more prone to rupture. The observation that for all compounds the hardness and the moduli increase and eab decreases upon ageing, indicates that ageing results in continued crosslinking of the EPDM rubber. Proba-bly, desulphuration of the labile, longer sulphur crosslinks exerts sulphur, which is used for further vulcanisation. For the mineral oil vulcanisate an increase in crosslink density due to ageing results in a decrease of TS (right flank of TS curve in Figure 6). For the coconut oil and butter fat vulcanisates TS increases and then decreases upon ageing (around maxi-mum of TS vs. M100% curve). Finally, for the olive oil compound increased crosslinking due to ageing results in a TS increase (left flank of TS curve). Plots similar to that in Figure 6 have been con-structed for the tear strength of the 33/50 (phr/phr) oil/black compositions and for TS and tear of the other com-pound compositions. These findings sug-gest a new way of producing (EPDM) rubber products with optimum heat age-ing resistance. By on purpose slightly under-curing a compound, vulcanisates with a somewhat sub-optimum TS are obtained ( just on left side of TS optimum in Figure 6). Upon heat ageing further crosslinking occurs, which results in a small increase of TS and upon further ageing in a small decrease of TS (passing TS maximum). Overall, such a sub-opti-mum vulcanised EPDM product will show rather good TS retention upon age-ing. Obviously, sub-optimum vulcanisa-tion of the original compound is not beneficial for the elasticity and oil resist-ance. As usually, one has to find the best balance in properties for the particular EPDM application.

In summary, the properties of the EPDM vulcanisates with (bio-based) oils simply follow correlations with the crosslink density as known from rubber textbooks, which in its turn is deter-mined by the competition for sulphur vulcanisation between EPDM and the unsaturated oils as shown in the previ-ous section. As a result, increasing the EPDM ENB content and the amount of sulphur (and accelerators) provides an easy way to compensate for the loss in crosslink density and, thus, to “repair” the vulcanisate properties. Plots have been constructed showing that the changes of TS and tear upon ageing are

related to the changes in the crosslink density, as a result of continued crosslink-ing upon ageing.

Sustainable fillers

Black fillersOur first study with respect to alterna-tive fillers was to replace the standard FEF N550 carbon black by pyrolysis black in an automotive, solid seal formulation. Previous compound studies have shown differences in the reinforcement behav-ior, because of the somewhat lower sur-face area and structure of the pyrolysis black compared to N550 [13]. Therefore, the pyrolysis black level was chosen as 12.5% higher than the N550 level (Table 5). The rheometer data show that the scorch time ts2 and the final state of cure ∆S are quite comparable, but that the compound with pyrolysis black shows a

longer vulcanisation time tc90. This is a known phenomenon of the use of pyrol-ysis black, probably due to the fact that pyrolysis black not only consists of car-bon black, but also contains around 5 wt% of zinc oxide and zinc sulfide (Table 3). The presence of zinc oxide/sulfide is obviously related to the presence of zinc oxide and other zinc salts, like zinc soaps and accelerators, in the original tire com-position. In principle, some of the addi-tional ZnO could be left out from the EP-DM compound formulation. Compared to other commercially available pyrolysis blacks the particular pyrolysis black used in this study actually shows a rather lim-ited increase of tc90. For the same rea-son pyrolysis black also contains silica from the original tire formulation, the level varying with the tire type used as raw material for the pyrolysis process. As an aside, it is worth noting that the Pol-



yAromatic Hydrocarbon (PAH) content of the pyrolysis black used is below the de-tection limit, whereas for furnace blacks PAH levels are detectable. The data in Table 5 indicate that all the physical properties before and after ageing and the elastic properties of the vulcanisates are similar when the pyrolysis black con-tent is increased by 12.5%. The overall conclusion is that pyrolysis black can be considered as a technical alternative for medium reinforcing furnace blacks.

White fillersA white bull-eye EPDM compound with silica and clay as white fillers in presence of silica coupling agent was used to eval-uate the performance of rice husk ash and micro-cellulose as bio-based fillers with the idea to replace the reinforcing silica (Table 6). The compound Mooney viscosity (ML) of the first silica control compound, mixed with a starting mixer body temperature of 70°C, is rather low. This is probably due to polymer degrada-tion, since it took an excessively long time (around 17 min.) to reach a batch tem-perature of 150°C, which is required to reach completion of the silanisation reac-tion. Therefore, all additional experi-ments were performed with a starting body temperature of 130°C, which gave reasonably reproducible results for the silica control compounds. Nevertheless, for both the rice husk ash and micro-cel-lulose compounds lower compound ML were measured, suggesting a lack of cou-pling of these fillers to the rubber. The addition of maleated EPM to the micro-cellulose compound resulted in a com-pound ML which is comparable to that of the silica reference, suggesting an im-proved coupling of the cellulose fibers to the EPDM rubber matrix. The rheometer data show that the vulcanisation kinetics of the compounds with the bio-based, white fillers are comparable to those of the silica reference compound (similar ts2 and tc90 values). The ∆S values of the bio-based filler compounds are significantly smaller than that of the silica compound though. This probably does not reflect a lower state of cure for the former, but a lack of reinforcement, since the hardness, TS, eab and tear of all the compounds with bio-based, white fillers are (much) lower, compared to the silica reference. Comparing the physical properties of the compounds with the bio-based, white fillers shows that rice husk ash actually yields the poorest performance. The two micro-cellulose grades show similar prop-

erties. The addition of maleated EPM to the micro-cellulose compound results in improved eab and tear, which is probably due to better dispersion/coupling of the cellulose fibers. The properties after age-ing are quite similar for all white fillers, when expressed as relative changes (data not shown), with micro-cellulose Arbocel UFC M8 being a positive exception (low-est relative change in tensile properties upon ageing). The CS values at 23 and 70°C are comparable for all fillers, but CS at 100 °C is the lowest for the silica con-trol and one of the micro-cellulose sam-ples. The overall conclusion of this limited screening of some bio-based, white fillers is that they do not have the reinforcing properties of silica. Indeed, a similar per-formance has been observed in other studies on bio-based fillers in rubber compounds [9-12], although rice husk ash seems to be finding applications in tire treads [31]. This disappointing result is probably due to a lower surface area/structure of the bio-based fillers com-bined with a lack of reactivity to silane coupling. Still, these bio-based, white fillers will be used as green alternatives for inert white fillers in the final study on compounds with maximised sustainabil-ity content as presented in the final sec-tion.

Maximising content of sustainable ingredientsIn this study the best options from the screening studies in the previous sec-tions were combined in a final effort to maximise the content of sustainable in-gredients in EPDM compounds. Two highly filled, automotive, solid seal EP-DM compounds have been used for that purpose. The first compound has low-temperature flexibility for dynamic sealing applications and, thus, is based on an amorphous EPDM (Table 7). The second compound is typical of a static seal, where low-temperature flexibility is not required and, thus, is based on a crys-talline EPDM. It is noted that these two automotive, sealing compounds are mo-re highly filled than typically practiced in industry to maximise the sustainable content of the compounds. Squalane is used as plasticiser, replacing the mineral oil. As in the previous section the content of pyrolysis carbon black was chosen 12.5% higher than the corresponding furnace N550 black content. Rice husk ash was used as an inert filler (see previ-ous section), replacing the calcium car-bonate whiting. The total amount of

green ingredients, viz. the sum of the bio-based part of the Keltan Eco EPDM rubber, the green oil and the white filler plus the sustainable black filler (Table 7) amounts to 86% for the dynamic, auto-motive seal and as high as 90% for the static, automotive seal, due to the higher weight content of sugar-cane-derived ethylene in the crystalline EPDM used in the latter compound. Table 7 shows that the compound ML of both sustainable compounds are significantly below those of the reference compounds by about 10 MU, which is due to the lower molecular weight of squalane, as discussed above. The Garvey strip extrusion results show that the extruder throughput of the sus-tainable compounds is comparable to those of the reference compounds, but the head pressure is much lower for the former. As a result, the extruder through-put normalised to the pressure is signifi-cantly higher for the sustainable com-pounds, which is in agreement with the lower compound ML. The total score for edge, corner and surface for the Garvey die ranking is the maximum of 12 for all extruded strips, showing excellent pro-cessing also for the sustainable com-pounds with squalane, pyrolysis black and rice husk ash. The scorch sensitivity of the sustainable compounds is substantially less than that of the reference com-pounds, as witnessed by the much longer Mooney scorch time ts5. The rheometer ts2 value of both sustainable compounds are similar to those of the reference com-pounds. The same now holds for tc90 val-ues, which is not consistent with the longer tc90 values presented in the previ-ous section. The rheometer torque differ-ence ∆S of the sustainable compounds is comparable to those of the reference compounds, which explains why hard-ness, eab and CS at 23 and 70°C are also comparable. Interestingly, the CS at -25°C of the dynamic automotive seal based on the amorphous EPDM with squalane as plasticiser is much better than that of the paraffinic oil reference (42 vs. 71%). This is because squalane has a much lower glass transition temperature com-pared to mineral oil (-105 vs. around -70°C) and, thus, is a superior plasticiser at (very) low temperatures. The tensile and tear strengths and CS at 100°C of the sustainable compounds are somewhat inferior. The test results after ageing of the sustainable compounds are clearly inferior to those of the reference com-pounds. This is fully accountable to the use of squalane as bio-based oil, since



the weight loss of the sustainable com-pounds upon ageing for 168 hr @ 135°C is similar to the original squalane content (19.2 versus 20.2 wt% and 20.2 versus 20.9 wt% for the dynamic and static seal compounds, respectively). There is hardly

any weight loss for the reference com-pounds with Sunpar 2280 mineral oil up-on ageing. It seems that despite an at-mospheric boiling point of around 350°C, squalane is still too volatile at 135°C com-pared to regular mineral oil. This seems to

be no issue for ageing at temperatures up to 125°C (see previous sections), but be-comes critical at 135°C and, thus, is a topic for further investigations.

To have a fully sustainable EPDM com-pound with 100% sustainable ingredi-

6 White bull-eye EPDM compound composition, used for evaluating rice husk ash and micro-cellulose versus silica.compound formulation silica silica rice husk ash micro-cellulose 1 micro-cellulose 1 +

maleated EPMmicro-cellulose 2

starting mixer temperature (°C) 70 130 130 130 130 130Keltan 6471 EPDM 115 115 115 115 115 115Keltan 1519R maleated EPM 5

PoleStar 200R clay 110 110 110 110 110 110Ultrasil VN 3 silica 30 30rice husk ash 30Arbocel UFC M8 micro-cellulose 30 30Arbocel FD 600-30 micro-cellulose 30titanium dioxide 9 9 9 9 9 9Sunpar 2280 mineral oil 70 70 70 70 70 70Si 69 coupling agent 2 2 2 2 2 2TEA 2 2 2 2 2 2ZnO 5 5 5 5 5 5stearic acid 1 1 1 1 1 1sulfur-80 0,6 0,6 0,6 0,6 0,6 0,6DPTT-70 1,14 1,14 1,14 1,14 1,14 1,14DTDM-80 1,2 1,2 1,2 1,2 1,2 1,2MBT-80 1,2 1,2 1,2 1,2 1,2 1,2TMTD-70 1,14 1,14 1,14 1,14 1,14 1,14ZDBC-80 2,5 2,5 2,5 2,5 2,5 2,5total 351,8 351,8 351,8 351,8 356,8 351,8compound propertiesML 1+4 @ 100 °C (MU) 18,8 28,9 17,6 24,0 28,3 23,8ts5 @ 125 °C (min) 14,2 13,6 10,4 13,8 14,8 14,6ML (dNm) 0,28 0,52 0,23 0,34 0,40 0,32MH - ML = ΔS (dNm) 5,7 8,2 5,7 6,3 6,7 6,7ts2 (min) 1,4 1,2 1,3 1,4 1,4 1,5tc90 (min) 3,5 3,1 2,6 3,2 3,3 3,2vulcanisate propertieshardness (Sh A) 42,1 49,3 41,5 46,7 47,1 48,1modulus @ 100% (MPa) 1,5 1,8 1,4 1,9 2,0 1,6modulus @ 300% (MPa) 3,9 4,7 3,9 4,6 4,0 4,0tensile strength (MPa) 7,2 9,4 5,4 6,1 6,3 5,7elongation at break (%) 683 647 574 487 718 551tear resistance Delft (N/mm) 27,1 31 23,3 26,4 29,2 22,5compression set 72h @ 23 °C (%) 12,1 10,5 11,1 12,8 13,5 12,2compression set 24hr @ 70 °C (%) 19,9 18,2 18,1 19,7 22,2 20,3compression set 24 hr @ 100 °C (%) 43,2 36,4 44,7 37,5 41,5 40,7after ageing for 168 hr @ 100 °Chardness (Sh A) 46,6 53,8 45,6 50,5 50,7 51,4modulus @ 100% (MPa) 1,9 2,7 1,9 2,5 2,7 2,0modulus @ 300% (MPa) 5,1 6,7 4,4 5,5 5,1 4,8tensile strength (MPa) 6,6 8,7 4,8 6,6 5,8 5,3elongation at break (%)] 468 459 381 407 466 365tear resistance Delft (N/mm) - 31,1 20,3 24,6 28,7 21,3



7 Composition of highly filled, automotive, solid seal compounds based on amorphous or crystalline EPDM, used to maximise the content of sustainable ingredients.compound formulation dynamic, automotive seal static, automotive seal

traditional sustainable traditional sustainableKeltan 8550 EPDM 100Keltan Eco 8550 EPDM 100Keltan 5470 EPDM 100Keltan Eco 5470 EPDM 100N550 carbon black 155 147BBC 500 carbon black 174 165Superfine S whiting 77 110rice husk ash 77 110Sunpar 2280 mineral oil 98 100squalane 98 100CaO 5 5 5 5PEG 1000 1,5 1,5 1,5 1,5ZnO active 3 3 3 3stearic acid 1 1 1 1sulfur-80 0,8 0,8 0,8 0,8DPG-80 0,5 0,5 0,5 0,5TBBS-80 0,625 0,625 0,625 0,625CBS-80 1,25 1,25 1,25 1,25ZBEC-70 1,7 1,7 1,7 1,7TP-50 2 2 2 2CLD-80 1 1 1 1Vulcalent E/C 0,8 0,8 0,8 0,8total 449,2 468,2 476,2 494,2percentage bio-based/sustainable (%) 0 86 0 90compound propertiesextruder throughput (g/min.) 32,6 32,8 35,2 34,8extruder head pressure (bar) 27 21 26 21die swell (%) 11,9 18,9 8,0 9,0Garvey die ranking (total score) 12 12 12 12ML 1+4 @ 100 °C (MU) 59,5 47,8 55,0 44,5ts5 @ 125 °C (min) 18,0 26,4 19,1 28,0ML (dNm) 1,82 2,63 1,33 2,31MH - ML = ΔS (dNm) 13,2 13,6 14,1 14,4ts2 (min) 1,0 1,1 1,2 1,1tc90 (min) 2,8 3,2 3,6 3,3vulcanisate propertieshardness (Sh A) 67,3 66,9 67,9 68,9modulus @ 100% (MPa) 3,5 2,3 3,2 2,4modulus @ 300% (MPa) 9,5 - 8,3 7,3tensile strength (MPa) 9,5 7,5 9,5 8,3elongation at break (%) 304 291 368 349tear resistance Delft (N/mm) 28,4 20,6 31,6 25,6compression set 24 hrs @ -25 °C (%) 70,8 42,3 97,6 97,8compression set 72 hrs @ 23 °C (%) 9,2 12,7 27,2 25,4compression set 24 hrs @ 70 °C (%) 12,1 13,1 13,7 17,3compression set 24 hrs @ 100 °C (%) 27,2 36,7 29,1 44,9after ageing for 168 hr @ 135 °Chardness (Sh A) 72,8 83,3 75,8 84,8modulus @ 100% (MPa) 6,1 - 5,2 -tensile strength (MPa) 9,7 7,7 9,7 10,1elongation at break (%) 179 7 226 46mass change upon ageing (%) -0,6 -20,2 -0,7 -19,2after ageing for 336 hr @ 135 °Chardness (Sh A) 74,8 93,4 76,7 93,6modulus @ 100% (MPa) 7,3 - 6,2 -tensile strength (MPa) 10,2 11,1 10,3 13,7elongation at break (%) 161 14 207 26



ents, the residual 10 – 15% non-sustaina-ble content of the EPDM compounds in Table 7 should be further addressed. A major step would be to develop a second generation Keltan Eco EPDM not only based on green ethylene, but also on green propylene, which would bring the total bio-based content of EPDM rubber to ~95% and of the EPDM compounds al-so to ~95%. Currently, the production of propylene based on green resources is being explored [32], amongst others via i) production of methanol from wood, fol-lowed by conversion of methanol to pro-pylene, ii) sugar-based routes either via ethanol to ethylene and then via metath-esis to propylene or via isopropanol to propylene and iii) direct fermentation of glucose using genetically engineered mi-cro-organisms to a mixture of olefins, in-cluding propylene. The finishing touch will then be a green diene for EPDM. As an example to stimulate interest, it is mentioned that first experiments with an amorphous EPDM with 7 wt% 2,4-dime-thyl-2,7-octadiene [33] (natural terpene supplied by Dérivés Résiniques & Terpé-niques) as diene showed fair sulphur vul-canisation characteristics and corre-sponding vulcanisate properties, similar to a 4.5 wt% ENB-EPDM. The final step towards a fully sustainable EPDM rubber compound will require the development of bio-based rubber additives, especially the curatives, which considering their chemical structure will be a more chal-lenging development.

ConclusionsIn an effort to develop EPDM compounds based on Keltan Eco EPDM with the high-est level of sustainable ingredients a se-ries of bio-based oils and sustainable fillers were screened. Typical issues en-countered when exploring the relatively polar and unsaturated natural oils in EPDM compounds are the lack of com-patibility (mixing issues and oil bleeding) and the competition for sulphur vulcani-sation (reduced crosslink density and cor-responding inferior vulcanisate proper-ties). Modified natural oils, such as hy-drogenated coconut oil and trans-esteri-fied mono-esters, have improved compatibility and/or vulcanisation per-formance. Squalane (“EPM hexamer”) provides the best bio-based alternative for mineral oil plasticiser in this study, since it is as apolar as EPDM and is fully saturated. As far as sustainable fillers are concerned, pyrolysis black was shown to have a reinforcing efficiency 90% of that

of furnace N550 black. Rice husk ash and micro-cellulose do not show reinforcing properties, but can still be used as inert, white fillers, substituting traditional, mineral white fillers. Combining these leads has resulted in automotive solid seal EPDM compounds based on Keltan Eco with more than 85% sustainable con-tent and properties reasonably compara-ble to the reference EPDM compounds.

AcknowledgementsWe would like to acknowledge dr. Nikhil Kumar Singha of the Rubber Technology Centre of the Indian Institute of Technol-ogy in Kharagpur (India) for a useful liter-ature survey on green rubber compound-ing ingredients. Next, we would like to thank Rutteman, Friesland Campina, Amyris, Cargill, Hansen+Rosenthal and Emery Oleo Chemicals for supplying us with the samples of the bio-based oils and Black Bear, Sílica Verde do Arroz and J. Rettenmaier & Söhne for the alternative filler samples used in this study. We also express our gratitude to both the AR-LANXEO Polymer Testing group in Lev-erkusen (Ge) and the former Keltan Rub-ber Processing & Testing Laboratory in Geleen (NL) for performing all the mixing and testing.

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EPDM Green EPDM Compounds[1] Compounding€¦ · isotridecyl stearate Loxiol G40 EmeryOleo 466 0.86...

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