14 Rubber & Plastics News • January 27, 2020 www.rubbernews.

com

Technical
Developing eco-friendly curatives for rubber compounds
By Joel Neilsen, Hermann-Josef types of curatives (curing bladders, etc.).
Weidenhaupt and Dirk Kaempfer
Lanxess
Executive summary A more active halogen source, SnCl2 ,
will significantly improve cure rates
Eco-friendly, or “green” efforts to re- Rubber is an essential component of many everyday and specialized products and state of cure for resol systems (Fig.
duce negative effects on environmental used in a variety of ways. To produce rubber compounds with the physical 4). This Resol/ SnCl2 system still exhib-
and biological health of industrial oper- properties necessary for good product performance, vulcanization systems may its a marching modulus and somewhat
ations and manufacturing are steadily contain curatives that have negative environmental and/or biological impact. slower cure rates vs. a peroxide system.
increasing. Every major industry is fac- Fortunately, a significant number of curatives exist that will reduce the nega- Additionally, major issues with SnCl2
ing growing challenges to reduce pollu- tive impact on health and environmental safety. are that it is very hydroscopic, has limit-
tion and to produce products that per- This paper will present an overview of curatives that are more eco-friendly ed storage stability and is difficult to
form well but do not negatively impact but still appropriate and effective for various compound applications. Specifi- disperse (small weighments).
biological health or are detrimental to cally, the area of reducing or eliminating carcinogenic nitrosamine-generating To overcome these drawbacks of res-
the environment. curatives will be explored. in-halogen curing, Lanxess Business
The Rubber Industry is no exception A novel approach to this is the use of Lanxess Business Unit Rhein Chemie’s Unit Rhein Chemie has developed a
to this challenge. In the area of vulcani- Rhenogran-brand Zeolite-70 combined with resol resins to develop fast and heat unique product, Rhenogran-brand Zeo-
zation, the “best” chemistry to achieve a stable vulcanizates in elastomers with low unsaturation. Additionally, Rhe- lite-70, which acts as an activator for
compound with the required perfor- nocure-brand DR and Vulcuren brands will be presented as safer alternatives to resin curing. Zeolites are microporous,
mance properties may not be best rela- 1, 3-diphenyl guanidine (DPG), which produces large volumes of volatile organic alumino silicate minerals commonly
tive to environmental or health impact. compounds during decomposition. Rhenogran HPCA-50 combined with Rhe- used as commercial adsorbents and cat-
nogran MTT-80 will be shown to be an effective replacement for ethylene-thiourea alysts. An example of Zeolite structure
TECHNICAL NOTEBOOK (ETU), which is considered to be both carcinogenic and mutagenic. can be found in Fig. 5.
Edited by John Dick This information will assist the rubber compounder in making choices that With the addition of Rhenogran Zeo-
meet the compound performance needs as well as contribute to the overall en- lite-70, a resol resin cure system dramat-
Effective curatives used for many de- vironmental and biological health of our world. ically improves. Comparing Figs. 6 and
cades can fall into categories that pre- 7 illustrates these improvements. Fig. 6
vent them from being “eco-friendly.” and thiurams, most of which generate activate vulcanization, and also an acid shows an EPDM compound cured with
These types of curatives can generate secondary amines during the vulcaniza- scavenger such as zinc oxide or magne- resol and three different halogen sources:
carcinogenic nitrosamines as well as be tion process. These amines then form sium oxide because the necessary halogen CR, brominated resin and SnCl2 .
classified as mutagens. nitrosamines when exposed to nitrogen will form an acid during vulcanization. The activity of the halogen donor de-
This paper will review curatives that oxides, which are found on the surface of A schematic of a resol crosslink reac- termines the rate and state of cure, with
are considered less hazardous vs. others. additives such as zinc oxide and carbon tion is found in Fig. 2. Strong carbon-car- SnCl2 showing the overall best perfor-
Performance in rubber compounds will black.1 Nitrosamines as a group are bon crosslinks are formed which offer mance. The CR and BR donors exhibit
be compared. considered carcinogenic.2 superior performance for heat resistance slower cures and some marching modu-
Peroxides are a well-known alterna- and compression set. An additional posi- lus. Fig. 7 shows the significant increase
Phenolic resin curing: The use of tive to sulfur curing of low unsaturated tive is that far less extractables occur vs. in both cure rates and maximum torque
Zeolites as activators elastomers, but the use of phenolic res- highly accelerated sulfur cures. with the addition of Rhenogran Zeo-
Elastomers with low levels of unsatu- ins also can be considered. These resol A significant drawback to resin curing lite-70. Marching modulus disappears.
ration such as butyl rubber and EPDM resins are polymeric “oligomer” struc- with the halogen coming from polychlo- The comparative data presented shows
need high levels of acceleration if sulfur tures with typically 10-20 repeating roprene (CR, a stable halogen source) is that resin cure systems which include
cure systems are used. The accelerators units. These resins form very strong, that cure rates are relatively slow, and Rhenogran Zeolite-70 can produce effi-
chosen often produce secondary amines stable vulcanizates with exclusively often marching modulus occurs (Fig. 3). ciently cured vulcanizates with desirable
upon formation of intermediates during carbon-carbon type crosslinks. This cure system limits the use of resol properties such as fast cure rates, level
vulcanization. Examples of these resins are shown in resins to just a few applications that re- maximum torque and excellent physi-
Examples include dithiocarbamates Fig. 1. Resol resins require a halogen to quire the properties produced by these cal properties.

Fig. 1: Resol cure basics monomer and polymer structure of the resol resin. Fig. 3: Resol cure basics examples.

Fig. 2: Resol cure basics crosslinking mechanism. Fig. 4: Resol curing or EPDM comparison of sulfur, peroxide and resol cure.
www.rubbernews.com Rubber & Plastics News • January 27, 2020 15

Technical
Alternatives to nitrosamine-
generating ultra accelerators The authors
Typically more than a single accelera-
tor is used in a sulfur-cured rubber Joel Neilsen is a technical applica- manager of technical service. tant professor at the University of Ha-
compound. The choice of a multiple ac- tions specialist at Lanxess Corp. In his current position at Lanxess’ nover for “Chemical Vulcanization” in the
celerator “cure package” depends upon He has been working in the rubber Rhein Chemie business unit, Neilsen study course “Rubber Technology.”
the other compound ingredients: elasto- industry for more provides technical support for the rub- He holds about 50 patents and has 15
mers, fillers, plasticizers, etc. The re- than 42 years. Af- ber additives prod- publications. He earned a doctorate in
quired cure rate, cure state and final ter obtaining a de- uct portfolio. chemistry at the University of Muen-
physical properties also will help deter- gree in chemical Hermann-Josef ster.
mine the preferred cure package. engineering from Weidenhaupt has Dirk Kaempfer is
Accelerators tend to be classified as Cleveland State been working in the the head of global
primary (eg. thiazoles, sulfenamides) and University, he be- rubber industry application technolo-
secondary (eg. thiurams, dithiocarba- gan his career with since 1986, starting gy for the Rhein
mates, dithiophosphates and guanidines) the BFGoodrich at Akzo Chemicals Chemie Rubber Ad-
Primary accelerators typically offer good Tire Co. in Akron, Germany as a white ditives business unit
processing safety whereas secondary ac- with assignments filler specialist. From of Lanxess Deutsch-
celerators have less scorch delay and in tire development Neilsen 1989 on, Weiden- land GmbH. He
work in conjunction with the primary and tire production. haupt worked for Weidenhaupt holds a doctorate in
accelerators to boost cure properties and After BFG, Neilsen joined Uniroyal Bayer A.G. and la- polymer science from
achieve higher levels of final torque. Chemical Co. in sales development, and ter Lanxess Deutschland GmbH in vari- the University of Kaempfer
The groups of accelerators and sul- then Bayer as a technical service repre- ous positions in the rubber department. Freiburg in Germany.
fur-donating accelerators that signifi- sentative for rubber chemicals and syn- Weidenhaupt’s current position is se- Kaempfer joined Lanxess in 2004 and
cantly speed cure rates and increase thetic elastomers. He then joined Sid nior specialist application technology in continues to work on various international
modulus for the most part generate car- Richardson Carbon as a technical service Rhein Chemie for the rubber additives projects based on rubber and thermoplastic
cinogenic nitrosamines. Two well-known representative and eventually became business line. Since 2008 he is an assis- elastomers.
groups of these are the dithiocarbamates
and thiurams. Structures for a number • Synergies with additional accelera-
of both types are found in Figs. 8 and 9. tors; and Fig. 7: Accelerated resol cure comparison of different activators with Rhenogran
These curatives are frequently used • No bloom—good rubber compatibili- Zeolite-70.
with an accelerator such as a sulfenam- ty/solubility.
ide with more scorch delay to prevent Fig. 12 illustrates in general terms
precure of the compounds during mixing the cure performance of the major accel-
and processing. erator groups. It can be seen that dithio-
A group of fast, non-nitrosamine cura- phosphates are somewhat slower than
tives that can replace the above men- the fastest group, the dithiocarbamates,
tioned nitrosamine generators are the but quite similar to the thiurams for
dithiophosphates. These curatives are cure speed, but with higher torque
not as fast as dithiocarbamates on a achievement. When dithiophosphates
one-to-one basis, but in conjunction with are combined with other accelerator
other accelerators, they can be quite ef- types, their positive combined effect can
fective. Chemical structures are similar be clearly seen. With the addition of a
to those of the dithiocarbamates but thiazole to the dithiophosphate system,
with a phosphorous atom replacing ni- the similarity to the dithiocarbamate is
trogen (see Figs. 10 and 11). These cu- quite evident.
ratives have many positive features: Fig. 12 shows that nitrosamine-gener-
• Nitrosamine-free; ating ultra-accelerators can be replaced
• Good reversion resistance; See Compounds, page 17

Fig. 5: Accelerated resol cure using Zeolites.

Fig. 8: Thiuram curative comparisons.

Fig. 6: Resol cure basics comparison of different activators in EPDM. Fig. 9: Dithiocarbamate curative comparisons.
www.rubbernews.com Rubber & Plastics News • January 27, 2020 17

Technical
Compounds Alternatives to 1, 3-diphenyl
guanidine
A significant reason for the environ-
mental/biological concerns of many cura-
scorch properties and had been found to be
an effective replacement for DPG. A sum-
mary of a compounding study comparing
Vulcuren to DPG is seen in Fig. 16. Over-
eration between DPG and Vulcuren is
seen in Fig. 17. Additionally, with its
anti-reversion properties, Vulcuren will
reduce any reduction in crosslink densi-
Continued from page 15 tives is the fact that they generate volatile all performance is quite comparable with ty caused by high-curing temperatures
with safer, less hazardous alternatives. organic compounds during vulcanization better scorch delay and reduced loss factor or service temperatures.
A more specific comparison of dithio- and post-vulcanization (Fig. 14). 1, 3-di- as pluses for the Vulcuren substitution. For carbon black-filled compounds, Rhe-
carbamate replacement by a combina- phenyl guanidine (DPG) is of particular Substantial reduction in aniline gen- See Compounds, page 18
tion of a dithiophosphate and thiazole is concern, because its decomposition gen-
illustrated in the next few figures. Fig- erates large quantities of aniline, which Fig. 13: Accelerator speed in EPDM comparison of different accelerators.
ure 13 shows individual cure curves in is considered a probable human carcino-
an EPDM compound with Rhenogran gen.3 When DPG is compared to other
ZBEC-70 and Rhenogran MBT-80, re- common rubber chemicals it can be seen
spectively. Then shown is how the com- that it emits a significant quantity of
bination of a dithiophosphate (in this aniline during decomposition (Fig. 15).
case Rhenogran TP-50) with the thiazole Two effective replacements for DPG
comes quite close to the dithiocarba- that do not generate substantial quanti-
mates cure curve. ties of aniline are Vulcuren-brand and
There are a number of dithiophos- Rhenocure-brand DR/S. In rubber com-
phates available with each generating a pounds that are highly loaded with sili-
specific cure curve dependent on its ca, DPG has been found to be an effective
particular alkyl structure. With this secondary accelerator because it does
variety, and also thiazole choice (MBT, not interfere with the salinization reac-
MBTS, etc.) and loading variation, a tion between silane and silica and has a
non-nitrosamine replacement for a par- relatively long scorch time.
ticular dithiocarbamate can be quite Vulcuren (1,6-bis(N,N-dibenzylthio-
achievable. carbamoyldithio)-hexane) has similar

Fig. 10: Dithiophospate curative comparisons.

Fig. 14: Volatile organic compounds.

Fig. 11: Example of a dithiophospate ZDBP structure compared to the dithiocar-

bamate ZDBC. Fig. 15: DPG is a very significant source for aniline in emissions from rubber.

Fig. 12: Dithioates additives for rubber compounds accelerator velocities. Fig. 16: “Green tire” tread compound Vulcuren vs. DPG.
18 Rubber & Plastics News • January 27, 2020 www.rubbernews.com

Technical
Compounds tra-accelerator frequently used to cure
polychloroprene and other diene rub-
bers. Extensive studies have determined
that ETU is both a potent teratogen
modulus typical of CR compounds. Scorch
values in Figs 23 and 24 show the im-
portance of including Rhenogran HPCA,
because alone Rhenogran MTT-80 will
Overall, compound physical properties
are quite comparable as can be found in
Fig. 25. Fig. 26 shows improved extend-
ed heat-aged properties (modulus and
Continued from page 17 (cause of birth defects) and it also has typically produce very short scorch safety elongation) with the MTT/HPCA system.
nocure DR/S (polyethyleneimine, an in- been classified as a Group B2, probable in CR compounds. See Compounds, page 19
ert filler) can effectively replace DPG. human carcinogen by the EPA.4
The structure of Rhenocure DR/S is not Because of these health issues, exten- Fig. 20: Eplexor test.
aromatic, and therefore aniline cannot sive efforts have been made to replace
be formed during its decomposition in ETU in rubber compounds. Rhein Che-
the vulcanization process. A comparison mie has developed alternatives that
of Rhenocure DR/S and DPG is found in provide similar cure properties and final
the next few figures. physical properties that will be dis-
Fig. 18 shows a model NR compound cussed in this section. The combination
carbon black filled with no secondary ac- of Rhenogran HPCA-50 (combination of
celerator; DPG at 0.5 phr; and Rhenocure aminic co-activator and antioxidant)
DR/S at 0.5, 0.4 and 0.3 phr. Figs. 19 and Rhenogran MTT-80 (3-methyl-thi-
and 20 summarize the results of physi- azolidine-thione-2) has proved to be an
cal property testing. Overall, lower levels effective replacement.
of Rhenocure DR/S showed equivalence These two curatives were compared in
to DPG with one positive exception: dy- a generic CR compound (Fig. 21). Fig.
namic properties (Fig. 20) show improved 22 shows rheometry of both cure sys-
performance of Rhenocure DR/S in a low tems. The ETU/MgO system shows
strain temperature sweep. higher torque, but increased loading of
the HPCA/MTT system should increase
Alternatives to ETU the level closer to that of the control.
Ethylene Thiourea (ETU) is an ul- Both systems show the marching

Fig. 17: Aniline emission reduced to detection limit with Vulcuren compound. Fig. 21: CR compound, 65 shore A.

Fig. 18: New accelerator Rhenocure Dr in NR compound. Fig. 22: Comparison of cure pattern at 170ºC.

Fig. 19: Rhenocure DR (at lower concentration) vs. DPG in NR compound. Fig. 23: Comparison: Mooney scorch at 130ºC.
www.rubbernews.com Rubber & Plastics News • January 27, 2020 19

Tessy adds injection presses, clean room space

By Bill Bregar For the new project, Tessy is adding eight injection
Plastics News molding machines with up to 420 tons of clamping force.
ELBRIDGE, N.Y.—Tessy Plastics Corp. will spend Two are for molding liquid silicone rubber components.
about $20 million in 2020, much of it to add more clean The investment also includes an automated assembly line
room space to a factory in Elbridge. The company also for producing 13 million units per year, Beck said.
plans to invest in injection presses, including two for The customer originally wanted some parts with an-
liquid silicone rubber parts, at the same facility. other material, but after a design review with the cus-
The project includes molding and assembly of a surgi- tomer, Tessy research and development engineers opted
cal filtration device. The company moved deodorant for LSR instead.
stick production to another plant to make room for the Tessy molded prototype LSR parts, which were test-
new medical work. ed and approved by the customer.
Tessy also will add 100,000 square feet of warehouse Tessy also built the prototype LSR molds, Beck said,
space to the building, known as the South Plant, for the Tessy will add warehouse space to its South Plant. noting that his company already does LSR molding and
medical customer, according to President Roland Beck. has in-house talent in that process.
That factory currently measures 190,000 square feet, cal customer in 2019 for the single-use product. The “There will be no purchased components and we’ll
including 69,000 square feet of warehouse space. finished assembly, comprising seven molded compo- mold everything,” Beck said.
The expansion will create 50 additional jobs. nents, is a filtration device that goes on a surgical suc- The Central New York Regional Economic Develop-
In late 2017, the company relocated the deodorant work tion instrument that collects specimens, he said. It fil- ment Council made the Tessy expansion project one of
from its South Plant to the North Plant, in nearby Bald- ters out polyps and other objects for testing. its 30 priority projects for state funding. The state is
winsville, N.Y., to mold, assemble, pack and ship from one He declined to identify the customer. providing $5 million for the expansion.
location. The move freed up space in the South Plant. The medical product probably won’t go into production Tessy, based in Skaneateles, N.Y., has a total of
Beck said that Tessy won business from a new medi- until 2021, Beck said. 135,000 square feet of clean room space at its factories.

Pyrolyx U.S.A. secures funding for second rCB plant

By Miles Moore $70 million, but we are expecting the plant will have a production capacity In November, Pyrolyx A.G.—Pyrolyx
Rubber & Plastics News Staff actual amount borrowed to be less than that is identical to the existing Terre U.S.A.’s Stegelitz, Germany-based par-
TERRE HAUTE, Ind.—Recycled car- this,” Redd said. Haute plant, which is 13,000 metric ent company—signed a five-year agree-
bon black manufacturer Pyrolyx U.S.A. Pyrolyx estimates the construction of tons of rCB annually, according to Redd. ment with the Tire Division of Conti-
has obtained approval for up to $70 mil- the second Terre Haute plant at $52 The company expects the new plant nental A.G. for Pyrolyx to provide
lion in bonds to finance the building of a million. to bring 50 new jobs and $2.5 million in increasing amounts of rCB to Conti tire
second rCB plant in Terre Haute. The company expects to break ground annual payroll to Terre Haute, he said. plants worldwide, rising to 10,000 tons.
The Terre Haute Economic Develop- on the facility in the first quarter of The bonds for the first Terre Haute Redd said he could not comment di-
ment Corp. approved the issuance of 2020, and have it operational in the Pyrolyx plant have a 10-year payback; rectly on Pyrolyx’s agreement with
the Solid Waste Facility revenue bonds second quarter of 2021. the company does not yet know the ex- Conti or how it affected the decision to
in December, and the city of Terre “We have not closed financing on act terms of the bonds for the second build the second Terre Haute plant.
Haute gave its approval in January, Plant 2 yet, so the schedule assump- facility, according to Redd. “However, the additional capacity
according to Pyrolyx U.S.A. CEO tions are dependent on that successful “We will be working to have a longer that the second plant in Terre Haute
Thomas Redd. financing close,” Redd said. payback period (for the second set of represents will be sold to customers in
“The maximum amount of the bonds is When completed, the second Pyrolyx bonds),” he said. the U.S. and abroad,” he said.

Technical
Compounds ing dispersion in rubber compounds. Balloons,” Dec. 18, 2007. Scientific Committee on Agency for Toxic Substances and Disease Registry.
Ease of handling, dust free and safer Consumer Products, European Commission. 4. “Ethylene Thiourea—Hazard Summary,” Janu-
3. “ToxFAQs—Aniline.” April 2002. U.S. Dept of ary 2000. U.S. Environmental Protection Agency,
package disposal all contribute to a bet- Health and Human Services, Public Health Service. Integrated Risk Information System.
ter, more positive work environment,
Continued from page 18 which should aid in improving worker Fig. 25: Comparison of physicals.
Conclusions morale.
The global concern about environmen-
tal safety and biological health has in- Acknowledgments
creased substantially in the past few A great deal of appreciation is extend-
decades. Development of chemicals and ed to the co-authors of this paper, Dirk
other materials that have less negative Kaempfer and Hermann-Josef Weiden-
impact on the environment is gaining haupt, for the extensive amount of infor-
more and more focus. mation they have contributed to its con-
The curatives produced by Lanxess tent.
discussed in this paper are examples of Appreciation also is extended to for-
products that can be used more safely mer Rhein Chemie associate, Steven
and at the same time produce rubber Monthey, for the significant amount of
compounds with the desired physical information he provided.
properties and overall performance.
In addition to the safer chemistry of References
the products, their encapsulation in 1. “Prevention of Nitrosamine Exposure in the Rubber
Industry,” March 28, 1994. Chaper 4, pp 42-51. ACS
elastomeric binders adds to their more Symposium Series. B. Spiegelhalder and C.D. Wacker.
positive environmental impact vs. raw 2. “Opinion on the Presence and Release of Nitro-
powders or liquids in addition to improv- samines and Nitrosatable Compounds from Rubber

Fig. 24: Influence of HPCA on MTT scorch safety is increased. Fig. 26: Aging in air at 100ºC; hardening of vulcanizates.