Rubber chemical

1. ‘‘NITROSAMINE SAFE’’ THIURAM DISULFIDE
RANVIR VIRDI,1,
* BOYD GROVER,1
KIRUAN GHUMAN
1,2
1
ROBINSON BROTHERS LIMITED, PHOENIX STREET, WEST BROMWICH, B70 0AH, U.K.
2
SCHOOL OF CHEMISTRY, UNIVERSITY OF BIRMINGHAM, B15 2TT, U.K.
RUBBER CHEMISTRY AND TECHNOLOGY, Vol. 92, No. 1, pp. 90–109 (2019)
ABSTRACT
An investigation into the technological performance of a new nitrosamine safe thiuram disulfide,
tetraisononylthiuramdisulfide (TINTD), in natural rubber was undertaken. Initially, TINTD was synthesized from
di(3,5,5-trimethylhexyl)amine. It was then demonstrated to function as a sulfur donor, a primary accelerator, and as a
secondary accelerator when combined with sulfenamides. These investigations found that the long-branched alkyl chain on
the nitrogen of TINTD and of its vulcanization breakdown product zinc diisononyldithiocarbamate (ZDNC) makes both
chemical species very soluble in the elastomer. This high solubility of TINTD and ZDNC in the rubber makes TINTD highly
attractive for use in soluble efficient vulcanization systems. In addition, the nature of the long-branched alkyl chain means
that the formation of carcinogenic N-nitrosamine is difficult, and if formed, it is toxicologically much less hazardous in terms
of both acute toxicity and metabolic activity. Thus, concerns of accelerator toxicity, irritant dermatitis from thiuram and
dithiocarbamate, and type IV allergy may be reduced or totally eliminated. The curing efficiency of various thiuram
disulfides was also investigated as a function of alkyl chain length and the degree of chain branching. The cure performance
was found to be determined by both chain length and chain branching. [doi:10.5254/rct.18.82617]
INTRODUCTION
Thiurams are a group of sulfur-containing organic compounds that act as ultra-rubber
accelerators, where only the disulfides and polysulfides also act as sulfur donors.1
They are known
for their high rate of cure and ability to create high cross-link densities in sulfur-cured diene-
containing elastomers such as natural and synthetic rubbers. As sulfur donors, thiurams are used in
cure systems where short cure times, low sulfur, and excellent heat-resistant compounds are
desired. They are generally slower than the dithiocarbamates and give greater scorch safety.2
They
are also commonly used to modify thiazole and sulfenamide cure systems to reduce scorch times as
well as improve overall state of cure.3
There are many commercially available thiurams commonly used in the rubber industry as
primary and secondary accelerators, as well as activators for other cure systems when used in small
amounts. There is slight variation in their chemical structure, which influences their functionality.
Thethiuram disulfides haveacommon reactivefunctional group,R2N-C(S)-S-S-(S)-C-NR2,which
is responsible for the vulcanization characteristics, but they differ in the nature of R groups (alkyl or
aryl) attached to the nitrogen, making up the other regions of the molecule. These alkyl or aryl
functional groups, while relatively inactive, influence the vulcanization in ways that can be used to
obtain certain desirable properties. For example, the long alkyl R groups can make the thiurams
more rubber soluble compared with the short alkyl groups.4
The most popular and technologically effective thiurams used in the rubber industry are
synthesized from the lower molecular weight, short chain alkyl secondary amines where R is
methyl or ethyl groups, that is, tetramethylthiuramdisulfide (TMTD), tetramethylthiurammono-
sulfide (TMTM), and tetraethylthiuramdisulfide (TETD). Other common ‘‘traditional’’ thiurams
used are based on piperidine and butylamine, that is, dipentamethylenethiuramdisulfide (PTD),
dipentamethylenethiuramhexasulfide (DPTH), and tetrabutylthiuramdisulfide (TBuT), respec-
tively. Although these traditional thiurams are most effective in cross-linking the rubber, they all
have limitations or concerns associated with them when used alone or in combination. They are
*Corresponding author. Email: rsvirdi@robinsonbrothers.co.uk
90

2. highly toxic and can cause irritant dermatitis and type IV allergic contact dermatitis.5–9
During the
vulcanization reaction, they can also thermally breakdown to generate the parent secondary amine,
which in the presence of oxides of nitrogen, produce regulated carcinogenic N-nitrosamines and
nitrosatable substances.10–14
Therefore, they are not very favorable for new compositions and
should be avoided in the formulation to reduce the risk of developing irritant dermatitis and type IV
allergic contact dermatitis, in addition to the formation of carcinogenic N-nitrosamines and
nitrosatable substances.
Because of various regulations,15–19
there has been a push in all areas of the rubber industry to
use safer accelerators. Some environmentally safer thiurams have appeared on the market as a
replacement of traditional thiurams for a number of reasons. They do not produce N-nitrosamines
that are restricted by the German TRGS 552 list, and the N-nitrosamines are reported to be less
carcinogenic than those generated by the traditional thiurams. These thiurams are based on
sterically bulky secondary amines such as diisobutylamine and dibenzylamine-producing
tetraisobutylthiuramdisulfide (TiBTD),20
and tetrabenzylthiuramdisulfide (TBZTD),21
respec-
tively. Because of the sterically bulky R groups on the secondary amines, these safer thiurams are
slightly less effective, on a weight-to-weight basis, during the vulcanization reaction.22
Over the years, 3 types of sulfur vulcanization systems have been developed in the rubber
industry, namely, conventional vulcanization (CV), efficient vulcanization (EV), and semi-
efficient vulcanization (semi-EV). The CV cure system uses high sulfur with low accelerator
loading to provide better flex and dynamic properties but gives poor thermal and reversion
resistance to the vulcanizate. The EV cure system uses low sulfur with high accelerator loading to
achieve an extremely high heat and reversion resistance in the rubber. The semi-EV cure system
uses intermediate sulfur and accelerator loading for optimum levels of mechanical and dynamic
properties of vulcanizates with intermediate heat and reversion resistance. Some thiuram disulfides,
TBuT in particular, are also used in soluble EV cure systems. These cure systems are designed for
the lowest compression set, lowest rates of creep and stress relaxation, and high precision of
stiffness. Stearic acid is replaced by the rubber soluble activator zinc 2-ethylhexanoate (ZEH). In
addition rubber soluble accelerators are used, which give soluble vulcanization products in the
presence of zinc oxide. The vulcanizates are particularly suitable for engineering applications. A
rubber-soluble activator also improves resistance to primary creep and stress relaxation in
conventional vulcanizates.2
Neither TiBTD nor TBZTD, which are solid in nature, are suitable for
use in soluble EV cures. TBuT, being a liquid, is a well-known sulfur donor accelerator for soluble
EV cure systems in natural and polyisoprene rubbers, as it takes advantage of the high solubility of
the zinc dibutyldithiocarbamate (ZDBC), which is formed during vulcanization.2
However, as
stated previously, it is capable of producing regulated nitrosamine and N-nitrosatable substances. A
safer alternative sulfur donor accelerator to TBuT is desirable for the rubber industry.
Robinson Brothers Limited, over the past 20 years or so, has been active in the replacement of
conventional accelerator chemicals with sustainable, safer, and toxicologically less hazardous
compounds.23–28
One such ‘‘nitrosamine safe’’ accelerator chemical that has been successfully
introduced into the rubber and latex industry is Robac Arbestab Z (ZDNC).29
It is highly soluble in
the elastomeric medium, has high molecular weight, is highly thermally stable (no decomposition
occurs below 250 8C), and does not produce diisononylamine readily. Also, diisononylamine does
not nitrosate easily, because of the presence of branching of the R chain in the molecule, giving
ZDNC even greater ability to avoid N-nitrosamine formation.
It has also been found that if diisononylamine, di(3,5,5-trimethylhexyl)amine, is nitrosated, its
N-nitrosamine is involatile and also toxicologically much less hazardous in terms of both acute
toxicity and metabolic activity. Genotoxic studies on N-nitrosodiisononylamine (NDiNA) showed
no evidence of mutagenic activity when tested through Ames test either with or without metabolic
activation.30
Furthermore, no gene mutation effects were found when testing in vitro transgenic
NITROSAMINE SAFE THIURAM DISULFIDE 91

3. mammalian cells (HPRT mutation test); therefore, NDiNA is not mutagenic.31
These experimental
findings show no mechanism for carcinogenic activity from NDiNA.
The aim of the present article is to introduce and demonstrate the technological performance in
natural rubber of a new nitrosamine-safe thiuram disulfide synthesized, at Robinson Brothers
Limited, from diisononylamine. The new thiuram disulfide will be known as tetraisononylthiur-
amdisulfide (TINTD).
EXPERIMENTAL
PREPARATION AND CHARACTERIZATION OF TINTD
TINTD was synthesized using a two-stage process. In stage 1, sodium diisononyldithio-
carbamate (SDINDTC) was prepared by reacting diisononylamine (DINA) and sodium hydroxide
in a nonpolar solvent with carbon disulfide. In the second stage, SDINDTC (see Scheme 1) was
oxidized to make TINTD, which was then isolated and purified. TINTD gave a yield of 86% and
was found to be technically pure based on the following analysis: purity by potentiometric titration
with sodium sulfide, 97.9%. It was further purified by preparative high-performance liquid
chromatography HPLC and freeze drying for CHNS analysis: found 67.2% C, 10.8% H, 4.2% N,
and 17.2% S; expected from pure compound, C38H76N2S4, 66.2% C, 11.1% H, 4.1% N, and 18.6%
S. The product was further characterized using modern instrumental analysis (DSC/TGA, 1
H
NMR, 13
C NMR, and FTIR). The properties of TINTD are given in Appendix A.
MATERIALS
Natural rubber black filled masterbatch (IOM 3 B012) was obtained from Clwyd
Compounders in Wales. It contained standard Malaysian rubber CV 60 (100), carbon black FEF
N550 (50), naphthenic oil (10), stearic acid (1), and antioxidant, octylated diphenylamine (1.5).
TMTD PM75, TBZTD PM70, CBS PM75, MBS PM75, sulfur PM80, and ZnO PM85 were
obtained from Chemipat Ltd. (Manchester, UK). TiBTD was obtained from RT Vanderbilt, 2-
ethylhexylthiuramdisulfide was obtained from Miki & Co (Japan), and both dithiocaprolactam (used
as DTCL PM80) and alkylphenol disulfidepolymer (APDP), that is, Vultac TB7,were obtainedfrom
MLPC International. Commercial-grade TBuT was produced at Robinson Brothers Ltd.
EQUIPMENT AND PROCEDURES
A two-roll open mill with a friction ratio of 1:1.25 was used for mixing additives into the
rubber masterbatch, complete within 15 min, using cooling water and steam heating for
SCHEME 1. — Oxidation of sodium diisononyldithiocarbamate to TINTD.
92 RUBBER CHEMISTRY AND TECHNOLOGY, Vol. 92, No. 1, pp. 90–109 (2019)

4. temperature control. Rheological study of all compounded rubber mixes was carried out at 160 8C
using Alpha Technologies (Monsanto) Moving Die Rheometer MDR2000E with an oscillating
frequency of 1.667 Hz and DAISY software version 8.60. Mooney viscosity determinations were
carried out at 100 8C by using a large rotor on an SPRI (Negretti Automation) pneumatically
operated Mooney viscometer. Appropriate test pieces were compression molded for tensile
strength, hardness, and elongation all to BS903 using an electrically heated hydraulic press.
Tensile sheets were cured for T90 for 1.5 min. All tensile properties were determined to BS903:
part A2 type 1 dumbbells (large) using an Instron 4302 tensile testing machine with Blue Hill
software. The international rubber hardness degree (IRHD) of the samples was tested using the
Wallace rubber hardness tester. Thermal aging studies were carried out in hot air using Wallace
cell ovens at 70 8C and 100 8C for either 7 days or 22 h to determine the influence of elevated
temperature and time on tensile properties. Accelerated aging and heat resistance tests were
carried out in accordance with BS 903-A19:1998. The heat resistance test results are reported as
the percentage change in the value of the property measured as calculated from the formula:
XaX0
X0
3 100 , where X0 is the value of the property before aging and Xa is the value of the property
after aging.
Compression set determinations for 22 h at 100 8C were carried out using BS903 Part A6
(1992) method B (25% compression). Fatigue to failure tests were carried out using the Monsanto
Fatigue to Failure Tester. Results are expressed in Japanese Industrial Standard (JIS) average using
the highest four results from six used in every test.
MEASUREMENT OF CROSS-LINK DENSITY
The cross-link densities were determined on black filled natural rubber vulcanizates using the
Flory–Rehner equation32
:
lnð1 v2Þ þ v2 þ v1v2
2
¼ V1n v
1
3
2
v2
2
A circular test piece, 25 mm in diameter, was punched out from a cured sheet of rubber that is
approximately 1.5 to 2 mm thick. Its thickness was accurately measured using a Mitutoyo
Digimatic thickness tester. These measurements were used to calculate the initial volume, Vi, of the
test piece.
The test piece was then placed into a 100 mL glass jar containing approximately 70 mL
toluene, the lid was closed tightly, and the immersed test piece was swelled for 24 h at room
temperature to reach diffusion equilibrium. The swollen test piece was removed from the toluene
with tweezers, and its surface was rapidly wiped with an absorbent paper to remove the adhered
solvent. It was then immediately weighed, to determine the mass of swollen test piece, mf. It was
then placed inside the oven at 50 8C for 24 h to remove the solvent, cooled, and reweighed, to
determine the deswollen weight, mi. The volume fraction of the polymer in the swollen mass, V2,
is calculated as
v2 ¼
Initial volume
Initial volume þ Final swollen weightdeswollen weight
0:867
¼
vi
vi þ
ðMf MiÞ
0:867
That is, V2 ¼Vi/Vi þ(Mf – Mi )/0.867. Where the density of toluene¼0.867 g/cm3
.
This is then used in the Flory–Rehner equation to calculate cross-link density, n, in mol/cm3
.
Where V1 is the molar volume of the solvent. For toluene, it is 106 cm3
/mol. v1 is the Flory solvent–
polymer interaction term; for NR-toluene, it is 0.3795.33
NITROSAMINE SAFE THIURAM DISULFIDE 93

5. MEASUREMENT OF CROSS-LINK DECOMPOSITION
The cross-link decomposition was evaluated from the reversion degree (R), using the
following equation34
:
Rð%Þ ¼
MH MHþ15
MH
3 100
where MH is the maximum torque and MHþ15 is the torque after 15 min from the maximum torque.
RESULTS AND DISCUSSION
PERFORMANCE OF TINTD AS A SULFUR DONOR IN NATURAL RUBBER
TINTD was evaluated for its cross-linking efficiency in black filled natural rubber when used
as asulphur donor,that is, curing of natural rubber withTINTD without addingadditional elemental
sulfur. The performance was compared with the most effective traditional thiuram, TMTD, and
with some safer thiuram disulfides/sulfur donors, with the R group on the thiuram being isobutyl,
benzyl, and 2-ethylhexyl.
Sulfur donor comparison was carried out at 12.5 mmol addition of each thiuram/sulfur donor,
as given in Table I.
Although different weights of thiurams have been used, they are in equivalent moles (12.5
mmol). The relative molar mass of each sulfur donor is TMTD, 240; benzyl, 554; isobutyl, 408; 2-
ethyl hexyl, 632; TINTD, 688; and DTCL, 288.
Comparative rheographs taken at 160 8C are shown in Figure 1. Rheological, Mooney, and
tensile data of natural rubber vulcanizates are given in Table II.
It can be seen from Figure 1 and Table II that the TMTD has some superior curing properties in
terms of cure rate, T90, and higher final torque compared with the cure profiles of safer thiurams/
sulfur donors when comparison is carried out on equal molar addition basis. Furthermore, the safer
thiuram disulfides, including TINTD, show a higher cure rate and state of cure compared with the
dithiocaprolactam (DTCL) and APDP.
In Figure 1, it appears that the final torque of 2-ethyl hexyl is slightly higher than TINTD, but
when the initial torque istaken into consideration, the rise in torque,delta torque, ismore for TINTD
TABLE I
FORMULATION WITH DIFFERENT SULFUR DONORS PRESENT AT 12.5 MMOL
a
Formulation Mix 1 Mix 2 Mix 3 Mix 4 Mix 5 Mix 6 Mix 7
Masterbatch IOM 3 B012b
162.5 162.5 162.5 162.5 162.5 162.5 162.5
ZnO 5 5 5 5 5 5 5
TMTD 3
Benzyl 6.9
Isobutyl 5.1
2-ethyl hexyl 7.9
TINTD 8.6
DTCL 3.6
APDP 3.6
a
Weights given in grams.
b
StandardMalaysianrubber CV60(100),carbonblackFEFN550(50),naphthenicoil (10),stearic acid(1),andantioxidant,
octylated diphenylamine (1.5).
94 RUBBER CHEMISTRY AND TECHNOLOGY, Vol. 92, No. 1, pp. 90–109 (2019)

6. than for 2-ethyl hexyl, as shown in Table II. This shows that TINTD generates a greater state of
cross-linking than 2-ethyl hexyl thiuramdisulfide. It may also be noted that APDP and DTCL gives
a peaky cure indicating reversion taking place after maximum cure.
So the order of cure efficiency in terms of cure rate at 160 8C is TMTD . benzyl . TINTD .
isobutyl . 2-ethyl hexyl . APDP . DTCL, and the order of cross-linking efficiency in terms of
delta torque (MH-ML) at 160 8C isTMTD . isobutyl .benzyl .TINTD . 2-ethyl hexyl .DTCL
. APDP. This is clear evidence showing that the shorter alkyl chain on the nitrogen of the thiuram
disulfide produces the most efficient cure.
TINTD, being a viscous liquid, behaved like a plasticizer in the rubber mix; hence, the
compounded mix had the lowest Mooney viscosity value, see Table II.
TMTD showsthe overall best cure properties in terms of ultimate tensile strength, elongation at
break, and modulus at 100% to 300% strain. This is followed by isobutyl and benzyl thiuram
disulfides, giving only slightly inferior properties to TMTD. 2-ethyl hexyl and TINTD give better
tensile properties compared with APDP and DTCL as sulfur donors but inferior to TMTD.
Furthermore, benzyl thiuram disulfide cured rubber sheets showed heavy bloom on storage
because of high insolubility of the product. The bloom was identified as mainly zinc
dibenzyldithiocarbamate (ZBEC), from the breakdown of TBZTD in the presence of zinc oxide,
FIG. 1. — Comparative rheographs of natural rubber taken at 160 8C, cured with different sulfur donors present at 12.5
mmol.
NITROSAMINE SAFE THIURAM DISULFIDE 95

7. whereas the sheets cured with APDP and DTCL gave a sticky ‘‘bubbly’’ surface, indicating
insufficient or undercure.
It is clear from the above data that TINTD functions as a sulfur donor to cure natural rubber in
the absence of elemental sulfur. The structure of the R group on the thiuram disulfide has an
influence on the curing efficiency and on physical properties of the vulcanizate. TINTD has a
similar cure profile, as a sulfur donor, when compared with the safer thiurams studied.
COMPARATIVE STUDY OF TMTD AND TINTD AS A PRIMARY ACCELERATOR IN CV, SEMI-EV AND EV
CURE SYSTEMS IN NATURAL RUBBER
The curing efficiency of TMTD and TINTD as sulfur donors in black filled natural rubber was
reported in the previous section. In the following study, TMTD and TINTD were evaluated as
acceleratorsintheCV,semi-EV,andEVcuresystemsusingblackfilledNRmasterbatchIOM3B012.
Six formulations as given in Table III were studied. Comparative rheographs taken at 160 8C
are shown in Figure 2.
The rheological and Mooney data, reversion degree, tensile properties before and after thermal
aging (percentage heat resistance is given in brackets), hardness, compression set, and fatigue to
failure results for the CV, semi-EV, and EV cure systems are given in Table IV.
Figure 2 and Table IV show that TMTD has superior curing properties in terms of cure rate,
T90, and higher final torque compared with the cure profiles of a safer thiuram TINTD irrespective
of the type of cure used. As expected, the conventional cure systems in which the network is mainly
polysulfidic and thermally unstable, shows more reversion and has a reversion degree of 25% 6
2%, compared with the EV systems, where the network is mainly monosulfidic and thermally
stable, with the reversion degree being 4% 6 1%. Semi-EV cure systems show a compromise
between the CV and EV system, as indicated by the reversion degree, 13% 6 1%. The reversion
TABLE II
RHEOLOGICAL AND TENSILE PROPERTIES OF NATURAL RUBBER CURED WITH DIFFERENT SULFUR DONORS PRESENT AT
12.5 MMOL
Formulation mix Mix 1 Mix 2 Mix 3 Mix 4 Mix 5 Mix 6 Mix 7
Active accelerator TMTD Benzyl Isobutyl
2-ethyl
hexyl TINTD DTCL APDP
Rheological data at 160 8C
TS1, min 1.28 1.93 3.23 4.25 3.11 16.43 3.15
T10, min 1.32 1.86 3.17 3.94 2.92 12.97 2.08
T90, min 6.27 12.84 16.50 17.93 16.33 35.80 10.87
MH-ML, lb.in 11.10 8.96 9.52 7.83 8.35 5.63 4.4
Rate, lb.in/min 3.39 1.65 1.13 0.89 1.38 0.37 0.6
Mooney viscosity
Initial torque 30.8 22.2 34.3 41.4 19.3 46.9 44.1
ML1þ4 at 100 8C 22.8 16.3 24.5 28.8 13.0 33.7 32.3
Initial tensile properties
U.T.S., MPa 16.0 15.1 15.1 13.2 12.8 3.9 5.4
Strain at break, % 560 608 568 579 602 388 477
100% Modulus, MPa 1.32 1.02 1.00 0.89 0.77 0.61 0.63
300% Modulus, MPa 6.78 4.99 5.36 4.89 4.13 2.55 2.67
500% Modulus, MPa 13.98 11.18 12.44 10.58 9.62
96 RUBBER CHEMISTRY AND TECHNOLOGY, Vol. 92, No. 1, pp. 90–109 (2019)

8. process reflects the cross-link degradation taking place in the vulcanizate. Higher cure torque
curves, an indication of the state of cure, are given by the EV systems with minimum reversion
taking place after optimum cure.
The Mooney viscosity values of the mixes containing TINTD (mixes 9, 11, and 13) are much
lower compared with the mixes containing TMTD. This is because TINTD is a viscous liquid that
behaves like a plasticizer, giving softer mixes, whereas TMTD is a powder hence with a higher
Mooney viscosity.
Overall, the tensile properties of TMTD are slightly superior in tensile strength at break,
modulus at 100%, 200%, 300%, and 500% compared with the safer thiuram TINTD. The
elongation at break is also lower in the CV and EV cure, indicating a superior degree of cross-
linking. However, the initial tensile properties of semi-EV cures are very similar. In the EV cure, the
tensile strength of the TMTD cure has been matched by the TINTD but with lower modulus
compared with the TMTD cure. The hardness of all TMTD cures is higher compared with the
TINTD, again indicating superior cross-linking.
After 1 week of storage at room temperature, mixes 10, 12, and 13 started to show heavy bloom
on the surface. The bloom for mixes 10 and 12, containing TMTD, was identified as mainly zinc
dimethyldithiocarbamate (ZDMC) from the breakdown of TMTD in the presence of zinc oxide.
The bloom from mix 13 was identified as ZDNC byultraviolet (UV) spectrophotometric absorption
technique. These observations and analysis indicate that both TMTD and TINTD function in a
similar manner, and they break down during the vulcanization reaction to produce corresponding
zinc dialkyl dithiocarbamate in the presence of zinc oxide.
The thermal aging properties of TINTD after 7 days at 70 8C are very similar or only marginally
inferior to TMTD in all types of cure system. The heat resistance properties of the vulcanizates, as
measured bythe change in ultimate tensile stress, cured with either TMTD or TINTD in CV or semi-
EV cure, are almost identical. However, there is a slight difference in the EV cure, possibly because
of blooming. There is a larger change in vulcanizate properties upon aging at 70 8C, with respect to
elongation at break and 200% modulus, cured with TINTD as slow curing is still ongoing. The
hardness figures for the semi-EV cures are identical after aging.
TMTD produces the lowest compression set (22 h at 100 8C) in the CV and semi-EV cure
systems compared with TINTD. However, TINTD produces a lower compression set than TMTD
in the EV cures. The overall lower compression set is produced in the EV cures with slightly lower
mechanical strength. The EV cures also give good heat and reversion resistance; however, they
produce poor flex-fatigue properties because of the network being mainly monosulfidic.
TINTD gives thebestfatigue tofailure inthe CV,semi-EV,and EVcures systems incomparison
with TMTD. This is due to the high solubility of TINTD producing more flexibility in the network.
TABLE III
FORMULATIONS FOR CV, SEMI-EV, AND EV CURES WITH TMTD AND TINTD PRESENT AT 2.5, 6.25, AND 20.5 MMOL,
RESPECTIVELY
a
CV Semi-EV EV
Mix 8 Mix 9 Mix 10 Mix 11 Mix 12 Mix 13
Masterbatch IOM3 B012 162.5 162.5 162.5 162.5 162.5 162.5
ZnO 5 5 5 5 5 5
Sulphur 2.5 2.5 1.5 1.5 0.5 0.5
TMTD 0.6 1.5 4.9
TINTD 1.72 4.3 14.1
a
Weights given in grams.
NITROSAMINE SAFE THIURAM DISULFIDE 97

9. Overall, for both thiurams, the conventional cure systems provide better flex and dynamic
properties but poor thermal and reversion resistance. The bond dissociation energy is the underlying
reason for the variation in the above properties of the different vulcanizates. The higher the number of
sulfur atoms, the lower the bond dissociation energy of the linkage. Thus, the vulcanizates containing
mainly mono- or disulfidic linkages (EV and semi-EV) have better heat stability and reversion
resistance than those containing relatively high polysulfidic linkages, as in the conventional cures.
The above data clearly show that TINTD functions as an accelerator in the CV, semi-EV, and
EV cure systems in natural rubber. The initial and thermally aged tensile properties of TMTD are
onlyslightly superior toTINTD.Furthermore, TINTD produceslower compressionsetthan TMTD
in the EV cures and gives better fatigue to failure in the CV, semi-EV, and EV cure systems in
comparison with TMTD when used on an equal molar basis.
FIG. 2. — Comparative rheographs of TMTD and TINTD in natural rubber taken at 160 8C using conventional, semi-
efficient, and efficient cure systems.
98 RUBBER CHEMISTRY AND TECHNOLOGY, Vol. 92, No. 1, pp. 90–109 (2019)

10. COMPARATIVE STUDY OF TINTD AND TBUT IN SOLUBLE EV CURE IN NATURAL RUBBER
The efficacy of TINTD in CV, semi-EV, and EV cure systems was reported in the previous
section. It was found that TINTD clearly functions as an accelerator in all three systems but
performs best in the EV cure system. TINTD, being an oily liquid, highly soluble in rubber, and
capable of functioning as a sulfur donor and a primary accelerator, led to the investigation of its
TABLE IV
RHEOLOGICAL PROPERTIES OF NR VULCANIZATES AT 160 8C USING CV, SEMI-EV, AND EV CURE SYSTEMS, MOONEY
VISCOSITY AT 100 8C, TENSILE PROPERTIES BEFORE AND AFTER HEAT AGING, COMPRESSION SET, AND FATIGUE TO
FAILURE
Formulations mix
CV Semi-EV EV
Mix 8 Mix 9 Mix 10 Mix 11 Mix 12 Mix 13
Active accelerator TMTD TINTD TMTD TINTD TMTD TINTD
Rheological data at 160 8C
TS1, min 1.15 1.87 1.24 1.93 0.95 1.97
T10, min 1.20 1.90 1.32 2.02 1.14 2.32
T90, min 2.49 3.56 2.13 3.66 3.74 8.25
MH-ML, lb.in 16.42 11.39 15.67 12.6 24.9 19.22
Rate, lb.in/min 16.72 8.60 23.72 9.62 10.88 3.70
Reversion degree (R), % 26.78 24.98 13.85 13.28 4.07 4.02
Mooney viscosity
Initial torque 33.11 20.73 35.06 25.13 35.20 19.13
ML1þ4 at 100 8C 20.85 16.41 22.74 16.65 22.80 13.80
Initial tensile properties
U.T.S., MPa 19.8 17.8 20.8 19.8 16.9 17.9
Strain at break, % 511 599 583 545 351 406
100% Modulus, MPa 2.16 1.48 2.04 1.66 3.13 2.17
200% Modulus, MPa 5.64 3.67 5.44 4.41 8.27 6.33
300% Modulus, MPa 10.24 6.98 9.79 8.43 14.19 11.81
500% Modulus, MPa 16.33 14.86 18.29 17.77
Hardness (IRHD) 58 52 61 55 65 52
Tensile properties: aged 7 days at 70 8C
U.T.S., MPa 15.8
(20%)
14.2
(20%)
18.5
(8%)
18.6
(6%)
15.3
(10%)
15.2
(15%)
Strain at break, % 359
(30%)
345
(42%)
366
(37%)
361
(34%)
293
(17%)
294
(28%)
100% Modulus, MPa 3.05 2.77 3.42 3.29 3.61 3.12
200% Modulus, MPa 7.83
(þ39%)
7.13
(þ94%)
9.0
(þ65%)
8.75
(þ113%)
9.44
(þ14%)
8.95
(þ41%)
300% Modulus, MPa 13.28 12.48 15.15 15.06
Hardness (IRHD) after aging 64 62 63 63 64 59
% Compression set: 22 h at
100 8C
58.2 63.2 52.9 56.1 36.8 32.6
Fatigue to failure (100%
extension, cycles 3 100)
73 92 58 60 22 36
NITROSAMINE SAFE THIURAM DISULFIDE 99

11. performance in soluble-EV cures using black filled natural rubber masterbatch IOM 3 B012. In this
study, TINTD was evaluated against the most commonly used soluble EV accelerator, namely,
TBuT.
TINTD was initially compared with TBuT as asulfur donor and then as a secondary accelerator
in the presence of the sulfenamides, N-oxydiethylene-2-benzothiazole sulfenamide (MBS), and N-
cyclohexyl-2-benzothiazole sulfenamide (CBS) in black filled natural rubber.
COMPARISON OF THE PERFORMANCE OF TBUT AND TINTD AS SULFUR DONORS
Sulfur donor comparison was carried out at 12.5 mmol addition of TBuT and TINTD and also
at optimized dosage of 16.5 mmol for TINTD, as given in Table V.
Comparative rheographs taken at 160 8C are shown in Figure 3. Rheological, tensile properties
before and after aging (percentage heat resistanceis given in brackets), compressionset, trouser tear
test, fatigue to failure, and cross-link density data are given in Table VI.
It can be seen from Figure 3 and Table VI that the TBuT has superior curing, sulfur-donating
properties in terms of cure rate, T90, and higher final torque compared with the cure profile of safer
TINTD when the comparison is carried out on equal molar addition basis, that is, 12.5 mmol each.
The sulfur-donating or cure efficiency of TINTD can be increased by using a slightly higher
loading, 16.5 mmol, to match that of TBuT.
The heat resistance properties of vulcanizates containing TINTD after thermal aging for 7 days
at 70 8C are superior and for 7 days at 100 8C are very comparable to vulcanizates containing TBuT.
Also, TINTD provides lower compression set values compared with TBuT when vulcanizates are
tested for 22 h at 70 8C and 22 h at 100 8C. Furthermore, TINTD shows superior performance in the
trouser tear test, in fatigue to failure, and in terms of cross-link density when compared with TBuT.
The above findings clearly show that the traditional sulfur donor/accelerator TBuT, which is
most commonly used in soluble EV cure systems, can be substituted for performance by a safer
sulfur donor/accelerator TINTD.
COMPARISON OF THE PERFORMANCE OF TINTD AGAINST TBUT AS A SECONDARY ACCELERATOR
IN THE PRESENCE OF A SULFENAMIDE IN BLACK FILLED NATURAL RUBBER
In the previous section, it was determined that a 32% excess TINTD is required to match the
performance of TBUT as a sulfur donor; therefore, in the following mixes, 32% more moles of
TINTD was used.
Table VII shows the four formulations studied. Here, TINTD is compared against the soluble
EV accelerator TBuT in the presence of the most commonly used sulfenamide, MBS.2
MBS is not a
desirable accelerator, as it can form regulated carcinogenic N-nitroso-morpholine during the
TABLE V
FORMULATIONS FOR TBUT AND TINTD COMPARISON AS SULFUR DONORS AT 12.5 MMOL AND ALSO TINTD AT 16.5
MMOL
a
Mix 14 Mix 15 Mix 16
Masterbatch IOM3 B012 162.5 162.5 162.5
ZnO 5 5 5
TBuT 5.1
TINTD 8.6 11.7
a
Weights given in grams.
100 RUBBER CHEMISTRY AND TECHNOLOGY, Vol. 92, No. 1, pp. 90–109 (2019)

12. vulcanization reaction.Therefore,itwas substituted with another sulfenamide, CBS, fora safer cure
system.
Comparative rheographs taken at 160 8C are shown in Figure 4. Rheological, tensile properties
before and after aging (percentage heat resistanceis given in brackets), compressionset, trouser tear
test, fatigue to failure, and cross-link density data are given in Table VIII.
Figure 4 and Table VIII show MBS giving a higher torque compared with a CBS-based cure;
however,CBSprovidesaquickeronsetofcurescomparedwithMBS.ThemixescontainingCBShave
similar rheological properties with TBuT and TINTD and reach the same degree of change in torque.
However, for the MBS comparison, this may mean slightly more than 32% excess TINTD is required.
The tensile properties of vulcanizates containing TINTD after aging for 7 days at 70 8C and for
22 h at 100 8C are very comparable to vulcanizates containing TBuT. All four mixes have good heat
FIG. 3. — Rheographs taken at 160 8C of TBuT present at 12.5 mmol and TINTD present at 12.5 and 16.5 mmol as sulfur
donors.
NITROSAMINE SAFE THIURAM DISULFIDE 101

13. resistance properties, as minimum changes in tensile properties upon aging were observed. TINTD
gives comparable compression set values compared with TBuT when vulcanizates are tested for 22
h at 70 8C and 22 h at 100 8C. However, the compression set values with MBS are much lower
compared with the CBS cures. TINTD in combination with CBS gives agood tear strength, which is
comparable to the TBuT/MBS cure.
All four mixes have very similar cross-link densities, with a difference of only 0.093105
mol
cm3
between the highest and lowest value. This is in agreement with the tear strength and fatigue to
failure data, which are all relatively similar.
The above results indicate that TINTD has the potential to replace the most commonly used
soluble EV cure accelerator, for example, TBuT, when used in combination with sulfenamides.
TABLE VI
RHEOLOGICAL AND TENSILE PROPERTIES OF NATURAL RUBBER CURED WITH TBUT AND TINTD AS SULFUR DONORS,
PRESENT AT 12.5 AND 16.5 MMOL, BEFORE AND AFTER AGING FOR 7 DAYS AT 70 8C AND 7 DAYS AT 100 8C, ALSO
MISCELLANEOUS PROPERTIES: COMPRESSION SET, TROUSER TEAR TEST, FATIGUE TO FAILURE, AND CROSS-LINK DENSITY
Formulations mix Mix 14 Mix 15 Mix 16
Active accelerator
TBuT
(12.5 mmol)
TINTD
(12.5 mmol)
TINTD
(16.5 mmol)
Rheological data at 160 8C
TS1, min 2.53 3.11 2.74
T10, min 2.54 2.92 2.81
T90, min 13.18 16.33 15.42
MH-ML, lb.in 10.12 8.35 10.93
Rate, lb.in/min 1.47 1.38 1.44
Initial tensile properties
U.T.S., MPa 15.6 12.8 16.2
Strain at break, % 573 602 570
100% Modulus, MPa 1.03 0.77 1.0
300% Modulus, MPa 5.79 4.13 5.65
500% Modulus, MPa 12.88 9.62 13.30
Tensile properties: Aged 7 days at 70 8C
U.T.S., MPa 17.5 (þ11%) 16.9 (þ4%)
Strain at break, % 513 (11%) 525 (8%)
100% Modulus, MPa 1.51 1.21
300% Modulus, MPa 8.19 (þ41%) 7.12 (þ26%)
500% Modulus, MPa 17.0 15.84
Tensile properties: Aged 7 days at 100 8C
U.T.S., MPa 14.9 (5%) 14.5 (11%)
Strain at break, % 387 (33%) 428 (25%)
100% Modulus, MPa 2.03 1.64
300% Modulus, MPa 10.46 (þ81%) 8.57 (þ52%)
% Compression set: 22 h at 70 8C 18.97 14.42
% Compression set: 22 h at 100 8C 39.58 35.14
Trouser tear strength, kgf/cm 9 13
Cross-link density, mol cm3
8.30 3 105
8.49 3 105
Fatigue to failure (100% extension, cycles 3 100) 483 680
102 RUBBER CHEMISTRY AND TECHNOLOGY, Vol. 92, No. 1, pp. 90–109 (2019)

14. GENERAL DISCUSSION ON THE PROPERTIES AND BEHAVIOR OF TINTD IN BLACK
FILLED NATURAL RUBBER
The new experimental findings described in the present article show that TINTD functions as a
sulfur donor to cure natural rubber in the absence of elemental sulfur. The nature of the R group, such
as length of the alkyl chain or branching of the chain causing steric hindrance or aromatic rings on the
nitrogen in the thiuram disulfide, has an influence on the curing efficiency of the rubber. It was found
that even on an addition of equal molar basis, 12.5 mmol, the efficiency of cure decreases with
increasing molar mass of the thiuram disulfide. This was unexpected as the molar ratio addition took
account of the relative thiuram content of each molecule. That is, thiuram content of TMTD is 74.9%,
TiBUT is 44.1%, TBZTD is 33.0%, 2-ethylhexyl TD is 28.44%, and TINTD is 26.2% based on the
molarmassofthethiuramgroupbeing180withinthewholemolecule.Themolarratioadditionmeant
that an equal amount of sulfur donation should have taken place for each thiuram. The R group was
shown to have an influence such as steric hindrance, which is likely to reduce the rate of formation of
the active sulfurating agent responsible for sulfur cross-linking during the vulcanization reaction.
Therefore, the branched diisononyl alkyl R group increases the molecular weight and
molecular volume of TINTD relative to TMTD, thus reducing its cure efficiency. However, TINTD
has a similar cure profile, as a sulfur donor, when compared with the other safer amine-derived
thiuram disulfides studied, which are also based on large bulky alkyl or aryl R groups that give rise
to steric hindrance.
In addition, TBZTD cured rubber sheets showed heavy bloom on storage because of the high
insolubility of the aromatic nature of the bulky R group of this curative. Analysis of the bloom, by
UV spectrophotometric method35
and spot analysis,36
showed it to be a mixture of TBZTD and
ZBEC. No such bloom was observed with TINTD because of the high solubility of the long alkyl R
group on this molecule (see Scheme 2).
Experimental data also showed that TINTD functions as an accelerator, like other thiuram
disulfides, in the presence of elemental sulfur in natural rubber. The initial and thermally aged
tensile properties of TMTD were only slightly superior to TINTD. However, the extent of change as
measured by the reversion degree and heat resistance of the vulcanizates was almost identical.
Furthermore, TINTD produced lower compression set than TMTD in the EV cures and gave better
fatigue to failure in the CV, semi-EV, and EV cure systems in comparison to TMTD when used on
an equal molar basis. These superior results may be due to the high solubility nature of the TINTD.
TMTD in the semi-EV and EV cures showed heavy bloom on the surface of the vulcanizates.
TINTD also showed some bloom in the EV cure as a high dosage exceeded its solubility in natural
rubber. The blooms from TMTD and TINTD were identified as mainly ZDMC and ZDNC,
TABLE VII
FORMULATIONS OF TBUT AND TINTD IN EV CURES, AS SECONDARY ACCELERATORS, USED IN COMBINATION WITH MBS
AND CBS SULFENAMIDES
a
Mix number Mix 17 Mix 18 Mix 19 Mix 20
Masterbatch IOM3 B012 162.5 162.5 162.5 162.5
ZnO 5 5 5 5
Sulfur 0.6 0.6 0.6 0.6
TBuT 0.6 0.6
TINTD 1.33 1.33
MBS 1.5 1.5
CBS 1.5 1.5
a
Weights given in grams. TBuT loading¼1.47 mmol. TINTD loading¼1.93 mmol.
NITROSAMINE SAFE THIURAM DISULFIDE 103

15. respectively. These observations and analysis indicate that both TMTD and TINTD function in a
similar manner during the vulcanization reaction to produce corresponding zinc dialkyldithio-
carbamate in the presence of zinc oxide (see Scheme 2). The longer alkyl chain, R group on the
nitrogen of thiuram disulfide, is responsible for the high solubility of the product. This is further
evidenced byZDNC,which is alsohighlysoluble in theelastomeric medium. Also, ZDNCis highly
thermally stable (no decomposition occurs below 250 8C), and it does not produce diisononylamine
readily. Diisononylamine does not nitrosate easily, because of the presence of branching of the R
chain in the molecule. Hence, ZDNC, which is based on diisononylamine, has been established as a
nitrosamine safe accelerator.
Nitrosamine safe means that either the high molecular weight and bulkiness of the nitrosatable
substances dramatically decrease their accessibility, thus restricting nitrosation or limiting the
availability of their nitrosated amines and their related alkylating substances, as in the case of N-
FIG. 4. — Rheographs taken at 160 8C of TBuT and TINTD when used as secondary accelerators in combination with MBS
and CBS in natural rubber.
104 RUBBER CHEMISTRY AND TECHNOLOGY, Vol. 92, No. 1, pp. 90–109 (2019)

16. nitrosodiisononylamine (NDiNA), or safe due to the chemical structure of the related nitrosamines,
which can produce only a stable carbenium ion, these being weak alkylating substances and so are
unable to damage RNA and DNA to the extent of causing carcinogenesis. As a result, their
toxicology is noncarcinogenic.18
TABLE VIII
RHEOLOGICAL AND TENSILE PROPERTIES OF NATURAL RUBBER CURED WITH TBUT AND TINTD AS SECONDARY
ACCELERATORS USED IN COMBINATION WITH MBS AND CBS SULFENAMIDES BEFORE AND AFTER AGING FOR 7 DAYS AT
70 8C AND 7 DAYS AT 100 8C, ALSO MISCELLANEOUS PROPERTIES: COMPRESSION SET, TROUSER TEAR TEST, FATIGUE TO
FAILURE, AND CROSS-LINK DENSITY
Formulations mix Mix 17 Mix 18 Mix 19 Mix 20
Active accelerator
TBuT
þ MBS
TINTD
þ MBS
TBuT
þ CBS
TINTD
þ CBS
Rheological data at 160 8C
TS1, min 4.01 4.43 3.04 3.35
T10, min 4.23 4.64 3.08 3.40
T90, min 8.05 8.27 5.14 5.52
MH-ML, lb.in 14.98 14.37 13.29 13.29
Rate, lb.in/min 3.14 3.17 5.16 5.02
Initial tensile properties
U.T.S., MPa 18.9 18.1 17.7 18.7
Strain at break, % 536 531 575 572
100% Modulus, MPa 1.70 1.53 1.41 1.42
300% Modulus, MPa 8.37 7.81 6.65 7.19
500% Modulus, MPa 17.31 16.76 14.44 15.62
Tensile properties: aged 7 days at 70 8C
U.T.S., MPa 19.6
(þ4%)
18.4
(þ2%)
18.3
(þ3%)
19.6
(þ5%)
Strain at break, % 470
(12%)
438
(18%)
442
(23%)
475
(17%)
100% Modulus, MPa 1.84 2.10 2.16 2.12
300% Modulus, MPa 9.49
(50%)
11.11
(41%)
10.87
(39%)
10.76
(43%)
Tensile properties: aged 22 h at 100 8C
U.T.S., MPa 18.5
(2%)
17.3
(4%)
18.2
(þ3%)
18.1
(3%)
Strain at break, % 457
(15%)
454
(15%)
462
(20%)
483
(16%)
100% Modulus, MPa 2.25 1.80 2.05 1.89
300% Modulus, MPa 11.00
(42%)
9.79
(46%)
10.32
(42%)
9.44
(50%)
% Compression set: 22 h at 70 8C 22.61 24.27 30.43 31.40
% Compression set: 22 h at 100 8C 48.61 49.46 56.71 58.69
Trouser tear strength, kgf/cm 24.2 23.8 20.0 24.4
Cross-link density, mol cm3
5.71 3 105
5.71 3 105
5.67 3 105
5.62 3 105
Fatigue to failure (100%
extension, cycles 3 100)
638 583 563 600
NITROSAMINE SAFE THIURAM DISULFIDE 105

17. Because of the high solubility of TINTD and ZDNC in natural rubber, TINTD had the
characteristics for being a candidate to replace TBuT. TBuT, as stated above, is a highly effective
soluble thiuram disulfide for soluble EV cure systems; however, it produces regulated carcinogenic
N-nitrosodibutylamine, whereas TINTD does not.
It was shown that TINTD can replace TBuT as a sulfur donor and also as a secondary
accelerator in the presence of a sulfenamide, for example, MBS and CBS in black filled natural
rubber. In both cases, a higher level of TINTD in comparison with TBuT, on an equivalent molar
basis, was required. This observation is consistent with the findings by Scheele et al.,37
who found
smaller reaction velocity constants with increasing length of the R alkyl group on the nitrogen of
the thiuram disulfide. The branching of the alkyl chain increases the steric effects, hence
decreasing the rate of formation of the sulfurating intermediate, which is responsible for the cross-
linking.
It was also shown that the traditional sulfur donor and accelerator TBuT, which is most
commonly used in soluble EV cure systems, can be substituted while maintaining cure performance
by a safer sulfur donor and accelerator TINTD. The tensile properties of vulcanizates containing
TINTD initially and after thermal aging for 7 days at 70 8C and for 7 days at 100 8C are very
comparable to vulcanizates containing TBuT. TINTD also gives lower compression set values
when vulcanizates are tested for 22 h at 70 8C and 22 h at 100 8C. Furthermore, TINTD shows
superior performance in the trouser tear test, in fatigue to failure, and in terms of cross-link density
when compared with TBuT.
SCHEME 2. — During the vulcanizationreaction, thiuram disulfidesbreakdownto form respective zinc dithiocarbamates in
the presence of zinc oxide.
106 RUBBER CHEMISTRY AND TECHNOLOGY, Vol. 92, No. 1, pp. 90–109 (2019)

18. CONCLUSION
The new nitrosamine safe thiuram disulfide, TINTD, has been shown to function as a sulfur
donor and a primary or a secondary accelerator for curing natural rubber. The long-branched alkyl
chain on the nitrogen of TINTD makes it more soluble in the elastomer. Furthermore, ZDNC
formed during the vulcanization reaction from TINTD is also highly soluble because of the long-
branched alkyl chain on the nitrogen of the dithiocarbamate. The high solubility of TINTD and
ZDNC in rubber, similar to traditional TBUT and ZDBC, coupled with the safer nature of TINTD
and ZDNC, makes the use of TINTD highly attractive for soluble-EV systems, especially where
carcinogenic N-nitrosamine and nitrosatable substances’ formation and also accelerator toxicity,
irritant dermatitis, and type IV allergy are of concern.
Because of the higher molar mass of TINTD, in which only 26.2% is active thiuram, and the
increased steric hindrance from the alkyl chain, there is a need to add a higher amount of accelerator
to obtain optimum technological properties in the rubber. Because TINTD is a viscous liquid, the
addition of higher loading has a plasticizing effect on the compound, thus making the rubber softer
whilst having a similar cross-link density. This can be used to advantage by reducing or omitting the
addition of oils or plasticizer in the rubber compound, which reduces mixing times and improves
temperature gain in an internal mixer.
CONFLICTS OF INTEREST
The following authors are employees of Robinson Brothers Limited: Ranvir Virdi and Boyd
Grover.
ACKNOWLEDGEMENTS
The permission of Robinson Brothers Limited to publish this work is greatly appreciated. The
authors would also like to thank Dr. Allen Bowden and Chi Tsang from the University of
Birmingham for their help with the structural characterization of TINTD.
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[Received August 2017, Revised January 2018]
APPENDIX A:
PROPERTIES OF TINTD
Chemical name Bis(3,5,5-trimethylhexyl) carbamothiolsulfanyl-N,
N-bis (3,5,5-trimethylhexyl) carbamodithiote
Synonym name Tetraisononylthiuramdisulfide
Empirical formula C38H76N2S4
Relative molar mass 688
Appearance Yellow to light-brown viscous oil
Solubility Insoluble in water; soluble in toluene and some
other nonpolar solvents
Thermal stability Thermally stable up to 150 8C
108 RUBBER CHEMISTRY AND TECHNOLOGY, Vol. 92, No. 1, pp. 90–109 (2019)

20. APPENDIX B:
LIST OF ABBREVIATIONS USED IN THE MAIN TEXT
TMTD Tetramethylthiuramdisulfide APDP Alkylphenol disulfide polymer
TETD Tetraethylthiuramdisulfide DTCL Dithiocaprolactam
DPTH Dipentamethylenethiuramhexasulfide MBS N-oxydiethylene-2-benzothiazole
sulfenamide
PTD Dipentamethylenethiuramdisulfide RNA Ribonucleic acid
TINTD Tetraisononylthiuramdisulfide DNA Deoxyribonucleic acid
TBuT Tetrabutylthiuramdisulfide NDMA N-nitrosodimethylamine
TMTM Dimethylthiurammonosulfide NDEA N-nitrosodiethylamie
TBZTD Tetrabenzylthiuramdisulfide NDBzA N- nitrosodibenzylamine
TiBTD Tetraisobutylthiuramdisulfide NDBA N-nitrosodibutylamine
ZDNC Zinc diisononyldithiocarbamate NDiBA N-nitrosodiisobutylamine
ZBEC Zinc dibenzyldithiocarbamate NMOR N-nitrosomorpholine
ZDBC Zinc dibutyldithiocarbamate NPIP N-nitrosopiperidine
ZDMC Zinc dimethyldithiocarbamate NDiNA N-nitrosodiisononylamine
SDINDTC Sodium diisononyldithiocarbamate DINA Diisononylamine
CBS N-cyclohexyl-2-benzothiazole
sulfenamide
ZEH Zinc 2-ethylhexanoate
NITROSAMINE SAFE THIURAM DISULFIDE 109