Compensating extra sulfur to TESPD-silica-filled NR
compounds
Wisut Kaewsakul*, Kannika Sahakaro, Wilma K. Dierkes, Jacques Noordermeer and Anke Blume
Elastomer Technology and Engineering (ETE), Department of Mechanics of Solids, Surfaces and Systems (MS3), University of Twente, The Netherlands
Background
Experimental
Results
Conclusions
TESPT can liberate free sulfur into the
system, resulting in an undesired high
compound viscosity caused by ‘premature
scorch’ [1].
An alternative silane: TESPD, has been
made available.
[1] W. Kaewsakul, K. Sahakaro, W.K. Dierkes and J.W.M. Noordermeer, Rubber Chemistry and Technology 2012, 85 (2), 277-294. [2] W. Kaewsakul, K. Sahakaro, W.K. Dierkes and J.W.M. Noordermeer, Rubber Chemistry and Technology 2013, 86 (2), 313-329. [3] W. Kaewsakul, K. Sahakaro, W.K. Dierkes and J.W.M. Noordermeer, Kautschuk Gummi Kunststoffe 2014, 67 (5), 33-39.
The addition of extra sulfur in an internal mixer during non-productive step gives a
positive contribution towards improved silica dispersion, and hence final properties.
Adding extra sulfur during productive mixing on a two-roll mill has practically no effect.
Extra sulfur at 3.4-5.1 wt% relative to the TESPD amount (0.15-0.20 phr), added during
mixing of TESPD-silica-NR in an internal mixer is an optimal amount.
Compound viscosity and cure properties
An internal mixer with fill factor of 70 %,
a rotor speed of 60 rpm, starting
temperature of 100oC to reach 140-145oC.
*Correspondence: W. Kaewsakul, PhD, assistant professor; e-mail: w.kaewsakul@utwente.nl
0 20 40 60 80 100 120 140 0 2 4 6 8 10 12 14 16 18
Extra sulfur (wt% rel. to TESPD)
ML (1 + 4 )100 o C Two-roll mill Internal mixer TESPT 0 10 20 30 40 50 60 70 80 0 2 4 6 8 10 12 14 16 18
Extra sulfur (wt% rel. to TESPD)
B ound r ubbe r c ont e nt ( % ) TESPT Chemically BdR Total BdR Physically BdR Without extra sulfur
0.000 0.001 0.002 0.003 0.004 0.005 0.006 20 30 40 50 60 70 80 90 Chemically BdR content (%) Flocc ulation ra te c ons tant , k a ( s -1 ) 0 10 20 30 40 50 60 70 80 90 100 110 120 ML (1 + 4 )1 00 o C ka_TESPT ML(1+4)_TESPT increase in extra sulfur increase in extra sulfur 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 20 30 40 50 60 70 80 90 Chemically BdR content (% ) [G '( 0 .56 )-G '( 100 )] , G ' (M P a ) 0 1 2 3 4 5 6 7 8 9 R ei n fo rcem en t p a ram et er , α F _TESPT _TESPT increase in extra sulfur increase in extra sulfur ΔG' (TRM) αF (TRM) ΔG' (IM) αF (IM) αF ΔG' ∆ 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 0 2 4 6 8 10 12 14 16 18
Extra sulfur (wt% rel. to TESPD)
Reinforce ment inde x , M 3 00 /M 1 00 Two-roll mill Internal mixer TESPT 0 5 10 15 20 25 30 35 0 2 4 6 8 10 12 14 16 18
Extra sulfur (wt% rel. to TESPD)
Te ns ile s tr e ngt h ( M P a ) 0 100 200 300 400 500 600 700 800 900 1000 E longa tion a t br e a k ( % ) Two-roll mill Internal mixer TESPT
Mechanical properties of vulcanizates
Indicators of filler-rubber interactions and lightly crosslinked rubber networks.
References:
TESPT – the most commonly used silane coupling agent
Chemical name: Bis-triethoxysilylpropyl tetrasulfide (-S4-)
TESPD – An alternative to TESPT, preventing a scorch problem
Chemical name: Bis-triethoxysilylpropyl disulfide (-S2-)
Extra networks can suppress the mobility of
silica clusters but give undesired high viscosity at a certain content of extra sulfur added.
Adding extra sulfur during non-productive mixing gives a significant impact on filler-filler interaction or
Payne effect & reinforcement.
S4 (CH2)3 (CH2)3 Si Si OC2H5 OC2H5 OC2H5 H5C2O H5C2O H5C2O S2 (CH2)3 (CH2)3 Si Si OC2H5 OC2H5 OC2H5 H5C2O H5C2O H5C2O
According to the previous study [2], the TESPT-based compounds showed
superior overall properties compared to those containing TESPD, mainly
attributed to the influence of free sulfur liberated.
The present study investigates an effect of extra sulfur added to silica-filled NR
compounds during non- and productive mixing processes [3].
Remark: The results presented in this poster have been published in Kautschuk Gummi Kunststoffe 2014, 67 (5), 33-39 or the reference [3].
Mixing sequence: NR for 2 min, ½ silica+silane (+ ½ extra sulfur)
for 5 min, ½ silica+silane+TDAE oil (+ ½ extra sulfur) for 5 min,
ZnO+stearic acid+TMQ+ ½ DPG for 3 min, and discharged.
Sulfur (+extra sulfur)+accelerators+ ½ DPG were added on two-roll mill.
The measurement methods are described in [3].
0 1 2 3 4 5 6 7 8 9 0 2 4 6 8 10 12 14 16 18
Extra sulfur (wt% rel. to TESPD)
S c or c h & opt im um c ur e t im e s ( m ins .) t10 (IM) tc,90 (TRM) tc,90 (IM) TESPT t10 (TRM) Two-roll mill Internal mixer Note: TRM = Two-roll mill IM = Internal mixer Note: TRM = Two-roll mill IM = Internal mixer Note:
The compounds with extra sulfur added in an internal mixer.
Note:
The compounds with extra sulfur added in an internal mixer.
