www.rubbernews.com Rubber & News • July 27, 2020 21 Technical Reinforcement of deproteinized NR by nano silica By Siti Salina Sarkawi Reinforcing such as carbon black Executive summary and silica are used in synthetic and The key element in the reinforcement of rubber by silica is the chemical cou- to improve its properties. pling between silica and rubber, which applied for both synthetic and natural Compared to carbon black, mixing of rubbers. Non-rubbers in the natural rubber are shown to compete in the silaniza- silica in rubber compounds involves tion reaction during silica and natural rubber mixing. many difficulties due to the large polar- This paper presents an investigation on the effect of different types of silane ity difference between silica and rubber.1 coupling agents on rheological, physical and dynamic properties of silica reinforced A bifunctional organosilane is common- deprotenized natural rubber (DPNR). The use of DPNR in silica compound provides better silanization during silica-rubber mixing and improves filler dispersion. TECHNICAL NOTEBOOK Comparison is made between sulfur containing silane of polysulphide silanes, Edited by John Dick mercaptosilane and blocked mercaptosilane. The filler-to-rubber and filler-to-fill- er interactions in silica-reinforced natural rubber and DPNR are evaluated by ly used as a coupling agent in enhancing bound rubber content and Payne effect study. The use of bis-triethoxysilylpropyl the compatibility of silica and rubber. in silica reinforced DPNR gives good physical as well as dynamic properties. Silanization of silica leads to funda- mental changes in its reinforcing charac- teristics. The dispersive component of the Experimental subjected to a strain sweep at 0.5 Hz. surface energy of modified-silica drops Materials The Payne effect was calculated as the below the value of unmodified silicas and Natural rubber, SMR20 and deprotein- difference between the storage modulus, Sarkawi the polar component becomes negligi- ized natural rubber from the Malaysian G’ at 0.56 percent and G’ at 100.04 per- ble.2-4 Rubber Board were used in this study. All cent strain. The Payne effect after cure Organofunctional silanes used for experiments were performed using a was measured after in the The author sulfur-cured rubber compounds can be tread composition based on natural rub- RPA 2000 at 150ºC for 10 minutes and Siti Salina Sarkawi is a senior categorized into the following three ber as shown in Table 1. The commercial subsequent cooling to 100ºC, making research officer under the Technol- types:5 precipitated silica, Ultrasil 7000, from use of the same strain sweep conditions. ogy & Engineering Division of the Di- and polysulphide silanes: Evonik was used. The types of silanes The bound rubber content (BRC) mea- Malaysian Rubber Board.

[(RO)3 – Si – (CH2)3 – S]2-Sx used were Si-69 (bis-triethoxysilylpropyl surements were performed on uncured She joined MRB in 2000 as a re- or TESPT) and X50S for polysulfidic si- samples by extracting the unbound search officer. From 2014-18, she Mercaptosilanes: lane, Si-363 for mercapto silane and NXT rubber with toluene at room tempera- was the head of Silica Dispersion

(RO)3 – Si – (CH2)3 – SH silane for blocked-mercapto silanes. ture for seven days in both normal and Technology for Green program ammonia environments. The ammonia in MRB. Her research interest and Blocked-Mercaptosilanes: Mixing treatment of BRC was done to obtain the expertise include ,

(RO)3 – Si – (CH2)3 – S-B The compounds were mixed in three chemically bound rubber as ammonia silica technology, epoxidized natural steps. The first step mixing was done us- cleaves the physical linkages between rubber, deproteinized natural rub-

Where R = CH3 or C2H5 or other ing a laboratory internal mixer Farrel rubber and silica. The amount of BRC ber and nano-fillers. groups; B = CN or C7H15C=O; x = 0-8 Banbury BR1600. The fill factor of the (percent) was calculated by: Sarkawi completed her doctorate mixer was fixed to 70 percent, the starting at University of Twente in the Neth- The in-situ reaction of silica and silane temperature of the mixing chamber was erlands in 2013, with the thesis enti- during rubber mixing needs an optimum 80°C and the rotor speed was 80 rpm. tled “Nano-Reinforcement of Tire high temperature, around 150°C, for sev- The masterbatch was sheeted out on a Rubber: Silica Technology for Natu- eral minutes to ensure a complete si- SKK 9-inch by 18-inch two-roll mill. After ral Rubber.” She gained a master’s lanization process.6 For natural rubber 24 hours, the masterbatch was re-milled in polymer materials science and

(NR), this high mixing temperature is not in the same internal mixer for three min- Where wo is the initial weight of the engineering from the University of advisable as degradation of NR can occur, utes to improve the dispersion of silica. sample, wdry is the dry weight of the ex- Manchester Institute of Science and which will affect the final properties of After 24 hours, the curatives were added tracted sample, winsol is the weight of insol- Technology in the United Kingdom. 7,8 the compounds. Silica can interact with to the compound on the two-roll mill. uble (mainly filler) in the sample, wfiller,phr She did her undergraduate study at proteins in the NR and lead to the si- is the total filler weight in phr and wtotal, phr Vanderbilt University in the U.S. in lanization being partially hindered.9-11 Analyses is the total composite weight in phr. The chemical engineering. In the present work, the reinforcement Vulcanization curves were measured total BRC is referred to BRC obtained She has been involved in various of silica-silane system in deproteinized using a rheometer MDR 2000 from Al- from normal atmosphere while chemically aspects of material science and rub- natural rubber (DPNR) compounds is in- pha Technologies, under conditions of BRC is the data obtained from ammonia ber technology, particularly in areas vestigated. The silane coupling agent in 0.833 Hz and 2.79 percent strain over a treated BRC measurement. of mixing and compounding, rubber the compound is varied in type of polysul- period of 30 minutes at a temperature of Vulcanizates were prepared by curing formulation, compound design, rub- fide, mercaptosilane and blocked-mer- 150ºC. the compounds for their respective t95 ber analysis and processing technol- captosilane. Comparison of vulcanization The Payne effect was measured in the (time to reach 95 percent of torque dif- ogies. She is active in consultancy properties, filler-to-filler interaction or rubber process analyzer (RPA 2000) ference in the curemeter) at 150ºC using works in evaluation of new materials Payne effect, and physical properties be- from Alpha Technologies. an electrical press (Tung Yu) at 100 bar. and additives for rubber and com- tween NR and DPNR compounds are Before cure, the sample was heated to Tensile properties of the vulcanizates pound development, giving technical discussed. 100ºC in the RPA and subsequently were measured using a Zwick Z020 ten- advisory services to the industries sile tester according to ISO-37. The and related government agencies, as Table 1: Compound formulation. hardness of the cured samples was de- well as lecturing on topics related to termined according to DIN-53505. rubber and tire technology. The dynamic properties of vulcanizates: Her research and development storage modulus, loss modulus and glass projects include rubber-coated car- transition temperature were measured us- bon black, kenaf fiber, rice husk as ing a Mettler Toledo Dynamic Mechanical bio-filler, reduction of zinc oxide Analyzer (DMA1 Start system). The sam- level, epoxidized palm oil, latex ples were cut from the vulcanized sheets of stimulant, green retreads and low See Silica, page 21 rolling resistance tires.

Table 3: Bound rubber content of DPNR-silica compounds.

Table 2: Payne effect of DPNR-silica compounds.

P021_P022_ RPN_20200727.indd 21 7/23/20 4:00 PM 22 Rubber & Plastics News • July 27, 2020 www.rubbernews.com evaluated from the bound rubber content. nizates from the DMTA measurement Table 3 shows the bound rubber content can be used to predict the important tire of the DPNR-silica with and without tread rubber properties. For high wet names GM, co-CEO ammonia treatment. Ammonia treatment skid resistance of a tire, a high tan delta European Rubber Journal to head the direction and control of on the bound rubber of the compound at temperature around 0°C is required. MILAN—Pirelli & C. SpA has launched strategy and extraordinary operations. separates the physically or loosely bound However, for low rolling resistance tire, a reorganization plan to broaden its He will maintain as his reports: rubber, and only chemically or tightly a lower tan delta at 60°C is needed. management team in line with the corporate affairs, compliance and bound rubber was obtained.12,13 Comparison of temperature depen- company’s succession plan for 2023. company secretary; strategic planning It is observed that chemically bound dence of tan delta at 10Hz for DPNR At the suggestion of Marco Tronch- and controlling and investor relations; rubber is retained for all compounds with compounds is shown in Fig. 2 and Table etti Provera, executive vice chairman communication and brand image; polysulfidic silane, but not with mercapto 5. All vulcanizates show comparable tan and CEO, the board on July 23 ap- global institutional affairs and sus- and blocked-mercaptosilanes. This must delta at 0°C, indicating comparable prop- proved the appointment of Angelos tainability. be due to the interaction of sulfur moiety erties of wet grip. DPNR with mercapto- Papadimitriou as the general manag- The general manager co-CEO will with rubber during the mixing and even silane has the lowest tan delta at 60°C, er and co-CEO. Papadimitriou will be tasked with “all the necessary exec- before the vulcanization. This is normally indicating the potential of low rolling re- step into his new role on Aug. 1, and utive levers, as well as all the staff ar- associated with increase of the viscosity of sistance of the tire from the compound. will report directly to Tronchetti Pro- eas not reporting directly to the execu- the compound. The compounds with mer- vera. tive vice chairman and CEO, and the capto and blocked-mercaptosilanes are Conclusions According to Pirelli, the reorganiza- general manager operations, Andrea only giving the shielding of silica surface The effect of different types of silanes tion aims to expand the management Casaluci.” and are effective in lowering the filler-fill- in DPNR-silica compounds is investigat- team for the future succession path Papadimitriou is the CEO of Italian er interaction in the compound. ed. Both mercapto and blocked mercap- outlined by the procedure adopted by packaging firm Coesia. He previously to-silane DPNR-silica compounds show the tire maker earlier this year. served as president and managing di- Rheological properties lower silica-silica interaction compared The procedure foresees that, by Oc- rector of GlaxoSmithKline. Fig. 1 shows the comparison of vulcani- to polysulfidic silane. tober 2022, a candidate should be According to his LinkedIn profile, zation curve at 150°C for DPNR-silica The physical properties of the identified to be proposed as the new Papadimitriou has almost 30 years of compounds with different type of silanes. DPNR-silica vulcanizate are less affect- CEO of Pirelli in the first half of 2023. professional experience in the ad- DPNR-silica compounds with polysulfidic ed by the type of silane used. The use of Under the proposed new “macro-or- vanced industrial and the health care silane and blocked-mercapto silane show polysulfide silane in DPNR-silica gives ganizational structure,” the executive sectors, having worked in various comparable vulcanization properties. the good overall physical properties. vice chairman and CEO will continue countries in Europe and in the U.S. However, mercaptosilane containing For dynamic properties, DPNR-silica compound shows faster cure and scorch with mercaptosilane show the lowest The different type of silane has an ef- time. This is due to the free mercapto tan delta at 60°C, but the tan delta at fect on filler-filler interactions as ob- group of Si363, which makes it more re- 0°C is comparable to polysulfidic silanes. Silica served from Payne effect for DPNR active as compared to TESPT. compounds (Table 2). The Payne effect A slight reversion is observed for References Continued from page 21 1. Noordermeer, J.W.M. and Dierkes, W.K., 2008 in of masterbatch after the second stage of NR-silica compound. This is in agree- “Rubber Technologist’s Handbook,” Vol.2, J. White, 2mm thickness. A temperature sweep mixing are comparable for polysulphide ment with earlier works reported where S.K. De and K. Naskar, eds., Smithers Rapra Tech- measurement from -100° to +100°C was and mercaptosilane. However, the com- DPNR-silica compound show more stable nology, U.K., Chapter 3. performed in tension mode at a frequency pound with blocked mercapto silane has and show plateau curve compared to 2. Wang, M.J., Wolff. S., and Donnet, J.B., 1991, 7,8,11 Rubber Chem. Technol., 64, 559-576. of 10Hz and dynamic strain of 0.1 percent. the lowest Payne effect. NR-silica compound. However, for 3. Wolff, S, and Wang, M.J., 1992, Rubber Chem. After the finalizing stage, both mercapto DPNR-silica with mercapto silane, rever- Technol., 65, 329-342. Results and Discussion and blocked mercapto-silane have lower sion sign is observed after five minutes. 4. Wang, M.J., and Wolff, S. 1992, Rubber Chem. Filler-to-filler interactions Payne effect compared to polysulfidic sila- Technol., 65, 715-735. 5. Meon, W., Blume, A., Luginsland, H.D., and Uhr- Filler-filler interaction is commonly nes. The Payne effect carried out after cure Physical properties landt, S., 2004 in “Rubber Compounding Chemis- measured by the so-called Payne effect: or vulcanization also showed that both A summary of physical properties of try and Applications Handbook,” Rodgers, B., ed., the drop in storage modulus in a dynamic mercapto and blocked mercapto-silane DPNR vulcanizate is shown in Table 4. Marcel Dekker Inc., New York, Silica and Silane. mechanical test when the strain (deforma- have lower Payne effect compared to poly- The different type of silane used has little 6. Reuvekamp, L.A.E.M., ten Brinke, J.W., van Swaaij, P.J., and Noordermeer, J.W.M., 2002, Rub- tion) is increased from low (0.56 percent) sulfidic silanes. The polysulfidic silanes in effect on the physical properties of the ber Chem. Technol., 75, 187. to a high value (100 percent) at constant the compound shows competitive effect of DPNR-silica vulcanizate. The tensile 7. Kaewsakul, W.K., Sahakaro K., Dierkes, W.K., frequency and temperature. The storage lowering the filler-filler interaction and in- properties are almost comparable for and Noordermeer, J.W.M., 2012, Rubber Chem. modulus of filled rubber drastically de- creasing filler-rubber interaction due to polysulfidic and blocked-mercapto and Technol., 85, 277. 8. Sarkawi, S.S., Dierkes, W.K., and Noordermeer, creases as strain increases as the result of the sulfur functionality in the silane. only slightly lower for mercaptosilane. J.M., 2014, Rubber Chem. Technol., 87, 103-119. breakage of physical bonds between filler The abrasion resistance and tear 9. Sarkawi, S.S., Dierkes, W.K., and Noordermeer, particles, for example van der Waals, hy- Filler-to-rubber interactions strength for blocked-mercaptosilane vul- J.W.M., 2013, Eur. Polym. J., 49, 3,199. drogen bonds and London forces. Rubber-to-filler interactions can be canizate is the lowest. In general, the use 10. Sarkawi, S.S., Dierkes, W.K., and Noordermeer, J.W.M., 2012, Rubber World, 247(2), 26 . of bis-triethoxysilylpropyl or polysulfide 11, Sarkawi, S.S., Kaewsakul, W., Sahakaro, K., Fig. 1: Vulcanization curve of DPNR compounds with different type of silanes. silane in silica-reinforced DPNR gives Dierkes, W.K., and Noordermeer, J.W.M., 2015, J. the good overall physical properties. Rubb. Res. 18(4), 203-233. 12. Polmanteer, K.E., and Lentz, C.W., 1975, Rub- ber Chem. Technol., 48, 795-809. Dynamic properties 13. Wolff, S., Wang, M.J., and Tan, E.H., 1993, Rub- The dynamic properties of the vulca- ber Chem. Technol., 66, 163.

Fig. 2: Tan delta dependence of temperature for DPNR vulcanizates.

Table 4: Physical properties of DPNR-silica vulcanizate with different silanes.

Table 5: Dynamic properties of DPNR-silica vulcanizate with different silanes.

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