ARID ZONE JOURNAL OF ENGINEERING, TECHNOLOGY & ENVIRONMENT AZOJETE March 2020. Vol. 16(1):58-64 Published by the Faculty of Engineering, University of Maiduguri, Maiduguri, Nigeria. Print ISSN: 1596-2490, Electronic ISSN: 2545-5818 www.azojete.com.ng Corresponding author’s e-mail address: mgbemena.ogonna@fupre.edu.ng 58 ORIGINAL RESEARCH ARTICLE PERFORMANCE STUDIES OF NATURAL RUBBER�ORGANOMODIFIED KAOLIN VULCANIZATES DEVELOPED FOR TIRE SIDEWALL APPLICATIONS C. O. Mgbemena1 and C. E. Mgbemena2 (1Department of Mechanical Engineering, Federal University of Petroleum Resources, Effurun, Delta State, Nigeria 2Department of Industrial and Production Engineering, Nnamdi Azikiwe University, Awka, Anambra State, Nigeria) * Corresponding author’s email address: mgbemena�ogonna@fupre�edu�ng 1.0 Introduction Rubber Clay Nanocomposites �RCNs� have emerged as novel advanced materials, attracting the interests of the academia and industry (Bhowmick et al., 2010)� One of the unique features of RCNs is the exceptional improvement in their physical ��� mechanical properties, such as barrier properties �impermeability to gases�, thermal stability, storage modulus, tensile properties, wear resistance and flame resistance at low filler concentrations� In a pioneering study, it was shown that the mechanical properties of NR with 10 phr of organo�montmorillonite are comparable to one containing 40 phr of carbon black (Arroyo et al., 2003). A review of related publications on RCNs shows that apart from natural rubber �NR�, various synthetic rubbers have been used along with clays such as montmorillonites, bentonites, saponite, fluorohectorites with and without organomodifiers which are mostly petrochemical- based and are quite expensive� Studies on the use of nano kaolin for vulcanised rubber ARTICLE INFORMATION ABSTRACT This study aims at evaluating the performance of Natural Rubber/organomodified kaolin vulcanizates to ascertain its suitability for tire sidewall applications. The cure characteristics, filler dispersion, tensile and tear properties and De�Mattia flex fatigue characteristics of natural rubber �NR� �attra with 2�10 phr of Rubber Seed Oil �RSO�, and Tea Seed Oil �TSO� modified kaolin developed specifically for tire sidewall applications were assessed. The NR compounds containing RSO and TSO modified kaolin showed lower optimum cure time �t90 at 150°C� as against that containing the same dosage of unmodified kaolin� The results show significant increases in tensile modulus, tensile strength and tear strength for the NR vulcanizates containing the organomodified kaolins, compared to vulcanizates containing unmodified kaolin� �Ro �taa�ara �宱tta宽 �XtO宱宽aD宱QrL 宱Q ���� showed better resistance to crack initiation and flex fatigue failure� The SEM and AFM micrographs of the vulcanizates containing organomodified kaolins also showed an excellent uniform dispersion of the filler particles in the NR matrix� �　૒ �૒�宨�宱� �i宱per૒i ��� �p宱宨�p� �宨ii૒���૒p �૒૒i �e� ��ie�e૒i �p��er �宨�OpreDp宱૒� p宱 �Ꮜ�　� �　�⹉� p �　��宱 ��宱e�宨� O宨�૒ 宱e�૒� 　e޷　 �p䁙e�宨� 宱��ၾ宨૒� i૒宱宱૒� 宱૒p� �宱�૒r޷宱　� ૒䁙O૒��૒r宱 �૒�e�宱prO૒ 宱� O�pO� ere宱ep宱e�r pri ��૒䁙 �p宱e޷宨૒ i૒　p�e�宨�⹉ �　૒�૒ erieOp宱૒ 宱　p宱 宱　૒ �p宱宨�p� �宨ii૒���૒p �૒૒i �e� ��ie�e૒i �p��er �宨�OpreDp宱૒� p�૒ ��૒�૒��૒i �p宱૒�ep�� ��� 宱e�૒ �ei૒⹉p�� p���eOp宱e�r�. © 2020 Faculty of Engineering, University of Maiduguri, Nigeria. All rights reserved. Submitted 21 October, 2018 Revised 01 November, 2019 Accepted 05 November, 2019 Keywords: Natural rubber Organomodified Kaolin nanocomposites. mailto:mgbemena.ogonna@fupre.edu.ng http://www.azojete.com.ng Arid Zone Journal of Engineering, Technology and Environment, March, 2020; Vol. 16(1) 58-64. ISSN 1596-2490; e-ISSN 2545-5818; www.azojete.com.ng Corresponding author’s e-mail address: mgbemena.ogonna@fupre.edu.ng 59 nanocomposites are limited (Dai, 1999; Liu et al., 2008; Mgbemena et al., 2016; Puşcă et al., 2010; Sookyung et al., 2014; Yahaya et al., 2009). For large scale industrial applications, it is imperative that RCN compositions be tailored to meet the required technical specifications� The selection of low cost renewable natural resources such as kaolin and organomodifiers such as RSO and TSO for RCNs could be an ideal proposition� Earlier studies have shown that derivatives of RSO and TSO could be used as organo�modifiers for kaolin to function as �reinforcing nano�fillers� for natural rubber at very low dosages (Mgbemena et al., 2013; Sukumar and Menon, 2008; Yahaya et al., 2009)� Recent findings also support the above observations (Mgbemena et al., 2016). The purpose of this study is to evaluate the properties of Natural Rubber/Organomodified kaolin nanocomposites to determine its suitability for vehicle tire sidewall applications. 2� Materials and Method Kaolin �grade BCK� was obtained from M�s� English Indian Clays Ltd�, Thiruvananthapuram� TSO was obtained from Nigeria� RSO, NR �grade RSS5� and rubber chemicals were obtained from local suppliers� The organomodified kaolins were prepared by modification of kaolin with sodium salts of the oils �RSO & TSO� and hydrazine hydrate according to (Ihueze and Mgbemena, 2016, Mgbemena et al., 2013, Mgbemena et al., 2016 and Yahaya et al., 2009). Rubber mixes, as shown in Table 1 were prepared by mixing on an open, two�roll mixing mill at room temperature of 25℃� Table 1� Composition of mixes Mix code� Ingredient �phr� URK2 Unmodified kaolin 2 URK6 Unmodified kaolin 6 URK10 Unmodified kaolin 10 MRK2 RSO modified kaolin 2 MRK6 RSO modified kaolin 6 MRK10 RSO modified kaolin 10 MTK2 TSO modified kaolin 2 MTK6 TSO modified kaolin 6 MTK10 TSO modified kaolin 10 � Base mix� NR 100, ZnO 5, Stearic acid 2, sulfur 2, Mercapto Benzothiazole 2 2�1 Characterizations of the materials The cure characteristics at 150°C of the mixes were tested with an oscillating disk rheometer �ODR� [MV-ODR brand; Micro-Vision Enterprises, India] according to ASTM D 5289 � 1979� The essential data deduced from the rheographs are as follows� the minimum torque �ML�, maximum torque �MH�, Scorch time �ts2�, optimum cure time �t90� and cure rate index �CRI�� The tensile properties of the vulcanizates were according to IS: 3400 (Part 1) � 1977. The resistance to flex cracking of the vulcanizates was measured on a Goodrich flexometer according to IS: 3400 (Part 7) � 1985 and IS: 3400 (Part 8) � 1983. The tear strength of the vulcanizates was measured with a Universal Testing Machine �Hounsfield H5 KS; United Kingdom� according to standard ASTM � D624�86� The fracture surfaces of the vulcanizates were file:///C:/Users/user/Downloads/azojete143/www.azojete.com.ng Mgbemena and Mgbemena: Performance studies of Natural Rubber�organomodified kaolin vulcanizates developed for tire sidewall applications. AZOJETE,16(1):58-64. ISSN 1596-2490; e-ISSN 2545-5818, www.azojete.com.ng Corresponding author’s e-mail address: mgbemena.ogonna@fupre.edu.ng 60 observed under a scanning electron microscope �SEM model �JSM 5600LV; Jeol, USA� after sputter coating with gold� 3D images of the failure surfaces of the vulcanizates were obtained using an atomic force microscope �AFM model � NT�MDT, Russia� using the tapping mode probe� 3� Results and Discussion 3�1 Cure characteristics and Scanning Electron Microscopy Table 2 shows the results on the cure characteristics of the rubber compounds at 150°C, as obtained from ODR� Table 2� Cure characteristics at 150°C of NR compounds containing Unmodified and Organomodified kaolin Mix code Scorch time, ts2 �s� Optimum cure time, t90 �s� Minimum torque ����om� Maximum torque ����om� ��� � ��� � ����om� CR= 100 �90���2 (min) URK2 113 274 0�58 4�71 4�13 37�17 URK6 99 273 0�51 5�16 4�65 34�48 URK10 93 255 0�80 5�51 4�71 37�04 MRK2 82 222 0�60 5�20 4�60 42�92 MRK6 86 205 0�71 5�56 4�85 46�51 MRK10 78 222 1�07 5�58 4�51 41�67 MTK2 91 250 0�65 5�19 4�54 37�74 MTK6 84 234 0�87 5�65 4�78 40�00 MTK10 63 216 0�84 6�80 5�96 38�46 The observed reduction in scorch time and optimum cure time of the mixes as above is similar to that reported by Liu et al. (2008). Liu et al. (2008) has reported that the smaller value of minimum torque �ML� is related to slightly large size of kaolinite flakes and weaker interactions between kaolinite particles. Thus, the higher values of ML for the mixes containing RSO modified kaolin and TSO modified kaolin could be an indication of smaller sizes of kaolinite flakes and more interaction between them, as evidenced by SEM images of vulcanizates containing NR�Unmodified kaolin at 10 phr in Figure 1; NR/RSO modified kaolin in Figure 2 and NR/TSO modified kaolin in Figure 3� However, the increases in cure rate index �CRI�, maximum torque �MH� and delta torque ���� of the mixes containing RSO and TSO modified kaolins as against that of the unmodified kaolin indicate an overall increase in the ultimate state of cure and crosslinking efficiency in presence of the organomodified kaolins� A previous report also shows a higher cure rate and state of cure for NR containing RSO modified kaolin (Sukumar and Menon, 2008)� http://www.azojete.com.ng Arid Zone Journal of Engineering, Technology and Environment, March, 2020; Vol. 16(1) 58-64. ISSN 1596-2490; e-ISSN 2545-5818; www.azojete.com.ng Corresponding author’s e-mail address: mgbemena.ogonna@fupre.edu.ng 61 Figure 1� SEM Micrograph for NR/Unmodified kaolin (10 phr) Figure 2� SEM Micrograph for NR/RSO modified kaolin (10 phr) Figure 3� SEM Micrograph for NR/TSO-modified Kaolin (10phr) 3�2 Mechanical properties The result on the mechanical properties of the vulcanizates is given in Table 3. The crack initiation and failure frequencies in the De Mattia flex�crack test are almost similar for all the vulcanizates, except that the vulcanizates containing 2�6 phr of TSO modified kaolin show some improvements over that containing the same dosage of unmodified kaolin� It shows that in all the vulcanizates there is a steady increase in the tensile modulus with the increase in dosage of filler from 2 to 10 phr� However, the values for the vulcanizates containing RSO modified kaolin and TSO modified kaolin are higher than that containing the same dosage of unmodified kaolin� A higher degree of intercalation in the morphological structure resulted in higher tensile file:///C:/Users/user/Downloads/azojete143/www.azojete.com.ng Mgbemena and Mgbemena: Performance studies of Natural Rubber�organomodified kaolin vulcanizates developed for tire sidewall applications. AZOJETE,16(1):58-64. ISSN 1596-2490; e-ISSN 2545-5818, www.azojete.com.ng Corresponding author’s e-mail address: mgbemena.ogonna@fupre.edu.ng 62 strength and other mechanical properties; this was particularly the case of RSO-modified kaolin/NR composites at 10 phr filler loading where there was an increase in tensile strength which is attributed to the increase in interfacial area of kaolin platelets and good interaction between the kaolin platelets as clearly seen in the SEM and AFM morphologies of RSO-modified Kaolin at 10 phr and a magnification of 10000X. Poor filler dispersion lowers the tensile strength of the material. The surface chemistry of the layered silicates in a polymer matrix plays a crucial role in composites formation. Electrostatic forces present in the silicate layers could complicate the filler dispersion in the polymer matrix. The incompatibility between the hydrophilic silicates and the hydrophobic polymer results in strong inter-particle forces and agglomeration as indicated at 10 phr pristine kaolin filler loading. Table 3� Mechanical properties of NR vulcanizates containing unmodified and organomodified kaolins Sample code Tensile modulus M�300� �MPa� Tensile strength �MPa� Elongation at break ��� De Mattia flex Tear strength �kN�m� Crack initiation �cycles� Failure �cycles� URK2 1�42 13�1 696 71884 373451 12�78 URK6 1�64 12 628 69488 206057 27�48 URK10 2�00 12�7 712 75016 298065 26�79 MRK2 1�9 11�7 658 62116 194867 16�20 MRK6 2�19 15�8 649 52116 225380 24�73 MRK10 2�35 15�8 625 63126 290584 18�46 MTK2 1�17 11�1 815 74629 272480 22�20 MTK6 2�01 16�2 687 73542 256491 24�79 MTK10 2�73 20�7 648 74172 288283 29�29 3�3 The Atomic Force Microscopy �AFM� The results obtained from the tensile tests and SEM revealed that the following selected composites have high tensile strength: NR/Unmodified kaolin composites at 10phr, NR/Rubber Seed Oil modified kaolin composites at10phr and NR/Tea Seed Oil modified kaolin composites at 6phr. These three composite samples were further analyzed by AFM using the tapping mode probe. The AFM 3D images of NR vulcanizates are shown in Figures 4�6 respectively� Figure 4� 3D image of NR vulcanizate containing unmodified kaolin (URK10) Figure 5� 3D image of NR vulcanizate containing RSO modified kaolin (MRK10) http://www.azojete.com.ng Arid Zone Journal of Engineering, Technology and Environment, March, 2020; Vol. 16(1) 58-64. ISSN 1596-2490; e-ISSN 2545-5818; www.azojete.com.ng Corresponding author’s e-mail address: mgbemena.ogonna@fupre.edu.ng 63 Figure 6� 3D image of NR vulcanizate containing TSO modified kaolin (MTK 6) The 3D images for the unmodified kaolin filled NR composite as indicated in Figure 4 clearly show filler agglomeration within the NR matrix. In Figure 5 the 3D image in NR/RSO-modified kaolin composites further revealed a good dispersion of the fillers on the rubber matrix as indicated by the white colored peaks while in Figure 6 the level of dispersion of STSO-modified kaolin is an indication that the fillers were well intercalated on the NR matrix. 4� Conclusion The organomodified kaolins were prepared by modification of kaolin with derivatives of rubber seed oil �RSO� and tea seed oil �TSO�� Natural rubber �NR� compositions containing 2�10 phr of the modified kaolins showed higher cure rate and state of cure, compared to that containing the same dosage of unmodified kaolin� The vulcanizates containing the organomodified kaolins showed an increase in tensile modulus, tensile strength, tear strength and resistance to fatigue failure� Morphological analysis of the vulcanizates using SEM and AFM showed a more uniform distribution of smaller kaolinite particles in the NR matrix, upon organomodification with RSO and TSO� �　૒ �૒�宨�宱� �i宱per૒i ��� 宱　૒ ��宱e�宨� O宨�૒ 宱e�૒�� �p䁙e�宨� 宱��ၾ宨૒� pri 宱૒p� �宱�૒r޷宱　� �� 宱　૒ �宨�OpreDp宱૒� �宨�宱　૒� �૒�૒p�૒i 宱　p宱 ������ ��ie�e૒i �宨�OpreDp宱૒� p宱 �Ꮜ�　� ⹉p� ��宨ri 宱� i૒ 宱　૒ i૒�宱 �p宱૒�ep� ��� 宱e�૒ �ei૒⹉p��� ⹉e宱　 宱　૒ �p�宨૒� �i宱per૒i p� �Q⹉�QG��� ��� 宱　૒ 宱૒p� �宱�૒r޷宱　� �⹉䁒Ꮜi�� ��� 宱　૒ �p䁙e�宨� 宱��ၾ宨૒ pri ���� ��� 宱　૒ Optimum cure time, t90 as indicated in Tables 2 and 3. This observation is in tandem with an earlier study on mechanical properties of industrial tire rubber compounds which posited that NR compounds with higher torques and shorter cure times are better sidewall materials (Bijarimi, Zulkafli, and Beg, 2010). Acknowledgements The authors would like to thank DST, New Delhi and CICS, Chennai for the award of RTFDCS fellowship one of the authors under which programme this work was carried out� Our sincere thanks to NIIST, Thiruvananthapuram for providing the necessary facilities and to the Technical Consultancy Division, Rubber Research Institute of India, Kottayam for the measurements of cure characteristics, mechanical properties and resistance to fatigue failure� References Arroyo, M., López-Manchado, MA. and Herrero, B. 2003. Organo-montmorillonite as substitute of carbon black in natural rubber compounds. Polymer, 44: 2447–2453. 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