EFFECT OF ZnO NANOPARTICLES ON CURE BEHAVIOR OF THE EPDM RUBBER Nuttiya Sa-nguansak a and Stephan Thierry Dubas* a a The Petroleum and Petrochemical College, Chulalongkorn University, Bangkok, Thailand Keywords: EPDM, ZnO, Rubber ABSTRACT Ethylene-propylene-diene-monomer (EPDM) rubber is a synthetic rubber that has been used in a various applications. Many rubber industries mainly use an activator, which is commonly zinc oxide (ZnO), to promote the accelerator during the vulcanization process. In this study the morphology, particles size, dispersion of synthesized ZnO nanoparticles in rubber matrix, and degree of vulcanization are examined. ZnO nanoparticles are prepared by using different concentration of alginic acid, a polyelectrolyte, as a capping agent and the synthesized nanoparticles are later mixed into the EPDM rubber. The morphology and properties of EPDM rubber with ZnO nanoparticles are studied by different techniques such as scanning electron microscopy (SEM), optical microscope, X-Ray diffraction (XRD) and moving die rheology (MDR). The results showed that the ZnO particle size is decreased from 243 to 39 nm with increasing alginic acid concentration. The scorch time of EPDM rubber filled synthesized ZnO using 0, 0.1, 1 and 10 mm alginic acid are not different significantly, moreover; 10 mm alginic acid cured the slowest. Also, the M H -M L or the torque difference of EPDM rubber with ZnO using 10 mm Alginic acid was the highest meaning that it has the highest cross-linked density. * Stephan.d@chula.ac.th INTRODUCTION Ethylene-propylene-diene-monomer (EPDM) rubber is a synthetic rubber has been gaining attention from many researchers. In recent years, EPDM has been used in a various applications such as automobile manufacturing, external body seal, piping industries, seal and washing machine parts due to its durability, good flexibility, fatigue resistance, excellent electrical insulation properties, very good chemical resistance and good anti-aging properties for heat, light, oxygen and ozone, so it is useful for outdoor applications. However, EPDM rubber requires additives to improve the quality and reduce cost of the products. Many rubber industries mainly use an activator to promote the accelerator for vulcanization process. The most common activator is zinc oxide (ZnO) which can improve the thermal conductivity of rubber, abrasion resistance, heat resistance of the valcanizates, decrease the shrinkage of molded products. And also enhance mechanical properties. Currently, many applications require nanoparticles for high-quality product and high surface area. For this reason the development of, ZnO nanoparticles is interested and should be use in rubber due to smaller size and higher surface area when compared with Petrochemical and Materials Technology Tuesday May 23, 2017, Pathumwan Princess Hotel, Bangkok, Thailand Page 1
commercial ZnO. The ZnO nanoparticles might lead to an increase in degree of vulcanization and an improvement mechanical properties. But there is some limitation of commercial ZnO nanoparticle which is the expensive cost. Consequently, the objective for this work is to synthesize ZnO nanoparticles and introduce into the rubber. Polyelectrolyte has been used as stabilizing agent for the synthesis of a wide range of nanoparticles including organic, inorganic carbon and metallic nanoparticles. Favorable interactions between the charged functional group on the polyelectrolyte with the surface of the nanoparticles are needed to insure polyelectrolyte wrapping around the nanoparticles. In this work, ZnO nanoparticles will be prepared with polyelectrolyte as capping agent, the parameter in this studies is type and concentration ratio of polyelectrolyte. The purpose of this work is to achieve nano-size ZnO to fill in EPDM rubber and study the dispersion of ZnO nanoparticles in rubber matrix, degree of vulcanization and mechanical properties. EXPERIMENTAL A. Synthesis of ZnO nanoparticles ZnO nanoparticles was synthesize by a mixer of Zn(CH 3 COO) 2.2H 2 O 200 mm in 200 ml DI water and alginic acid at different polyelectrolyte concentration in 200 ml DI water. Add NaOH for adjust ph to 10 in mixture solution and stirred for 1 hour, get white precipicate and filtrate them. After that, dry in oven at 100 C overnight. B. Preparation of rubber compound Masticate EPDM rubber 50 g in Two-roll mill for 5 min. ZnO 3 phr and stearic acid 2 phr were added and mixed it for 7 min and then add sulfur 2 phr and TBBS (or other accelerator) 1.5 phr until it was homogeneous (around 7 min). After that, foaming and valcanising EPDM rubber in compression mould at 140 C for a certain time obtained from MDR machine. C. Characterization The morphology of ZnO nanoparticles was characterized by using scanning electron microscopy (SEM). The particles size by using particle size analyzer (PSA). Cure time, cure rate, scorch time were characterized by using die rheology (MDR). The mechanical properties were characterized by using universal testing machine (UTM). The structure of crystalline materials was characterized by using X-Ray diffraction (XRD). The dispersion of ZnO fill in rubber was characterized by using optical microscope. RESULTS AND DISCUSSION A. Synthesized ZnO nanoparticles by varies polyelectrolyte concentration X-ray diffraction (XRD) showed clearly results to confirm that the product from the synthesis is ZnO as shown in figure 4.1. The peak at scattering angles (2θ) of 31.3670, 34.0270, 35.8596, 47.1635, 56.2572, 62.5384, 67.6356, and 68.7978 correspond Petrochemical and Materials Technology Tuesday May 23, 2017, Pathumwan Princess Hotel, Bangkok, Thailand Page 2
Integrated Intensity (cps deg) Na2 Na4 Zn 2 O3 2 4 H2 H2 O O Na2 Na4 Zn 2 O3 2 4 H2 H2 O O Na2 Na4 Zn 2 O3 2 4 H2 H2 O O Na2 Na4 Zn 2 O3 2 4 H2 H2 O O Na2 Na4 Zn 2 O3 2 4 H2 H2 O O Na2 Na4 Zn 2 O3 2 4 H2 H2 O O Intensity (cps) to the reflection from: 100, 002, 101, 102, 110, 103, 200, and 112 crystal planes, respectively. The XRD pattern is indicate to the hexagonal phase with Wurtzite structure when compared to the standard peak of ZnO. 6.0e+004 4.0e+004 2.0e+004 0.0e+000 20 40 60 80 Figure 4.1 The components of the elements was characterized by using XRD Zinc Oxide,, 01-075-0576 Sodium Zinc Oxide Hydrate, Na4 3 4 H2 O, 00-002-1013 Sodium Zinc Oxide Hydrate, Na2 2 2 H2 O, 00-002-1014 8.0e+004 6.0e+004 4.0e+004 2.0e+004 0.0e+000 20 40 60 80 2-theta (deg) Figure 4.2 Morphology of ZnO nanoparticles at different concentration of Alginic acid without calcination (left side) and calcination (right side) Alginic acid Mean particles size (nm.) concentration (mm) Without calcination Calcination 0 108 98.5 0.1 173.3 (agglomerate) 69.9 (agglomerate) 1.0 103.2 68.25 10 39 37 Table 4.1 particle size of ZnO at different capping agent concentration Petrochemical and Materials Technology Tuesday May 23, 2017, Pathumwan Princess Hotel, Bangkok, Thailand Page 3
From figure 4.1 shows the morphology of ZnO nanoparticles at different concentration of alginic acid. The result shows that ZnO nanoparticles have sphere shape and agglomerate into huge particles. The size of ZnO nanoparticles was shown in Table 4.1. At alginic acid concentration 0, 0.1, 1.0 and 10 mm, mean particles size is 108, 173.3, 103.2 and 39 nm., respectively. For ZnO nanoparticles without calcination, the result showed that at 0 mm Alginic acid, the size of ZnO is around 108 nm and agglomerate into big particles. At 0.1 mm alginic acid, ZnO is bigger and also agglomerate because the amount of capping agent isn t enough to cap the Zn 2+. Therefore, it causes the ZnO nanoparticles to stick together. At 1 mm alginic acid, the size of ZnO particles is still bigger but it isn t agglomerate. Hence, the capping agent increases, most of Zn 2+ was capped which causes ZnO disperses in the solution via electrostatic force. However, there is some Zn 2+ which isn t encapsulated by capping agent that causes some agglomeration in the sample. At 10 mm Alginic acid, ZnO particles have the smallest size compared to other concentrations of Alginic acid and not agglomerate. For this concentration, the amount of capping agent is high enough to encapsulate all Zn 2+ which control the growth of the ZnO particles. Additionally, the ZnO synthesized has some impurities due to the byproduct from the reaction. These impurities decreases the activator efficiency of ZnO in the EPDM rubber; therefore, it could be removed the impurities by calcination at 600 C. Under this condition, The calcined sample 600 C at concentration 0 and 10 mm are not significantly different in morphology between the ZnO with calcination and without calcination but at concentration 0.1 and 1.0 mm, the particle size after calcination are are smaller than before calcination shown in figure 4.2. calcination B. Effect on cure behavior of EPDM with ZnO nanoparticles without Scorch time (Ts2) is an indication of the time required for the beginning of rubber started cross-linking (vulcanizing). From figure 4.3 shows scorch time of synthesized ZnO without calcination by using various concentration of alginic acid filled EPDM rubber. The scorch time of each condition isn t significant different. The reason might be the size of ZnO isn t effect to the scorch time or the ZnO synthesized by using capping agent has too much agglomeration into big particles that reduces the surface area of ZnO. Petrochemical and Materials Technology Tuesday May 23, 2017, Pathumwan Princess Hotel, Bangkok, Thailand Page 4
Time (min) 25 20 15 10 5 Figure 4.3 Show the scorch time (Ts2) of EPDM rubber by added ZnO without calcination using different concentration of Alginic acid. 0 Alginic acid concentration (min) Figure 4.4 Optimum cure time (Tc90) of EPDM rubber by added synthesized ZnO without calcination by using different concentration of Alginic acid. Figure 4.4 At 0, 0.1 and 1 mm Alginic acid, the value are not significant because of big particles or agglomerate particles. At 10 mm Alginic acid, it has slowest cure time due to small particle has high surface area that can more activate vulcanization reaction, it lead to higher crosslink density occurred. These results can confirm by torque from Figure 4.5. At 10 mm Alginic acid, different torque (M H -M L ) is the highest. M H -M L is referred to the cross-linked density of rubber. Petrochemical and Materials Technology Tuesday May 23, 2017, Pathumwan Princess Hotel, Bangkok, Thailand Page 5
Figure 4.5 Different torque (M H -M L ) of EPDM rubber by added synthesized ZnO without calcination by using different concentration of Alginic acid. C. Effect on cure behavior of EPDM with ZnO nanoparticles after calcination From figure 4.6, 4.7 and 4.8 after calcination ZnO, scorch time at 0, 0.1, 1.0 and 10 mm are not significant different when compared with ZnO without calcination because particles size are not different dramatically. Figure 4.6 Scorch time (Ts2) of EPDM rubber by added synthesized ZnO calcination by using different concentration of Alginic acid Petrochemical and Materials Technology Tuesday May 23, 2017, Pathumwan Princess Hotel, Bangkok, Thailand Page 6
Figure 4.7 Optimum cure time (Tc90) of EPDM rubber by added synthesized ZnO calcination by using different concentration of Alginic acid. Figure 4.8 difference torque (M H -M L ) of EPDM rubber by added synthesized ZnO calcination by using different concentration of Alginic acid. D. The effect of ZnO dispersion in EPDM rubber In these experiments, the cross section of EPDM rubber sample with synthesized ZnO was prepared for observed by using microscope. Petrochemical and Materials Technology Tuesday May 23, 2017, Pathumwan Princess Hotel, Bangkok, Thailand Page 7
Figure 4.9 the cross-section of EPDM rubber blend with commercial ZnO 5 phr. Figure 4.10 the cross-section of EPDM rubber blend with various concentration of stabilizer at ZnO 5 phr. Figure 4.10, showed the 5 phr of ZnO dispersion in EPDM matrix by various stabilizer concentration of capping agent at 0, 0.1, 1.0 and 10 mm. At 1 mm alginic acid, ZnO are homogenous dispersion in EPDM matrix and not appear excess ZnO in matrix like commercial ZnO (Figure 4.10) blend with EPDM rubber due to ZnO could be enough for react with accelerator and sulfur. And then, at this condition, ZnO are not agglomerate. At 0mM alginic acid, ZnO are not homogenous dispersion in matrix and the ZnO nanoparticles due to actually, accelerator and sulfur were form complex or react with ZnO at the surface but at this condition, ZnO particles are agglomerate to big particle. Therefore it appear the excess ZnO in EPDM matrix while 0.1 mm alginic acid, ZnO are not homogenous due to the polymer not enough for capping Zn 2+ led to created agglomerate ZnO. Futuremore, at Petrochemical and Materials Technology Tuesday May 23, 2017, Pathumwan Princess Hotel, Bangkok, Thailand Page 8
10 mm alginic acid, ZnO are not homogenous dispersion in matrix and the ZnO nanoparticles due to from table 4.1, this condition are create smallest but we use concentration of capping agent too much, it provided agglomerate ZnO. Therefore, at 0.1mM aginic acid is optimum concentration to synthesized ZnO filled EPDM rubber. The effect of content of ZnO filled in EPDM rubber at different concentration of capping agent was observed. Figure 4.11 the cross-section of EPDM rubber blend with various concentration of stabilizer at ZnO 1 phr. From figure 4.11, at all capping agent concentration which indicates that the EPDM rubber are not fully vulcanized and have a bubble. ZnO are not homogenous dispersion led to ZnO particles appear in matrix in the matrix due to the small amount of ZnO was added in EPDM rubber which not enough to form complex with accelerator and sulfur for improve vulcanization time. Petrochemical and Materials Technology Tuesday May 23, 2017, Pathumwan Princess Hotel, Bangkok, Thailand Page 9
Figure 4.12 the cross-section of EPDM rubber blend with various concentration of stabilizer at 3 phr. From figure 4.12, at 0 and 0.1 mm alginic acid the bubble occurred at the surface cross-section due to some part of EPDM rubber are not fully cure and all concentration observed the ZnO are not homogenous dispersion due to agglomerate ZnO Figure 4.13 the cross-section of EPDM rubber blend with various concentration of stabilizer at ZnO 10 phr. Petrochemical and Materials Technology Tuesday May 23, 2017, Pathumwan Princess Hotel, Bangkok, Thailand Page 10
Figure 4.13, at 10 phr., showed a smaller of ZnO particles in the matrix that similar to ZnO 5 phr (figure 4.10). At 0, 0.1 and 10 mm alginic acid, ZnO are almost homogenous in the matrix ZnO particles size in the matrix are smaller than ZnO 5phr indicate that ZnO at 10 phr is a better react with the accelerator and curing agent than ZnO 5 phr. On the other hand, at 1.0 mm alginic acid, ZnO 5 phr is react better than ZnO 10 phr due to at 5 phr is enough for activate accelerator and curing agent for vulcanization while 10 phr is excess added ZnO in EPDM rubber. Therefore, at 0.1mM aginic acid at 5 phr is optimum concentration and content to synthesized ZnO and filled in EPDM rubber. CONCLUSIONS ZnO nanoparticles synthesized by using alginic acid as a capping agent, which could be characterized by using XRD and SEM techniques. The results showed that the ZnO particle size is decreased from 243 to 39 nm with increasing alginic acid concentration. After calination ZnO, the particles size is not different significantly when compared with ZnO without calcination. Scorch time, cure time and different torque of EPDM rubber with synthesized ZnO without calcination and ZnO calcination are not different significantly. However, at 10 mm alginic acid, it has slowest cure time. This result is related to the torque difference of EPDM rubber. ACKNOWLEDGEMENTS This research is financially supported by the Petroleum and Petrochemical College, Chulalongkorn University, Thailand. REFERENCES Akhlaghi, S., Kalaee, M, Mazinani, S. and Jowdar, E. (2011). Effect of zinc oxide nanoparticles on isothermal cure kinetics, morphology and mechanical properties of EPDM rubber. Thermochimica and Acta, 527, 91-98. Bakar, N., Ismail, J. and Barkar, M. (2007). Synthesis and characterization of silver nanoparticles in natural rubber. Materials Chemistry and Physics, 104, 276-283 Detsri, E. and Popanyasak, J. (2014). Fabrication of silver nanoparticles/polyaniline composite thin films using Layer-by-layer self-assembly technique for ammonia sensing. Colloids and Surfaces A: Physicochemical and Engineering Aspects, 467, 57-65. Kim, S., Park, C. and Sain, M. (2008). Foamability of thermoplastic vulcanizaties blown with various physical blowing agents. Journal of cellular plastics, 44, 53-67 Limsavarn, L., Sritaveesinsub, V. and Dubas, S. (2006). Polyelectrolyte assisted silver nanoparticles synthesis and thin film formation. Materials Letters, 61, 3048-3051. Petrochemical and Materials Technology Tuesday May 23, 2017, Pathumwan Princess Hotel, Bangkok, Thailand Page 11
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