International Journal of Chemical Studies

Transcription

1 ISSN: Volume 1 Issue 2 Online Available at International Journal of Chemical Studies Study of Compatiblity Behaviour of Solution Blends of NBR- SBR Using Ultrasonic and Other Related Techniques Poonam Tiwari 1, Pratibha Singh 1, K. N. Pandey 1*, Vishal Verma 1, Vijai Kumar 1 1. Central Institute of Plastics Engineering and Technology, Lucknow, India [ knpandey09@gmail.com] The present investigations deal with the study of compatibility behavior of styrene -butadiene- rubber (SBR) and acryonitrile-co-butadiene (NBR) blends. Ultrasonic velocity, absolute viscosity and density measurements have been performed on solution blends of SBR and NBR in various blend ratios with and without addition of chlorinated polyethylene (CPE) as a compatibilizer. The ultrasonic velocity has been observed to deviate from linearity with variation in the blend ratio without the compatibilizer. The addition of compatibilizer, however, results in a marked increase of the ultrasonic velocity and it varies linearly with blend composition. The ultrasonic velocity and viscosity of the solution blends are significantly dependent of temperature and solid content of the blend solution. In order to understand the phase behavior of the blend with and without compatibilizer, morphological study has also been carried out using scanning electron microscope (SEM). Physico-mechanical properties like tensile strength and elongation at break and hardness of blends, NBR and SBR rubbers (50:50 blends) with and without compatibilizer has also been studied. Mechanical properties of blends with compatibilizer are more than that of without compatibilizer. Keyword: Rubber, Compatibilization, Mechanical Properties, Blends, Morphology. 1. Introduction Polymeric blends present one of the most rapidly growing areas in polymeric materials. These materials are mixture of two structurally different polymers bonded together by secondary force [1]. However, the gain in newer properties depends on the degree of compatibility or miscibility of the polymer at molecular level. Thus the compatibility is the fundamental property in polymer blend deciding their practical utility. Many experimental and theoretical methods have been used to investigate compatibility of polymer blend system [2,3]. A.I Khalif et.al. [4] studied the effect of grafted cellulose acetate and methyl metha acrylate as compatibilizer onto NBR-SBR blends and the compatibilised blends were evaluated by rheometric characteristics, physicomechanical properties, swelling behavior, scanning electron microscopy (SEM) and thermal analysis. Asish Malas et.al. [5] investigated the selective dispersion of various organoclays in SBR in the presence of a compatibilizer. They used carboxy gelated styrene butadiene rubber (XSBR) as a compatibilizer between organoclay and the non polar SBR. Wide angle X-ray diffraction (WAXD) and high resolution transmission electron microscopy (HR-TEM) techniques were used to characterize the developed nanocomposites. Hisham Essawy et.al. [6] studied the reinforcing and compatibilizing performance of the montmorilonite clay (MMT) filler using rheometric measurement, physic-mechanical properties, scanning electron microscopy (SEM) and differential scanning calorimetry (DSC). The determination of glass transition temperature, morphology by scanning electron microscopy and atomic force microscopy and dynamic mechanical response or some of the method extensively cited in the literature [7-10]. Hourston Vol. 1 No Page 54

2 and Hughes [11] and Kaleznev et al. [12] have indicated the use of sonic and melt viscosity measurement for compatibility determination. Singh and Singh [13] have measured the ultrasonic velocity and absolute viscosity in solution of compatible, incompatible and semi compatible blends. Sidkey et al. [14] have studied the degree of compatibility of the blend solution of rubber blends using ultrasonic methods. The present studies include acrlonitrile-co-butadiene rubber (NBR) and styrene butadiene rubber (SBR) as the materials of the study. They have been chosen partly because of their difference in relative polarity and solubility parameter as well as the ease of distinguishing them under electron microscopy through their electron density constant. By the sonic [11] and ultrasonic techniques [12,15], it has been established that the sonic and ultrasonic velocity vary linearly with blend ratio for compatible blend, whereas there are deviation from linearity for incompatible blends. The present paper discusses in detail extensive investigation of compatibility of NBR- SBR by Ultrasonic, viscometry and morphological study by scanning election microscopy. 2. Materials and Methods 2.1. Materials NBR rubber was obtained from Japan Synthetic Rubber, grade JSR 220 having acrylonitrile content of 38%. SBR rubber, grade Chlorinated Polyethylene (CPE) was obtained from Dow Chemical, Plaquemine, LA, USA, grade Tyrin CPE 0316 having chlorine content 36 mol%. All other chemicals are of pure analytical grade. Toluene AR grade is used as common solvent for the preparation of solution blends. Analytical grade ZnO, stearic acid and dicumyl peroxide are used for the preparation of solid blend was obtained from M/s. E-Merck, Germany Preparation of Solution Blends Master solutions of NBR and SBR have been prepared by dissolving these materials separately in desired concentrations (2 wt% and 8 wt %) in toluene at room temperature (30 0 C) and then kept for 16 hrs resulting in transparent solution. After this, solution blends have been prepared in varied blend ratios of NBR/SBR (100/0, 90/10, 80/20, 70/30, 60/40, 50/50, 40/60, 30/70, 20/80, 10/90, 0/100) taking appropriate amount from stock solution for the ultrasonic velocity, viscosity and density measurement. 2.3 Preparation of Solid Blend To analyse the physico-mechanical properties of NBR and SBR rubbers (50:50 blend) they were masticated separately and then mixed together along with other ingredients (Table 1.) Mixing was carried out in a conventional laboratory open mill (150 x 330 mm) at o C. Different ingredients were added by careful control of temperature, nip gap, time of mastication and uniform cutting operation. The compounding ingredients were then added in the blend. Optimum cure time at C for the mixes was obtained by using Rubber Process Analyzer (RPA-2000). The mixes were cured to their respective optimum cure time in hydraulic press at C for 15 minutes and at 4.5 MPa pressure. The compatibilizer CPE (2 wt. %) was used to prepare the compatibilized blend.compounding formulations of NBR/SBR blend without and with compatibilizer have been depicted in Table 1. Table 1: The compounding formulations of NBR/SBR blend without and with compatibilizer Ingredients Content of Mix [parts by weight], gm Blend without compatibilizer Blend with CPE NBR SBR CPE -- 2 Vol. 1 No Page 55

3 Zinc Oxide 5 5 Stearic acid 2 2 Dicumyl peroxide Ultrasonic Velocity Measurement Ultrasonic velocity of solution blends of NBR- SBR with and without compatibilizer (CPE) has been measured at 5 MHz frequency by an Ultrasonic Interferometer (Model F-05D Mittal Enterprises, New Delhi, India). The Interferometer used is a relatively simple instrument that directly measures the ultrasonic velocity with an accuracy of ± 1 ms 1. The water (temperature accuracy ± 0.5oC) is passed between the double walls of the measuring cell to control the temperature of the experimental liquid during the velocity measurements. The operation and principle is narrated below. The measurement of velocity (v) is based on the accurate determination of the wavelength (λ) in the medium. The measuring cell, duly filled in with experimental liquid, is connected to the output terminal of the generator through a coaxial shielded cable. Ultrasonic waves of known frequency (f) are produced by a quartz crystal fixed at the bottom of the cell. A moveable metallic plate kept parallel to the quartz crystal reflects these waves. If the separation between these two plates is exactly a whole multiple of the sound wavelength, standing waves are formed in the medium. The acoustic resonance gives rise to an electrical reaction on the generator driving the quartz crystal and the anode current of the generator becomes at its maximum value. If the distance is now increased or decreased and the variation is exactly one half wavelengths (λ/2) or multiple of it, anode current becomes at its maximum value. From the knowledge of wavelength (λ), the velocity (v) can be obtained by the relation; Velocity = Wavelength (λ) x Frequency (f) or v = λ x f A number of 10 reading of anode currents were passed and the ultrasonic velocity was recorded in each case. The average velocity values were found to have randomness or scatter in the measurements within the range of ± 2 m/s Determination of Viscosity The viscosity of solution blends of NBR-SBR of varied blend ratios have been determine with the help of Ubbelohde viscometer at room temperature ( 30 0 C) Density Measurement by Pycnometer The densities of all solution blends have been measured by pycnometer and those of concentrated solution blends by specific gravity bottle at room temperature (30 0 C) Morphological Studies by SEM Morphological studies of solvent cast film of blends have been carried out by JEOL JSM 6380 LA Scanning Electron Microscope. Prior to SEM analysis, specimens were gold coated with the help of gold sputtering unit in order to avoid charging effect and enhance the emission of secondary electrons. 2.8 Physico-Mechanical Properties Tensile Strength Tensile test, in a broad sense, is a measurement of the ability of a material to withstand forces that tends to pull it apart and to determine to what extent the material stretches and finally breaks. An universal testing machine (UTM) of a constant rate of cross head movement at a speed of 3 mm/min is used. It has a fixed or essentially stationary manner, carrying one grip and a moveable member carrying a second grip. Self aligning grips employed for holding the test specimen between the fixed and moveable member, prevents alignment problems. A load cell (load indicating mechanism) is capable indicating total tensile load with an accuracy of ± 1 percent of the indicated value. Tensile tests were carried as per ASTM method D at room temperature Hardness Share A hardness was measured according to ASTM D T. The term hardness has been Vol. 1 No Page 56

4 applied to scratch resistance and to rebound resilience, but for polymers it is taken to refer to a measure of resistance to indentation. The mode of deformation under an indenter is a mixture of tension, shear and compression, and hardness by no means a fundamental property. The result depends on the indenter geometry and the degree of indentation as well as the time of indentation after which the measurement is made Compression Set Compression set at constant (25%) strain was measured according to ASTM D Compression set is normally expressed as a percentage of the applied deformation, i.e., t Set t 0 o t t r s 100% but can be expressed as a percentage of the original thickness. The measurement of set is very effective quality control test as it is a relatively simple test and the results are sensitive to state of cure. 3. Results and Discussion 3.1. Ultrasonic Velocity The ultrasonic velocity of pure toluene (solvent) at room temperature 30 0 C and 5 MHz is 1132 m/s. Figure 1 shows the variation in the ultrasonic velocity of solution blends at room temperature (30 0 C) with respect to varied blends ratios. A non-linear type of propagation of the ultrasonic wave due to immiscibility between NBR-SBR phases without a compatibilizer is evident in Figure. Fig 1: Ultrasonic velocity vs. blend ratio of NBR and SBR without a compatiblizer, and the effect of the addition of CPE. Polymer-polymer immiscibility and the nature of the polymer-solvent interaction might be the reason for rise and fall of the ultrasonic velocity with varied blend ratios. Singh and Singh [15] and Sidkey et al. [16] have reported similar observations. Gibbs free energy change vs. composition plots for binary solution mixture as discussed earlier by Pandey et al. [3], represent the total incompatibility and the condition required for miscibility per the criteria of ( 2 Gm/ ø2 2 ) > 0. The formation of rise and fall type of plot is due to the phase separation of the two polymers. Complete miscibility requires Gm 0 and at the same time over the entire composition range of the polymer or solvent the total immiscibility. Figure 1 also shows, the variation of ultrasonic velocity with varied blend ratio when chlorinated polyethylene (CPE) has been added as a compatibilizer. A remarkable enhancement in the ultrasonic velocity values has been observed. The non-linear plot has been converted into linear plot (Figure 1). Vol. 1 No Page 57

5 Setua and White [17] observed a significant reduction in the scale as well as the final dispersion of the dispersed particles into the continuous matrix as a result of compatiblization of binary and ternary rubber blends. The polar interaction between NBR and CPE coupled with similar backbone structure of CPE and SBR might cause intermolecular coalescence resulting stabilized and homogenous morphology which is evident from scanning electron microscopic observations. The state of polymer-polymer solvent interaction is controlled in such a fashion that the phase separation and equilibrium point is prevented. Therefore, the ultrasonic velocity vs. blend ratios of the compatiblized blend in solution exhibits a linear variation. In addition a significant increase in the velocity depicts the generation of a finer morphology i.e. homogenous and without any point of inflection, as is observed in the case of immiscible blends. The ultrasonic velocity varies due to changes in the concentration of the polymer in the solution. The ultrasonic velocity has been determined for 2 wt% and 8 wt% of solid content of the polymer in the solution. The ultrasonic velocity vs. blend ratios plots are shown in Figure 2 (a) for NBR- SBR blends without compatibilizer and Figure 2 (b) for NBR-SBR with compatibilizer CPE. The sound velocity depends on the particle density since propagation of sound is a particle phenomenon. Therefore, by increasing the concentration of the polymer in solutions results in an increase of the ultrasonic velocity without changing the nature of plots. However, the effect of increasing temperature, on the ultrasonic velocity has been observed to be reversed. The phase equilibrium of the polymer solution has strongly affected the changes in the solution temperature. The polymer structure, molecular weight, solubility parameter etc, also play significant role in the varying polymer solubility. This leads to upper critical solution temperature (UCST) and lower critical solution temperature (LCST). The decrease of velocity may be partly due to an increase in the free length of the liquid due to thermal expansion at higher temperature and structural changes associated with the state of association of the liquid molecules. These factors probably may be responsible for a negative temperature coefficient of the ultrasonic wave vs. temperature rise of the medium. Figure 2(a): Variation of ultrasonic velocity with polymer concentration in solution of NBR-SBR blends without a compatiblizer. Vol. 1 No Page 58

6 Figure 2(b): Variation of ultrasonic velocity with polymer concentration in solution of NBR-SBR blends containing CPE as compatibilizer The variation is linear at all temperatures when compatibiliser (CPE) is present in the blend system retains the state of dispersion and morphology of solution at the temperature range studied (i.e. from C) and keeps intact the velocity profile (Figure 3 (a) - (b)). An attempt has also been made to investigate the ultrasonic velocity changes with respect to a varied radio frequency from 2 to 12 MHz and compatibilizer concentration from 2 to 10 wt %. However, no remarkable change has been observed. Perhaps, the range of frequency only up to 12 MHz may not be sufficient to make any prediction about the ultrasonic relaxation process. Figure 3(a): Variation of Ultrasonic velocity with temperature for NBR-SBR blends without a compatiblizer Vol. 1 No Page 59

7 Figure 3(b): Variation of Ultrasonic velocity with temperature for NBR-SBR blends with CPE as compatiblizer Viscosity The variation in the absolute viscosity of solution blend at room temperature (30 o C) with respect to varied blend ratio is shown in Figure 4. A nonlinearity in blend ratio vs. viscosity plot may be attributed to idea that polymer mixtures show uncontrolled migration of low molecular weight fraction from the phase of the first polymer to that of the second and this may change the viscosity of each phase. This behavior shows the immiscibility between NBR-SBR without a compatibilizer. Fig 4: Viscosity vs. blend ratio of NBR-SBR without a compatiblizer and the effect of the addition of compatiblizer CPE. Vol. 1 No Page 60

8 Figure 4 also depicts variation of absolute viscosity with varied blend ratio when CPE is been added as a compatibilizer. A significant increase in the absolute viscosity value has been observed and the nature of plot changes from non-linear to linear. This may be due to single phase morphology of two phases of blends. The resultant homogeneous viscosity may be due to disappearance of phase boundary. The formation of single phase morphology has further been confirmed by scanning electron microscopy studies Density The variation in the density of solution blend at room temperature (30 0 C) with respect to varied blend ratio is shown in Figure 5.A nonlinear plot shows the immiscibility between NBR-SBR phases without a compatibilizer. This behavior is observed which may be due to polymer-polymer relative polarity and polymer-solvent interaction. This behavior shows the immiscibility between NBR-SBR without a compatibilizer. Figure 5 also depicts variation of density with varied blend ratio when CPE is present as compatibilizer. A remarkable enhancement in the density value has been observed and non-linear plot has been converted in to linear plot. This may be due to strong interaction of compatibilizer (CPE) with SBR content of NBR-SBR blend. Further this may be because of formation of discrete single phase morphology as is evident from SEM micrograph. In this case disappearance of phase boundary between the interface of NBR and SBR may be the cause of homogenous density. Fig 5: Density vs. blend ratio of NBR-SBR without a compatiblizer and the effect of the addition of compatiblizer CPE 3.4. Morphological Studies by Scanning Electron Microscopy (SEM) The scanning electron microscopy (SEM) has emerged as an important tool for investigation of the microphase properties of polymer blends and composites. SEM offers valuable information on homogeneity of blending, degree of distribution and dispersion of dispersed phase into continuous matrix as well as formation of any vacuoles, phase coalescence or interpenetration network formation etc. With the above objectives in mind, a study has been conducted for investigation of the morphology of rubber blends with the help of SEM. The criticality of this technique involves the necessity of sufficient contrast between the rubber components. With resolution limits as low as a few angstroms, the SEM can be used to Vol. 1 No Page 61

9 probe rubber-rubber blends. Generally, SEM is used to provide morphological information of polymer surfaces. Fig 6: SEM micrograph of NBR-SBR (50-50) without compatibilizer. Fig 7: SEM micrograph of NBR-SBR (50-50) with CPE as compatibilizer. The surface morphology of the NBR-SBR (50:50) blend without a compatibilizer is shown in Figure 6. This figure shows the formation of the cavities in both the phases. SEM micrograph shows that the sample is continuous in nature associated with the phase separation. Figure 7 shows the morphology of the NBR-SBR (50:50) blend containing CPE as a compatibilizer. It is evident that the phase separation appears to be diminished to a greater extent. The dispersed SBR phase is seen more evenly dispersed in the NBR phase. A broader distribution of particle size with a lesser number of agglomerated dispersed particles and a sharp reduction in the average dispersed phase size ( μm) are observed. 3.5 Physico-mechanical Properties Physico-mechanical properties of the elastomeric materials are important for end use applications. The material selection for a variety of applications is quite often used based on physico- Vol. 1 No Page 62

10 mechanical properties such as tensile strength, modulus, elongation, hardness and compression set. Tensile strength, elongation at break and tensile modulus measurement are among the most important indications of strength in material. Tensile strength, in a broad sense, is the measurement of the ability of a material to withstand forces that tend to pull it apart and to determine the extent upto which the material stretches before breaking. Tensile modulus is an indication of the relative stiffness of a material. Table 2: Physico-mechanical properties of NBR/SBR blends without and with compatibilizer Blend type Property Without compatibilizer With CPE Tensile strength, Kg/cm Elongation at break % Modulus at 100% elongation, Kg/cm Hardness, Shore A Compression set at 70 o C for 24h at 25% reflection, % It is evident from Table 2 that the physicomechanical properties of NBR/SBR blend without a compatibilizer is poor. These, however, observed to be improved remarkably due to the addition of CPE. This may be due to reduction of the size of the dispersed particles and the interfacial tension coefficient by the addition of compatibilizer CPE. The extent of compatibilization depends on the type of mixers and mixing time, size of the dispersed particles, relative affinity of the compatibilizer with the two polymers, molecular weight of the principal ingredients, the orientation of the emulsifier at the interface and its ability to stabilize the interface against flocculation and coalescence. SEM results also support these results. 4. Conclusions The present investigation indicates clearly that the compatibility of rubber blend may be studied by ultrasonic techniques, viscometry and density measurements. It is evident that the simplest measurements of ultrasonic velocity, viscosity and density may predict compatibility of blends which is in general obtained by sophisticated techniques. Our SEM studies offer supporting evidence for the compatibility of NBR-SBR blend and the effect of addition of chlorinated polyethylene (CPE) in the blend system as a compatibilizer. The physico-mechanical properties of the blend system showed significant enhancement due to the addition of compatibilizer (CPE). This may be due to reduction of the size of the dispersed particles and the interfacial tension coefficient by the addition of CPE. 5. References 1. Shen M, Kawai H. Properties and structure of polymeric alloys. American Chemical Engineering 1978; 24(1): Krause S. Polymer blends. Vol. 1, Academic press, Newyork, Pandey KN, Setua DK, Mathur GN. Polymer Engineering and Science 2005; 45: Khalf AI, Nashar DEEl, Maziad NA. Effect of grafting acetate and methylmethacrylate as compatibilizer onto NBR/SBR blends. Materials & Design 2010; 31(5): Ashish Malas, Chapal Kumar Das, Selective dispersion of different organoclays in styrene butadiene rubber in the presence of a compatibilizer, Materials & Design 2013; 49: Hisham Essawy, Doaa El- nashar. The use of montmorillonite as a reinforcing and compatibilizing filler for NBR/SBR rubber blend. Polymer Testing 2004; 23(7): Singh K, Pandey KN, Debnath KK, Pal RS and Setua DK. Development of elastomer blends for specific defense application. Bulletin of Material Science 1996; (19): Vol. 1 No Page 63

11 8. Setua DK, Soman C, Bhowmick AK and Mathur GN. Oil resistant thermoplastic elastomers of nitrile rubber and high density polyethylene blend. Polymer Engineering Science 2002; (42): Setua DK, Pandey KN, Saxena AK and Mathur G N. Characterization of elastomer blend and compatibility. Journal of Applied Polymer Science 1999; (74): Pandey KN, Debnath KK, Rajagopalan PT, Setua DK and Mathur GN. Thermal analysis on influence of compatibilizing agents. Journal of Thermal Analysis and Calorimetry. 1997; (49): Hourston DJ and Hughes ID. Dynamic mechanical and sonic velocity behaviour of polystyrene-poly (vinyl methyl ether) blends. Polymer 1978; (19): Kuleznev VN, Meilnikova OL and Klykova VD. Dependence of modulus and viscosity upon composition for mixtures of polymers. Effects of phase composition and properties of phases. European Polymer Journal 1978; (14): Singh YP and Singh RP. Compatibility studies on solid polyblends of poly (methyl methacrylate) with poly (vinyl acetate) and polystyrene by ultrasonic technique. European Polymer Journal 1983; (19): Sidkey MA, Fattah Abd El AM and Abd El All NS. Compatibility studies on some solutions of rubber blends by ultrasonic techniques. Journal of Applied Polymer Science 1992; (46): Singh YP and Singh RP. Compatibility studies on solutions of polymer blends by viscometric and ultrasonic techniques. European Polymer Journal 1983; (19): Sidkey MA, Fattah Abd El AM, Yehia AA and Abd El NS All. Ultrasonic investigation of some rubber blends. Journal of Applied Polymer Science 1991; (43): Setua DK and White JL. Flow visualization of the influence of compatibilizing agents on the mixing of elastomer blends and the effect on phase morphology. Polymer Engineering Science 1991; (31): Vol. 1 No Page 64