Multifunctional additive performance of liquid crystal blended dodecylacrylate in lube oil

Transcription

1 Indian Journal of Chemical Technology Vol. 21, July 2014, pp Multifunctional additive performance of liquid crystal blended dodecylacrylate in lube oil M Upadhyay, K Dey & P Ghosh * Natural Product and Polymer Chemistry Laboratory, Department of Chemistry, University of North Bengal, Darjeeling , India Received 9 January 2013; accepted 21 December 2013 Homopolymer of dodecylacrylate has been synthesized, characterized (FTIR and NMR) and evaluated for its additive performance as antiwear (AW), pour point depressant (PPD), viscosity modifier (VM) and thickening agent in different lube oils (base oil). Physical blend of it with liquid crystal (LC) of cholestryl benzoate has also been prepared and evaluated, and their performance is compared. Viscosity analyses of the prepared polymer and that of its blends are performed in toluene at 313 and 373 K to obtain the value of intrinsic viscosity and hence the viscosity average molecular weight of the polymer. The findings indicate that the LC blended polymer sample has more thermal stability and shows potentiality to act as more efficient multifunctional additives (AW, PPD, VM) than the homopolymer itself for lubricating oil. Keywords: Antiwear, Liquid crystal, Lube oil, Multifunctional additive, Pour point depressant, Viscosity modifier Presence of layered structure in between metal surfaces prevents direct contact between them and thereby reduces wear. Compounds like tungsten disulphide (WS 2 ) and molybdenum disulphide (MoS 2 ) are used as lubricant additive for this reason. Since liquid crystal molecules also give rise to surfacealigned ordered layers, they are in use as antiwear additives for lubricating oils 1-4. On the other hand, several kinds of poly acrylates are generally used as performance additives 5, especially as pour point depressant (PPD) and viscosity modifier (VM) in lubricating oil. However, attempts to introduce antiwear (AW) performance into acrylate based polymeric additives are very scanty 6. Keeping these views in mind and as a part of our ongoing studies on the synthesis and evaluation of polymer additives, attempts have been made to investigate the performance of the cholesteryl benzoate (CB) blended dodecyl acrylate (DDA) in lube oils with the anticipation that the morphology of liquid crystal (LC) of CB in the blend may enhance its performance in comparison to the performance of the respective homopolymer. Oil thickening property of the polymer has also been investigated. This property is taken as the measure of extent of interaction of the polymer with the base stock. The greater the thickening property, the higher is the extent of *Corresponding author. pizy12@yahoo.com interaction 7. Fuel economy may also be predicted by the thickening power of a lube oil additive. Experimental Procedure Materials and methods Toluene, hydroquinone and H 2 SO 4 were purchased from Merck Specialities Pvt. Ltd. Acrylic acid (stabilised with 0.02% hydroquinone monomethylether) and dodecyl alcohol were obtained from Sisco Research Laboratories Pvt. Ltd. Cholesteryl benzoate was purchased from Sigma- Aldrich Pvt. Ltd. Hexane was purchased from S D Fine Chem. Ltd. Methanol was purchased from Thomas Baker (Chemicals) Pvt. Ltd. Benzoyl Peroxide (BZP) was obtained from LOBA Chemicals and recrystallised from CHCl 3 -MeOH before use. Rest of the materials were used as they were obtained without further purification. Esterification and product purification Dodecyl acrylate (DDA) was prepared by reacting 1.1 mole of acrylic acid with 1 mole of dodecylalcohol. The process of esterification and subsequent purification of the ester was carried out by following the procedure as reported earlier 8. Preparation of the homopolymer The polymerization was carried out in a four-necked round bottom flask equipped with a stirrer, condenser, thermometer, and an inlet for the introduction of nitrogen by the process as reported earlier 9.

2 UPADHYAY et al.: PERFORMANCE OF LIQUID CRYSTAL BLENDED DODECYLACRYLATE IN LUBE OIL 245 Molecular weight determination The molecular weight of the polymer is determined by Mark-Houwink-Sukurda relation, measuring the intrinsic viscosity of the polymer solution in toluene 8, as shown below: [η] = KM a (1) where [η] is the intrinsic viscosity which can be calculated by different equations (Huggins, Kraemer, Martin, Schulz-Blaschke); M, the viscosity average molecular weight; K and a, the Mark-Houwink constants. Parameters K and a depend on the type of polymer, solvent and temperature. Preparation of LC-Polymer blend Polymer-LC blend was prepared by mixing the polymer (P-1) with desired amount of CB (100 ppm with respect to the polymer) in a mechanical stirrer at 60 C for one hour. The blended sample was assigned as P-2. Five different concentrations (1 5%, w/w) of additive (P-1 and P-2) doped base oils, namely BO1 (of two different sources, S1 and S2) and BO2 (of two different sources, S1 and S2) were prepared by the addition of required amount of sample to the base oils, followed by heating at 60 C with constant stirring for 30 min. Spectroscopic analysis IR spectra was recorded on a Shimudzu FTIR 8300 spectrometer using 0.1 mm KBr cells at room temperature within the wave number range cm -1. NMR spectra were recorded in Brucker Avance 300 MHz FT-NMR spectrometer using 5 mm BBO probe. CDCl 3 was used as solvent and TMS as reference material. Viscometric and TGA analyses Viscometric properties of the samples were determined at 313 K in toluene, using an Ubbelohde OB viscometer. Experimental determination was carried out by determining the time of flow of at least five different concentrations of the sample solution. The time of flow of the solution was manually determined by using a chronometer. In the single point measurement, the lowest value of solution concentration was chosen for calculation. For the viscosity average molecular weight determination, the constants K = dl/g and a = were employed in Mark Houwink Sukurda relation, as has been earlier reported by the previous workers 9. The thermograms in air were obtained on a mettler TA 3000 system, at a heating rate of 10 o C / min. Evaluation of PPD properties The prepared samples (P-1 and P-2) were evaluated as pour point depressants (PPD) using two different base oils through the pour point test according to the ASTM D97-09 method on a Cloud and Pour Point Tester model WIL-471(India). Evaluation of viscosity modifier properties The prepared samples (P-1 and P-2) were evaluated as viscosity modifier (VM) in two base oils according the ASTM D2270 method by using the equations as reported elsewhere 14. The kinematic viscosity of the oil containing the different concentrations of the tested polymers was determined at 40 C and 100 C. Different concentrations (1-5 wt %) of additive doped base oils were used to study the effect of additive concentration on the viscosity index (VI). Evaluation of antiwear properties Antiwear (AW) properties of the base stocks as well as additive doped base stocks were studied in sliding contact by means of a Four Ball wear test Machine as per ASTM D-4172 method. The tests were carried out employing 20 kg and 40 kg load condition. Evaluation of thickening and base oil properties Kinematic viscosity of the base oils and that of additive doped base oils in different concentrations were evaluated. Thickening power of the polymer was determined by evaluating the % increase in viscosity of the base stocks by the addition of unit amount of additive. Physical properties of the base oils are shown in Table 1. Results and Discussion Spectroscopic analysis FTIR spectra of homopolymer, polydodecyl acrylate (PDDA) exhibits absorption band at 1732 cm -1 for the ester carbonyl stretching Property Table 1 Properties of base oils Base oil samples BO1 BO2 S1 S2 S1 S2 Density at 313K, kg.m Viscosity 10-6 at 313K, m 2 s Viscosity 10-6 at 373K, m 2 s Cloud point, 0 C Pour point, 0 C BO1 Base oil of type 1, BO2 Base oil of type 2, S1 Source 1, S2 Source 2.

3 246 INDIAN J. CHEM. TECHNOL., JULY 2014 vibration along with other peaks at , 1379, 1260 and cm -1. In its 1 H-NMR spectra, PDDA shows a broad singlet centred at 4.02 ppm due to the protons of OCH 2 group. Methyls of the PDDA chain appears between 0.81 ppm and 0.86 ppm and the absence of singlets between 5 ppm and 6 ppm indicate the absence of any vinylic proton in the polymer. In the 13 C-NMR spectrum of the polymer, the carbonyl carbon appears at ppm along with other sp 3 carbons appeared in the region ppm. Viscometric analysis Viscometric data (kinematic viscosity values) have been obtained using the six equations available in literature A linear relation for the plot of log[η] sp vs. log c[η], obtained for all samples, indicates that measurement is performed in Newtonian flow 15,16. Intrinsic viscosities [η] of the samples (P-1 and P-2) are shown in Table 2. The SB equation is commonly applied in single point determination along with the graphic extrapolation method because the constant k sb is found to be very close to 0.28 in most of the polymer solvent systems 14. The same is used here also. Comparison between P-1 and P-2 indicates that the latter has greater [η] values than the pure polymer. This indicates a more extended conformation of the polymer chain of the LC added composition compared to the pure polymer. The viscosity average molecular weight as obtained from the intrinsic viscosity data (Table 2) using Huggins (M h ), Kraemer (M k ), Martin (M m ) and Schulz-Blaschke (M sb ) equations is found to be within the range Thermogravimetric analysis TGA data show slightly better thermal stability of P-2 as compared to P-1. P-1 shows 16% loss in its weight at 240 o C and 96% loss at 330 o C, whereas for P-2 the weight loss is 12% at 250 o C and 92% at 360 o C. Efficiency as pour point depressant Different concentrations ranging from 1 wt% to 5 wt% of the polymer solution in base oils are tested Table 2 Intrinsic viscosity values of prepared sample in toluene as solvent Intrinsic viscosity Sample, m 2 s [η] h [η] k [η] m [η] sb P P Subscripts h, k, m and sb stand for values obtained using Huggins, Kraemer, Martin and Schulz-Blaschke equation respectively. as PPD and the experimental data are grouped in Table 3. The data indicate that the prepared compounds are efficient as pour point depressant and up to a certain limit (4%) the efficiency increases by increasing the concentration of additive. This fact may be explained by considering the hydrodynamic volume of the polymer doped in oil. The hydrodynamic volume increases with increase in polymer concentration in base oil and thus the interaction increases. Again more depression in the pour point is observed in the case of P-2 doped base oils. The extended conformation of the polymer chain of the LC added composition may be responsible for showing its better efficiency in comparison to the pure polymer. Efficiency as viscosity modifier Table 4 presents the viscosity index values of the additives doped base oils. Looking at the data it can be seen that the VI values of P-2 doped base oils are higher than those of P-1 doped base oils. Like PPD properties, in general, there is once again a gradual increase in VI values with the increase in Sample Base oil Source Table 3 Pour point data Pour point ( C) of additive doped base oils 0% 1% 2% 3% 4% 5% P-1 BO1 S S BO2 S S P-2 BO1 S S BO2 S S Sample Base oil Source Table 4 Viscosity index values Viscosity index of additive doped base oils 0% 1% 2% 3% 4% 5% P-1 BO1 S S BO2 S S P-2 BO1 S S BO2 S S

4 UPADHYAY et al.: PERFORMANCE OF LIQUID CRYSTAL BLENDED DODECYLACRYLATE IN LUBE OIL 247 additive concentration. The increase in polymer concentration leads to an increase in total volume of polymer micelles in the oil solutions. Consequently, a high concentration of polymer will impart a high viscosity index rather than a low concentration of the same polymer 17. Efficiency as antiwear additive Antiwear contributions of the additives are measured with respect to wear scar diameter (WSD) under two load conditions (20 kg and 40 kg). Effect of additive concentration on the antiwear performance is also studied. Experiments are conducted at first with pure base oils followed by the additive doped base oils. The WSD measured in all these cases are depicted in Table 5. As expected, both the samples (P-1 and P-2) show better antiwear performance compared to pure base oils and P-2 is found to be more efficient. Irrespective of base oils or load condition, WSD decreases with increasing additive concentration. That is, both the additives are acting more efficiently at higher concentration level. Comparison between load conditions indicates that under milder condition (20 kg load), additive performance is found better (lower WSD value). Efficiency as thickening agent Thickening power of both the samples (P-1 and P-2) as evaluated in different base stocks indicates a gradual decrease with the increase in concentration of the additive (Table 6). This may be because of the fact that the polymer molecule assumes a coil like aggregation with increase in its concentration in the base stock. The result also shows that the thickening power of P-2 is slightly higher in comparison to P-1. This indicates that as far as the fuel economy is concerned the CB blended polymer is better than the pure homopolymer. Table 5 WSD of base oil and additive-base oil blend Sample Base oil Source WSD (mm) of additive-base oil blends P-1 P-2 20kg load 40kg load 0% 1% 2% 3% 4% 5% 1% 2% 3% 4% 5% BO1 S S BO2 S S BO1 S S BO2 S S Table 6 Oil thickening property of the additives at 313K in base oils Sample Base Source Thickening (%) of base oils oils 1% 2% 3% 4% 5% P-1 BO1 S S BO2 S S P-2 BO1 S S BO2 S S Conclusion Comparison on the basis of additive performances in lube oil indicates that the addition of only 100 ppm of liquid crystal of cholesteryl benzoate induces excellent antiwear performance along with the enhancement of existing pour point depressant, viscosity modifier and thickening property of the polydodecyl acrylate. Hence, it can be concluded that the blended sample is effective as multifunctional lubricating oil additive. Acknowledgement One of the authors (MU) is thankful to Department of Science and Technology, New Delhi, India for financial support. Thanks are also due to Indian Oil Corporation, India and Bharat Petroleum Corporation Limited, India for supplying us the base oils. References 1 Francisco-José Carrión, Ginés Martínez-Nicolás, Patricia Iglesias, José Sanes & María-Dolores Bermúdez, Int J Mol Sci, 10 (9) (2009) Gribailo A P, Kupreev M P & Zamyatnin V O, Chem Tech Fuels Oils, 19 (1983) 342.

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