Journal of Scientific & Industrial Research Vol 76, February 2017, pp. 303-307

Acrylate-α-Pinene Copolymer as Biodegradable Multifunctional Additives for Lube Oil

M Upadhyaya1, P Ghosh* and K Dey

*Natural Product and Polymer Chemistry Laboratory, Department of Chemistry, University of North Bengal, Darjeeling-734013, India 1Office of the Superintending Archaeologist, Archaeological Survey of India, Kolkata Circle, C. G. O. Complex (4th Floor), Block - DF,

Sector- I, Salt Lake City, Kolkata-7000 64,

Received 16 March 2016; revised 10 November2016; accepted 23 March 2017

Copolymer of α-pinene (AP) with dodecyl acrylate (DDA) and myristyl acrylate (MA) were synthesized and characterized by spectral analysis (IR, NMR). Thermal stability was measured by thermogravimetric and average molecular weight by gel permeation chromatographic (GPC) analysis. Their performance as pour point depressant (PPD) and viscosity index improver (VII) was tested in two different base oils. DDA - AP copolymer showed better performance over MA – AP copolymer. In addition, introduction of α-pinene (AP) structure in the acrylate backbone has induced significant biodegradability in the copolymers. Homopolymers of dodecyl acrylate (HPDDA) and myristyl acrylate (HPMA) were also synthesized, characterized and evaluated in lube oils to make a comparison with their respective AP - copolymers.

Keywords: Lube Oil Additive, Pour Point Depressant, Viscosity Index Improver, Viscosity Index Improver.

Introduction

The basic fluids of lubricants are known as base oils or lube oils. They are the mixture of various fractions obtained from the refining process of crude oil. The performance of lubricant base oils is determined by their viscometric and rheological properties, such as low temperature fluidity, viscosity and viscosity temperature relationship. Properties of such base oils can be improved by the incorporation of suitable performance polymers, generally called additives. The additives are mixed with these base oils to impart additional desirable properties already present in them. At present, the commonly used lube oil additives are detergents, dispersants, antioxidants, corrosion inhibitors, extreme pressure agents (EP), viscosity index improvers (VII) and pour point depressants (PPD). Mostly applied of them are VII and PPD. Additives of different polymeric structures1,2 have been published in patent reviews. However, the present demand of greener lubricants has limited their widespread application in automobile industries. And with this emerging trend of greener approach people have started producing greener lubricants or greener additives for lubricant formulation for introducing better fuel economy, multifunctional performance and to reduce chemical

hazards3,4. With this background, we have started introducing bioactive skeleton into the acrylate backbone through copolymerisation, in anticipation that they may offer useful performances including biodegradability for the lube oil. In the present investigation, naturally occurring bio active α-pinene (AP) was chosen as a potential candidate for copolymerization as it is easily available and contains polymerizable active unsaturation. Two sets of acrylate - AP copolymers were prepared, one with DDA and another with MA using different concentration of α-pinene (w/w) in the mass (1-3%). The study comprises synthesis, characterization, performance evaluation and biodegradability analysis of the additives. The prepared polymers have been characterized by spectral analysis (IR, NMR). Thermal stability of the polymers was measured using thermo gravimetric analysis (TGA) and molecular weight was determined with gel permeation chromatography (GPC). Soil burial degradation test and disc diffusion method was used to determine the biodegradability of the polymer. GPC was also used to determine the extent of biodegradability5. A comparative performance evaluation was carried out among the homo polymers and their respective copolymers.

Experimental

Materials ___________ *Author for Correspondence E-mail: pizy12@yahoo.com

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Toluene, Hydroquinone and H2SO4 were purchased from Merck Specialities Pvt. Ltd. Acrylic acid (stabilised with 0.02% Hydroquinone monomethyl ether) and dodecyl alcohol were obtained from Sisco Research Laboratories Pvt. Ltd. Hexane and myristyl alcohol was purchased from S D Fine Chem. Ltd. Methanol was purchased from Thomas Baker (Chemicals) Pvt. Ltd. and α-pinene from Across Organics. Benzoyl peroxide (BZP) obtained from LOBA chemicals was recrystallised from CHCl3-MeOH before use. Rest of the materials was used as they were obtained without further purification. Two different base oils (BO1 and BO2) with pour point -3 oC and -6 oC respectively, were collected from IOCL, Dhakuria, Kolkata. Esterification

Dodecyl acrylate was prepared by reacting 1.1 mole of acrylic acid with 1 mole of dodecyl alcohol by following the method as described earlier6. Using the same procedure myristyl acrylate (MA) was also prepared from acrylic acid and myristyl alcohol.

Purification of prepared esters

The prepared esters were purified by the standard procedure as described earlier from our laboratory 6.

Preparation of copolymer and homopolymer

Homopolymer of DDA and MA (PDDA and PMA, respectively) were prepared and in the preparation of DDA + α-pinene and MA + α-pinene copolymers, different mole fractions of α-pinene were used. The polymerization was carried out by following the method as described elsewhere6. Homopolymer of DDA, homopolymer of MA and also copolymer of MA with α-pinene were similarly prepared and purified under the same condition for use in reference experiments.

Measurements

Spectroscopic measurements

FT-IR spectra were recorded on a Shimudzu FT-IR 8300 spectrometer using 0.1 mm KBr cells at room temperature within the wave number range 400 to 4000 cm-1. NMR spectra were recorded in Brucker Avance 300 MHz FT-NMR spectrophotometer using 5 mm BBO probe. CDCl3 was used as solvent and TMS as reference material.

Thermogravimetric analysis (TGA)

Thermogravimetric analysis was carried out in air on a mettler TA-3000 system, at a heating rate of 10 K·min-1 at room temperature under atmospheric pressure taking 0.2 g of each polymer sample in a platinum crucible.

Evaluation of PPD properties of the additives in lube oil

The prepared polymers 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 the prepared additives as Viscosity Index

Improver in lube oil

The Viscosity index values of the polymer doped base oil solutions have been determined according to the ASTM D2270 method by using the following equation7.

VI = 3.63(60-10n) ... (1)

Where, n = (ln v1- ln k)/ ln v2 For which, v1 and v2 are the kinematic viscosities

of the solution at lower and higher temperature, respectively. The kinematic viscosity of the oil containing the different concentrations of the tested polymers was determined at 313 K and 373 K and k is a constant which is equal to 2.714 for the temperature range performed. Different concentrations ranging between 1.0 and 3.0 wt % were used to study the effect of copolymer concentration on the VI.

Biodegradability analysis

The extent of biodegradability of the polymers was measured by (i) disk diffusion method against fungal pathogens and by (ii) soil burial test as per ISO 846:1997 method. Polymer samples recovered after the tests were measured for weight loss and IR spectra was taken to observe any considerable shift of IR frequencies8. GPC analysis of the recovered polymers was performed to see the change in Mn and Mw after biodegradation5.

Disc diffusion method

Culture media for fungal strains were prepared with suitable amount of potato extract, dextrose and agar mixture in Petri dishes. All glass apparatus were autoclaved prior to use. Five fungal pathogens namely Colletotrichum camelliae (CC), Fusarium equiseti (FE), Alternaria alternata (AA), Colletotrichum gloeosporioides (CG), and Curvularia eragrostidis

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(CE) were used in this test. The fungal growth was confirmed by change in colour of the culture media from yellow to black. Definite amount of polymer samples (1g) were added in Petri dishes and incubated at 310K for 30 days. After 30 days polymer samples were recovered, washed with chloroform, purified and dried in open vessel9. The weights of dried samples were measured, followed by IR and GPC analysis.

Soil burial degradation test

The soil burial test was performed as per ISO 846:1997 method. Polymer films were buried in soil collected from University campus. Prior to use humidity of the soil was adjusted to 50% - 60% and temperature was maintained at 303K with a thermostat in a humidity chamber. The buried films were recovered after 60 days. Polymer samples were washed with chloroform, purified and dried10 . The dried samples were weighed followed by FT-IR and GPC analysis.

Results and discussion

Spectroscopic analysis

FT-IR spectrum of the homo polymer of dodecyl acrylate (PDDA) showed a sharp peak at 1732 cm-1 due to ester carbonyl group. In its 1H-NMR spectra, homo polymer of DDA showed a multiplet centered at 3.2 ppm due to the proton of -OCH2- group; a broad singlet at 0.73 ppm was due to methyl groups of dodecyl chain. The proton decoupled 13C-NMR of the above sample was in complete agreement with the homopolymer which shows the presence of ester carbonyl group at 171 ppm and absence of any sp2 carbon in the range 130-150 ppm. FT-IR spectrum of the homo polymer of MA also showed similar peaks

1H and 13C-NMR was also in complete agreement with the MA homopolymer. In case of copolymer, absence of peak between 4 to 6 ppm in the 1H-NMR and that between 130 to 150 ppm in the 13C NMR spectrum indicated the absence of the sp2 hydrogen and sp2 carbon, respectively which clearly indicated the formation of the copolymers (DDA + α-pinene and MA + α-pinene copolymers). The value of extent of incorporation of α-pinene in the copolymer composition was determined from IR and FT-NMR method as was reported in our earlier papers6.

Thermogravimetric analysis

A comparison between the values of TGA analysis for homo and copolymers (table 1) shows that in case of DDA polymers, the copolymers are better in thermal stability than the homopolymer and with increasing concentration of α-pinene in the feed, the stability increases. Similar trend but to a lesser extent, is also observed for the polymers of MA. The copolymers are more stable than the homopolymers and with increasing concentration of α-pinene, there is a gradual increase in thermal stability. Also, comparison among the TGA values indicates that DDA homopolymer is more stable than the MA homopolymer.

Efficiency of the prepared compounds as pour point depressant

The efficiency of the prepared polymers as pour point depressant were tested by using 1 wt % to 3 wt % polymer doped base oils and the experimental data are presented in table 2. The result showed that the copolymers are more effective as pour point depressants. The results also indicate that, in general, the pour point depression efficiency of the investigated polymers gradually increases with the

Table 1- GPC data of the polymer samples before and after biodegradation and the TGA data of all the polymers

Polymer samples Before biodegradation After biodegradation

TGA values of all the polymers

Mn Mw Mn Mw Decom. Temp./K PWL

P1 26983 36975 20453 36975 562/612 22/86 P2 19546 33254 17217 31209 555/634 18/84 P3 17878 31765 16654 29334 558/643 18/88 P4 15145 30712 14954 27563 549/654 16/86 P5 19630 35128 19630 35128 503/576 17/84 P6 18674 34596 17131 33165 521/588 15/86 P7 16958 32870 15768 31113 529/591 15/89 P8 14592 30437 13645 28076 541/595 13/83

P-1 is the homopolymer of dodecyl acrylate); P-2 to P-4 are the copolymer of dodecyl acrylate + different mole fractions of AP; P-5 is the homopolymer of myristyl acrylate; P-6 to P-8 are the copolymer of myristyl acrylate + different mole fractions of AP. Decom. Temp. Means: decomposition temperature; PWL is: percent weight loss.

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increasing additive concentration. This may be explained by considering the solvation power of the oil11. The reduction in solvation power becomes more obvious when the concentration of the polymer increases. It is also observed that, homopolymer and copolymer of dodecyl acrylate always acts as a better PPD than the MA polymers. Although the trend is similar in BO2 but the variations is not regular as it was observed in BO1. This is expected since it is well established that the function of additive is very much dependent on the composition of the oil. Efficiency of the prepared polymers as viscosity index improvers

The viscosity index (VI) values of the prepared homo and copolymers in two base oils BO1 and BO2 are presented in table 3. Homopolymer and copolymer of of dodecyl acrylate showed higher VI that is better VII properties in comparison to MA polymers. Copolymers are always better than their respective homopolymers. In case of copolymers, increase in α-pinene content in the feed, the VI is found to increase gradually. Again, with increasing concentration of the polymer in oil, there is always an increase in the VII properties. This may be because of the fact that, at a higher temperature, the polymer molecules change from tight coil to expanded ones as a result of increase in the

interaction between the polymer chain and the solvent molecule 12. This increase in volume enhances the viscosity of the mixture and offsets the normal reduction in viscosity of the oil with the rise in temperature. The increase in concentration of the polymer also leads to an increase in total volume of polymer coils in the oil solutions as was reported earlier2,13. As a result, a high concentration of polymer will impart a high viscosity index rather than a low concentration of the same polymer13.

Analysis of biodegradability test

The copolymers of both the acrylates showed significant weight loss against fungal pathogen Alternaria alternate(about 30 -55% for DDA copolymers and 20-38% for the MA copolymers). In soil burial test the extent of measured weight loss of the copolymers was lower than the disc diffusion method (25 – 55% and 15 – 40% in case of DDA and MA copolymers respectively). GPC analysis of the polymer samples, collected after disc diffusion method was performed and the result was compared with respective samples before biodegradation and the % loss of mol.wt which is also significant, is shown in table 1. FT-IR spectra of the polymer samples, before and after disc diffusion test, were also compared to confirm the biodegradable nature of the prepared

Table 2-Dependence of pour point (PP) on the concentration of additives in base oil [BO1] and [BO2]

Conc. PP in presence of P1 P2 P3 P4 P5 P6 P7 P8

0 % -3.0 [-3.0]

-3.0 [-3.0]

-3.0 [-3.0]

-3.0 [-3.0]

-3.0 [-3.0]

-3.0 [-3.0]

-3.0 [-3.0]

-3.0 [-3.0]

1% -6.0 [-9.0]

-9.0 [-9.0]

-9.0 [-9.0]

-12.0 [-15.0]

-6.0 [-9.0]

-9.0 [-9.0]

-12.0 [-12.0]

-12.0 [-15.0]

2 % -9.0 [-9.0]

-12.0 [-12.0]

-12.0 [-15.0]

-15.0 [-18.0]

-9.0 [-9.0]

-12.0 [-12.0]

-12.0 [-12.0]

-15.0 [-15.0]

3 % -6.0 -15.0 -15.0 -18.0 -6.0 -12.0 -12.0 -15.0 [-6.0] [-15.0] [-18.0] [-21.0] [-9.0] [-12.0] [-15.0] [-18.0]

Pour point of base oil [BO1] is - 3 and [BO2] is - 6

Table 3 - Dependence of VI on the concentration of additives in base oil BO1 and BO2

Conc. VI in presence of P1 P2 P3 P4 P5 P6 P7 P8

0%

85 [80]

85 [80]

85 [80]

85 [80]

85 [80]

85 [80]

85 [80]

85 [80]

1% 90 92 96 98 86 89 91 92 [85] [88] [90] [88] [83] [86] [85] [88]

2% 94 96 93 102 89 89 92 95 [91] [90] [95] [94] [86] [89] [91] [93]

3% 99 105 111 120 95 99 104 106

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copolymers. IR peaks of a representative copolymer sample showed considerable shift after disc diffusion test. Again the broad band appeared in the region 2800-2960 cm-1 has changed into a triplet after the test. The shift in the IR peaks for the polymer samples after biodegradation as well as a considerable weight loss and changes in Mn and Mw has clearly indicated the biodegradable property of the newly developed copolymers (P-2 to P-4 and P-6 to P-8).

Conclusion

DA polymers (homo and copolymers) are thermally more stable than the MA polymers.

Introduction of AP enhances thermal stability of both the copolymers.

In general, the PPD properties of the additives, doped in the base oils, gradually increase with the increasing additive concentration in the polymer-oil blends. Homo and copolymer of DDA showed better PPD properties in comparison to MA polymers.

Homopolymer and copolymer of dodecyl acrylate showed higher VI and hence better VII properties in comparison to MA polymers. Copolymers are always better than their respective homopolymers. Again, with increasing concentration of the polymer in oil, there is always an increase in the VII properties.

Introduction of α-pinene structure in the acrylate backbone has induced excellent biodegradability in the above polymers which also showed excellent multifunctional performance in lube oil.

Acknowledgement

Authors are thankful to CSIR, New Delhi for financial support.

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