Indi an Journal of Chemical Technology Vol. 8, May 2001 , pp. 176- 180

Studies on epoxidised oil and its blend with polystyrene and poly(methyl methacrylate)

Sharif Ahmad*, S M Ashraf, Abu! Hasnat & Azeem Noor Materi als Research Laboratory, Department of Chemi stry, Jamia Millia lslamia, New Delhi I I 0 025. India

Receil'ed 21 Seplember 2000; accep!ed 7 FebntW)' 2001

Attempts have earlier been made to replace aromatic epox ies by renewable reso urce based vege table oi l epox ies. However the latter lack in toughness and strength. To improve these properties linseed oil epoxy was blended with po lystyrene and poly(methyl methacrylate). The polyblends were prepared in varying proportion of oil epoxy and po lystyrene/po ly(methyl methacrylate), for inves ti gat ion of their physical and mechanica l characteri stics wi th reference to their use in coatings. The bl end fo rmati on was confi rmed by DSC, Ff-IR and solution tests. The epoxy eq ui valent , hydroxyl va lue, iodine value, viscosity, refract ive index, and specific grav ity of oil epoxy, oil epoxy -polystyrene blends and oil epoxy-poly( methy l methacrylate) blend were determined. Glass transition temperatures of linseed oil epoxy-polystyrene blends were found to occur in the range of 60-77.6°C and fo r the linseed oi l epoxy-po ly( methyl methacrylate) blends in the range of 75-82.4°C in the composition range in vestigated. Di stinct shift in IR peaks of epoxy ring, ester group and hydroxyl group was observed in both the polyblends systems indicating electrostat ic interaction between the constituents of the blends. Linseed oil epoxy was found to turn into ri gid mass by the addit ion of these polymers to the ex ten t of on ly 16.6o/t (11'/111) . Prelimi nary in ves ti gat ions al so revea led higher toughne~:s and rigidi ty in linseed oi l epoxy-poly(methylmethacrylate) bl ends than in lin seed oi l epoxy polysty rene blends. Both the polyblends systems show solubility in various organ ic solvents.

Aromatic epoxy resins are a class of versati le thermosetting polymers which have wide application in surface coatings and paints in addition to their application in adhesives, composi tes and laminates' ·' . Epoxy res ins have hi gh strength , low creep, very low cure shrinkage, resistance to corrosion and show good adhesion to the surface of many substances4

.

However, the major drawback of these epox ies is that, in the cured state they are brittle having fracture energy far less than engineering thermoplastics and metals5

. Furthermore the use of petroleum based polymers is expected to go down in coming years because of their spiraling prices and the high rate of depletion of stocks6

. 1 n recent years , the use of renewable resources has attracted the attention of many workers as a potential substitute for petrochemicals7

·8

• Keeping these facts in mind, a long chai n aliphatic epoxy from linseed oi l (a renewable resource) has been synthesized through the epoxidation of unsaturation present in fatty ac id chain. It is expected to show hi gh flexibility and good corrosion resistance properties, particularly against water and acids because of its long hydrophobic chains. However. these aliphatic epoxies fail to give

*For correspondence

satisfactory mechanical properties like toughness, hardness and possess low load beanng capacit/. With a view to improve these properties the linseed oi l epoxy (LOE) has been blended with hard and brittle polymers like polystyrene and poly(methyl methacry late) . Polystyrene (PS) is a hard, brittle and transparent polymer which show low weathreabiltl. It is also susceptible to environmental stress cracking9

. Poly methyl methacrylace is a hard, britt le and transparent polymer which has been found to show good weatherabi!ity9

. Literature survey reveals that no work has been reported on the blending of oil epoxy wit.h these polymers 11

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• In present work the vegetable oil epoxy has been chosen with the objective of using a precursor obtained from a renewable resource and enhancing the physico mechanical properties of the epoxy through blending with polystyrene and (polymethyl methaerycate) so that it can be used as an anticorrosive coating material.

Experimental Procedure

Materials Oi l was extracted from linseed (obtained from local

market) through Soxh let apparatus. Petroleum ether

AHMAD eta/.: EPOXIDISED OIL & BLEND 177

l ,_J~uud

i 1 I 6 5 4 3

0 (ppm)

Fig. I- 1H-NMR spectra of LOE

0

(b.p. 60-80°C) was used as solvent. Fatty acid composition of the oil is given 16 in Table 1. Hydrogen peroxide (30% ), sulphuric acid, glacial acetic acid, and benzene used were of analytical grade (Merk, Ind ia). The poly(methyl methacrylate) (PMMA) of Mw 350,000 (Tg 120°C) and polystyrene (PS) of Mw 140,000 (Tg 94°C) were procured from Aldrich Chemical Company, SA.

Synthesis Linseed oil epoxy was prepared using a reported

method for the synthesis of vegetable oil epox/ 7.

Linseed oil 40 g (l.V. 180) equivalent to 0.2899 mol of unsaturation , 40 mL of benzene, 7.995 mL (0.1326 mol) of glacial acetic acid , and one mL of concentrated sulphuric acid diluted to 50% with water were taken in a three neck round bottom flask equipped with a mechanical stirrer, dropping funnel and thermometer. The flask was then immersed in cold water bath, 48.5 mL (0.427 mol ) of 30% hydrogen peroxide was added drop wise with continuous stirring. The temperature of the reaction mixture was kept at 20°C during the addition of entire hydrogen peroxide. The temperature was then raised to 60°C which was maintained till the reaction continued . The progress of the reaction was monitored by determining the epoxy equivalent4 at regular intervals .

Preparation of blends

Linseed oil epoxy-polyestyrene (LOE-PS) and linseed oil epoxy-poly(methyl methacrylate) (LOE­PMMA) blends were prepared by solution method 18•

Table !-Physico-chemical char<Jcterization of linseed oil

Characteristics

Acid value (mg of KOH) Saponification value Iodine v<Jiue Specific gravity Refracti ve index Fatty acid composition

Linseed oil

8.3

160 181 0.896 1.478

Lenolenic acid 44% Linoleic acid 14% Oleic acid 20%

60% solution (wlv) of PS and PMMA were mixed in varyi ng ratios with 60% solution (w/v) of LOE separately in different reaction vessels under vigorous stirring at room temperature. The solvent was evaporated slowly in a fuming cupboard under exhaust till it appears to be dry . The remaining so lvent is removed in a vacuum oven at 40°C for 24 h. The compositions of LOE-PS and LOE-PMMA polyblends are summarized in Table 2. The formati on of blends were checked by observing that no separation of phases occurred under boiling and cold conditions of the blend solutions. The formati on of blends were also confirmed by glass transiti on temperature (Tg) of blend samples recorded with the help of DSC.

Characterization The Iodine value 19

, hydroxy l value 1 ~, colour val ue. epoxy equivalent4 specific gravity, refractive index of oil epoxy and its blends were determined by standard methods. Solubility of these blended polymers were checked 111 various organic solvents at room temperature. The blend fo rmation was also studied by FT-IR spectroscopy. The spectra of these polymers were recorded on Perkin Elmer 1750 FT-I R spectrometer on NaCI cell. The formation of oil epoxy was also confirmed by the 1H-NMR spectra. 1H-NMR spectra was recorded on JEOL 200 MHz FXlOO spectrometer using DMSO as solvent and TMS as an internal standard . The thermal analyses of these polymers were carried out by DSC (9 10 Dupont) in N2 atmosphere at a heating rate of 10°C/m in . The polymeric film of LOE, LOE-PS and LOE­PMMA were applied on aluminium coupons (70x25x 1) mm fo r specular gloss (at 60°), scratch hardness (BS 3900) and impact resistance test (IS: 10 I, Part 5/Sec 3).

178 INDIAN J. CHEM. TECHNOL., MAY 2001

Table 2- Physico-chemi cal properties of LOE and its blend with PS and PMMA

Properties LOE LOE-PS Polyblends (LOE:PS) w/w LOE-PMMA Polyblens (LOE:PMMA) w/w 10:2 10:4 10:6 10:8 10:10 10:2 10:4 10:6 10:8 10: 10

Colour vn lue

Refractive index

Specific grav ity

Inherent viscosity (dl/g)

Epoxy equivalent

Iodine value

Hydroxyl value

1.486

1.142

0.78

320

18.5

21.0

1.482

1.132

1.1 3

385.7

15.41

17.5

1.48 1 1.480 1.479

1.11 8 1. 108 1.102

1.2 1 1.22 1.31

448.4 511.8 574.2

13.28 11 .25 10.2

14.64 12.81 11 .38

---------- LOE : PMMA-10

0 X w

1 3: 0 ...J u. l:i w :X:

l 0 0 z w

125

LOE:PS-6

LOE:PS-4

LOE:PS-2

225 325

Temperature, °C

Fig. 2-DSC scans for LOE-PS and LOE-PMMA po1yb1ends

Result and Discussion The conversion of linseed oil into linseed epoxy

has been cofirmed by Ff-IR and 1H-NMR spectropic analyses. The IR spectra of oil epoxy shows the presence of the characteristic absorption bands of oxirane ring at 910-950 cm- 1

• The other peaks observed were methyl and methylene groups at 2900-

1.478 1.483 1.483 1.48 1 1.480 1.478

1.091 1.138 1.129 1.121 1.11 8 1.092

1.32 1.2 1 1.25 1.38 1.48 1.52

634.8 264.5 446.3 514.8 571.8 636.8

9.12 15.14 13.12 11 .35 10.0 9. 15

10.25 17.45 14.64 11.89 11.28 10.22

3000 em-', olefenic double bond at 1635 em-' , ester group of oil at 1760 em-'. The strong band at 3554 em-' indicates the formation of OH group. 1H-NMR spectra of LOE (Fig. 1) shows proton of terminal methyl group at 8 = 0.85-0.9 ppm, chain CH2 at 8 =1.25-1.30 ppm, methylene group attached to carbonyl at 8 = 2.1-2.3 ppm, proton of the oxirane ring of LOE at 8 = 2.7 ppm, proton of glyceryl methylene group at 8 = 3.60 ppm, proton attached to olefenic double bond at 8= 5.3 ppm. The presence of characteristic peak of epoxy ring at 9 10-950 em_, and the 1H-NMR value for protons of epoxy ring at 8 = 2.7 ppm confirm the formation of LOE.

LOE-PS Polyblend Characteristic absorption bands of LOE-PS at 900-

930 em-' for epoxy, 1630 em-' for double bond, 1740 cm-1 for ester of oil, 1650 em-' for phenyl group of styrene, 2900 cm-1 for aromatic proton, 3460 em-' for OH were observed .

LOE-PMMA Polyblend Characteristic absorption bands of LOE-PMMA

polyblend are observed at 900-915 em-' for epoxy, 1630 cm-1 for double bond, 1460 em-' for deformation mode of methylene group, 1730 em·' for ester and 3400 em·' for OH group. The presence of bands at 910-930 cm-1 for epoxy, 3460 em-' for OH in LOE-PS

AHMAD et al.: EPOX IDISED OIL & BLEND 179

Table 3-Giass transition temperatures of LOE-PS and LOE-PMMA ployblends

Sl No. Ratio of Tg (OC) Ratio of Tg LOE:PS LOE:PMMA (OC)

I 10:2 60.00 10:2 75.00 2 10:4 66.13 10:4 75.00 3 10:6 70.25 10:6 78.25 4 10:8 73.50 10:8 81.35 5 10:10 77.63 10:10 82.43

and corresponding peaks at 900-915 cm-1, and

3400 cm- 1 in LOE-PMMA confirm the presence of both the oxirane ring as well as hydroxyl group in the blends. The above observations lead to the conclusion that there is no chemical interaction between the constituent polymers in the formation of the blends . However the shifting of bands to low frequency indicates electrostatic interaction between partially charged positi ve and negative si tes on both the constituent polymers in the blends20

·21

. The shifting of bands are higher in the case of LOE-PMMA polyblend due to higher polarity of PMMA.

Table 2 shows the effect of blending on the value of epoxy equivalent (EEW). hydroxyl value, specific grav ity, iodine value. The EEW is found to increases i.e. number of oxi rane ring decreases on increasing the ratio of PS and PMMA in the blend; hydroxyl value and iodine value also decreases in the same manner, but remains constant for the same amount of LOE used in blending. These observations also confirm that no chemical changes occur in blending, only physical interactions occur between LOE and PS/PMMA phases. The solubility of the polymers were visually tested in solvents like DMSO, ethanol, methanol, carbon tetra chloride, chloroform, acetone, tolue e, xylene and benzene. LOE-PS shows good solubi lity only m DMSO, benzene, toluene, chloroform and xylene. In the rest of the above solvents the solubility is poor. The LOE-PMMA is also soluble in ethanol, methanoL acetone besides the other solvents used for sol ubility test of LOE-PS. Surprisingly LOE-PMMA shows solubility both in polar and nonpolar solvents . It is presumed that the PS and PMMA phases in the LOE-PS and LOE­PMMA polyblends envelop LOE phase at molecular level, which results in the restricted solubility of LOE-PS polyblends and fairly good solubility of LOE-PMMA blends. The observed solubility trend of these blends match with the solubility behaviour of polystyrene and poly methyl methacrylate.

Thermal studies

Table 3 shows the variation of Tg wi th the amount of PS and PMMA added to LOE as determined by DSC. The Tg values were determined from the inflexion point on the heat curves. From the figure and data on Tg followi ng inferences can be drawn:

(i) Apparently the polyblends exhibit a si ngle Tg, a characteristic of single phase systemsn-25

.

(ii) Tg's of polyblends of LOE -PMMA are higher than those of LOE-PS . In case of LOE-PMMA the increase in Tg values with the increasing amount of PMMA is sluggish while in case of LOE-PS blends the rate of increase in Tg values with increasing amount of PS in the blends is more pronounced. In case of LOE-PS blends the total variance of Tg has been found to be l7 .6°C, while in case of LOE­PMMA blends this variance was found to be only 7.4°C. This may be due to the rel atively smaller size of the PS chain as evident by lower viscosity of LOE­PS system (Table 2). Smaller size of PS molecule causes the incorporation of progressively larger number of chains per unit mass of LOE-PS blends as compared to LOE-PMMA blends which results into more pronounced increase in Tg values in LOE-PS blends. In the DSC thermograms (Fig. 2) of polyblends only single glass transition temperature, Tg is observed. This clearly indicates the homogeneous miscibility of constituents in LOE-PS and LOE-PMMA blends . Several authors22

-27 have

used Tg value in blends to deduce complete miscibility of constituent phases in the blends.

Film properties

The films of LOE, LOE-PS and LOE-PMMA were cast on aluminium coupons for studying such coating characteristics as impact resistant, tlexibility and scratch hardness. Film of LOE takes 48 h in turning from dry to hard while LOE-PMMA and LOE-PS films take 16 and 18 h respectively for this change. All blend samples pass the impact test ( 100 lbs/in) which indicates good adhesion of the film to the metal surface. The scratch hardness results show that it increases on increasing the ratio of PS and PMMA in polyblends, which indicates the increasing rigidity of the film with the increasing amount of PS and PMMA in the blends. PMMA fi lms were found to show higher scratch resistance, which may be attributed to higher molecular interaction in LOE-PMMA blends because of the presence of polar group in PMMA and epoxy. Flexibility of the films of these blends was

180 INDI AN J. CI-IEM. TECHNOL.. MAY 200 1

found to decrease regularly with the increasing amount of PS and PMMA in the blends but passed the bend test (1/8" conical mandrel ). Small cracks were observed in case of LOE-PS (10: 10) blend ; presumably because of the presence of closely spaced benzene rings of styrene 111 the polyblend. In terestingly no cracks appear in LOE-PMMA polyblend films in their entire composition range due to longer chain length PMMA molecule and the absence of any sti ffening moiety like benzene ring in the poly bl end.

Conclusions (i) LOE-PMMA and LOE-PS make mi scible

homogeneous blends as shown by the presence of single glass transition temperature in these blends and shifting of IR peaks of OH group, oxirane ring and ester groups in these blends.

(ii ) Only a small amount of PMMA and PS ( 16.6% w/w) in LOE turns it into a ri gid mass

(i ii ) LOE-PMMA blends are found to be more ri gid and tough as compared to LOE-PS blends.

(iv) Polyblends are not transparent like pure PS and PMMA but are faintly white with a color value of I.

(v) These information can be used in making hi gh performance coatings and paints.

Acknowledgment This work was

Defence, India) 134/ II 0/ I 06/934

References

funded by ARDB (Ministry of through grant No. Aero/RD-

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