Journal of Scienti fic & Industrial Research

Vol. 6 1. Febru ary 2002. pp I 10- I 16

Preparation and Characterization of Penta Alkyds Based on Mahua Oil

Sangeeta Tiwari and Mohini Saxena

Regional Research Laboratory, Hoshangabad Road. Bhopal. Indi a

and

S K Tiwari *

Ahmedabad Textile Indu stry ' s Research Association, PO Ambawadi Vistar, Ah medabad , Indi a

Received : 30 March 200 I ; accepted 2 1 November 200 I

A med ium oi l length alkyd resin is prepared from mahua oil (a non-tradit ional oil) , pentaerythritol and phthalic anhydride. The alkyd was characteri zed by TR analysis. Other properties viz. , viscosity, specific grav ity, ac id number, saponification va lue etc. were determined. Fi lm characteristics of the resin like drying time, thickness, scratch hardness. impact resistance and adhesion were also assessed. The performance of the res in was found to bc comparab ie to a commercial resin . Penta alkyd developed using mahua is of non-d ry ing nature. It can be used as a baking sys tem by curing with melamine at 140"C for 4 hr. The baked film offers good mechanical properties as well as resistance to water and al kali. Combinati on of es ter gum with mahua alkyd gives an air dying res in .

Introduction

Alkyd resins are the most versatile polymeric binders used by the coating industry. They owe their wide applications to the ir versatility and capability to be engineered to give a wide variety of acceptable properties in terms of usage by the coating industry' . Chemically, alkyds are the reacti on products of polybas ic acids with polyhydric alcohols, modified by some oil s or its fatty ac ids. The type of o il and extent of oil modification has an overwhelming effect on the properties of the res ins. Oil modifications reduce overall functionality of the resin , thereby adding flexibility and improved solubility in aliphatic so lvents2.

Some of the traditional oil s3 employed in a lkyd manufac turing are linseed, soybean , safflower, etc. However, there are certain non-traditional oils that have been attempted for use in resin preparation. Neem oil 4, tobacco seed oil 5, Nahor oil 6, Kamala oil7 , Golchara seed oil 8, Undi oil 9, Karanj a oil'o, Niger seed oil" , Babool oil' 2, etc. are some examples reported in literature.

* Author for correspondence

Mahua is another non-traditi onal oil obtained from Mahua tree (Madhuca indica). It is non-edible and non-drying and is available abundantl y in most parts of the world. Its main use is in soap manufacture particularly for laundry purposes 13 .

The present work aims at using mahua oil to prepare medium oil length alkyd resins based on pentaerythritol. Fatty acids are separated from the oi I by saponificati on for preparation of the res in . Characterization of the res ins was done by IR-spectroscopy. Phys ico-chemical and film properties of the resin s were also eval uated . Resistance against water, chemical and organic solvents was studi ed. The performance of the resin was compared with a commercial resin .

Materials and Methods

Raw Materials

Phthalic anhydride and pentaerythritol were procured from Mis Impex Chemical Corporati on , Mumbai . Mahu a oil was obtained from the local market. The properties of Mahua oil are li sted in Table I . Melamine formaldehyde, employed as modifier in the present work was obtained from Mis

_0

KHANNA et at.: HOT PRESSED ALUMINIUM NITRIDE CERAMIC III

Table I- Properties of mahua oil

SI. No. Property Observed value

Colour Light yellow

2 Specific gravity 0.86

3 Acid number 18.38

4 Iodine val ue 73.30

5 Saponification va lue 180

Table 2-Formul ation of penta alkyd

Ingredients Compos ition , per cent (by weight)

Phthalic anhydride

MOFA

Pentaerythritol

26 .0

55.0

19.0

Resins and pl astics Ltd, Mumbai. Another mod ifier used was ester gum , which was prepared by esterification of gum rosin procured from M/s Howrah Chemical works, Kolkata. The performance of the resin was compared with a commercial alkyd resin (CAL).

Isolation of Fatty Acids

Fatty ac id mixture was separated from the oi l by saponificat ion. Mahua oil and its fatty acids were subjected to IR spectroscopic analysis on Perkin Elmer Spectrophotometer, Model 1430.

Formulation of Mahlla Oil Based Penta Alkyd Resin (MPAL)

A medium oil length alkyd resin was formulated using phthalic anhydride, pentaerythritol and mahua oil. The formul ation of the resin is mentioned in Table 2.

Preparation of the Resin

The form ul ated penta a lkyd was prepared by conventional method empl oying fusion technique. Viscosity and acid number of the res in were determined at regular interva ls till the des ired value was achieved . Figure I g ives the chemical reaction for the form ation of penta a lkyd .

Curing of Penta Alkyd with Melamine Formaldehyde (MF)

The penta alkyd prepared from the mahua oil was non air- drying and was therefore, cross-linked with 20 per cent melamine formaldehyde (MF) at 140°C for 4 hr. The poss ible curing reaction is given in Figure 2.

~H.1OH HOH.1C- ~-CH:lOH +

CH:lOH

o

01 \ ~ / o

+ FA _ COO H

Ptntaerythritot PhI hallie Fatty acid Qnhydrid~

Pf'nta alkyd

Figure I-Chemical reacti on showing fo rmation of penta alkyd

( i) Reaction of methyol group (- CHzOH) of MF with - OH group of alkyd

~+ ~ - CHZOH OH

( Penta al~yd ) (Melomine formaldehyde)

~ O- CH2-~

Cured alkyd

(ii) React ion of l'therified methylol group (-C¥C4H9) of MF wifh - OH group of alkyd

~ + EI -CH20C4H9 I OH

( Pl'nta alkyd) 1 H+ (Melamine formaldehyde )

t.WN@wM I

O-CHz - B + C4~OH Cured alkyd

(iii) Reaction of etherfied methylol group (- CHzOC4 H9) with - COOH group of alkyd

~ + ~ - CH2OC4H9 COOH (Melamine formaldehyde)

(Penta alkyd)

~ C=Q I

-CHz-O

Curl'd alkyd

Figure 2-Curing reaction of penta alkyd with melamine formaldehyde (MF)

112 J SCI IND RES VOL 61 JANUARY 2002

Modification of Penta Alkyd with Ester Gum (EG)

The prepared resin was alternatively made to air dry by mixing with rosin ester gum in a ratio of 62 .5 : 37.5 percent by weight. Rosin ester gum was prepared by esteri fication of the gum rosin 14.

Characterization of the Resins

Physico-chemical Properties

The properties of the resin like viscosity, specific gravity, solid content and acid number were determined by standard techniques IS.

Film Properties

To determine the film properties of resins , samples were prepared by application of resin on mild steel substrate l5. The drying time of the film was recorded and the dried film of the resin was tested for film thi ckness, scratch hardness, impact resistance and adhes ion.

Co rrosion Resistance

The resis tance to corrosion was evaluated in different conditions which includes immersion in di still ed wate r, sodium carbonate (5 per cent so luti on), sodium hydroxide (I per cent solution) , sulfuric acid (2 per cent solution) and solvents

(toluene and mineral spirit)1 6. Visual observations were made in all cases for appearance of blisters or any other physical damage. After completion of the specified duration of test, the film was removed and surface was observed for signs of corrosion.

Results and Discussion

IR Analysis of Mahua Oil and Its Fatty Acids

Table 3 gives IR spectral band s for mahua oil and its fatty acids. In the spectrum of mahua oill7 , a strong absorption band is visible for C-O stretching of ester in oil, with maxima at 1730 cm-I . Other bands characteristic of fatty oils appear at 1380 cm-I

(symmetric bending of CH3 of long chain fatty oil s) IS and 1170 cm-I (C-O stretching) are not found in fatty acid spectrum. The conversion of oil to fatty acid is evident from the peak appearing at 1720 cm-I for C-O stretching of - COOH group of fatty acid s 19. Other peaks, which strengthen the formation of fatty acids, are a doublet at 1300 - 1250 cm-I (for C-O stretching of acids) and a weak band at 940 cm-I (for in and out of plane vibration of -OH of -COOH group). No unsaturation was found in the IR of either mahua oil or its fatty acids20 or if at all is present, it may be too low, so as to be detected by normal IR examination .

Table 3-IR Spectral data o f mahua oil , fally acid and penta alkyd Infrared bands, cm,l

O il

Region (max ima)

3700-3200 (br)

:; 100-2700 (2950 & 28(0) s

1850- I GOO ( 17 lOs)

1550-1 400 ( 1470m)

1400-1350 ( 137()w)

800-650 (730)

Fa tt y acid MPAL alkyd Ass ignment

Region (maxima) Region (max ima)

3800-3200 (br) OH st retch ing

3 100-2700 (2940 & 2870) s 3 100-2700 (3050, 2950 & 2870) s a. aromati c rin g

1850- 1600 ( 17 I Os)

1550- 1400 ( 14 70m)

1400-1 350 ( 1380w)

1340- 1200 ( 1260m)

800-650 (730)

1850- 1650 ( 1745s)

1650-1 550 ( 1600 & 1580m)

1550- 1400 ( 1470m)

1400-1 350 ( 1380)

1340-1200 ( 1270s)

1200-1000(11 20& 1070)

850-650 (740 & 700 )

b. Symmetri c. asymmetric C-H

C=O stretching

overtones o f o-di substituted aromati c ring

asymmetri c bend ing of C-H

symmetric bend ing of C-H

a. CoO st retching b. Ar-CO-O- gpo stretch

contribu tions from Ar-CO-O- vibr.

a. C-H wagging of long chain hydrocarbon (C > 4)

b. o-di substituted aromati c ring

;

....

KHANNA et al.: HOT PRESSED ALUMINIUM NITRIDE CERAMIC 11 3

Table 4 - IR Spectral data or melamine rormaldehyde (MF), penta alkyd and MF mod ified penta alkyd Infrared bands, em' !

Melamine-Fonnaldehyde MPAL alkyd MF modified MPAL Assignment

Region (Max ima) Region (maxi ma) Region (maxima)

3700-3200 (3300m ) 3800-3200 (br) 3800-3200 (br) OH stretching

3 100-2700 (2900) 3 100-2700 3100-2700 a. conj ugated C=C, aromatic ring (3050, 2950 & 2870) (3060, 2960& 2870) b. symmetric. asymmetric C-H 1850-1650 ( 1745s) 1800- 1650 (1730s) C=O stretch ing

1750-1550 « 1570s. 1500s) 1650-1520 (1550s) C=N deformati on stretch 1550-1 300 (1370s) 1550-1400 (1470m) 1550-1340 ( 1470, 1340s) Asymmetric bending orC-H

1340-1 200 (1270s) 1340-1200 ( 1270st, br) a. C-O st retch of ac id b. c-o stertch of estcr/Ar-CO-O-

820-800 (8 1 Os) 850-650 (740 & 700) 800-690 (750, 120m) Triazine ring of MF o-S ubstituted benzene ring

Table 5-1R Spectral data of ester gum (EG), penta alkyd and EG modified alkyd Infrared bands , em'!

Rosin Ester (Methyl) Alkyd (MPAL)

Region (Maxima) Region (Max ima)

3700-3300 (br) 3800-3200 (br)

3 100-2700 3 100-2700 (3050, 2950 & 2870) (3040. 2940 & 2870)

1850- 1650 1850- 1650 ( 1745s) ( 1745s)

1650-1550 1650- 1550 ( 1600 & 1580m) ( 1600 & 1580w)

1550-1300 1550- 1400 ( 1470m) ( 1475 , 1380)

1340-1200 (1260m. br) 1340-1200 (1270s)

IR Analysis of Penta Alkyd Resin and Its Modifications

The IR spectral bands of mahua oil based penta a lkyd (Table 3), were compared with a long cha in fatty o il based alkyd, as reported2 ' . The formation of a lkyd is confirmed by the occurrence of a characteri stic band with maxima at 1740 cm" for carbonyl group stretching. The sharp and broad absorpti on in 1340 - 1200 em" region with maxima at 1265 cm" and a doublet of medium intensity with maxima at 11 20 and 1070 cm-', were attributed to Ar-CO-O group vibrations. These three bands characterize phtha late este r with some contributions from the ester linkages of the oi l modifi er' ?

EG Modified MGAL Assignment

Region (Max ima)

3800-3200 (3400br) OH stretching

3 100-2700 a. conj ugated C=c, aromatic ring (3050.2950& 2870) b. Symmetric. asymmctric C-H

1850- 1650 c =o stretchin g ( 1740s)

1650- 1550 Overtones of o-disubstituted ( 1615 & 1585 m) aromatic ring

1550- 1000 Asymmetric bending orC-H ( 1470, 1380)

1340- 1200 ( I 250m, br) C-O stretch of es ter/ Ar-CO-O-

In Table 4, the melamine formaldehyde (MF) cured a lkyd shows the presence of ethe r li nkages formed during the curing process, at 1170 cm" for C-O stretch of cross linked ether22. Bands at 1650 -1500 cm-' (broad doublet of med ium intensity) fo r C=N stretching and at 8 10 cm for out of plane deformation vibration of triazine ring23 confi rms the presence of tri azine ring of melamine.

Table 5 shows the IR spectral bands of ester gum (EG) modified penta alkyd . The characteri sti c band is a sharp band with maxi ma at 1700 cm" due to C=O vibration of acidic group which is shi fted to a higher wave number at 1745 cm-' of es ter24. A weak band near 1610 cm-' indicates un saturati on or conjugation .

114 J SCIIND RES VOL 61 JA NUAR Y 2002

Physico-chemical Properties

The determination of viscosity and acid number at regul ar intervals during alkyd preparation helped in assessing the progress of reacti on or the degree of polymeri zation. The fa ll in ac id number was recorded and the reaction was stopped when the acid number of 1.1 3 was achieved. This ac id number indicated completion of the reaction . The viscosity of the prepared res in was observed to be 12.00 Poise. The solid content of the res in was 60 per cent and the spec ific gravity of the resin was found to be 0.95. The va lues obtained for the resin were comparable to the commercial res in , as shown in Table 6.

Film Properties

The penta alkyd, prepared from mahua oil , was non-drying primarily due to low degree unsaturation of mahua oil. The res in was , therefore, cured by cross-linking with melami ne fo rmaldehyde (MF). The cross- lin king occurred on heat ing the resin at 140°C for 4 hI'. Alternatively the resi n was made air-drying by mod ifying it with ester gum (EG) in the rati o 62.5 : 37.5. The films of the res in s, obtai ned after mod ificat ion with MF or EG and subsequent drying,

Tallie ()-Compari son of physico-chemical properties of mah ua oi l based alkyd and commercial alkyd

SI. '0. Properl y Observation

MPAL CAL

Acid Value. mg KOH/g 1.1 3 10

2 Solid con ten t. per cent 60 60

3 Oi l length , pCI' cent 64 52

4 Vi scosity (P) (60 per cent in 12.00 11 .00 min . spirit)

5 Spec ifi c gravity 0.95 0.98

were subjected to the determination of film properties viz., thickness, scratch hardness, impact res istance and adhesion. The results have been shown in Table 7.

The MF and EG cured penta alkyd res ins were found to possess film thickness of 50 and 51 ~m . It is known25 that the thickness of a coating is related to its ability to provide protection against corrosion. As reported26, all organic films permit di ffusion of water to some or the other extent. Thin films are generall y porous but films ranging in thickness from 20 to 75 ~m have no measurable number of pores, large enough to permit physical transmiss ion of water. It is therefore evident that the film thickness of the prepared resin is in the des ired limit, suited for protecti on of the substrate. Also, these values are comparable to the film thickness of the commerc ial alkyd (CAL).

The scratch hardness of the alkyd cured with MF was 1.4 kg, whereas that of the EG cured res in was 1.2 kg. The adhesion values obtained for MF and EG cured resi ns were 40 and 35 kg/cm2 as compared to 30 kg/cm 2 observed for CAL. Both mahua oil based alkyd and commercial alkyd passed the direct as well as indirect impact test of 2 Ibll 2 in . This being the requirement as per the standard test method27 .

Evaluation of the results reveal superior scratch hardness and adhes ion properties of MPAL cured with MF as compared to that cured with EG. This may be due to the formati on of three-d imensional network (cross-linking) on curing of alkyd with MF. The possible reaction mechani sm is illustrated in Figure 2. The cross-linked structure in the cured res in is formed as a result of reaction between res idual hydroxyl groups of alkyd with methylol or etherified

Table 7-Comparison of film properties of mahua oi l based alkyds and commercial alkyd

SI. No. Property Observation

MPAL+MF MPAL + EG CAL

DrYll1g time. h Baking at 140"C for 4 h Air drying: 2 h Air drying; 2 h

2 Av. film thi ckness. ~m 50 5 1 49

3 Scratch hardness. kg 1.4 1.2 1.3

4 Impact resistance. 2 Ibl 12 in Direct Passed Passed Passed Indirect Passed Passed Passed

5 Adhesion. kglcm2 40 35 30

KHANNA el ai.: HOT PRESSED ALUMINIUM NITRIDE CERAMIC 115

Table 8-Compari son of performance of mahua oil based alkyds with commercial alkyd against water. chemical and solvents

SI. No.

2

3

4

5

6

Immersion in

Distilled water

5 per cent Na2CO}

I per cent NaOH

2 per cent H2SO4

Mineral spirit

Toluene

MPAL+ MF

Slight swelling

Not affected

Not affected

Dissolution & blistering of the film

Not affec ted

Not affec ted

methylol groups of MF. The resultant ether groups have been identified in the IR spectrum of the cured alkyd, as di scussed above. Thi s network structure is absent in EG cured resin , which dries by air oxidation of unsaturation in the structure of EG. resulting III comparatively inferior mechanical properties.

Resistance to Water, Chemicals and Solvents

Table 8 summari zes the visual changes that occurred in the resin samples after immersion in di st illed water, chemicals and solvents. A comparative assessment indicates superior performance of MF cured penta alkyd than that of EG cured resin , when resistance to alkali and solvent were taken into consideration. Inferior performance of EG cured penta alkyd may be attributed to possible hydrolysi s of ester linkages in alkali. When immersion in solvents is taken into consideration the EG cured res in remai ned unaffected in toluene but dullness and dissolution was observed when the film was exposed to mineral spirit. During the immersion in distill ed water, swelling of the film was recorded in EG cured res in which was slight in case of MF cured resin . In ac idic medium, the MF cured penta alkyd developed bli sters.

It may be mentioned here that the chemical and solvent resistance of the resins depends on the relative inertness of the molecular structure and the degree of cross-linking between the molecules28. Due to the presence of ester groups in alkyds, which are easily hydrolysable, they posses poor water and alkali resistance. On modification with EG, the number of ester groups are increased which renders the res in , more prone to water and alkali hydrolys is. The same may be improved by cross-linking with melamine

Visual observation

MPAL+EG CAL

Swelling of the film Slight blistering

Film swelling and detachment Yellowing of solution

Detachment of the film Yellowing of soluti on

Bli stering and fi lm Film removal from the detachment substrate

Not affected Dullness of gloss

Loss of gloss and colour Not affected

eMF). Performance of commercial alkyd (CAL) was good in alkaline medium but the film was observed to leave the substrate when immersed in ac idic medium .

Conclusions

Mahua oil based penta alkyds can be obtained which are non-drying in nature. These can be converted into baking system or air drying res in by modifying with mel amine formaldehyde and ester gum, respectively. The res ins possess good film properties like scratch hardness and adhesion. Melamine formaldehyde modified resins have better resistance to alkali in comparison to those of alkyd modified with ester gum. The resins can be employed for coating applications with good performance.

Acknowledgements

The authors are grateful to A K Basu, J M Modwell and Rajkumar, BHEL, Bhopal, for extending laboratory facilities and giving valuable suggestions. One of the co-authors, Sangeeta, is thankful to CSIR, New Delhi (India), for the award of fellowship.

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