Cd and Zn-incorporated polyesteramide coating materials from seed oil—A renewable resource

Progress in Organic Coatings 59 (2007) 68–75

Cd and Zn-incorporated polyesteramide coating materials from seed oil—A renewable resource Fahmina Zafar, S.M. Ashraf, Sharif Ahmad ∗ Materials Research Laboratory, Department of Chemistry, Jamia Millia Islamia, New Delhi 110025, India Received 21 August 2006; accepted 16 January 2007

Abstract Cd and Zn metal (with completely filled ‘d’ orbital) incorporated linseed oil polyesteramides [Zn-LPEA and Cd-LPEA] were synthesized by in situ condensation polymerization reaction between linseed fattyamide diol (HELA), phthalic anhydride and divalent cadmium/zinc acetate (different mole ratios) obviating the use of any solvent. The structures of these resins were confirmed by FT-IR, 1 H NMR and 13 C NMR spectral studies. The solubility of the resin was checked in different polar and non-polar solvents. The physico-chemical and physico-mechanical properties were studied by standard methods. Curing and thermal behavior were investigated by DSC and TGA techniques. The corrosion protective performance of coatings on mild steel strips was investigated by standard methods. Agar diffusion method was used to determine the antibacterial activities of these polymers. The studies revealed that the minor incorporation of divalent cadmium and zinc in virgin linseed oil based polyesteramide [LPEA] enhances the physico-mechanical and anticorrosive properties as well as reduces the curing temperature. Besides these properties they also show effective antibacterial behaviour against the Escherichia coli and Staphylococcus aureus. The Zn-LPEA and Cd-LPEA resins are, therefore, inexpensive coatings material, developed from renewable resource, for anti-corrosive and antibacterial applications. © 2007 Elsevier B.V. All rights reserved. Keywords: Linseed oil; Polyesteramide; Divalent metal; Anticorrosive; Antibacterial activity; Coatings

1. Introduction Coatings on substrates such as metals, plastics, wood, clothes, paper and leather are largely used to give protection against various detrimental environments and to enhance aesthetic appeal of articles originated long time ago, found application in various forms [1–4]. Generally, polymeric surface coatings are based on materials obtained from petroleum resources. They are expensive, require high technology processing systems; furthermore their stocks are expectedly going to exhaust in 21st century [5–7]. There is urgency, therefore for replacing the petroleumbased monomer/polymer raw materials by alternative ones that are based on renewable resources. Over last two decades the trend has received great attention by scientists and technologists worldwide not only by the realization that the supply of fossil resource is inherently finite, but also by a growing concern for environmental issues [8–11]. Seed oils are expected to be an ideal alternative renewable resource to petroleum-based raw

∗

Corresponding author. Tel.: +91 112 682 3268; fax: +91 112 684 0229. E-mail address: sharifahmad [email protected] (S. Ahmad).

0300-9440/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.porgcoat.2007.01.009

materials since they are inexpensive, non-toxic, biodegradable and relatively harmless to the environment as well as are found in abundance over the world [12–14]. Seed oils—a triglyceride molecules of different fatty acids have been traditionally used in inks, agrochemicals, and organic coatings, both as resin by themselves and as raw material components for coatings [15–19]. They have different reactive functional sites [20] through which several valuable polymeric resins, viz., alkyds [21,22], polyurethanes [1,5,23–26], polyepoxies [23,27,28], polyetheramides [29], polyesters [10,30], polyesteramides [31,32] and others [8,9,12–15,17,19,20,33] have been developed. Most of these polymers have found application in the field of paints, coatings and other areas [1,9,10,14,17,19,21,22,25–33]. Oil based polyesteramide possess both ester and amide linkages in one polymer chain which has improved the performance of polyesteramide over normal alkyds in terms of drying time, hardness, water vapor resistance, chemical and thermal resistance, as well as durability and other physicochemical properties [34,35]. Several polyesteramides have been synthesized from conventional and non-conventional seed oils [31,32,34–43]. To improve their curing temperature/time or drying ability,

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mechanical and corrosion protective efficiency for their commercial application, several modifications have been done. These modifications involve incorporation of metals/metalloids [36,44–46], styrene [47], vinyl acetate [47], poly(styrene-comaleic anhydride) [31,32,35], urethane linkages [48], and other groups [40,49]. These polyesteramide have good chemical and excellent thermal resistance properties and some of them can be used as an effective antibacterial and biologically safe corrosion protective coating materials [31–49]. Metal incorporated polymers are the most versatile and useful of the new polymeric materials currently being developed. It has gained significance from the scientific and industrial viewpoints due to their unusual properties that lead to versatile applications [50]. Thermal stability, electrical conductivity, fracture toughness, flame retardancy, catalytic and biocidal activities, gloss, protective efficiency, reduction in curing temperature as well as the functional properties of these polymers have been drastically altered by the incorporation of metals [34,44,45,50–53]. Jayakumar [50] and Matsuda et al. [54] have lately reviewed the work on metal incorporated-epoxies, polyesters, polyurethanes, polyureas, polyurethane-ureas, polyurethane ethers, etc., which are generally derived from petroleum resource. These polymers find application as aqueous thickeners, impregnates, textile sizers, catalysts, polyelectrolytes in soil conditioning, antimicrobial agents and in biomedical field [50,54–56]. Literature survey reveals that scanty literature is available on metal incorporated polymers derived from sustainable resource [34,44–46]. Sharif Ahmad et al. have successfully modified oil-based polyesteramides by the incorporation of alumina, antimony and boron, which find application as protective coating materials [34,44–46]. In our earlier work we have studied the structural, physico-chemical and antibacterial properties of divalent zinc incorporated linseed oil polyesteramide and overcome the use of harmful volatile organic solvents, VOCs, through solvent less synthesis [53]. Reports on the work of the anticorrosive properties of the resins developed from ‘d’ orbital filled divalent metals Zn (II) and Cd (II), incorporated linseed oil polyesteramide are lacking in the literature. The present paper describes the solvent free synthesis of divalent Cd-incorporated polyesteramide [Cd-LPEA] from linseed oil, its characterization, anticorrosive and antibacterial behaviour. It also includes the investigation of physicomechanical and anticorrosive properties of Zn incorporated linseed oil polyesteramide [Zn-LPEA] coatings and the comparison of the performance of these resins between themselves and with the virgin linseed oil polyesteramide [53].

pure grade (Merck, India), diethanolamine, phthalic anhydride [PA] (S.D. Fine Chemicals, India) was of analytical grade. 2.2. Synthesis of N,N bis (2 hydroxyethyl) linseed fatty amide [HELA] and their polyesteramides HELA and polyesteramides were prepared after a reported method [34]. 2.3. Synthesis of Cd-LPEA/Zn-LPEA Cd-LPEA/Zn-LPEA was synthesized as reported earlier [53]. It was synthesized in different compositions [Table 1] by the reaction of HELA (0.2 mol), PA (0.2 mol) and different amount of cadmium/zinc acetate [Cd(OCOCH3 )2 /Zn(OCOCH3 )2 ] (0.0175, 0.025, 0.0325, 0.04 and 0.0475 mol). HELA (0.2 mol) was taken in a four-necked flat bottom flask equipped with a condenser, nitrogen gas inlet, a thermometer and temperature at 70 ± 5 ◦ C. At this temperature fine powdered PA (0.05 mol) was added very slowly over a period of 15 min under continuous stirring. The reaction mixture was further stirred for additional 15 min at this temperature, followed by very slow addition of different amount of fine powder of cadmium/zinc acetate over a period of 15 min with continuous stirring under N2 atmosphere for 15–20 min. After complete addition of cadmium/zinc acetate, the temperature was raised up to 80 ± 5 ◦ C. TLC (thin layer chromatography) and acid value determination was used to monitor the progress of the reaction. The reaction was conducted under vacuum. The reaction was allowed to continue under the same conditions till the desired acid value, followed by the addition of the rest of the PA (0.15 mol). TLC and acid value determination was further used to monitor the progress of the reaction. The reaction was allowed to continue till the desired acid value was obtained. After the completion of the reaction the final product [Cd-LPEA/Zn-LPEA] was transferred to a sample container. Table 1 FT-IR spectral assignments of LPEA, Zn-LPEA and Cd-LPEA Functional groups

OH (alcoholic) C–O (primary alcohol) C O (ester) –C–C( )–O str.

2. Experimental 2.1. Materials Oil was extracted from linseed (procured from local market) using soxhlet apparatus. Petroleum ether (boiling range 60–80 ◦ C) was used as a solvent. The fatty acid composition of the oil was determined by gas chromatography (GC; 111/8s.s column, FID detector) [34]. Sodium methoxide, xylene, metal acetate [M(OCOCH3 )2 where M = Cd (II) and Zn(II)] of extra

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C O (amide) C–N CH2 bend CH2 sym CH2 asym C=C–H str. Ar C C–H Ar C C– Ar C C–H bend Ar: aromatic.

IR assignment (cm−1 ) LPEA

Zn-LPEA

Cd-LPEA

3460 1069 1725 1274.5, 1166, 1138 1636 1463.6 1391 2855.7 2928 3008.8 3080 1615, 1585 750

3456.3 1072.9 1732 1282.3, 1164.8, 1138 1633.6 1463.6 1385.3 2854.1 2926.2 3009.9 3079 1600, 1580 747.5

3457.2 1072.3 1733 1279.5, 1163.5, 1137.8 1633.8 1463.6 1392.4 2853.2 2925.1 3011.2 3078 1600, 1579 744.9

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Table 2 Physico-chemical characterizations of LPEA, Zn-LPEA and Cd-LPEA Resin code

Hydroxyl value (%)

Saponification value (mg KOH/g)

Iodine value (g I2 /100 g)

Specific gravity (g/ml)

Refractive index

Inherent viscosity (dl/g)

LPEA Zn-LPEA-1 Zn-LPEA-2 Zn-LPEA-3 Zn-LPEA-4 Zn-LPEA-5 Cd-LPEA-1 Cd-LPEA-2 Cd-LPEA-3 Cd-LPEA-4

7.87 7.78 7.75 7.72 7.67 7.0 7.73 7.70 7.65 7.02

128 97 93 91 89 81 92 88 86 78

48.0 46.0 45.7 45.3 45.0 42.5 45.2 44.7 44.3 41.8

0.9380 1.2035 1.2055 1.2080 1.2105 1.2140 1.2058 1.2078 1.2124 1.2145

1.5070 1.5102 1.5140 1.5261 1.5322 1.5476 1.5191 1.5243 1.5380 1.5482

0.652 0.685 0.693 0.702 0.712 0.748 0.696 0.704 0.723 0.750

2.4. Antibacterial activity of Cd-LPEA/Zn-LPEA Cd-LPEA/Zn-LPEA [53] and LPEA was screened for their antibacterial activity against gram positive (Staphylococcus aureus) and gram negative (Escherichia coli) bacteria. The antibacterial activity was evaluated with respect to Amekasin (amino glycoside) as standard controlled drug in the nutrient agar diffusion method [58]. All the samples are soluble in xylene. The antibacterial tests were therefore, carried out in xylene. It has no effect on the growth of microorganism. One loopful of bacteria was inoculated in 10 ml of nutrient broth (peptone 5 g/L, pH 6.8) and incubated at 37 ◦ C for 28–30 h in a test tube shaker at 100 rpm. The actively growing bacterial cells were used for inhibition studies. The nutrient agar (20 ml) was poured into sterile petridishes and allowed to solidify at room temperature. After solidification 0.1 ml of the bacterial culture was spread on the nutrient agar. A circular well (9 mm, diameter) was made with a sterilized steel borer. The CdLPEA/Zn-LPEA test samples were prepared in xylene, as this solvent had no effect on growth of microorganisms. These test samples containing different wt% of metal were used to study the antibacterial activity. 0.1 ml of each Cd-LPEA/Zn-LPEA resin test solution was added into the well and incubated at 37 ◦ C for 24 h. After incubation the zone of inhibition was measured in millimeter and represented as inactive (−), mild (+), moderate (++) and highly active (+++) depending upon the diameter and clarity of zone (Table 5). 2.5. Test methods The chemical structure of Cd-LPEA/Zn-LPEA [53] was characterized by FT-IR, 1 H NMR, and 13 C NMR. FT-IR spectra of these resins were taken on Perkin-Elmer 1750 FT-IR spectrophotometer (Perkin Elmer Instruments, Norwalk, CT) using a NaCl cell. 1 H NMR and 13 C NMR spectra were recorded on JEOL GSX 300MHZ FX-1000 spectrometer using deuterated chloroform as a solvent, and tetramethylsilane (TMS) as an internal standard. The thermogravimatric analysis (TGA) was done with thermogravimatric analyzer, TA-51 (T.A. Instruments, USA) at 20 ◦ C/min in nitrogen atmosphere. Differential scanning calorimetric analysis (DSC) was done in Dupont 910 model at 10 ◦ C/min in nitrogen atmosphere. Solubility of these

resins were tested in various polar and non-polar solvents by taking 25 mg of each resin in 5 ml of different solvents in a closed test tube and set aside for a day. Iodine value, hydroxyl value, saponification value, inherent viscosity, specific gravity and refractive index were determined by standard laboratory methods (Table 2). 2.6. Preparation of coatings Cd-LPEA/Zn-LPEA coatings were cured in an oven at different temperature (150–250 ◦ C) and time (5–30 min) in order to get optimum curing temperature and time. The curing temperature and time are given in Table 3. The coatings were prepared by brush technique using solution containing 60 wt% resin in xylene applied on mild steel strips. The strips were polished on various grade of silicon carbide papers and then washed with water and degreased with alcohol and carbon tetrachloride. They were dried under vacuum for several hours. The standard sizes of strips of 30 mm × 10 mm × 1 mm size were taken for chemical resistance test in water, acid (5 wt% HCl), alkali (5 wt%), xylene solvent by placing them in 3 in. diameter porcelain dishes, and of 70 mm × 25 mm × 1 mm size to evaluate their physico-mechanical properties such as scratch hardness (BS 3900), bending (ASTM D3281-84), impact resistance (IS: 101 part 5/Sec.3, 1988) and specular gloss at 45◦ by gloss meter (model RSPT 20; Digital Instrument, Santa Barbara, CA). The thickness of the coating was found to be between 75 and 100 ␮m as measured by Elcometer (Model 345; Elcometer Instrument, Manchester, UK). Salt spray test (ASTM B177-94) in 3.5 wt% NaCl solutions was also carried out for a period of 10 days in salt mist chamber. 3. Results and discussion 3.1. Synthesis In situ synthesis of Cd-LPEA/Zn-LPEA was carried out by the direct condensation reaction of HELA, PA and divalent zinc acetate/cadmium acetate obviating the use of any solvent at low temperature (80 ± 5 ◦ C) and in a shorter time period as compared to the reported temperature and time for the in-solvent synthesis of virgin LPEA resin [34]. The above reaction characteristics

d e e e c e e e e

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a: film completely removed, b: film cracked and partially removed, c: slight loss in gloss, d: loss in gloss, e: unaffected and f: film slightly swells. * Film completely removed in 1 h.

d c e e c e e e c c e e e f f f e f a* a a a a a a a a e e e e c f f e c 50 110 120 130 130 141 148 155 155 10 20 20 20 20 20 20 20 20 220 180 170 160 160 170 160 150 150 LPEA Zn-LPEA-1 Zn-LPEA-2 Zn-LPEA-4 Zn-LPEA-5 Cd-LPEA-1 Cd-LPEA-2 Cd-LPEA-3 Cd-LPEA-4

Time (min) Temperature (◦ C)

2.00 2.5 2.7 3.2 2.6 2.8 3.0 3.5 3.0

100 150 150 150 100 150 150 150 100

1/4 1/8 1/8 1/8 1/8 1/8 1/8 1/8 1/8

HCl (5%) (10 days) NaOH (5%) (2 h) H2 O (10 days)

Gloss at 45 ◦ C Impact resistance (lb/in.) passes Scratch hardness (kg) Baking Resin code

Table 3 Physico-mechanical and anticorrosive/chemical resistance properties of LPEA, Zn-LPEA and Cd-LPEA

Bending in. passes

Corrosion resistance

NaCl (3.5%) (10 days)

Xylene (10 days)

F. Zafar et al. / Progress in Organic Coatings 59 (2007) 68–75

Scheme 1. Synthesis of Cd-LPEA/Zn-LPEA.

results from the fairly good fluidity of HELA that act as a reactive diluent [59] and the catalytic activity of the metals [54]. The reaction scheme for the synthesis of Cd-LPEA and its proposed structure is given in Scheme 1. During the synthesis a noticeable increase in viscosity of the product was observed in a short time by the addition of 0.755 wt% of cadmium/zinc acetate, beyond this resin ultimately sets into gel. This happened due to the increase in the size and complexity of the resin molecules as a result of the coordination of discrete cadmium/zinc acetate molecules with oxygen of pendent chain (–O C–R) of neighboring polyesteramide molecules and/or the oxygen/nitrogen present in the main polyesteramide chain [53]. From the above observation it is concluded that the incorporation of cadmium and zinc contents in LPEA resin can be safely carried out up to 0.755% to have useful resin compositions. Table 3 reveals that resin composition Cd-LPEA-3 and Zn-LPEA-4 show the best results. 3.2. Spectral analysis IR spectral analysis of LPEA and Cd-LPEA/Zn-LPEA [53] are summarized in Table 1. It reveals that the shifting is observed in the characteristic bands of C O (ester) str., C–C( O)–O str., Ar–C C– str., and Ar–C C–H bending by the incorporation of divalent cadmium and zinc metals. The 1 H NMR spectra (Fig. 1) Cd-LPEA/Zn-LPEA [53] resin shows all the characteristic peaks of LPEA. The carboxyl hydroxy peak which appeared at δ = 8.5 ppm in LPEA is found to be absent in the spectra of Cd-LPEA/Zn-LPEA. The characteristic peaks for aromatic rings which were found at δ = 6.92–7.3 in LPEA, appeared at δ = 6.97–7.56 ppm in Cd-LPEA/Zn-LPEA, thus confirming the incorporation of Cd/Zn in LPEA resins. 13 C NMR spectra (Fig. 2) of Cd-LPEA and Zn-LPEA resins shows all the charac-

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Fig. 1. 1 H NMR spectra (a) LPEA, (b) Zn-LPEA and (c) Cd-LPEA.

teristic peaks of LPEA and shows additional peaks in aromatic region at δ = 137.56 ppm (ring carbon attached to –COOCd/Zn–) and at δ = 132.979 ppm (ring carbon attached to –COOCH2 group), along with these peaks. Four additional aromatic carbon peaks are also observed at δ = 123.01–127.18 ppm. One additional peak for –C O, appears at δ = 174.0 ppm, due to the attachment of divalent Cd/Zn to the carboxyl carbon. The above spectral studies confirm the incorporation of cadmium and zinc in the polyesteramide resin. 3.3. Physico-chemical characterization It is observed from Table 2, that the hydroxyl, saponification and iodine values decrease (Cd-LPEA < Zn-LPEA < LPEA) while the specific gravity, refractive index and inherent viscosity values increase (Cd-LPEA > Zn-LPEA > LPEA). The same trends in the aforementioned values are found when the mole

Fig. 2.

13 C

NMR spectra (a) LPEA, (b) Zn-LPEA and (c) Cd-LPEA.

ratio of cadmium/zinc content is increased in the resins. These results may be correlated to the reaction affinity of cadmium/zinc acetate with LPEA. It is also observed that the hydroxyl, saponification and iodine values of Cd-LPEA systems are lower while their specific gravity, refractive index and inherent viscosity are higher than Zn-LPEA systems. These results may be correlated to higher molar mass of Cd-LPEA systems than Zn-LPEA systems. The solubility behavior of Cd-LPEA/Zn-LPEA [53] resins have been carried out in xylene, toluene, chloroform, carbon tetrachloride, diethyl ether, petroleum ether, acetone, ethanol,

F. Zafar et al. / Progress in Organic Coatings 59 (2007) 68–75

methanol, dimetylsulfoxide (DMSO), dimethylformamide (DMF). These resins show good solubility (100 wt%) in xylene, toluene, chloroform, carbon tetrachloride, ether, acetone, DMSO and DMF, and show lower solubility (20 wt%) in the rest of the solvents. The solubility behaviour of Cd-LPEA/ZnLPEA was similar to that of virgin LPEA. Generally, metal incorporated polymers have poor solubility in organic solvents due to ionic bonds [50,54]. Contrary to this, solubility of Cd-LPEA/ZnLPEA can be correlated to the formation of covalent bonds by the reaction of polyesteramide with cadmium/zinc acetate [60]. The solubility behaviour of these resins can be attributed to the presence of long fatty acid hydrocarbon chains as well as polar groups. 3.4. Coating properties In order to get optimum curing temperature and time, coatings of Cd-LPEA and Zn-LPEA were baked in an oven at different temperatures (140–250 ◦ C) and time (5–30 min). The baking/curing temperature and time of Zn-LPEA and Cd-LPEA are given in Table 3. The results reveal the effect of cadmium and zinc incorporation on the baking/curing properties of ZnLPEA and Cd-LPEA resins. The baking/curing temperatures are found to decrease with the incorporation of zinc and cadmium content in LPEA. Furthermore, the decrease in baking/curing temperature is also observed with an increase in metal content in Zn-LPEA and Cd-LPEA coatings. The LPEA coatings were cured at 220 ◦ C for 10 min, where as Zn-LPEA were cured at 180–160 ◦ C/20 min and Cd-LPEA at 170–150 ◦ C/20 min. The reasonably lower baking/curing temperatures of Cd-LPEA and Zn-LPEA are observed as compared to LPEA. It is further noted that the baking/curing temperature of Cd-LPEA is lower than that of Zn-LPEA. The lowering of baking/curing temperature Zn-LPEA and Cd-LPEA can be attributed to the higher molecular mass and chain length as well as catalytic activity of metals. However, cadmium metal has higher atomic weight than zinc metal [60]. The results of physico-mechanical and anticorrosive characteristics of coatings of LPEA and different compositions of Cd-LPEA and Zn-LPEA are summarized in Table 3. The effect of zinc and cadmium incorporation on the physico-mechanical and anticorrosive properties of Cd-LPEA and Zn-LPEA coatings have been investigated among themselves, and are also compared with those of LPEA coatings. Physico mechanical properties such as scratch hardness increases from LPEA to Zn-LPEA and Cd-LPEA coatings. The scratch hardness further increases with the increase in Cd/Zn metal content upto a certain limit, beyond which a reduction in scratch hardness was observed. The impact resistance of all compositions of CdLPEA and Zn-LPEA coatings are found better than those of LPEA and follows the same trend as observed in case of scratch hardness. The increase in scratch hardness and impact resistance can be attributed to the presence of Cd/Zn metal and the increase in chain length leading to a highly cross-linked structure. The coatings of LPEA pass only the 1/4 in. conical mandrel bend test while coatings of all compositions of Cd-LPEA and Zn-LPEA pass 1/8 in. conical mandrel bend test as no crack or detachment

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of coatings was observed up to 1/8 in. bending test. The incorporation of cadmium and zinc in LPEA increases the chain length, which leads to further increase in the flexibility of the chains. The gloss value is found to increase considerably by the incorporation of cadmium and zinc in LPEA resin; it further increases with the progressive increase in the cadmium/zinc metal content in all resin systems. Cd-LPEA coatings have higher gloss value than those of Zn-LPEA coatings. The increase in gloss value by the increase in zinc and cadmium contents can be attributed to the presence of metal in the resins and their dense structure, since metal-based polymers reportedly show better gloss value and adhesion properties [44,45]. Like physico-mechanical properties corrosion resistance performance of these resins are also found to improve with increase in Cd/Zn metal content. They showed better corrosion/chemical resistance performance specially in water, NaCl (3.5 wt%) and acid (5 wt%) than LPEA coatings, while the alkali (5 wt%) resistance behaviour of these systems is not improved. This can be due to the increase in the ester groups along with the Cd/Zn metal in the above resins, which are prone to alkali (easy conversion of cadmium/zinc of the resin into cadmium/zinc hydroxide). The higher corrosion resistance of Zn-LPEA-4 and Cd-LPEA-3 coatings can be attributed to the presence of optimum amount of cadmium and zinc contents in the system, providing a uniform and firmly adhered coating on the surface of the substrate. 3.5. Thermal analysis The effect of divalent cadmium and zinc content on thermal stability of LPEA was investigated by TGA; the results are summarized in Table 4 (Fig. 3). Thermal stability of Cd-LPEA and Zn-LPEA [53] coatings are also compared with that of LPEA [34] coatings. The considerable improvements in thermal stability of these coatings are observed. Zn-LPEA and Cd-LPEA coatings show higher thermal stability than LPEA. Thermal stability is found to increase with the Cd/Zn metal up to a certain limit, beyond which a reduction in thermal stability is observed. The higher thermal stability is observed in case of Zn-LPEA-4 in Zn-LPEA system while Cd-LPEA-3 in Cd-LPEA system. The Cd-LPEA-3 has higher thermal stability than Zn-LPEA-4. The higher thermal stability of these resins can be attributed as a charTable 4 Thermal stability of LPEA, Zn-LPEA and Cd-LPEA Polymer

T5 (◦ C)

T20 (◦ C)

T50 (◦ C)

T80

LPEA Zn-LPEA-1 Zn-LPEA-2 Zn-LPEA-3 Zn-LPEA-4 Zn-LPEA-5 Cd-LPEA-1 Cd-LPEA-2 Cd-LPEA-3 Cd-LPEA-4

255 310 310 320 320 305 325 325 330 310

315 355 360 370 375 365 385 390 395 370

370 440 440 450 455 445 465 470 475 450

470 630 640 650 655 645 665 670 675 650

T5 , T20 , T50 and T80 are temperature at 5 wt%, 20 wt%, 50 wt% and 80 wt% decomposition, respectively.

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F. Zafar et al. / Progress in Organic Coatings 59 (2007) 68–75 Table 5 Antibacterial activities of Zn-LPEA and Cd-LPEA Resin code

E. coli

S. aureus

LPEA Zn-LPEA-1 Zn-LPEA-2 Zn-LPEA-3 Zn-LPEA-4 Zn-LPEA-5 Cd-LPEA-1 Cd-LPEA-2 Cd-LPEA-3 Cd-LPEA-4

− − − + +++ ++ + + +++ ++

− + ++ ++ +++ ++ + + +++ +++

−: inactive (0–9 mm); +: mildly active (10–15 mm); ++: moderately active (16–20 mm); +++: highly active (21–30 mm).

Fig. 3. TGA thermogram of Cd-LPEA and Zn-LPEA.

acteristic of metal-based polymer systems [45,50,53–57]. DSC thermograms (Fig. 4) of Zn-LPEA-4 [54] and Cd-LPEA-3 show no weight loss up to 320 and 330 ◦ C, respectively. These DSC thermograms match with the TGA (Fig. 3) of the same where no weight loss is observed in this region. DSC thermogram of Zn-LPEA-4 shows small endothermic peak at 120–135 ◦ C, centered at 126 ◦ C, while in Cd-LPEA-3, this peak is observed at 134–140 ◦ C and centered at 136 ◦ C. TGA thermogram of the same does not show any noticeable change in this temperature range. These endotherms can be correlated to the melting of the resin. The higher value of melting point in case of Cd-LPEA-3

in comparison with that of Zn-LPEA-4 can be due to the higher molar mass and chain length in the former case as well as the higher stability of cadmium [60]. 3.6. Antibacterial activity Screening of the Cd-LPEA/Zn-LPEA resin for antibacterial activity was done against the S. aureus and E. coli as test organism since these are the most common nosocomial (originating in a hospital) pathogens [53]. The results of antibacterial activities of Cd-LPEA and Zn-LPEA are summarized in Table 5. It reveals that the antibacterial activity of all compositions increases with the increase in cadmium/zinc contents up to a certain extent. In all compositions Cd-LPEA-3 and Zn-LPEA-4 exhibited the highest antibacterial activities against E. coli and S. aureus. It is observed from the literature that metals incorporation in polymeric resins inhibit the microbial growth [50,53]. The mode of action probably involves destruction of bacterial cell wall, denaturation of cellular protein, damage of lipid complexes in cell membranes and dehydration of microbial cells [58]. The virgin LPEA did not show any antibacterial effect [53] but the presence of fatty acid chain, free hydroxyl and ester along with metal (Scheme 1) collectively show the inhibitory influence on the cellular metabolic activities. 4. Conclusion

Fig. 4. DSC thermogram of (a) Zn-LPEA-4 and (b) Cd-LPEA-3.

Divalent cadmium and zinc-incorporated linseed oil polyesteramide [Zn-LPEA and Cd-LPEA] were solventless synthesized and their coatings obtained at lower baking temperature (150–170 ◦ C/20 min) than virgin LPEA. It was found that the incorporation of divalent cadmium and zinc metal enhances the physico-mechanical and physico-chemical/anticorrosive properties as well as show excellent gloss value in comparison to those of plain LPEA coatings. Among all compositions Zn-LPEA-4 and Cd-LPEA-3 coatings show higher physicomechanical and anticorrosive properties. Cd-LPEA-3 has shown best results among all compositions. Cd-LPEA-3 and Zn-LPEA4 has higher thermal stability than LPEA, whereas Cd-LPEA-3 has highest thermal stability among all coatings. The maximum temperature up to which the best sample can be safely used

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was found around 300–330 ◦ C. Zn-LPEA-4 and Cd-LPEA-3 were found to exhibit highest antibacterial activity against E. coli and S. aureus. among all systems. They can find commercial application as eco-friendly anticorrosive and antibacterial coating materials. Acknowledgements The authors are thankful to the Department of Chemistry for providing the necessary facilities during the work and also grateful to Dr. Pillai and Sister Bina of Majidia Hospital, Jamia Hamdard, New Delhi, India for carrying out the antibacterial studies. Fahmina Zafar is also thankful to CSIR (New Delhi), India for SRF against Grant No. 91466 (86) 2K6-EMR-I. References [1] K.H. Badri, F.H. Shahaldin, Z. Othman, J. Mater. Sci. 39 (2004) 4331. [2] N.S. Sangaj, V.C. Nalshe, Prog. Org. Coat. 50 (2004) 28. [3] S.K. Singh, S.P. Tambe, A.B. Samui, V.S. Raja, D. Kumar, Prog. Org. Coat. 55 (2006) 20. [4] C. Ocampo, E. Armelin, F. Liesa, C. Aleman, X. Ramis, J.I. Iribarren, Prog. Org. Coat. 53 (2005) 217. [5] K.H. Badri, Z. Othman, S.H. Ahmad, J. Mater. Sci. 39 (2004) 5541. [6] B. Reddy, J.M. Sykes, Prog. Org. Coat. 52 (2005) 280. [7] H.P. Bhunia, A. Basak, T.K. Chaki, G.B. Nando, Eur. Polym. J. 36 (2000) 1157. [8] L. Yu, K. Dean, L. Li, Prog. Polym. Sci. 31 (2006) 576. [9] H. Uyama, M. Kuwabara, T. Tsujimoto, M. Nakano, A. Usuki, S. Kobayashi, Chem. Mater. 15 (2003) 2492. [10] N. Dutta, N. Karak, S.K. Dolui, Prog. Org. Coat. 49 (2004) 146. [11] H.P. Bhunia, G.B. Nando, T.K. Chaki, A. Basak, S. Lenka, P.L. Nayak, Eur. Polym. J. 35 (1999) 1381. [12] U. Bierman, W. Friedt, S. Lang, W. Luhs, G. Machmuller, Metzger, M. Rush Gen Klaas, H.J. Schafer, M.P. Schneider, Angew. Chem. 112 (2000) 2212. [13] U. Bierman, W. Friedt, S. Lang, W. Luhs, G. Machmuller, Metzger, M. Rush Gen Klaas, H.J. Schafer, M.P. Schneider, Angew. Chem. Int. Ed. 39 (2000) 2206. [14] H. Uyama, M. Kuwabara, T. Tsujimoto, M. Nakano, A. Usuki, S. Kobayashi, Macromol. Biosci. 4 (2004) 354. [15] T. Akbas, U.G. Beker, F.S. Guner, A.T. Erciyes, Y. Yagci, J. Appl. Polym. Sci. 88 (2003) 2373. [16] D.H. Solomon, The Chemistry of Organic Film Formers, 2nd ed., Robert E. Krieger Publishing Co. Inc., Malabar, FL, 1982. [17] G.H. Hutchinson, Surf. Coat. Inter. Part B: Coat. Trans. 85 (B1) (2002) 1. [18] V.D. Athwale, S.C. Rathi, M.D. Bhabhe, Separ. Purif. Technol. 18 (2000) 209. [19] D. Deffar, G. Teng, M.D. Soucek, Surf. Coat. Inter. Part B: Coat. Trans. 84 (B2) (2001) 91. [20] S.N. Khot, J.J. Lascala, E. Can, S.S. Morye, G.I. Williams, G.R. Palmese, S.H. Kusefoglu, R.P. Wool, J. Appl. Polym. Sci. 82 (2001) 703. [21] C.O. Akintayo, K.O. Adebowale, Prog. Org. Coat. 50 (2004) 207. [22] S. Tiwari, M. Saxena, S.K. Tiwari, J. Appl. Polym. Sci. 87 (2003) 110. [23] S. Ahmad, S.M. Ashraf, E. Sharmin, F. Zafar, A. Hasnat, Prog Cryst Growth Ch. 45 (2002) 83. [24] A. Zlatanic, C. Lava, Z. Zhang, Z.S. Petrovic, J. Polym. Sci. Part B: Polym. Phys. 42 (2004) 809.

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