Polyesteramides Based on Linseed and Safflower Oils for Protective Coatings

 

M. M. El-sawy, N. O. Shaker, E. M. Kandeel

 

ABSTRACT:

Polyesteramide resins were obtained and evaluated as vehicles and the variations of film performance in relation to the amide linkage were studied. Treatment of either linseed or safflower oils with diethanolamine with catalytic amounts of alkali metal alkoxide under relatively mild conditions led to a substantially complete conversion to N,N-(hydroxyethyl) linseed amide (HELA) and N,N-(hydroxyethyl) safflower amide (HESA). Polymerization of the polyols with diadipyl aromatic amines (aniline, p-toluidine, p-aminophenol and p-aminobenzoic acid) was carried out to yield polyesteramide derivatives having interesting surface coating properties. Such a substitution was claimed to give much harder, tougher, more flexible films with excellent chemical resistance in comparison with alkyd resins of similar oil length. The study includes stoving films mechanical evaluation as gloss percent at 60ºC, adhesion, impact, pencil hardness and bending tests using mild steel plates. The films also possess excellent impact resistance, high scratch hardness values, excellent bending test and good adhesion.

 

 

 

1. INTRODUCTION:

There has been an increasing trend over the past twenty year in the use of synthetic resins and polymers to meet the requirements of faster drying tougher and more chemically resistant films for the surface coating industry including varnishes and printing inks. Linseed oil or alkyds containing vegetable oil fatty acids are important as vehicles in protective coatings for exterior use on wood. While these products are generally satisfactory, improvement in some of their properties, e.g., durability and mildew resistance, by chemical modification of the basic vehicle has been, and continues to be an important objective of coatings research. Naser et al (Nassar 1982, Nasar 1977) reported preparation and evaluation of alkyds containing a variety of polyols and dibasic acids in combination with vegetable oil fatty acids to produce coatings having a wide range of film properties.

 

The preparation of polyesteramides from linseed and soybean oils was described previously by many authors. (Gast 1968, Gast 1966) The base catalysed aminolysis of these oils with excess diethanolamine produced the corresponding N,N-bis(2-hydroxyethyl)fatty amides (HEFA) that were separated from the liberated glycerol and were subsequently reacted with a variety of dibasic acids or anhydrides to give polyesteramides.

 

To improve durability and film performance of coatings with a new raw materials precursor-m-phenylene dioxy diacetic acid (PDODA) (Saminu M. 2012) It has been proposed that the partial replacement of the phthalic anhydride by m-phenylene dioxy diacetic acid would expect to improve the performance of the dry film due to the introducing of aromatic ring and new ether group.

 

Imide-modified alkyds is made from glycerylamine, phthallic anhydride and glycerol had improved film characterstics over conventional alkyds with respect to drying, hardness and water vapor resistance. (Wright et al 1963) The use of other amino alcohols in the preparation of synthetic resins for coatings had also been reported (House, R.R., et al 1963, Jordan, W.A., et al 1951, Lycan, W.H., 1945)

 

Recently, polyesteramides from nonedible seed oils were also reported by many Co-workers (Sharif Ahmad, et al 2003, Sharif Ahmad, et al 2006) It has been observed that vinylation of resins as well as the nature and amount of unsaturation in the fatty acid chain and its conversion into the cross-links all were found to improve the curing, physicomechanical and anticorrosive performance of polyesteramides. The oil-based polyesteramide was prepared in two steps; viz., in the first step, oil fatty amide was synthesized, and in the second, it was directly converted to polyesteramide by condensing amide with phthalic anhydride (Ashok Chaudhari, et al 2013)

 

Poly (urethane fatty amide) [PULFA] resin was synthesized by using a one-shot technique at room temperature from diol linseed fatty amide [DLFA; a monomer obtained from the aminolysis of renewable resource, such as linseed oil with diethanolamine and sodium methoxide used as a catalyst], 1.0moles, and varying ratio of toluylene-2,4(6)-diisocyanate [TDI, 0.08–1.5moles] in minimum amount of xylene without any chain extender and catalyst (Suman Yadav, et al 2009) Polyesteramide [LMPEA] nanocomposite coating material [LMPEA/Ag] using N,N-bis­(2-hydroxyethyl) fatty amide obtained from non-edible Leucaena leucocephala [LL] seed oil [LLO], and maleic anhydride, reinforced with silver nanoparticles [SNPs], biosynthesized in Leucaena leucocephala leaf extract. UV, XRD, TEM, and particle size analyses confirmed the biosynthesis of NP (37.55 nm). FTIR and NMR established the structure of LMPEA formed by esterification reaction, without any solvent/diluent. (Alam, et al 2020) New modified polyesteramide compositions were prepared and evaluated as anticorrosive varnish. The resin prepared by partial replacement of hydroxy ethyl fatty acid amide (HEFA) by polyethylene glycol (PEG) without affecting the resin constants. Primer formulations based on this resin showed good corrosion inhibiting properties. (Salem. aqeel, et al 2009) New modified PEA compositions were prepared based on 4-amino-N, N-bis(2-hydroxyethyl) benzamide (AHEB) as the ingredient source of the polyol used and evaluated as vehicles for surface coating. (Ahmed Mohamed, et al 2020)

 

Polymeric systems based on polyesteramides (PEA) are high performance material, which combine the useful properties of polyester and polyamide resins, so new modified polyesteramide compositions were prepared and evaluated as vehicles for surface coating. (H. Abd El-Wahab, et al 2011) The aim of the present work was to characterize and evaluate new modified polyesteramide resins for use in protective coating formulations. These modified resins were prepared polymerization of the polyols (N,N-(hydroxyethyl) linseed amide (HELA) and N,N-(hydroxyethyl) safflower amide (HESA)) with diadipyl aromatic amines (aniline, p-toluidine, p-aminophenol and p-aminobenzoic acid) was carried out to yield polyesteramide derivatives having interesting surface coating properties.

 

2. EXPERIMENTAL METHODS:

2.1. Materials:

Diethanolamine was obtained from Rasagan Laboratory (RL). Linseed oil was purchased from local market and safflower oil was obtained by cold extraction with hexane. Adipic acid was Merck – Schuchardt chemically pure grade. P-toluidine, P-amino benzoic acid, P-amino phenol and aniline were chemically pure grade obtained from Fluka chemicals. All other reagents and solvents used throughout this study were obtained from the chemicals pure grade. Cobalt octoate, manganese octoate and lead octoate driers were obtained from BDH laboratory.

 

2.2. Preparation of Hydroxy - Ethyl Fatty Amide (HEFA) (Stahl, E; 1956):

Linseed oil was taken as a typical example.

Diethanolamine (31.5 g, 0.3 mole) was placed in a round bottomed flask fitted with a stirrer, nitrogen inlet tube and dropping funnel. Sodium methoxide (0.19 g, 0.0035 mole) was added and the contents were heated to 115ºC. Linseed oil (LO) (44 g, 0.05 mole) was added dropwise over a period of 15-20 min. Samples for TLC analysis were withdrawn periodically to study the progress of the reaction which was completed in about 35 min. The product was dissolved in ether, washed with 15% aqueous sodium chloride solution and dried over anhydrous sodium sulfate. The ethereal solution was filtered and the ether was removed to yield 51.9 g of yellow-orange oil (94.1% yield). Thin layer chromatography (TLC) of the products on silicic acid plates using ether, hexane, acetic acid (70: 30: 1) showed to be pure N,N- bis(2-hydroxy ethyl) linseed amide (HELA) fatty acids. Fig.1

 

Figure 1. Synthesis of HEFA

 

The previous steps were repeated using safflower oil to give N,N–bis(2-hydroxy ethyl) safflower amide (HESA).

 

The infrared spectrum of N,N-bis(2-hydroxyethyl) linseed amide (HELA)  and N,N – bis (2-hydroxyethyl) safflower amide (HESA), respectively showed that there is no absorption band for ester carbonyl at  1725 cm^-1 and showed a broad band at  3400 cm^-1  which is characteristic for  OH  group and a band at about 1620 cm^-1 which is characteristic for  C-N  and titration for amines was essentially zero. Thus no isomeric acid amines are present in these products.

 

Analytical data of N,N-bis(2-hydroxy ethyl) linseed amide (HELA) and N,N- bis(2-hydroxy ethyl) safflower amide (HESA) are shown in Table 1.

 

2.3.Synthesis of N,N-diadipylamides:

Synthesis of N,N–diadipylaniline (DAA) was taken as an example.

Aniline (9.3 ml, 0.1 mole), Adipic acid (29.22 gm, 0.2 mole) and 50 ml xylene were placed in a round – bottomed flask fitted with nitrogen inlet tube and Dean & Stark trap to collect the water formed. The reaction mixture was heated at reflux temperature (140–145ºC) until approximately the theoretical amount of water was collected. The xylene was removed using rotary evaporator under pressure of 2 mm. and a colourless solid material was obtained and recrystalized from xylene. (M.P 124ºC).Fig. 2

 

Figure 2. Synthesis of DAA

 

Infrared spectra (IR) of DAA showed the expected absorption band of C=O of the carboxylic group at 1700 cm^-1, --OH stretching at 3252 cm^-1, --N—CO at 1600 cm^-1, C—N stretching at 1300 cm^-1 and the aromatic C=C stretching  at 1501 cm^-1.

 

The bands in the area 2778—3030 cm^-1 are due to aromatic C—H stretching vibrations.

The previous steps were repeated using p-toluidine, p-amino benzoic acid & p-amino phenol to give the corresponding N,N-diadipylamides. Table 2 illustrates A.V, M.P & the crystallizing solvents of all the prepared amides.

 

2.4.Preparation of Polyesteramide Resins:

The hydroxy – ethyl fatty amide (HEFA) was placed in a 4-necked 250ml flask equipped with an efficient stirrer, an inert gas inlet, a thermometer and a syphoning device for withdrawing samples without interrupting the reaction. Then N,N^\ dicarboxylic aromatic amide was charged and few drops of concentration sulfuric acid were added and the mixture was heated to 220ºC until an acid value about  20 mg KOH/gm was reached. The weight ratio of HEFA/N,N^\ dicarboxylic aromatic amide depends on the desired excess hydroxyl content. Table 3 collects the time of formation, acid value, iodine value, color & viscosity of the prepared polyesteramide resins.

 

2.5. Preparation of 30 percent excess hydroxyl alkyd resin:

30 percent excess hydroxyl alkyd resins (based on linseed and safflower oil) were prepared. Linseed oil and adipic acid were taken as a typical example:

The process involved heating a mixture of linseed oil (0.56 mole, 106.4 gm), glycerol (0.86 mole, 38.0 gm) and PbO (0.1 gm) as a catalyst at 220ºC till monoglyceride formation was obtained. This was achieved by testing the solubility of samples removed from the reaction mixture in absolute methanol. The reaction mixture was allowed to cool to 100ºC  followed by an addition of the adipic acid (1mole) and xylene and refluxed in an atmosphere of nitrogen. The reaction was stopped at different acid values in order to obtain resins of various acidity. The temperature was raised to 220ºC and maintained constant until a low acid value product was obtained. Then the previous steps were repeated using safflower oil.

 

3. MEASUREMENTS:

Infrared spectra (IR) were obtained from a perkin-Elmer 2000 and Gas Chromatography (GC) HP Agilent 6890 series II GC equipped with a flame – ionization detector.

 

4. METHODS OF ANALYSIS:

Acid value (ASTM: D1639 – 90), hydroxyl value (ASTM:D 1957-86), iodine value (Paquot, C., et al 1987)  saponification value (Official and Tentative Methods of the American Oil Chemists Society, 1979), ester value (ASTM D 196, 1980) and amine content  (ASTM: D 2073-92)  were carried out according to standard methods.

 

5. METHODS OF EVALUATION:

5.1. Preparation of test panels:

Glass and mild steel plates of 50 x 150mm were cleaned from grease by dipping them into petroleum ether, then the surfaces were cleaned by fine cloth, washed and wipped. The plates were washed with ethyl alcohol and allow to dry in air. Films were applied on the clean plates and each run was performed in duplicates or triplicates. The plates were left for half an hour to remove slowly the greatest part of the solvent. Then the plates were then stoved at the required temperature of the specified time in a thermostatically controlled well – ventilated oven.

 

5.2. Drying time:

Drying, or film formation of coatings were carried out at room temperature and at higher temperatures (at 110 C for 3 hour, at 150 C for 1 hour and at 160 C for 1 hour).

 

5.3. Film resistance:

Water, alkali (ASTM: D1647-89) (1% NaOH), acid (Indian Standard Specification, 1950) (10% HNO₃), salt (10% NaCl) and solvent (ASTM:D 1647 – 59) resistances (acetone) were carried out according to standard methods.

 

5.4. Evaluation of film characteristics:

The polyesteramide compounds were thinned to brushable consistency and appropriate quantities of driers were added. Coating were applied on previously prepared mild steel and glass panels with a brush to obtain a uniform coat. After tack-free drying, the film properties such as: bending test (ASTM: D 522-93a) adhesion (tape test) (ASTM: D 3359-95, 1995), impact (ASTM: D 2794 – 93), gloss (ASTM: D 3928 – 93), scratch hardness by pencil test (ASTM:D 3363 – 92a), were determined by standard methods.

 

6. RESULTS AND DISCUSSION:

In order to understand the performance and use of safflower oil, how these uses and product performance are related to its composition and why it has been widely accepted, a comparison of the component acids of linseed and safflower oils which are commonly used in the coating industry must be considered. The property of any coating oil composition is a function of the predominating fatty acid with respect to both type and the amount. The fatty acids composition of linseed and safflower oils which were identified as the methyl esters using Gas Chromatography (GC) technique showed that linseed oil is high in linolenic acid (43.47%) while for safflower oil, linoleic acid (48.93%) predominates. Consequently, it would be expected that the properties of these oils are a function of the amount of linolenic and linoleic acids respectively present in each. It was found also that the total unsaturated fatty acids composition in linseed and safflower oils is 89.13 and 84.73 percent, respectively.

 

Alkyd resins showed satisfactory film performance and mildew resistance but low chemical resistance of the finished films. This is attributed to the presence of the easy hydrolysable ester linkages present. However the inclusion of C–N linkages in the alkyd backbone would be expected to lead to the formation of resins of improved film durability over the conventional alkyds (Krzysztof, M.et al 2002)

In this work attention has been directed towards improving the alkyd by the insertion of two amide linkages in the molecule. This modification greatly improves the drying time, water, acid, salt, solvent and impact resistances. Paints based on this type of modified – polyesteramide would be expected to show no sign of checking, cracking, erosion, discoloration or loss of gloss after application for a long time. The oils selected in this study were the semi – drying safflower and the drying linseed oils because they are not used in edible purposes but used in technical ones.

 

The sodium alkoxide – catalyzed reaction of linseed and safflower oils with diethanolamine produces almost exclusively linseed and safflower diethanolamides. The best conditions for producing diethanolamide directly from linseed and safflower oils required adding oil to the sodium alkoxide in diethanolamine (6 moles) and heating at 110–115ºC for about 35 min. The linseed and the safflower diethanolamides isolated in 93 – 95% yield were amber oil.

 

Table 1 lists the analytical data of N,N- bis (2-hydroxyethyl) linseed amide (HELA) and N,N – bis (2-hydroxyethyl) safflower amide (HESA). The products contain 97.5% of the theoretical hydroxyl value, they have no loss in unsaturation during their preparations as evidenced by the iodine value and only a trace amount of acid was found.

 

Table 1: Typical Analytical Data of N,N-bis (2-hydroxy ethyl) Fatty Amide (HEFA):

 

N,N–diadipyl amides were prepared by reacting various aromatic amines (aniline, p-toluidine, p-amino phenol and p-amino benzoic acid) with dibasic adipic acids.

The chemical characteristics of N,N–diadipylamides are illustrated in table 2 and the identity of the products were checked by acid values and melting points. The acid values confirm the presence of two carboxylic groups which agreed with the theoretical values. The products were obtained in pure forms by crystallization from either xylene and water and the melting points ranged from 120 - 130ºC.

 

Table 2:Characteristics of N,N-Diadipyl Amides

 

The diethanolamide derivatives of various drying (linseed) and semidrying (safflower) vegetable oils were prepared. Polymerization was carried out by the condensation of dihydroxy-diethyl linseedamide with N,N – diadipylaniline (DAA) which was taken as a typical example and can be explained by the following equation, in which  R  represents linseed fatty chain :

 

Following the successful preparation of the polyesteramide derivatives of various fatty acids (Fig. 3) in high percentage yield, attention was directed towards their utilization in resin formation. Such resins, of course, contain both ester and two amides linkages and therefore would be expected to show outstanding film performances over the conventional alkyds. The weight ratio of hydroxyethyl fatty amide diadipylamide depends on the desired excess hydroxyl content.

 

Figure 3. Synthesis of polyesteramide derivatives

Moreover unmodified alkyd resins with 30% excess hydroxyl were prepared. Lead oxide was used as a catalyst to promote the formation of the monoglyceride before the addition of adipic acid.

 

The most suitable temperature for the preparation of various resins is 150ºC (±5ºC). At this temperature, the esterification proceeds smoothly and can be terminated at any required acidity and the amount of unreacted materials is low.

 

Various polyesteramide resins were formulated covering a wide range of resin compositions based on the hydroxyethyl fatty acid amide (HEFA). These resins correspond to 0, 10, 20 and 30% excess hydroxyl contents.

 

The course of esterification of the various resins is shown graphically in figures 4 and 5 The acid value decreases with increasing the time of the reaction.

 

 

Figure 4:The course of preparation of polyesteramides resins using HELA

 

It is clearly seen from these figures that the rate of esterification depends upon the percent of hydroxyl content. In fact, the 30 percent excess resins containing linseed or safflower oil fatty acids can be reacted to a low acid value without danger of gelation. These observations are in agreement with the theoretical expectations.

 

 

Figure 5: The course of preparation of polyesteramides resins using HESA

 

Physicochemical characteristics of the obtained polyesteramide resins are shown in table 3. It is noticed that the time taken for the resins formation ranged between 4-8 hours, and the acid values were generally low except the acid values of HELA and DAPABA resins were relatively the highest because the acid was insoluble in the reaction mixture and gave a product with a small amount of unreacted finely dispersed acid.

 

Table 3: Physicochemical Characteristics of Polyesteramide Resins:

Where: Ia, Ib, Ic, Id are resins No. of 0, 10, 20, 30 excess hydroxyl % of HELA & DAA.

IIa, IIb, IIc, IId are resins No. of 0, 10, 20, 30 excess hydroxyl % of HELA & DAPT.

IIIa, IIIb, IIIc, IIId are resins No. of 0, 10, 20, 30 excess hydroxyl % of HELA & DAPAP.

IVa, IVb, IVc, IVd are resins No. of 0, 10, 20, 30 excess hydroxyl % of HELA & DAPABA.

Va, Vb, Vc, Vd are resins No. of 0, 10, 20, 30 excess hydroxyl % of HESA & DAA.

VIa, VIb, VIc, VId are resins No. of 0, 10, 20, 30 excess hydroxyl % of HESA & DAPT.

VIIa, VIIb, VIIc, VIId are resins No. of 0, 10, 20, 30 excess hydroxyl % of HESA & DAPAP.

VIIIa, VIIIb, VIIIc, VIIId are resins No. of 0, 10, 20, 30 excess hydroxyl % of HESA & DAPABA.

 

The viscosities of the prepared resins were measured. It was found that the viscosities depend on the molecular weight. And it is clear from the data that as the percent excess hydroxyl increases the viscosity increases and it can be reduced by addition of suitable volatile solvent.

 

Resin and film performance:

In order to evaluate all the prepared resins, they were thinned with the suitable solvent to 25 percent solid content, filtered and driers were added to the resin solutions and the solutions were filtered to remove any suspended particles, then varnishes were stoved in a well – closed container for further use.

 

The drying time test was conducted by applying the coating on a glass plate. They were air dried, then stoved at 110ºC for 3 hours, at 150ºC for one hour and at 160ºC for one hour. The data indicate that the time taken for the films to air dried ranged from 40 to 50 hours for hydroxy ethyl linseedamide (HELA) resins and a significantly longer drying time was required for hydroxy ethyl saffloweramide (HESA) resins (40-60 hours). It was noticed that linseed polyesteramide films air dried more rapidly than the corresponding safflower films. This is noteworthy in that the linseed polymers contain more unsaturation than the safflower polymers and differences in molecular weight are not great enough to account for the improvement in drying properties. (table 4).

 

Table 4: Drying Characteristics of hydroxyl ethyl linseed amide (HELA) resins

Where; T = Tacky, ST= Slight Tackiness, VST = Very Slight Tackiness, D =Dry and  HD = Hard Dry.

 

The work was extended to show the effect of temperature on the time of drying. The data in table 4 shows that stoved films at 110ºC for 3 hours were not so hard and most films were soft and tacky. Increasing the temperature of stoving to 150ºC for one hour increased the hardness of the films for most of the linseed polyesteramide films, while the films of safflower polyesteramide were completely dried. Great improvement was reached on further increasing the stoving temperature to 160ºC for one hour and all films were hard dried.

 

It can be concluded that stoved films exhibit better film performance than air dried films in a very short time and the optimum stoving schedule was found to be one hour at 160ºC.

 

Extensive Evaluations:

Resins are required to resist a wide range of condition, and in order to examine the extent to which the film breaks down and to show how far the films will withstand various chemical and physical effects, baked films were subjected to water, alkali (1% NaOH), acid (10 % HNO₃), salt (10 % NaCl) and solvent (acetone) resistance tests. Chemical resistance is determined largely by the relative inertness of their molecular structure and the extent of cross-linking between the molecules. For example, ester groups are readily attacked by alkalies, and ether groups are hydrolyzed by acids if these groups occur as side groups and not part of the main structure.

 

The results obtained in table 5 shows that all films exhibited satisfactory durability and excellent water, acid, salt and solvent resistances except films of resins III and IV showed good acid resistance and films of resins I--IV, V, VII and VIII showed good solvent resistance, while films of resins VI showed fair resistance.

 

Table 5: Film resistances of various polyesteramide resins:

Where ; Ex means excellent , almost no change ,  G  means good , very slight change and  F  means fair , partially attacked .

 

Following the drying time temperature, water, alkali, acid, salt and solvent resistances, attention was directed towards drying films evaluation.

 

The study includes film thickness measurements, gloss percent at 60ºC, adhesion, impact, pencil hardness and bending tests. Table 6 show all the mentioned tests on stoved films applied on mild steel plates.

 

Table 6: Drying film Characteristics data of various polyesteramide resins

Where ; Ex means excellent , almost no change , G  means good , very slighlt change.

 

 

Gloss of a film is the measurement of how well a surface function as a mirror. Table 6 shows the gloss percent at 60ºC and it is noticed that the gloss percent decreases gradually by increasing the excess hydroxyl in all resins. All the 0%, 10%  and 20% excess hydroxyl resins  from II to VIII resins are glossy except resins I are semiglossy, and all the 30% excess hydroxyl resins are semiglossy. Adhesion of the resins on the surfaces depend on the strength of the resin-substrate enhanced by the inclusion of particular chemical groups in the molecules of the resin films, e.g. carboxyl groups promote adhesion to metals. The presence of the ester and amide linkages may result in hydrogen bonding between chains which could lead to a more tightly packed structure. Table 6 shows that all the resin films have good adhesion. The visual observations data of resistance to impact indicate that all film resins passed this test and their impact resistances were excellent. Hardness (lead pencil) is connected to the molecular weight of the polymer. High molecular weight linear polymers produce harder, tougher, more durable films than their low molecular weight equivalents. Measurement of hardness was achieved by rating the hardness of lead pencils. Pencils graded from  6B to 9H were tested on coated mild steel panels. Table 6 shows that scratch hardness values of all film resins were relatively high.

 

All films examined passed the bend test and showed satisfactory flexibility and no cracks were observed when subjected to the test as it covers the determination of the resistance to cracking (flexibility) of attacked organic resins on substrates of metal sheet by bending apparatus.

 

It can be concluded that all these preliminary experiments show that linseed and safflower polyesteramides containing both ester and amide groups produce films that range from soft to very hard, possess excellent impact resistance, excellent bending test and good adhesion but lack alkali resistance.

 

From the above data, attention may be drawn for the production of polyesteramides of linseed and safflower oils which may be used in alkyds, varnishes, plasticizers, etc…..and paints based on this type of modified polyesteramide would be expected to show no sign of checking, cracking, erosion, discoloration or loss on gloss after application for a long time.

 

CONCLUSION:

Vegetable oil (VO) are abundantly available, easy to procure and cost-effective sources of nature. These bear unique natural functional attributes for environment friendly materials. VO have found practical applications as biodiesel, lubricants, cutting fluids (metal cutting and forming), coatings and paints along with other applications. Although the use of VO in paints and coatings is decades old and well-studied, today emphasis is being laid on research pertaining to the modifications of these materials to introduce novel properties, improved performance coupled with environment friendliness at affordable costs. With persistent and extensive research efforts, VO coatings may compete well performance and applications and may establish themselves as ‘‘greener’’ precursors to environment friendly coatings, in future.

 

We have successfully modified polyesteramide resins where the time of reaction and curing time are the only minor drawbacks. The modified resin shows enhanced physico-mechanical properties such as gloss, adhesion, scratch hardness and resistance to mechanical damage. It is also observed that the modified resin shows better film performance in terms of chemical resistance to water, acid, alkali and different solvents.

 

The results obtained show that most films exhibited satisfactory durability and excellent water, acid, salt and solvent resistances, while the alkali resistance is poor and this is expected because of the residual acidity of the resins. Linseed and safflower amides containing both ester and amide groups produce films that range from soft to very hard, and from semiglossy to glossy.

 

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32.   Standard Test Method for Film Hardness by Pencil Test, Philadephia, ASTM:D 3363 – 92a.

33.   Krzysztof, M. and Pawel, S., (2002) J. Progress in organic coatings. 44: 2, 99-109.

 

 

 

 

 

Received on 03.02.2021       Modified on 26.02.2021 Accepted on 20.03.2021      ©A and V Publications All right reserved Research Journal of Science and Technology. 2021; 13(2):89-99. DOI: 10.52711/2349-2988.2021.00014