Chapter 2shodhganga.inflibnet.ac.in/bitstream/10603/36955/9/09_chapter 2.pdf · epoxidation, [21, 22] hydroformylation, ... neem oil by reaction of its fatty amide with trimer of

Ph. D. Thesis, Mr. A. B. Chaudhari, School of Chemical Sciences, N. M. U., Jalgaon, 2014.

Chapter 2

PU Coatings Based on Neem Oil Fatty Amide and IPDI Trimers

CHAPTER 2

Ph. D. Thesis, Mr. A. B. Chaudhari, School of Chemical Sciences, N. M. U., Jalgaon, 2014. 29

PU Coatings Based on Neem Oil Fatty Amide and IPDI Trimers

ABSTRACT

This chapter shows an entirely new application of Azadirachta indica juss

(neem oil) i. e. the preparation of polymeric resin from it. In the regards, we have

attempted to synthesize the neem seed oil based poly (urethane fatty amide) by reaction

of neem oil fatty amide (AIJFA) with trimer of isophorone diisocyanate (IPDI).

Initially fatty acid composition of neem seed oil was obtained by gas chromatographic

(GC) method and then we synthesized AIJFA. Spectral study of synthesized AIJFA

was done by FT-IR and 1H NMR techniques. Molecular weight of AIJFA was

determined by gel permeation chromatography (GPC). The prepared polyurethane was

applied as a coating on mild steel plates and evaluated for its coating performance,

chemical and corrosion resistances.

N

N

N

O

OO

OCN

NCOOCN

CH2

N

CH2

CH2

OH

CH2

OH

C

O

R

OCO CH2

CH2

N

CH2

CH2

C R

O

OCNH

O

NH OC

O

CH2

CH2

N

CH2

CH2

C R

NH

N

N

N

O

OONHCO

O

CH2

N

CH2

CH2

CH2

O

C

O

R

C

O

NH

O

OCNH

O

+

Trimer of IPDIAIJFA

Polyurethane

Published in Progress in Organic Coatings (2013) 76, 1779-1785

(Impact Factor - 2.43)

CHAPTER 2


INTRODUCTION

Now day’s natural feed stock of fossil fuel is reducing continuously and due to

this, there is emergent interest in developing new feed stocks to prepare polymers. [1-3]

For preparation of polymers, renewable resources such as cellulose, carbohydrates,

polysaccharides, starch, fatty acids and vegetable oils have been focused in the

literature. [4-8] Amongst all of these, vegetable oil is having more importance in

polymer sectors by considering the sustainable energy resource and easy availability.

Vegetable oils such as linseed, tall, palm, nahar, cotton, jatropa, karanja, tung and

castor oils were used to prepare the polymeric resins according to their characteristic

properties. [9-13] Tons of vegetable oils are having their uses as renewable raw

materials for other industrially important chemicals such as soaps, surfactants, cosmetic

products, lubricants, inks, diluents, plasticizers, agrochemicals, food industry,

composite materials, etc. [14-16] In addition to this, vegetable oils have also been used

for decades in paint formulations and as binders for different types of coatings. The

most important parameters influencing on properties of oil based coatings are their

composition with respect to presence of fatty acids of different saturated and

unsaturated types, degree of unsaturations, the position and stereochemistry of the

double bonds and extent of oil content. [17] Types of binders used in coatings and

prepared from vegetable oils include alkyds, diethanolamides, polyesteramides,

polyetheramides and polyurethanes (PU). [18] In addition to above mentioned

applications of oil based polymers, PU are also having incredible significant

applications for adhesives, elastomers and foams. [19] For the preparation of PU,

vegetable oil need to convert into hydroxyl terminated polyols by chemical

modification or reaction on triglyceride molecules.

CHAPTER 2


Numbers of experimental reports are available in the literature for conversion of

vegetable oils into polyols by chemical modifications such as ozonolysis, [20]

epoxidation, [21, 22] hydroformylation, [23] esterification [24] and amidation. [25] PU

obtained from vegetable oils (e. g. castor oil) and copolymers of them with styrene,

methyl methacrylates and other monomers have noticed with much attention over the

last decades due to their remarkable properties. [26] Preparation of epoxidized plant

oils (canola, sunflower, soybean, linseed and corn) were also used to prepare polyols

[27, 28] Meshram et al developed the polyetheramide resin from cottonseed oil and

utilized it in moisture curing coatings after reacting it with TDI and shown cottonseed

oil is a good source of renewable material for preparing high performance coatings.

[29] Oils have also been reported for preparation of PU coatings by Gite et al from the

combination of monoglycerides (dehydrated castor, linseed, soybean and sesame oils)

with trimer of isophorone diisocyanate (IPDI). [30] The overall study shown that the

PU prepared from the four monoglycerides and IPDI trimer exibited significant

enhancement and have a strong potential to be used in the application as binder for

surface coatings.

Azadirachta indica juss (neem oil) is present in plentiful amount with annual

production rate of 88, 400 tons in the India and the Indian continent. Neem seed

contains 33 - 38 % oil, which possesses total five fatty acids such as palmitic, stearic,

arachidic, oleic and linoleic acids. However their application in the preparation of

polymer is not studied and majority of the earlier applications of neem seed oil reported

are in agrochemical [31] and pharmaceutical [32] sectors. In other application of neem

tree, Peter et al investigated use of tree extracts as corrosion inhibitors and found high

inhibition efficiency to the surface of metal from corrosion comparing with root and

CHAPTER 2


leaf extracts of it. [34] Chaudhari et al first time reported preparation of polymeric

resins from neem oil. [33]

This chapter represents development of the poly (urethane fatty amides) from

neem oil by reaction of its fatty amide with trimer of IPDI. Initially, we have prepared

neem oil fatty amides (AIJFA) by the reaction of neem oil with diethanol amine. The

prepared AIJFA was treated with laboratory synthesized and commercially obtained

IPDI trimers for the preparation of PU coatings. All the prepared PU coatings were

tested for their coating properties by standard experimental methods. Use of neem oil

in the development of PU coatings may definitely show environmental rewards like

declination in the requirement of fossil or petroleum resources and configuration of

very low greenhouse gas emission. The prepared PU coatings by this route may be

suitable for maintenance coatings for petrochemical refineries and tank linings in the

future.

EXPERIMENTAL

Materials and Methods

Neem (Azadirachta indica) seed oil was obtained from local supplier and

subjected for its characterization such as specific gravity, refractive index,

saponification and iodine values. These values of neem oil were matched with the

standard values and therefore it was used without any further chemical modification.

IPDI was purchased from Merk, Germany and used as such for the synthesis of its

trimer. Commercial IPDI trimer was purchased from Bayer Material Science, Mumbai

and characterized for its isocyanate content by ASTM D-2572-97 before use.

Laboratory grade dibutyltin dilaurate (DBTDL) was purchased from Aldrich

Chemicals, UK. Cylcohexanone, tetrahydrofuran (THF) and diethanolamine of

CHAPTER 2


analytical grade were obtained from SDFCL, India. Remaining chemicals and solvents

used for synthesis or analysis were of either synthesis or of analytical grade as per their

need.

Synthesis of Azadirachta indica juss Fatty Amides (AIJFA)

AIJFA was synthesized by the base-catalyzed amidation of neem seed oil with

diethanolamine as shown in Figure 1. In the experimental process three-necked round

bottom flask of 500 mL capacity was used. Diethanolamine (0.3 mol, 31.8 g) and

sodium methoxide (0.05 %) based on an amount of oil were introduced in the flask and

heated with agitation by a over head motor stirrer at temperature of 80 0C for 20 min.

After maintaining inert atmosphere (purging of N2 gas for 20 min), the assembly was

immersed in an oil bath having arrangement of temperature controller. Neem seed oil

(0.1 mol, 90.4 g) was added drop-wise into the reaction mixture over a period of 60 min

with gradual increase in temperature to 120 0C and continued for next three hours under

constant agitation. The formation of product was tested by two ways viz. checking

solubility of the reaction mass in methanol and determining amine value. Completion

of reaction was confirmed by the complete solubility of reaction mass in methanol and

or the amine value near to zero. The obtained product was dissolved in a solvent

diethyl ether and washed with 15 % aqueous NaCl (salt) solution.

R

C

N

O

OHOHO

O

C R'

C R'''

O C R''

O

O

O

NaOCH3

120 0C

OH

OH

OHN

OHOH

H

+ +

Neem oil Diethanol amine GlycerolGlycerol

AIJFA

3 3

Where, R', R'' and R''' = Fatty acid chain R = R', R'' and R'''

Figure 1: Reaction for Synthesis of AIJFA

CHAPTER 2


The upper organic ethereal layer containing product AIJFA was separated from

aqueous layer by separating funnel. The trace amount of solvent present in AIJFA was

evaporated in a rotary vacuum evaporator.

Synthesis of IPDI Trimer

General structure of trimer and the reaction for trimerization of IPDI is as

shown in Figure 2. For the trimerization of IPDI, the catalyst choline hydroxide was

synthesized in the laboratory according to the method reported in the literature. [35]

Trimerization reaction of IPDI was carried in a three-necked round bottom flask

equipped with thermometer, dropping funnel, mechanical stirrer, condenser, nitrogen

purging system and maintained at 75- 80 0C in an oil bath. Catalyst was added drop-

wise in to the round bottom flask containing IPDI. The reaction was continued for next

5-7 h until the isocyanate content of the reaction mixture reach to half of the initial

value. At last catalyst deactivation was carried out by adding appropriate quantity of p-

toluene sulphonic acid.

N

N

N

O

OO

OCN

NCOOCN

OCN NCO

Trimer of IPDI

3Cholin hydroxide

75 0C

IPDI

Figure 2: Synthesis of IPDI trimer

Preparation of PU Coatings

The general reaction for the preparation of PU is given in Figure 3. The

prepared neem oil based AIJFA was reacted with IPDI trimer by varying an NCO/OH

ratio (1:1, 1.1:1 and 1.2:1). Mixture of cyclohexanone and THF (80:20) was mixed

with AIJFA (1 mole) to obtain required solid content (50 %) solution of AIJFA.

CHAPTER 2


Initially DBTDL (0.05 %) as a catalyst was added to AIJFA part in order to control the

rate of urethane formation. Then appropriate amount of trimer was added to the 50 %

solid AIJFA solution. The reaction mixture was stirred for next 5 min at 27 0C

temperature to attain pourable viscosity. After attaining pourable viscosity, the mixture

was used to prepare coating samples using bar applicator (Raj Scientific Company,

Mumbai, India) with a wet film thickness of 120 µm on MS panels of 4 × 6 inch

dimensions. Different PU coated samples were prepared by changing the ratios of

NCO/OH as mentioned earlier. The prepared coating panels were allowed to cure at

room temperature under visual examination, until the coatings were dry to touch.

Before application of the coatings, steel panels were pretreated with sand paper,

washed with acetone and dried in an air-circulated oven.

N

N

N

O

OO

OCN

NCOOCN

CH2

N

CH2

CH2

OH

CH2

OH

C

O

R

OCO CH2

CH2

N

CH2

CH2

C R

O

OCNH

O

NH OC

O

CH2

CH2

N

CH2

CH2

C R

NH

N

N

N

O

OONHCO

O

CH2

N

CH2

CH2

CH2

O

C

O

R

C

O

NH

O

OCNH

O

+

Trimer of IPDIAIJFA

Polyurethane

Figure 3: Preparation of PU Coatings

CHAPTER 2


CHARACTERIZATION

Characterization of Raw Materials

Oil was characterized by the standard experimental methods such as specific

gravity (ASTM D5355-95), refractive index (ASTM D1747-09), saponification value

(ASTM D464-05), acid value (ASTM D5768-02) and iodine value (ASTM D-5768-

02). The fatty acid composition of neem oil was determined by gas chromatography

(GC) using methyl esters of it. Neem oil fatty acid methyl esters (FAME) were

prepared by refluxing neem oil in a dry methanol in the presence of sodium methoxide

as a catalyst. Analysis of FAME was carried on gas chromatography (GC) (Shimadzu

GC-14B) having specially designed program for oven temperature starting from 180 to

250 0C, injection temperature 230

0C, column (Restek, Rtx-Wax) and FID detector.

Isocyanate content of the synthesized IPDI trimer was determined by the n-butyl amine

method as per ASTM D-2572-97 standards. The hydroxyl value of neem oil and

AIJFA was determined by acetylating reagent method as per experimental procedure

recommended by ISI: 354 (1987) and amine value was determined by IS 354 (Part-5),

1986.

Gel Permeation Chromatography (GPC)

Molecular weights of AIJFA were measured by a gel permeation

chromatography (GPC) with Agilent GPC-Addon Rev A02.02 series HPLC system.

The experimental conditions required an injection volume upto 20 μL and flow 1

mL/min using a column PL-Gel Agilent with RI detector and tetrahydrofuran as a

solvent.

CHAPTER 2


Fourier Transfer Infrared (FT-IR) Spectroscopy

The FT-IR spectra were scanned 50 times on a FT-IR spectrometer (Perkin-

Elemer 2000 FTIR spectrometer) in the range of 4000 to 500 cm-1

by making the

pellets of AIJFA using KBr.

1H NMR Analysis

The 1H NMR measurements were performed on a

1H NMR spectrometer

(Varian Mercury 300 MHz spectrometer). The reported chemical shifts were against

tetramethyl silane (TMS) and deuteriated chloroform (CDCl3) as a solvent.

Thermal Analysis of PU Coatings

Thermal analysis of the prepared PU coating samples was performed in a

Mettler Toledo TGA/SDTA- 85 instruments in the range of 40-700 0C. Samples (about

2 mg) were placed in a platinum pan and heated under N2 atmosphere (20 mL/min) at a

heating rate of 10 0C/min. During the heating, the weight loss versus temperature curve

was recorded and analysed further.

PU Coatings Characterizations

Gloss

Gloss measurement is important for finding the capacity of a surface or coating

to reflect light. Precautions taken during the measurement in such a way that the

coated samples should not contaminated by any chemical or oil. A digital gloss meter

(Model BYK Additive & Instruments, Germany) was kept on the coated samples with

on auto calibration mode at an angle of 60 0 after calibration of it as per the procedure

given by the manufacture.

Flexibility

Flexibility of film or coating is measured to check the ability of the coatings for

elongation under bent condition or it is test that gives tolerance of the coatings against

CHAPTER 2


cracking when elongated. The flexibility of the coated samples was performed on a

conical mandrel instrument (Raj Scientific Company, Mumbai). While performing the

test, mandrel was freed to rotate on its axis and then coated sample was kept in between

the rotating axis. The handle of conical mandrel was lowered in a vertical direction to

obtain specific angles.

Pencil Hardness

To determine the hardness of polymeric coating films, pencil hardness

measurements is essential. The pencil hardness of the coating was measured by using

a pencil hardness tester (Model BYK Additive & Instruments, Germany). In this test

pencils having different grades were used to move over the surface of the coated panels

from the distance of 6 mm at fixed 45 0 by using a standard holder. The force were

applied on the pencil and moved over the surface of the test sample at a fixed angle.

The coated panels were checked for the removal of the film. The same procedure was

repeated with pencil of higher grades of hardness until the film is scratched or

penetrated. The pencil which does not remove the coating denoted the pencil hardness

of the particular coating.

Cross Cut Adhesion

In this test a cross cut adhesion tester consisting of a die with 11 number of

closed set of parallel blades was passed and pressed on the coated panel in two

directions at right angle to each other so that the lattice of 100 squares of 1 mm2 area

each were formed. The adhesion tape was placed at the centre over of lattice pattern

made on the panel. After 5 min, self adhesive tape was removed by pulling it steadily

in 2 seconds at an angle close to 60 0. Then the sample was examined carefully with

the help of magnifier to determine the percentage of cubes remained on the coating

panel.

CHAPTER 2


Scratch Resistance

Scratch hardness of the coated panel studied by a ‘Automatic Scratch Tester’,

(Rajdhani Pvt. Ltd., India).

Impact Resistance

The impact resistance test of the prepared coatings was carried out for

evaluating the load carrying capacity of them. During this test the dried PU coating

panels were placed on hock properly and movable weighted indenter (1.818 lb) was

lifted from the certain height starting from 0 - 40 inch until the film cracked. After

falling the weighted indenter peeling, cracking and film detachment from the coated

substrate was examined. If there are any cracks on coatings test is considered as failed

otherwise it is passed.

Mar Resistance

The mar resistance of the prepared PU coating was evaluated in the laboratory

using a mar resistance tester of BYK Instruments, Mumbai. Mar resistance is express

in gram, the term of load that fails to spoil the coating film.

Chemical Resistance and Anticorrosive Properties

The chemical resistance of sample was measured by dipping the coated panel in

alkali solutions (10 % NaOH and 10 % NH4OH), acid solutions (25 % H2SO4 and 25%

CH3COOH) and xylene as a solvent for 7 days. Periodic visual inspection was taken

for 7 days to find any evidence of softening, deterioration or development of cracks.

Anticorrosion properties of the prepared PU coatings were also evaluated

through immersion studies and compared coated (crossed and uncrossed) and uncoated

steel panels with each other. The crossed panels were obtained by crossing panels with

sharp razor blade. Immersion study of these coatings was carried out in an aqueous

solution of NaCl (3.5 wt. %). The sample panels were tested for a total exposure time

CHAPTER 2


of 144 h and further extend to 192 h. The panels were continuously monitored time to

time by visual inspections and recorded using a digital camera (Sony, 16 mega pixels).

RESULTS AND DISCUSSION

Characterization of Raw Materials

The chemical analysis of neem oil and AIJFA is furnished in Table 1. The

isocyanate content of the synthesized trimer of IPDI was found to be 15.60 %.

Molecular weight of the AIJFA was measured by GPC and it was found to be 520

( , weight average) and 431 ( , Number average) with polydispersity index (PDI)

of 1.20. The amine value of AIJFA was found to be 0.37 indicated almost all

secondary amines present in diethanol amine have been converted into amide groups

during formation of the AIJFA.

Table 1: Chemical Analysis of Neem Oil and AIJFA

Properties

Specific

gravity

@ 30 0C

Refractive

index @

40 0C

Acid

value

(mg of

KOH/g)

OH value

(mg of

KOH/g)

Iodine

value (g of

I2/ 100g)

Amine

value (mg

of KOH/g)

Neem oil 0.920 1.503 0.5 0.0 64.55 0.0

AIJFA 0.927 1.542 0.6 205 59.82 0.37

Fatty Acid Composition of Neem Oil

Table 2 is representing the composition of fatty acids for the utilized neem oil

which was determined by GC. Total five fatty acids were found in the gas

chromatogram of neem oil FAME. These fatty acids included palmitic, stearic and

arachidic acids as saturated fatty acids, while oleic and linoleic acids as unsaturated

fatty acids. The obtained qualitative and quantitative fatty acid composition of the

CHAPTER 2


neem oil (utilized in preparation of PU coatings) is in agreement with the values

available in the literature. [36]

Table 2: Composition of Fatty Acids in Neem Oil

Name of fatty

acids Structure

Composition % by

weight

Oleic acid

50.04

Stearic acid

29.96

Palmitic acid

11.90

Linoleic acid

05.15

Arachidic acid

02.94

FT-IR Spectroscopy

400600800120016002000280036001/cm

10

20

30

40

50

60

70

80

90

100

110%T

34

87

.42

29

41

.54

28

37

.38

23

26

.23

16

45

.33

15

43

.10

14

60

.16

14

19

.66

13

61

.79

13

00

.07

10

64

.74

93

5.5

1

86

6.0

7

Viscous

Figure 4: FT-IR Spectrum of AIJFA of Neem Oil

The results of FT-IR analysis of AIJFA is represented in Figure 4. FT-IR

spectra of AIJFA showed the absorption broad band at 3487 cm-1

for presence of OH

stretching. Absorption bands at 2837 and 2941 cm-1

were attributed to symmetrical and

asymmetrical stretching’s of –CH2 and –CH3 groups respectively. The characteristic

CHAPTER 2


band at 1645 cm-1

indicated the presence of C=O stretching of amide carbonyl groups.

Presence of absorption bands at 1361 and 1460 cm-1

in the FT-IR spectra revealed the

CH2– bending vibrations and band at 1300 cm-1

was a result of C–O stretching. The

medium absorption band at 1250 cm-1

was assigned to presence of C–N stretching in

AIJFA. Overall result showed absence of –COOH group and appearance of >N–C=O

group which confirmed the formation of AIJFA.

1H NMR Analysis

Figure 5: 1H

NMR of AIJFA of Neem Oil

1H

NMR spectrum of AIJFA (Figure 5) showed the peak at 0.88 - 0.9 ppm of

terminal CH3 group of fatty acid chain, 2.04 -2.06 ppm for –CH2–C= and 2.37 - 2.41

ppm for –CH2–C=O protons. It also showed peak at 1.27 ppm for presence of protons

of –CH2– in fatty acid chain. The protons of –CH2 attached to amide nitrogen appeared

at 2.86 - 2.97 ppm, while –CH2– attached to –OH occurred at 3.71-3.88 ppm and

alcoholic –OH at 5.24 ppm. For C=C–H proton of fatty acid chain was observed at

5.43 ppm. The results of 1H

NMR spectra confirmed the proposed structure of neem oil

fatty amide.

CHAPTER 2


Thermal Analysis (TGA)

Figure 6: TGA Curve of AIJFA Based PU Coatings

Initially the TGA curve (Figure 6) of polyurethane coating sample showed

about 4 % of weight loss at 200 0C that may be due to entrapped moisture and solvent

moiety. Then it went through three steps degradation. The first step occurred with 17

% of weight loss at 300 0C, the second with 37 % of weight loss at 420

0C and the last

with 30 % of weight loss at 600 0C. Normally it is observed that decomposition of

urethane bond starts between 150 and 200 0C depending on the type of substituent like

isocyanate and polyol as reported in the literature. [37] In our case urethane bond

decomposition started at higher temperature range than mentioned in the literature

revealed higher thermal stability of urethane linkage. Second and last decomposition

step corresponded to decomposition of amide and hydrocarbon chains. Thermal

stability of neem oil based fatty amide and trimers of IPDI based PU system is higher

in comparison to urethane fatty amide of linseed oil. [10] (27.7 wt % at 260 0C, 21.11

wt% at 360 0C and 40.62 wt% at 505

0C), alkyd and uralkyd (10 wt % at 95.4

0C, 20 wt

% at 147.6 0C and 50 wt % at 367.12

0C). Cross-linked structure of polyurethanes

CHAPTER 2


synthesized from trimers of IPDI and presence of isocyanurate heterocyclic ring may

also be responsible for higher thermal stability.

PU Coating Properties

The coating properties tested for the prepared PU coated samples include dry to

touch, gloss, scratch resistance, mar resistance, pencil hardness, impact resistance,

flexibility and cross cut adhesion. These coating properties are furnished in Table 3a

and 3b.

Table 3a: Coatings Properties of PU from AIJFA and Synthesized IPDI Trimer

Sr. No. Samples/ Property

PU coatings with

ratio of NCO/OH

1:1 1.1:1 1.2:1

1) Cross cut adhesion (%) 99 100 100

2) Gloss 94.3 98.1 93.9

3) Mar resistance (g) 100 130 110

4) Impact resistance (lb.inch) 33 44 40

5) Pencil hardness 1H 1H 1H

6) Flexibility at 180 0 Pass Pass Pass

7) Scratch resistance (Kg) 3.5 4 4

8) Dry to touch (h) 40 32 38

Table 3b: Coatings Properties of PU from AIJFA and Commercial IPDI Trimer

Sr. No. Samples/ Property

PU Coatings with

ratio of NCO/OH

1:1 1.1:1 1.2:1

1) Cross cut Adhesion (%) 99 100 100

2) Gloss 96.3 99.6 98.9

3) Mar resistance (g) 110 140 120

4) Impact resistance (lb.inch) 33 43 40

5) Pencil hardness 1H 1H 1H

6) Flexibility at 180 0 Pass Pass Pass

7) Scratch resistance (Kg) 3.5 4 4

8) Dry to touch (h) 40 26 38

CHAPTER 2


Gloss of the PU samples of ratio 1.1:1 (NCO/OH) was found better for both

types of PU coatings. The flexibility of all prepared samples of PU coatings were

excellent with adhesion (measured by pencil hardness tester) of 1H. Mar, scratch and

impact resistances of the synthesized IPDI trimer based PU coating prepared from same

ratio were found to be higher compared with samples prepared from other ratios.

Similarly properties of the coatings prepared from commercial IPDI trimer based PU

coatings were also higher than the samples prepared from other ratios. It concludes that

the PU coatings were almost similar for synthesized as well as commercial IPDI trimer

and 1.1:1 NCO/OH ratio was the best amongst all three.

Corrosion Resistance of PU Coatings

It has been noticed that no significant change in the physical appearance of the

PU coating samples was found after exposing them to acids, alkalis and solvent. In

H2SO4, specimens upto some extent became deteriorated and showed slightly loss in

gloss when dried. Corrosion properties of the PU coated, uncoated and cross-cut

coated panels were done by immersion of the panels in an aqueous solution of NaCl

(3.5 wt. %) for 144 h (6 days). The results of study are shown in Figure 7. The panel

without PU coating quickly corroded within 144 h, while slight corrosion was observed

to the cross-cut coated panel even though the metal surface exposed to a salt solution.

It has been found that coated panels were free from corrosion and blister even after 144

h. After achieving excellent results from the immersion study of AIJFA based PU

coatings after 144 h, we extended the test upto 192 h and we found no cracking or any

physical damage to coated panels and only little deterioration was observed to cross-cut

film. Good corrosion resistance to the PU coatings may be due to the presence of

excellent adhesion of coatings with the substrate (as reported by cross cut adhesion in

CHAPTER 2


earlier part of the report). This study conclusively revealed the presence of extensive

corrosion resistance to the AIJFA based PU coatings in salt solution.

Figure 7: Anticorrosive Test of the Prepared PU Coatings

CONCLUSIONS

The Azadirachta indica juss (neem oil) based fatty amide has been prepared and

characterized by physical properties as well as by spectroscopic techniques. Further,

AIJFA was used as a polyol in the preparation of the PU coatings. The impact

resistance, flexibility and adhesion test showed excellent results for the prepared PU

coatings. The results also showed that the polyurethanes prepared from AIJFA and

trimers of IPDI were of similar coating properties and chemical resistance in

comparision with commercial IPDI trimer based PU coatings. Thermal stability of

AIJFA based PU coatings was also better over normal urethane and alkyd coatings.

CHAPTER 2


From this study it can be concluded that the neem seed oil is one of the important

renewable material for the synthesis of PU to be used for the application in coatings.

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Chapter 2shodhganga.inflibnet.ac.in/bitstream/10603/36955/9/09_chapter 2.pdf · epoxidation, [21, 22] hydroformylation, ... neem oil by reaction of its fatty amide with trimer of