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CHAPTER 3

EXPERIMENTAL

Electron Beam Curable Nanocoatings Experimental

69

Chapter 3: Experimental

3.0 Experimental

In the present work effect of type of polyol, diisocyanate, diacrylate and acrylate on

properties of EB curable urethane acrylate coatings were studied. The EB coating

system properties were also studied using nanoalumina and nanosilica.

3.1 Materials

The polyols used for present study are pentaerythritol, glycerol, 1,4-butanediol, 1,6-

hexanediol, NPG were supplied by s.d.fine-chem limited, Mumbai and of laboratory

reagent (LR) grade. Pentaerythritol, procured from Asian PPG, Mumbai. Adipic acid

supplied by s.d.fine-chem was also of LR grade. IPDI, TDI and MDI were supplied

by Merck, India and were of LR grade. HEA, TMPTA and EGDMA were supplied by

ChemFine Int.Co.,Ltd (China).

Nanosilica and nanoalumina dispersion were provided by BYK, Mumbai. Catalyst

Dibutyl tindilaurate (DBTDL) was obtained by Maharashtra organic chemicals.

Xylene, toluene and DMSO were of LR grade from s.d.fine-chem Ltd, Mumbai.

3.2 Experimental

3.2.1 Raw material analysis

The raw materials used for present work were assessed for their purity (%). The

polyols were analyzed on the basis of hydroxyl value, diisocyanates were analyzed by

determination of NCO (%) and adipic acid was analyzed by determination of acid

value.

3.2.2 Determination of percentage purity of Pentaerythritol

Weigh 2 gm of the sample into a 100 ml flask. Dissolve in minimum quantity of water

and diluted to 100 ml. Mix 10 ml of this solution with 1 ml of p-nitrobenzaldehyde

distilled (prepared by dissolving 1gm p-nitrobenzaldehyde in 5 ml of methanol and 2

ml of concentrated HCl) heat to boil under reflux condition in water bath for 1hr 30

min in a 250 ml flask. Cool and neutralize the contents with NaOH solution. Add

sufficient quantity of methanol. Boil the contents for a short time. Cool and filter

under vacuum. Wash the residue and weigh.


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Percentage purity of Pentaerythritol = .

Where, M= Weight in g of residue obtained

M1= Weight in g of material taken.

M = Weight of the residue = 6.0 g

M1 = Weight of the material taken = 2.06 g

Purity of monopenta = . . .

100 = 98.55 %

Purity of pentaerythritol = 98.55 %

3.2.3 Determination of Glycerol content

Weigh the sample in a conical flask and add 100 ml of water and 3 drops of phenol

red and acidify with 0.1 N aqueous H2SO4 solution till solution turns to yellow colour.

Heat the contents to boiling and cool to room temperature. Adjust pH to 8-9 by 0.1 N

aqueous NaOH solution till contents become just pink. 50 ml of sodium metaper

iodate solution was added to the solution. Swirl and keep it in dark for 30 minutes.

Wash the sides with distilled water and add 5 ml of ethylene glycol. Shake well and

keep it in dark for 20 min. Titrate liberated formic acid with 0.1N standardized

aqueous NaOH solution. End point is yellow to pink. Carry out blank under identical

conditions.

Percentage purity of glycerol content by weight = .

S = Volume in ml of standard NaOH solution for sample

B = Volume in ml of standard NaOH for blank

N = Normality of standard NaOH solution

W = Weight of sample in g

Sample reading (S) = 30.5 ml

Blank reading (B) = 17.6 ml

S – B = 30.5 – 17.6 = 12.9 ml

= . . ..

= 98.43 %

Purity of glycerol = 98.43 %


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3.2.4 Percentage purity of 1, 6-hexanediol, NPG, 1, 4-butanediol

The percentage purity of all the three diols is determined by OH value. (ISO 4629-

1978 (E))

Weigh 1 gm of sample in Erlenmeyer flask, to this add 5 ml of pyridine-acetic

anhydride reagent in the ratio of 3:1 by volume. The contents are thoroughly mixed

by gentle swirling. Keep flask on a steam bath using reflux condensers and heat it for

1 hour. (Add a few porcelain pieces to prevent bumping). Add 10 ml of distilled water

through the condenser into the flask and heated on the steam bath for 10 minutes with

reflux condenser. Allow the flask to cool to room temperature. Add about 10 ml of

neutralized butanol, through the condenser to the flask. Remove the condenser and

add 20 ml butanol to wash down the sides of the flasks. Add 1 ml of phenolphthalein

indicator solution and titrate the contents 0.5 N alcoholic solution till contents

becomes just pink. The blank readings were conducted under identical conditions.

Calculations:

The hydroxyl value is calculated as follows

Hydroxyl value = .

Where, B = ml of KOH solution required for the reagent blank.

S = ml of KOH solution required for the titration of the acetylated

sample

NKOH = Normality of alcoholic KOH solution

W = Weight of the sample used for acetylation

Theoretical OH value =

3.2.4.1 Purity of 1,6-hexanediol

Molecular weight of 1,6-hexanediol = 118 g/mol

Theoretically hydroxyl value was calculated using following empirical

formula

OH-value of 1, 6-hexanediol = = 950.847 %

Theoretical OH-value = 950.847 mg of KOH/ g of resin


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Average OH-value = . . . ..

= 938.29

Average hydroxyl value of 1,6-heaxanediol = 938.29 mg of KOH/ g of resin

Purity of 16-hexanediol =

Purity = 938.29/ 950.847 = 0.9868 x 100 = 98.68 %

3.2.4.2 Purity of 1,4-butanediol

Molecular weight of 1, 4-butanediol = 90 g/mol


formula

OH- value of 1, 4-butanediol = = 1246.67 mg of KOH/g of resin

Actual OH-value = . . . . .

1225.51

Average hydroxyl value of 1,4-butanediol = 1225.51 mg of KOH/g of resin

Purity = 1223.51/1246.67 = 0.9830 x 100 = 98.30 %

3.2.4.3 Purity of Neopentylglycol

Molecular weight of NPG = 104 g/mol


formula

OH value of Neopentylglycol = = 1078.85 mg of KOH/g of resin

Actual OH-value = . . . ..

= 1016.34

Average hydroxyl value of NPG = 1016.34 mg of KOH/g of resin

Purity = 1078.85/1016.34 = 0.94.21 x 100 = 94.21 %


73

3.2.5 Percentage purity of adipic acid

The percentage purity of adipic acid is found by the determination of acid value as per

the ASTM D 1639-70.

Weigh about 1.5 g +/- 0.1 of the sample accurately into conical flasks and dissolved it

in neutral alcohol-toluene mixture. 3-4 drops of the phenolphthalein indicator was

added. The contents were titrated against 0.5 N aqueous KOH solution till pink colour

persist.

Practical acid value was calculated using following formula

Acid value = .

Average acid value of adipic acid = 762.35 mg KOH/g of resin

Molecular weight of adipic acid = 146 g/mol

Theoretically acid value was calculated using following empirical formula

Acid value of adipic acid = .

2 768.49 %

Average acid value = . . . .

762.70

Purity =

99.20 %

3.2.6 Percentage purity of monomers (hydroxy ethyl acrylate and hydroxy

methacrylate)

The percentage purity of the monomers was found by determination of hydroxyl value

as per the ISO 4629-1978 (E).

3.2.6.1 Hydroxy ethyl acrylate

Molecular weight of Hydroxy ethyl acrylate = 116 g/mol


formula

Theoretical hydroxyl value = .

483.62

Actual value hydroxyl value = . . . ..

= 478.09

Average hydroxyl value = 478.09 mg of KOH/g of resin

Purity =

.

.98.86 %


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3.2.6.2 Hydroxy ethyl methacrylate

Molecular weight of Hydroxy ethyl methacrylate = 130 g/mol


formula

Theoretical hydroxyl value = .

431.54

Practical hydroxyl value = . . . ..

422.43

Average hydroxyl value = 422.43 mg of KOH/ g of resin

Purity =

.

.97.89 %

3.2.7 Isocyanate Content (Isocyanate value) for determination of percentage of

purity of isocyanate monomer

3 g of TDI (Toluene diisocyanate) was weighed accurately into a 250 ml Erlenmeyer.

20 ml of dry toluene was added, followed by 25 ml of Dibutyl amine solution (diluted

260 g of dry Dibutyl amine to one liter with dry toluene). Flask was shaked during the

addition of the Dibutyl amine solution. Side’s of the flask was washed with 5 ml of

dry toluene. The flask was closed and allows it to stand at room temperature for 15

minutes. 110 ml of isopropanol was added from a graduated cylinder. 0.4 ml of

bromocrysol green indicator was added. The solution was titrated against 1 N aqueous

hydrochloric acid solution while shaking the flask contents to effect a rapid mixing till

a yellow color which persists for atleast 15 seconds. Blank sample was also prepared

under identical condition omitting the sample. The percentage purity of isocyanate is

calculated using the following formula

% purity =

Where, B = ml of acid for blank

S = ml of acid for sample

N = Normality of acid used

E = Equivalent weight of isocyanate

W = weight in gms of sample used


75

3.2.7.1 Percentage purity of methylene diisocyanate (MDI)

Theoretically isocyanate value was calculated using following empirical

formula

Molecular weight = 250 g/mol

Equivalent weight of MDI = 125

Actual value

Weight of MDI = 1.31 g

Blank = 41.2

Burette reading = 31.9 ml

NCO content = . . . .

40.73 %

Equivalent weight of MDI = .

103.12

Purity =

103.12 .

82.50 %

3.2.7.2 Percentage purity of Toluene diisocyanate (TDI)


formula

Molecular weight =174 g/mol

Equivalent weight of TDI = 87.0

Actual value

Weight of TDI = 1.26 g

Blank = 41.2



50.08 %

Equivalent weight of TDI = .

83.86

Purity =

100 ..

96.39%


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3.2.7.3 Percentage purity of isophorone diisocyanate (IPDI)


formula

Molecular weight = 221

Equivalent weight of IPDI = 110.5

Weight of IPDI = 1.51 g

Blank = 22.2



43.31 %

Equivalent weight of IPDI = .

96.98

Purity =

100 ..

87.76 %


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3.3.0 Synthesis of Polyester polyol with varying type of polyol

In polymer chemistry, polyols are compounds with multiple hydroxyl functional

groups available for organic reactions. A molecule with two hydroxyl groups is a diol

one with three is a triol, one with four is a tetrol and so on. Polymeric polyols are

generally used to produce other polymers. They are reacted with isocyanates to make

polymers. Polyesters formed by condensation or step-growth polymerization of diols

and dicarboxylic acids (Alper et al 2009; Kaszynki et al 2009).

The polyester polyols were synthesized using adipic acid, 1, 6-hexanediol and varying

polyol viz., PENTA, glycerol, 1, 4-butanediol and NPG. The polyester polyols were

synthesized with hydroxyl number 160-170 mg of KOH/gm of resin.

3.3.1 Synthesis of Polyester polyol from PENTA, adipic acid and 1, 6-hexanediol

The schematic representation of polyester polyol formation are depicted in Fig. 3.1

+ 4 H2O

Polyester polyol


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The above structure is represented as

Figure 3.1: Two-Dimensional theoretical representation of the synthesis of PENTA co-polyester polyol.

The polyester polyols were synthesized with adipic acid, 1, 6-hexanediol and

PENTA. In polyester reaction the synthesis was done with different solvents, with

varying ratio of PENTA, 1,6-hexanediol, with varying concentration of DBTDL as

a catalyst, varying ratio of carboxylic acid : hydroxyls. The reaction was melt

condensation type.

The reactions were carried out in nitrogen atmosphere using xylene as azeotropic

solvent for removal of water from reaction mixture. The progress of reaction was

monitored by amount of water of reaction as well as acid value. The reactions were

terminated when required water of reaction is collected azetropically and acid value

reached to 10 mg of KOH/gm of resin. The typical formulations for synthesis of

polyester polyols with varying concentration of DBTDL and varying type of

solvents are presented in Table 3.1. The typical formulations with varying

concentration of 1, 6-hexanediol, PENTA and acid: hydroxyl ratios are presented in

Table 3.2.

Typical reaction conditions

Catalyst: DBTDL

Reaction time: 10 hrs

Atmospheric condition: Nitrogen purging


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Table 3.1: Effect of type of solvent and catalyst concentration on properties of

polyester polyol

Batch PENTA Adipic

acid

1,6-

Hexanediol

Solvent Catalyst

(%)

Temp

(°C)

Pgel

(%)moles g moles g moles g

PP1 0.5 68 1.0 146 0.5 59 xylene 0.1 140 100

PP2 0.5 68 1.0 146 0.5 59 DMSO 0.1 153 100

PP3 0.5 68 1.0 146 0.5 59 DMF 0.1 189 100

PP4 0.5 68 1.0 146 0.5 59 - 0.1 189 100

PP5 0.5 68 1.0 146 0.5 59 - 0.05 190 100

PP6 0.5 68 1.0 146 0.5 59 - 0.05 160 100


Catalyst: DBTDL

Conc. of catalyst: 0.05%

Reaction temperature: 160°C

Reaction time: 7 hrs 30 min Atmospheric condition: Nitrogen purging

Table 3.2: Typical formulation for polyester polyols with varying acid to

hydroxyl ratio as well as varying ratio of diol to tetrol

Batch PENTA Adipic

acid

1,6-

Hexanediol

acid :

polyol

diol :

tetrol

Pgel

(%)

moles g moles g moles g

PP7 0.50 68 1.0 146 0.25 29.5 1.0:0.75 1.0:2.0 87.34

PP8 0.40 54.4 1.0 146 0.50 59 1.0:0.9 1.25:1.0

PP9 0.20 27.2 1.0 146 1.0 118 1.0:1.2 5.0:1.0 109

PP10 0.16 21.8 1.0 146 1.0 118 1.0:1.16 6.25:1.0 108


80

3.3.2 Synthesis of Polyester polyol from Glycerol, adipic acid and 1, 6-hexanediol

The polyester polyols were synthesized with adipic acid, 1, 6-hexanediol and glycerol.

The schematic representation of polyester polyol formation are depicted in Figure 3.2

+ 3H2O

Polyester polyol

The above polyol is represented as

O

O

O

OH

OH

HO

Figure 3.2: Two-Dimensional theoretical representation of the synthesis of

glycerol co-polyester polyol.





reached to 10 mg of KOH/gm of resin. The mole ratio was decided for the hydroxyl to


81

be approximately around 160-170 mg of KOH/gm of resin. The typical formulations

with varying concentration of 1, 6-hexanediol, glycerol and acid: hydroxyl ratios are

presented in Table 3.3.


Catalyst: DBTDL






hydroxyl ratio as well as varying ratio of diol to triol

Batch Glycerol Adipic

acid

1,6-

Hexanediol

acid :

polyol

diol :

triol

Pgel

(%)


GP1 0.2 18.6 1.0 146 0.9 94.4 1.0:1.1 4.5:1.0 105

GP2 0.3 27.9 1.0 146 0.9 94.4 1.0:1.2 3.0:1.0 110

GP3 0.4 37.2 1.0 146 0.9 94.4 1.0:1.3 2.25:1.0 115

3.3.3 Synthesis of Polyester polyol from 1, 4-butanediol, adipic acid and 1, 6-hexanediol

The polyester polyols were synthesized with adipic acid, 1, 6-hexanediol and 1,4-

butanediol.



82


Figure 3.3: Two-Dimensional theoretical representation of the synthesis of 1,4-

butanediol co-polyester polyol.







with varying concentration of 1, 6-hexanediol, glycerol and acid: hydroxyl ratios are



Catalyst: DBTDL






83


hydroxyl ratio as well as varying type of diol

Batch 1,4-

butanediol

Adipic

acid

1,6-

Hexanediol

acid :

polyol

Pgel

(%)


BP1 0.6 54 1.0 146 0.7 82.6 1.0:1.3 115

BP2 0.7 63 1.0 146 0.7 82.6 1.0:1.4 119

BP3 0.8 72 1.0 146 0.7 82.6 1.0:1.5 125

3.3.4 Synthesis of Polyester polyol from NPG, adipic acid and 1, 6-hexanediol

The polyester polyols were synthesized with adipic acid, 1, 6-hexanediol and NPG.








with varying concentration of 1, 6-hexanediol, NPG and acid: hydroxyl ratios are



84


Figure 3.4: Two-Dimensional theoretical representation of the synthesis of NPG

co-polyester polyol.


Catalyst: DBTDL Conc. of catalyst: 0.05% Reaction temperature: 210°C

Reaction time: 7 hrs Atmospheric condition: Nitrogen purging


hydroxyl ratio as well as varying ratio of diol

Batch Neopentyl

glycol

Adipic

acid

1,6-

Hexanediol

acid :

polyol

Pgel

(%)


NP1 0.6 62.4 1.0 146 0.7 82.6 1.0:1.3 115

NP2 0.7 72.8 1.0 146 0.7 82.6 1.0:1.4 119

NP3 0.8 83.2 1.0 146 0.7 82.6 1.0:1.5 125


85

3.4.0 Synthesis of urethane acrylate oligomer

Urethane acrylates are simple addition products of multifunctional isocyanates, like

toluene diisocyanate (TDI), hexamethylene diisocyanate (HDI), isophorone

diisocyanate (IPDI) with polyols and hydroxyalkyl acrylates, for instance

hydroxyethyl acrylate (HEA), hydroxy butyl acrylate or pentaerythritol acrylate.

Urethane acrylates with low functionality exhibit a high flexibility and are often based

on flexible polyester or polyether diols, which are reacted with bifunctional

isocyanates and endcapped with hydroxyalkyl acrylates (Jianwen et al 2006; Srba et

al 2004). The higher functional urethane acrylates are often used to obtain hard,

scratch and chemical resistant coatings (Enis et al 2012). Besides the good

mechanical properties, these aliphatic type urethane acrylate resins exhibit good

weatherability and do not yellow upon exposure to exterior conditions (Byoung and

Hyun 2006; Seubert et al 2003; Valet et al 1999; Yang et al 2001).

The majority of commercial urethane oligomers are based on polyisocyanates, such as

TDI or MDI. Polyester oligomers based on IPDI are often used for weatherable

coating applications. Aliphatic isocyanates such as IPDI are less susceptible to

yellowing and UV-induced photo degradation than their aromatic counterparts and

polyesters are also more resistant to UV degradation (Wang and Pourreau 2004).

Treating branched polyester polyols with diisocyanates usually causes rapid

crosslinking of the polymer chains and produces highly viscous or gelled products

which are not suitable for high-solids coatings. However, by using IPDI, polyester

based polyols with all secondary OH functionality and carefully controlling the

reaction conditions, low viscosity aliphatic urethane oligomer were obtained in

quantitative yield (Guo et al 2002).

The urethane acrylate oligomer was synthesized using three different isocyanates

MDI, TDI and IPDI further reacted with two different acrylates viz., HEMA and

HEA. Varying molar ratio of polyol: isocyanate: acrylate was used to synthesize the

oligomer. The progress of reaction was monitored by determining isocyanate content

(%) isocyanate as well as acrylation reaction.


86

The typical formulations and mode of reaction of urethane acrylate are described as

follows.

3.4.1 Synthesis of urethane acrylate using PENTA polyol, diisocyanate and

hydroxyl acrylate

A three neck flask equipped with nitrogen inlet, condenser and addition funnel is

placed in a water bath. Diisocyanate is charged in the reactor, and dropwise addition

of hydroxyl acrylate. After the addition of diisocyanate, isocyanate content is

determined. Further the dropwise addition of polyester polyol. The reaction is carried

out in an inert atmosphere. The reaction was performed till the resultant had an

isocyanate value ≤ 0.5%. The reaction mode is as shown in Figure 3.5 and Figure

3.6.

NCONCO + OHO

O

CH2

NH O

O

OCH2

ONCO

IPDI HEA

Isocyanate terminated prepolymer

Figure 3.5: Two-Dimensional Theoretical Representation of the Synthesis of

Isocyanate terminated prepolymer

Figure 3.6: Synthesis of Urethane Acrylate Oligomer from PP9


87

Table 3.6: Typical formulations of urethane acrylate using varying isocyanate

and acrylate monomer from PENTA polyol

Batch

Polyol Isocyanate Hydroxyl

acrylate

Solvent

(wt %)

Catalyst

(wt %)

Temp

(°C)


PUA1 0.015 5.19 MDI-0.03 3.09 HEMA-

0.015

1.99 - 0.01 30

PUA2 0.01 3.46 MDI-0.02 2.06 HEMA-

0.01

1.33 Xylene-

1.37(20)

0.01 20

PUA3 0.015 5.19 TDI-0.03 2.52 HEMA-

0.015

1.99 - 0.0097 30

PUA4 0.015 5.19 TDI-0.03 2.52 HEMA-

0.015

1.99 Xylene-

0.097(10)

0.0097 30

PUA5 0.5 172.92 TDI-1.2 100.06 HEMA-

0.6

69.06 Xylene-

68.40(20)

0.342 30

PUA6 0.5 172.92 TDI-1.2 100.06 HEMA-

0.6

69.06 Xylene-

68.40(20)

0.342 20

PUA7 0.6 207.50 TDI-1.2 100.06 HEA-0.6 70.40 Xylene-

75.59(20)

0.342 20

PUA8 0.5 172.92 TDI-1.2 100.06 HEA-0.6 70.40 Xylene-

68.68(20)

0.343 20

PUA9 0.6 207.50 TDI-1.2 100.06 HEA-0.5 58.67 Acetone-

36.62(10)

0.366 20

PUA10 0.6 207.50 IPDI-1.2 116.38 HEMA-

0.6

79.68 - 0.404 55

PUA11 0.6 207.50 IPDI-1.2 116.38 HEA-0.6 70.40 - 0.394 55

PUA12 0.7 207.50 IPDI-1.4 135.77 HEA-0.7 82.14 - 0.425 55

PUA13 0.9 311.25 IPDI-1.6 155.17 HEA-0.7 82.14 - 0.549 55

Not e: MDI (Methylene biphenyl diisocyanate), TDI(Toluene diisocyanate), IPDI (Isophorone diisocyanate), HEA

(hydroxy ethyl acrylate), HEMA (hydroxy ethyl methacrylate)


88


Catalyst: DBTDL

Conc. of catalyst: 0.01 wt % (catalyst is added on the basis of total weight of polyol,

isocyanate, and hydroxy acrylate)

Reaction time: 1 hr 15min (in case of MDI)

4 hr (in case of TDI)

6 hr (in case of IPDI)

Atmospheric condition: Nitrogen blanket

3.4.2 Synthesis of urethane acrylate using glycerol polyol, diisocyanate and

hydroxyl acrylate


placed in a water bath. Diisocyanate is charged in the reactor, and dropwise addition

of hydroxyl acrylate. After the addition of diisocyanate, isocyanate content is



isocyanate value ≤ 0.5%.

Figure 3.7: Synthesis of Urethane Acrylate Oligomer from GP2


89

Typical reaction condition

Catalyst: DBTDL



Reaction time: 4 hr (in case of TDI)

6 hr (in case of IPDI)


Table 3.7: Typical formulation for Urethane Acrylate synthesized from polyester

polyol

Batch

Polyol Isocyanate Hydroxyl

acrylate

Solvent

(wt %)

Catalyst

(wt %)

Temp

(°C)

moles g moles g moles G

GUA1 0.5 173.26 TDI-1.0 83.86 HEA-0.5 58.67 Acetone-

31.58

0.032 20

GUA2 0.5 173.26 TDI-1.0 83.86 HEMA-

0.5

66.4 Acetone-

32.35

0.032 20

GUA3 0.5 173.26 IPDI-1.0 96.98 HEMA-

0.5

66.4 - 0.034 55

GUA4 0.5 173.26 IPDI-1.0 96.98 HEA-0.5 58.67 - 0.033 55

3.4.3 Synthesis of urethane acrylate using 1,4-butanediol polyol, isophorone

diisocyanate and hydroxyl ethyl acrylate


placed in a water bath. IPDI is charged in the reactor, and dropwise addition of

hydroxyl ethyl acrylate. After the addition of diisocyanate, isocyanate content is





90


Catalyst: DBTDL



Reaction time: 8 hr



Table 3.8: Typical formulation for Urethane Acrylate synthesized from 1,4-

butanediol polyester polyol

Batch IPDI Polyol HEA Catalyst moles g moles g moles g (wt %)

BUA1 1.0 96.98 0.5 169.53 0.5 58.67 0.033

BUA2 2.0 193.96 1.0 339.05 1.0 117.34 0.065

Figure 3.8: Synthesis of Urethane Acrylate Oligomer from 1,4-butanediol

polyester polyol


91

3.4.4 Synthesis of urethane acrylate using Neopentyl glycol polyol, isophorone

diisocyanate and hydroxyl ethyl acrylate


placed in a water bath. IPDI is charged in the reactor, and dropwise addition of

hydroxyl ethyl acrylate. After the addition of diisocyanate, isocyanate content is




Table 3.9: Typical formulation for Urethane Acrylate synthesized from NPG

polyester polyol

Batch IPDI Polyol HEA Catalyst moles g moles g moles G (wt %)

NUA1 1.0 96.98 0.5 170.71 0.5 58.67 0.33

NUA2 2.0 193.96 1.0 341.43 1.0 117.34 0.65


Catalyst: DBTDL



Reaction time: 8 hr

Reaction temperature: 55°C Atmospheric condition: Nitrogen blanket

Figure 3.9: Synthesis of Urethane Acrylate Oligomer synthesized from Neopentyl

glycol polyester polyol


92

3.5 Characterization and analysis

3.5.1. Characterization and analysis of polyester polyols

The polyester polyol obtained were analyzed by determination of acid value, hydroxyl

value, and viscosity. Characterization was done by FTIR, NMR, UV

spectrophotometer, GPC.

3.5.1.1 Acid Value

It is defined as milligrams of KOH required to neutralize the free carboxylic acid

present in one gram of resin. Acid value of the obtained polyester polyol was

measured according to ASTM D 1639-70 during the reaction.

3.5.1.2 Hydroxyl Value

The hydroxyl value is defined as the number of milligrams of KOH required to

esterifies the hydroxyl (-OH) groups. The hydroxyl value of polyester polyols was

determined as per ISO 4629-1978(E).

3.5.1.3 Viscosity by Brookfield (ASTM D 1638 -74)

Viscosities were measured using a Brookfield viscometer. The viscosity in centipoise

was found by multiplying the reading by the factor (f) that goes with the spindle and

speed used.

Viscosity = Reading x f.

3.5.1.4 FTIR analysis

The FTIR spectra were recorded using a NaCl cell on a Perkin-Elmer spectrum BX

FT-IR (USA) spectrophotometer taking 256 scans. The transmission mode was used

and the wave number range was set from 400-4000 cm-1. Fourier transform infrared

(FTIR) method was employed to study the formation of polyester polyol, urethane

acrylate and the electron beam curing of the samples.

3.5.1.5 1H NMR and 13C NMR analysis 1H NMR and 13C NMR was recorded on a Bruker Avnace (Germany) with 5 mm BBI

probe (500 MHz) in CDCl3 with tetramethylsilane as an internal standard.


93

3.5.1.6 Gel permeation chromatography (GPC)

Molecular weight and molecular weight distribution were estimated by Gel

permeation chromatography (GPC) on a Shimadzu LC-10 GPC System (Japan)

calibrated with polystyrene as a standard and chloroform as an eluent at a flow rate of

1.0 ml/min at 30°C.

3.5.2. Characterization and analysis of polyester urethane acrylate oligomer

The polyester urethane acrylate obtained was analyzed by determination of hydroxyl

value, isocyanate content, unsaturation and viscosity. Characterization was done by

FTIR, NMR, UV spectrophotometer, GPC.

3.5.2.1 NCO content

This method is used to determine the amount of the isocyanate groups present in the

sample. The sample is taken and then dissolved with Dibutyl amine solution and

isopropanol is added. The indicator bromo-cresol green is used. Then titrated against

0.1 N HCl. End point of the titration is blue to yellow.

3.5.2.2 Unsaturation by wij’s method

This method is used to determine the unsaturation present in the resin. Weigh the

sample in a dry flask, add CCl4, pipette 25 ml Wijs solution into flask and swirl to

insure an intimate mixture. Store the flasks in a dark place for 30 minutes. Prepare

and conduct blank determinations with samples simultaneously and similar manner in

all respect. Remove the flasks from storage and add 20 ml of KI solution, followed by

100 ml of distilled water. Titrate with 0.1 N Na2S2O3 solution, adding it gradually and

with constant and vigorous shaking. Continue the titration until the brown color is

yellow. Add 1 to 2 ml of starch indicator solution and continue the titration until the

blue color has just disappeared.

The iodine value = (B-S) x N x 12.69/ Weight of sample

B = Titration of blank

S = Titration of sample

N = Normality of Na2S2O3


94

3.5.2.3 UV visible spectrophotometer

UV visible spectra was determined using double beam spectrophotometer 6.84,

chemito spectra scan 2700.

Other procedure and instruments were same as given in section 3.5.1.

3.6 Formulation of UV and EB curable coating

3.6.1. Effect of concentration of reactive diluent

The coating systems cured by UV and EB were formulated using crosslinked

monomers viz., TMPTA, EGDMA and HEA.

UV curable formulations with varying concentration of IRGACURE-184 as a

photoiniator were prepared. The photoinitiator 1-5% of wt/wt of total oligomer and

reactive diluent were used. In case of EB curable coating formulation photoiniator

was not used. The effect of exposure time in UV-curable system was studied whereas

effect of EB dose variation in EB curable system was studied. For UV-curable

systems UV-curing assemble and for EB curing system the EB accelerator (model

ILU-6). The typical UV curing formulations with varying ratio of photoinitiator,

oligomer, reactive diluent and irradiation time are presented below.

3.6.1.1 UV curing of UA oligomer (PUA13)

The urethane acrylate oligomer with desired properties PUA13 was optimized for

further study. The UV formulations with different types of reactive diluent viz.,

Trimethylol propane triacrylate (TMPTA), Ethylene glycol diacrylate (EGDMA) and

Hydroxy ethyl acrylate (HEA) with varying ratio to oligomer are presented in

Table.3.10. Oligomer and reactive diluent were mixed in different proportions with

continuous stirring at 40°C to get homogeneous mixture to be used for coating. These

formulations were applied onto glass plates and pretreated MS-panels using bar

applicator.

The UV curing was performed by passing the sample under a medium pressure

mercury vapor lamp (200 watts/inch). The typical curing behaviour is presented in

Table 3.11. For UV curing only basic coating properties like flexibility and impact

was checked. The thickness of the cured coating was found to be approx. 100 µm.


95

Films for FTIR, gel fraction were cured on glass plates, were peeled off to conduct

these studies.

Table3.10 Typical UV curing formulations with photoinitiator, oligomer and

reactive diluent

Batch Oligomer

(wt %)

Reactive diluent

(HEA) wt %

Photoinitiator

(wt %)

PUA2

90

10

5% PUA6

PUA7

PUA8

PUA9

PUA10

PUA11

PUA12

Table 3.11 Typical UV curing with varying irradiation time

HEA

Batch↓ No. of Passes Conveyor speed (m/min)

PUA2 2 7

PUA6 2 7

PUA7 2 7

PUA8 2 7

PUA9 2 7

PUA10 2 7

PUA11 2 7

PUA12 2 7


96

Table 3.12 Typical UV curing formulations with varying ratio of photoinitiator,

oligomer (PUA13) and reactive diluent

Urethane acrylate

oligomer (%)

Adhesion

Promoter (wt %)

Reactive Diluents (%)

TMPTA EGDMA HEA

95 0.5 05 05 05

90 0.5 10 10 10

85 0.5 15 15 15

80 0.5 20 20 20

75 0.5 25 25 25

Table 3.13 Typical UV curing with varying irradiation time and reactive diluents

TMPTA EGDMA HEA

% PI

(%)

No. of

Passes

Conveyor

speed

% PI

(%)

No. of

Passes

Conveyor

speed

% PI

(%)

No. of

Passes

Conveyor

speed

5 2 2 4.2 5 3 2 5.0 5 3 2 4.2

10 2 2 4.2 10 3 2 5.0 10 3 2 4.2

15 2 1 6.1 15 3 1 6.1 15 3 2 4.2

20 2 1 6.1 20 3 1 6.1 20 3 1 5.1

25 2 1 6.1 25 3 1 6.1 25 3 1 5.1

3.6.1.2 UV curing of UA oligomer (GUA4)

The UV formulations with reactive diluent viz., Trimethylol propane triacrylate

(TMPTA) with varying ratio to oligomer are presented in Table 3.14. Oligomer and

reactive diluent were mixed in different proportions with continuous stirring at 40°C

to get homogeneous mixture to be used for coating. These formulations were applied

onto glass plates, and pretreated MS-panels using bar applicator.

The UV curing was performed by passing the sample under a medium pressure

mercury vapor lamp (200 watts/inch). The typical curing behaviour is presented in


97

Table 3.15. For UV curing only basic coating properties like flexibility and impact

was checked. The thickness of the cured coating was found to be approx. 100 µm.

Table 3.14: Typical UV curing formulations with varying ratio of photoinitiator,

oligomer (GUA4) and reactive diluent

Urethane acrylate

oligomer (%)

TMPTA (%) Adhesion

promoter

PI (wt %)

100 00 0.5 5

95 05 0.5 3

90 10 0.5 3

85 15 0.5 3

80 20 0.5 2

75 25 0.5 2

Table 3.15: Typical UV curing with varying irradiation time (GUA4)

TMPTA (%) No. of Passes Conveyor speed (m/min)

0 2 6.0

5 2 6.0

10 2 6.0

15 2 5.0

20 1 5.0

25 1 5.0


98

3.6.1.3 UV curing of UA oligomer (BUA2)

The UV formulations with different types of reactive diluent viz., TMPTA with

varying ratio to oligomer are presented in Table 3.16. Oligomer and reactive diluent

were mixed in different proportions with continuous stirring at 40°C to get

homogeneous mixture to be used for coating. These formulations were applied onto

glass plates, and pretreated MS-panels using bar applicator. The UV curing was

performed by passing the sample under a medium pressure mercury vapor lamp (200

watts/inch). The typical curing behaviour is presented in Table 3.17. For UV curing

only basic coating properties like flexibility and impact was checked. The thickness

of the cured coating was found to be approx. 100 µm.


oligomer (BUA2) and reactive diluent

Urethane acrylate

oligomer (%)

TMPTA (%) Adhesion

promoter (wt %)

PI

(wt %)

100 00 0.5 5

90 10 0.5 3

80 20 0.5 3

75 25 0.5 3

Table 3.17: Typical UV curing with varying irradiation time (BUA2)


00 2 5.0

10 2 5.0

20 1 5.0

25 1 5.0


99

3.6.1.4 UV curing of UA oligomer (NUA2)

The UV formulations with different types of reactive diluent viz., TMPTA with

varying ratio to oligomer are presented in Table 3.18. Oligomer and reactive diluent

were mixed in different proportions with continuous stirring at 40°C to get

homogeneous mixture to be used for coating. These formulations were applied onto

glass plates, wood panels and pretreated MS-panels using bar applicator. The UV

curing was performed by passing the sample under a medium pressure mercury vapor

lamp (200 watts/inch). The typical curing behaviour is presented in Table 3.19. For

UV curing only basic coating properties like flexibility and impact was checked. The

thickness of the cured coating was found to be approx. 100 µm.


oligomer (NUA2) and reactive diluent

Urethane acrylate

oligomer (%)

TMPTA (%) Adhesion

promoter

PI (wt %)

100 00 0.5 5

90 10 0.5 3

80 20 0.5 3

75 25 0.5 3

Table 3.19: Typical UV curing with varying irradiation time (NUA2)


00 2 5.0

10 2 5.0

20 1 5.0

25 1 5.0


100

3.6.1.5 EB curing of UA oligomer (PUA13)

The EB formulations with different types of reactive diluent viz., Trimethylol propane

triacrylate (TMPTA), Ethylene glycol diacrylate (EGDMA) and Hydroxy ethyl

acrylate (HEA) with varying ratio to oligomer are presented in Table 3.20. Oligomer

and reactive diluent were mixed in different proportions with continuous stirring at

40°C to get homogeneous mixture to be used for coating. These formulations were

applied onto glass plates, wood panels and pretreated MS-panels using bar applicator.

The EB curing was performed by passing the sample under the EB accelerator,

BARC, Vashi-complex, at the energy= 1.0 MeV, frequency = 25 Hz, Average beam

current = 2.0 mA, conveyor speed = 3 cm/sec, dose/pass = 10 KGy. The EB curing

and evaluation of film characteristics of 100% oligomer at varying dose rate are

described in Table 3.21.EB curing and evaluation of film characteristics at varying

dose rate and reactive diluents are described in Table 3.22. The thickness of the cured

coating was found to be approx. 100 µm. Films for FTIR, DSC, gel fraction, and

swelling ratio were cured on glass plates, were peeled off to conduct these studies.

Table 3.20: Typical formulations of EB curing coating systems with varying ratio

of oligomer (PUA13)

Urethane acrylate

oligomer (%)

Adhesion

Promoter (wt %)

Reactive Diluents (%)

TMPTA EGDMA HEA

95 0.5 05 05 05

90 0.5 10 10 10

85 0.5 15 15 15

80 0.5 20 20 20

75 0.5 25 25 25


101

Table 3.21: EB curing and evaluation of film characteristics of 100% UA

oligomer (PUA13)

Oligomer EB dose

(KGy)

Results after irradiation to EB

100 % 10 Tacky

30 Tacky

40 Slightly Tacky

60 Slightly Tacky

70 Non Tacky

80 Non Tacky film with shrinkage

Table 3.22: EB curing and evaluation of film characteristics at varying dose rate

and reactive diluents (PUA13)

Results after irradiation to EB doses (KGy)

TMPTA EGDMA HEA

% 10 20 30 50 70 % 30 40 50 70 % 50 60 70 80

5 1 2 3 4 - 5 1 2 3 4 5 1 2 3 4

10 1 2 3 4 - 10 1 2 3 4 10 1 2 3 4

15 1 3 3 4 - 15 1 2 3 4 15 1 2 3 4

20 1 3 3 4 - 20 1 2 3 4 20 1 2 3 4

25 1 3 3 4 - 25 1 2 3 4 25 1 2 3 4

Ratings: 1, tacky; 2, slightly tacky; 3, non-tacky, 4, non-tacky film was brittle


102

3.6.1.6 EB curing of UA oligomer (GUA4)

The EB formulations with different types of reactive diluent TMPTA with varying

ratio to oligomer are presented in Table 3.23. Oligomer and reactive diluent were

mixed in different proportions with continuous stirring at 40°C to get homogeneous

mixture to be used for coating. These formulations were applied onto glass plates,

wood panels and pretreated MS-panels using bar applicator.



current = 2.0 mA, conveyor speed = 3 cm/sec, dose/pass = 10 KGy. The typical EB

curing coating of 100% oligomer and with varying ratio of oligomer and varying dose

rate are described in Table 3.24 and Table 3.25 respectively. The thickness of the

cured coating was found to be approx. 100 µm. Films for FTIR, DSC, gel fraction,

and swelling ratio were cured on glass plates, were peeled off to conduct these

studies.


of oligomer (GUA4) to reactive diluent (TMPTA)

Urethane acrylate

oligomer (%)

TMPTA (%) Adhesion

promoter (wt %)

100 00 0.5

95 05 0.5

90 10 0.5

85 15 0.5

80 20 0.5

75 25 0.5


103

Table 3.24: EB curing and evaluation of film characteristics of 100% UA

oligomer (GUA4)

Oligomer EB dose

(KGy)

Results after irradiation to EB

100 % 10 Tacky

30 Tacky

40 Slightly Tacky

60 Slightly Tacky

70 Non Tacky

80 Non Tacky film with shrinkage


and reactive diluents (GUA4)

TMPTA

(%)


30 40 50 60 70

05 1 1 2 3 4

10 1 1 2 3 4

15 1 2 2 3 4

20 2 3 4 3 4

25 2 3 4 4 4



104

3.6.1.7 EB curing of UA oligomer (BUA2)

The EB formulations with different types of reactive diluent TMPTA with varying

ratio to oligomer are presented in Table 3.26. Oligomer and reactive diluent were

mixed in different proportions with continuous stirring at 40°C to get homogeneous

mixture to be used for coating. These formulations were applied onto glass plates,

wood panels and pretreated MS-panels using bar applicator.



current = 2.0 mA, conveyor speed = 3 cm/sec, dose/pass = 10 KGy. EB curing and

evaluation of film characteristics at varying dose rate are described in Table 3.27. The

thickness of the cured coating was found to be approx. 100 µm. Films for FTIR, DSC,

gel fraction, and swelling ratio were cured on glass plates, were peeled off to conduct

these studies.


of oligomer (BUA2)

Urethane acrylate

oligomer (%)

TMPTA (%) Adhesion

promoter (wt %)

100 00 0.5

90 10 0.5

80 20 0.5

75 25 0.5


105


(BUA2)

TMPTA

(%)


110 120 130 140 150

00 1 1 2 3 4

10 1 1 2 3 4

20 1 1 2 3 4

25 1 2 2 3 4


3.6.1.8 EB curing of UA oligomer (NUA2)

The EB formulations with different types of reactive diluent viz., Trimethylol

propane triacrylate (TMPTA) with varying ratio to oligomer are presented in Table

3.28. Oligomer and reactive diluent were mixed in different proportions with

continuous stirring at 40°C to get homogeneous mixture to be used for coating. These

formulations were applied onto glass plates, wood panels and pretreated MS-panels

using bar applicator.



current = 2.0 mA, conveyor speed = 3 cm/sec, dose/pass = 10 KGy. EB curing and

evaluation of film characteristics at varying dose rate and reactive diluent are

described in Table 3.29. The thickness of the cured coating was found to be approx.

100 µm. Films for FTIR, DSC, gel fraction, and swelling ratio were cured on glass

plates, were peeled off to conduct these studies.


106

Table 3.28: Typical formulations of EB curing coating systems with varying

ratio of oligomer (NUA2)

Urethane acrylate

oligomer (%)

TMPTA (%) Adhesion

promoter (wt %)

100 00 0.5

90 10 0.5

80 20 0.5

75 25 0.5


(NUA2)

TMPTA

(%)


70 80 90 110 120

00 1 1 2 3 4

10 1 1 2 3 4

20 1 1 2 3 4

25 1 2 2 3 4



107

3.6.2 Effect of addition of nanoparticles on properties of EB curable coating

systems

The coating formulations with varying concentration (wt/wt) of nanosilica and

nanoalumina were prepared in the optimized ratio of reactive diluents. The

nanoparticles used in these formulations were provided by nanoBYK. The particles

size of nanosilica and nanoalumina were almost 20 nm dispersed in TMPTA and

TPGDA respectively. The dispersion contained 50 % of nanoparticles. The addition

of nanoparticles to oligomer was sonicated 40°C to ensure proper mixing. These

formulations were applied onto glass plates, wood panels and MS-panels using bar

applicator. The coated panels were cured by electron beam at optimized dose for

particular reactive diluent. The thickness of the cured coating was found to be approx.

100 µm. FTIR, DSC, gel fraction, swelling ratio, SEM, XRD, TGA and all coating

properties were studied according to ASTM standards.

3.6.2.1 EB curing of formulation with varying percentage of nanosilica and

nanoalumina in urethane acrylate oligomer with PENTA

Coating formulations with nanosilica and nanoalumina in different reactive diluents

viz., TMPTA, EGDMA and HEA are presented in Table 3.30 – Table 3.35. The

optimized ratio of oligomer: TMPTA, oligomer: EGDMA and oligomer: HEA were

85: 15, 85: 15 and 80: 20 respectively. The optimized dose for the same was 30 KGy,

50 KGy and 70 KGy respectively.


108

Table 3.30: EB curing and typical formulations with varying concentration of

nanosilica at optimized concentration of TMPTA

UA

(%)

TMPTA

(RD)

TMPTA

content (%)

NanoSi

dispersion (%)

NanoSi

content (%)

EB

Cured

85

15.00 00 0 0

30 kGy

14.50 0.5 1.0 0.5

14.00 1.0 2.0 1.0

13.50 1.5 3.0 1.5

13.00 2.0 4.0 2.0

12.50 2.5 5.0 2.5


nanosilica at optimized concentration of EGDMA

UA

(%)

EGDMA

(RD)

TMPTA

content (%)

NanoSi

dispersion (%)

NanoSi

content (%)

EB

Cured

85

15.00 00 0 0

50 kGy

14.50 0.5 1.0 0.5

14.00 1.0 2.0 1.0

13.50 1.5 3.0 1.5

13.00 2.0 4.0 2.0

12.50 2.5 5.0 2.5


109


nanosilica at optimized concentration of HEA

UA

(%)

HEA

(RD)

TMPTA

content (%)

NanoSi

dispersion (%)

NanoSi

content (%)

EB

Cured

85

15.00 00 0 0

70 kGy

14.50 0.5 1.0 0.5

14.00 1.0 2.0 1.0

13.50 1.5 3.0 1.5

13.00 2.0 4.0 2.0

12.50 2.5 5.0 2.5


nanoalumina at optimized concentration of TMPTA

UA

(%)

TMPTA

(RD)

TPGDA

content (%)

NanoAl

dispersion (%)

NanoAl

content (%)

EB

Cured

85

15.00 00 0 0

30 kGy

14.50 0.5 1.0 0.5

14.00 1.0 2.0 1.0

13.50 1.5 3.0 1.5

13.00 2.0 4.0 2.0

12.50 2.5 5.0 2.5


110


nanoalumina at optimized concentration of EGDMA

UA

(%)

EGDMA

(RD)

TPGDA

content (%)

NanoAl

dispersion (%)

NanoAl

content (%)

EB

Cured

85

15.00 00 0 0

50 kGy

14.50 0.5 1.0 0.5

14.00 1.0 2.0 1.0

13.50 1.5 3.0 1.5

13.00 2.0 4.0 2.0

12.50 2.5 5.0 2.5


nanoalumina at optimized concentration of HEA

UA

(%)

HEA

(RD)

TPGDA

content (%)

NanoAl

dispersion (%)

NanoAl

content (%)

EB

Cured

85

15.00 00 0 0

70 kGy

14.50 0.5 1.0 0.5

14.00 1.0 2.0 1.0

13.50 1.5 3.0 1.5

13.00 2.0 4.0 2.0

12.50 2.5 5.0 2.5


111


nanoalumina in urethane acrylate oligomer with Glycerol

Coating formulations with nanosilica and nanoalumina in reactive diluents viz.,

TMPTA, are presented in Table.3.36 and Table 3.37 respectively. The optimized

ratio of oligomer: TMPTA was 80: 20. The optimized dose for the same was 60 KGy.



UA

(%)

TMPTA

(RD)

TMPTA

(%)

NanoSi

dispersion (%)

NanoSi

content (%)

EB

Cured

80

20.00 00 0 0

60

kGy

19.50 0.5 1.0 0.5

19.00 1.0 2.0 1.0

18.50 1.5 3.0 1.5

18.00 2.0 4.0 2.0

17.50 2.5 5.0 2.5

17.00 3.0 6.0 3.0

16.50 3.5 7.0 3.5


112



UA

(%)

TMPTA

(RD)

TPGDA

(%)

NanoAl

dispersion (%)

NanoAl

content (%)

EB

Cured

80

20.00 00 0 0

60

KGy

19.50 0.5 1.0 0.5

19.00 1.0 2.0 1.0

18.50 1.5 3.0 1.5

18.00 2.0 4.0 2.0

17.50 2.5 5.0 2.5

17.00 3.0 6.0 3.0


nanoalumina in urethane acrylate oligomer with 1,4-butanediol

Coating formulations with nanosilica and nanoalumina in reactive diluents viz.,

TMPTA, are presented in Table 3.38 and Table 3.39 respectively. The optimized

ratio of oligomer: TMPTA was 80: 20. The optimized dose for the same was 140

KGy.


113



UA

(%)

TMPTA

(RD)

TMPTA

(%)

NanoSi

dispersion (%)

NanoSi

content (%)

EB

Cured

80

20.00 00 0 0

140kGy

19.0 1.0 2.0 1.0

18.0 2.0 4.0 2.0

17.0 3.0 6.0 3.0

16.0 4.0 8.0 4.0

15.0 5.0 10.0 5.0

14.0 6.0 12.0 6.0

13.0 7.0 14.0 7.0



UA

(%)

TMPTA

(RD)

TPGDA

(%)

NanoAl

dispersion (%)

NanoAl

content (%)

EB

Cured

80

20.0 00 0 0

140

KGy

19.0 1.0 2.0 1.0

18.0 2.0 4.0 2.0

17.0 3.0 6.0 3.0

16.0 4.0 8.0 4.0

15.0 5.0 10.0 5.0


114


nanoalumina in urethane acrylate oligomer with NPG

Coating formulations with nanosilica and nanoalumina in reactive diluent TMPTA,

are presented in Table 3.40 and Table 3.41 respectively. The optimized ratio of

oligomer: TMPTA was 80: 20. The optimized dose for the same was 110 KGy.



UA

(%)

TMPTA

(RD)

TMPTA

(%)

NanoSi

dispersion (%)

NanoSi

content (%)

EB

Cured

80

20.0 00 0 0

110

KGy

19.0 1.0 2.0 1.0

18.0 2.0 4.0 2.0

17.0 3.0 6.0 3.0

16.0 4.0 8.0 4.0

15.0 5.0 10.0 5.0

14.0 6.0 12.0 6.0


115



UA

(%)

TMPTA

(RD)

TPGDA

(%)

NanoAl

dispersion (%)

NanoAl

content (%)

EB

Cured

80

20.0 00 0 0

110

KGy

19.0 1.0 2.0 1.0

18.0 2.0 4.0 2.0

17.0 3.0 6.0 3.0

16.0 4.0 8.0 4.0

15.0 5.0 10.0 5.0

3.7 Electrochemical Impedance Spectroscopy (EIS)

Corrosion is defined as the deterioration of the material, usually a metal, because of

reaction with its environment and which requires the presence of an anode, a cathode,

an electrolyte and an electric circuit (Rosliza and Wan 2010; Rosliza et al 2010). One

of the most popular uses of EIS is the characterization of the protective properties of

coatings on corrodible metals (Gordon et al 2003; Yasuda et al 2001). Many EIS

studies have been developed to study the changes in the impedance of coated metals

as they undergo either natural or artificial exposure to conditions that cause corrosive

failure of such systems. EIS has many advantages in comparison with other

electrochemical techniques. It is a non-destructive method for the evaluation of a wide

range of materials, including coatings, anodized films and corrosion inhibitors (Abdel

et al 2006; Patel et al 2012).

3.7.1 Experimental

The DC polarization study was performed during immersion in 3.5% NaCl solution

open to air and at room temperature. A Pyrex glass cell with a capacity of 300 ml was

used for the electrochemical corrosion tests. A three-electrode set-up was used with

impedance spectra being recorded at the corrosion potential Ecorr. The system was


116

composed of a working electrode, counter electrode, and reference electrode. A

saturated calomel electrode (SCE) was used as the reference electrode. It was coupled

capacitively to a counter electrode made of platinum wire to reduce the phase shift at

high frequencies. The probe tip was easily adjusted to bring it at a distance of about 2

mm from the working electrode schematic diagram of electrochemical cell used in

EIS is as shown in Figure 3.10.

A potentiostat (Versa STAT 3, by Princeton Applied Research) was used for the

electrochemical measurements. VersaStudio corrosion analysis software was used to

analyze the data and calculate the Tafel constants. DC polarization tests of specimens

were made at a scan rate of 1.66 mV/sec in the applied potential range from -1.5 V to

0.2 V with respect to Ecorr. The exposed surface area was 7 cm2. The corrosion rates

of hybrid coatings were reported as millimeter per year (mmpy).

Figure 3.10: Schematic diagram of electrochemical cell used in EIS

The EIS was performed for the optimized coating samples of different urethane

acrylates with TMPTA as reactive diluents with nanosilica and nanoalumina viz.,

PUA (85%): TMPTA (15%) with 2.5% nanosilica and 2.0% nanoalumina.

GUA (80%): TMPTA (20%) with 3.0% nanosilica and 2.5% nanoalumina.

BUA (80%): TMPTA (20%) with 6.0% nanosilica and 4.0% nanoalumina.

NUA (80%): TMPTA (20%) with 5.0% nanosilica and 4.0% nanoalumina.


117

3.8.0 Characterization of EB cured coatings

3.8.1 Curing characteristics of EB curing

3.8.1.1 Gel fraction

The cured films of known weight were extracted for 12h in acetone and xylene using

soxhlet extraction were dried in vacuum and weighed to estimate gel fraction using

relation

3.8.1.2 Swelling ratio

Cured films of known weight were dipped in acetone and xylene for 50 h and

weighed after blotting the excess solvent from the surface to estimate the swelling

ratio of the cured film using relation:

Swelling ratio = swelled weight / initial weight

3.8.1.3 FTIR

IR spectrum was recorded using a cell NaCl cell on a Perkin-Elmer spectrum BX FT-

IR spectrophotometer taking 16 scans. The range of spectrophotometer is 400-4000

cm-1.

3.8.2 Performance characteristics of EB for mechanical properties

3.8.2.1Pendulum Hardness Tester (ASTM D4366)

This method evaluates hardness by measuring the damping time of an oscillating

pendulum (TQC SP0500 Pendulum Hardness Tester). The pendulum rests with 2

stainless steel balls on the coating surface. A physical relationship exists between

oscillation time, amplitude and the geometric dimensions of the pendulum. The

viscoelastic behavior of the coating determines its hardness. When the pendulum is

set into motion, the balls roll on the surface and put pressure on the coating.


118

3.8.2.2 Pencil Hardness Test (ASTM D3363)

Pencil hardness measurement are used to determine the hardness of a coating, relative

to a standard set of pencil leads (3B to 8H), is determined by scratching the leads

across the coating at a controlled angle of 45º for a distance of approximately ¼ inch

(Komal scientific LTD. India).

3.8.2.3 Scratch resistance (ASTM D2027)

This test method describes a laboratory procedure using an instrumented scratch

machine to produce and quantify surface damage under controlled conditions (Sakova

Instruments, India). This test method is able to characterize the mar and scratch

resistance of polymers by progressively increasing scratch load which eventually

induces a critical point of damage such as coating delamination, coating cracking or

whitening in a single lot.

3.8.2.4 Impact resistance (ASTM 2794)

This method is to predict the ability of the coating resist cracking caused by rapid

deformation. Tubular impact resistance test was carried out using an indenter with

hemispherical head of diameter 0.625 inch and 2lb load (Precision Engineers, India).

3.8.2.5 Flexibility Testing (ASTM D522)

ASTM D522 is a method of determining the resistance to cracking on elongation of

organic coatings on metal panels. This method describes the use of both conical and

cylindrical mandrels. Here in our study flexibility was checked with conical mandrel

(HENRY ZUHR, Newyork).

3.8.2.6 Cross-hatch adhesion (ASTM D3359-83)

This test carried out as per ASTM D3359-83. Crosscut adhesion tape test was used to assess

the adhesion of coating films to metallic substrates. Cuts were made on the coating in one

steady motion with sufficient pressure on the cutting tool having a cutting edge angle between

15⁰ and 30°. After making two such cuts at 90° the grid area was brushed and a 2.5 cm wide

semi-transparent pressure-sensitive tape was placed over the grid (Khushboo Scientific India).

After 30 seconds of application, the tape was removed rapidly and the grid inspected


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according to the ASTM standards. The amount of coated area retained under the tape

corresponds to the adhesion efficiency of the coating. The more coated material removed by

the tape, the poorer the adhesion of the coating to the substrate.

3.8.2.7 Tensile strength properties of thin films (ASTM D882)

In this test method the material is pulled until it breaks in order to measure elongation, tensile

modulus, tensile yield strength and elongation at break (Universal Testing Instrument,

LLOYD INSTRUMENTS, LR 50K, UK). However, it is designed specifically for thin film

less than 1mm (0.04 inch) thick. In this the specimens are rectangular strips of film and are

not “dumbbell” or “dogbone” shaped. The average of at least five measurements for each

sample was reported, the experimental error is +/- 10%.

3.8.2.8 Taber abrasion (ASTM 4060-01)

The wear resistance of the coatings was determined by Taber abrasion test [ASTM

4060-01]. CS-10 abrasive wheels were used with a 500 g weight in each wheel. The

regeneration of the wheel was done with an abrasive paper of S-11 (Khushboo

Scientific Pvt. Ltd, India). Before abrasion process the weight of the sample was

determined with an accuracy of 1mg. Every hundred cycles the weight of the

specimen was determined again and the weight loss calculated. Successive abrasion

cycles were performed till 500 cycles, showing the wear evolution on a graph of

weight loss versus the number of abrasive cycles.

3.8.2.9 Gloss (ASTM D523-99)

Gloss is a measure of ability of coated surface to reflect light at a particular angle without

scattering. Gloss was determined according to ASTM D523-99. Gloss of the cured sample

was measured at 45º and 60 º of reflectance using a digital mini gloss meter calibrated against

internal standard i.e. refractive index (Komal Scientific Co. Mumbai, India).

3.8.3 Characterization of EB curable systems for performance properties

3.8.3.1 Xenon Arc Weatherometer (ASTM G115)

The ability of a paint or coating to resist deterioration of its physical and optical

properties caused by exposure to light, heat and water can be significant for many

applications. Xenon arc testers are considered the best simulation of full spectrum


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sunlight because they produce energy in the UV, visible and infrared regions

(Solarbox 1500e). The results are reported in terms of % gloss retention. The results

were noted in terms of % gloss retention after every 100 hrs upto 500 hrs.

3.8.3.2 QUV accelerated weathering testing (ASTM D4329)

Accelerated weathering simulates damaging effects of long term outdoor exposure of

materials and coatings by exposing test samples to varying conditions of the most

aggressive components of weathering- ultraviolet radiation, moisture and heat. A

QUV test chamber uses fluorescent lamps to provide a radiation spectrum centered in

the ultraviolet wavelengths. Moisture is provided by forced condensations and

temperature is controlled by heaters (Q-Panel Lab products, Europe). The results were

noted in terms of % gloss retention after every 100 hrs up to 500 hrs.

3.8.3.3 Salt spray testing (ASTM B117)

Corrosion resistance effect on long term exposure especially in a automotive

applications is studied in ASTM B117. In this 5% NaCl solution is prepared and

sprayed in the corrosion Box from UK.

3.8.3.4 Chemical resistance

Resistance to acid and alkali was determined by using ASTM D-4274-88 standard

while for detergent resistance standard ASTM D-2248a was followed. For this test,

the coated panels were immersed in 5% solution of HCL (acid), 5% solution of NaOH

(alkali) and 5% solution of detergent. The immersed panels were maintained at

constant temperature. The panels were removed for examination after 6, 12, 18 and 24

hours from the start of the test and observed loss of adhesion, blistering, popping or

any other deterioration of the film.

3.8.3.5 Solvent resistance

The resistance of the coating towards the solvents like methyl ethyl ketone (MEK)

and xylene was determined as per the procedure given in ASTM D-5402-93. The

coated panels were rubbed with the cotton moist with the respective solvent and

observed for any softness of the film, peeling of the film and loss of gloss etc


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3.8.4 Surface characteristics of coatings

3.8.4.1 Scanning electron microscope (SEM)

Scanning electron microscopical (SEM) images of the coating-free films were

obtained by the aid of FEI Quanta 200 SEM (Netherland). The SEM conditions for all

measurements were working distance of 9.1 mm, acceleration voltage of 15 kV, and

probe current 100 pA. The pictures were taken using a BSE detector.

3.8.4.2 Contact angle

Contact angle of water on the coating was determined by GBX, France model

Digidrop.

3.8.4.3 XRD analysis

To analyze the crystalinity of urethane-acrylate with dispersed nanosilica, X-Ray

analysis of films exposed to inside air was carried out on RIGAKU MINIFLEX.

3.8.5 Thermal properties

3.8.5.1 Thermogravimetric analysis (TGA)

Thermal properties of the EB cured polymer films were studied by thermal

gravimetric analysis (TGA) and differential scanning analysis (DSC). TGA was

carried out by using a DTG-6514 Shimadzu (Japan), with film samples weighing 4.5

mg. The temperature ranged from 20 to 500° C and the heating rate was 10° C/min in

a nitrogen flow rate of 75 ml/min.

3.8.5.2 Differential scanning calorimeter

DSC was studied by using a Q 100 TA (USA) instruments. The glass transition

temperatures (Tg) of various networks at a heating rate of 10° C/min.

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