NEW APPROACH FOR DEVELOPING EPOXY-AMINE ADDUCT CURATIVE WITH MODIFIED EPOXY RESINS

Vipin Shukla *, D.K. Singh, M. Singh and Ravi ShuklaJaydeep Polycon (P) Ltd.

Panki Industrial Area, Site-4, D-37,38Kanpur (India)

Key words : Solid epoxy resin, DAPA, PGE, adduct, modified epoxy

resins, curing.

ABSTRACT

Pure aliphatic amines (i.e. triethylenetetramine, diethylenetriamine etc.) are

not recommended as hardener in surface coating formulations, as they give

blooming, handling problem and toxic hazards, but epoxy-amine adduct is

used very conveniently without any type of toxic hazards. Similar adducts

are prepared using a variety of amines to provide adduct that will permit a

range of cure rates and potlives and provide very good impact strength and

flexibility. I am also trying to prepare epoxy-amine adduct but with new

approach and also studies its curing behaviour with different modified epoxy

resins.

To whom all correspondence should addressed.E-mail : vipin_1222@rediffmail.com vipin_shukla@sify.comTel : +91-512-2201515, 2692564 & 2674452

INTRODUCTION

The hardeners fall broadly into many type of such as polyamines,

polyamides, acid anhydrides, aminos, phenolics, thermosetting acrylics,

catalytic chemicals etc. The choice of hardener for particular type of an

epoxy resin depends on :

the handling properties required such as viscosity, potlife,

exotherm and todicity;

the physical, chemical, mechanical and electrical properties

required;

the cure, post-cure time and temperature requirements;

the cost of the hardener.1,2

Other factors are involved in selecting amines besides reaction rates.

Many amines are toxic while they are easily handled safely in a chemical

plant, toxic hazards can arise if inexperienced, careless or uninformed

personnel mix and apply two package epoxy coating incorporating certain

amines. In general, toxic hazards are reduced by increasing molecular

weight and reducing water solubility. As molecular weight increases,

volatility decreases, which reduce the chances of inhaling dangerous amount

of amine. Also, as water solubility decreases and molecular weight

increases, permeability through body membranes such as skin decreases,

generally reducing toxic hazards.

Other disadvantages of utilizing low molecular weight, highly

functional amines are their low equivalent weight and viscosities. The

equivalent of pure DETA is 21. If DETA is used with the epoxy resin

having an equivalent weight of about 500. The stoichiometric weight ratio

of the two components would be about 25:1. This disparate amount of two

components would increase the difficulty of obtaining proper mixing and

would also result in a high risk of significant error in mixing stoichiometric

amount in two-pack system.3,4

One approach to designing amine crosslinkers with higher equivalent

weight and lower toxic hazard is to make so-called amine adducts. Amine

adducts are prepared by reacting excess primary amines with epoxy resin

even at room temperature (R.T.). Each hydrogen atom attached to nitrogen

opens upon an epoxy ring. Thus primary amine is first converted to

secondary amine and secondary hydroxyl. The reaction between liquid

epoxy resin and an aliphatic polyamine is shown below:

These type of adduct react faster than the free amines because of the increase

in hydroxyl groups and also reduce or eliminate blush formation because the

primary amine hydrogens are pre-reacted with epoxide groups. Epoxy-

amine adduct is used very conveniently for manufacture of chemical

resistant paints, having very good impact strength and flexibility. The

protection of structural steel work and processing equipments, chemical

plants, oil refineries and food factories are examples of the user of these

coatings in corrosive atmosphere. These coatings will withstand wine, beer,

cider, molasses, alkalies, detergents and crude and refined oil products. Due

to the excellent alkali resistance of these coatings, paint for concrete,

cement, plaster surface are formulated from these system also. They are

employed as protective coatings for paper book covers, fatty food

wrappings, and as finish for bar table tops, floors and other wooden

surfaces.5,6

EXPERIMENTAL

Material used :

JNR-GP-502 [DGEBA] : Jaydeep Polycon (P) Ltd.

Kanpur

JNR-BG-701 : - do -

JNR-BG-708 : - do -

JNR-BG-710 : - do -

JC – 43 [Catalyst] : - do -

JC – 40 [Catalyst] : - do -

PGE [Phenyl glycidylether] : - do -

Bisphenol-A : C.J. Shah and Co., Mumbai

Dimethylamino propylamine [DAPA] : - do -

Dibutylphthlate [DBP] : Vikas Agrotech., M.P.

Solvent-61 : Jaydeep Polycon (P) Ltd.

Kanpur

Method :

Synthesis of high molecular weight epoxy resin

Liquid epoxy resin (JNR-GP-502) and JC-43 were taken in a half litre

reaction three neck flask equipped with a stirrer, thermometer, condenser

and in nitrogen inlet. After adding the reactants, the JC-40 was added at

70ºC and then temperature was maintained at 155-160ºC for 1 hour. After

this bisphenol-A was charged at 160ºC under vacuum. The resin formed

was checked by calculating epoxide equivalent weight (EEW) after regular

intervals of time, until the required EEW (800-850) was acquired. The

formulation used for the preparation of above resin in Table-2

Synthesis of epoxy-amine adduct

Before the preparation of epoxy-amine adduct, we prepare blend of

solid epoxy resin in PGE (40%), then we add this resin in DAPA slowly-

slowly and maintain temperature 65-70ºC, after that we add DBP and

solvent-61. After conclusion of the reaction, the product is cooled to 55ºC.

Determination of epoxide equivalent weight (EEW)

Epoxide equivalent weight of epoxy resin was determined by

hydrogen bromide method.7

Determination of amine value

Amine value of epoxy-amine adduct was calculated by

perchlorine/aceticacid method.8

Preparation and characterisation of coatings

All the modified epoxy resins cured with epoxy-amine adduct

hardener with appropriate quantity and determine the film properties of

coatings like potlife, hardcure time, scratch hardness, flexibility, adhesion

and chemical resistance.

Result and Discussion

Table-1 shows some important properties of epoxy resins and PGE.

Table-2 shows the formulation and properties of solid epoxy resin.

Table-3 exhibits the formulation and properties of epoxy-amine

adduct.

Table-4 shows the curing schedule of epoxy resins with epoxy-amine

adduct and also showed the potlife and hardcure time for samples S1, S2, S3

& S4 and it is clearly visible from Table-4, sample S1 has least potlife and S3

has large potlife which is due to variation in EEW because greater the EEW,

greater will be the potlife of samples.

Table-5 shows the chemical properties of cured samples and it appears

from the table that samples S1, S2 and S3 remain unaffected against

immersion tests conducted for assessing the 10% NaOH solution, ethanol,

kerosene, toluol and ethyl acetate, sample S4 also remain unaffected against

ethanol, kerosene and toluol but appear very slightly blisters against 10%

sodiumhydroxide solution and shows slightly blister against ethylacetate.

Table-6 exhibits the physical properties of cured samples and it proves

from the table that except sample S4, all other samples pass flexibility test.

Scratch hardness of samples S1, S2, S3 and S4 are 2600 gms., 2800 gms.,

2200 gms., and 2000 gms. respectively and adhesion, as measured for all

cured samples. Sample S2 possess 70 kg/cm2, which was superior to that of

the samples S1, S3 and S4 showing adhesion of 65, 55, 50 kg/cm2

respectively.

CONCLUSION

This type of epoxy-amine adduct reduces the exotherm, which

developed during the synthesis of epoxy-amine adducts.

This adduct also reduces the cost as compare to other epoxy-amine

adducts.

The observation indicate that the use of this curative in coating

results improved chemical resistance and physical properties.

It was found that the use of this curative had no adverse effect on

coating properties.

REFERENCES

1. Lee, H. and Neville, K.; “Handbook of Epoxy Resins,” McGraw

Hill Book Company (N.Y.), P. 7-15, (1967).

2. Joshi, P.L.; “Epoxy Resins,” Paint India, Vol. 40, No. 7, P. 20,

(1990).

3. Wicks, Z.W.; Jones, F.N. and Pappas, S.P.; “Organic Coatings :

Science and Technology.” Vol. 1, Wiley Interscience Publication,

New York, P. 172, (1992).

4. Panda, H.; “Epoxy Resins : A Review” (Part-1), Chemical Weekly,

20 November, P. 148, (2000)

5. Weinmann, D.J.; Dangayach, K. and Smith, C.; “Amine-

Functional Curatives for Low Temperature cure Epoxy Coating”,

Journal of Coating Technology, Vol. 60, No. 863, December, P.30,

(1996).

6. Meeus, F.; “New developments in ambient cure epoxy resins for

high performance industrial coatings”, Journal of Oil Colour and

Chemist Association, Vol. 73, No.5, P. 187, (1990).

7. Lee, H. and Neville, K.; “Handbook of Epoxy Resin,” McGraw

Hill Publication (Inc.) New York, Chapter 4, P. 17, (1967).

8. Patil, S.; “Testing of Paints”, Current Awareness Service, Mumbai,

P. 47, (1993).

ACKNOWLEDGEMENT

The author would like to thank Mr. Sandeep Shukla, Managing Director and

Mr. Sanjay Shukla, Director for their valuable suggestions and guidance

extended to me during the course of study and preparation of the paper.

Table-1 : Properties of epoxy resins and PGE

Grade of epoxy

resins

Specific gravity @ 25ºC

Viscosity @ 25ºC

(cps)

Epoxide equivalent

weight (gm/eq.)

Colour (gardener)

Type

JNR-GP-502 1.14 12000 200 G Pure DGEBA

JNR-BG-7011.12 600 185 2G

Modified epoxy resin

JNR-BG-7101.12 650 215 G

Modified epoxy resin

JNR-BG-7081.10 500 220 2G

Modified epoxy resin

PGE 1.14 20 165 3G Reactive diluent

Table-2 : Formulation and properties of solid epoxy resin

Ingredients Amount

JNR-GP-502 60 gm.

JC-43 0.09 gm.

JC-40 0.03 ml

BPA 28.8 gm.

Properties Values

Specific gravity @ 25ºC 1.10

Viscosity (40% solution in high butylcorbital) cps 550

Epoxide equipment weight (gm/eq.) 875

Softening point (ºC), Duran Hg method 95

Table-3 : Formulation and properties of epoxy-amine adduct curative

Ingredients Amount (gm)

40% solution of solid epoxy resin in PGE 82

DAPA 42.5

DBP 7

Solvent-61 16

Properties Values

Aspect (visual) Very slightly yellowish

Amine value 340

Viscosity @ 25ºC (cps) 10,000

Table-4 : Curing schedule of modified epoxy resins with epoxy-amine adduct

Samples S1 S2 S2 S4

JNR-GP-502 100 - - -

JNR-BG-701 - 100 - -

JNR-BG-710 - - 100 -

JNR-BG-708 - - - 100

Epoxy-amine adduct (phr) 30 50 50 50

Potlife (min.) @ 25ºC 22 24 25 30

Hardcure (hours) 8 12 12 12

Table-5 : Chemical properties of cured samples

Samples10%

NaOH solution

Ethanol Kerosene ToluolEthyl

acetate

S1 NE NE NE NE NE

S2 NE NE NE NE NE

S3 NE NE NE NE NE

S4 VSB NE NE NE SB

NE= No effect, VSB= very slightly blisters, SB=slightly blister

Table-6 : Physical properties of cured samples

SamplesFlexibilitya (1/8

mandrel)

Scratch hardnessb

(grams)

Adhesionc

(kg/cm2)

S1 Pass 2600 65

S2 Pass 2800 70

S3 Pass 2200 55

S4 Fail 2000 50

a- ASTM-D-522b- BS-3900c- ASTM-D-879