Supplementary information
Figure 1. 1H-NMR spectrum of ENR
Figure 2. SEM micrographs of neat epoxy system
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Characteristics of ENR
1. Determination of hydroxyl value
Hydroxyl value is defined as the number of milligrams of KOH (equivalent to the amount of
acetic acid) that reacts by acetylating with 1 g of a hydroxyl group containing material. It can be
calculated using equation 1. The acid value of the sample must also be taken into consideration.
56.1 x (B - A) x N
W
Hydroxyl value =
Where
 Acid Value
…. 1
A
=
Volume of KOH required for sample
B
=
Volume of KOH required to titrate blank
W
=
Weight of sample used
N
=
Normality of alcoholic KOH
Hydroxyl value was estimated by acetylation method. In this method the hydroxyl groups in the
sample were acetylated using acetic anhydride in pyridine (acetylating mixture).
Excess acetic anhydride was converted to acetic acid and this was estimated using standard
alkali. Presence of acidic components leads to greater consumption of the alkali and was
accounted for by determining the acid value separately.
About 3 g of the sample was weighed out into an RB flask and 20 ml acetylating mixture (1
volume of acetic anhydride + 3 volumes of pyridine) was added. The flask was connected to a
water condenser and the contents were refluxed for half an hour. The mixture was cooled to
room temperature and 50 ml distilled water was added through the reflux condenser. The free
acid was determined by titration with standard KOH using phenolphthalein. A blank was also
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carried out using 20 ml acetylated mixture using the same method.
2. Determination of epoxy value
In order to find out the epoxy value, pyridine hydrochloride was prepared by mixing 250 ml
pyridine with 5 ml concentrated hydrochloric acid. About 20 ml of pyridine hydrochloride was
added to approximately 1 gm of the sample. It was dissolved by heating and refluxed for one
hour. During heating, the epoxide ring breaks open and chlorohydrine is formed. The excess
hydrochloride was then back titrated with 0.1 N KOH using phenolphthalein as indicator. A
blank was also conducted. The epoxy value was calculated using the equation 2.
(B - A) x N x 56.1
W
Epoxy value =
…. 2
B =
Volume of KOH solution required by the blank
A =
Volume of KOH solution required by the sample
N =
Normality of KOH
W=
Weight of sample used
3. Determination of acid number
About 0.5 gm of the sample is dissolved in 50 ml of 1:1 mixture of benzene and denatured
ethanol by volume and titrated immediately with 0.1 N KOH (ethanol) in presence of
phenolphthalein until a light pink colour appears. A blank titration with 50 ml solvent was also
done. The acid number or carbonyl value is defined as the number of milligrams of KOH
required for 1 gm of the substance. Acid number is calculated by the equation 3.
Acid number
=
56.1 (A-B) x N
W
…. 3
A
=
Volume of KOH required to titrate sample
B
=
Volume of KOH required to titrate blank
3
N
=
normality of KOH
W
=
Weight of sample used
4. Determination of iodine value
Unsaturation of a polymer is expressed by iodine value. The iodine value is the weight of free
iodine absorbed by 100 parts by weight of the substance. A low iodine value implies a low
degree of unsaturation. Wij’s method was adopted for the estimation of iodine value. The
sample (about 0.1 to 0.2 g) was accurately weighed into a 500 ml iodine flask. It was dissolved
in about 25 ml of chloroform. Wij’s solution (25 ml) was added, closed the flask and shaken
vigorously and allowed to stand in the dark for about 2½ hrs, with vigorous shaking. At the end
of the reaction, 20 ml of potassium iodide solution (15%) and 100 ml of water were added. This
was titrated against standard 0.1 N sodium thiosulphate solutions with constant shaking to ensure
the extraction of iodine from the organic layer, until the liquid became yellow. The titration was
completed after adding starch as indicator. A blank was also performed on 25 ml of the iodine
monochloride solution. Equation 4 is used to calculate the iodine value.
Iodine Value
=
(V1 -V2 ) N1 x 12.69 x 100
…. 4
W x 100
V1
=
Volume of thiosulphate solution used for blank
V2
=
Volume of thiosulphate solution used for sample
N1
=
Normality of sodium thiosulphate solution
W
=
Weight of the sample in gms.
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