166
In order to obtain polyester containing reactive hydroxyl groups, in the raw
materials the ratio of glycols to dicarboxylic acids must be more than one (Ionescu
2005). Before synthesizing polyester, some theoretical problems such as Mw,
degree of branching acid value of polyester, etc. must be addressed. In order to calculate theoretical value for producing polyester, there are some factors that must be
taken into consideration, namely hydroxyl value (HV), theoretical amount of
released water of reaction (w H2O ), theoretical Mw of polyester reacted to acid value
(AV), theoretical yield at acid value 0 (Y 0 ), theoretical yield at acid value A (Y A ),
total equivalent weights of carboxylic acid groups (e COOH ), total equivalent weights
of hydroxyl groups (e OH ), total moles of starting materials (m i ) and total weight of
starting materials (w i ) (Husbands et al. 1987). Table 8.1 shows as an example a
polyester formulation for food packaging applications.
Based on the data from Table 8.1, the above-mentioned parameters are the following: w i = 2532, m i = 19, e OH = 21, e COOH = 18, w H2O = 324. The theoretical weight
of water produced in the reaction is calculated in moles based on dicarboxylic acids
because their moles are less than hydroxyl. Each carboxylic acid group reacts with
a hydroxyl group which produces a water molecule. The carboxylic acids mentioned in Table 8.1 each have two carboxylic groups which produce two water molecules. Therefore, for the formulation mentioned in Table 8.1, the number of moles
released into the water is 2 × 9 × 18 = 324, where 18 is the Mw (g/mol) of water.
The excess hydroxyl is calculated by Eq. 8.1:
e
e
OH
COOH
= =
21
18
1 17
.
(8.1)
When the polyesterification precedes the number of hydroxyl and carboxylic
acid groups, the values of HV and AV decreases. AV = 0 is not practically reachable,
and depending on the final application, the reaction is stoped when it reaches a
Table 8.1 A typical formulation of polyester for adhesives and essential parameters for calculating
Mw and gel point of polyester
Starting
materials
Mw
(g/mol)
Equivalent
weight
Charged
weight
(g)
mole
Hydroxyl
equivalents
(e OH )
Carboxylic
acid
equivalents
(e COOH )
Theoretical
weight of
released
water (g)
DEG
106
53
424
4
8
–
–
Isophthalic
acid
166
83
830
5
–
10
180
Terephthalic
acid
166
83
332
2
–
4
72
Adipic acid 146
73
292
2
–
4
72
NPG
104
52
520
5
10
–
–
TMP
134
44.7
134
1
3
–
–
Sum
–
–
2532
19
21
18
324
Source: Husbands et al. (1987).
M. Akbari and R. Najjar
In order to obtain polyester containing reactive hydroxyl groups, in the raw
materials the ratio of glycols to dicarboxylic acids must be more than one (Ionescu
2005). Before synthesizing polyester, some theoretical problems such as Mw,
degree of branching acid value of polyester, etc. must be addressed. In order to calculate theoretical value for producing polyester, there are some factors that must be
taken into consideration, namely hydroxyl value (HV), theoretical amount of
released water of reaction (w H2O ), theoretical Mw of polyester reacted to acid value
(AV), theoretical yield at acid value 0 (Y 0 ), theoretical yield at acid value A (Y A ),
total equivalent weights of carboxylic acid groups (e COOH ), total equivalent weights
of hydroxyl groups (e OH ), total moles of starting materials (m i ) and total weight of
starting materials (w i ) (Husbands et al. 1987). Table 8.1 shows as an example a
polyester formulation for food packaging applications.
Based on the data from Table 8.1, the above-mentioned parameters are the following: w i = 2532, m i = 19, e OH = 21, e COOH = 18, w H2O = 324. The theoretical weight
of water produced in the reaction is calculated in moles based on dicarboxylic acids
because their moles are less than hydroxyl. Each carboxylic acid group reacts with
a hydroxyl group which produces a water molecule. The carboxylic acids mentioned in Table 8.1 each have two carboxylic groups which produce two water molecules. Therefore, for the formulation mentioned in Table 8.1, the number of moles
released into the water is 2 × 9 × 18 = 324, where 18 is the Mw (g/mol) of water.
The excess hydroxyl is calculated by Eq. 8.1:
e
e
OH
COOH
= =
21
18
1 17
.
(8.1)
When the polyesterification precedes the number of hydroxyl and carboxylic
acid groups, the values of HV and AV decreases. AV = 0 is not practically reachable,
and depending on the final application, the reaction is stoped when it reaches a
Table 8.1 A typical formulation of polyester for adhesives and essential parameters for calculating
Mw and gel point of polyester
Starting
materials
Mw
(g/mol)
Equivalent
weight
Charged
weight
(g)
mole
Hydroxyl
equivalents
(e OH )
Carboxylic
acid
equivalents
(e COOH )
Theoretical
weight of
released
water (g)
DEG
106
53
424
4
8
–
–
Isophthalic
acid
166
83
830
5
–
10
180
Terephthalic
acid
166
83
332
2
–
4
72
Adipic acid 146
73
292
2
–
4
72
NPG
104
52
520
5
10
–
–
TMP
134
44.7
134
1
3
–
–
Sum
–
–
2532
19
21
18
324
Source: Husbands et al. (1987).
M. Akbari and R. Najjar