HUNGARIAN JOURNAL 
OF INDUSTRIAL CHEMISTRY 

VESZPREM 
Vol. 30. pp. 73 -76 (2002) 

MEASUREMENT OF THE SWELLING FORCE OF SOME SODIUM STARCH 
GLYCOLATE PRODUCTS WITH NEW SOFTWARE 

A. KELEMEN
1
, A. SZOLLOSI, A. ZSOTER, K. PINTYE-H6DI, C. TdR6K2 and I. EROS 

(~epartment ofPh~ceutical 'J'ec?nolog~, U~vertity of Szeged, Eotvos str. 6, H-6720 Szeged, HUNGARY 
Department of Me~cal Informatics, Umvers1ty of Szeged, Koranyi fasor 9, H-6720 Szeged, HUNGARY 

Agrokemia Sellye Ltd, Malom str. 1 H-7960 Sellye, HUNGARY) 

Received: October 12, 2001 

The swelling properties of several experimental sodium starch glycolates (SSG) were investigated with new equipment 
and s.oft~are. The charact~ristic ~~elling time (tt;3.2%? was calculated. The effects of the molecular structure (degree of 
subs~tutwn~ _on the swelling abthty were also studied. It was found that the degree of cross-linking influenced the 
swell~ng abthty of SSG products. The described equipment and the developed software are suitable for study of the 
swelhng process and characterization of the different disintegrants. 

Keywords: disintegrant, swelling force, force-time curve, characteristic swelling time 

Introduction 

Disintegrants are always added to conventional tablets 
in order to promote the break-up of the tablets when 
they are placed in an aqueous environment. 

The flrst step in the process of dissolution of the 
drug is disintegration. The disintegrant causes rapid 
disintegration of the tablet~ the increase in the surface 
area of the tablet promoting rapid release of the drug. 

The mechanism of disintegration is influenced by 
different factors, among which the water uptake and 
swelling play very important roles [1-3]. The uptake of 
water by disintegrants is thought to initiate the process 
of disintegration [4, 5]. 

The swelling force is responsible for the breaking-up 
of the tablet. List and Muazzam [5] drew attention to the 
importance of the swelling force, and Caramella et al. 
(6, 9] also dealt with measurement of the swelling force. 

The most common disintegrant employed in tablet 
formulation is starch. There are many types of modified 
starches (sodium starch glycolate = SSG) on the market. 
This material can be regarded as a super -disintegrant. It 
is official in the USP, BP and Ph.Eur. While the 
quantity of starch required is about 20%, 4-5% of SSG 
is sufficient. 

Many reports have been published on Primojel and 
Explotab [8-16], the most widely used types. 

The effectiveness of SSG is influenced by various 
factors. The degree of substitution, the degree of 
crosslinking and the sodium chloride content play 

important roles in the disintegration of the tablets [12. 
16]. 

The present artiCle reports an examination of the 
influence of the above-mentioned parameters on the 
swelling process. The most informative factor, the 
characteristic swelling time (4;3_2<J>), was calculated from 
the modified Weibull equation (Rosin-Rammler-
Sperling-Benett-Weibull = RRSBW) by nonlinear 
regression, 4;3.2% being the time needed to attain 63.2% 
of the maximum swelling force. This factor could be 
utilized to compare the different disintegrants. 

Experimental 

Materials 

The present experimental SSG samples (from 
Agrochemia Co., Sellye, Hungary) are based on a 
sodium salt of a partially substituted carboxymethyl 
ether of potato starch. They have a moisture content that 
is lower than that of starches (<10%). The sodium 
chloride content is less than 1%. Different types are 
produced as regards the degree of crosslinking. The 
degree of substitution is the same {Table 1). 

Indifferent tablets were prepared from the SSG 
products with the aim of a study of the swelling (Table 
2). Dicalcium phosphate dihydrate (Panncompress

11
• 

Parmentier AG, Germany) was used as binder. It was 



74 

Table 1 Parameters of SSG products 

NaCl Na-
Degree of. 

Product content glycolate 
Sedimentation substitution 
(ml/100 ml) (mol-COOH/ 

(%) (%) mol starch) 

SSGl 0.65 0.80 82 0.24 
SSG2 0.62 0.80 57 0.24 
SSG3 0.72 1.00 48 0.25 
SSG4 0.74 1.00 36 0.25 
SSGS 0.81 1.05 28 0.24 . 

SSG6 0.94 1.10 17 0.24 

c:!J; I 2 

I. punch, 2. holder. 3. water container, 4. water 

Fig. I Measuring part of swelling force equipment 

necessary to apply a lubricant as well (magnesium 
stearate<t Ph.Eur. 3ro.). These materials do not swell in 
aqueous medium. 

Methods 

Sedimentation: A 2.00 g sample was suspended in 200 
ml boiled distilled water. 100 ml of this suspension was 
poured into a cylinder. The volume of the sediment was 
~read off after 24 hours. 

Mixture: After sieving (0.8 mm wire distance), the 
components were blended at 50 rpm for 10 min in a 
Turbula mixer (Willy A. Bachofen Maschinenfabrik~ 
Switzerland). 

The moisture content of powder mixtures was 
determined gravimetrically, through water removal with 
an 'IR lamp mounted on a quick dryer (Organic 
Chemistry Co.. Budapest. Hungary). The moisture 
content was in every case 0.3~0.4%. 

Compression: Pressing was carried out with a 
Korsch EKO eccentric tablet machine (E. Korsch 
Mascbinenfabrik, Germany) mounted with strain gauges 
and a displacement transducer was applied: 

punches: simple. 10 mm in diameter 
pressure force: 5~ 10 and 15 ± l kN 
mass of tablet: 40% 
air temperature: 
rate of pressing: 

23°C 
36 tablets/min 

Table 2 Compositions of tablets 

Materials 

SSG (1-6) 
Parmcompress 

Ma esium stearate 
Total mass 

( ) 
4.8 

114.6 
0.6 

120.0 

Mass 

Fig.2 Scheme of measurement 

Swelling force measurement 

(%) 
4 

95.5 
0.5 

100.0 

The equipment used to measure the swelling force (SF) 
was prepared on the basis of the principle of the List 
apparatus [5]. 

The measurement is performed with a balance 
(Sartorius microbalance) with electronic compensation, 
which is built in the equipment. The tablet-holder is a 
copper cylinder 10 mm in diameter with slits in the side. 
In this cylinder, a copper punch with the same diameter 
is fitted. The tablet-holder is in a copper cup. The tablet 
is placed in the holder and 5 m1 distilled water is 
injected at the start of the measurement. The water 
penetrates into the tablet through the slits. The force that 
builds up inside the comprimate as it absorbs the water 
is transmitted vertically and is detected by the balance 
(Fig.l). 

The equipment is linked with a PC by a RS232 cable 
(Fig.2). Software has been developed for data 
acquisition, evaluation and demonstration· of the 
sweUing process. The monitor displays the SF vs. time 
curve with the important parameters (SF, time 
characteristic swelling time (4l3.2%)}. 

Mirroring the close logical or functional relationship 
between them, the SF functions are arrayed in separate 
groups (Acquisition, Settings, Analysis). Under the 
Acquisition menu poin~ it is possible to receive data 
from the serial port. During acquisition, the monitor 
shows the current SF and baseline values. At the end of 
the acquisition, the software saves the data on disk. 
With the Settings menu point, it is possible to configure 
the system (e.g. serial communication, acquisition file 
name, etc.). With the Analysis menu point, it is possible 
to evaluate the saved data. The screen depicts the SF vs. 
time curves (a maximum of 5) with the important 
parameters (time, SF. baseline, f<i3.l%) and dF/dt). The 
user can evaluate curves manually with the cursor, 
create reports. or print screen shots to the bitmap or to 
the printer. 

The characteristic swelling time and shape 
parameter were calculated from the following form: 



Table 3 Results of the swelling test 

Pressure 
Swelling force 

force f3 ~3.2% 
(kN) 

(N) (s) 

5 8.56 0.830 119.13 
RSD=5.57 

SSG1 10 10.09 0.836 108.82 
RSD=9.95 

15 12.49 0.858 125.87 
RSD=5.46 

5 5.45 0.858 66.35 
RSD=ll.56 

SSG2 10 7.16 0.832 61.67 
RSD=8.74 

15 14.23 0.830 78.99 
RSD=11.09 

5 6.96 0.816 48.55 
RSD=6.44 

SSG3 10 8.18 0.814 47.48 
RSD=7.62 

15 18.33 0.830 95.03 
RSD=3.80 

5 6.92 0.864 53.36 
RSD=6.21 

SSG4 10 8.14 0.808 30.10 
RSD=9.74 

15 9.59 0.832 33.10 
RSD=ll.09 

5 9.94 0.832 89.24 
RSD=7.36 

SSG5 10 13.81 0.819 82.33 
RSD=8.58 

15 13.49 0.831 40.71 
RSD=3.11 

5 8.59 0.825 40.38 
RSD=0.37 

SSG6 10 11.25 $ 0.813 48.88 
RSD=4.22 

15 11.87 0.816 38.74 
RSD=2.85 

fJ 
M(t)=M~{l-exp{-[~] ) } 

"C 

where "Cis the time parameter, f3 is the shape parameter, 
Mmax is the maximum value of the swelling, M is the 
swelling at time t, and t0 is the start time. It is possible to 
calculate the characteristic swelling time. f3=1 implies 
ftrst-order kinetics in the swelling process; f3<1 impliest 
fast swelling at the beginning of the process, followed 
by a slower swelling; 13> 1 implies a sigmoid curve: slow 
swelling is followed by a faster swelling process. 
In the literature, these parameters are generally 
calculated by means of the Weibull distribution 
equation rearranged in linearized form [8]. Another way 
to solve this equation is nonlinear fitting. In the present 
paper, this method was used with GLOBAL software 
(http://www.jate.u-szeged.hu#csendes.htm) (Fig.3). 

75 

Titte ; 34.6 
.ll..l Jill& b) 

SF 4.6n 
91.. : .1.0'19 
d#F/dt : O,IJOll 
SF Max: ?.407 
TC63,JI): 34.6lla 
Sh-(J): o . .-u 

SF= swelling force (where the vertical measuring line is); BL 
= basic line; SFmax = maximum value in swelling force; 
T(63.2) =characteristic swelling time; dsF/dt =the speed of 
changing of force (where the vertical measuring line is) 

Fig.3 Swelliilg force profile (1) and nonlinear fitting according 
to RRSBW equation (Pressure force: 5 kN) 

12.36 .. , I 
6.18 

Fil• n-: 
$$02-15.002 (1} 
ssoo -11; ooa 121 
es~-11.00~ (3) 

0 

(1) 
SF o.ooo 
IlL 1.040 
dSF,.dt : o.ooo 
SF .tYX : a.aa& 
T(6ll.2>1 811.,6? 

0 
(2) 

o.ooo 
.1.030 
o.ooo 
-.i .. :t,S. 

46.620 

(3) 
o.:at>3 
t.0"/9 
u.tltlO 

11.aaa 
45.62.1. 

au 
i•l 

SF= swelling force (where the vertical measuring line is); BL 
= basic line; SFmax = maximum value in swelling force; 
T(63.2) =characteristic swelling time; dsF/dt =the speed of 
changing of force (where the vertical measuring line is) 

Fig.4a Swelling process of SSG2. SSG3 and SSG5 
comprimates (Pressure force: 5 k:N) 

Results and Discussion 

Results are shown in Table 3. It can be seen that at 5 kN 
the SSG5 comprimates exhibited the highest, and the 
SSG2 comprimates the smallest SF (Table 3. Figs.4/a 
and 4/b). The SSGl and SSG6 comprimates (5 k.N) had 
almost the same SF maximum~ but there was. a 
considerable difference in the l63.~ values. 

The SF increased at higher pressure force, but to 
different degrees. The reason lies in the texture of the 
comprimates and in the properties of the mate~als. 
Increase of the pressure force generally resulted m a 
decrease in the porosity. The texture of the comprimates 
is more compact. This has an imJX>rtant role in the 
disintegration. If the character of the composition is 



76 

:.1?!18.04.30 

<H> r-r---------:;:-------, 
!1.!13 

FU• ..-.: 
$$1Jf-5.~ (11 
UG4~5.~ !2) 
tliM-;s.OQ.;I (3) 

0 
Yo-----~--~.~35~--~----~.16~70 

m (2) (3) (s) *"' : o.on o.ooo o.QOO 
1lll- : 1.040 .1.00.1 o.,9J. 
dSI"I'dt ; o.ooo o.ooo l),OI)Q 
$1" ,_ ; ••••• "·"1& 8.6 .... 1 
T<,:t.a>: ua.a!l4 u.,;sa 3.1.soa 

SF= swelling force (where the vertical measuring line is); BL 
= basic line; SFmax = maximum value in swelling force; 
T(63.2) =characteristic swelling time; dsF/dt =the speed of 
changing of force (where the vertical measuring line is) 

Fig.4b Swelling process of SSGl, SSG4 and SSG6 
comprimates (Pressure force: 5 kN) 

hydrophilic, the SF (disintegration force) can be better 
mediated by the water and the disintegration process 
will be rapid. The degree of the increase in the SF 
depends on the properties and the swelling ability of the 
disintegrants. By changing the disintegrant at the same 
composition, it is possible to study the influence of the 
pressure force on the SF. 

The data allow the samples to be arranged in 
sequence. 

For the SF: 

SkN: SSG5 >SSG6= SSGl > SSG4=SSG3> SSG2 
10 kN: SSG 5 > SSG 6 >SSG 1 >SSG 4 =SSG 3 >SSG 2 
15kN: SSG3 > SSG2> SSG5 >SSG 1 > SSG6>SSG4 

For taz": 
SkN: SSG6<SSG3<SSG4<SSG2<SSG5 <SSG 1 
lOkN: SSG4>SSG6=SSG3 <SSG2 <SSG5 <SSG 1 
15 kN: SSG4<SSG6=SSG5 <SSG2 <SSG3 <SSG 1 

It can be stated that increase of the degree of 
crosslinking and of the sodium chloride content led to a 
higher SF. However, this effect was observed only at 
pressure forces of 5 and 10 kN. The degree of 
crosslinking influenced the swelling ability of the SSG 
products. It was seen that, for the samples with a smaller 
degree of cross-linking (SSGI~SSG3)., the SF increased 
in a stepwise manner with increase of the pressure force., 
The samples with a higher degree of crosslinking 
(SSG4-SSG6) demonstrated an increase in swelling 
only between 5 and 10 kN. but not when the pressure 
force was increased from I 0 to 15 kN. The reason is the 
inflexible skeleton with a compact texture. 

It can further be seen that the characteristic water-
uptake time (tu2~) is influenced primarily by the 
deformability of the particles and by the texture of the 
comprimates. 

Conclusion 

The results of these experiments suggest that the 
maximum SF and the factor lci3.2% may be used to 
compare the intrinsic capability of a disintegrant. Study 
of the swelling process is also important with respect to 
the pressure force. The porosity of the tablets depends 
on the deformability of the particles and the porosity has 
an important role in water transport into the interior of 
the tablets and hence in the swelling process, too. 

On the basis of such results, it is possible to choose 
the pressure force suitable for tableting. If increase of 
the pressure force causes no change or only a very small 
change in the SF, it is unnecessary to use a high 
pressure force during tableting. The described 
equipment and the developed software are suitable for 
study of the swelling process and for comparison and 
characterization of the different disintegrants. 

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1711 

2. KANIG J. L. and RUDNIC E. M.: Pharm. Technol. 
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3. BOLHUIS G. K., VAN KAMP H. V., LERK C. F. and 
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4. VAN KAMP H. V., BOLHUIS G. K., DE BOER A. H., 
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6. CARAMELLA C., COLOMBO P., CONTE U. and LA 
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11. RUDNIC E. M., KANIG J. L. and RHODES C. T.: J. 
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