THE LUBRICANT PROPERTIES OF SOME LOCAL TALC DEPOSITS IN SOUTH
WESTERN NIGERIA
Tolulope O. Ajala 1, Oluwatoyin A. Odeku 2*
1
Department of Pharmaceutics and Pharmaceutical Technology, Faculty of Pharmacy, Olabisi
Onabanjo University, Sagamu, Nigeria
2
Department of Pharmaceutics and Industrial Pharmacy, Faculty of Pharmacy, University of
Ibadan, Ibadan, Nigeria
*Corresponding Author
pejuodeku@yahoo.com; o.odeku@mail.ui.edu.ng
Tel: 234 8057320466
1
Abstract
The lubricant properties of local talc samples from three different locations in south western
Nigeria have been investigated in comparison with talc BP in lactose tablet formulations. The
effect of the addition of 1% magnesium staterate on the lubricant activity of the local talc
samples was also evaluated. Lactose tablets were formulated by wet granulation method and
three concentrations (5, 7.5 and 10%w/w) of the local talc samples were mixed with the granules
before compression. The three concentrations of local talc samples were also mixed with 1%w/w
magnesium stearate and used as lubricant. The weight variation, crushing strength, friability, the
crushing strength-friability ratio (CSFR) disintegration time tablets were assessed. The results
showed that the crushing strength and disintegration time increased with increase in lubricant
concentration while the friability decreased. The local talc samples were found to possess good
lubricant activity similar to talc BP and the lubricant activity was improved by the addition of
1% w/w magnesium stearate although there was a significant (p<0.001) increase in the
disintegration time of the tablets. The local talc samples could be useful as a lubricant in
pharmaceutical tablet formulations. However, further processing might be necessary to improve
their physicochemical properties and lubricant activity.
Keywords: Talc, lubricant, tablets, magnesium stearate, mechanical properties, disintegration
time
2
Introduction
Most pharmaceutical formulations include a certain amount of lubricant to improve their
flowability and prevent their adhesion to the surfaces of processing equipment. Lubricants
reduce friction by interposing an intermediate layer between the tablet constituents and the die
wall during compression and ejection. They also prevent sticking of granules to the tooling (antiadherent) and improve granule flow properties (glidant)1,2. A given lubricant may provide one or
more of these actions to varying degrees but no one material is highly efficient in all categories.
Accordingly combinations of lubricants are often selected to provide the necessary total lubricant
effect and a careful selection is necessary since some lubricants may interact adversely when in
combination3.
Talc is used in the pharmaceutical industry as a lubricant in tablet formulations, drycoating of oral tablets and as filter medium. It is a naturally occurring hydrous magnesium
silicate with the chemical formula Mg3Si4O10 (OH)2. Chemically, talc ores are made up of SiO2,
MgO, Fe2O3 and minor Al2O3. Structurally, talc is comprised of a sheet of brucite or Mg (OH)2
sandwiched between SiO2 sheets. The elementary sheets are weakly bonded to each other. As a
result the layers slide apart with minimal force giving talc its inherent softness and lubricity 4.
Talc is naturally hydrophobic which contributes to its functional lubricity. It can withstand
temperatures up to 1300ºC and has low electrical and thermal conductivity. Talc can be easily
powdered, cut and sawn into any shape and size and is found in three forms: fibrous, non-fibrous
and massive. The fibrous variety consists of rich proportions of tremolite, anthophyllite, and
serpentine. The non-fibrous variety contains mostly of serpentine and carbonates5. Talc tends to
form in plates and this platy structure gives its reinforcing performance properties in plastics6.
Talc lubricant efficiency in plastic deforming binders/fillers increases with decreasing
particle size and increasing surface area7. Magnesium stearate when used as tablet lubricant has
been found to retard the dissolution of salicylic acid from model compressed tablets8. However,
talc has been used effectively in combination with magnesium stearate to restore the
disintegration and dissolution properties impaired by magnesium stearate9.
Talc deposits are available in several parts of Nigeria and an estimated reserve of over
100 million tons of talc has been obtained in Nigeria10. Research has shown that talc samples
from some states in Nigeria complied with the British Pharmacopoeia (BP) standard11 indicating
it’s potential as local source of pharmaceutical grade talc. However, the usefulness of this locally
available talc in pharmaceutical formulations has remained widely uninvestigated. The
development of local starch will provide a more readily available, cheaper alternative which
could serve as valuable substitutes to the imported talc in the pharmaceutical industry. Thus in
the present study, talc samples obtained from three locations in two states (Ogun and Osun) in
Southwestern region of Nigeria have been evaluated as lubricant in lactose tablet formulations
and compared with purified talc BP. The effect of the addition of 1% magnesium staterate on the
lubricant activity of the local talc samples was also evaluated.
Materials and Methods
Materials
The materials used were corn starch (Hopkins and Williams, Chadwell, Heath Essex,
UK), lactose (DMV Veghel, Netherlands), purified talc B.P (Riedel-de Haen AG D-30167
Seelze, Germany) and magnesium stearate (Hopkin and Williams, Chadwell, Health, Essex,
UK). All other reagents were analytical grade. The local talc samples were obtained from three
3
locations Apomu (Osun state), Iregun (Osun state)) and Oshosun (Ogun state)) in Nigeria and
purified at the Department of Geology, Obafemi Awolowo University, Ile-Ife, Nigeria and
referred to as TAP, TIR and TOS respectively according to their sources. The talc samples were
crushed using a mortar and pestle and then sieve through a 250µm mesh sieve.
Methods
Physicochemical analysis of local talc samples
The physicochemical properties of the local talc samples were determined to ascertain
compliance with compendia specifications for purified talc BP. Tests carried out include
macroscopy, microscopy, solubility and chemical tests (BP, 1998).
Preparation of granules
Batches of lactose granules were prepared with varying concentrations (5.0, 7.5 and
10.0%w/w) of the local talc sample (TAP, TIR, TOS) and purified talc B.P (TBP) (5% w/w) as a
standard. Granules containing the local talc samples in addition to 1% w/w magnesium stearate
were also prepared. Batches (200g) of a basic formulation of lactose (85% w/w) and cornstarch
(10% w/w) were dry mixed in a Z-blade mixer (Erweka apparatebau AR 400, Germany) for five
minutes and then moistened with 5% w/w of binder solution (corn starch mucilage). The wet
masses were granulated by passing the wet mass manually through a number 12 mesh sieve
(1400µm) (Endecotts Ltd, London, UK) and dried in a fluidized bed drier (7859 Glatt, Germany)
at 450C until the moisture content as determined using an Ohaus moisture balance (Ohaus Scale
Corporation, USA) was 1.3%. The granules were then screened through a No 16 mesh sieve
(1000µm) and stored in air-tight containers.
Preparation of Tablets
To each batch of granules the appropriate amount of lubricant was added and dry mixed
for 5minutes. Tablets (600mg) were prepared from the granules (500-1000 µm) by compressing
the materials at a pressure of 75Kg/cm2 in a single punch tabletting machine fitted with a 12mm
flat faced punch and die set (Diaf Copenhagen NV, Denmark). After ejection, the tablets were
stored over silica gel for 24hours to allow hardening and elastic recovery.
Weight Uniformity, Crushing Strength and Friability Tests
The weight of ten tablets was determined by weighing each tablet individually on an
electronic balance and the mean weight calculated. The Crushing Strength (CS) of the tablets
was determined at room temperature by diametral compression using a PTB 301 hardness tester
(Pharmatest, Switzerland). The friability (F) of the tablets were determined using a Friabilator
(Model TF 20, Scientific Equipment Ltd., Bombay, India) operated at 25 revolutions per minute
for 4 minutes.
Disintegration Test
The disintegration time (DT) of the tablets was determined in distilled water at 37±0.5ºC
using an Erweka disintegration test apparatus (Model: Copley ZT2, Erweka Apparatebau
GMBH, Heusenstamm, Germany).
4
Statistical Analysis
Data analyses were done using Analysis of Variance (ANOVA). At 95% confidence
interval, p-values less than or equal to 0.05 were considered significant.
Results and Discussion
The physicochemical properties of the talc samples are shown in Table 1. The results
indicate that the local talc samples appear to be similar in terms of their physical and chemical
properties. However, there were differences in their % loss on drying and the average plate
length. TOS exhibited the highest moisture content as measured by the loss on drying indicating
higher moisture content compared to the other talc samples. It has been found that talc samples
from different locations vary in their physicochemical properties such as colour, size and
moisture content4. The local talc samples passed all the official tests for talc except that the
colour was not pure white like that of purified talc BP. This may be due to incomplete removal
of the impurities during the purification process. This also affected the appearance of all tablets
compressed with local talc as lubricants which were grayish in colour compared to the white
tablets obtained with purified talc BP. The intensity of the colour increased with increase in the
concentration of local talc used.
Lubricants such as magnesium stearate have been shown to form monolayer which could
prevent granule separation with subsequent reduction in weight variation1. The results of the
properties of the lactose tablets produced using the various talc samples as glidant are presented
in Table 2. The result shows that the tablets complied with the BP standard for weight variation
in that not more than 5% deviation was observed from the mean except for tablets prepared using
10%w/w local talc samples which had deviations of about 8 %. However, tablet prepared using
purified talc BP as lubricant showed 1% deviation.
It has been reported that any tablet excipient which can improve flowability of tablet
granulation would produce hard and less friable tablets because the granules become more
compact13. The results indicate that the crushing strength (CS) and CSFR (Crushing StrengthFriability Ratio) of the tablets increased with increase in the concentration of the lubricants while
the friability (F) decreased. The ranking of the parameters for the talc samples obtained from the
different sources depended largely on the source and concentration of talc used in the
formulation. The ranking of CSFR was generally TIR>TOS>TAP. Thus, TIR which showed the
lowest plate length (61.27micron) gave tablets with higher mechanical properties. The platy
nature of talc, the slipperiness that results from its crystalline structure, its softness and
hydrophobicity have been shown to contribute to its performance as a glidant and lubricant in
tableting. The effectiveness of talc glidant activity has been shown to be dependent particle size,
surface area and the concentration of the fine particles14. The lower the particle size, the better
the performance15. However, there was no significant (p<0.05) difference between the CSFR
values of the tablets prepared using the various lubricants. Furthermore, it was observed that
during the compression of tablets containing 5%w/w talc lubricant, a loud screeching sound was
made by the tableting machine and there was about 4.5% capping of the tablets which was not
observed with tablets made with talc BP. There was a reduction in the sound and capping with an
increase in the concentration of the local talc samples. Tablets containing 10%w/w of the local
talc samples gave smoother and glossier tablets compared to the tablets prepared using lower
concentration of lubricant.
5
Lubricants are often used in combination to improve their efficiency and provide better
total lubricant effect. Magnesium stearate, one of the most frequently used lubricants, is
hydrophobic and is capable of forming films on other tablet excipients during prolonged mixing,
leading to a prolonged drug liberation time, a decrease in hardness, and an increase in
disintegration time16. Talc has been used effectively in combination with magnesium stearate to
restore disintegration and dissolution properties impaired by magnesium stearate9. Thus, the
effect of 1% magnesium stearate on the lubricant activity of the local talc samples was
investigated and the results of the tablet properties are presented in Table 3. The results show
that CS increased with increase in the concentration of lubricant while the friability decreased
and the screeching sound produced by the tableting machine was reduced and more elegant
tablets were obtained. There was also a decrease in the weight variation of the tablets indicating
better glidant activity. The addition of 1%w/w of magnesium stearate to the local talc samples led
to a slight increase in the mechanical properties of the tablets but a significant (p<0.001) increase
in the disintegration time of the tablets. This could be due to the effect of magnesium stearate
which has the ability of forming a monolayer and subsequent prevention of granule separation
thus production of more compact tablets17. Hence, the addition of magnesium stearate improved
the glidant properties of the local starch samples.
The CSFR/DT ratio has been found to be a better index for measuring tablet quality
because in addition to measuring tablet strength (crushing) and weakness (friability), it
simultaneously evaluates the negative effects of these parameters on disintegration time18. In
general, higher values of the CSFR/DT ratio indicate a better balance between binding and
disintegration properties19. The CSFR/DT of the tablets generally increased with increase in the
percentage of the lubricant when only local talc samples was used. However, when 1% w/w
magnesium stearate was added the values of CSFR/DT reduced significantly (p<0.001),
indicating less balance between the binding and disintegration properties of the tablets. On the
other hand, the glidant mixture of talc BP and magnesium stearate still showed a better balance.
Conclusion
The results indicates that the local talc samples possess good lubricant activity similar to talc BP
and the lubricant activity was improved by the addition of 1% w/w magnesium stearate although
there was a significant increase in the disintegration time of the tablets. The local talc samples
could be useful as lubricant in pharmaceutical tablet formulations. However, further processing
might be necessary to improve their physicochemical properties and lubricant activity.
References
1. Train, D., Hersey, J.A. The use of laminar lubricants in compaction processes, J. Pharm.
Pharmacol., 1960, 12, 97T-104T.
2. Staniforth, J. N., Aulton, M. E. Powder flow. In: Aulton’s Pharmaceutics. The design of
medicines. Aulton, M. E., (Ed.), 3rd edn. Harcourt Publishers Ltd. Philadelphia USA, 2007,
pp: 169 - 179.
3. Moody, G., Rubinstein, M. H., Fitz Simmons, R. A. Tablet lubricants I. Theory and modes of
action, Int J Pharm Int. J. Pharma 1981, 9(2), 75-80.
4. Nkoumbou, C. F., Villieras, O. B., Bihannic, M. P., Razafitianamaharavo, A. V., Metang, C.
Y., Njopwouo, D., Yvon J. Physicochemical properties of talc ore from Pout-Kelle and
Memel deposits (central Cameroon) Clay Minerals, 2008, 43 (2), 317-337.
6
5. Turner, F. J. International Series in the Earth and Planetary Sciences. 2nd Ed Hill Book
Company, US. 1969, pp. 160 -168.
6. http://www.specialtyminerals.com/our-minerals/what-is-talc/ Last assessed on March 15,
2011.
7. Rawlins, E.A Bentley’s Textbook of Pharmaceutics 8th edition, English Language Book
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Society, UK, 1977, pp. 269-289
Levy, G., Gumtow, R. H. Effect of certain tablet formulation factors on dissolution rate of
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http://www.specialtyminerals.com/specialty-applications/specialty-markets-forminerals/nutritional-supplements/talc-as-a-glidant-lubricant/ Last assessed on March 15,
2011.
http://farriconsultingng.blogspot.com/2010/07/talc-deposits-in-nigeria-opportunities.html.
Last assessed on March 15, 2011.
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Cosmetic Chemists, 1970, 21(7), 483-500.
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Pharm. 2005, 55, 263-276.
7
TABLE 1: PHYSICOCHEMICAL PROPERTIES OF LOCAL TALC SAMPLES
PROPERTIES AND TESTS
TAP
TIR
TOS
1. Colour
Grey
Grey
Grey
2. Odour
Slight
Slight
Slight
3. Texture
Greasy to the touch
Greasy to the touch
Greasy to the touch
MACROSCOPY
Insoluble in water, Insoluble in water, Insoluble in water,
SOLUBILITY
dilute acid and alkali
dilute acid and alkali
dilute acid and alkali
1. Carbonate
++
++
++
2. Chloride
++
++
++
3. Iron
++
++
++
4. Readily Carbonisable
Grey residue
Grey residue
Grey residue
1.0
0.0
7.0
CHEMICAL
Matter
5. Loss on drying (%)
MICROSCOPY
1. Description of mount
Transparent irregular Transparent irregular Transparent irregular
plates with jagged plates with jagged plates with jagged
laminated ends.
2. Appearance
polarized
laminated ends.
laminated ends.
under Shone brightly on a Shone brightly on a Shone brightly on a
light
dark background
3. With 0.1% w/w methylene Plates
blue in 96% ethanol
dark background
remain Plates
dark background
remain Plates
unstained
unstained
unstained
70.27
61.27
82.78
4. average length of plates
(µm)
++ ---Positive
8
remain
Table 2: Properties of Lactose tablets formulated with different Local Talc Samples as Lubricant (mean±SD, n=10)
Lubricant
Concentration
Tablet wt
Tablet
Crushing
Friability
code
(%w/w)
(mg)
Thickness
Strength (CS)
(F) (%)
(mm)
(N)
CSFR
Disintegration
CSFR/DT
time (min)
TAP
5.00
557.80±1.72
3.50±0.00
52.33±14.78
0.94±1.10
55.67
2.50±0.04
22.27
TAP
7.50
582.20±1.90
3.50±0.01
58.60±10.68
0.88±0.01
66.59
2.55±0.02
26.11
TAP
10.00
581.60±8.41
4.00±0.01
70.95±10.98
0.82±0.01
86.52
2.65±0.04
32.64
TIR
5.00
555.30±1.78
4.00±0.01
55.08±18.33
0.80±0.04
68.85
2.42±0.03
28.45
TIR
7.50
584.40±1.95
3.50±0.01
59.78±7.06
0.76±0.04
78.66
2.48±0.07
31.72
TIR
10.00
581.30±8.39
4.00±0.04
72.23±7.74
0.72±0.03
100.31
2.51±0.05
39.96
TOS
5.00
556.90±1.63
3.50±0.04
41.36±15.88
0.96±0.01
43.08
2.18±0.11
19.76
TOS
7.50
581.40±1.83
3.50±0.03
54.98±9.89
0.82±0.02
67.05
3.60±0.12
18.63
TOS
10.00
582.10.±8.43
4.00±0.01
72.32±8.13
0.79±0.11
91.54
4.80±0.02
19.07
TBP
5.00
554.60±1.02
3.50±0.01
53.12±7.55
0.75±0.01
70.83
2.35±0.01
30.14
9
Table 3: Properties of Lactose Tablets Formulated with different Local Talc Samples and 1% w/w Magnesium Stearate as
Lubricant (mean±SD, n=10)
Lubricant
Concentration
Tablet wt
Tablet
Crushing
Friability
code
(% w/w)
(mg)
Thickness
Strength (CS,
(F) (%)
(mm)
(N)
CSFR
Disintegration
CSFR/DT
Time (min)
TAPM
5.00
581.60±0.17
3.50±0.02
48.02±11.86
0.85±0.02
56.49
8.24±0.03
6.86
TAPM
7.50
599.10±0.72
3.50±0.01
67.72±10.09
0.82±0.02
82.58
15.22±0.51
5.43
TAPM
10.00
614.90±5.50
4.00±0.08
47.04±8.72
0.79±0.02
59.54
16.20±0.64
3.68
TIRM
5.00
580.50±0.93
3.50±0.03
47.80±8.89
0.83±0.07
57.59
8.68±0.42
6.63
TIRM
7.50
599.40±0.63
3.50±0 .02
64.88±7.35
0.83±0.03
78.17
16.10±0.41
4.86
TIRM
10.00
615.60±6.51
3.50±0.02
79.38±9.90
0.80±0.01
99.23
16.25±0.55
6.11
TOSM
5.00
581.20±0.34
3.50±0.01
45.08±14.79
0.76±0.03
59.32
7.30±0.21
8.13
TOSM
7.50
599.80±0.55
3.50±0.04
63.21±6.76
0.80±0.01
79.01
12.40±0.36
6.37
TOSM
10.00
617.10±5.56
3.50±0.04
80.95±6.57
0.75±0.93
107.93
15.22±0.48
7.09
TBPM
5.00
580.60±0.12
3.50±0.01
55.17±8.13
0.70±0.01
78.81
3.50±0.10
22.52
10