Technical Bulletin 1301
Talc in Plastics
Contents
Introduction
Benefits of Talc in Polypropylene
Compounds
1. Stiffness (E-Modulus)
2. Thermal Conductivity
3. Nucleation
4. Impact Strength
5. Deflection Temperature
6. Creep Resistance
7. Barrier Properties
8. Chemical Resistance
New Markets for Talc-Filled Polymers
Introduction
Pure talc, the softest of all minerals with a Mohs
hardness of 1, is an organophilic, water repellent
and chemically inert mineral. It is characterized
as a hydrated magnesium sheet silicate with the
formula Mg3 Si4O10 (OH)2.
Weak Van der Waal’s forces bond the crystal lattice of talc. Thus, talc undergoes cleavage very
readily, is very soft and has a soapy feel.
The term „talc” covers a wide range of natural
products. Impurities commonly encountered
include magnesite (magnesium carbonate), calcite, quartz and chlorite (a mix of Mg- Al- and
Fe- silicate / Mg(OH)2). Among the different
modifications of talc, mostly pure and lamellar
talc grades are used in the plastic industry.
Talc is usually lamellar (platy), but the aspect
ratio can vary considerably. Its high aspect ratio
is the most important property for its use in
plastics.
Talc is a functional component in paper, paints,
plastics, rubbers, ceramics, fertilizers, animal
feed, cosmetics, pharmaceuticals and other
applications.
In plastics, it is used to stiffen thermoplastics,
mainly polypropylene but also polyethylene and
polyamide (nylon). Main applications are automotive parts, household appliances and engineering plastics.
Talc consists of a layer or sheet of brucite
(Mg(OH)2) sandwiched between two sheets of
silica (SiO2) (see figure 1).
Figure 1:
Talc crystal structure
Si
O
OH
Mg
2
Mondo Minerals B.V. · Technical Bulletin 1301
Benefits of Talc in Polypropylene Compounds
1. Stiffness (E-Modulus)
The main reason for incorporating talc in plastics
is to increase the stiffness (E-modulus).
The degree of rigidity depends on the filling level,
aspect ratio and fineness of the talc (Figure 1).
Stiffness and Aspect Ratio
4000
Figure 1:
Stiffness of a PP
3500
compound with high
Tensile modulus (MPa)
High aspect ratio talc
aspect ratio talc,
3000
a mineral with
medium aspect ratio,
Medium aspect ratio talc
2500
and calcium
carbonate
2000
Calcium carbonate
1500
1000
0
10
20
30
Mineral loading (wt%)
40
2. Thermal Conductivity
Because of talc’s significantly higher thermal conductivity (compared to the polymer), the heat
introduced and generated during processing is
transmitted through the mixture more quickly
(Figure 2). The heat is also transported out of the
compound faster during cooling.
Incorporating talc in a compound increases the
thermal conductivity, resulting in faster production rates. Experience with filled polymers is that
conductivity depends only on the filler content,
within reasonable tolerances.
Thermal Conductivity of PP Compounded with Talc
Thermal conductivity (W/m°K)
0,55
Figure 2:
Fine medium aspect ratio talc
0,50
Thermal conductivity
of PP/talc
0,45
Medium lamellar talc
0,40
0,35
Fine lamellar talc
0,30
0,25
0
5
10
15
20
25
30
35
40
Mineral loading (wt%)
Mondo Minerals B.V. · Technical Bulletin 1301
3
3. Nucleation
is improved (Graph 3) but this is primarily due to
an increase in the crystallization of the PP and
not the mechanical properties of the talc itself.
There is also a change in modulus (Figure 4) as a
result of the change in crystallinity.
Nucleation of PP: Impact Strength
Nucleation of PP: E-modulus
Figures 3 and 4:
Impact and rigidity
of nucleated PP
45
40
35
30
25
20
15
10
5
0
2000
Flexural Modulus (N/mm2)
Charpy Impact Strength (kJ/m2)
The crystallization of polypropylene is promoted
by small amounts of preferably fine talc, which
acts as a nucleating agent. Crystallization starts
at a higher temperature in the presence of talc,
compared to unfilled PP. The impact strength
1800
1600
1400
1200
1000
0
0.5
1
1.5
Loading (wt%)
2
0
0.5
1
1.5
Loading (wt%)
2
Talc
Sodium benzoate
Ca-carbonate
Talc
Sodium benzoate
Ca-carbonate
4. Impact Strength
Addition of mineral fillers will not generally
improve impact strength. There are exceptions,
for example the use of fine talc in PP compounds for car bumpers.
In the latter case, 5 to 10 % of fine talc is
added. Impact strength decreases at higher
loadings (Figure 5).
Impact Strength and Rigidity
of Talc/PP compounds
Figure 5:
2000
Influence of
Flexural Modulus (MPa)
high impact PP
60
1900
50
40
1600
30
20
1300
10
1000
0
0
4
Impact Strength (kJ/m2)
70
fine talc on
5
10
15
Talc loading (wt%)
20
Mondo Minerals B.V. · Technical Bulletin 1301
5. Deflection Temperature
In many applications such as in plastic parts for
cars or packaging, rigidity is required at elevated
temperatures.
The heat distortion temperature (HDT) can be
used to demonstrate how a mineral influences
the stiffness of a plastic compound at elevated
temperatures. Lamellar talc with high aspect
ratio improves the deflection temperature of
polyolefins to a greater extent than talc with a
lower aspect ratio (Figure 6).
Deflection Temperature (°C)
Impact Strength and Rigidity of Talc/PP Compounds
160
Figure 6:
140
Deflection tempera140
120
100
80
ture of compounds
121
with medium aspect
109
97
ratio talc (I), high
aspect ratio talc (II)
60
and unfilled PP
40
20
0
PP + 20 %
medium talc I
PP
PP + 20 %
medium talc II
PP + 40 %
medium talc II
6. Creep Resistance
Substantial reduction of creep is achieved with
filled polymers in comparison to unfilled ones.
Best results in our creep tests were obtained with
fine platy talc. Various fillers and filler combinations reduced creep as follows:
High aspect ratio talc >
medium aspect ratio talc >
blend of talc and carbonate >
calcium carbonate >
unfilled polypropylene (Figure 7).
Long-term Creep of PP and PP Compounds with Talc and Calcium Carbonate
1.4
Figure 7:
PP
Creep of PP
1.2
Strain (%)
and filled
PP + 20 % Calcium
carbonate
1
polypropylene
0.8
PP + 20 % Lamellar
talc
0.6
0.4
PP + 40 % Medium
aspect ratio talc
0.2
PP + 30 % Lamellar
talc
0
0
2
4
Time (years)
Mondo Minerals B.V. · Technical Bulletin 1301
5
Information obtained from short-term tests of PP
can be extrapolated to predict properties over a
longer period of time at a constant temperature
service life under load, can be calculated from
creep tests. The figure below applies to a fiveyear period (Figure 8).
The conventional short-term modulus is replaced
in formulas by the creep modulus. The creep
modulus, which is important for expected
Typical products where creep has to be taken
into consideration are buried plastic pipes (e. g.
for sewage water).
Creep Modulus of PP and PP Compounds
900
Creep modulus
800
(for five years)
700
Creep Modulus (N/mm2)
Figure 8:
600
500
400
300
200
100
0
PP
PP + 20 %
Calcium
Carbonate
PP + 20 %
Talc/
Carbonate (1:2)
PP + 20 %
Talc
PP + 30 %
Talc
7. Barrier Properties
Water vapor and oxygen transmission are important factors to control in food packaging. They
directly influence the shelf life of the food contained inside. Talc provides the opportunity to
reduce transmission rates for water vapor
(Figure 9) and oxygen (Figure 10). The lamellar
talc particles are mostly orientated in films and
will constrain the water vapor and oxygen on its
way through the packaging.
Water vapor transmission g/(m2 x 24 h)
Water Vapor Transmission Rate
Figure 9:
Water vapor
transmission rate
0.6
0.5
0.4
0.3
0.2
0.1
0
PPH
PPH + 30% talc
d50 = 3.0µ
PPH + 30% talc
d50 = 2.1µ
PPH + 30 %
Ca-carbonate
Reduced water vapour transmission in polyolefin food packaging by talc
6
Mondo Minerals B.V. · Technical Bulletin 1301
Oxygen transmission cm3/(m2 x 24 h)
Oxygen Transmission Rate
500
Figure 10:
450
Oxygen
400
transmission rate
350
300
250
200
150
100
50
0
PPH
PPH + 30 %
PPH + 30% talc
Ca-carbonate
d50 = 2.1µ
Reduced oxygen transmission in polyolefin food packaging by talc
PPH + 30% talc
d50 = 3.0µ
8. Chemical Resistance
EN 1186-5:
Talc is water repellent and chemically inert. This
is very important for the direct contact of mineral filled packaging material with food-stuffs.
Migration tests are done with different simulants
(distilled water, 3 % acetic acid, 10 % ethanol
and rectified olive oil).
Test methods for overall migration from
plastics into aqueous food simulants by cell.
Simulant 3 % acetic acid
Test conditions 10 days, 40°C
The overall migration limit is 10 mg/dm2
Even with 3 % acetic acid, overall migration
requirements can be fulfilled (< 10mg/dm2
sample). (Figure 11)
PP homopolymer + 30%
Ca-carbonate (EXH1 SP)
79 – 128
PP homopolymer + 30%
Talc d50 = 3.0 µm
0.4 – 1.0
Sample
Figure 11:
Overall migration
of PP/Talc, simulant
3 % acetic acid
Overall migration
mg/dm2 sample
New Markets for Talc-Filled Polymers
The automotive and domestic appliances markets are still the dominating users of talc-filled
compounds, but new markets are being developed. Their growth depends partly on the extent
to which end-users actively seek alternative
materials to PVC and PS. Markets of interest
here include profiles, pipes and food packaging.
In replacement of PVC for plastic pipes, there is
a need to compensate for the lower ring stiffness of polyolefins, but also to reduce undesirable long-term properties of unfilled polypropylene and polyethylene, such as their tendency to
creep (deform under long-term strain). Talc is the
preferred additive in this application, as it
imparts high stiffness, which allows a reduction
Mondo Minerals B.V. · Technical Bulletin 1301
in wall thickness. Impact resistance at sub-zero
temperatures is unimpaired.
Talc-filled polypropylene is also finding new markets in food packaging applications. Migration
requirements according to EN 1186-5 can be
met, and higher rigidity and barrier properties
(e.g. reduction of oxygen permeability) are
imparted. Talc improves output in extrusion and
shortens cycle times in thermoforming, due to
crystallization and better heat transfer.
These benefits make talc compounds very competitive for food packaging, so there is considerable potential in this application.
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TA L K
TA L C
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Kajuitweg 8 · NL -1041 AR Amsterdam · Phone +31 20 448 7 448 · Fax +31 20 448 7 437 · E-Mail: info@mondominerals.com
The information contained in this Technical Bulletin relates only to the specific tests designated herein and does not relate to the use of our products in combination with any other material or
in any process. The information provided herein is based on technical data that Mondo Minerals believes to be reliable, however Mondo Minerals makes no representation or warranty as to the
completeness or accuracy thereof and Mondo Minerals assumes no liability resulting from its use for any claims, losses, or damages of any third party. Recipients using this information must
exercise their own judgement as to the appropriateness of its use, and it is the user´s responsibility to assess the materials suitability (including safety) for a particular purpose prior to such use.