mondo bulletin plastics

Technical Bulletin 1301

Talc in Plastics

2 Mondo Minerals B.V. · Technical Bulletin 1301

Contents

Introduction

Benefits of Talc in PolypropyleneCompounds

1. Stiffness (E-Modulus)2. Thermal Conductivity3. Nucleation 4. Impact Strength5. Deflection Temperature6. Creep Resistance7. Barrier Properties8. 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 repellentand chemically inert mineral. It is characterizedas a hydrated magnesium sheet silicate with theformula Mg3 Si4O10 (OH)2.

Talc consists of a layer or sheet of brucite(Mg(OH)2) sandwiched between two sheets ofsilica (SiO2) (see figure 1).

Weak Van der Waal’s forces bond the crystal lat-tice of talc. Thus, talc undergoes cleavage veryreadily, is very soft and has a soapy feel.

The term „talc” covers a wide range of naturalproducts. Impurities commonly encounteredinclude magnesite (magnesium carbonate), cal-cite, quartz and chlorite (a mix of Mg- Al- andFe- silicate / Mg(OH)2). Among the differentmodifications of talc, mostly pure and lamellartalc grades are used in the plastic industry.

Talc is usually lamellar (platy), but the aspectratio can vary considerably. Its high aspect ratiois the most important property for its use in plastics.

Talc is a functional component in paper, paints,plastics, rubbers, ceramics, fertilizers, animalfeed, cosmetics, pharmaceuticals and otherapplications.

In plastics, it is used to stiffen thermoplastics,mainly polypropylene but also polyethylene andpolyamide (nylon). Main applications are auto-motive parts, household appliances and engi-neering plastics.

Figure 1:

Talc crystal structure

Si

O

OH

Mg

Mondo Minerals B.V. · Technical Bulletin 1301 3

Figure 1:

Stiffness of a PP

compound with high

aspect ratio talc,

a mineral with

medium aspect ratio,

and calcium

carbonate

Figure 2:

Thermal conductivity

of PP/talc

Ten

sile

mo

du

lus

(MPa

)Th

erm

al c

on

du

ctiv

ity

(W/m

°K)

Stiffness and Aspect Ratio

High aspect ratio talc

Medium aspect ratio talc

Calcium carbonate

4000

3500

3000

2500

2000

1500

10000 10 20 30 40

Mineral loading (wt%)

0 5 10 15 20 25 30 35 40

Thermal Conductivity of PP Compounded with Talc

0,55

0,50

0,45

0,40

0,35

0,30

0,25

Fine medium aspect ratio talc

Medium lamellar talc

Fine lamellar talc

Mineral loading (wt%)

2. Thermal Conductivity

Because of talc’s significantly higher thermal con-ductivity (compared to the polymer), the heatintroduced and generated during processing istransmitted through the mixture more quickly(Figure 2). The heat is also transported out of thecompound faster during cooling.

Incorporating talc in a compound increases thethermal conductivity, resulting in faster produc-tion rates. Experience with filled polymers is thatconductivity depends only on the filler content,within reasonable tolerances.

Benefits of Talc in Polypropylene Compounds

1. Stiffness (E-Modulus)

The main reason for incorporating talc in plasticsis to increase the stiffness (E-modulus).

The degree of rigidity depends on the filling level,aspect ratio and fineness of the talc (Figure 1).


3. Nucleation

The crystallization of polypropylene is promotedby small amounts of preferably fine talc, whichacts as a nucleating agent. Crystallization startsat a higher temperature in the presence of talc,compared to unfilled PP. The impact strength

is improved (Graph 3) but this is primarily due toan increase in the crystallization of the PP andnot the mechanical properties of the talc itself.There is also a change in modulus (Figure 4) as aresult of the change in crystallinity.

Figure 5:

Influence of

fine talc on

high impact PP

Figures 3 and 4:

Impact and rigidity

of nucleated PP

TalcSodium benzoateCa-carbonate

0 0.5 1 1.5 2

Nucleation of PP: Impact Strength

Impact Strength and Rigidity of Talc/PP compounds

Ch

arp

y Im

pac

t St

ren

gth

(kJ

/m2 )

Loading (wt%)

Talc loading (wt%)

45

40

35

30

25

20

15

10

5

0

TalcSodium benzoateCa-carbonate

0 0.5 1 1.5 2

Nucleation of PP: E-modulus

Flex

ura

l Mo

du

lus

(N/m

m2 )

Loading (wt%)

2000

1800

1600

1400

1200

1000

2000

1900

1600

1300

1000

Flex

ura

l Mo

du

lus

(MPa

)

70

60

50

40

30

20

10

0

Imp

act

Stre

ng

th (

kJ/m

2 )

0 5 10 15 20

4. Impact Strength

Addition of mineral fillers will not generallyimprove impact strength. There are exceptions,for example the use of fine talc in PP com-pounds for car bumpers.

In the latter case, 5 to 10 % of fine talc isadded. Impact strength decreases at higher loadings (Figure 5).

5. Deflection Temperature

In many applications such as in plastic parts forcars or packaging, rigidity is required at elevatedtemperatures.

The heat distortion temperature (HDT) can beused to demonstrate how a mineral influences

the stiffness of a plastic compound at elevatedtemperatures. Lamellar talc with high aspectratio improves the deflection temperature ofpolyolefins to a greater extent than talc with alower aspect ratio (Figure 6).


Figure 6:

Deflection tempera-

ture of compounds

with medium aspect

ratio talc (I), high

aspect ratio talc (II)

and unfilled PP

Figure 7:

Creep of PP

and filled

polypropylene

Impact Strength and Rigidity of Talc/PP Compounds

Long-term Creep of PP and PP Compounds with Talc and Calcium Carbonate

PP

PP+20% Calciumcarbonate

PP+20% Lamellartalc

PP+40% Mediumaspect ratio talc

PP+30% Lamellartalc

160

140

120

100

80

60

40

20

0

1.4

1.2

1

0.8

0.6

0.4

0.2

0

PP

0 2 4

97109

121

140

PP + 20%medium talc I

PP + 20%medium talc II

PP + 40%medium talc II

Stra

in (

%)

Time (years)

Def

lect

ion

Tem

per

atu

re (

°C)

6. Creep Resistance

Substantial reduction of creep is achieved withfilled polymers in comparison to unfilled ones.Best results in our creep tests were obtained withfine platy talc. Various fillers and filler combina-tions reduced creep as follows:

High aspect ratio talc > medium aspect ratio talc > blend of talc and carbonate > calcium carbonate > unfilled polypropylene (Figure 7).


Information obtained from short-term tests of PPcan be extrapolated to predict properties over alonger period of time at a constant temperature

The conventional short-term modulus is replacedin formulas by the creep modulus. The creepmodulus, which is important for expected

service life under load, can be calculated fromcreep tests. The figure below applies to a five-year period (Figure 8).

Typical products where creep has to be takeninto consideration are buried plastic pipes (e. g.for sewage water).

Figure 9:

Water vapor

transmission rate

Creep Modulus of PP and PP Compounds

900

800

700

600

500

400

300

200

100

0PP + 20%Calcium

Carbonate

PP PP + 20%Talc/

Carbonate (1:2)

PP + 20%Talc

PP + 30%Talc

Figure 8:

Creep modulus

(for five years)

Cre

ep M

od

ulu

s (N

/mm

2 )

Water Vapor Transmission Rate

0.6

0.5

0.4

0.3

0.2

0.1

0PPH + 30%talc

d50=3.0µPPH PPH + 30%talc

d50=2.1µPPH + 30%

Ca-carbonate

Wat

er v

apo

r tr

ansm

issi

on

g/(

m2x

24h

)

7. Barrier Properties

Water vapor and oxygen transmission are impor-tant factors to control in food packaging. Theydirectly influence the shelf life of the food con-tained inside. Talc provides the opportunity toreduce transmission rates for water vapor

(Figure 9) and oxygen (Figure 10). The lamellartalc particles are mostly orientated in films andwill constrain the water vapor and oxygen on itsway through the packaging.

Reduced water vapour transmission in polyolefin food packaging by talc


8. Chemical Resistance

Talc is water repellent and chemically inert. Thisis very important for the direct contact of mine-ral filled packaging material with food-stuffs.Migration tests are done with different simulants(distilled water, 3% acetic acid, 10% ethanoland rectified olive oil).

Even with 3% acetic acid, overall migration requirements can be fulfilled (< 10mg/dm2

sample). (Figure 11)

New Markets for Talc-Filled Polymers

The automotive and domestic appliances mar-kets are still the dominating users of talc-filledcompounds, but new markets are being develo-ped. Their growth depends partly on the extentto which end-users actively seek alternativematerials to PVC and PS. Markets of interesthere include profiles, pipes and food packaging.

In replacement of PVC for plastic pipes, there isa need to compensate for the lower ring stiff-ness of polyolefins, but also to reduce undesira-ble long-term properties of unfilled polypropyle-ne and polyethylene, such as their tendency tocreep (deform under long-term strain). Talc is thepreferred additive in this application, as itimparts high stiffness, which allows a reduction

in wall thickness. Impact resistance at sub-zerotemperatures is unimpaired.

Talc-filled polypropylene is also finding new mar-kets in food packaging applications. Migrationrequirements according to EN 1186-5 can bemet, and higher rigidity and barrier properties(e.g. reduction of oxygen permeability) areimparted. Talc improves output in extrusion andshortens cycle times in thermoforming, due tocrystallization and better heat transfer.

These benefits make talc compounds very com-petitive for food packaging, so there is consider-able potential in this application.

Figure 11:

Overall migration

of PP/Talc, simulant

3% acetic acid

Figure 10:

Oxygen

transmission rate

500

450

400

350

300

250

200

150

100

50

0PPH PPH + 30%talc

d50=2.1µPPH + 30%

Ca-carbonate

Oxy

gen

tra

nsm

issi

on

cm

3 /(m

2x

24h

)

EN 1186-5:Test methods for overall migration from plastics into aqueous food simulants by cell.Simulant 3% acetic acidTest conditions 10 days, 40°CThe overall migration limit is 10 mg/dm2

PP homopolymer+30%Ca-carbonate (EXH1 SP) 79 – 128

PP homopolymer+30%Talc d50 = 3.0 µm 0.4 – 1.0

Sample Overall migrationmg/dm2 sample

Oxygen Transmission Rate

PPH + 30%talcd50=3.0µ

Reduced oxygen transmission in polyolefin food packaging by talc

WE TALK TALC

Mondo Minerals B.V. · www.mondominerals.comKajuitweg 8 · NL -1041 AR Amsterdam · Phone +31 20 448 7 448 · Fax +31 20 448 7 437 · E-Mail: [email protected]

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 orin 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 thecompleteness 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 mustexercise 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.

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