Heavy Compound II

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Heavy compounds Part II – Metal powder and other highly filled compounds mimic

metalsOct 25, 2005

Michel BIRON

IntroductionProcessing of heavy thermoplasticsWhat cost? Some applicationsConclusionShelf-Life PotentialWhy Enzyme-Based Catalytic Coatings?

Introduction

On the one hand, metals such as lead are more or less banned by regulations and environmentaltrends and, on the other hand they are difficult and expensive to process. Consequently, a market isdeveloping for heavy polymers with densities in the same order, easier to process, environment-friendly and economically competitive after processing and finishing.There also some markets for intermediate density polymers that can evolve between less than 2 upto 11.

Metal filled thermoplastics are well placed to meet these requirements with:

l The possibility to obtain densities of 11 with non-toxic metal additionl Design freedoml Acceptable processingl Fair final performancesl Interesting final costs.

High densities can be also unintentional, resulting from the use of metals or other heavy additives toobtain specific properties such as electrical or thermal conductivity, magnetic behaviour etc.

A broad market, estimated at more than $5 mil lion per year for USA, is developing thanks to a greatdiversity of:

l Polymers:¡ Commodity such as polypropylene and ABS…¡ Engineering thermoplastics such as polyamides 6 and 12, PBT…¡ High-temp ETP such as PPS…¡ Thermoplastic elastomers such as TPU and SEBS…

l Metals:¡ Aluminium: density of 2.3 to 2.7¡ Stainless steel: density of 7.9¡ Copper: density of 9¡ Silver: density of 10.5¡ Tungsten: density of 19.3…

l Amounts of metals: from a few percent up to more than 50%

l Recipes:¡ General purpose¡ High impact…

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Such a large diversity leads to the versatility of densities and performances. For example, figure 1displays Izod notched impact strengths versus density for 11 grades of heavy polymer compounds.

To identify the general rules of performance evolutions it is necessary to examine the properties bypolymer families. Table 1 analyzes performances versus density for three polymer families.

Figure 1: Examples of notched impact strength versusdensity.

Table1: performances versus density for three polymer families

Engineering thermoplastics

PA6

Advantages Drawbacks gfhgjuykoliul; Advantages Drawbacks Drawbacks Drawbacks

Specific

Gravity D792 2 3 5 6 8 11

FlexuralModulus, GPa

D790 3 6 5 15 9 15

TensileModulus, MPa

D638 7 16

TensileStrength, MPa

D638 56 68 53 46 59 52

Elongation at

Break,%D638 10 2 45 1 0.5

Izod, J/m D256 69 54 54 54 64

HDT, °C D648 149 152

PA12

Specific

Gravity D792 6.9 11 11


D790 5 8 5

TensileModulus, MPa

D638 8 9 8


D638 45 45 34

Elongation atBreak,%

D638 2 1 2

Izod, J/m D256 112 80 112

HDT, °C D648 159 155

Thermoplastic elastomer

TPU

Specific

Gravity D792 8 11


D790 0.1 0.2

TensileModulus, MPa

D638 0.01 0.3


D638 10 3

Elongation atBreak,%

D638 70 10

Izod, J/m D256 160 160





When the density increases, table 1, figures 2 and 3 show for the same polymer, PA6 filled withdifferent metals, tungsten, stainless steel, copper:

l A clear increase of the flexural modulusl A slight decrease of the tensile strengthl

Erratic variations of elongation at break and notched impact strength depending on theformulation.

For the same density (11) and the same metal (tungsten), table 2 displays a clear effect of thepolymer family on:

l The moduli and tensile strength increasing from TPU up to PA6l The elongation at break and notched impact strength decreasing from TPU down to PA12 or

PA6

Processing of heavy thermoplastics

The weight fraction of filler in heavy thermoplastics is high but the volume fraction is acceptable and

Figure 2: Examples of notched impact strength versusdensity.

Figure 3: PA6 Examples: Tensile strength versus density

Table2: performances versus polymer families for a density of 11

Engineering thermoplastics

TPU

High Impact

PA12PA12 PA6

Specific Gravity D792 11 11 11 11

Flexural Modulus, GPa D790 0.2 5 8 15

Tensile Modulus, MPa D638 0.3 8 9

Tensile Strength, MPa D638 3 34 45 52

Elongation at Break,% D638 10 2 1 0.5

Izod, J/m D256 160 112 80





heavy thermoplastics can generally be run on conventional moulding machines. However, for agiven polymer, the processing is more difficult when the level of filler increases but processability canbe optimized with processing aids and other additives. Mould, screw, and barrel wears are higherthan those of conventional plastics and it is often recommended to use hardened-steel tooling.Processing difficulty can be compared to that of highly glass-reinforced materials. However, runs of100,000 parts are possible without unbearable damages for tools and machines.

What cost?

Because of the high density, the cost must be considered per weight and per volume.

Most common heavy thermoplastics are in the range of:

l €10 to €40 per kgl €20 to €500 per litre.

The cost increases with density, the more so as it is expressed per volume. Figure 4 schematizesthese costs versus the compound density.

The raw materials are far more expensive than conventional materials but, as for the othercomparisons between thermoplastics and conventional materials it is necessary to take into accountthe other advantages of thermoplastics allowing to obtain a better final cost. Let us remember someof these advantages:

l Technical features:¡ Ease and freedom of design (realization of forms impossible with metals).¡ Ease of processing.¡ Reduction or suppression of finishing steps¡ Ease of maintenance.¡ Non-rusting.¡ Acoustic damping (noise reduction).

l Aesthetics:¡ Much more design freedom.¡ Decoration possibilities: bulk colouring, in mould decoration…¡ Pleasant finish.

l Economical features:¡ The economical response to mass production quite as much as "niche" production.¡ Reduction of manufacturing times.¡ Reduction of the finishing costs: thermoplastics allow the integration of functions and,

consequently, lead to the reduction of assembly costs.¡ Higher productivity due to adapted processes, integration of functions, decrease of

processing steps...

Figure 4: High density compoundsCost versus density





l Environmental features:¡ Heavy thermoplastics without toxic additives replace lead.

Some applications

First industrial high-density plastics were originally designed to satisfy environmental requirements of

the US Department of Defense worried of the lead contamination of firing ranges. The experimentslead to a 11 density thermoplastics that found other applications related to lead replacement alwaysfor its toxic properties : weighting, nuclear shielding, medicine sector…

Figure 5 schematizes some of the main applications.

Let us quote some examples and details on these uses:

l Weighting¡ Ammunition

n Training and shooting projectiles: Compounds of polyamide and tungsten canexactly match the lead density and avoid pollution with lead fragments.

n Less-lethal ammunitions used in crowd control or hostage situation: the principleis to decrease impact strength by lowering density. J.E PUSKAS and All. (KGK,58, 6, 2005, p. 288) propose a compound based on a blend of butyl rubber and

SIBS filled with 233 parts of iron powder with a final density of 2.4. Numerousother polymers are proposed such as EPDM, SBR, natural rubber,polybutadiene, TPEs, silicone and their blends with thermoplastics.

¡ A high-density polypropylene compound is utilized to make a perfume -bottle cap that ismetal plated eliminating costly machining of metal caps.

¡ A high-density SEBS compound (density 2) is used to sink tubing of vacuum cleanersfor swimming pools to the bottom of the pool.

¡ Balance weights, wheel weights, inertia weights…

l Nuclear Power Radiation Shielding: special radiation-shielding formulations provide efficiencycomparable to lead with a lower density. Targeted applications are, for example:

¡ Temporary reactor shielding, employee protection¡ Medical radiation shielding, imaging device shielding

¡ Neutron shielding¡ X-ray collimators, syringe shields¡ X-ray tube shielding, radioisotope shipping containers¡ Radiation therapy

Figure 5: Heavy polymer applications examples.





¡ Nuclear medicine…

l Industrial¡ Flywheels…

l Sports and leisure¡ Fishing tackle: the choice of density and size of sinkers allows to obtain floating or

sinking fishing lines¡ Golf club heads: series of weights moulded with a high-gravity TPU compound replace

lead weights previously adjusted by grinding. Parts are coloured in accordance of theirweight.

¡ Toys…

l Vibration Damping¡ Acoustical Damping

l Electrical and thermal conductivity: table 3 displays examples of thermal conductivity andresistivity of some additives with densities ranging from more than 2 up to 9.

l Magnetic behaviour: table 4 displays examples of polymer magnets with densities rangingfrom more than 3 up to 6.

Conclusion

The replacement of lead because of the environmental concerns has opened the way to a panoply ofmetal filled polymers with medium or very high density according to the amount and density of theused metal.

Several markets are developing where the high density allows to compete with metals with an easierprocessability, a better design freedom, a better respect of the environment and lower final costsdespite the high raw material costs.

The density of these polymers can evolve from less than 2 up to more than 11 thanks to the use ofvarious polymers, commodities, engineering thermoplastics, TPEs, rubbers and varied metals from

aluminium up to tungsten or heavy fillers such as barium sulphate.

The application field is as broad as the diversity of formulations and shapes, opening the way touses ranging from gadgets up to high-tech parts.

Table 3: Thermal and electrical properties of some special ceramics and metals

Material Density Thermal conductivity Resistivity

Silicon nitride 2.2 to 3.2 33 1010

Al2O

3 99 % 2.9 to 3.9 25 to 36 10

14

Silicon carbide 3.2 60 to 120 106 to 10

7

Aluminium nitride 3.3 50 to 260 1014

to 1015

Aluminium diboride 4.25 60 to 120

Boron nitride 2.2 to 3.2 125 to 300

Copper 9 400 <10

Aluminium 2.7 60 to 237 <10

Table4: Property examples of polymer magnets

Ferrite/Plastic Rubber/ferrite Rare earth/plastic

Density G/cm 3 3.5 to 3.7 3.5 to 3.7 5 to 6

Tensile strength MPa 60 to 80 5

HDT °C 100 to 120 35 to 50

Service temperature °C -40 up to +100 Up to 110





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References

Technical guides and websites: Bayer, Bondline, Degussa, DSM, Ecomass, Huber, Krasol, LNP, Multibase, Omya, PolyOne,RTP, SartomerJ.E PUSKAS and Coll. (KGK, 58, 6, 2005, p. 288)Market developments for white minerals in plastics, 2003, www.klinegroup.comR.D. LEAVERSUCH (Now they want Plastics to be heavy, Gardner Publications)

G. LU and All. (Antec 2003, p. 273)BHATTACHARJEE AND All (ACS, Pittsburgh, October 2002, paper 18)G.MELI (ACS, Cincinnatti, October 2000, paper 17)J.H. NAM (Polymer Engineering and Science, avril 2000, 40, 4, p.857)L.R. EVANS (ACS, Anaheim, May 1997, paper O)

R.JEZIORSKA and All. (IPST 24, 7, 1997, p. T/100)



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