FILLED THERMOPLASTICS

Thermoplastics & typical applications

Thermoplastics are an important class of material used for many types of product. The name thermoplastic indicates that the materials can be melted and reformed into new objects by the application of heat. This distinguishes them from thermosetting plastics, which once formed, cannot be reshaped by heating. Thermoplastics are a diverse group of materials so that it is possible to select one that provides the performance needed for a particular application. Considerations include mechanical performance, aesthetics, resistance to chemicals, cost, stability to heat and recycleability to name just a few. Plastics are often perceived as cheap materials, whereas in reality the price and performance of polymers varies over a huge range and the best solution is usually the one that meets the design criteria at the lowest cost. Materials cost is just one aspect though. Often metals or other materials offer a cheaper solution if compared to plastic. However, the design flexibility that plastics offer allows the integration of several parts and the resultant reduction in complexity and assembly costs is what may make the use of plastic a better overall solution. In recent years, recycleability has become progressively more important in terms of public perception and new legislation forces manufacturers to recycle their products. This is an advantage of thermoplastics compared to thermosetting polymers and is expected to increase the growth of thermoplastics which is currently in the range 5-10 percent per annum.

Figure 1 Use of Thermoplastics in Western Europe Thermoplastic demand in Western Europe is 37 x 106 tonnes compared to 10 x 106 tonnes for thermosetting polymers. A breakdown of thermoplastics by application area is given Figure 1.

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The five main thermoplastics listed below account for 75 percent of the total thermoplastics market. Polyethylene (Low Density) LDPE, LLDPE 7.6 x 106 tonnes Polyethylene (High Density) HDPE 5.0 x 106 tonnes Polypropylene PP 7.0 x 106 tonnes Polyvinyl Chloride PVC 5.8 x 106 tonnes Polystyrene (General Purpose) GPPS 3.1 x 106 tonnes with HIPS Polystyrene (High Impact) HIPS Polyesters (Thermoplastic) PET 3.1 x 106 tonnes As mentioned, there is a very wide selection of commercial polymers and it would not be possible to consider each one separately. Fortunately, that is not necessary because the effect of fillers on different polymers is often similar. Broadly speaking we can consider the thermoplastics to fall into two main groups: semi-crystalline and amorphous (non-crystalline). Of the top five commercial polymers, PE, PP and PET are semi-crystalline. Polystyrene is amorphous and PVC only contains small amounts of crystallinity. Interestingly, the crystals act as a filler, improving some mechanical properties and contributes to the domination of semi-crystalline polymers in the market. There is a huge amount of data available on filled polypropylene and so we will use that to exemplify principles. Where the amorphous polymers show different behavior, that will be noted in the text.

Bulk and Process Related Properties

Specific Gravity or Relative Density

By far the most commonly used fillers are mineral, which have densities in the range 2.4 – 2.8 gcm-3. Most polymers have densities in the range 0.8-1.4 gcm-3 and so addition of mineral fillers gives a composite with higher density than the polymer. Usually the linear rule of mixtures can be used to predict the density of a composite from those of the

constituents and their relative amounts. (Equation 1). Where ρc, ρf and ρp are the densities of the composite, filler and polymer, respectively and mf is the mass fraction of filler. Deviations from the density predicted can occur when there are air inclusions (bubbles) or when one or both materials are altered by preparation of the composite. As mentioned before, examples are changes in the crystallinity (and therefore density) of the polymer, or a breaking of hollow fillers.

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0

1

2

3

4

5

0 10 20 30 40 50 60 70 80 90 100

Talc in PP

Magnetite in PP

Tungsten in Nylon

Weight % Filler

Density g

/cm

³

ρc = ρf x ρpρpmf + ρf x (1-mf)

ρc - density of the compositeρf - density of the fillerρp - density of the polymermf - weight fraction of filler (between 0 & 1)

Figure 2 Composite density is not linear with weight % filler but is with volume %

In practice, the filler content of a composite can be evaluated by burning away the polymer. This requires a temperature of 300°C or more and is therefore only of utility for fillers that do not lose significant mass when heated to such temperatures. Some fillers, such as silica, contain significant amounts of surface bound water which is lost during heating, but that can be corrected using the known water loss from the filler alone. For heat sensitive fillers, especially flame retardant filler, microwave ashing can be used as this allows for polymer removal at lower temperatures. Rather than calculating the density of the composite, one can also measure it directly using one of two common methods. One uses an electronic balance to measure the volume of liquid displaced by a known mass of composite. The other method uses a density gradient column. In such a column, a gradient of densities is induced in a liquid but varying salt concentration or by mixing water and alcohol for example. The composite is placed in the column and floats at a position where its density is the same as that of the liquid at that location. Calibrated samples of known density are also placed in the column and their position is used to indicate the density of the liquid at various heights.

)1( fffp

pf

cmm −+

=ρρ

ρρρ

Equation 1 Composite density

Often, the increase in density is a negative consequence of filler addition because heavier products are more expensive to transport and have a higher environmental impact due

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to increased fuel usage and emissions during transportation. There are cases when a lighter plastic is needed and in those instances special fillers such as glass spheres can be used. Expancel® is a speciality filler composed of microspheres made of thermoplastic and filled with liquid. Upon heating the liquid filling become gaseous and causes the spheres to expand to many times their original size. This can be used to create special effects, like visible whitening of the plastic, decreased density or to create a syntactic foam.

Acoustic properties

Acoustic properties are affected by density. Dense fillers such as barium sulphate (BaSO4, 3.8 gcm-3) have long been used to damp sound. More recently magnetite (Fe3O4, 5.1 gcm-3) has been gaining popularity in such applications. The very high density is one attractive property, but magnetite also conducts electricity and heat to some extent. This means that it can contribute to cooling of parts and also give some EMI shielding in the composite. Apart from or as well as using dense fillers to dampen sound, it is also desirable whenever possible to tune the polymer phase to maximise sound damping. Soft rubbery or viscous materials are effective in this respect. An effective way to compare the sound damping properties of plastics and elastomers (rubbers) is to analyse them by dynamic mechanical thermal analysis (DMTA). The technique can be used to measure the elastic and viscous response over a range of frequencies and at different temperatures. The loss

factor (tan δ) is the parameter used to judge sound damping performance as it represents the ability of the material to dissipate energy (as heat) by non-elastic processes. A high

tanδ is therefore sought and it is important to consider the tanδ over the particular frequency range that needs to be damped. It is well known that the mechanical response of polymers is time / frequency dependent. At low frequencies a material that is above its glass transition temperature (Tg) may damp effectively, but at some higher frequency the polymer will become harder and glassy (as if it were below its Tg) and will then lose its damping ability. The same would occur if the polymer were cooled to a temperature below its Tg. Fortunately, the effect of frequency and temperature changes can be calculated for polymers using the WLF equation. Fillers can help in sound damping by another mechanism as well. It has been reported that the filler can help reflect the sound within the polymer so that it does not pass straight through. This gives the polymer phase more opportunity to absorb the sound energy. Platy fillers such as mica are said to be especially effective in this respect. The effect is lost at high filler levels however because the filler particles percolate to give a continuous network that actually helps to transmit sound.

Melt viscosity (MFI)

The viscosity of a polymer melt influences extruder throughput and ease of forming by processes such as calendaring or injection moulding. For that reason the viscosity of thermoplastics (MFI) is always given in the specification along with key mechanical properties. Polymer melts are strongly non-Newtonian, meaning that the viscosity does not change linearly with shear rate. Furthermore, the viscosity depends on temperature

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and so the conditions used to measure the viscosity must be carefully controlled. Ideally, the measurement of viscosity should be done at the temperature at which the melt will be processed and over the range of shear rates that it will be exposed to. This can be done using a rheometer. Although such measurements are time-consuming and require specialised equipment, they give the most meaningful results. For calculating the filling of the mould during injection moulding, such advanced rheological information is a necessity. For quickly comparing the relative viscosities of different polymer grades a more cheap, fast and simple method is used. The so-called Melt Flow Index (MFI) measures the mass of polymer melt that is pushed through a hole of known diameter in a set time (units g/10 min). Naturally, the temperature is also controlled. Due to the method of measurement, higher MFI means lower viscosity and vice versa. The value given is not a true viscosity, but just an indication. Although very popular, the MFI is only a very rough guide to viscosity and may give misleading results. For thermoplastic polymer melts, the non-Newtonian behaviour depends upon such factors as chain branching and molecular weight distributions. So that two polymers with equal MFI may behave very differently during processing, which is done at higher shear rates than the MFI measurement. For polymer composites the use of MFI is even more perilous and it is widely misused in the literature and in industry. The problem is that for filled polymers the addition of filler changes the density of the polymer melt significantly. This means that the apparent MFI may increase due to the density increase. This would be erroneously interpreted as a decrease in melt viscosity, when in reality the melt viscosity may be constant or, more probably, will have increased. One must allow for changes in density due to filler addition by reporting the Melt Volume Index, which is the MFI divided by the density (calculated from the densities of the components and their relative proportions). Some polymer producers give the MVI as it provides a fairer comparison of melt viscosity. Shenoy has done some interesting work to allow the MFI to be used in predicting the viscosity at other shear rates than that of the measurement. Addition of filler to the polymer almost always results in a rise in viscosity. At low filler loadings the effect may not be noticeable in comparison to the already viscous polymer melt. However, as the loading is increased the viscosity begins to rise more and more rapidly until at some critical filler amount the viscosity approaches infinity and the material loses all processability. This effect is particularly important for systems with high filler loadings, examples include PVC flooring formulation, flame retarded polyolefins (containing Mg(OH)2 or Al(OH)3) or polymer-bound magnets. The rise of viscosity depends upon the volume percentage of filler and it can be altered in several different ways. Adding dispersant can lower the viscosity, whereas a coupling agent binds the particles to the polymer and may therefore increase the viscosity. The shape of the particles is important and this may vary from one filler to another and even for the same filler depending upon the production method (milling etc.). The viscosity of a very dilute dispersion of rigid spherical particles in a Newtonian fluid is

described by the Einstein equation (Equation 2). Where η is the viscosity of the

dispersion, ηl is the viscosity of the fluid alone, φ is the volume fraction of particles and kE is the Einstein coefficient, which is 2.5 for spherical particles. kE depends upon both particle shape and orientation.

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)1( φηη El k+=

Equation 2 Einstein equation of dispersion viscosity Although it is a starting point for understanding the effect of filler on viscosity, the Einstein equation is not applicable to filled polymer melts. Polymer melts are non-Newtonian, and the filler concentrations are usually too high to ignore particle-particle interactions. A plethora of equations exist for modelling dispersions of particles. However, the best approach is to make the desired formulation and test it under real conditions, such as measuring the torque and volume throughput during extrusion, plus mould filling when injection moulding.

Compounding and Extrusion

Introduction

Extruders are cylindrical devices containing one or two screws that rotate and mix additives into the heated, molten polymer. They are very common in the plastics industry and are also used in other areas such as in the food industry. The solid polymer is fed into the hopper (a funnel at the beginning of the extruder screw) in solid form as powder, flakes, or more usually, as pellets. In the initial region the polymer is melted through heat and application of shear. The polymer or compound is exposed to extremely high shear and Hornsby has shown that much of the dispersion occurs in this initial zone. There are some reasons not to add the filler in the hopper, one is that anisotropic fillers, and especially fibres, are broken down by the high shear in the melt zone. They lose anisotropy and this results in lower mechanical performance in the composite. Another reason is that in the initial zone the filler is not yet wetted by the polymer. The harder filler types can cause rapid wear if added at this point and are usually added at a port later in the extruder where the polymer is molten. The configuration of the screw is optimised to encourage good mixing whilst maintaining good throughput. At the end of the extruder barrel the molten polymer is forced out through an aperture of some kind. Often a round hole is used, the polymer string is cooled using a water bath and then dried with air and chopped to give pellets. Alternatively the aperture may be more complex so that the final part is extruded directly. This is possible for simple geometries such as for pipes, cables and profiles.

Volume throughput

The cost of extrusion is not especially high, but as a rule of thumb one can consider that it adds about 15 Euro cents per kilo of compound. This means that although at first sight adding filler may give an apparent cost reduction, in reality the compounding step negates some of the potential reduction. For a compounder, the throughput of the extruder determines productivity and has an influence on their production costs and therefore on the price of the compound. Many scientific papers report composites with good properties achieved by good mixing. Achieving good mixing is important, but must be balanced against the need to retain maximum throughput. This is an area that deserves much more attention that it receives now as the throughput can make the

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difference between an economically viable and a non- viable compound. When comparing different fillers it is therefore not enough to consider mechanical and aesthetic aspects, but also the throughput of the extruder as this impacts the cost. Two common types of extruder are exploited industrially. These are single screw and twin crew, the latter having different variants depending on whether the two screw rotate in the same direction (co-rotating) or in opposite directions (counter-rotating). Single screw machines are less expensive to buy and maintain whereas twin screws are used when optimal dispersion is needed such as for filled polymers or for dispersing pigments in a masterbatch (pigment concentrate in polymer). It has been assumed that twin-screw extruders are intrinsically better for achieving dispersion. Recently however, that assumption has been challenged. It has been claimed that the R & D efforts have been focused on optimisation of twin screw extruders and that the relatively poor performance of single screw variants is low mainly because they have not been optimised to the same extent. Allegedly a properly tuned single screw extruder can achieve good dispersion when properly configured. This is corroborated by recent work showing good dispersion for a formulation of 40 weight % surface treated CaCO3 in PP made in a single screw extruder.

Dispersion

It is necessary to disperse fillers and pigments effectively in order to obtain the best possible performance. For fillers, impact strength, gloss and other properties are improved by good dispersion. In the case of pigments, excellent dispersion is needed to attain maximum tinting strength. Quality of dispersion can be measured by scanning electron microscopy (SEM). It is advisable to measure using two different magnifications. At low magnification, one can assess the macroscopic distribution of the filler in the composite. Then other pictures are taken at higher magnification to show the dispersion on individual particles and whether agglomerates are present. For pigments, streaking indicates uneven dispersion whereas a loss in tinting strength is observed if the pigment is not fully deagglomerated. The mechanical property most affected by dispersion is impact strength. Agglomerates act as flaws that can initiate crack formation and thus lower impact strength. Agglomerates above a certain size are to be avoided, for

PP they should be kept below about 10-30µm in size. There are many methods for measuring impact strength and some are much more sensitive to agglomerates than others.

Machine wear

Some level of machine wear is inevitable and its importance is recognized to some degree. When the barrel or screw becomes worn, the level of dispersion is diminished until at some point the machine must be stopped for maintenance. There are costs associated with spare parts and labour to install them, but the main problem is the down-time because that means a loss in productivity. Another issue is that metal

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particles removed from the extruder (or other equipment) can act as catalysts that destabilize the polymer. This necessitates the addition of extra antioxidant as a compensatory measure. Although the importance of machine wear is recognized, there are rather few studies looking at the factors contributing to it. Those studies that have been done indicate that hard, large, irregular particles cause most wear, by a gouging mechanism. Surface treated fillers that are coated with organic additives tend to cause less wear because of the soft lubricious layer around the particles, which shields the metal from the hard mineral surface below.

Thermal Properties

Thermal conductivity and specific heat capacity

The thermal conductivity of the filler influences the processing of the composite as well as the conductivity of the final material. The thermal conductivity of mineral fillers is in the range 0.02 – 3 WK-1m-1, an order of magnitude higher than for polymers. Thus the filler helps transfer heat and facilitates the heating and cooling stages during part manufacture. The reduced cooling time in particular is of value as it allows for increased productivity. It should be noted that the thermal conductivity of the composite is also determined by the thermal conductivities of the two constituents and the volume fraction of each. However, unlike for some other properties, there is not a linear relationship. The conductivity goes through a sharp increase when there is enough filler to form a continuous network (percolation threshold). After that point, addition of further filler has much less impact on the conductivity. Analogous to the electrical conductivity (mentioned later) the filler content needed to achieve percolation depends upon the size and shape of the filler particles with smaller, anisotropic fillers giving a lower percolation threshold. The heat capacity of the composite represents the amount of heat energy required to heat up and cool down a material whereas the conductivity determines the speed of the heat transfer. Lower values are preferred as it costs money to heat and cool parts. It is possible to calculate the specific heat capacity for a composite using the linear rule of mixtures if the capacities of the two phases and their volume fractions are known. Normally, units of J•Litre-1K-1 are used to express specific heat capacity. For composites however, this is not appropriate because one needs to know the heat capacity of a part whose volume is determined by the volume (not mass) of material in the mould. The volume specific heat capacities of mineral fillers (~1900-2600 J•Litre-1K-1) are similar to those of polymers (~1500-3000 J•Litre-1K-1) so fillers aid cooling in terms speed of heat removal but not through a reduction in heat capacity. There is a market for thermal pastes and composites with high thermal conductivity. This is driven by the ever-increasing heat output of processors. In order to maximise the conductivity fillers of high conductivity are used (metals, graphite, diamond and some ceramics). The particle size distribution is tuned to optimise packing and giving the maximum possible number of inter-particle contacts to help conduction.

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Thermal expansion

The thermal expansion coefficient represents the amount of expansion upon heating and contraction when cooling a material. A positive value indicates that the material expands when heated. The expansion coefficient may change versus temperature, but for the sake of simplicity we will just consider approximate values here. The expansion coefficients (CTE) for thermoplastics is usually in the range (~10 x 10-5 mm•mm-1°C-1), approximately an order of magnitude more than for mineral fillers (~10 x 10-6 mm•mm-

1°C-1) or for metals (~20 x 10-5 mm•mm-1°C-1). The CTE has practical significance because it gives an idea how much a part will shrink once removed from the mould for cooling. Amorphous polymers such as polystyrene SAN and ABS tend to shrink less on cooling than semi-crystalline polymers like PE, PP and nylon. That means that a mould designed for a polymer with a certain shrinkage level will produce out of specification parts if used with another polymer showing different shrinkage. One point to remember is that due to the macromolecular nature of polymers they do not achieve their final form instantaneously. Further shrinkage can occur for 24-48 hours after cooling of the part and so it is recommended to wait before taking shrinkage measurements. As the CTE of fillers is far lower than for polymers, the addition of mineral fillers gives a composite with less shrinkage than the parent polymer. This is useful for example if attempting to match the shrinkage of two polymers so that they can both be used successfully in the same mould. Moulds are very expensive and it is desirable to avoid investing in a new one unless there is no other option. A special case of shrinkage is warpage, where the material shows uneven CTE in different directions. The differential shrinkage causes parts to deform. This effect can be reduces using isotropic fillers but may be exacerbated by anisotropic fillers, especially fibres. Sometime filler blends are used to reach a compromise solution. One example is the use of mica / glass fibre blends. The glass fibre alone gives very good mechanical properties but may lead to warpage under some conditions. The addition of the (less anisotropic) mica reduces the warpage while maintaining sufficient mechanical performance.

Electrical properties

Nearly all polymers are good electrical insulators, hence their widespread use in cable insulation. Typical resistivities are from 1012 – 1018 Ω•cm. There are some polymers that are intrinsically conductive examples include polyaniline, polypyrrole, polythiophene and their derivatives. These are however low volume speciality materials that are difficult to process. Despite the fact the electrical resistivities for mineral fillers are not as good as for plastics, they are sufficiently high to allow mineral fillers to be used in many cable formulations. A growing area is the use of flame retardant fillers such as Al(OH)3 and Mg(OH)2. This growth is partially due to the introduction of legislation banning the use of some halogenated flame retardants. For some cable types the requirements are far stricter and in those cases calcined clay is the preferred filler as the calcining process removes much of the water and binds in some of the metal impurities.

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There are occasions when it is desirable to have some degree of electrical conductivity in a composite. Very low conductivities are needed to eliminate static build up that could otherwise cause damage to sensitive electronic components, or merely contribute to dust pick-up. Higher levels of conductivity are needed to impart EMI shielding behaviour to the material. Organic anti-static additives can be used to reduce static. They are polar additives that migrate to the surface and attract a water layer that helps dissipate charge. Alternatively, conductive fillers such as graphite, metals, or more commonly carbon black may be used. Recently, carbon nano-tubes have shown promise as their high anisotropy allows for good conductivity at low loadings. Their price is currently too high for most applications however. Analogously to thermal conductivity, the electrical conductivity varies with the volume fraction of each phase and their individual conductivities. As progressively more conductive filler is added, the conductivity of the composite remains low until some critical filler level where a continuous network of conductive particles is reached i.e. the percolation threshold. At that point the conductivity rises sharply to almost that of the neat filler and remains relatively constant as more filler is added. As for the thermal conductivity mentioned previously, percolation occurs at lower filler levels if the particles are finer and more anisotropic in shape. Typically, percolation occurs at between 10-30 volume percent filler.

Barrier properties

Thermoplastics are used very extensively as packaging for all types of goods. Sometimes they protect the goods physically and provide an attractive case. In many other instances the plastic is there for its barrier properties. Plastic water and gas pipes are used throughout the world. Another example is food packaging such as cling-film (PE) and plastic boxes (PP) for keeping food.

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Clay platelet Interphase layer

Diffusantgas

Figure 3 Aligned platy fillers are good at retarding permeation

Permeability depends on the solubility of the penetrant and its diffusion coefficient in the material. One may therefore lower the permeability of a material by lowering the solubility and / or the permeability of the penetrant. Mineral fillers are practically impermeable, liquids and gasses cannot dissolve in them to any appreciable extent, so they can be added to lower the permeability of a plastic. The filler physically blocks the path of diffusion so that the diffusing molecule is forced to take a longer path, around the particles (Figure 3). This effect is limited for isotropic fillers but becomes more effective for aligned anisotropic fillers like mica. The permeability of a composite can be calculated using an equation that allows for the reduction in permeant solubility and for the tortuosity (Equation 3). Where Pc and Pp are the permeability of the composite and the unfilled polymer respectively. The terms w

and t refer to the width and thickness of the filler and φp and φf represent the volume fraction of polymer and filler.

f

p

p

c

twP

P

φ

φ

)2/(1+=

Equation 3 Composite permeability

As mentioned previously, the addition of filler may also change the amount of crystallinity in the polymer. As polymer crystals are impermeable to low molecular weight species, an increase in crystallinity also results in improved barrier properties, through increased tortuosity. This effect is expected to be especially prevalent for fillers that induce a high degree of transcrystallinity.

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Dispersion and wetting of the filler can also affect the permeability of the composite. It has been shown that PE filled with 25 volume percent calcium carbonate was actually four times more permeable to oxygen compared to the unfilled reference PE. This was attributed to poor wetting of the filler, so that the diffusant was able to travel unimpeded along the polymer / filler interface. In contrast, stearic acid coated calcium carbonate at the same loading resulted in three times lower oxygen permeability than the unfilled PE. Similarly, Tiburcio and Manson showed that the water vapour permeability of glass-bead filled phenoxy films decreased sharply as the degree of adhesion between the filler and the matrix was increased. In some cases, it is desirable to increase the permeability of a polymeric material. One example is breathable films. For example, calcium carbonate filled PP films are first made by solvent casting, or extrusion casting or as blown film and subsequently stretched to delaminate the filler – polymer interface. High filler loadings are used to ensure interconnecting voids, giving unimpeded diffusion.

Mechanical properties

Introduction

The mechanical properties are often important for the selection of a particular polymer for a certain part or product. Each application will have its own unique set of demands so that polymer and filler must be chosen to tune the material for the intended use whilst maintaining a reasonable cost. There are many mechanical properties to consider and only the main ones will be covered here. Adding filler usually changes all properties, some improve and others worsen. One cannot optimise all properties and that means it is vital to cleary define the key properties for the material in a certain application. Only then can one use knowledge of polymers and fillers to make the right compromise in tailoring the material. There are many parameters to play with and many potential formulations that will satisfy the criteria. The best solution is the one that meets the demands at the lowest cost. For visible parts, the appearance of the material must be considered. Addition of fillers and pigments (coloured fillers) can alter the aesthetics and this must be considered together with their effect on mechanical properties.

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Stress or Force (MPa)

Strain or elongation (%)

Increasing temperature or

lower testing speedBrittle failure

Ductile failure

Break or

ultimate

Yield

Energy to break

Figure 4 Tensile testing

Modulus – tensile and flexural

Most fillers are minerals and have much higher moduli than the polymer into which they are placed. The filler raises the modulus, the amount of stiffening depends on the volume percent of filler and its shape. As seen in equation 4, the modulus increases linearly with the volume fraction of filler. Usually modulus is plotted versus the weight percent of filler, which is to be avoided as it gives confusing curved fits.

fpfc EEE φφ +−= )1(

Equation 4 The dependence of composite modulus on volume fraction of filler

As seen, the isotropic fillers such as calcium carbonate and dolomite give the least stiffening. Platy fillers like talc and mica give more stiffening per unit volume of added filler. Glass fibres have the highest aspect ratio of common fillers and this gives the highest level of stiffening. Particle size has no direct effect on the modulus of thermoplastics and neither does level of adhesion. This latter point can be demonstrated by looking at a formulation with and without a coupling agent. The coupling agent improves adhesion (as seen by an increase in yield strength) but there is no effect on modulus. The reason is that modulus measurements are done at very low strains where the adhesion between filler and polymer is not broken. There is always some level of adhesion due to van der Waals forces and additional adhesion due to the compressive force created when the polymer cools and contracts around the filler particles. The orientation of anisotropic fillers can change the modulus. This is especially prevalent in injection moulded parts because the high shear during injection orientates the filler particles. The result is a material that has different moduli in different directions. This

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can cause problems but can also be beneficial if the injection points are carefully chosen to take advantage of the improved stiffness in certain areas. Compression moulded specimens are largely free from orientation. The effect of some common fillers is shown in Figure 5. It must be remembered that the values will depend on the exact grade of polymer chosen, the grade of filler and the processing conditions. Some fillers vary widely in their aspect ratio from one grade to another and it is a mistake to consider talc, mica or glass fibres as generic products.

0

1

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3

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0 5 10 15 20 25

Filler Volume (%)

Modulu

s (GPa)

Glass FibreMineral FibreMicaTalcCaCO3Wood FibreNanoclayWollastonite

Figure 5 The effect of common fillers on the tensile modulus of PP homopolymer

Heat deflection temperature (HDT)

The HDT gives an idea of the maximum temperature that a material can withstand before it starts to deform under load. Mineral fillers increase HDT and the trends are similar to those for modulus. The more anisotropic fillers are best. Ideally one should perform creep measurements where the deformation over time at some elevated temperature is recorded. However, in practice, HDT is quicker and simpler and therefore far more widespread. Interestingly, HDT for amorphous and semi-crystalline polymer responds differently to filler addition. For amorphous polymers, filler addition increases HDT. The maximum HDT is for high loadings of high aspect ratio filler, as occurs near the Tg of the polymer, i.e. the temperature at which the polymer phase softens. For semi-crystalline polymers the maximum HDT is also for high loadings of anisotropic filler, but the limiting HDT is near the melting point of the polymer (Figure 6).

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40

60

80

100

120

140

160

0 5 10 15 20 25 30 35

Filler Volume (%)

HDT 1

.8 M

Pa (°C

)

Glass Fibre

Mineral Fibre

Mica

Talc

CaCO3

Wood Fibre

Wollastonite

Figure 6 The effect of common fillers on the HDT of PP homopolymer

Yield strength

For plastics the yield strength is taken as the maximum point on the stress-strain curve and is usually measured in tensile mode. It is not the true yield strength as defined for metals and this may lead to some confusion. In any case the yield strength is a measure of the maximum force the plastic can withstand before it is irreversibly damaged. It is one of the most important properties for many types of part. As for modulus, the yield strength is best for the most anisotropic fillers. Unlike of the modulus adhesion is important with better filler-polymer adhesion giving higher yield strength. Yield strength is measured at higher strains where the bonding between the particles and the polymer is challenged. It is observed that the isotropic fillers usually do not improve yield strength and indeed may decrease it as in the example below (Figure 7). Often the anisotropic fillers are called reinforcing fillers because they improve both modulus and yield strength. That classification is not advisable because talc and mica may not reinforce in a given polymer depending on the aspect ratio of the particles. Grades of talc or mica with higher aspect ratio will give better performance although at a higher cost. Conversely, an isotropic filler such as calcium carbonate may reinforce if the level of adhesion between the filler and the polymer is increased sufficiently. The level of adhesion may be improved by greatly increasing the amount of contact between the filler and polymer. Thus nano-particles can give improved yield even if the amount of adhesion per unit area of filler-polymer contact is unaltered. The other approach is to add a coupling agent to improve the adhesion. So, for example, adding maleated PP to a normal calcium carbonate filled PP formulation can result in reinforcement. These principles apply to other polymers and fillers and allows nano-particles to perform well.

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0

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30

40

50

60

70

80

90

0 5 10 15 20 25

Filler Volume (%)

Yie

ld S

tress (M

Pa)

Glass FibreMineral FibreMicaTalcCaCO3Wood FibreNanoclayWollastonite

Figure 7 The effect of common fillers on the yield strength of PP homopolymer

Impact resistance (toughness)

Impact resistance is another key property. It gives an indication of the materials resistance to rapid deformation. The mechanical response of polymer is very time dependant because of the extreme length of the polymer chains. They cannot instantly flow to accommodate deformation like small molecules can. Imagine how quickly water adapts to the shape of the container it is poured into. In contrast a molten polymer flows very slowly taking many minutes to flow out to give a flat surface. This behaviour is mirrored in a polymer’s response to mechanical deformation. A polymer may be ductile during tensile testing, which is a slow process. At that testing speed the polymer chains have time to flow and adapt to the imposed force. The same polymer may be brittle when exposed to impact because the chains cannot move and dissipate the energy of the impact. In general, the addition of filler will worsen the impact resistance of a polymer for two reasons. One is that the filler gives an increase in viscosity, i.e. it further restricts the polymer’s ability to flow and adapt to change. The other reason is that the filler is brittle and cannot itself absorb the energy of impact. Adding a stiff filler reduces the amount of polymer in the test specimen and thereby there is less material capable of dissipating the impact energy. There are very important exceptions. For example, it may be that the addition of filler changes the fracture mechanism of the polymer. An example of which is given in Figure 8 where some fillers are very beneficial to the impact strength of PP homopolymer. The fillers initiate crazing of the polymer (micro void formation upon stress) and the formation of the craze zones adsorbs a great deal of the impact energy. There is at present no way to predict impact resistance and there are so many exceptions that it is

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hard to make any generalisations. It can be said that the various ways of measuring impact strength give some indication of the relative performance of thermoplastics and composites. However, in the final analysis the best way to be sure is to do impact testing on the final part, for example a drop test simulating real use.

0,0

2,0

4,0

6,0

8,0

10,0

12,0

14,0

16,0

0 5 10 15 20 25

Filler Volume (%)

Impact Strength

(kJ/m

²)

Glass Fibre

Mineral Fibre

Mica

Talc

CaCO3

Wood Fibre

Wollastonite

Figure 8 The effect of common fillers on the impact resistance of PP homopolymer

Fatigue

It has been estimated that of all failures of plastic parts 30 % are due to fatigue. People are familiar with the term metal fatigue, which has caused airplane crashes. Plastics also suffer from fatigue, namely the repeated application of stress. Even when the stress is far lower than the yield or break stress of the plastic it may eventually cause a breakage after some large number of cycles. Unfortunately, despite its importance, fatigue is a neglected area. Like creep, the measurements require a lot of time and effort and this hold back progress. The only advice is that if a part is to be exposed to repeated loading and unloading then it should be designed with very large safety margins. The effect of fillers on fatigue is presently unknown.

Effects of filler on the polymer phase

Introduction

In previous sections we have seen that the properties of a composite can often be modeled using the properties of each component weighted for its volume percentage in the material. That approach assumes that neither component was altered in the composite compared to its original properties. In fact, in some instances that assumption is invalid, for example some fillers can change the crystallisation behaviour of some thermoplastics and thus the properties of the polymer phase are not those of the virgin

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material. This and other examples will be covered in this section. One must be aware that these complications may exist because it helps in interpreting studies on filled polymers and because the knowledge can be of use in composite manufacture.

Nucleation

Nucleation is the initial stage of crystal formation and is therefore applicable only to semi-crystalline polymers. Thermoplastics are melted to process them and must be cooled until they solidify enough for the part to be removed from the mould and handled. In injection moulding and other forming processes, the necessity to wait for solidification is undesirable because it is not possible to make a new part while the existing one is still occupying the tool / mould. For semi-crystalline polymers the solidification is largely due to the formation of crystals, which are stiff compared to the surrounding amorphous polymer phase. Nucleating agents encourage the formation of crystals at an earlier stage during cooling, namely at higher temperatures. This enables the parts to be removed earlier with a corresponding improvement in productivity. There is no successful theory that allows prediction of nucleation so a trial and error approach is the only option. Furthermore nucleating agents are specific to each polymer. There is no universal nucleating agent. Chemical nucleating agents that dissolve in the polymer have been commercially available for many years. Similarly, mineral fillers are used as nucleating agents. Fine talc for example is a good nucleating agent for PP (Figure 9). This has been utilised for many years. What is not well known is that dolomite is also a nucleating agent, albeit a weaker one than talc.

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Untreated

Surface treated

Crystallisation Onset

Temperature (C)

120

122

124

126

128

130

132

134

Unfilled PP

Calcium

Carbonate

Dolomite

Talc

Silica

Mineral

Fibre

Mica

Figure 9 Effect of fillers on the nucleation of PP

Transcrystallinity

It has been observed that some fillers (and other surfaces) cause such intense nucleation in a polymer that the result is a special type of crystallinity. The effect is quite rare and is specific to various combinations of filler (usually glass or carbon fibre) and polymer. In this case the fibre surface nucleates crystal formation at many sites along its length. The crystallites begin to grow but they are so close together that they impinge at an early stage and thereafter and forced to grow perpendicular to the fibre. Normally, polymers crystallise in spherical form to give “spherullites”. The transcrystalline sheath around the polymer is composed of the same type of crystal phase and the normal spherullites, but there is a high level of crystallinity and it is orientated in a particular way, as mentioned. This may be observed by optical microscopy under polarised light or by SEM. In theoretical studies on fibre filled thermoplastics one must be on the lookout for this effect to ensure that the mechanical results are interpreted correctly.

Interphase

There is always some amount of interaction between filler and polymer even if no specific covalent bonds are formed. The ubiquitous van der Waals forces are enough to provide significant attraction between two materials. The effect of this interaction is to provide some adhesion and so there is an adsorbed polymer layer on the filler surface. The adsorbed layer is restricted in movement and therefore has different properties than

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those of the surrounding free polymer. The modified polymer layer is termed the “interphase”. For normal composites the volume fraction of interphase is very low and so it has little influence on the properties of the composite. However, for finer fillers, especially nano-fillers, more surface area is present and the effect of the interphase becomes more important. Indeed, the interphase is responsible in part for the somewhat unexpected properties of nano-composites. For example, the interphase is one reason for the good barrier properties of nano-composites. The restricted polymer layer has less free volume that the bulk and this reduces permeability. That plus the well-known tortuosity effect combine to give the surprisingly good barrier properties.

Surface science aspects

Introduction

To understand the properties of a composite, one must have an idea about the properties of the polymer (polymer science) the fillers (materials science) and the interface between the two (surface and colloid science). This makes the composites area an interesting and challenging one. Many studies fail to consider all three of these aspects and consequently the results may not be interpreted correctly. On the other hand, there is the opportunity to master all of these areas and thereby develop better materials with superior performance. In this section there is a brief mention of some aspects that should be considered. Specialised texts should be consulted for an in-depth treatment.

Surface energy and surface tension

These two terms refer to the same phenomenon. Surface molecules have a different energy and behave differently to those in the bulk. This affects wetting and adhesion to surfaces. The units are the same for both parameters. SI units for surface tension are mN/m and this term should be applied for liquids. Surface energy applies to solids and units are mJ/m2. Older units include dyne/cm and ergs. Fortuitously, all of these different units give the same numerical value for a given surface.

Wetting and Spreading

When mixing the filler into the polymer melt wetting is the process by which the liquid polymer spreads on the filler surface and displaces the air. This process should ideally happen quickly and completely so that there are no trapped pockets of air. There is much confusion and no general agreement about wetting of fillers. Fillers have high surface energies compared to polymers, this gives a thermodynamic driving force favouring wetting. However, in reality there are major complications. Firstly, high energy surfaces such as those of fillers, attract and adsorb a layer of hydrocarbons from the atmosphere. This means that although when created they have a high surface energy, the actual effective surface energy is low because of the adsorbed layer. The result is that the driving force for wetting by the polymer is reduced or removed. The other complication is that compounding is dynamic so that equilibrium conditions do not

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apply and it is not appropriate to consider only the thermodynamics, the kinetics also come into play.

Adhesion

The adhesion between filler and polymer is important for some properties. Modulus is measured at very low extension so adhesion is not tested. On the other hand yield strength depends on adhesion. Adhesion, like wetting depends on the surface energies of the two materials, plus any specific bonding between them such as covalent or Lewis acid-base interactions. The level of adhesion can be modified using additives that work at the polymer-filler interface. These include coupling agents and dispersants. Good adhesion is not always desirable, more important is the ability to tune the adhesion depending on the required properties.

Dispersion and agglomeration

Good dispersion is essential for composites with good properties. Several properties rely on dispersion. Impact strength decreases rapidly when large particles or agglomerates are present. These acts as flaws, weakening the polymer to impact by concentrating stress and initiating crack formation. The larger the agglomerate is, the greater the loss in impact strength. Gloss also depends on filler dispersion. Small, well dispersed particles are best. Dispersants help to improve gloss by reducing agglomeration.

Surface treatments – dispersants and coupling agents

The use of surface modifiers is common as it provides yet another opportunity to tailor the properties of the composite. These additives are divided into two classes as discussed below (Figure 10).

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Dispersant Coupling Agent

Figure 10 Dispersants versus coupling agents

Dispersants

Dispersants are organic additives that adsorb to the filler particles. They are bi-functional, that is, part of the molecule must have a strong affinity for (bond to) the filler whereas the rest of the dispersant must be soluble in the polymer. A typical example is stearic acid, which is an effective dispersant for calcium carbonate and several other fillers. The dispersant coats the particles helping to disperse them and helping to prevent reagglomeration. Note that dispersants do not form a bond with the polymer and that is what differentiates them from coupling agents. Good filler-polymer bonding is not always desirable. Dispersants are generally cheaper than coupling agents and are used widely.

Coupling agents

To function as a coupling agent an additive must bond both filler and polymer, thereby bonding the two together. The two most common types are silanes (applied to the filler) and functionalised polymers (added to the polymer). It should be noted that whether a silane or functionalised polymer actually does its job as a coupling agent depends on the surface chemistry of the filler and the nature of the polymer. An additive that works in one formulation may be completely ineffective in another. Silanes are described as coupling agents, but a given silane will only work for a limited number of filler / polymer combinations. The ideal coupling agent should not couple during compounding as that would raise the viscosity of the compound unacceptably. When the product cools then the coupling agent must function as intended.

Aesthetics

Introduction

Often the primary function of a part is simply to look good, or to cover some less attractive area. In other instances one must combine good mechanical properties with aesthetic considerations such as colour, gloss and scratch resistance.

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Colour / pigmentation

Thermoplastics usually have no intrinsic colour. They tend to be either completely transparent and colourless, or they may be somewhat milky with a yellow tinge. The lack of colour is an advantage as the polymer can be modified using additives to obtain virtually any colour. Two types of colourant exist. Dyes dissolve in the polymer and as they are not particulate fillers will not be discussed further here. The other type is pigments. These are organic or inorganic coloured particles. They affect mechanical properties just as any other filler would, but are usually used at low dosage levels so their effect on mechanical properties is not appreciable. An exception is the case when the pigment nucleates crystallisation in semi-crystalline polymers (see the section on nucleation). This may give rise to warping as the part cools and is generally undesirable. To obtain the maximum tinting from a pigment one must disperse the particles very effectively. As pigments are far more expensive than fillers or the polymer it is desirable to ensure good dispersion to minimize the required pigment level.

Surface finish & gloss

The surface plastic parts may be smooth or textured to alter its appearance and how the part feels when touched. In either case it is essential that the polymer flows well so that it conforms to the surface of the mould or roller it is formed against. This is necessary to accurately transfer the desired texture to onto the plastic surface. Glossy surfaces are popular as they are often associated with quality and are perceived as being easier to clean. Unfortunately, addition of filler may have a negative impact on gloss. The magnitude of the effect is not easy to predict as it depends on many parameters such as mould and polymer melt temperature. Filler level, particles size and shape also play a role. Finally, the shape of the part, speed of injection, position of the gates and the finish on the mould surface all have an effect. The net result is that in one mould it may be that high gloss is possible for one part at 40 weight % filler whereas another part may show poor gloss at just 10-20 % filler. This area is not well studied. There is data to show that finer filler treated with dispersant gives better gloss. In practice this effect may be small or even negligible compared to the other factors mentioned. In some cases the filler is needed to give sufficient mechanical properties, but the filler reduces the gloss unacceptably. Further work must be done to find ways to overcome this limitation.

Scratch and abrasion resistance

Surface finish and gloss are important for the as produced part and make products appealing to the customer at the point of sale. Thermoplastics are relatively soft and may become scratched or abraded in use. This is to be avoided as far as possible so that the initial attractive appearance of the products can be maintained. There are two distinct aspects to consider. One is the physical scratching such as the depth and number of scratches or the amount of material removed. In many cases the physical scratching is of little concern as long as the customer is not able to see the

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scratch. Fillers may make scratches more visible and this is of major concern for the automotive industry where talc filled PP copolymer is used. The talc is exposed upon scratching to leave a highly visible white line. Additives and other filler types (such as wollastonite) are used to ameliorate the problem. The area is complicated because there are physical and aesthetic aspects to scratching and because there is no good, universal method for assessing the scratches. There are a multitude of methods, but many are invalid. Some companies have designed their own internal methods that are used to evaluate the scratch resistance of different materials.

Stabilisation & recycleability

Introduction

Contrary to public perception, polymers are not stable indefinitely. All organic materials are susceptible to attack by oxygen, ozone, UV light and high temperatures. Many of the most common thermoplastics could not be used at all without additives to increase their resistance to degradation. Once properly stabilised, these same materials may last many tens of years depending upon the stabiliser type, amount and the exposure conditions. The term stabiliser and antioxidant are used interchangeably to describe this type of additive. Although used in low amounts, stabilisers are expensive compared to thermoplastics and so the goal is to minimise costs by keeping stabiliser levels down.

The effect of filler chemistry and impurities on stability

Mineral fillers come from natural deposits and even after processing they are rarely completely pure. An exception is precipitated fillers such as certain grades of calcium carbonate. The impurities may be very harmful to the stability of plastics. It is well known that low levels of transition metals such as copper, iron, chromium and vanadium can catalyse the degradation of polymers. In fact, this effect is used to degrade polymers purposely in some applications. In general though, the goal is to preserve the polymer through its service life and preferably have enough stability left so that the plastic can be recycled and used again to make a new part. In cases where the filler destabilises the polymer there are four approaches to rectify the problem. One is to add more antioxidant, which adds to the material price. The second is to add a specific type of antioxidant called a metal deactivator. These adsorb on the filler surface blocking the metal ions from attacking the polymer. The third way is to use some other (non antioxidant) additive, such as an epoxy, that coats the filler and physically blocks it from coming into direct contact with the polymer. Lastly, one may choose another supplier or filler grade that has less effect on stability. Currently the only way to know whether a particular grade destabilises a polymer is to measure the stability of the composite, or that of the filler dispersed in some material chemically similar to the polymer. In practice there is a belief that the concentration of iron is a gauge of the destabilising tendency of a filler. Therefore one must pay a premium for grades of talc with lower levels of iron. Unfortunately, there is no direct correlation between the level of iron and the propensity of the talc to destabilise a polymer. For example, pure iron oxide can be used in a polymer with little or no effect on stability. Likewise, some grades

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of mica are very high in iron but this does not cause stability problems in the composites. There may be two grades of talc with the same iron content, where one does not destabilise and the other one does. This is because it is not the amount of iron (or other transition metal) that counts, it is the form that the iron is in that matters. For example, the oxidation state of the metal and whether it is at the surface of the mineral particles.

The effect of antioxidant adsorption on stability

Antioxidants usually contain some polar groups that are attracted to the filler surface and bound there. This bound antioxidant is then unable to perform its function in protecting the polymer. This effect is very well-known. For thermosetting polymers and rubbers an analogous effect occurs whereby the filler adsorbs curing agents. The adsorption of Irganox 1010 (a very common antioxidant) on calcium carbonate is shown as an example (Figure 27). Twenty weight percent of calcium carbonate (surface area 5 m2g-1) is able to adsorb 350 ppm of Irganox 1010. Thus one is faced with adding more antioxidant to compensate for that which is deactivated. This adds significantly to the formulation cost. The other choice is to use a surface treated grade of filler, where the surface treatment will block antioxidant adsorption. Again the treated filler will increase the cost of the material but it will also bring other benefits in terms of processability, mechanical properties and gloss.

Concentration Irganox 1010 added (ppm)

OIT

(m

inute

s)

0 500 1000 1500 2000

10

20

30

40

50

60 Irganox 1010 in squalane

Supernatant

Figure 27 The effect of calcium carbonate on the stability of squalane

Environmental Issues & Recycleability

In recent years there has been a growing awareness of environmental issues and a wish to look for ways to create a sustainable way of living. Environmental awareness is relatively new and still in its infancy. At present there is a focus on these issues, but the

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real facts and the way forward are not yet clear. Much of the driving force is controlled by politics and people’s intuition about what is “friendly” and what is not. For example, the public perceive PVC as an unfriendly plastic when in reality there is little or no evidence to support that view. Likewise, many consider that plastics create a waste problem or that our valuable oil resources are being used to create polymers. These views are not supported by fact either. Lastly there is a tendency to revert to the use of natural products like wood and other plant derived fibres as fillers under the supposition that natural products are automatically more friendly than synthetic materials. There are now tools to quantitatively assess the relative environmental impact of different materials and processes. As these are applied a very different picture is emerging, one that is largely counterintuitive. When all factors are considered such as raw materials, energy use, lifetime, pollution and end-of-life it has been revealed that plastics are not bad from an environmental standpoint. In fact polyolefins, such as polyethylene and polypropylene have an extremely low environmental impact. These are the number one and two thermoplastics and together they account for a large proportion of all thermoplastics used today. The other polymers also do well in terms of life cycle analysis (LCA). If the polymers themselves are not a problem then we must consider what the influence of filler addition might be. As far as the author is aware there has not been any study devoted to this question so it is only possible to mention some points to consider. One of the perceived advantages of thermoplastics is that they can be recycled simply by grinding and melting them to reform them into new articles. This is an overly simplistic view as there are many complications. Products are not at present designed to be disassembled and recycled. However, new legislation is in place to force manufacturers to collect their used products and deal with the waste. A minimum amount of the product must be recycled, approximately 70 percent by weight for household appliances for example. This means that companies will now have to ensure that materials are sufficiently stabilized for use and then recycling one or many times. The automotive industry has taken the lead and has already homologised their materials selection so that just a few standard materials are used. Other industries are likely to follow as using a few standard materials reduces cost and facilitates sorting of the used materials for recycling. A filled thermoplastic can still be remelted and reformed just as the unfilled polymer. The different filler types and levels could complicate sorting as some classification processes rely on flotation. Unfilled PE and PP are readily sorted because they float on water. Mineral fillers increase the density so that most PE and PP composites do not float. Although isotropic fillers such as calcium carbonate have rather low performance, these fillers are not broken down by reprocessing. In contrast, the anisotropic fillers, especially glass fibres, have high performance initially but the anisotropy is progressively lost as the material is recycled multiple times. The result is that a calcium carbonate filled material can be reused after some years of use to make the same part whereas glass fibre filled materials probably cannot as the recycling process lowers their performance appreciably.

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Natural fillers such as wood fibres, hemp, cotton, bamboo and others are under investigation as potential “friendly” fillers. The idea is that they are natural and come from a renewable source so they are probably friendly to the environment. However, these materials are heat sensitive and cannot be easily recycled without damaging them. Closer examination may well reveal that adding these natural fibres actually prevents recycling of polymers that could have been recycled either unfilled or filled using conventional mineral fillers. More research needs to be done in this area and it must be done soon because the products we make today need to be recycled in some years time. That means that we need to know the best solution now.

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Conclusions

The use of thermoplastics has grown inexorably since their introduction less than a hundred years ago. Typical growth rates at present are 5-10 percent per annum. Thermoplastics are a widespread class of material, owing their success to a combination of formability, good properties and low cost. It has long been recognised that the discovery of new major plastics is unlikely; instead the focus has been on tuning existing plastics by improved polymerisation methods and by the skilful use of additives. The addition of fillers provides a way of tuning the properties of thermoplastics, thermosets and elastomers (rubbers). Fillers are fallaciously viewed as passive substances added primarily to reduce cost. This is occasionally true, but generally fillers are added to improve performance. Recently the term “functional fillers” has come into use to emphasise the active role that fillers have in altering the properties of the neat plastic. The filler changes all properties of the plastic, mechanical, physical, electrical, thermal and aesthetic. This presents a bewildering array of choices, but also a great opportunity to gain a competitive advantage through skilful formulation. The area of composites is even newer than that of plastics and we are far from a complete understanding of all aspects. Recent advances in nano-composites show that there are still new frontiers to be investigated. The future for composites is bright. The use of fillers is plastics has been growing at a healthy rate for many years and will continue to do so. Environmental concerns are helping as banned halogenated flame retardants are replaced by flame retardant fillers, while plant derived fillers gain popularity and as nano-composites begin to enter the market. © Chris DeArmitt 2009