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AddTime:2016-01-06

Fillers in Focus

 

What are fillers?

Plastics are an irreplaceable part of our everyday lives due to their excellent properties, processability and versatility. That  versatility  comes, to a large  extent,  from  the  use  of additives and in particular, from the addition of fillers which  can  enhance the intrinsic properties of plastics, compensate for deficiencies, or introduce completely new properties not attainable in pure plastic materials. This article looks at the latest news with an emphasis on specialty fillers.

 

What types are there?

Any particulate material can potentially be used as a filler for plastics and elastomers. Minerals are often used, and as there are tens of thousands of different minerals, the possibilities are almost endless. However, not all candidates are ideally suited to use as fillers. The best materials tend to be those with the following properties:

 

          Readily available Worldwide

          Chemically inert and insoluble

          Low hardness to avoid undue wear

          Safe, i.e. non-toxic and nonflammable

          Free from transition metal impurities that can degrade plastics

 

 

Thus, of the countless potential options, a narrower list emerges, including such materials as calcium carbonate, dolomite, silica (as beads or fibers), carbon black, mica, wollastonite and kaolin. That small group represents by far the majority of fillers by volume usage or by total value (estimated to be over 5 Billion Euros per year). They are used primarily to tune mechanical properties of polymers whereas other, more esoteric fillers, are used to achieve other performance goals.

 

Three of the main weaknesses of plastics are:

 

  1. Specific modulus / stiffness (stiffness per unit weight)

2. HDT / Vicat softening temperature (maximum temperature for load bearing parts)

3. Creep (slow flow of the plastic under load)

        

 

It turns out that fillers help overcome all three of these three drawbacks, so it is easy to understand why filled plastics have been so successful.

 

Conventional Fillers 

The effect of conventional fillers on the mechanical properties of thermoplastics is summarized in the following table. Isotropic (round, or cubic) fillers include calcium carbonate, dolomite, glass beads, fly ash and silicas. Common platy fillers are kaolin and mica. Short fiber fillers include mineral fibers and wollastonite. The most dramatic   property enhancements come from the high aspect ratio fibers such as glass fiber, carbon fibers, graphite fibers and Kevlar fiber.

 

 

 

Property                                                     Isotropic                     Platy                                                                                            Fibers

Modulus                                                                                                          ↑↑                         ↑↑↑

Yield Strength                                                                                                   ↑↑

HDT amorphous polymer                                                                                        

HDT semi crystalline polymer                                                ↑↑                         ↑↑↑

Impact resistanc                                      or                                                      or

Elongation to break                                                                                                      ↓↓                         ↓↓↓

Permeability                                                                                                                                                                                                                                                          ↓                              ↓↓                              

 

 

 

Dispersants help processing by lowering viscosity and raise impact resistance by breaking up agglomerates that can act as stress concentration sites where cracks form. Coupling agents are used to improve filler-resin adhesion which improves the strength of the composite particularly in hot, humid conditions.

 

We will now look at some individual fillers to see the property improvements that each type brings.

 

Calcium Carbonate

Although fillers like calcium carbonate, kaolin, mica, wollastonite and silica have been around for decades, new advances are still occurring regularly, either to improve performance in existing applications or to enable their use in completely new areas. Imerys is one of the most respected names in the field of engineered fillers where careful control of particle size distribution and surface treatment lifts the filler to new heights (www.imerys.com). Whereas their FilmLink® products dominate in the breatheable films market, they have now developed a new FiberLink™ range of engineered, surface treated calcium carbonates for use in fiber and non-woven products. The presence of even traces of large particles can cause serious production problems during fiber spinning. Renita Anderson explains that the FiberLink™ products eliminate that problem by controlled top- cut and through optimized surface treatment that enables excellent dispersion, breaking up any agglomerates.

 

 

 

 

There are many advantages such as increased production rate due to the high thermal conductivity of the filler, reduced carbon footprint compared to an unfilled PP and also a welcome reduction in raw materials costs.

 

Renewable Fillers

 

Fly Ash

RockTron, the specialist eco-minerals producer, has announced further impressive results, substituting fillers such as talc and carbon  black with its MinTron™ product range.

 

Significant improvements in both scratch resistance and emissions have been observed when working with producers of Polypropylene (PP), replacing talc in a PP co-polymer. The objective was to meet the specification of an automotive OEM (Original Equipment Manufacturer) and the substitution of MinTron™ solid glass microspheres for talc resulted in the requirements of the specification being exceeded. In addition, the Heat Deflection Temperature (HDT) was increased.

   

 

 

These successes create the possibility of producing interior, under bonnet and exterior components using MinTron™. MinTron™’s low  density (2.1-2.3  gcm-3) offers weight reduction possibilities  by replacing  talc (density 2.7 gcm-3)  and, being 100% recycled with a low carbon footprint ( 0.08 kg CO2 / kg product),  MinTron™ can also help the automotive OEMs realize their desire to use more recycled materials in their vehicles.

 

 

Another recent development is the partial substitution of carbon black with MinTron™ by an OEM tyre manufacturer, which resulted in improved physical properties for certain parts of the tyre compound. This is leading on to further development and testing, with the possibility of tyres containing MinTron™ being manufactured and under test by autumn 2010.

 

Nano Fillers

 

Halloysite

Nanofillers can give remarkable properties at low filler levels. However, such small particles can be difficult or impossible to disperse leading to problems, especially with impact resistance and elongation to break. Recent advances have helped with the dispersion issue. Whereas platy type nanoclays are hard to exfoliate, these issues can be avoided using tubular nanoclays instead. Halloysitetubular nanoclay is easier to disperse and does not   require exfoliation to achieve good properties. Applied Minerals

(www.appliedminerals.com) have shown that 35-40 weight % of Halloysite can be incorporated without the need for surface treatment. Modulus and strength are both improved but without sacrifice in impact resistance or weld-line strength.

 

 

Halloysite can also be used as a flame retardant synergist, increasing decomposition temperature, reducing peak heat release rate, and improving char density. Other enhancements include nucleation of crystallization for reduced cycle time and the possibility to encapsulate additives within the hollow core of the tubules. In particular, there is a lot of interest in slow release of active ingredients which can be anything from fragrances to insecticides.

 

 

Particle shape                                                                                                                                                                                                                    Halloysite

  Dimensions                                Length 0.5-3 microns, Diameter  50-70nm

                                                       

Material                                                                                                                                                                                                                                                                   Silicate

  Density                                                                  2.52 gcm-3

 

 

 

Nano Hydrotalcite

Sasol (www.sasol.com) have been developing and marketing nanoparticulate   materials for many years. Their Boehmite aluminas are well known as they are easy to disperse and are very pure to the synthetic route used to produce them. More recently, their hydrotallcite products have gained increasing attention. In contrast to the well-known montmorillonite nanoclays composed of anionic sheets, the hydrotalcite are just the opposite.  The sheets are cationic in nature and can be readily dispersed in polymers. Surface treatments are available whereby anionic organic molecules bond to the surface and prevent agglomeration.

 

 

Sasol’s Olaf Torno points to a recent publication entitled “The Influence of the Compatibilizer on the Morphology and Thermal Properties of Polypropylene-Layered Double Hydroxide Composites”. Untreated nano hydrotalcite was successfully dispersed in PP with a corresponding boost in mechanical and barrier properties, comparable to that obtained using nanoclays. Dodecylbenzene sulfonic acid acted as a dispersant whereas maleated PP acted as a coupling agent by bonding to both the filler and the PP matrix. These results were achieved using only a Brabender mixer and could be expected to be even more impressive with more thorough dispersion, for example using a twin screw extruder.

The  Influence of the Compatibilizer on the Morphology and Thermal Properties of Polypropylene-Layered Double Hydroxide Composites Serena Coiai, Elisa Passaglia, Alexandra  Hermann, Sylvain Augier, Daniele Pratelli, Rouven C. Streller POLYMER COMPOSITES 2009 DOI 10.1002/pc.20857

Specialty Fillers

Micaceous Iron Oxide

 

These are often dual or multifunctional and blur the line between fillers and other types of additive. A prime example is  MIOX  micaceous iron oxide, a filler that  has enjoyed commercial  success in coatings  for decades  and  is now  making  inroads  into the plastics market.  Due to its platy shape, MIOX enhances modulus, yield strength   and barrier properties. Because, finer grades of MIOX have a characteristic red color they are also used for the pigmentation they provide. Courser grades are black in color, again useful as a pigment and for UV protection. Christian Rupp of Kärntner Montanindustrie   (www.kmi.at) says that the versatility of MIOX does not end there. Two newly developed   grades have proven to be extremely effective process aids for thermoplastics like PE, PP and nylon.

 

Dramatic reductions in cycle time, thermal conductivity and shrinkage have been reported in a recent study. MIOX is a very inert material and can be used even in very high temperature plastics like polysulfones and PEEK.

 

 

Nano Silica

 

Nan-O-Sil is another specialty filler that has the ability to act as a process aid for thermoplastics including polyolefins, nylons and polyesters. Richard Oder of Energy Strategy Associates (www.nanosilasd.com)  explains that even at loadings of just 0.4-0.8 weight percent, Nan-O-Sil can greatly lower cycle times as shown in independent   studies. Not surprisingly, the product has enjoyed commercial success for several years at major compounders and continues to penetrate new markets. Because   Nan-O-Sil  is  an engineered silica, it  does  not  give  any  color  of  its  own,  a  big  advantage  in  some applications. In fact addition of Nan-O-Sil can actually improve color. When used in pigment masterbatches, Nan-O-Sil boosts pigment strength allowing more intense colors or a reduction in the amount of pigment needed to achieve a set color.

 

Specialty  Acid Scavenger

 

NX     Ultra  is a   new product      from     Stabilization Technologies (www.stabilization-technologies.com). Fillers are used in elastomers to help processability and to tune hardness. NX Ultra goes beyond the role of a typical filler as it also acts as an acid scavenger. Although several fillers are acid scavengers, NX Ultra is unique in its performance in fluoropolymers and fluoroelastomers. Joe Webster of Stabilization Technologies explains that most acid scavengers like calcium carbonate or hydrotalcite are basic in character and actually promote degradation of fluoropolymers at high temperatures. NX Ultra is not itself basic so it does not induce thermal degradation and yet, due to its special molecular structure, it can trap acids liberated as the polymer begins to degrade    and prevent them from catalyzing further degradation. The result is fluoropolymers  that are stable at higher temperatures for longer periods. Other interesting technologies from Stabilization Technologies include a range of zeolites that can stabilize dyes and additives for plastic film that help prolong the shelf-life of flowers and foods.

 

PP filled with PP fibers

 

Curv® is a revolutionary material from Propex and perhaps the most novel use of a filler (www.curvonline.com). Curv is supplied as a sheet and is made up of 100% polypropylene where a woven PP fabric has been pressed and heated to melt the fiber skin and fuse them together. The resultant material can be thought of as PP filled with PP fibers and the properties are truly remarkable. The material has been commercially available for some time and is now enjoying commercial success.  With a modulus and strength far higher than PP, one can already begin to see the advantages. However, it doesn’t end there, as Kirk Smith explains. Curv has spectacular impact resistance. Whereas PP becomes brittle around 0°C , Curv retains and even gains impact resistance as the temperature is lowered down into the cryogenic domain.  An impressive  demonstration  of “Curv  appeal”  is the new  range  of Samsonite Cosmolite suitcases  marketed as “The  Strongest  and  Lightest Samsonite  Ever”. Naturally, the light weight is appreciated   by customers and the superb impact resistance means that there has never been a single instance of failure. Other applications for Curv include speaker cones, soccer shin-pads and personal armor.

 

 

 

 

Property                                                                                                                                Value 

 

Tensile Modulus (MPa)                                                                       3500

 

Tensile Strength  (MPa)                                                                      150

 

Elongation  to break (%)                                                                   17.0

 

Puncture Impact (J)                                                                              26

 

Density (gcm-3)                                                                                                                                                                                                                                                                                                                                                                        0.92

Properties of a 1mm thick sheet of Curv

 

 

 

Conclusion

As you can see, the fillers arena is full of innovation in all areas from the established fillers to new entrants. If this article has whetted your appetite to know more  about  the latest developments in filled  plastics then you might want to  attend  the upcoming AMI conference Minerals in Compounding to be held in Atlanta USA on December 1st  and 2nd. You will get a chance to see the new developments and also to meet many of the companies mentioned in this article so you can discuss face to face. As conference Chairman, I am looking forward to seeing you there!

 

Dr. Chris DeArmitt

Phantom  Plastics LLC

Consultant to the Plastics Industry

+1 601 466 8342

chris@phantomplastics.com

 

Chris DeArmitt is one  of the  top  names  in plastics,  additives  and  problem  solving. With experience   from  companies   like  Electrolux  and  BASF,  he  has  now  founded   his  own company,  Phantom  Plastics. With over 30 publications  including  numerous  patents, book chapters   and  encyclopedia   articles,  he  puts  his  expertise   to  good   use  helping   clients around   the  World.  Chris’s  track  record   of  innovation   includes   two  Innocentive  open innovation   cash   prizes   and   the   development  of  many   revolutionary   new   products including  plastics, smart materials and more.

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