Nanofillers - Improving Performance & Reducing Cost - Nanopinion

ObservatoryNANO Briefing September 20111BRIEFING No.21NANOFILLERS ‐ IMPROVING PERFORMANCE AND REDUCING COSTFillers are one of the most common raw materials in the world with 50 million tonnes produced everyyear 1 . Fillers are mainly utilised to reduce the consumption of expensive binder material and to improvethe physical properties of the resulting composite material. They are widely used in paper, rubber, plastics,adhesives & sealants, paints & coatings, and also in concrete. Today fillers are undergoing a paradigmshift; their former primary function to lower the production costs is changing towards a distincttuning of material properties such as compression strength, processability, and flame retardancy. This isespecially true for ultra‐fine grades or so called nanofillers which provide an improvement in propertiessuch as material reinforcement due to their larger surface area. In general, a smaller filler particle sizewill have a greater impact on the material properties when the particles are properly dispersed. Therefore,nanofillers may provide a route towards future material innovations, cost efficiency, and competitiveness.This BRIEFING will discuss the purpose, uses and potential of a number of nanofillers beforeexamining the economic impacts and challenges facing their route to wider commercialisation.BackgroundNanofillers can be either small spherical particlesor rod shaped objects and flakes with at least onecritical dimension below 100nm. In general, theproperties of filler materials are determinedthrough particle size, particle geometry and chemicalcoatings, or functionalisation. Smaller particlesprovide new functionalities such as control ofrheological properties, improved mechanical properties,an increased transparency or electrical conductivity,or enhanced flame retardancy. They canbe also used to ensure the free flow of powdersand to prevent the settling of pigments. Fillers arewidely used in the construction sector in adhesivesand sealants, in paints and coatings, but also inplastics, rubber and concrete.Synthetic fillers are now gaining more importance;they allow the production of smaller particle sizeswith controlled surface chemistry or tailoredchemical functionalisation. Ultra‐fine grades or socalled nanofillers are under investigation. Besidesdownsizing existing filler materials, completelynew technological approaches can also be observedsuch as organic‐inorganic hybrid materialsin polymers or nanotubes as reinforcing filler materialin concrete. However, the share of nanofillersin today’s construction filler market is negligible.An example of well established nanofillers canbe found in another sector; carbon black filledtyres for longer life and improved performance.Particle SizeThe filler particle size determines the “inner” orspecific surface area which is the potential contactarea between filler material and surroundingbinder matrix. Since nanomaterials tend to agglomerateor may already occur in agglomeratedstates, the resulting surface area is largely affectedby the degree of exfoliation and dispersion. Fullyexfoliated and perfectly dispersed nanofiller willCONSTRUCTIONhave the greatest effect on the physical properties.A comparison between different particle sizes isshown in Figure 1. The specific surface area is increased100‐fold when going from 10µm to 100nmwhile keeping the theoretical volume or the fillinglevel constant.Figure 1: Different filler particle sizes at the samefilling level. Going from 10µm to 100nm: a milliontimes more particles exhibit a 100‐fold increasedinner surface area (adapted from 2 ).GeometryThe particle geometry will also strongly influencethe properties of the nanocomposite material.Elongated nanostructures such as carbon nanotubesexhibit high aspect ratios. Higher aspect ratioswill increase the reinforcing ability on the surroundingmatrix material. Therefore nanotubes orother elongated nanofillers excel over sphericalparticles in terms of reinforcement. Nanotubes canbe considered as (quasi‐)one‐dimensional fillerparticles in terms of reinforcement. Similar nanomaterialsare nanowhiskers 3 , nanorods, nanowiresand nanofibres which have also been reported asnanoscopic reinforcing filler material for polymers.Natural occurring representatives of a two dimensionalfiller material are layered silicates or socalled nanoclays. The most widely used nanoclaysin material applications are so called montmorillonitesas flame retardant in polymers.

ObservatoryNANO Briefing September 20112NANOFILLERS ‐ IMPROVING PERFORMANCE AND REDUCING COSTA common approach is the production of threedimensionalfiller particles by either grinding, millingor precipitation techniques. In contrast, alsobottom‐up approaches have been studied wherethe filler material is incorporated as a buildingblock on the molecular level. This case can be regardedas zero‐dimensional nanofillers. In this regardinorganic‐organic hybrid materials have beeninvestigated intensively. Figure 2 gives an overviewof the different filler particle geometries.Figure 2: Different filler particle geometries.POSS moleculesPolyhedral oligomeric silsesquioxane (POSS) moleculesrepresent a comparatively new approach as abuilding block for new nanocomposite materials.The biggest advantage of using a molecular approachcan be found in a true dispersion at thenanometre level. POSS molecules can be used asreinforcing filler in plastics to increase the mechanicalstrength. They are also relevant as abrasionprotection in paints and coatings and as fireretardant material in polymers.Precipitated Calcium Carbonate (PCC)Calcium carbonate (CaCO 3 ) is by far the mostwidely used filler material in the world, particularlyas a filler in paper and plastics. Traditionally, CaCO 3is mined from natural resources (limestone andprocessed by milling techniques. The resulting materialis therefore called ground CaCO 3 (GPP). Itssynthetic counterpart is called precipitated CaCO 3(PCC) exhibiting finer particles sizes and smallerparticle size distribution. It is available in fine andultra‐fine grades whereby the latter one is sometimesreferred to as nano‐precipitated CaCO 3 . Particlessizes range from 60nm to 150nm. It is usedas filler in adhesives and sealants to adjust therheological properties and also in plastics to improvemechanical strength and durability.Fumed SilicaFumed or pyrogenic silica is a form of noncrystallinesilicon dioxide. Primary particle sizes arebetween 5‐30 nm which aggregate into larger agglomerateswhile maintaining a fairly large specificsurface area of 10‐600 m²/g. 4 Fumed silica iswidely used as anti‐caking additive and thickeningagent with thixotropic property (becomes liquidwhen stirred or shaken but return to original statewhen at rest). It is also used in paints, coatings,adhesives and sealants but also as filler in plasticsand rubber. Many different untreated and treatedgrades with varying properties are on the markettoday. Fumed silica is also used in thermal insulationmaterial such as vacuum insulation panels 5 .Precipitated SilicaPrecipitated silica is produced from aqueous sodiumsilicates precipitated with sulphuric acid. Incontrast to fumed silica precipitated silica consistsof porous particles with a primary particle size ofabout 5‐100 nm which form large agglomerates ofseveral micrometres. The specific surface area canbe as high as 200m²/g. 6 Precipitated silica is mainlyused as reinforcing filler in the rubber industry butalso as filler in plastics and sealants (silicone rubber)and adhesives (epoxy).Precipitated Barium sulphatePrecipitated barium sulphate (BaSO 4 ) is called“Blanc fixe” due to its whitening ability. It is usedas brightener or white pigment. Blanc fixe is mainlyused as filler in paints and coatings but also in plastics.The production of ultrafine or nanoprecipitatedbarium sulphate (nanoPBS) has beeninvestigated recently 7 . However, particle sizes ofBlanc fixe are generally well above the nanometrerange so is not considered as nanomaterial.Titanium DioxideTitanium dioxide (TiO 2 ) is naturally occurring inthree different forms; rutil, anatase, and brookite.Rutil is mainly used as white pigment in paints andcoatings while the anatase modification is widelyused in photocatalytic applications. TiO 2 is alsoused as filler in silicone rubber 8 and thermoplasticssuch as PVC.NanoclaysNanoclays are plate‐like nanoparticles of naturaloccurring layered silicates. Clay minerals are dividedin numerous classes such as bentonites orhectorites. Bentonites mainly consist of so calledmontmorillonites, the most widely used nanoclayin material applications today. Montmorillonitesare build up of stacked nanoscopic aluminosilicateplates each around 1nm in height and 1 µm in diameterand are used as filler in plastics. Organicallymodified montmorillonites, so called organoclays,are used to increase the flame retardancy of polymersespecially in cables; the flame propagation issignificantly reduced and no dripping of burningpolymer is observed 9 . However, aluminium trihydroxide(ATH) currently dominates the world marketfor fire protection agents.Carbon nanotubesCarbon nanotubes (CNT) have been investigatedintensively due to their unique mechanical and

ObservatoryNANO Briefing September 2011NANOFILLERS ‐ IMPROVING PERFORMANCE AND REDUCING COSTelectrical properties. A key application of multiwalledcarbon nanotubes (MWNT) is seen as functionalfillers in plastic composites and paints 10 .They have been also studied as reinforcing filler inconcrete and have been proven to prevent crackpropagation 11 .Carbon BlackCarbon black (CB) is a (nano‐) particulate amorphousform of carbon, mainly used as a filler inrubber and as pigments. It is also used as a filler inplastic and paints to induce electrical conductivity.It has additionally been proven as a UV‐stabilizer inplastics application improving the weatherability 12 .However, the market for non‐rubber applicationsis comparatively small.GrapheneBesides Carbon black, graphite is also used as fillerin paints and coatings inducing electrical conductivity,thereby obtaining antistatic property. Its 2‐dimensional counterpart is called graphene whichcan be considered as a single sheet of graphite.Graphene could also serve as filler for conductiveand reinforcing applications; however, researchand production techniques are still in their infancy.AerogelsAerogels are nanoporous materials with the lowestbulk density of all solids. They have been investigatedas thermal insulation material due to theirextremely low thermal conductivity. In granularform aerogels can also be used as filler in concreteforming a lightweight construction material withunique thermal properties 13 .Economic impactsThe global filler market was about 50 million tonnesin 2006 with a market size of around €25 billion.Europe ranked second with 15.5 million tonnesafter Asia with 19 million tonnes. The annualgrowth rate of the European filler market is about3% 1 . Fillers represent one of the largest technicalmaterials in the world; however, today’s nanocompositemarket is comparatively small (Figure 3).Nevertheless, the global nanocomposite marketsize is predicted to increase to €1.47 billion by2015 14 . Market figures differ depending on theclassification of nanocomposite materials andsource though.The world market for precipitated CaCO 3 was 13million tonnes in 2007 15 , mostly due to the paperindustry. The share of nanoscale precipitatedCaCO 3 is significantly smaller; one of the world’sbiggest producers is the Chinese based ShengdaTechwith a current production capacity of250000 tonnes. The world market of fumed silicareached €980 million in 2010. Major producersinclude German based Evonik and Wacker togetherwith US‐based Cabot and Japanese Tokuyama(Figure 4).Figure 4: Fumed silica market 2010 by company(adapted from 17 ).The world market of CNT is expected to grow from€1.6 billion in 2010 to €3.3 billion in 2016 18 . Majorproducers are US based Cnano, Belgium basedNanocyl and German based Bayer Materialsciencewith a production capacity of 500 tons, 460 tonnesand 200 tonnes respectively. French based Arkemahas announced to boost its production capacity to400 tonnes within a short time. The global nanoclaymarket was around €139 million in 2009 and ispredicted to grow moderately to around €208 millionby 2015 19 . Major manufacturers include theUS based Nanocor, Chinese based FCC Inc and UKbased Elementis Specialities plc amongst others.The biggest manufacturer of precipitated silica isRhodia based in France. Other producers areEvonik, Germany, PPG Industries and Tulco Inc US,and Wuxi Quechen Silicon Chemical Co.,Ltd. China.3Figure 3: The European market for nanocompositesis predicted to grow from 23 000 tonnes (2006) to120,000 tonnes in 2016 1 .EU Competitive PositionThe nanocomposite market is mainly driven by theUS and Europe. The US is the present leader; however,Europe and Asia are predicted to catch up incoming years. Europe also having a strong positionin the production of CNT. Regarding fumed andprecipitated silica Europe is leading followed bythe US and Asia; however, Europe’s position isweak in nanoclays and nanoscale CaCO 3 . Asia leadsthe graphite and carbon black sectors.

NANOFILLERS ‐ IMPROVING PERFORMANCE AND REDUCING COSTTechnology Readiness Levelslong‐term environmental implications.ObservatoryNANO Briefing September 20114Figure 5: TRL levels indicating the developmentlevel of filler technologies.ChallengesTechnologicalA major barrier for the wider commercialization ofnano‐enabled fillers is the poorer dispersion abilityof ultra‐fine grades or nanomaterials. In this regard,a suitable treatment or functionalisation ofnanoparticles or aggregates depending on the intendeduse is helpful. In addition, higher costs ofraw materials and treated grades are a disadvantage.An increase in the brittleness of nanocompositeswith high filling degrees has also been observed.Further key challenges include exfoliationand dispersion of nanomaterials.Environmental, Health & Safety ImplicationsNanomaterials in powder form can easily becomeairborne. For fillers, this applies at the stage ofboth material production and of composite productionand processing. Nanomaterials used asfillers include both high volume production materialsfor which there is already considerable historyof toxicity research (e.g. PCC, silica), as well as newmaterials (e.g. CNT, graphene) for which potentialhazard has been highlighted and is currently subjectto extensive investigation. Excessive exposureto any of these nanomaterials has potential to resultin risks to health and the environment. Whilstfor many of these materials (e.g. PCC), previousexposures have been observed with no significantill effects, for some new materials (e.g. CNT), a potentialfor much greater toxicity has been identified,particularly with respect to inhalation exposure.In line with the precautionary principle, appropriateoccupational health and safety mechanismsshould therefore be in place in order to preventexposure. Life cycle assessments, includingrecycling processes, are also required to preventSummary• Nanofillers are characterized by their particlesize, specific surface area, particle geometry andchemical functionalisation.• Smaller filler particle sizes provide new functionalitiessuch as improved mechanical strengthand control of rheological properties.• The high specific surface area of nanomaterialsprovides a route towards novel properties anddecreased filling levels.• Needle‐like nanofillers have a stronger impacton the mechanical properties.• Hybrid materials provide a route towards fullydispersed nanomaterials and superior nanocomposites.• Critical issues are exfoliation and dispersion ofnanomaterials, and a poorer processability.• Due to some EHS concerns, appropriate occupationalhealth and safety mechanisms should bein place in order to prevent exposure.ContactMichael Gleiche, VDI Technologiezentrum GmbH,gleiche@vdi.deReferences1 Market Report “Fillers” (Marktstudie Füllstoffe (UC‐805)), CeresanaResearch, 2007.2„Reinforcing mechanisms on the macro‐, micro‐ and nanoscale inheterogeneous polymer materials“ (Verstärkungsmechanismen aufMakro‐, Mikro‐ und Nano‐Längenskalen in heterogenenPolymerwerkstoffen), Habilitation thesis, Gyeong‐Man Kim, Universityof Halle3Yang Li and Arthur J. Ragauskas, Advances in Diverse Industrial Applicationsof Nanocomposites, ISBN 978‐953‐307‐202‐9, InTech, March20114http://www.freepatentsonline.com/20040253164.pdf5„MICRO‐NANO POROUS MATERIALS FOR HIGH PERFORMANCE THER‐MAL INSULATION“ CSTB French Building Research Institute, 2nd InternationalSymposium on Nanotechnology in Construction, Bilbao 2005.6http://www.iri.net.in/conference/images/stories/pdf/IRI/Presentation/Technical/18/3/Laurent.Guy.EA.090.pdf7“Precipitation of Barium Sulphate Nanoparticles in Microemulsion:Experiments and Modelling”, PhD thesis of Dendy Adityawarman,University of Magdeburg.8G. Momen and M. Farzaneh, Rev.Adv.Mater.Sci. 27 (2011), 1‐13.9http://belgianpolymergroup.be/Flame/Beyer.pdf10J.M. Makar and J.J. Beaudoin, Proceedings of 1st InternationalSymposium on Nanotechnology in Construction June 23‐25, 2003,Paisley, Scotland11Raki, L. et al, Materials 2010, 3, 918‐94212J. V. Accorsi, KGK Kautschuk Gummi Kunststoffe 54. Jahrgang, Nr.6/200113Lorenz Ratke, Beton‐ und Stahlbetonbau 103 (2008), Heft 414http://www.electronics.ca/presscenter/articles/1404/1/Global‐Nanocomposites‐Market‐to‐Reach‐13‐Billion‐Pounds‐‐by‐2015/Page1.html15http://www.roskill.com/reports/industrial‐minerals/pcc/16http://www.shengdatechinc.com/files/09‐07‐09%20SDTH%20profile.pdf17http://www.wacker.com/cms/media/documents/investorrelations/factbook2010.pdf18"Global Carbon Nanotube Market ‐ SWCNT, MWCNT, Technology,Applications, Trends & Outlook (2011 ‐ 2016)" published by MarketsandMarkets(http://www.marketsandmarkets.com)19http://www.marketresearch.com/product/display.asp?productid=2873964