EU filler focus

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Published: Wednesday, 26 October 2011

Professor Roger Rothon reports on the themes and revelations at this year’s Eurofillers conference, held 21-25 August in Dresden, Germany



Dealing with all aspects of filled polymers, Eurofillers 2011 was the eighth conference in the series first started at Mulhouse in 1995, following the merger of the preceding Moffis and Filplas conferences. This was the first time that the conference had been held in Germany, despite the dominance of this country in the filled compounding business (it is estimated that 25% of European compounding is carried out in Germany).

Eurofillers 2011 was organised this year by the Leibniz-Institute of Polymer Research, Dresden and held under the joint chairmanship of Professors Heinrich and Wagenknecht. It was a great success, despite the difficult economic times. The conference was exceptionally well attended, with about 180 delegates from 25 countries.

Being a European conference, most of the speakers and delegates were from this region. The majority (almost 50%) were from the host country, Germany; but there were good representations also from France, Italy and Poland. The UK representation was disappointing, given that they were one of the founders of the Eurofillers conference, but this continues a trend seen over recent years with a decline in the number of UK academic institutions active in this area. While primarily an academic meeting, there were a pleasing number of industrial attendees (about 25).

Eurofillers has always been an important forum for presentations from academics working in the field of filled composites and the event is a valuable pointer to emerging themes in the area. As usual the conference was themed and those chosen this time were: processing and applications, compounding and properties, fillers in elastomers, nanocomposites, functional fillers, carbon nanotubes, filler surface modification, rheology and biofillers and biopolymers.

The number of quality papers that were accepted was so high (over 90, including seven plenaries and seven keynotes) that the conference had to use parallel sessions despite being held over four days. Posters have always been a feature of Eurofillers, mainly to encourage young researchers from universities and this meeting was no exception, with over 70 on show. All were of very high quality and generated a lot of lively discussion. As always there were prizes for the best posters.

Ever since the first Eurofillers, there has been a steady decline in presentations dealing with conventional fillers and a rise in those dealing with nano-fillers and nano-composites. This evolution continues and there were few papers dealing with established fillers such as calcium carbonate, conventional clay or talc; with much more attention being given to natural fibres and to nano-technologies. This report tries to focus on the presentations that the author found of most relevance to the minerals industry.

Conventional fillers

The conventional filler area was mainly covered by the present author (Professor Roger Rothon) in the first plenary session. He gave an account of the development of filler markets up to the present day, identifying some of the winners and losers, and he also tried to identify future trends.

According to Professor Rothon, annual world consumption of particulate fillers in all types of polymer is about 24m. tonnes, with Europe accounting for about 5m. tonnes. The two biggest ones by volume are carbon black and ground natural carbonates. Looking at it by value, carbon black is out on its own - with the natural carbonates vying with aluminium hydroxide and precipitated silicas for second place.

Elastomers are the main polymer type using fillers, with about 60% of the total by volume. He pointed out that nano-fillers were nothing new, with carbon black, fumed silica and precipitated silica and calcium carbonates being long established examples. He added that, while establishing important niche applications such as gas barrier film and flame retardant synergists, the nano-clays had not lived up to initial high expectations with world use in filler applications probably under 20,000 tpa. While agreeing that carbon nanotubes were very interesting materials with a future in advanced composites, the current price was far too high and was unlikely ever to be low enough for general filler applications.

Green (energy) tyre technology, silane coupling agents and metal hydroxide flame retardants were given as examples of success stories, while the main emerging trends were thought likely to be:

  • Increased polymer prices making the use of fillers more attractive;
  • Slow growth in European markets, except for precipitated silica, which would continue to benefit from the ‘green’ tyre application;
  • Rapid growth in emerging markets with emphasis on local mineral sources for the lower cost fillers (wollastonite in India for example);
  • Demand for fillers with a low carbon footprint and especially from recycled sources. These were not easy to find, but fly ash being promoted by RockTron was one example. The company has a major resource and good beneficiation technology and was already working with compounders and end users such as Ford Motors;
  • No major new filler or modifier types emerging, although the mineral halloysite was worth watching as a potential nanotube with good dispersability and low cost relative to other types of nanotube. As always with natural minerals the size, location and quality of the deposit was key to successful development and Applied Minerals in the USA claims to have a deposit that meets all these criteria.

Other presentations to address conventional inorganic filler applications included Dr Chris Liauw on the use of coupling agents in fly ash polypropylene composites and their effect on mechanical properties and matrix crystallinity. The best properties were found using Solplus C800¨ an unsaturated carboxylic acid coupling agent.

Dr Graham Lees spoke on the potential for upgrading the performance of mixed polyolefin waste streams by using calcium carbonate/ coupling agent additions.

Nariman Yousefi presented on the effect of surface treatment on the processing and properties of highly filled barium sulphate sound-insulating composites.

There were a number of papers dealing with the use of natural fibres, especially ligno-celluloses. Their use in biopolymers to make fully biodegradable composites was of particular interest.



Professor Roger Rothon, giving a plenary on conventional
fillers, at the Eurofillers 2011 conference in Dresden,
Germany. 180 participants attended the four-day event.
IPF Dresden e. V.


Nano-fillers

Achieving adequate dispersion is one of the issues limiting the use of nano-particles in polymers and several presentations addressed this, including three of the plenary lectures.

In her plenary Professor Ica Manas-Zloczower of Case Western University, USA, described the present understanding of the fundamentals of dispersing fine particles into polymers with special emphasis on carbon nanotubes. She also described the possibility of treating the particles with a responsive material which could vary the degree of dispersion in response to an external stimulus such as temperature.

In another plenary Professor Linda Schadler from the Rensselaer Polytechnic Institute, USA, described the design of interface modifiers for use with nano-particle systems. Mixed short and long chain modifiers were found to be especially useful. Her work is especially focused on dielectric and optical properties of nano-composites and these properties can be enhanced by correct choice of modifier.

Finally Professor Robert Schuster from the German Institute of Rubber Technology gave a plenary describing a new technique called continuous dynamic latex compounding (CDLC), primarily intended for dispersing nano-clays into elastomers without the need for intercalation of organic pre-treatments.

The CDLC technique makes use of the availability of many elastomers in latex (emulsion) form and combines them with montmorillonite slurries. There have been previous attempts to do this, including by the present author, but they have had limited success. The difference with the CDLC approach is that after the aqueous slurry of the clay is mixed with a rubber latex, the mixture is pumped through a flow reactor designed to provide elongational and turbulent flow. The clay is swollen by the water enough for the plates to become delaminated and dispersed into the polymer during this mixing process.

Morphology results were provided showing that a high degree of dispersion and exfoliation could be achieved. The use of the CDLC technique provides a significant decrease in polymer film permeability at low loadings (the best result so far achieved is a 55% reduction in permeation coefficient at 3% volume fraction, corresponding to an estimated aspect ratio of about 90 for the clay plates).

While the nano-filler topic in the previous Eurofillers was mainly focused on nano-clays, these were of lesser importance this time, with the main focus being on carbon nanotubes and on layer dihydroxides of the hydrotalcite type.



Delegates discuss some of the 65 posters presented
at Eurofillers 2011.
IPF Dresden e. V.


Carbon nanotubes

While of great scientific interest and potential for reinforcing and other polymer applications, carbon nanotubes (CNTs) are still very expensive and only produced in small quantities. Production costs are reducing, but it will be several years before the manufacturing processes will evolve to the point where they can be considered for more than very high added-value applications.

Most CNTs are produced as powders, but a group at Cambridge University under Professor Windle have been focusing on making continuous yarn, as this has the potential to be used in conventional reinforced composite processes employing polymer back diffusion to preserve fibre alignment. Professor Windle gave a very impressive plenary describing the outlines of the process which is now in small-scale pilot plant operation. It is expected that a kg/day pilot plant will be operational by 2013 and there are plans for a 1,000 tpa plant costing an estimated $50m. to be constructed by 2016. Professor Windle also addressed the cost issue and pointed out that as CNT production used a cheap feedstock (methane) and had similarities to carbon black production, it should in principle be less expensive to produce than carbon fibre.

Layered double hydroxides

Layered double hydroxides (LDH) of the hydrotalcite family have established a significant market as PVC stabilisers following the pioneering work by Kyowa Chemicals, which has production facilities in Japan and Europe. LDH are fairly easy to produce, have a tuneable composition and layer density and have potential for delamination and dispersion similar to the nano-clays and several groups reported work with these materials.

In his keynote presentation Dr Labuschagne from the University of Pretoria, South Africa, described a zero-effluent dissolution-precipitation method for the manufacture of LDH products. This process is described in patent application WO 2006/123284 A2. The production of the commonest hydrotalcite LDH used (magnesium aluminium hydroxy carbonate) can be cited as an example of the process.

Magnesium oxide and aluminium hydroxide are mixed with water and sodium bicarbonate and subjected to hydrothermal treatment, followed by filtration, washing, drying and calcination. The magnesium oxide can be made from magnesite and the carbon dioxide generated in this step can be used to regenerate sodium bicarbonate, and water can also be recycled. Dr Labuschagne went on to describe an Mg/Al/CO3-LDH made by the process and described its optimisation for use as a heat stabiliser in PVC. He also described making nano-composites in polyamide and other polymers.

Professor Leroux from University Blaise Pascal, France gave another keynote lecture concerning the importance of correctly modifying the LDH materials to ensure optimum dispersion into, and interaction with, the polymer matrix. The use of modified LDH materials for controlled release was also described.

Nano-pigments

Nano-pigments are becoming of increased interest and were addressed by two papers.

In his keynote Professor Walter Caseri from ETH Zurich described how the optical properties of particles change as their size decreases. In particular, scattering decreases and composites with randomly dispersed particles with diameters below about 25 nm can be virtually transparent. Sunscreens using nano-particle titanium dioxide are a well-established example of this.

Professor Caseri went on to show how transparent polymers with effective refractive indices outside of the normal range can be produced using this principle. These are useful for optical products such as Bragg reflectors and lenses. Titanium oxide hydrates have been found to be easier to make for this purpose than titanium dioxide and are being used to produce polymeric materials with refractive indices up to 2.1. He also described the use of nano-pigments as dyes and how effects such as reversible colour switching were possible. A potential use of this was in liquid crystal display (LCD) screens. The titanium oxide hydrates turn blue under UV irradiation (due to partial reduction of Ti IV to Ti III) and this can be reversed by exposure to water. This effect might be useful in sensors or in photochromic clothing.

Christain Wilms from Aachen University presented work on nano-scale luminescent pigments which are expected to give better luminance, lower pigment dosage and better light, heat and wet fastness than conventional systems. Among the materials being investigated are zinc sulphide doped with copper or manganese, strontium aluminate doped with rare earths and dyes encapsulated in silica nano-particles. Identifying appropriate dispersing agents is a key part of the work. Intended applications are warning and security systems, clothing and paper.

While fire retardancy featured as an application area for filled polymers, there was relatively little discussion of traditional fire retardant fillers such as aluminium and magnesium hydroxides, with the main emphasis being on nano-technologies.

In his plenary Professor Giovani Camino from the Polytechnic of Turin in Italy spoke about how concerns over the potential negative environmental effects of flame retardants had driven European regulations since the year 2000. Some halogenated compounds had already been banned and others were currently undergoing a risk assessment procedure.

The use of brominated flame retardants is also discouraged by Directive 2002/96/EC of the waste electrical and electronic equipment regulations (WEEE) where it has become mandatory to separate brominated fire retardant plastics prior to recovery and recycling of end of life electrical and electronic equipment.

This has, of course, led to increased opportunities for flame retardant fillers such as aluminium and magnesium hydroxides; but Professor Camino focused his talk on the prospect of using nano-particles of various types to improve flame retardance by promoting the formation of surface ceramisation and charring. According to Professor Camino, we now have, for the first time, materials available in which a small amount of filler (typically 2-3%) significantly reduces fire hazard while simultaneously improving other material properties and with low environmental impact.

Finally it was announced that Eurofillers 2013 will be held in Bratislava, Slovakia at the end of August 2013. The themes will be similar to those at Eurofillers 2011.

Contributor:
Professor Roger Rothon, Rothon Consultants and Manchester Metropolitan University, UK.