摘要：
    For the rubber technology the urgent challenges are to use more conscious existing raw materials, to explore the functionality of nanoscale fillers and to develop efficient strategies for filler dispersion at low-energy consumption and cost. The expectations related to the use of nanofillers are directed to interfacial effect that can change mechanical properties significantly as well as permeation resistance. For achieving these goals among others the role of polymer-filler interaction has to be understood in more detail. In this respect major contributions from the surface specific area, the shape (anisometry) and surface activity has to be considered. Even at dimensions were classical rules continue to apply, particle size reduction and the increased fraction of atoms at the interface will bring about significant changes in material properties.

    By investigating the effects of nanofillers with high surface specific area but relatively homogeneous surface energy site distribution in comparison to carbon black with relatively moderate surface specific area and heterogeneous surface energy site distribution it can be demonstrated to which extend the novel nanofillers can offer advantages, were they fill an existing gap or were are unexpected limitations. For this comparison have been selected multiwalled carbon nanotubes, pristine montmorillonite (MMT), industrial furnace blacks (CB) and precipitated silica.

    These nanofillers offer not only the chance to mechanically reinforce polymers at far less volume fractions alone or in combination with conventional fillers, but they offer the possibility for preparing elastomers with anisotropic mechanical properties, or in the case of layered silicates for efficient permeation barriers. The advantages of both groups of new fillers is the large surface specific area (>250 m2/g) and the high aspect ratio (100-1000). However, quantitative differences will arise from particle shape, surface properties and the final in-polymer morphology of the filler.Irrespective of the type of the nanoscale filler and its provenience the major challenge in achieving the desired goals in elastomeric materials is to provide both a high degree of dispersion and a strong polymer-filler phase adhesion.

    The main focus of the presentation is to emphasize common features as well as discrete system specific aspects in the mechanical behaviour and transport properties of  the nanocomposites con-tainning fillers with different shape, as-pect ratio, surface functionality and de-gree of dispersion.

    To visualize the effect of the different preparation techniques on the morpho-logy of the nanocomposites, ultramicro-tomed cryosections of cured samples were examined by TEM (Fig. 1). The investigation the MMT/Rubber nano-composites obtained by means of CDLC reveal a high concentration of exfoliated platelets

    The filler loading and the states of dispersion achieved with the employed mixing techniques result in a significant increase of the viscosity and the storage mo-dulus G’ of the mix (Fig. 2). The resistance to shear deformation of the melt is more pronounced when the amount of exfoliated MMT or the dispersed CNTs  platelets increases. Investigations of the storage modulus G¢ and loss modulus G²of the non-cross-linked melts by RPA underscore the reinforcement at much lower volume fractions than for conventional fillers and the typical decrease in the filler networks’ storage modulus as a function of strain amplitude (Payne effect).

    The formation of a filler network is derived for CNTs and CB from electrical conduc-tivity measurements and for MMT from the scaling behaviour of the Young’s Modulus and G’, respectively. For constant mixing conditions in the internal mixer the following material parameters have been identified to play a determinant role are (i) chain length (or vis-cosity) of the polymer, (ii) the polarity, (iii) type of functional groups, (iv) tube diameter and (v) functional groups present on the CNTs surface. It was found that for constant mixing time and rotor speed the percolation threshold (PT) occur within a narrow concentration range (i.e. NR=1.2, FKM=1.2, Q=1.3, NBR =1.5, HNBR =1.8 vol.%) Furthermore the PT decreases with increase of ACN content in NBR and HNBR, indicating the specific interaction of nitrile groups with p-electrons of the CNT surface. It was found that an additional mixing stage on the two roll contribute significantly to better dispersion and a shift of the percolation towards smaller CNT concentrations. The effect is even more pronounced for CNTs dispersed by latex compounding.

    The percolation threshold for MMT/rubber nanocomposi-tes, determined from the change of G’ as a function of the filler volume fraction, was found to occur at even lower  concentrations than for CNTs. Above the PT the storage modulus G¢ increases exponentially in all systems, following the scaling law: G’ ~ fa The exponent a has not a constant value. For CNT- and MMT-compound the exponent is higher  than for CB filled systems. 

    The reinforcement effects observed in the dynamic-mechanical properties are found in the characteristic variables of the stress-strain behavior: Young’s modulus, stress values, tensile strength. All these values are superior for properly dispersed CNT/Rubber and MMT/Rubber systems (Fig. 4). To achieve similar high mechanical values 5-8 times higher CB loadings are necessary. It is observed that CNTs with a small tube diameter provide much higher reinforcing effects than the ones with large diameter, indicating an important quality criterion for CNTs. The effect is attributed to the higher filler surface specific area and the surface activity of these CNTs. Typical differences in stress-strain behaviour between CNT/Rubber and CB/ Rubber are shown in Fig. 4. 

Remarkable improvements of the mechanical properties were observed for hybrid compounds were small amounts of CNTs (≤ 5) were added to Silica- or CB-filled compounds. Either the high aspect filler is incorporated into the conventionally filled masterbatch or the filler is added as an ingredient in the compound in the vulcanized systems synergistic effects can be observed especially in terms of a substancial improvement of the stress values and electrical conductivity.Besides an increase in Young’s modulus, the stress values (e <250%) provided by 2.5 vol.% CNTs to 20 vol. % CB in the compound, the dynamic cut growth resistance measured with the Tear Analyzer demonstrates a higher tear energy and a 5 times lower cut propagation. The effects are attributed to an improved dispersion of the CNTs and to bridging effects between CB aggregates in the rubber matrix.

However, compounds made from MMT as well as from CNTs show as a characteristic difference to CB filled compounds considerably higher values for the compression set and residual elongation after extensive multi-hysteresis experiments (Fig. 5). This difference is attributed to the special surface energy site distribution. Both nanofillers can be considered to not have a larger share of high energy sites on their uniform surface. Therefore molecular slippage can occur much easier on such filler surfaces than on CB.

Due to the outstanding high surface specific area of CNTs and exfoliated MMT significant interfacial effects can be observed: (i) reduced chain dynamics in spin-spin relaxation time of MMT filled compounds, (iii) solvent up-take in equilibrium swelling experiments and (iv) transport phenomena.

As a consequence of the large polymer-filler contact surface formed in CNT and MMT-compounds even at far less volume fractions, the rubber matrix demonstrates a significant lower degree of swelling. Only with 10 times higher loadings of CB necessary such low values of the degree of swelling can be achieved. 
  Support for the major significance of well-dispersed MMT platelets is demonstrated in diffusion experiments by both a significant increase in “time lag” and a reduction in mass flow. The result points to the contribution of two factors: the high aspect ratio and the size distribution of the highly exfoliated platelets in the flow stream during the CDLC process. Support for the major significance of well-dispersed MMT platelets is demonstrated in Fig. 6

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个人简介：

Date of birth: 08.09.1942 in Bucharest (Romania)

Office: Deutsches Institut für Kautschuktechnologie e. V. (DIK)

Private: Eupener Straße 33, 30519 Hannover, Germany

Education:

Dipl.-Chem. (1960-1967)

Institute of Organic Chemistry, University "Al. J. Cuza" Yassy (Romania)

Dissertation: 1984 "Thermodynamic Investigations on polystyrene-solvent Interaction",Univ. Freiburg, (Prof. Dr. H.-J. Cantow)

Scientific and educational activities:

1969 - 1980 Researcher at the Institute of Physical-Chemistry, Academy of

Science (Bucharest, Romania)

1980 - 1984 Researcher at the Institute of Macromolecular Chemistry (Freiburg, Germany)

1984 - 1992 Head of the Department "Chemistry and Physics of elastomers" at the German Rubber Institute (DIK)

Director of the DIK since September 1992 until 2010

2010-2012  Member of the DIK Board

Since 2012 Consultant to Lanxess

Lectures at Institutes and Universities

since 1987 Institute of Macromolecular Chemistry, University of Hanover,

           since 1996 Professor at the University of Hanover

       since 2012 Professor at the Qingdao Institute for Science and Technology

Teaching courses and seminars at the

- Federal University Porto Alegre (Brasil) 2003, 2005, 2007, 2008, 2010,2012

- Rubber Institute Sao Leopoldo (Brasil) 1995, 1998, 2010, 2012

- Polytechnical University of Timisoara (Romania) 1999 – 2003

- Kyoto Institute of Technology 2009

- Quingdao University of Science and Technology (China) 2011, 2012

- European Summer School (Gargnano, Italy) 2001

Supervisor for 45 PhD Thesis

Publications:

45 Plenary and Invited lectures of International Conferences

Publications with referee 420

Lectures 570

Scientific books 3

Awards:

"Carl Harries" Award Medal from the German Rubber Society (1998)
Melwin Mooney Distinguished Award from ACS Rubber Division (2012)