Introduction

Using (in)organic fillers in a polymer matrix has a long history in polymer science and engineering in order to achieve desired mechanical, rheological, chemical, or thermal properties [1–3]. There is ample (published) experience on which properties of the filler and the filler–matrix interface influence the compound [4–6], but still a major lack of fundamental knowledge and understanding exists on the interaction between the filler and the polymer matrix as well as on the mode of operation. When it comes to nanoscale fillers, such as layered silicates, carbon nanotubes, graphene, or cellulose nanofibers, it is even more important to know accurate structure–property relationships as well as identifying the influencing parameters, e.g., at the filler–matrix interface as structural arrangements on the molecular level influence the mechanical behavior at the macro level [7–14]. It has already been shown [15,16] that using nanofillers in polymer matrices poses a number of challenges, which includes the modification of the filler (e.g., ionic exchange reactions), the processing of the composite material (e.g., high residence time and shear rate needed simultaneously), or the material characterization (e.g., under mechanical loading). Previous results with layered silicates illustrated that for improved mechanical properties a highly intercalated structure and for enhanced barrier or flame retardancy a highly exfoliated structure is needed [17,18]. This example demonstrates the importance of structural arrangements on the molecular level for the mechanical behavior at the macroscale level and the need for the determination of accurate structure–property relationships as well as identifying the influencing parameters, e.g., at the filler–matrix interface [19,20].

These mentioned circumstances are the reasons for the complexity in processing polymer nanocomposites and why there are still only few applications. Furthermore, not only one scientific field is affected and joint efforts of several scientific communities are necessary. Starting from the filler manufacturing or preprocessing (e.g., the fiber manufacturers or the mineralogist who provides the raw material) over the polymer chemistry adding, e.g., the correct surface modification and functionalization, to the polymer processing using adequate techniques and processes for achieving flawless materials, every step in this chain is just a part of the puzzle.

Within this book for the first time, all involved scientific areas are working together providing an all-embracing look on processing of polymer nanocomposites bridging the gap from the raw material to the final composite. This book gives an impressive gain insight the physical/chemical preprocessing of layered silicates, their incorporation into a polymer matrix using sophisticated technologies (such as injection molding compounder or advanced compounding) as well as in-line, real-time quality control of nanocomposite production and prospects of nanocomposite materials. Finally, a nanotoxicological view on the new materials completes the book and covers all aspects of nanocomposite industry.

This book concentrates on one special class of nanofillers, which attracted both academic and commercial interest for several years due to their availability and costs, layered silicates. The main advantage of nanofillers is their high specific surface area which allows to achieve or exceed certain levels of specific properties with only a very small amount of filler compared to conventional fillers. Montmorillonite, hectorite, and saponite are the most commonly used layered silicates. Their crystal structure consists of layers made up of two tetrahedral coordinated silicon atoms fused to an edge-shared octahedral sheet of either aluminum or magnesium hydroxide. The layer thickness can be estimated with 1 nm. The other two dimensions vary from 30 nm to several microns or larger. Normally these layers form stacks, with a gap (due to van der Waals forces) between the single layers (see Chapter 1).

Two particular characteristics of layered silicates are helpful for satisfactory dispersion and forming of different structures (agglomerated, intercalated, and exfoliated) in the polymer matrix. On the one hand, the layered silicates have the ability to disperse into individual layers (swelling). On the other hand, the surface chemistry of the layered silicates can be changed via ion exchange reactions with organic and inorganic cations (see Chapter 2). The organomodified layered silicate can be incorporated inside the carrier polymer due to supportive thermodynamics, during the ultimate steps of processing, in methods such as extrusion (compounding) or injection molding, to generate nanocomposite materials. As mentioned before, layered silicate filled polymer nanocomposites are processable by most of the commonly used processing techniques in industrial scale (see Chapter 3).

During the process, the structures which are responsible for the level of reinforcement are formed by physical bonding between the hydrophilic clay, the hydrophobic polymer matrix, and if nonpolar polymers are used, a compatibilizer [21,22]. To characterize the homogeneity respectively the properties of the material, a variety of methods are used. These methods comprise offline as well as inline methods and outrun often the commonly used practice and interpretations for the specific needs of nanocomposite evaluation (see Chapter 4).

If implemented properly such polymer nanocomposite materials can display a property profile which exceeds that of conventional filled polymer systems in several ways. Such properties cover multiple aspects including strength, stiffness, thermal as well as oxidative stability, diffusion properties against gas molecules and flame retardancy [23,24]. This enhanced property profile, obtained only by the addition of comparably small amounts of silicate layers to the carrier polymer, is especially attractive for certain applications due to the fact that polymer layered silicates nanocomposites have a significantly improved weight to performance ratio [12,23,25,26] (see Chapter 5).

Another aspect that separates organomodified layered silicates as filler for polymers from conventional filler systems is indeed the significant reduction or absence of property trade-offs. Conventional polymer blends or composites implement the necessity to trade-off desired performance, mechanical properties (especially toughness and elongation properties), cost and processability. Polymer nanocomposites offer a passage to bypass these limitations of conventional polymer filler systems and thereby giving the opportunity to shape material properties without taking compromises in the cost of property trade-offs [23,24,27].

Especially for commodity matrix polymers such as polypropylene (PP) or polyethylene (PE), the addition of nanofillers offers great potential in improvement of certain properties, e.g., Young’s modulus and barrier properties simultaneously. Thereby the low cost of commodity plastics as well as their huge field of applications and the tuning of the final property profile with nanoscaled fillers offers tremendous opportunities in the application of such nanocomposites.

Besides the modification, processing, and application of nanocomposites, nanotoxicology is always a necessary and overall important topic. Regarding the environmental and human hazards, numerous potential exposure scenarios for nanofillers within polymers, e.g., during the manufacture and machining process or generated during usage/recycling for both workers and consumers need to be considered in comprehensive risk assessment (see Chapter 6).

Acknowledgments

The editor wants to thank all the authors for the contribution of their excellent and forward-looking work as well as their collaboration and effort for the “pit-to-part” idea. Furthermore, this book would not exist in this quality, if not many reviewers spent their rare time for revising the single chapter. At that point the editor wants to thank Dr. Hans Kolb, Dr. Joerg Schausberger, DI Tobias Struklec, Dr. Ivica Duretek, Ali Gooneie, Lis, and Dr. Lisa Bregoli.

June 2014

References

1. Suyev YuS. Reinforcement of polymers by finely dispersed fillers Review. Polym Sci U.S.S.R. 1979;21(6):1315–1333.

2. Mallick PK. Fiber-Reinforced Composites: Materials, Manufacturing, and Design third ed. Florida: CRC Press; 2007; ISBN-10: 0849342058, ISBN-13: 978-0849342059.

3. Shen L, Zhang ZY, Wang JJ, Li WC, Zheng Q. Polym Mater Sci Eng. 2006;22(4):107–109.

4. Katz HS, Mileski JV. Handbook of Fillers for Plastics first ed. Berlin: Springer; 1987; ISBN-10: 0442260245, ISBN-13: 978-0442260248.

5. Jancar J. Mineral Fillers in Thermoplastics I: Raw Materials and Processing. vol. 139 New York, LLC: Springer-Verlag; 1999; ISBN: 3540646213.

6. Wegner G. Acta Mater. 2000;48:253–262.

7. Baughman RH, Zakhidov AA, de Heer WA. Carbon nanotubes—the route toward applications. Science. 2002;297:787.

8. Stankovich S, Dikin DA, Dommett GHB, et al. Graphene-based composite materials. Nature. 2006;442 In: http://dx.doi.org/doi:10.2038/nature04969; 2006.

9. Ramanathan T, Abdala AA, Stankovich S, et al. Functionalized graphene sheets for polymer nanocomposites. Nat Nanotechnol. 2008;3 In:...