Composite microcomposites

The dispersion state of a typical phyllosilicate (except sepiolite and halloysite) in a matrix polymer depends on the preparation conditions and the matrix-nanolayer affinity. This effect determines the structure of the resulting composites, which can be either phase separated composites (microcomposites), intercalated nanocomposites, or exfoliated nanocomposites (Alexandre and Dubois 2000). 

Atomic number contrast Micro composition Microcomposition... 

There is currently considerable interest in processing polymeric composite materials filled with nanosized rigid particles. This class of material called "nanocomposites" describes two-phase materials where one of the phases has at least one dimension lower than 100 nm [13]. Because the building blocks of nanocomposites are of nanoscale, they have an enormous interface area. Due to this there are a lot of interfaces between two intermixed phases compared to usual microcomposites. In addition to this, the mean distance between the particles is also smaller due to their small size which favors filler-filler interactions [14]. Nanomaterials not only include metallic, bimetallic and metal oxide but also polymeric nanoparticles as well as advanced materials like carbon nanotubes and dendrimers. However considering environmetal hazards, research has been focused on various means which form the basis of green nanotechnology. 

To achieve the goal of required performance, durability, and cost of plate materials, one approach is improvement of the control of the composition and microstructure of materials, particularly the composite, in the material designing and manufacturing process. For example, in the direction of development of thermoplastics-based composite plate, CEA (Le Ripault Center) and Atofina (Total Group) have jointly worked on an irmovative "microcomposite" material [33]. The small powders of the graphite platelet filler and the PVDF matrix were mixed homogeneously by the dispersion method. The filler and matrix had a certain ratio at the microlevel in the powder according to the optimized properties requirements. The microcomposite powders were thermocompressed into the composite plate. 

Microcomposite tests have been used successfully to compare composites containing fibers with different prior surface treatment and to distinguish the interface-related failure mechanisms. However, all of these tests can hardly be regarded as providing absolute values for these interface properties even after more than 30 years of development of these testing techniques. This is in part supported by the incredibly large data scatter that is discussed in Section 3.2.6. 

Qiu, Y. and Schwartz, P. (1991). A new method for study of the fiber-matrix interface in composites Single fiber pull-out from a microcomposite. J. Adhesion Sci. Technol. 5, 741-756. 

Microcomposite tests including fiber pull-out tests are aimed at generating useful information regarding the interface quality in absolute terms, or at least in comparative terms between different composite systems. In this regard, theoretical models should provide a systematic means for data reduction to determine the relevant properties with reasonable accuracy from the experimental results. The data reduction scheme must not rely on the trial and error method. Although there are several methods of micromechanical analysis available, little attempt in the past has been put into providing such a means in a unified format. A systematic procedure is presented here to generate the fiber pull-out parameters and ultimately the relevant fiber-matrix interface properties. 

When the polymer is unable to intercalate between the lamella (for example, in silicate sheets) a phase-separated (aggregated) composite is obtained, whose properties are in the same range as for traditional microcomposites. The two types of lamellar PNCs are depicted in Fig. 1. 

This chapter aims to describe the principles behind the processing, microstructural development and properties of particulate ceramic composites and to illustrate these using experimental results. The main emphasis is on examples where the addition of particulates to a ceramic matrix causes new mechanisms to operate that give an improvement in properties greater than would be expected from a rule of mixtures . The chapter concentrates almost exclusively on structural composites, since this is where most work has been done to date. Particulate nanocomposites are included in the chapter, since the important examples described are currently at the coarse end of the nanoscale , and the principles underpinning their properties seem to be a simple extension of those relevant to the microcomposites with which the rest of the chapter is concerned. 

---