Polymer nanocomposites nanoadditives

Provided in this chapter is an overview on the fundamentals of polymer nanocomposites, including structure, properties, and surface treatment of the nanoadditives, design of the modifiers, modification of the nanoadditives and structure of modified nanoadditives, synthesis and struc-ture/morphology of the polymer nanocomposites, and the effect of nanoadditives on thermal and fire performance of the matrix polymers and mechanism. Trends for the study of polymer nanocomposites are also provided. This covers all kinds of inorganic nanoadditives, but the primary focus is on clays (particularly on the silicate clays and the layered double hydroxides) and carbon nanotubes. The reader who needs to have more detailed information and/or a better picture about nanoadditives and their influence on the matrix polymers, particularly on the thermal and fire performance, may peruse some key reviews, books, and papers in this area, which are listed at the end of the chapter. 

Over the past decade, polymer nanocomposites have attracted considerable interests in both academia and industry this is because of the outstanding mechanical properties like elastic stiffness and strength which can be achieved with only a small amount of the nanoadditives. This is caused by the large surface area to voliune ratio of nanoadditives when compared to the micro- and macro-additives. Other superior properties of polymer nanocomposites include barrier resistance, flame retardancy, scratch/wear resistance, as well as optical, magnetic and electrical properties. 

Since the 1990 s, clay polymer nanocomposites (CPN) have aroused a great scientific interest, not only because they have better properties in relation to the traditional polymer composites, but also because nanoclays are relatively cheap materials. Furthermore, the existing polymer processing techniques can be easily adapted to the use of this type of nanoadditive. 

Part II of this book deals with the most recent developments of polymer nanocomposites with other nanoadditives such as carbon nanotubes, graphite, nanoparticles and other inorganic-organic hybrid systems and has eight... 

The impact of the nanocomposite technology on polymers is huge, reflected in enhanced properties of the resulting PNs, such as enhanced mechanical, barrier, solvent-resistant, and ablation properties.12 The effect of nanocomposite technology on the thermal and fire performance of the polymers is primarily observed in two important parameters of the polymers (1) the onset temperature (7( ,nsct) in the thermogravimetric analysis (TGA) curve—representative of the thermal stability of the polymer, and (2) the peak heat release rate (peak HRR) in cone calorimetric analysis (CCA)—a reflection of the combustion behavior (the flammability) of the polymer. The Tonset will be increased and the peak HRR will be reduced for a variety of polymers when nanoscale dispersion of the nanoadditive is achieved in the polymer matrix. 

Clays, natural or synthetic, are the most widely investigated and understood nanoadditives used to enhance the flame retardancy of polymers through nanocomposite technology, because of their unique properties, particularly the ease of surface treatment and application in polymer matrices. Clay can be cationic and anionic materials, in accordance with the charge on the clay layers. In this chapter, the focus is on two kinds of clays montmorillonite (MMT), a naturally occurring cationic clay that belongs to the smectite group of silicates, and LDH, an anionic clay that does occur naturally but for which the synthetic form is more common. Other clays will also be mentioned as appropriate. 

Because of the unique combination of mechanical, electrical, and thermal properties, the CNTs have been excellent candidates to substitute or complement the conventional nanofillers in the fabrication of multifunctional PNs. The first PNs using CNTs as the nanoadditive was reported in 1994.20 By far, the CNTs have been the second most investigated nanoadditives to reduce the flammability of the polymers through nanocomposite technology. A difficulty of the application of the CNTs in polymers is the dispersion of CNTs in the matrix polymer, and the high cost of the CNTs is another problem. 

Although the nanoadditive can enhance both the thermal stability and the fire performance of the matrix polymer, it has been noted that the enhancement on the fire performance is not parallel to that on the thermal stability, i.e an observation about the reduction of the peak HRR of the resulting PN does not necessarily mean that an enhancement of the thermal stability of the PN can be observed. A typical example is PA-6. It has been seen that the PA-6/clay nanocomposite shows a significantly reduced peak HRR,98 but it does not show enhanced thermal stability. 

The organoclay as a nanoaddition to the polymers may change the temperature of the destruction, refractoriness, rigidity, and mpture strength. The nanocomposites also... 

Recently, numerous industrial and scientific research reports have shown enhancement of polymer performance by preparation of nanostructured polymeric materials [4,5]. Among different nanoadditives there is a prevailing share of layered silicates, especially montmorillonite (MMT) due to its relatively low costs, well developed techniques of modification and versatile influence on polymer properties [6-8]. Through the last decades nanocomposites of almost all large-scale produced polymers (e g. PE, PP, PA, PS, PVC or PC) were obtained and characterized, but there are... 

Appropriate preparation of nanoadditives in polymer matrices is a fundamental issue for both the mechanical and electrical properties of nanocomposites and good interaction between cells and materials [15], Nanomaterials have tendency to create aggregates in polymer matrices which have completely different properties to those observed for single nanomaterials. Moreover, uniform dispersion of nanomaterials in a polymer permits full interaction between bone cells and the surface of nanocoposites. 

For all nanocomposites an improvement of mechanical properties in comparison to pure polymer were observed. The improvement in the mechanical properties for nanocomposites indicates a homogenously dispersion of nanoadditives in PLDL solution. The most effective improvement of mechanical properties was observed for nanocomposites containing l%wt. of MWCNTs (MUl). For these samples, the tensile strength increased by about 35% while the Young s modulus increased by about 20% in comparison to pure PLDL samples. The hydrophobic nature of MWCNT and lack of chemical groups on their surface may suggest that the interaction between MWCNT and... 

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