Improving the tribological properties of polymer nanocomposites
There are a number of ways in which the addition of a particle to a polymer can improve its friction and wear properties and all of these have been exploited in the production of nanocomposites. One approach is to reduce the adhesion of the composite to its sliding counterface by adding friction-modifying reinforcements which may also reduce the heat generated in a sliding contact. These friction modifiers may be in the form of low-friction particles which form low-friction transfer layers at...
Polymerclay nanocomposites
PC nanocomposites are an emerging class of organic-inorganic hybrids that contain a relatively low wt of nanometer-sized clay. These were first developed in the late 1980s. The dispersion of the nanometer-sized clay in the polymer matrix significantly improves the mechanical, thermal, barrier properties and flame retardancy of the base polymer. Three main types of nanocomposites can be obtained when clay is dispersed in a polymer matrix. This depends on the nature of the components used,...
Friction coefficient measurements
For all materials the friction coefficient was approximately constant as a function of sliding speed until close to seizure when friction increases rapidly. Typical plots are shown in Fig. 9.2 and 9.3. Two important parameters can thus be extracted from the test data the average friction coefficient at all sliding speeds the speed at which seizure occurs under the contact conditions in the test. The average friction coefficient data for all the samples are collected in Fig. 9.4. It can clearly...
Principles of electrostatic selfassembly for creating nanolayer films
The Langmuir-Blodget LB technique allows monolayers to be created by using a non-solvent as a substrate. Once the monolayers have formed over the surface of a non-solvent system, they can be transferred onto a solid support. This technique, pioneered in the 1960s, is believed to be the first synthetic nano-scale heterostructure. These LB experiments were the first true nanomanipulations and they offered unprecedented control of the deposition of individual molecular layers. The creation of LB...
References Ifc
1. Kurauchi T., Okada A., Nomura T., Nishio T., Saegusa S. and Deguchi R., 'Nylon 6-clay hybrid - synthesis, properties and application to automotive timing belt cover', SAE Technical Paper Series 910584, International Congress and Exposition, Detroit, 1991. 2. Bailey S. W., 'The status of clay mineral structures', Clay and Clays Minerals Proc 14th National Conference, Berkley, California, Pergamon Press, 1966. 3. Greenland D. J., Laby R. H. and Quirk J. P., 'Adsorption of amino-acids and...
Producing continuous yarns
A common misconception in recent electrospinning literature is that the first literature on electrospinning dates back to 1934 when Formhals patented a method for manufacturing yarns from electrospun fibers.25 Some of the first publications on electrospinning date back as far as 1902, when first Cooley26 and then Morton27 patented processes for dispersing fluids. In both patents, the authors describe processes for producing very fine artificial fibers by delivering a solution of a fiber-forming...
Scaffolds for tissue engineering
It is well known that biological tissues consist of well-organized hierarchical fibrous structures14 ranging from nanometer to micrometer scale as described in Fig. 2.2. The successful regeneration of biological tissue and organs calls for the development of fibrous structures with fiber architectures conducive to cell deposition and cell proliferation. Of particular interest in tissue engineering is the creation of reproducible and biocompatible 3D scaffold for cell ingrowth, resulting in...
Polymerpolymer hybrid layers
Mixed and block-copolymer brushes are polymer-polymer hybrid thin films tethered to solid substrates. The well-defined architecture of end-tethered chains in polymer brushes allows for a deep study of the mechanisms of the brushes' response to their environment. Nevertheless, for practical applications a very similar mechanism can be approached using polymer layers when a polymer can be grafted by end groups, and also by side functional groups. The polymer chains randomly grafted by side...
Macromolecular platform for nanofabrication
The chemical grafting of polymers can be accomplished by either 'grafting to' or 'grafting from' methods.5 According to the 'grafting to' technique, end-functionalized polymer molecules react with complementary functional groups located on the surface to form tethered chains. The 'grafting from' technique utilizes the polymerization initiated from the substrate surface by attached usually by covalent bonds initiating groups. It is necessary to highlight that most of the developed grafting 'to'...
Enhancing the functionality of polymer nanocomposites
The results presented here demonstrate the benefit of nanoscale reinforcement to improve wear resistance of the composite material but to improve the overall performance of the materials for a sliding seal application no single reinforcement material is suitable. However, a combination of reinforcements can be developed which impart multiple functionality to the composite. For instance, both silica and MoS2 nanoparticles added to a polyurethane resin matrix can generate improvements in both...
References Idp
Bercea, M., Morariu, S., loan, C., loan, S. and Simionescu, B. C. 1999 European Polymer Journal, 35, 2019-2024. Bognitzki, M., Hou, H., Ishaque, M., Frese, T., Hellwig, M., Schwarte, C., Schaper, A., Wendorff, J. H. and Greiner, A. 2000 Advanced Materials Weinheim, Germany , 12, 637-640. Bognitzki, M., Czado, W., Frese, T., Schaper, A., Hellwig, M., Steinhart, M., Greiner, A. and Wendroff, J. H. 2001 Advanced Materials Weinheim, Germany , 13, 70-72. Buchko, C. J., Chen, L. C., Shen, Y. and...
References Odq
1. Decher, G., Fuzzy nanoassemblies toward layered polymeric multicomposites. Science, 1997. 277 p. 1232-1237. 2. Lvov, Y., Decher, G. and Moehwald, H., Assembly, structural characterization, and thermal behavior of layer-by-layer deposited ultrathin films of poly vinyl sulfate and poly allylamine . Langmuir, 1993. 9 p. 481-486. 3. Lvov, Y., Decher, G. and Sukhorukov, G., Assembly of thin films by means of successive deposition of alternate layers of DNA and poly allylamine . Macromolecules,...
The development of functional polymer nanocomposites
Making good samples of polymer nanocomposites is a challenge and a range of processing techniques are being actively developed at present including melt mixing Chan et al., 2002 , in situ polymerisation Yang et al., 1998, Reynaud et al., 2001 and other approaches. A full discussion of the technologies available is beyond this chapter but the interested reader is referred to the review of Jordan et al. 2005 . A single processing approach is unlikely to deliver viable composites in every system...
Nanosilica filled polypropylene nanocomposites
The incorporation of inorganic fillers in polymers contributes effectively to the improvement of the mechanical properties and in particular the toughness however, the procedure is often limited owing to the high filler contents that are needed for desired composite properties. For this reason nanocomposites with unique nano-scale microstructure, obtained by low particle loading represent a particular advantage. However, it is very difficult to disperse nanoparticles in a polymeric matrix...
Electrospinning of nanofibers and the charge injection method
D. R. SALEM, Charge Injection Technologies Inc., USA The use of electric charge to break up liquids into small particles has been well known and extensively studied for over a century, but commercial applications have been constrained by difficulties in surmounting flow rate limitations associated with the underlying physics of the process. This is true for both electrospraying, in which low-viscosity liquids can be atomized into droplets, and electrospinning, in which viscoelastic liquids can...
Compatibilization issues in polyolefinclay nanocomposites
Mere organophilization of the clay is often not sufficient to obtain intercalated or exfoliated PC nanocomposites. This is mostly true in the case of PO. This is mainly due to the low polarity of these polymers, which makes it difficult to get the exfoliation and homogeneous dispersion of the silicate layers at the nanometer level in the polymer. Silicate layers have polar hydroxyl groups, which are compatible only with polymers containing polar functional groups. This necessitates the use of a...
Mechanical properties of nylon 66 electrospun webs
Table 4.2 shows the mechanical properties of electrospun N6,6 nonwoven webs that were made under various experimental conditions. It is evident that the polymer concentration and the molecular weight of N6,6 influence the fiber morphology and, therefore, the elongation at break and initial modulus, as well as the strength of these materials. Figure 4.12 gives the dependence of these properties as a function of N6,6 concentration. The lowest elongation at break of 25.4 can be seen for the fibers...
Twisted nonwoven web yarn
This method, patented by Raisio Chemicals Korea Inc.,39 involves electrospinning nanofibers through multiple nozzles to obtain a nonwoven nanofiber web, either directly in a ribbon form or in a larger form, which is then cut into ribbons, and subsequently passing the nanofiber web ribbons through an air twister to obtain a twisted nanofiber yarn. A diagram depicting the process is given in Fig. 3.13. Table 3.1 shows process variables and yarn characteristics for three polymer yarns that have...