Mechanical strength of polymers

The mechanical strength of polymers is achieved through extensive cross-linking whereby a three-dimensional network of hydrocarbon chains is formed. Depending... 

Tyrosine is the only major, natural nutrient containing an aromatic hydroxyl group. Derivatives of tyrosine dipeptide can be regarded as diphenols and may be employed as replacements for the industrially used diphenols such as Bisphenol A in the design of medical implant materials (Kigime 1). The observation that aromatic backbone structures can significantly increase the stiffness and mechanical strength of polymers prowded the rationale for the use of tyrosine dipeptides as monomers. 

Fillers are veiy often added to engineer the mechanical strength of polymers. The use of rigid filler will increase modulus, and thus the polymer will be more prone to tensile cracking, whereas the use of rubber for blending will lower modulus and the scratch depth will increase (4). With the use of different types of rigid fillers, scratch pattern and deformation mechanism might be different... 

In addition to pore size, the mechanical strength of polymer substrates has an influence on the behaviour of cells, as cells sense their environment through the focal adhesions that attach the cytoskeleton to the scaffold.The mechanical properties of elastomeric poly(l,2-butadiene) (PB) honeycomb patterned films can be controlled by crosslinking the films under UV radiation.Crosslinking of the PB films resulted in a 15-fold increase in the elastic modulus but had no effect on the surface properties of the polymer. Murine fibroblasts exhibited stronger adhesions to the crosslinked PB films. When attached to a growth substrate, cells apply a traction force of 30 nN to the surface. Simulation of this force on the... 

Since CR spectra respond in a discrete manner to unfreezing of different segmental motion modes, the correlations between the spectrum and temperature peculiarities ( anomalies ) in the mechanical behavior of polymers could be expected. CRS can be the non-destructive method for the prediction of temperature points of changing in the mechanical property-temperature plots. Such points were revealed for the mechanical strength of polymers (PVB, PVC, PMMA, PS, epoxy networks, and others) [328]. 

Membrane is a potentially effective way to apply nanotubular materials in industrial-scale molecular transport and separation processes. Polymeric membranes are already prominent for separations applications due to then-low fabrication and operation costs. However, the main challenge for using polymer membranes for future high-performance separations is to overcome the tradeoff between permeability and selectivity. A combination of the potentially high throughput and selectivity of nanotube materials with the process ability and mechanical strength of polymers may allow for the fabrication of scalable, high-performance membranes [45,46]. 

Cost rules out almost all alternative materials for long-distance pipe lines it is much cheaper to build and protect a mild steel pipe than to use stainless steel instead - even though no protection is then needed. The only competing material is a polymer, which is completely immune to wet corrosion of this kind. City gas mains are now being replaced by polymeric ones but for large diameter transmission lines, the mechanical strength of steel makes it the preferred choice. 

That is all we need to know about structure for the moment, though more information can be found in the books listed under Further reading. We now examine the origins of the strength of polymers in more detail, seeking the criteria which must be satisfied for good mechanical design. 

Usually, crystallization of flexible-chain polymers from undeformed solutions and melts involves chain folding. Spherulite structures without a preferred orientation are generally formed. The structure of the sample as a whole is isotropic it is a system with a large number of folded-chain crystals distributed in an amorphous matrix and connected by a small number of tie chains (and an even smaller number of strained chains called loaded chains). In this case, the mechanical properties of polymer materials are determined by the small number of these ties and, hence, the tensile strength and elastic moduli of these polymers are not high. 

A surface is that part of an object which is in direct contact with its environment and hence, is most affected by it. The surface properties of solid organic polymers have a strong impact on many, if not most, of their apphcations. The properties and structure of these surfaces are, therefore, of utmost importance. The chemical stmcture and thermodynamic state of polymer surfaces are important factors that determine many of their practical characteristics. Examples of properties affected by polymer surface stmcture include adhesion, wettability, friction, coatability, permeability, dyeabil-ity, gloss, corrosion, surface electrostatic charging, cellular recognition, and biocompatibility. Interfacial characteristics of polymer systems control the domain size and the stability of polymer-polymer dispersions, adhesive strength of laminates and composites, cohesive strength of polymer blends, mechanical properties of adhesive joints, etc. 

However, the mechanical strength of the polymers tested was lacking since tube fragmentation and even breakage was observed less than five days after implantation (Wang et al., 2001). 

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