Elastic memory

The radiation-treated cables find wide applications in control instmmentation of nuclear power reactors, particle accelerators, aviation, and telephone equipments. Usually PE and PVC are radiation cross-linked for production of such cables. The heat shrinkable foils are widely used in packaging, electrical and electronic industries. The radiation cross-linked PE possesses the property of elastic memory which is utilized to produce heat shrinkable products. 

The CTM is capable of reducing nerve for problem compounds such as those based on natural rubber, by ironing out thermal inhomogeneities and overcoming elastic memory. However, it is not self-cleaning, it generates some additional heat, it does not have forward conveying ability and it can also create back pressure. 

Gross mobility of entire chains must be low. The cohesive energy forces between chains of elastomers permit rapid, easy expansion. In its extended state, an elastomeric chain exhibits a high tensile strength, whereas at a low extension it has a low modulus. Polymers with low cross-link density usually meet the desired property requirements. The material after deformation returns to its original shape because of the cross-linking. This property is often referred to as elastic memory. 

Polyethylene may be crosslinked by electron beams or by free-radical initiators. These polymers have elastic memory, i.e., stretched crosslinked Aims or tubing shrinks to the original dimensions when heated. 

The concept of traditional thermoset elastomers was pioneered by Goodyear s discovery in 1839 that heating natural rubber with some sulfur converted the material from one that was tacky when warm and brittle when cold into a vulcanized rubber that was conveniently useful over a wide temperature range. Crosslinking of the macromolecules of rubber with sulfur bonds endowed the naturally occurring material with some elastic memory and caused it to behave as we have come to expect elastomers to behave. Excessive sulfur crosslinking converts the stretchable, compressible, bouncy rubber into hard rubber such as the material found in the heads of mallets used in machine shops to pound sheet metal into desired shapes. A small dose of crosslinking prevents the macromolecules of natural rubber to crystallize at low temperatures and turn into a brittle solid and to become a tacky, sticky semifluid at elevated temperatures. 

Most common fluids of simple structure are Newtonian (i.e., water, air, glycerine, oils, etc.). However, fluids with complex structures (i.e., high polymer melts or solutions, suspensions, emulsions, foams, etc.) are generally non-Newtonian. Examples of non-Newtonian behavior include mud, paint, ink, mayonnaise, shaving cream, polymer melts and solutions, toothpaste, etc. Many two-phase systems (e.g., suspensions, emulsions, foams, etc.) are purely viscous fluids and do not exhibit significant elastic or memory properties. However, many high polymer fluids (e.g., melts and solutions) are viscoelastic and exhibit both elastic (memory) as well as nonlinear viscous (flow) properties. A classification of material behavior is summarized in Table 5.1 (in which the subscripts have been omitted for simplicity). Only purely viscous Newtonian and non-Newtonian fluids are considered here. The properties and flow behavior of viscoelastic fluids are the subject of numerous books and papers (e.g., Darby, 1976 Bird et al., 1987). 

More sophisticated versions of SMPs are those based on the so-called cold hibernated elastic memory as self-deployable intelligent structures (Sendijarevic, 2003). This technology is based on polyurethane foams whereby shape memory effect is combined with elastic recovery of the foam, thus allowing them to be packed into the smallest possible form and inserted into the body via catheters. Given the foam s excellent biocompatibility, porosity, and lightness, they can potentially be used in many other forms, e.g., orthopaedic braces and splints, vascular and coronary crafts, as well as other equally vital prosthetics and implants. 

Uses PU intermediate for prod, of flexible PU foams, cast PU, noncellular applies., e.g., coalings, adhesives, and elastomers Features Rec. for foam applies, where high str., solv. resist., and elastic memory are required, cast PU with superior resist, to HC-based lubricants, fuels, and soivs., and noncellular applies, where good flexibility and solv. resist, are required... 

Metcalfe, A., Desfaits, A.-C., Salazkin, I., Yahia, L. H., Sokolowski, W. M. Raymond, J. (2003) Cold hibernated elastic memory foams for endovascular interventions. Biomaterials, 24, 491—497. 

Campbell, D., Lake, M., Scherbarth, M., Nelson, E., and Siv, R. 2005. Elastic memory composite material An enabling technology for future furable space structures. In 46th ALAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics, and Materials Conference, Austin, Texas. 

The intent of this chapter is not to merely review the rheology cj)f liquid crystalline polymers (LCP) as this has been done elsewhere, but rather it is to compare their behavior with flexible chain polymer systems and to describe various rheological tests which can be used to characterize LCP. We will assume that the reader is somewhat familiar with the concepts of polymer rheology such as fluid elasticity, memory, and normal stresses. 

Biodegradable stents with elastic memory. Biomaterials, 27 (8), 1573 — 1578. 

Memory zone (elastic memory, plastic memory) n. The tendency of a plastic article to revert in dimensions to a size previously existing at some stage in its manufacture. For example, a film that has been oriented by hot stretching and chilled while under tension, will, upon reheating, tend to revert to its original pre-stretched size due to its memory . 

Recently, the concept of cold hibernated elastic memory utilising SMP in open cellular structures was proposed for space-bound structural applications [108]. The concept of cold-hibernated elastic memory can be extended to various new applications such as microfoldable vehicles, shape determination and microtags [109]. Recent studies on shape memory PU-based conductive composites using conducting polymers and carbon nanotubes show considerable promise for application as electroactive and remote sensing actuators [110]. 

In 2003, Metcalfe et al. reported on using polyurethane SMP foams, termed CHEM (cold hibernated elastic memory) foams, for treating carotid aneurysms in a... 

TEMBO Elastic Memory Composites are stated, by the manufacturers, to be a family of thermoset (epoxy) SMP developed by Composite Technology Development Inc., 2600 Campus Drive, Lafayette Co., 80026-3359, USA. 

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