Mechanical properties stiffness

Mechanical properties (stiffness, impact, and shock resistance), electrical properties, clarity, ease of processing, sealing properties, dimensional stability, resistance to hydrocarbons and other organic liquids, resistance to plasticizers, greases, and oils are the characteristic properties desired. In its mechanical properties it approaches polycarbonate most closely. However, since polycarbonate is cheaper than Trogamid T, Trogamid T will be preferred only where polycarbonate cannot be used. 

LTG with either PEK, PEEK, PPS, PEI, LCP, PC, PET, PBT or fluorinated polymers processability, mechanical properties, stiffness —Cortem" Alloys with either LCP or with PEEK Bahn etal., 1991... 

In the majority of applications of polymers, we are interested in one or more of three basic mechanical properties—stiffness, strength and toughness. To these can be added creep, which becomes important in many engineering applications. Stiffness represents resistance to deformation, and is a much simpler property than strength and toughness, which relate to failure. Strength is the ultimate stress which a material can withstand before it fails, whether by fracture or by excessive deformation, whilst toughness represents the work required to fracture a material. 

Polypropylene was the chosen polymer since it is one of the cheapest polymers, is chemically inert, provides adequate mechanical properties (stiffness and impact strength), will not absorb liquids, mouldings are easily cleaned and may be steam sterilized (hygienic), is easily processed, and will not rot or splinter. In addition, many SF products made up to that time (1975) were made from polypropylene so that some knowledge of the... 

Fibroin with high amounts of alanine possesses low mechanical properties (stiffness and toughness). Accordingly, fibroin is classified into the sUk types I-III [47]. Silk type I is untreated and raw fibroin. SUk type II indicates first class silk, with greater strength. Silk type III is the new generation of silk, which is obtained and purified in the air-water interface, with increased bias toward water [48]. The use of... 

We analyzed mechanical properties (stiffness) of the observed tail-like structures. The stiffness of a polymer chain is described by the persistence length p of the chain, that is, the length over which the average correlation in the tangent direction decays by 1/e. In two dimensions, the mean square point-to-point distance of the chain is given by... 

A newly developed third class of vinyl ester resins is represented by the even higher quality VE urethanes based on bisphenol A epoxy. Here, the secondary OH groups of the VE react in polyaddition with polyisocyanates to produce urethane bridges, see Eigure 1.3. Vinyl ester urethane resins (VEU resin, vinyl ester urethane-hybrid resins) combine the good mechanical properties (stiffness) of VE resins with excellent high-temperature resistance (T approx. 220 °C and HDT approx. 210 °C) and excellent chemical resistance (the long-term durability of VEUH resin exceeds that of normal VE). 

Since nearly two decades ago that lijima [203] reported the observation of carbon nanotubes, numerous researchers studied physical and chemical properties of this new form of carbons. From unique electronic properties and a thermal conductivity higher than diamond to mechanical properties (stiffness, strength, resilience) higher any current material, carbon nanotubes offer tremendous opportunities for the development of new materials. 

The various mechanical properties of polyamides may be traced in many instances to the possibility of intermolecular hydrogen bonding between the polymer molecules and to the relatively stiff chains these substances possess. The latter, in turn, may be understood by considering still another equilibrium, this one among resonance structures along the chain backbone ... 

Much more information can be obtained by examining the mechanical properties of a viscoelastic material over an extensive temperature range. A convenient nondestmctive method is the measurement of torsional modulus. A number of instmments are available (13—18). More details on use and interpretation of these measurements may be found in references 8 and 19—25. An increase in modulus value means an increase in polymer hardness or stiffness. The various regions of elastic behavior are shown in Figure 1. Curve A of Figure 1 is that of a soft polymer, curve B of a hard polymer. To a close approximation both are transpositions of each other on the temperature scale. A copolymer curve would fall between those of the homopolymers, with the displacement depending on the amount of hard monomer in the copolymer (26—28). 

Mechanical Properties. Although wool has a compHcated hierarchical stmcture (see Fig. 1), the mechanical properties of the fiber are largely understood in terms of a two-phase composite model (27—29). In these models, water-impenetrable crystalline regions (generally associated with the intermediate filaments) oriented parallel to the fiber axis are embedded in a water-sensitive matrix to form a semicrystalline biopolymer. The parallel arrangement of these filaments produces a fiber that is highly anisotropic. Whereas the longitudinal modulus of the fiber decreases by a factor of 3 from dry to wet, the torsional modulus, a measure of the matrix stiffness, decreases by a factor of 10 (30). 

Surfa.cta.nt-TypeAntista.ts, Inherently conductive antistats have the advantage of not being dependent on atmospheric moisture to function. Thek drawbacks include expense, coloration of the plastic, and alteration of the mechanical properties of the plastic. The added stiffness caused by conductive fillers may not be a problem with a rigid container, but it can be a problem for a flexible bag. 

For a part to exhibit stmctural stiffness, flexural moduH should be above 2000 N/mm (290,000 psi). Notched l2od impact values should be deterrnined at different thicknesses. Some plastics exhibit different notch sensitivities. For example, PC, 3.2 mm thick, has a notched l2od impact of 800 J/m (15 fdbf/in.) which drops to 100 J/m (1.9 fflbf/in.) at 6.4-mm thickness. On the other hand, one bisphenol A phthalate-based polyarylate resin maintains a 250-J /m (4.7-fdbf/in.) notched l2od impact at both thicknesses. Toughness depends on the stmcture of the part under consideration as well as the plastic employed to make the part. Mechanical properties, like electrical properties, ate also subject to thermal and water-content changes. 

---