Deformation of polymers

Turning to the macroscopic deformation of polyethylene, as experienced on drawing of fibers, one observes frequently the formation of a neck at the yield point, as illustrated in Fig. 5.108. The stress-strain curve in Fig. 5.108 illustrates a typical 

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TERMONIA SMITH Kinetic ModdfiirTensUe Deformation of Polymers 119... 

The deformation of polymer chains in stretched and swollen networks can be investigated by SANS, A few such studies have been carried out, and some theoretical results based on Gaussian models of networks have been presented. The possible defects in network formation may invalidate an otherwise well planned experiment, and because of this uncertainty, conclusions based on current experiments must be viewed as tentative. It is also true that theoretical calculations have been restricted thus far to only a few simple models of an elastomeric network. An appropriate method of calculation for trapped entanglements has not been constructed, nor has any calculation of the SANS pattern of a network which is constrained according to the reptation models of de Gennes (24) or Doi-Edwards (25,26) appeared. 

In view of the development of the continuous chain model for the tensile deformation of polymer fibres, we consider the assumptions on which the Coleman model is based as too simple. For example, we have shown that the resolved shear stress governs the tensile deformation of the fibre, and that the initial orientation distribution of the chains is the most important structural characteristic determining the tensile extension below the glass transition temperature. These elements have to be incorporated in a new model. 

The tensile curve of a polymer fibre is characterised by the yield strain and by the strain at fracture. Both correspond with particular values of the domain shear strain, viz. the shear yield strain j =fl2 with 0.04rotation angle of -0y=fl2 and the critical shear strain 0-0b=/iwith /f=0.1. For a more fundamental understanding of the tensile deformation of polymer fibres it will be highly interesting to learn more about the molecular phenomena associated with these shear strain values. 

Baltussen JJM (1996) Tensile deformation of polymer fibres. PhD thesis, Delft University of Technology... 

The EE and phE mechanisms for neat polymers proposed by ourselves and others all involve the consequences of breaking bonds during fracture. Zakresvskii et al. (24) have attributed EE from the deformation of polymers to free radical formation, arising from bond scission. We (1) as well as Bondareva et al. (251 hypothesized that the EE produced by the electron bombardment of polymers is due to the formation of reactive species (e.g., free radicals) which recombine and eject a nearby trapped electron, via a non-radiative process. In addition, during the most intense part of the emissions (during fracture), there are likely shorter-lived excitations (e.g., excitons) which decay in a first order fashion with submicrosecond lifetimes. The detailed mechanisms of how bond scissions create these various states during fracture and the physics of subsequent reaction-induced electron ejection need additional insight. 

Dinner, A.R. Local deformations of polymers with nonplanar rigid main-chain internal coordinates. J. Comput. Chem. 2000, 21, 1132 14. 

Interchain changes arising from the deformation of polymer networks are a result of strain-induced volume dilation. Typical results obtained by various methods (Fig. 6) demonstrate that the statistical theory predicts the volume dilation and... 

The thermomechanical data accumulated during the last years as a consequence of the improvement of the technique of deformation calorimetry contributed significantly to the understanding of thermodynamics and mechanisms of the reversible deformation of polymers in the glassy, semicrystalline and rubbery state. 

Surface tension plays a significant role in the deformation of polymers during flow, especially in dispersive mixing of polymer blends. Surface tension, as, between two materials appears as a result of different intermolecular interactions. In a liquid-liquid system, surface tension manifests itself as a force that tends to maintain the surface between the two materials to a minimum. Thus, the equilibrium shape of a droplet inside a matrix, which is at rest, is a sphere. When three phases touch, such as liquid, gas, and solid, we get different contact angles depending on the surface tension between the three phases. 

In general, shear flows can be divided into drag flows and pressure driven flows (Fig. 3.17). In addition, there are extensional flows, which are generated for instance by the deformation of polymer melts by compression or tensile deformation. 

Baltussen JJM, Tensile Deformation of Polymer Fibres", PhD Thesis, Delft, The Netherlands, 1996. Bauwens-Crowet C, Bauwens JC and Homes G, J Polym Sci A2, 7 (1969) 735. 

Measurements of rheological quantities on the tensile deformation of polymer melts used to be extremely difficult and required the development of special techniques. 

Extensional deformation of polymer solutions is applied technically in the so-called dry spinning of polymer fibres. The literature data in this field are not as numerous as in the field of shear viscosity, so that only a qualitative picture can be given here. 

Baltussen JJM, "Tensile Deformation of Polymer Fibres", PhD Thesis, Delft, 1996. 

Fig. 2a—c. Schematic drawing of several postulated microscopic steps in craze nucleation a Formation of a localized surface plastic zone and buildup of significant lateral stresses, b Nucleation of voids in the zone to relieve the triazial constraints, c Further deformation of polymer ligaments between voids and coalescence of individual voids to form a void network... 

Samuels, R. J. Quantitative Structural Characterization of the Mechanical Properties of Isotactic Polypropylene, in Plastic Deformation of Polymers (ed.) Peterlin, A., p. 241, New York, Marcel Dekker, Inc. 1971... 

BeardmoreP, RabinowitzS (1975) Fatigue deformation of polymers. In Arsenault RJ (ed) Treati on materials science and technology, vol 6, Academic Press, New York... 

Film formation requires deformation of polymer particles and reptation of polymer chains, and is strongly temperature dependent. The temperature at which a film will form is commonly measured on a minimum film formation temperature (MFFT) bar. Latex is applied to a metal bar with a pre-assigned temperature gradient. The coating is allowed to dry and a number of transitions are noted. Below a certain temperature the film displays cracks. This is called the crack point MFFT. At a lower temperature there is a transition from cloudy to clear, as the pores between particles become much smaller than the wavelength of light. This is called the cloudy-clear MFFT. A further transition is the temperature at which the film is able... 

Deformation of polymer material, which, in the first place, affects amorphous regions, takes place during its mechanical loading. First, there occur conformational transformations of passing molecules, and then, when reserve of their conformations is being partly exhausted, there begins mechanical deformation of valence angles and chemical bonds with their further break. 

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