Polymers behaviour

Most properties of linear polymers are controlled by two different factors. The chemical constitution of tire monomers detennines tire interaction strengtli between tire chains, tire interactions of tire polymer witli host molecules or witli interfaces. The monomer stmcture also detennines tire possible local confonnations of tire polymer chain. This relationship between the molecular stmcture and any interaction witli surrounding molecules is similar to tliat found for low-molecular-weight compounds. The second important parameter tliat controls polymer properties is tire molecular weight. Contrary to tire situation for low-molecular-weight compounds, it plays a fimdamental role in polymer behaviour. It detennines tire slow-mode dynamics and tire viscosity of polymers in solutions and in tire melt. These properties are of utmost importance in polymer rheology and condition tlieir processability. The mechanical properties, solubility and miscibility of different polymers also depend on tlieir molecular weights. 

Melt fracture results from a too large rubber-elastic deformation. This is governed by the polymer behaviour and by the rate of deformation. The strain rate must be lowered, which may be accomplished by a lower, and therefore unattractive, rate of production. The time scale of the elastic deformation can also be increased in another way, namely by making the conical channel to the die more pointed the same strain is then reached after a longer time. This goes at the cost of extra pressure and power, since the resistance of the chaimel is increased. 

G. Marrucci and N. Grizzuti, Predicted effect of polydispersity on rodlike polymer behaviour in concentrated solutions, J. Non-Newt. Fluid Mech., 14,103 (1984). 

A second important event was the development by Hosemann (1950) of a theory by which the X-ray patterns are explained in a completely different way, namely, in terms of statistical disorder. In this concept, the paracrystallinity model (Fig. 2.11), the so-called amorphous regions appear to be the same as small defect sites. A randomised amorphous phase is not required to explain polymer behaviour. Several phenomena, such as creep, recrystallisation and fracture, are better explained by motions of dislocations (as in solid state physics) than by the traditional fringed micelle model. 

Very important phenomena in polymer behaviour, such as viscoelasticity, stress, strain, volume and enthalpy relaxation, ageing, etc., are characterised by time-dependence of the polymer properties. 

To verily this hypothesis, a careful study concerning the azo-polymers behaviour in the presence of UVA IS irradiation was carried out. The trans- and cA-configuration... 

Polyethylene is a man-made homopolymer. Its chemical synthesis is well understood. It is a random walk polymer with little secondary or tertiary structure. A batch can largely be characterised by its molecular weight distribution, and its rheology can be related to these parameters by developed rules of polymer behaviour. The action of specific chemicals as plasticisers can be used to modulate these bulk properties in a predictable way, allowing the nature and characterisation of its glass to fluid transition to be predicted. 

Luminescence properties of and phenomena in polymer systems continues to be widely researched in connection with mechanisms of polymer degradation and stabilization, molecular dynamics, solubility, blend miscibility, and solar energy harnessing. A number of interesting reviews have appeared. Molecular dynamics of polymers in solution and in the solid state have been covered, as has excimer formation,photoresponsive polymers,behaviour of polymer gels, and photochromic phenomena. Photoisomerization of enzymes and model compounds has also been discussed in depth, with particular emphasis on proteins and synthetic polymers containing azo-compounds or spirobenzopyrans. ... 

The quest for a virtual material requires modelling of polymer behaviour. 

Polymer-polymer interfaces are an important area of study since the interfacial behaviour is fundamental to the bulk properties of the system. This is particularly true when two or more polymers are mixed to form a blend, but the interface also plays a dominant role in areas such as adhesion, welding, surface wetting and mechanical strength. To understand fully polymer behaviour in such applications, the interface must be characterised at a microscopic level. Through deuterium labelling the interface between otherwise indistinguishable polymers can be studied, and neutron reflectivity provides unprecedented detail on interfacial width and shape. In addition to the inherent interdiffusion between polymers at a polymer-polymer interface, the interface is further broadened by thermally driven capillary waves. Capillary waves... 

Principal structures of aminic stabilizers, their involvement in individual degradation processes of polymers, behaviour in mixtures with other polymer additives and an outline of environmental impacts due to the amines are included. The most relevant literature sources published by the first quarter of 1994 are reported. Some earlier data has to be mentioned as a reminder of the original ideas and to improve the interpretation of results. Where relevant, recent comprehensive reviews are cited. Principal types of commercial stabilizers are included in Appendix. 

We have discussed at some length theories which attempt to describe the stresses needed to cause yield and the molecular reorganisation resulting from yield. The yield criteria have related to measurements of somewhat arbitrary features of the stress-strain curves, with the implicit assumption that these features coincide with the onset of permanent deformation. Various models of elastic-plastic deformation have been used in describing the polymer behaviour. 

There are several references to this technique pioneered by Price [81-91] and his co-workers. Two systems have been investigated to model different aspects of flame-retarded polymer behaviour in a fire. One system uses a continuous laser to model radiative heat at a level similar to that from a burning item in a room Are and the other uses a pulsed laser to model conditions immediately behind the flame front. 

The measurements of the pressure drop across a porous filter due to polymers are intended to result in a phenomenological description of the polymer behaviour. Therefore, the most direct and simple scalings are used and the pressure drop is not turned into a nondimensional form. The pressure drop across the porous filter is scaled as... 

Solid Polymer Behaviour Under Longitudinal Load... 

Solid Polymer Behaviour Under Longitudinal Load 249 7.7.2 Plastic Deformation and Stretching... 

The atoms of a polymer are held together firmly by valence bonds, forming a single entity. In polymer substances, weaker van der Waals forces have an effect on the components of the macromolecules that form the system. Polymer behaviour is viscoelastic, which is closely connected with slow relaxation processes in systems. 

Legrand P, Lesieur S, Bochot A et al (2007) Influence of polymer behaviour in organic solution on the production of polylactide nanoparticles by nanoprecipitation. Int J Pharm... 

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