Rheology, polymer

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. 

Specialized training is an absolute requirement for technical service personnel. A typical example is a person involved in supporting a polymer for which the use is the manufacture of rotationaHy molded consumer products. The technical service person is expected to be reasonably familiar with topics such as polymer rheology evaluations, gel-permeation chromatography, rotational mol ding, color science, regulatory requirements for use, mechanical and photochemical behavior of the pigmented polymer, optics, and so forth. Expertise of this variety caimot be expected to be obtained without careful... 

The extent of the long-chain branching of a series of ethyl xanthogen disulfide modified polymers carried to increasing conversion is shown in Table 1. No branches are found until 56% conversion. The gel point is a Htfle over 82%. Polymer rheology deteriorates between 56 and 82% conversion. 

Real polymers require more elaborate systems of springs and dash-pots to describe them. This approach of polymer rheology can be developed to provide criteria for design with structural polymers. At present, this is rarely done instead, graphical data (showing the creep extension after time t at stress a and temperature T) are used to provide an estimate of the likely deformation during the life of the structure. 

BARRIE, I. T., Chapter in Polymer Rheology (Ed. lenk, r. s.), Elsevier Applied Science Publishers, London (1978)... 

R. S. Lenk, Polymer Rheology, Allied Pubis. Ltd., London (1978). 

Malkin AYa, Leonov Al (1970) In Advances in polymer rheology, Khimiya, Moscow, p 98... 

Vinogradov GV, Malkin AYa (1977) Polymer rheology (in Russian) Khimia Publ, Moscow, pp 123, 222... 

Advanced adhesives are composite liquids that can be used, for example, to join aircraft parts, thus avoiding the use of some 30,000 rivets that are heavy, are labor-intensive to install, and pose quality-control problems. Adhesives research has not involved many chemical engineers, but the generic problems include surface science, polymer rheology and thermodynamics, and molecular modeling of materials... 

Polymer Rheology and Processing Universite Pierre et Marie Curie Vitry-sur-Seine, France... 

Modeling the Effect of Polymer Rheology on the Performance of Underwater Pelletizers... 

One of the common problems associated with underwater pelletizers is the tendency of the die holes to freeze off. This results in nonuniform polymer melt flow, increased pressure drop, and irregular extrudate shape. A detailed engineering analysis of pelletizers is performed which accounts for the complex interaction between the fluid mechanics and heat transfer processes in a single die hole. The pelletizer model is solved numerically to obtain velocity, temperature, and pressure profiles. Effect of operating conditions, and polymer rheology on die performance is evaluated and discussed. 

DIXIT ETAL. Polymer Rheology and Undenvater Pelletizers... 

The polymer rheology is modeled by extending the usual power-law equation to include second-order shear-rate effects and temperature dependence assuming Arrhenius type relationship. 

Experimental polymer rheology data obtained in a capillary rheometer at different temperatures is used to determine the unknown coefficients in Equations 11 - 12. Multiple linear regression is used for parameter estimation. The values of these coefficients for three different polymers is shown in Table I. The polymer rheology is shown in Figures 2 - 4. 

Figure 2. Polymer rheology for Melt Index 24 resin.

The effect of polymer rheology on the pressure drop is shown in Figure 10. Top curve is for a polymer with low melt index (1.03), middle curve is for medium melt index (10.5), and the bottom curve represents a polymer with... 

Center of Excellence in Extrusion and Polymer Rheology, Eastern Regional Research Center, Agricultural Research Service, U.S. 

Lodge AS (1964) Elastic liquids an introductory vector treatment of finite-strain polymer rheology. Academic, London... 

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