Viscous flow of molten polyethylene resins

SynopsisThe role of the capillary end correction in flow analysis of molten lowdensity polyethylenes has been analyzed. In spite of limitations of accuracy a quantitative approach has been undertaken. The results are much more complicated than predicted by Bagley in his early reports. The elastic component of the end correction is controlled by shear stress and shear modulus. The latter is affected by the size of the subchain between entangles, M e , and by the degree of long-chain branches. Both are eventually dependent on the length of the chain, i.e., its molecular weight. In addition shear stress and temperature affect the process of disentanglement. Capillary end correction increases with increasing molecular weight and shear stress and with decreasing temperature. The available analysis of branching is still in controversy, and therefore no numerical parameters are yet proposed. A consistent theory of the response of entanglement couplings to shear forces and temperature is evaluated.

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“…For the same reasons, Guillet3* preferred to use eq. (26). The latter made a slight correction for the effect of short branches on 9.…”

Section: Increase Shear Itw (Log)mentioning

confidence: 99%

Role of capillary end correction in flow analysis of molten polyethylene

Ram

Narkis

1966

J of Applied Polymer Sci

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“…At very e ϭ 9(n ϩ 1) 2 (⌬P e ) 2 32Ͳ 2 (4) low shear rates (Ͳ Ͻ 10 Ϫ2 s Ϫ1 ), a molten polymer behaves roughly as a Newtonian fluid. Beyond this point the shear stress of molten HDPE has a nonlinand: ear relationship with shear rate.…”

mentioning

confidence: 98%

“…2 In a blow molding process HDPE is extruded into When a sinusoidal rotational shear strain is applied, a molten tube called a parison. After the bottle molds as done in dynamic measurements, G is a function are clamped around the parison air is blown into of the rotational speed, Ͷ, and as a complex function the parison which expands it to conform to the mold.…”

mentioning

confidence: 99%

The effect of multiple extrusion passes during recycling of high density polyethylene

Zahavich¹,

Latto

Takács

et al. 1997

Adv. Polym. Technol.

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“…6.5-7 kcal./mole at fixed shear stresses, and less than 5 kcal./mole at fixed shear rates. 5 The flow activation energy of 6-7 kcal./ mole has been also postulated by Kauzmann and Eyrings for normal hydrocarbon chains of high molecular weights. The absolute values of the viscosity thus obtained here also seem to indicate good agreement with the viscosity data directly obtained from flow experiments.…”

mentioning

confidence: 95%

Measurements of relaxation time of a polyethylene melt

Aloisio¹,

Matsuoka²,

Maxwell

1966

J. Polym. Sci. A‐2 Polym. Phys.

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SynopsisA device for measuring the elasticity of polymer melts: has been designed by one of us (B. Maxwell). The device was used to obtain the relaxation modulns in shear of a linear polyethylene melt. From these data a discrete relaxation spectrum was derived. The range of the obtained spect,rum was confirmed to correspond to the terminal zone of the "entanglement plateau" of the spectrum. The limiting dynamic viscosity (as frequency approaches zero) was obtained by integrating the relaxation modulus with respect to time. The viscosity and its activation energy were found to agree closely with the flow viscosity and the flow activation energy, respectively, involved in capillary flow.Even though it is well known that polymer melts are generally viscoelastic, in their flow studies they are often treated as if they are purely viscous liquids. This oversimplification is particularly serious in some materials where the elastic response to an external force is of the same magnitude as the viscous response. In processing polymeric materials, for example, there is a strong indication that the elastic energy plays an important role in melt the extent to which strains are frozen into the final product ifi also related to the elastic contribution and affects the mechanical properties of the solid.While there is a very large amount of data available on the flow viscosity of polyethylene melt^,^'-^ only a few investigations have been carried out on the viscoelastic properties within the linear range. ' We have constructed a device suitable for making measurements of stress relaxation on a polymer melt at elevated temperatures. In stress relaxation a strain is applied and held constant while the decaying stress is measured as a function of time. Hence, the possibility of errors arising from friction, as in a creep experiment, is eliminated. If the strain is kept small enough, the mathematics developed for linear viscoelasticity is applicable, thus simplifying the analysis and practical application of the data.The device for performing stress relaxation experinients in shear is shown in Figure 1. The sample is premolded in the form of two hollow cylinders. I t is then loaded in the apparatus and melted under nitrogen atmosphere. The shear strain is applied by rotating the inverted cup.

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Viscous flow of molten polyethylene resins

Cited by 52 publications

References 15 publications

Role of capillary end correction in flow analysis of molten polyethylene

Role of capillary end correction in flow analysis of molten polyethylene

The effect of multiple extrusion passes during recycling of high density polyethylene

Measurements of relaxation time of a polyethylene melt

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