Extrudate swell of high density polyethylene. Part I: Aspects of molecular structure and rheological characterization methods

Abstract

Two high density polyethylene (HDPE) resins–samples 801 and 802–both nominally the same material, as they are taken from successive batches of the same commercial grade, are characterized for their molecular structure and rheological properties. Gel permeation chromatography (GPC) and low angle laser light scattering (LALLS) results must be interpreted in combination with rheological data to show the presence of somewhat more high molecular weight material in 802 that in 801. Small amplitude oscillatory shear, steady shear, and capillary shear measurements performed in different laboratories show consistently higher shear viscosity values at low shear rates for sample 802. Extensional viscosity measurements show similar results. The interpretation of rheological data in terms of molecular structure could be complicated by the possible presence of long chain branching (LCB). The zero shear viscosity and discrete relaxation spectrum is estimated for both samples. The small rheological difference between 801 and 802 forms the basic information for understanding their time dependent extrudate swell behavior, as will be described in Part II.

Mixed finite element methods for viscoelastic flow analysis: a review

“…A significant portion of the work on numerical analysis of viscoelastic flow of polymer melts is based on streamline integration methods employing KBKZ-type constitutive models with a damping function due to Papanastasiou, Scriven and Macosko [144] (PSM) or Wagner [145]. For example, Goublomme and Crochet [11] and [146] analysed the extrudate swell of high-density polyethylene (HDPE) melt as reported by Koopmans [147] using a KBKZ model, see also related work in [148] and [149]. With a modified Wagner damping function giving a non-zero second normal stress difference, quantitative agreement with experimental results could be obtained, albeit at a large ratio of second and first normal stress difference.…”

Effect of long chain branching on linear-viscoelastic melt properties of polyolefins

“…[7] When the LCB content is very low (less than 1 LCB /10 4 C), its effect on the radius of gyration goes unnoticed and values of g ≈ 1 are obtained [42]. The effect of such a low amount of LCB has been explored in LDPE and in modified linear polymers of ethylene/α-olefins and propylene (PP) by irradiation, electron-beam treatment, peroxide reaction, and thermal/mechanical degradation [7,10,17,[44][45][46][47][48][49][50][51][52][53][54][55][56][57][58][59]. In principle, lowpressure processes (chromium-based and Ziegler-Natta type catalysts, developed in the 1950s and 1970s, respectively) yield linear species.…”

A comprehensive experimental study and numerical modeling of parison formation in extrusion blow molding

“…The higher the relaxation time is, the more pronounced the diameter and the thickness swell is because of the increased elastic behavior. The knowledge of the different molecular weight moments of the resin provides insight to its molecular weight distribution and to the amount of large molecules for each resin causing the difference in their swelling characteristics [10]. Once again, the overall swell profiles presented in Fig.…”

“…Koopmans [10][11][12] studied the swelling characteristics of two high density polyethylene (HDPE) resins taken from successive batches of the same commercial grade. He observed that the maximum swell and the time to reach this value are very sensitive to the molecular weight distribution of the resin.…”