Go to  Advanced Search

Rheology and processing of high-density polyethylenes (HDPEs) : effects of molecular characteristics

Show simple item record

dc.contributor.author Ansari, Mahmoud
dc.date.accessioned 2012-09-27T21:55:59Z
dc.date.available 2012-09-27T21:55:59Z
dc.date.copyright 2012 en
dc.date.issued 2012-09-27
dc.identifier.uri http://hdl.handle.net/2429/43283
dc.description.abstract In this study, the linear viscoelastic properties of two series of Ziegler-Natta and metallocene HDPEs (ZN-HDPEs and m-HDPEs respectively) of broad molecular weight distribution (MWD) have been studied. Relationships between the zero-shear viscosity and molecular weight (Mw) and molecular weight distribution show that the breadth of the molecular weight distribution (MWD) for m-HDPEs plays a significant role. Other interesting correlations between the crossover modulus and steady state compliance with MWD of both these classes of polymers have also been derived. Finally, the steady-shear viscosities from capillary rheometry are compared with LVE data to check the applicability of the empirical Cox-Merz rule. It is shown that the original Cox-Merz rule is approximately applicable for HDPEs for narrow to moderate MWD and fails for those HDPEs having a wide MWD due to the occurrence of wall slip. The processing behavior of both series of HDPEs was investigated. Their melt fracture behaviour was studied primarily as a function of Mw and MWD, and operating conditions i.e. temperature and geometrical details and type of die (capillary, slit and annular). It is found that sharkskin and other melt fracture phenomena are very different for these two classes of polymers, although their rheological behaviors are nearly the same for many of these. It is also found that critical conditions for the onset of various melt fracture phenomena depend significantly on the type of die used for their study. The slip behaviour of these resins was also studied as a function of Mw and MWD. It is found that the slip velocity increases with decrease of Mw, which expected to decay to zero as the Mw approaches a value with characteristic molecular dimension similar to surface asperities. For HDPEs that exhibit stick-slip transition (narrow to moderate MWD), the slip velocity has been found to increase with increase of polydispersity. The opposite dependence is shown for HDPEs of wider molecular weight distribution that do not exhibit stick-slip transition. A criterion is also developed as to the occurrence or not of the stick-slip transition which is found to depend strongly on Mw and its distribution. en
dc.language.iso eng en
dc.publisher University of British Columbia en
dc.relation.ispartof Electronic Theses and Dissertations (ETDs) 2008+ en
dc.title Rheology and processing of high-density polyethylenes (HDPEs) : effects of molecular characteristics en
dc.type Text en
dc.degree.name Doctor of Philosophy - PhD en
dc.degree.discipline Chemical and Biological Engineering en
dc.degree.grantor University of British Columbia en
dc.date.graduation 2012-11 en
dc.type.text Thesis/Dissertation en
dc.description.affiliation Applied Science, Faculty of
dc.degree.campus UBCV en
dc.description.scholarlevel Graduate en

Files in this item

Files Size Format Description   View
ubc_2012_fall_ansari_mahmoud.pdf 1.289Mb Adobe Portable Document Format   View/Open

This item appears in the following Collection(s)

Show simple item record

UBC Library
1961 East Mall
Vancouver, B.C.
Canada V6T 1Z1
Tel: 604-822-6375
Fax: 604-822-3893