Wall slip and melt fracture of poly(lactides)

Abstract

The wall slip and melt fracture behaviour of several commercial polylactides (PLAs) as well as their rheological properties under shear and extensional have been investigated. The PLAs have had weight-average molecular weights in the range of 10 4 -10 5 g/mol and studied in the temperature range of 160-200 • C. The solution properties and linear viscoelastic behaviour of melts indicate linear microstructure behaviour. PLAs with molecular weights greater than a certain value were found to slip, with the slip velocity to increase with decrease of molecular weight. The capillary data were found to agree well with linear viscoelastic envelope once correction for slip effects was applied. The onset of melt fracture for the high molecular weight PLAs was found to occur at about 0.2 to 0.3 MPa, depending on the geometrical characteristics of the dies and independent of temperature. Addition of 0.5 wt.% of a polycaprolactone (PCL) into the PLA that exhibits melt fracture was found to be effective in eliminating and delaying the onset of melt fracture to higher shear rates. This is due to significant interfacial slip that occurs in the presence of PCL.

Reactive extrusion of PLA, PBAT with a multi-functional epoxide: Physico-chemical and rheological properties

“…14 shows the dependence of ''R h '' on the average molecular weight Mw for the neat and modified PLA with Joncryl, compared to the scaling relation Rh ¼ 0:017 Â Mx 0:56 for monodisperse and linear PLA [27]. It can be noticed that the data of the modified samples diverge from the reported results by the relation since Joncryl is added in the system.…”

Transition from microcellular to nanocellular PLA foams by controlling viscosity, branching and crystallization

“…mg.mL -1 were prepared in THF for each polymer and injected sequentially to construct a curve with slope dn.dc -1 [24]. The refractive index values for PLA, PLA-TAM, and PLA-GMA were determined to be 0.0482 ml.gm -1 , close to values reported in the literature [25].…”

Entry flows of polylactides with slip

“…It has been reported that PLAs with molecular weight greater than a certain value exhibit slip [12]. This might be expected due to their linear structure and similarities with other linear molecules that exhibit slip and melt fracture [17][18][19][20][21][22][23][24].…”

“…The K-BKZ constitutive equation was used to model the rheological data satisfactorily, including strain hardening which might occur in spite of the linear macrostructure of these polymers [7,11]. The processability of PLAs has also being studied in the literature, particularly its processing as can be assessed by melt fracture phenomena [12][13][14]. Ways to eliminate melt fracture instabilities in the capillary flow of PLAs have been reported in detail by Jazrawi et al [14] using methods previously developed for polyethylenes [15,16].…”

“…The rheology of PLAs has been extensively studied in the literature [6][7][8][9][10][11][12]. The K-BKZ constitutive equation was used to model the rheological data satisfactorily, including strain hardening which might occur in spite of the linear macrostructure of these polymers [7,11].…”