Rheological characterization of linear low‐density polyethylene–Fischer–Tropsch wax blends

Abstract

The thermal and rheological behavior of blends of a Fischer-Tropsch (F-T) wax with linear low-density polyethylene (LLDPE) were investigated by differential scanning calorimetry and cone-and-plate rheometry. F-T wax is used as a possible low-cost processing aid alternative for LLDPE masterbatch applications. The melting-and crystallization thermograms indicated a two-phase solid-state morphology and full compatibility in the fully molten material.Both the high-melting and low-melting phase contained co-crystalized wax and polymer. Rheological data of F-T wax-LLDPE blends over the full composition range was also obtained. The zero-shear viscosity data was adequately predicted by the Friedman and Porter mixing rule:with α = 3.4. This implies that the melt viscosity is dominated by the effects of polymer chain entanglement and that the main consequence of adding the wax is to reduce the concentration of the polymer present. The complex viscosity also fitted this model albeit with α = 4.81. All Han plots, that is, plots of the logarithm of the storage modulus (G') against the logarithm of the loss modulus (G"), were linear. Within the experimental uncertainty, they were essentially unaffected by variations in blend composition, temperature and the applied angular frequency. Additionally, Cole-Cole plots were also in agreement that wax-LLDPE blends are miscible at melt state. This supports full miscibility of the F-T wax-LLDPE blend system down to temperatures as low as 120 C.

The role of additives in rheology and processing

“…[8] Finally, Ramjee et al describe the use of Fischer-Tropsch wax as rheological modifier for linear low-density polyethylene (LLDPE), even including material systems where LLDPE is the minor phase and the wax is the major phase. [9] Another topical category is reactive processing and compatibilization. Williamson and coworkers from Dow show how a free radical generator (FRG) can be incorporated into LLDPE to add long-chain branching to the material and change its flow behavior during extrusion of films.…”

“…[ 8 ] Finally, Ramjee et al describe the use of Fischer‐Tropsch wax as rheological modifier for linear low‐density polyethylene (LLDPE), even including material systems where LLDPE is the minor phase and the wax is the major phase. [ 9 ]…”