A novel processing aid for polymer extrusion: Rheology and processing of polyethylene and hyperbranched polymer blends

Abstract

The use of hyperbranched polymers (HBPs) as a processing aid for linear low density polyethylene (LLDPE) was investigated. Various generation (or pseudo-generation) HBPs were used which had either 16 carbon atom alkanes or a mixture of 20/22 carbon atom alkanes on the end groups. In addition, the degree of end group substitution was studied. Blends of up to 10% HBP content were mixed via extrusion at 170 °C to produce 1 mm diameter fibers. Processability, surface appearance and the rheological properties of the blends were evaluated. It was found the power requirement for extrusion was significantly decreased as a result of reduced blend viscosity, and also, the mass flow rate for a given extruder speed was greater than virgin LLDPE for all HBP blends. Melt fracture and sharkskin of the blends was successfully eliminated, and minimal preprocessing time was required for the effect to take place. Surface analysis using x-ray photoelectron spectroscopy and transmission electron microscope techniques were performed with both showing that the HBP had a preference to accumulate at the fiber surface. Rheological experiments were similarly affected, therefore, the blend viscosity is really a composite of a HBP rich phase and a neat LLDPE phase. It is hypothesized that the HBP rich phase acted as a lubricating layer at the polymer/die wall interface. The HBP with a greater degree of end group substitution acted better as a processing/rheological property aid. Blends of LLDPE and paraffin wax were also studied. The surface appearance of HBPs/LLDPE blends was superior to those blends mixed with paraffin wax, as was the extruder performance. The results suggest that HBPs, at trace levels (≈500 ppm), may offer a number of advantages when used as a processing aid for LLDPE.

Role of cyclization in the synthesis of hyperbranched aliphatic polyesters

“…We are convinced that these results possess significance with respect to the studies published on further functionalization, physical behavior and mechanical properties of these polymers [22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38] since in most of these works the materials have been considered to possess considerably higher molecular weights and hydroxyl functionality than observed in this work. …”

“…3. However, there is one major difference: instead of TMP, an ethoxylated pentaerythrol core was used for the synthesis of these materials 38) . For characterization, the same experimental techniques were applied as in section B of this work.…”

“…Hyperbranched aliphatic polyesters were first described by Baker et al 20) and investigated by Hult et al 21) Hult et al used a portionwise monomer addition strategy, adding 2,2-bis(dihydroxymethyl)propionic acid (BisMPA = AB 2 monomer) in "pseudo-generation" equivalent portions to a 1,1,1-tris(hydroxymethyl)propane core molecule (TMP = B 3 core) under acidic catalysis. In 1995, this work resulted in the commercially available hyperbranched polyols (Perstorp, Boltornm), which have been used by several research groups for potential application [22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38] . The incremental ("generationwise") addition mode was reported to permit control over the degree of polymerisation.…”

Viscoelastic properties and phase behavior of 12‐tert‐butyl ester dendrimer/poly(methyl methacrylate) blends

“…Blends of up to 10% hyperbranched polyesters were found to reduce melt viscosities and eliminate surface defects, melt fracture, and sharkskin. 27 These studies show that the blending of hyperbranched structures and dendrimers with linear polymers is a promising route to novel materials used in modern materials technology. Blends fabricated with dendrimers are of particular interest because these regularly branched, monomolecular structures are prepared in small batches.…”

Influence of end groups in hyperbranched polyesters used as modifiers in the characteristics of epoxy thermosets cured by adipic dihydrazide

“…Moreover, the great number of terminal groups has a significant effect on the reactivity, can increase the compatibility with the resin and helps to maintain thermomechanical characteristics [9,10]. Based on their unique properties, HBPs have been applied not only as tougheners for ther-Influence of end groups in hyperbranched polyesters used as modifiers in the characteristics of epoxy thermosets cured by adipic dihydrazide mosets but also in cross-linking or adhesive agents [11], compatibilizers [12], dispersers [13], processing aids, and rheology modifiers [14,15]. One of the most effective methods of inhibiting crack growth after impact is the addition of a second phase that induces the formation of particles that absorb the impact energy and deflect the crack [5].…”