Frictional properties of polyolefins treated with fluoroelastomer processing aids

Abstract

SYNOPSISA friction measurement system was designed that made possible the measurement of the friction coefficient between a polymer melt and a metal die wall. The shear stresses developed in the capillary rheometer and the friction coefficient measured in the friction measurement system were compared in a n attempt to understand the mechanism of fluoroelastomer processing aids (FPA) in the extrusions of polypropylene (PP) and linear low-density polyethylene (LLDPE). The apparent viscosity drops of LLDPE treated with FPA were larger than those of PP treated with FPA. The friction coefficient drops of LLDPE treated with FPA were also larger than those of PP treated with FPA. High viscosity FPA showed a moderate friction coefficient drop in the actual extrusion of PP even though it showed only a poor effect in the capillary rheometer. The frictional forces were calculated from the friction coefficient measurement made during extrusions of FPA-treated and untreated samples.

Friction of Nonwoven Wood–Polypropylene Fiber Mats on Heated Steel Platens

“…Table 1 provides the means and ranges for the values of k for the nonwoven mats at the different PP and normal stress levels. The values in Table 1 includes the data for the different temperature levels and dwell [12] and Gang et al [20] for solid PP. The frictional response of the mats with no PP fibers was substantially lower than the values in the literature [7][8][9].…”

“…Gang et al[20] found k for PP to drop to 0.017-0.021 at a higher temperature of 210 C. For solid wood, k was found to be between 0.10 and 0.13 at Representative frictional load curve for nonwoven mats at a surface temperature of 180 C, a 7.6-MPa normal load, and a 0-s dwell time.…”

Influence of Low Molecular Weight Additives on Die Extrusion Rheometer Flow of Thermoplastic Melts

“…This literature has had a rebirth in the late 1980s and 1990s [26 to 28] for linear low-density polyethylenes. The precipitation of fluoropolymers on die surfaces and its ability to induce slip in polyethylene [11,12,14,15,29] over a very wide range of conditions has also been noted. Reports of slippage with polymers other than polyethylene are scarce.…”

Influence of carboxylic acid additives on the flow behavior of molten thermoplastics

“…We have already mentioned the work of Turner and Moore 8 with stearic acid in rubber compounds. The precipitation of fluoropolymers on die surfaces and its ability to induce slip in PE over a very wide range of conditions has been described by various authors [23][24][25][26][27] in recent years. Reports of slippage with polymers other than PE are scarce.…”