The purpose of these screening extrusion experiments was to briefly assess the effect of MW and MWD on the melt fracture
characteristics of these CRPP materials.
Further, instabilities such as melt fracture
can be quantified and predicted if viscosity data is obtained from a capillary rheometer or slit-die viscometer.
Total says high extrusion speeds can be reached at low extrusion temperatures and without any melt fracture
, while keeping an excellent surface finish.
High extrusion speeds can be reached at low extrusion temperatures and without any melt fracture
while keeping an excellent surface finish, the company says.
The compound of CoBR with natural rubber was used as a reference for a BR grade which possesses good processability, as can be seen in figure 4a; while the standard NdBR (Buna CB24) compound produces smooth Garvey profiles at low extrusion rates; they turn rough at 90 rpm and finally exhibit melt fracture
at 120 rpm (figure 4b).
The phenomena he considers include the transformation of the characteristic viscoelastic spectrum with molecular-weight change and/or dilution; the molecular-weight dependence of the zero-shear viscosity and of the steady-state compliance, and their respective transition points; the relation between viscoelasticity and diffusion; the damping function; and the slip-stick melt fracture
Chemist Koopmans and physicist, mathematician Jaap den Doelder (both with a giant chemical company), and Jaap Molenaar (applied mathematics, Wangingen U., the Netherlands) address the problem that when polymer is extruded at a fast enough rate to make a satisfactory profit, it is often distorted, a phenomenon called melt fracture
. Their topics include pictures of polymer melt fracture
through optical microscopes and scanning electron microscopes, polymer characteristics, polymer rheology, polymer processing, melt fracture
experiments, variables, understanding melt fracture
, modeling it, and preventing it.
blown-film; - profile extrusion; - melt fracture
of polyolefines; - injection moulding of composites; - new simulation methods.
In this process, a polymer melt is extruded through a capillary and is subsequently stretched with a hot airstream until flow instabilities or melt fracture
cause it to break up into particles.
This form of melt fracture
is visually observable as a frosty white matte surface haze, and is undesirable for transparent bottle applications.