technology | Polymer foam
Right: Foams made with PP containing Dymalink 9200
from Total Cray Valley are more stable and display an
improved skin while cells are much more homogeneous
additives. He said the company’s Mistrocell talc, for example, can be used as a nucleant for physically foamed structures. Mistrocell is a micro-lamellar talc that is said to yield a cell density twice as high as with more conventional lamellar talc. “By virtue of its higher active surface area, micro-
lamellar talc enables more gas to be entrapped and so generates more cell nuclei,” Crépin-Leblond said. Optimum talc loading depends on the formulation and process used, so it is important to test different loadings, he noted. Tests using MuCell physical foam injection moulding process showed that, with 5% Mistrocell, a weight reduction of 10% could be achieved with same specific elastic storage modulus as unfilled solid PP. Speaking at a recent SPE conference, Reedy
Chemical Foam CEO Peter Schroeck explained how “Kinetic Nucleators” can improve cell distribution in extruded foams. Nucleating agents create a starting point from where a cell can form as gas comes out of solution. The Kinetic Nucleator is an inorganic compo- nent of a particular aspect ratio and is pelletised exclusively by Reedy. “A closed-cell structure is crucial in keeping
mechanical properties and part characteristics,” Schroeck said. “In order to maintain mechanical properties like impact strength, tensile strength and elongation-at-break, the goal is usually to achieve the smallest closed cell structure possible. A higher number of nucleation sites will yield smaller cells and
more rapid cell expansion.” Reedy’s new Kinetic Nucleator (KN) is claimed to
improve component dispersion by creating turbulent flow along the boundary layer during extrusion process- ing, where laminar flow is more typical. Talc typically builds up over time on the screw, barrel walls and die, requiring more frequent cleaning than in non-foaming processes, according to Schroeck. He said that the introduction of KN improves mixing and component dispersion along the boundary layer. “This creates smaller and more evenly dispersed cells overall allowing for more efficient use of the same volume of gas.” Development work has shown that polypropylene
foamed with KN yields smaller cells and lighter weights. Smaller particles typically yield smaller cells, but in this case the smallest cells were generated while using a particle 30 times larger than common talc. Schroeck attributes this to KN’s morphology, which generates a greater number of nucleating sites through the creation of turbulent flow in the barrel and at the exit. Reedy says that its Safoam KN-521M pellets are best
used alongside its Safoam foaming agent pellets. Last year, Reedy Chemical Foam introduced Safoam CE-335, a high temperature endothermic foaming agent with this premium nucleator. It offers a higher processing temperature than is typical for endothermic foaming agents and this has resulted in quick market accept- ance for TPO core back injection moulding, PP raffia and PET foam extrusion, the company says. Pending programs include HDPE extrusion. The price of CE-335 is said to be in line with common commercial CBAs.
This graph shows how dosing variation is reduced using Clariant’s latest generation Hydrocerol CFAs
66 COMPOUNDING WORLD | January 2017
CFA developments Clariant has just announced a new generation of its Hydrocerol chemical foaming agent (CFA) masterbatch- es for use in production of extrusion blow moulded (EBM) packaging. It says the new formulations include proprietary features that result in faster melting, better dilution in the matrix polymer, a more consistent
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