MACHINERY | ALTERNATIVE COMPOUNDERS
Comparison of available surface area in a 1cm3 for fillers with a range of particle sizes
Particle size, Surface area, nm (approx) cm2
30 500 500 500 Source: Gneuss
consists of agglomerates, thereby reducing the active surface area.” In addition, powders with particles finer than 300nm are no longer free flowing and present the additional problem that, where the finest particles are smaller than 100nm, they are not permitted for health reasons. Within the EU, handling of nanoparticles is not permitted unless as agglomerates or in a suspension. “In order to use additives with extremely small
size, it is necessary to include them in a liquid suspension before working them into the polymer,” Gneuss claims. “Only in this way can agglomerates be avoided. The combined surface area of all the particles can be drastically increased and the quantity of particles necessary for the required effect can consequently be drastically reduced.” Currently, powders are processed to give a
particle size of typically around 500nm. Nanopar- ticles on the other hand are normally processed
(approx) 6
2 1 < 0.5 Quality
Agglomerate-free. Introduction in suspension.
Agglomerate-free. Introduction in suspension.
Low proportion of agglomerates. Introduction in powder form.
Usual proportion of agglomerates. Introduction in powder form.
space
with an assumed average size of 30nm. “By introducing an additive with a smaller particle size into the polymer in a suspension, it is possible to increase the total surface area of the particles by a factor of three. Compared with introducing the particles in powder form, a 12-times total surface area increase is possible. By introducing smaller particles in a suspension into the polymer, it is possible to make major reductions in the quantity of additive needed to achieve the required result. This has the additional advantage of making the polymer easier to recycle,” Gneuss says.
Alternative options Another variant on the multi-screw extruder concept is the planetary roller extruder. Entex is well-known for its range, which has been used in PVC compounding for over 50 years. The company says that since the 1980s, the mechanical design and process control of the equipment has been further developed, opening up many new fields of application. “In particular, the improvement of the tempering performance due to the use of modern manufacturing processes, system structures with several modules, and the development of lateral feeding and degassing mechanisms enable processes today that were not conceivable on this type of machine for a long time,” it says. “This allows to question the traditional processing methodology of PVC with the result that it can also be realised in a direct extrusion process without dry blends as an intermediate product.” At K2019, Entex will be showing a new addition to the product line. The L-WE 30 laboratory
Finding the right compounding solution
As competition intensifies, making sure the compounding process is fully optimised is becoming ever more important and tools to do that are in increasing demand. “More and more I’m getting confronted with a battery of questions about the ‘right’ compound- ing system for a certain application,” says Hans-Ulrich Siegenthaler, formerly with Buss and now an independent consultant.
“Smaller and bigger players in the compounding industry are research- ing methodologies to evaluate and accelerate these processes. Following these requests, we have developed instruments and tools or are using
86 COMPOUNDING WORLD | October 2019
them with a novel approach,” he says. Siegenthaler calls this tool kit
“Compounding Analytics.” He says it covers process technology aspects as well as manufacturing and economi- cal demands and he discussed the development at this year’s ANTEC conference in the US. Siegenthaler says process technol- ogy aspects have been evaluated and analysed over the past 10 years “with a prestigious panel of experts” for the seven most important compounding systems, based on 20 criteria. “The scrutinised results have, meanwhile, attained general validity due to the broad data base and the reputation of
the parties who contributed,” he says. Typical criteria include mixing behaviour, throughput rates, degas- sing rates, dosing options, process length and torque or drive power of a compounding system. “The production-relevant aspects play a very important role,” Siegent- haller says. “If, for example, a broad formulation
portfolio is to be produced on a plant, not all systems are equally well-suited; flexibility often has to be bought with additional equipment at higher cost. The respective aspects should be carefully and thoroughly weighed up and evaluated,” he says.
www.compoundingworld.com
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