PROCESSING | SIMULATION
Kunststofftechnik Paderborn is working to improve the screw design tools in its Sigma13 software
Source: Kunststofftechnik Paderborn
Recycling demands There are also growth areas of plastics compound- ing where process simulation tools such as Sigma are proving to be of particular value, including processing of plastic recyclates and modification of polymers using carbon fibres and carbon fibre recyclates. “These recyclates accumulate as production residues,” says Malatyali. “There is also a steadily growing demand for fibre-reinforced thermoplastics resulting from their significantly improved physical and mechanical properties. In addition, new laws such as the EU Waste Frame- work Directive and the End-of-Life Vehicle Directive require carbon fibre residues to be recycled.” These new legal requirements will make sustain-
Right: Visualisation of velocity profiles in the extruder simulated
within Sigma3D software
able recycling methods for fibre composites essential in the future and production of thermo- plastic matrix/fibre recyclates can provide such a recycling route. “For this, the incorporation of carbon fibre recyclates into thermoplastics on various compounding extruders has been investi- gated,” Malatyali says. “The initial focus was on the dosing and feeding behaviour according to the fibre type. A model to describe fibre length change during compounding for carbon fibre recyclates was incorporated in Sigma, which takes into account the different input distribution of fibre lengths.” KTP says that the input variables of recycled plastics and fibres vary depending on the supply source. For that reason, the focus of its work in this area has been on validation of the model with different fibre types. Other areas of development in Sigma13 include development of screw design rules, the influence of processing conditions on molar mass degrada- tion, and an extension of the Sigma3D interface. KTP says the screw design rules currently established in the Sigma software contain two
38 COMPOUNDING WORLD | March 2021
major content-related parameters - geometric boundary conditions and process rules. To establish the geometric boundary, a number of properties are determined for all screw elements on the basis of geometric data. This includes conveying effect, residence time behaviour, pitch effect, volume, self-cleaning, mixing effect and shear effect. These characteristics result from the definition of the geometry and not from analytical simulations. These properties of the elements are automatically generated using the screw design rules. The set of rules is defined so that the designed
screw can be checked according to the process zones with the help of the screw design laws. The definition of generally valid process rules is of particular importance because this set of rules can be used to review the design of a process. After the user has designed the screw, a check can be carried out against the design rules. Depending on the result, Sigma13 reports an improvement or an error.
Modelling degradation Material degradation refers to mechanisms that cause a shortening of the molecular chains of plastics and consequently lead to a decrease in mean molecular weight. These processes lead to a change in the chemical structure and influence
IMAGE: KUNSTSTOFFTECHNIK PADERBORN
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