By: David Vink
EUROPEAN PLASTICS NEWS
November 5, 2013
The IKT Institute of Plastics Technology at Stuttgart University exhibited for the first time at a K show this year, focusing in the "Science Campus" area of the fair on lightweight construction and bioplastics themes.
IKT demonstrated the use of thermography as a non-destructive test method for lightweight plastic parts and compounding of additives into bioplastics with a mini-compounder fitted with an open processing zone.
In the area of high performance single-screw compounding machinery, Stefan Epple of IKT was involved in further development of the Helibar concept of extrusion machinery producer Extrudex.
Although the Helibar extruder's continuously helical grooved barrel achieves high melt throughput by generation of high pressure, Epple says the high throughput means short residence times that can cause decreasing melt homogeneity in some materials.
The IKT project on the Helibar system seeks to address the homogeneity issue by "development and investigation of suitable mixing section geometries through systematic variation of screw and barrel geometry, along with development of an objective method to evaluate melt homogeneity."
As part of its work in reactive extrusion of new polymers and further development of existing polymers, IKT has developed a new "RIM pultrusion" in-situ process for production of continuous glass-fiber-reinforced nylon 6 semi-finished products at speed of 1 meter per minute with potential of 2m/minute.
Reaction injection molding applies here, since the process involves mixing of low viscosity caprolactam monomer with 2.5 percent weight activator as one component and with 3.76wt percent catalyst as a second component in a protective gas atmosphere (against influence of humidity), followed by injection of the still low viscosity mixture into a mold tool.
In bioplastics, IKT has investigated bio-based thermoplastic polyurethane as an impact modifier for polylactide acid, together with 3 percent methylene diphenyl-diisocyanate coupling agent. Benefits were found in elongation at break and impact strength values, compared with the usual PBAT biodegradable impact modifier used in PLA. IKT researcher Linda Goebel says IKT will also look at compounding natural fibers into bio-TPU-modified PLA.
Having investigated welding properties of various PBAT-modified PLA compounds, Goebel says further work will be done with a coupling agent and has indicated IKT may also look at weldability of bio-TPU-modified PLA compounds too.
In development of compounds with new functional characteristics and advanced processing, IKT has compounded Carl Schenk's plate-like shaped Cubrotec 5000 copper particles in the Ultramid B40 grade of nylon 6 from BASF, using a special die with a narrow 0.5 millimeter diameter entry and a 15 percent angle leading to the exit as an expansion zone. This technique overcomes the problem of particle orientation in the length direction, resulting in molded test pieces with 2.4-3.9 times higher heat conductivity in the thickness direction. This could enable design of thinner walled compacter plastic moldings in applications as diverse as coil formers and heat exchangers, IKT researcher Otto Skrabla suggests.
In laser processing, Benjamin Neubig of IKT works on selective heating of thermoforming sheet and having obtained small thermoformed parts with better wall thickness distribution and increased compression resistance, he now seeks to apply the technique to larger parts.
IKT has worked in selective laser sintering (SLS), with the Fraunhofer ICT Institute for Chemical Technology in Pfinztal, Germany, with addition of PEEK from Victrex to produce a material that can absorb laser energy better and therefore heat more thoroughly underneath the material surface.
The special material is key to a new so-called "additive-supported selective laser sintering" process.
According to IKT researcher Michael Kroth, tensile strength and stiffness values of ASLS parts in the special carbon-black-modified PEEK "almost reached the values required of injection molded reference samples."
3D printing also was a theme at IKT in a new project aimed at development of 3D printing in bio-based plastics, with the company Biopro and Fraunhofer Institute as IKT's partners.