By: David Vink
EUROPEAN PLASTICS NEWS
December 23, 2013
The IKT Institute of Plastics Technology at Stuttgart University exhibited at a K show for the first time at the 2013 event in Düsseldorf, Germany in October, in the “Science Campus” area of the fair focusing 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 is developing 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 downside is short residence times which 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 and existing polymers, IKT has developed a new “RIM pultrusion” in-situ process for production of continuous glass-fiber-reinforced PA 6 semi-finished products. Production speeds are one meter per minute with potential of two meters/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 3.76 wt percent catalyst as a second component in a protective gas atmosphere (against influence of humidity). This is followed by injection of the still low viscosity mixture into a mold tool.
In bioplastics, IKT has investigated bio-based thermoplastic polyurethane (TPU) as an impact modifier for polylactic acid (PLA), 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.
IKT has developed compounds with new functional characteristics and advanced processing. It has compounded Carl Schenk’s plate-like shaped Cubrotec 5000 copper particles in the Ultramid B40 grade of PA6 from BASF. To do this, it used a special die with a narrow 0.5 mm 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 the design of thinner walled and more compact 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.
In selective laser sintering (SLS), IKT has worked with the Fraunhofer ICT Institute for Chemical Technology in Pfinztal, Germany, using PEEK polymer 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” (ASLS) 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 is also a theme for IKT in a new project aimed at developing 3D printing in bio-based plastics, with the company Biopro and Fraunhofer Institute.