Project Details
Projekt
Cross linked sheets for highly stressed thermoforming applications
Applicant
Professor Dr.-Ing. Dietmar Drummer
Subject Area
Plastics Engineering
Term
from 2016 to 2019
Project identifier
Deutsche Forschungsgemeinschaft (DFG) - Project number 283899356
Basic knowledge about the effects of a partial cross linking of macromolecules on the thermoformability of semi-crystalline thermoplastics was gathered in the preceding project using the example of polyamide 12 (PA12). Semi-crystalline thermoplastics are generally less suitable for thermoforming compared to amorphous thermoplastics due to their sharp drop in stiffness with crystalline melting and the melts insufficient elongational rheological properties. Thus the availability of semi-crystalline technical thermoplastics, which meet the requirements of the thermoforming process, is highly limited up to now. This hinders the development of technical thermoforming parts. It could be shown that partial cross linking of the macromolecules by high energy irradiation changes melt stiffness and elongational rheological properties of PA12, which has significant impact on the thermoforming process. The increased melt stiffness prevents excessive sagging of the sheet during heating, while the mainly elastic behavior of the melt reduces the chance of webbing. As a result the processing temperature window is greatly increased.Furthermore cross linking leads to strain hardening material behavior and thus to more homogenous wall thicknesses, especially for geometries with high draw ratios. It is the aim of the transfer project to enhance the knowledge from the preceding project and to transfer it into application by means of a demonstrator, which is a reusable tray for electric drive components. Large-area trays are generally suitable geometries for thermoforming. However available amorphous thermoforming materials do not meet all requirements of technical trays, e.g. they need a high heat resistance when taking up parts from an injection molding process.Furthermore a good wear resistance is needed to ensure reusability. Trays for metal parts often need additional chemical resistance against oils and greases. These requirements shall be met by using cross linked semi-crystalline thermoplastics. Besides verifying the results for the industrial production scale, additional fundamental questions arise. First of all it has to be investigated whether the results from PA12 are also valid for other materials like different polyamides, polyolefines or polyesters. Moreover possible interactions of additives like cross linking aids, stabilizers or pigments and high energy irradiation influencing the sheet properties as well as their processability and resulting part properties have to be investigated. Furthermore effects of sheet processing on thermoformability as well as effects of thermoforming conditions on part properties have to be measured. Here the range of investigated properties shall be expanded to include some of the relevant advantages of semi-crystalline thermoplastics for applications, like wear behavior or chemical resistance.
DFG Programme
Research Grants (Transfer Project)
