From Science & Research
From Science & Research PBS Particle Foam Article contributed by Pia Borelbach and Thomas Wodke, Scientists, Business Unit Renewable Resources Fraunhofer UMSICHT, Oberhausen, Germany Foamed plastics produced from fossil based polymers are found in many applications, for example as shock-absorbent packaging or as thermal insulating material. Particle foams based on bioplastics are the subject of recent developments. Scientists at Fraunhofer UMSICHT and the Ruhr-Universität Bochum (RUB) have developed, within a research project, a path to produce particle foam parts based on bioplastics and have realised this with polybutylene succinate (PBS) as an example. In a two-year joint research project Fraunhofer UMSICHT in Oberhausen and the Ruhr-Universität Bochum, both Germany, examined the idea of a novel, two-step process for particle foam from bioplastics. In a first step foamed particles, also containing a blowing agent, were to be manufactured using a high pressure spraying process. In the second process step foamed parts are produced from these particles. For this purpose the Ruhr-Universität Bochum examined for the first time the encapsulation of a liquid physical blowing agent in a highly viscous bioplastic using the PGSS process (Particles from Gas Saturated Solutions). The work carried out by Fraunhofer UMSICHT included the development of bioplastics compounds for the PGSS process, the construction of an experimental foam moulding device and the investigation of the foaming behaviour of bioplastic particles. The essential basic project objectives were achieved. Concerning the PGSS process, the possibility of encapsulating liquids in highly viscous polymers was proven experimentally. This was successfully achieved with the encapsulation of water in the biopolymer PBS. However, the PGSS process failed to produce free-flowing and conveyable bioplastic particles suitable for an Figure 1: Expandable particles from PBS 32 bioplastics MAGAZINE [04/10] Vol. 5
From Science & Research expanded foam process due to diverse unforeseeable technical difficulties. Therefore the consistency of the two-stage process idea, as specified in the project proposal, was not achieved. Figure 1 shows foam particles that were manufactured with the PGSS process from PBS. Due to the failure to produce suitable particle morphologies with the PGSS process, additional trials for the production of particles by extrusion were carried out. This approach was successfully converted into practice. Particles from PBS could be manufactured on a specific extrusion line and foamed to produce parts in a second step. Figure 2 shows the experimental foam moulding device and Figure 3 shows an expanded part from PBS. It is recommended, for industrial production, to develop an extrusion line with underwater pelletiser with back pressure for the first process step, which will enable the production of pressure-compressible, foamed polymer particles by the use of chemical or also physical blowing agents. With high level of probability, these foamed polymer particles can be converted to foamed parts on existing process lines and tools, comparable to the industrial expanded polypropylene (EPP) process. The essential future development approaches are the optimisation of the extrusion technique, the blowing agent system and the bioplastic compound in order clearly to lower the density of the expandable particles and the foamed parts to the level of EPS and EPP. The project idea, i.e. the production of foamed parts in a continuous process using the PGSS process, could not be realised. However, the scientific objectives, in particular the spraying of high viscosity polymers in the PGSS process by RUB and the production of foamed parts from a bioplastic by Fraunhofer UMSICHT, were achieved. The development work, which began with this project, should be continued. Concerning the PGSS process, various basis works with regard to the spraying and encapsulating of high viscosity polymers is still to be carried out. After completion of this basis work on the development of concrete applications can be decided. The development work concerning the use of bioplastics for particle foamed parts is supposed to be progressed quickly in collaborative projects with industry. The developments focus mainly on the extrusion and pelletiser technique, the blowing agent selection, as well as the material selection and optimisation of the bioplastic compound. Figure 2: Experimental foam moulding device Figure 3: Part of expanded PBS Interested companies can get in touch for application developments with the scientific research institutions. Furthermore, for detailed information the project final report can be downloaded (in German language) from www.bioplasticsmagazine.de/201004. The research project No.15383N of the research association VEU was supported via the AiF within the framework of the ‘promotion of the industrial cooperative research and development (IGF)‘ programme from the German Federal Ministry of Economics and Technology. www.umsicht.fraunhofer.de bioplastics MAGAZINE [04/10] Vol. 5 33
