Novel Manufacturing Processes for Polymer Bead Foams

Abstract

Polymer bead foams are manufactured through a sintering process using foamed polymer beads. It is worth emphasis that the bead foam technology is the only process that can produce 3-dimensionally shaped foam products with ultra-low densities. This unique feature of bead foam process has been attracting enormous attentions from various foam industries. However the conventional bead foam processes still have some limitations associated with manufacturing productivity and safety during the treatment. This thesis deals with novel approaches to innovative and cost-effective manufacturing processes for polystyrene (PS) and polypropylene (PP) bead foam materials, based on thorough understanding of the scientific issues in bead foam technologies. This study also demonstrates the feasibility of new processes by conducting a series of foaming experiments such as batch foaming and continuous extrusion foaming as well as steam chest molding which is a critical common process for all bead foam products. In addition, this study aimed at developing new bead foam processes based on the relationship between the cellular structure and processing/material parameters. When it comes to expandable PS (EPS) bead process, research efforts have been made to eliminate n-pentane which has some disadvantages related to its flammability and low boiling temperature. In addition, the bi-celullar PS foams that feature the superior thermal-insulation property was manufactured through continuous extrusion foaming process. With regard to expanded PP (EPP) bead process, research efforts were focused on the development of cost-effective continuous foaming process in order to resolve the high cost issue of conventional EPP beads. These research strategies were designed on the basis of the comprehension of thermoplastic foaming, steam chest molding process and gas dissolution/diffusion phenomena. The results in the thesis provided considerable introductory and advanced knowledge about the bead foam technologies so that further promising researches can be performed to invent entirely new bead foam materials such as ultrahigh–temperature-durable bead foam products, biodegradable bead foams, other highly functional bead foam products aside from EPS and EPP bead foams.