This thesis reports research work in the development of biodegradable foams in block forms based on wheat flour for cushion packaging application. A novel concept of Regular Packing and Stacking (RPS) was developed for production of macro-composites block foams that combines extrusion foaming of starch foams with selfadhesion aided by application of water to produce block foams with a network of reinforcing interfaces. The structure and material properties of the foams can be manipulated through control of foam cell structure and the interface network. Parameters controlling the evolution of cell structures including processing conditions and additives were systematically studied using a twin-screw extruder. Under constant screw speed and controlled feed rate, high barrel temperature profiles with appropriate water contents were found to result in finer cell structure foams. Short length reverse screw with tight pitch was found more effective to produce fine cell foams. Addition of 22 micron talc powder at 1 wt% was found effective as a nucleating agent. Addition of flax fibre resulted in fine cell and high strength foams. The key variables in design and operation of a RPS machine were investigated. A pultrusion technique has been employed to reform the extruded foam strands to modify their shape and density and facilitate self-adhesion. Uniform wetting was achieved by using water absorbent fabrics to apply water in a controlled manner. Foam strands were then bonded to form macro-composite block foams. A RPS demonstration machine was successfully developed. The key factors affecting the macro structure and performances of the RPS block foams were investigated in great detail. Extruded foam strands were anisotropic and this feature was utilised in the design of RPS block foams to manipulate their properties in different strands' orientations. Thicker interfaces formed a network within the RPS block foams, which was found to make a significant contribution to the strengthening of the RPS foams (by a factor of 3). High humidity conditioning of the RPS foams was found an efficient way to control density and refine cell structure of the foams which could increase foam density by a factor of 3.5 and compressive strength by a factor of 10. This work has made significant contributions to the development of a novel technology for processing of block foams based on starch foam and understanding of extrusion foaming process, structure and properties of the starch materials. The research results paved the way for the industrial development of biodegradable block foams for cushion packaging application, which are based on renewable resources and are bio-compostable and thus facilitate reduction of landfill at the end of their intended service life.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:486016 |
| Date | January 2009 |
| Creators | Kang, Yang Gang |
| Publisher | Brunel University |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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