Structure, mechanical properties and acoustic emissions of starch extrudates

• Main Author: Plews, Andrew G.
• Published: Imperial College London 2008
• Subjects: 664
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.485421

Structural characterisation, mechanical properties and acoustic properties of solid biopolymer food foams {starch extrudates) are the major subject areas studied through this thesis. Initial stages involved the development of a method for capturing mechanical destruction acoustic emissions. Consideration was given to mechanical test parameters, vibrations from the test rig, extrudate geometry and ensuring frequency spectra acoustic differences occur. Structural characterisation was developed using x-ray microtomography (XMT). Pore size distributions, volume fraction porosity and average oell wall thickness were taken from XMT images. A three dimensional watershed algorithm was successfully applied to the three dimensional XMT images to segment interconnected-regions into recognisable cells. This stage is required due to the open-cell nature ofextrudate porosity. In order to obtain samples of differing porosity but all other parameters constant an expansion control chamber (ECC) was used. The ECC alters the pressure differential across the extruder die face whilst leaving extrusion conditions constant Considering extrusion pressures, extrusion temperatures and extrudate skeletal material density the effect of the ECC on the extrusion process (and hence skeletal material) has been evaluated. The effect ofthe ECC on extrudate structure/porosity is also discussed. Modelling of the approximate vibration frequencies ofcell walls was carried out using simple models. The aim was to find if these vibrations are responsible for the frequency peaks seen in the mechanical destruction frequency spectra. This provides an understanding of what needs to be altered during production for control ofacoustic emissions. Relationships between pore structure and mechanical measures were considered as well as those between acoustic emissions and mechanical measures.