Alan Nesbitt

Microwave foaming of starch-based materials (I) dielectric performance

Extruded pellets from starch-based materials have been heated and foamed under microwave radiation. The foaming mechanisms and effects of some additives on the dielectric properties of the materials have been investigated using a microwave calorimeter. A rapid increase in dielectric loss factor (ɛ″) has been found for all the tested materials foamable under microwave heating and the onset of the ɛ″ increase is considered to be correlated to glass transition. It has been found that extruded starch materials can be foamed at 15℃/min but the expansion level reduced compared with that of the same material foamed at higher heating rate. The incorporation of organic additives in starch-based materials generally led to significant decrease of their microwave foamability when glycerol and polyvinyl alcohol are used as the additives in the extruded pellets.

Microwave foaming of starch-based materials (II) thermo-mechanical performance

The thermo-mechanical performance of extruded wheat starch/flour containing different additives was examined via microwave-heated thermo-mechanical analysis. Additionally, the dielectric property of the wheat starch-based materials was also studied using a microwave calorimeter. It has been found that when glycerol or polyvinyl alcohol was used as single additive in wheat starch, a content limit existed and using the additives at a concentration higher than the limit will lead to deterioration of the material’s microwave foamability. A good initial thermal expansion is essential for a proper foaming of the wheat starch-based materials; however, high enough dielectric loss factor (ɛ″) is also required for the formation of foam structure under microwave radiation. Glass transition temperature (Tg) for the extruded wheat starch materials was detected by microwave thermo-mechanical analysis at about 75–95°C when heated at 15°C/min; and for the foamable formulations, the foaming temperature (Tf) is generally 10–20°C higher than the corresponding Tg. Impurities like proteins play important roles in the microwave foaming of extruded wheat flour. Overall, the extruded wheat flour with additives is more difficult to foam under microwave heating than the wheat starch extruded from the similar formulations.

Effect of Cure Cycle Heat Transfer Rates on the Physical Properties of an Epoxy Matrix Composite

Although the autoclave technique produces composite parts of high quality, the process is time consuming and has intrinsically high capital and operating costs. QuickstepTM is a novel polymer composite manufacturing technique designed for the out-of-autoclave processing of highquality, low-cost components with a reduction in cure-cycle times. This paper assesses the use of the Quickstep method for the processing of an epoxy-carbon fibre aerospace composite material. The Quickstep process is compared both to a thermal vacuum-bag only process and the manufacturer’s specifications for autoclave cured panels. Higher process ramp rates, achievable by using Quickstep, have been shown to reduce resin viscosity and facilitate void removal. Through manipulation of the Quickstep cure cycle while the resin is at low viscosity, significant effects on the mechanical properties of the product are demonstrated. Using Quickstep curing it has been found that better interlaminar properties than the manufacturers autoclave data could be obtained while the flexural strength was a little lower. The work identifies key parameters associated with the Quickstep process giving an insight into how it can be optimised further in an attempt to produce panel properties that rival those produced by autoclave methods.