The Optimal Operation Conditions of Biodegradable Cushioning Extrudates and the Establishment of its Viscoelastic Models

• Main Authors: WAI- BUN LUI, 雷偉斌
• Other Authors: JINCHYAU PENG
• Format: Others
• Language: zh-TW
• Published: 2005
• Online Access: http://ndltd.ncl.edu.tw/handle/98777791225834332939

博士 === 國立中興大學 === 生物產業機電工程學系 === 93 === Today starch-based loose fills still represent the main application of starch-based materials and specifically of starch-based industrial packaging. Response surface methodology (RSM) was used to analyze the effect of polyvinyl alcohol (PVA) and calcium carbonate (CaCO3) on the objective attributes (shipping bulk density, radial expansion ratio, compressibility and spring index) of a biodegradable cushioning extrudate. A rotatable central composite design (CCD) was used to develop models for the objective responses. The experiments were run at 105°C with screw speed 500 RPM and die diameter 3.92mm. Responses were most affected by changes in polyvinyl alcohol (PVA) levels and to a lesser extent by calcium carbonate (CaCO3) levels. Individual contour plots of the different responses were overlaid, and regions meeting the optimum shipping bulk density of 6.1619 kg/m3, radial expansion ratio of 3.2855, compressibility of 42.5421 N, and spring index of 0.9096 were identified at the PVA level of 18.6627% and the CaCO3 level of 7.7779%, respectively. Another objective of this study is to focus on the composition levels affecting the cellular structure and the thermal properties (specific heat capacity and thermal conductivity) of extruded foams and to evaluate the possibility of using corn/PVA extrudates as packaging and insulating materials. The experimental results indicated that the cell sizes become smaller and more uniform and the cell walls become thinner with the increase in the PVA ratio. Moreover, using the CaCO3 also made the cell sizes become smaller and more uniform. For all the treatments, the specific heat increased linearly as the temperature increased. The mechanical responses of biodegradable cushioning extrudates at a wide range of strain rate were investigated in order to stimulate the transportation by truck and train. The linear and non- linear viscoelastic behavior was analyzed. The material was tested with dynamic mechanical and creep experiments and the correlation between strain rate effects and viscoelastic properties of the foam was obtained using viscoelasticity theory and separating strain and time effects. The models for the prediction of stress strain curve and creep curve at any and compressive force and cross head speed was developed. The generalized Maxwell model with three units in parallel and that of Burgers, in spite of being apparently simple, showed in a satisfying manner, the results of the tests of stress relaxation in biodegradable loose fill extrudates. The generalized Maxwell model predicted satisfactorily the behavior of stress relaxation of the biodegradable loose fill extrudates, with excellent correlation coefficients (R2 >0.99). The Burgers four element model predicted satisfactorily the behavior of creep behavior o f t h e biodegradable loose fill extrudates, but, with a rather poor correlation coefficients (R2 > 0.57).