Chaiwut Gamonpilas

Shear and normal stress measurements in non-Brownian monodisperse and bidisperse suspensions

We have measured the viscometric functions of mono- and bimodal noncolloidal suspensions of poly (methyl methacrylate) spheres in a density-matched aqueous Newtonian suspending fluid using parallel-plate and cone-and-plate rheometry for particle volume fractions in the range of 0.20–0.50. Cone-and-plate normal stress measurements employed the method of Marsh and Pearson, in which there is a finite gap between the cone tip and the plate. The monodisperse suspensions showed an unexpected particle size dependence of the viscometric functions, with the viscosity increasing with decreasing particle size. Normal stresses were very small in magnitude and difficult to measure at volume fractions below 0.30. At higher concentrations, N2 was negative and much larger in magnitude than N1, for which the algebraic sign was positive over most of the shear rate range for the monodisperse suspensions but indeterminate and possibly negative for the bimodal suspensions. The normal stresses were insensitive to bidispersity ...

Effect of Sodium Chloride and Osmotic Dehydration on Viscoelastic Properties and Thermal-Induced Transitions of Duck Egg Yolk

The effects of NaCl and osmotic dehydration on the linear viscoelastic behavior of duck egg yolk were evaluated. An increase in NaCl concentrations from 0% to 3.0% (w/w) resulted in a remarkable change in the linear viscoelastic behavior by inducing a sol–gel transition, specifically. The transition was more pronounced when 1.5% (w/w) NaCl was incorporated. The effect of dehydration on aggregation and network formation was predominant than that of the NaCl addition. Nevertheless, at a lower degree of dehydration, the addition of NaCl could modulate the viscoelastic behavior of duck egg yolk, resulting in a well-developed gel network. Addition of NaCl into duck egg yolk could stabilize the protein molecules as evidenced by an increase in denaturation temperature as well as a delay in gel network formation. As visualized by a scanning electron microscope, the denser network with smaller voids was observed in duck egg yolk gel with increasing NaCl concentration and degree of dehydration.

Effect of Freezing Rate and Starch Granular Morphology on Ice Formation and Non-Freezable Water Content of Flour and Starch Gels

Ice formation and non-freezable water (WNFW) of rice flour and tapioca starch gels were studied at two different freezing rates (–10 and –100°C/min) using differential scanning calorimetry. Ice crystal growth was observed in the slow freezing but not in the fast one. Ice melting enthalpies, however, were similar since more ice formed in holding and reheating steps. Melting enthalpy of fully gelatinized systems with water contents ~ 0.50–0.66 was associated to starch composition and granule morphology. Highly swollen tapioca starch gave the lowest enthalpy and the highest WNFW (0.40 g/g dry starch versus 0.32 and 0.38 g/g dry starch of normal and waxy rice flours, respectively). The further studies revealed that the WNFW values were associated to swelling power, solubility, and granule morphology.

Effect of Ethylene Vinyl Acetate on the Rheological and Mechanical Behavior of Low-Density Polyethylene-Based Greenhouse Film

In this work, the effect of ethylene vinyl acetate (EVA) on the rheological and mechanical properties of low-density polyethylene (LDPE)-based greenhouse plastic films was explored. The rheological experiments showed that, for given PE and EVA, both complex viscosity and storage moduli of LDPE/EVA blends were not significantly affected when EVA content is less than 30%wt but increased with increasing EVA content thereafter. However, the mechanical results inconsistently showed that blown films with 10%wt EVA content gave the most superior mechanical properties compared to other blends. It was found that, at higher EVA contents, immiscibility between the LDPE and EVA phases occurred, resulting in much poorer mechanical performance.

Pomelo (Citrus maxima) Peel-Inspired Property for Development of Eco-Friendly Loose-Fill Foam

For development of eco-friendly packaging foam from pomelo peel, physical and mechanical properties of the pomelo peel and effects of pomelo varieties, namely Kao-Nampueng, Thong-Dee, and Kao-Pan, on their properties were investigated. It was found that the pomelo variety showed somewhat significant effect on physical and mechanical of pomelo peel properties. Because of its thick peel with high moisture content (75-80%) and water activity (0.90-0.98), the peel weight accounted for almost half of the total fruit weight. Cell structure and pore size of the peel were examined using the environmental scanning electron microscope (ESEM). The result showed an open cell foam structure with pore size of approximately 151±31 µm. The pore size was more open and large towards the outer surface. Uniaxial compression tests on pomelo peel samples with and without flavedo showed good reproducible stress-strain curves despite its biological variation. Young’s moduli of both samples were calculated to be 200-300 kPa and 110-210 kPa, respectively. Moreover, the most important property of packaging foam is the ability to absorb energy during impact which can be characterised through the measurement of the onset strain of densification. It was found that the strain values at the maximum energy absorption efficiency (εcd) of peel samples with and without flavedo for all studied pomelo varieties were comparable and were approximately in the range of 60-65%. These preliminary results indicate very promising mechanical properties of pomelo peel as eco-friendly packaging foam although further modifications are required to improve their physical and shelf-stability properties.

Influence of the Laminate Configurations of Transparent Armor on its Ballistic Protection

The ballistic performance of transparent armors has been continuously developed for an application on security purposes. Generally, ballistic performance of the laminated glass increases with its thickness and weight while the user requirement prefers high level of ballistic protection with thin and light weight body. In this study, fabrication of light weight glass-PVB transparent armors with the level-3 protection according to the National Institute of Justice (NIJ) standard was attempted. The ballistic performances of various configurations of glass-PVB laminates were determined against 7.62 mm ammunitions. Results from fragmentation analysis indicated the influence of glass-sheet-arrangement in the armor structures on the ballistic damages. The minimum requirement on the thickness of front-face layer was also discussed. To verify the experimental results, finite element analysis was performed on all laminated systems. It was found that the results from computational analysis were in reasonable agreement with the experimental results.