Circular Die Swell Evaluation of LDPE Using Simplified Viscoelastic Model

Simplified viscoelastic model based finite element method was presented to evaluate circular die swell of LDPE. Differential viscoelastic models were firstly described for the incompressible viscoelastic flow with isothermal extrusion, and simplified viscoelastic model (SVM) was then selected for viscoelstic component in extra stress terms. Discrete elastic viscous stress splitting (DEVSS) method was used to stabilize elliptic term in momentum equations. Mini–element method for hexahedral element was applied to stabilize equal order velocity pressure interpolation. Interface–tracking approach was used to detect the position and moving of the free surface at extrudate region. In experiment, circular die was selected to study LDPE extrusion flow. The measured viscoelastic properties were employed as input data in LDPE flow simulation. CCD camera was used to capture extrudate swell. Simplified viscoelstic model was then used to predict extrudate swell in three flow rate conditions, 100, 264, and 490 mm3/s. Compared with experimental results, the die swell predicted by SVM were 1.37%, 2.37%, and 5.5% different, for the three flow rate conditions, respectively. The results showed that simplified viscoelastic model could be employed to predict circular die swell

Development and in vitro evaluation of chitosan-Eudragit RS 30D composite wound dressings

The purpose of this research was to design and evaluate chitosan-based films intended for wound dressing application. Required properties for successful wound dressing, such as liquid uptake, vapor and oxygen penetration, bioadhesiveness, and film elasticity, were examined. Water uptake and vapor penetration of the films were determined gravimetrically, while oxygen penetration was determined by Winkler’s method. The bioadhesive properties were determined with an in-house pulley system instrument using a pig gut model. Film elasticity was determined with a stretch test using an Instron apparatus. The results showed that pure chitosan films exhibited relatively high liquid uptake and the adsorption tended to decrease with the addition of Eudragit RS 30D. Moisture vapor and oxygen were found to be able to penetrate through all film formulations in comparable amounts. The bioadhesiveness test tended to show lower bioadhesive properties with the addition of Eudragit RS 30D. The formulation containing only chitosan exhibited low elongation of the film at 2 N, but the film elasticity increased with the addition of Eudragit RS 30D. In conclusion, the addition of Eudragit RS 30D could improve a film’s mechanical properties but lower its bioadhesiveness