calculating viscosity from melt flow index

IntroduetionIn an earlier publication, a start-up analysis of the flow behaviour in a melt flow index (constant shear stress) type apparatus was presented with the objective of indicating that the flow of highly viscous Newtonian liquids becomes steady within an extremely short time period since the inception of flow and Hagen-Poiseuille law can safely be used to determine the liquid viscosity. The start-up contribution, however, appears to be an order of magnitude lower than that introduced by the kinetic energy correction for commonly used iow-viscosity liquids encountered in practice.Key words: Capillary viscometer, start-up flow In gravity flow type capillary viscometer, the non-linear relationship between kinematic viscosity and efflux time can be due to two factors -the well known kinetic energy correction and the start-up flow during which the flow within the capillary attains its Poiseuillean character. Although plasticized film lost some flexibility after only 30 days of storage due to plasticizer migration to the surface of the film, sufficient plasticization performance still remained in plasticized PLA films for flexible packaging application even after a long storage period at ambient conditions. However, the ability of stored plasticized film to cold crystallize remained unaffected since both the cold crystallization temperature and melting temperature were not affected during storage. While the melt viscosity, glass transition temperature, degree of crystallinity, tensile strength, and modulus increased, the elongation at break and energy to break decreased with storage time up to 30 days and all properties remained constant thereafter. Infrared results indicate that plasticizer migration to the surface of the film occurred after only 30 days of storage, which significantly affected the performance of plasticized films. This study examined the effect of storage time at room temperature on the melt viscosity, thermal, and tensile properties of epoxidized soybean oil plasticized poly(lactic acid) (PLA) films manufactured through a cast extrusion process.

Calculating viscosity from melt flow index