Evaluation of Stresses in a Two-Layer Co-Extruded LDPE Melt Blown Film
Despite the fast growth of co-extruded film production, little research work has been devoted to this process. Films of LDPE, ULDPE, LDPE/ULDPE and ULDPE/LDPE were produced at various processing conditions. A continuous experimental set up was used to evaluate the in-plane birefringence during bubble formation. The data collected were used to derive the axial and transverse stresses. A non-isothermal Newtonian model that allows the determination of the kinematics and dynamics of the two-layer film blowing process was then used to calculate the axial and transverse stress. Generally the calculated stresses are in agreement with the experimental values.
A model for the two-layer blown film process with flow-enhanced crystallization
Abstract A 2-D model for non-isothermal bi-layer film blowing is developed based on the 1-D film blowing model of Henrichsen and McHugh [2007a. Analysis of film blowing with flow-enhanced crystallization: part 1. Steady-state behavior. International Polymer Processing XXII (2), 179–189] that accounts for viscoelasticity and flow-enhanced crystallization. Numerical results demonstrate the role of rheological, thermal, and crystallization properties on the development of crystallinity and stresses in a bi-layer system consisting of two crystallizable polymers. For a two-layer film consisting of the same materials, the evolution of the stress in an individual layer can be significantly different due to the temperature difference. Varying the material properties in a given layer, such as the plateau modulus and the maximum crystallization rate, not only leads to the corresponding responses in its own layer, but also influences stresses and crystallinity in the other layer through heat transfer between two layers. Results further demonstrate that stresses in the film after the frost line will be borne primarily by the layer that solidifies first, while the second, molten component will have a tendency to relax. The layer arrangement is also shown to have direct impact on the stresses and semi-crystalline phase orientation at the freeze point which will impact the final properties of the film.
The Italian Renaissance: Culture and Society in Italy
In this newly revised edition of his widely acclaimed work, Peter Burke presents a social and cultural history of the Italian Renaissance. He discusses the social and political institutions that existed in Italy during the fifteenth and sixteenth centuries, and he analyzes the ways of thinking and seeing that characterized this period of extraordinary artistic creativity. Developing a distinctive approach, the author is concerned not only with the finished works of Michelangelo, Raphael, Leonardo da Vinci, and others, but also with the social background, patterns of recruitment, and means of subsistence of this "cultural elite." He thus makes a major contribution both to our understanding of the Italian Renaissance and to our comprehension of the complex relations between culture and society. An excellent social history of the lives and culture of the artists and artisans which made it possible for the arts to flourish.