ISSN:
0032-3888
Keywords:
Chemistry
;
Chemical Engineering
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
,
Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
,
Physics
Notes:
Molecular orientation in film extrusion has been studied using an extrusion-grade commercial polyethylene resin. First quad (take-up) speed was varied over the range 50 to 120 m/min, Web crystallinities were found to be in the range 0.60 to 0.65 as determined by differential scanning calorimetry. Web crystalline orientation function fc was slightly negative below a takeup speed of 50 m/min and rose to a value of 0.4 at 120 m/min at a quench bath temperature of 37.8°C and a melt temperature of 251°C for one of the resins used. (Perfect orientation along the machine direction implies fc equal to 1.0). Amorphous orientation function fa remained below 0.1 and was almost constant with takeup speed. This behavior was modified in a minor way by changes in quench bath and melt temperature as well as resin lot. A qualitative model was proposed for this without definite proof. The major mechanism at work in the film-forming process is macromolecular network structure deformation in elongational flow. Die gap variation at uniform extrusion rate has a secondary effect on web orientation. With the present state of knowledge, it is not possible to quantitatively separate the amorphous orientation function into its various conformational contributions. It was also noted that high take up speeds and low air gaps tend to freeze the web at greater widths.
Additional Material:
7 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/pen.760240605
