Orientation in polypropylene sheets produced by die-drawing and rolling

Autor: Charles E. Chaffey, I. M. Ward, Ajay Kumar Taraiya
Rok vydání: 1997
Předmět:
Zdroj: Polymer Engineering & Science. 37:1774-1784
ISSN: 1548-2634
0032-3888
DOI: 10.1002/pen.11826
Popis: Two orienting techniques for stiffening semicrystalline polymers, rolling and die-drawing, are compared with respect to the anisotropy they produce in isotactic polypropylene (PP). Billets of PP were either drawn at 145°C through a tapered slotted die in the Leeds large-scale die-drawing machine to reduction ratios R of 2.2. 5.1 and 7.6, or rolled between rolls of 65 mm diameter at 120°C to R = 2 to 5. Drawing increased the crystallinity, as estimated from differential scanning calorimetry, density and wide-angle X-ray diffraction (WAXD); it thus disrupts the original PP structure, developing an oriented crystalline structure. WAXD pole figures showed that both die-drawing and rolling oriented the molecular chain axis nearly parallel to the machine direction and the b axis perpendicular to the drawing plane. This approximate uniaxial symmetry was confirmed by ultrasonic measurements of the stiffness matrix. In tensile and falling-dart impact tests, samples failed by delaminating in the drawing plane. Although stresses are applied to the material in quite different ways in die-drawing and in rolling, the geometry of deformation in both is similar, close to plane strain.
Databáze: OpenAIRE
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