CAVITATION DURING DEFORMATION OF PLASTICS

CAVITATION DURING DEFORMATION OF PLASTICS

Andrzej Pawlak

Centre of Molecular and Macromolecular Studies, Polish Academy of Sciences, Lodz, Poland

CAV 2012, Singapore

Plastics production

265 Mt

Semicrystalline polymers: polyethylene, polypropylene, polyamide, poly(ethylene tereftalate)....

Polarizing optical microscope: polypropylene film

Spherulite:

Cavities in polymers are observed:-in the molten polymer during its isothermal crystallization-during tensile deformation of solid polymer

Galeski, et.al., Macromolecules 21, 2761 (1988)

Nitta K.H., et.al., J. Mater. Sci. 38, 4889 (2003)

Thomas C, Seguela R. et.al., Polymer 48, 6041 (2007)

12 μm0

A. Pawlak, A. Galeski, Macromolecules , 38, 9688-9697 (2005)

CAVITATINGNON CAVITATING

DETECTION OF CAVITIES

Nanometer size - Small Angle X-Ray Scattering

Micrometer size-Scanning Electron Microscopy

Competition:- breaking of amorphous phase - cavitation- plastic deformation of crystals by chain slips

One polymer:-modification of morphology (crystallization, orientation, polymorphism, molecular mass)-changing of experimental conditions (temperature, deformation rate)

Polyethylene:a) rapidly cooled during solidificationb) slowly cooled during solidification

Polymorphism in polypropylene.Different crystalographic forms: α- monoclinic, β- triclinic

SCANNING ELECTRON MICROGRAPHS OF POLYPROPYLENE

Initial structure

Deformation:Strain = 30%, T= 20 oC

Deformation:Strain = 30%, T= 70 oC

STRETCHING DIRECTION

POLYPROPYLENE CRYSTALLIZED ISOTHERMALLY (125 oC)

CONCLUSION-Voids are observed in many semicrystalline polymers: during solidification from melt and during tensile deformation.

-Cavitation process in deformed polymers occurs when the crystals are enough perfect and strong, i.e. when the stress for plastic deformation of crystals is higher than the stress needed for cavitation of the amorphous phase.

-The cavities are nano- and micrometer size, usually ellipsoidal shape.

-At low strain the cavities are elongated perpendicularly to deformation direction. Reorientation process sets in for local strains of 80-100%.

-It is possible, by changing the processing or testing conditions, to control cavitating behavior of the selected polymer.

1. A. Pawlak, A. Galeski – “Plastic Deformation of Crystalline Polymers:The Role of Cavitation and Crystal Plasticity”, Macromolecules, 38, 9688-9697 (2005)

2. A. Pawlak – “Cavitation during tensile deformation of high-density polyethylene”, Polymer, 48, 1397-1409 (2007)

3. A. Pawlak, A. Galeski – „Cavitation during Tensile Deformation of Polypropylene”, Macromolecules, 41, 2839-2851 (2008)

4. A. Pawlak, A. Galeski, “Cavitation and Morphological Changes in Polypropylene Deformed at Elevated Temperatures”, J. Polym. Sci., Part B: Pol. Phys., 48, 1271--1280 (2010)

5. A. Pawlak, A. Galeski, “Cavitation during tensile drawing of annealed high density polyethylene”, Polymer, 51,(24), 5771-5779 (2010)

6. A. Pawlak, A. Gałęski, „Cavitation during tensile drawing of semicrystalline polymers”, Polimery, 56, (9), 624-633 (2011)

7. A. Pawlak, “Cavitation during deformation of polymers on the example of polypropylene”, J.Appl. Polym. Sci. (2012)