Crazing of isotactic polypropylene in the medium of supercritical carbon dioxide

Abstract

Uniaxial tensile drawing of films based on semicrystalline isotactic PP in the medium of supercrit ical carbon dioxide at a pressure of 10 MPa and a temperature of 35°C is studied. The tensile drawing of PP is shown to proceed in the homogeneous mode without necking and is accompanied by intense cavitation. The maximum level of porosity is 60 vol %. The porous structure that develops owing to the tensile drawing of the polymer in supercritical CO 2 is provided by formation of a set of crazes that are primarily localized in interlamellar regions. According to small angle X ray scattering data, the average diameter of fibrils that bridge craze walls changes slightly with an increase in tensile strain and is ~10 nm; the specific surface of the craze fibrils is 100-150 m 2 /cm 3 .

Evolution of Filament-Shaped Porous Structure in Polycarbonate by Stretching under Carbon Dioxide

“…This porous structure was quite different from that obtained under CO 2 at 2 MPa and under atmospheric pressure at elevated temperatures. A fibrillar-shaped porous structure was not obtained by stretching crystalline polymers under CO 2 where small voids (in a nanometer scale) were formed in the intercrystalline amorphous region [10,46,47], but this structure was similar to that obtained by a specially designed continuous three-point bending method [48,49,50].…”

“…Another is disentanglement crazing, which is caused by chain disentanglement due to accelerated molecular motion. In crystalline polymers, voids are formed in the intercrystalline amorphous region by stretching [46] and the void formation is enhanced by stretching under CO 2 [10,47]. On the other hand, in amorphous polymers, we found that a filament-shaped porous structure with periodic distance was obtained macroscopically throughout the whole specimen in OD-PC by stretching under compressed CO 2 [21].…”

Breathable Materials and Hybrid Nanocomposites with Antimicrobial Activity Based on Porous Poly(ε‐Caprolactone) Obtained via Environmental Crazing

“…The size was calculated by the Guinier method described in the work. [ 60 ] The thickness of the lamellae was determined as where L saxs was the large period determined from SAXS; ρ and ρ χ were the densities of the polymer (1.145 g cm −3 ) and its crystalline phase (1.2 g cm −3 ), [ 61 ] respectively; and χ was the sample crystallinity according to the DSC data.…”

Strain-induced softening of glassy and crystalline polymers

“…18. Supercritical carbon dioxide was used as AAM; 87 it is a good crazing agent, which causes the same structural rearrangements in crystalline polymers (PP, HDPE) as other liquid media (hydrocarbons) usually used for DSC.…”

“…Stress ± strain curves for stretching and shrinkage and repeated stretching in air of PP, which was preliminarily stretched in AAM (supercritical CO2) according to the delocalized solvent crazing mechanism by 100% and completely relaxed upon removal of AAM from its porous structure. 87 Stress /MPa Figure 19. Time dependences of stress in hard-elastic PP stretched by 50%.…”