Initiation of Cavitation of Polypropylene during Tensile Drawing

Abstract

The effect of stabilizers, additives, and low molecular weight fractions on cavitation during tensile drawing was studied in polypropylene. The additives were extracted from compression molded samples by critical CO 2 and also by a mixture of nonsolvents. The extract was an oily liquid composed of antioxidant, processing stabilizer, and a spectrum of low molecular weight fractions of polypropylene. Purified polypropylene exhibited surprisingly more intense cavitation than pristine polypropylene as it was determined by small-angle X-ray scattering and volume strain measurements. Intensification of the cavitation process in the purified samples was explained by the changes in the amorphous phase, namely, the changes in free volume by eliminating low fractions and soluble additives. An increase in free volume was probed with positron annihilation lifetime spectroscopy. Intense formation of cavitation pores in purified polypropylene proves that initiation of cavitation in polypropylene has a homogeneous nature.

Structural mechanics of semicrystalline polymers prior to the yield point: a review

“…Recently it was indicated for the stretched HDPE and i-PP that nanovoids are generated at rather low strain level [13,18] (see Fig. 3).…”

“…Along with the well-established data, new findings regarding structural defects occurring at small strains as well as their role in the global deformation behavior of semicrystalline polymers will be highlighted. At low strain level, stretching favors the occurrence of different structural defects such as nanocavities in the interlamellar amorphous layers [8][9][10][11][12][13][14][15][16][17][18][19] and damages of crystalline lamellae [20][21][22]. These imperfections could lead either to softening or modification of the plastic deformation mechanisms of semicrystalline polymers.…”

Physical state of the amorphous phase of polypropylene-influence on thermo-mechanical properties

“…In order to explain the observed effect, first we will analyze the systems in which the modifier was introduced into the amorphous phase regions of solidified polymer (SS samples). Additionally, in order to obtain full information on the influence of the modification process on the structure of crystalline component of the polymer we removed modifier from SSw and SSn samples through extraction in a Soxhlet apparatus-details of the methods were presented in the paper [42].…”

Modeling of pneumatic melt drawing of polypropylene super-thin fibers in the Laval nozzle

“…Experimental observations of the cavitation in polypropylene melt during tensile drawing led to the conclusion that cavitation in the amorphous phase has a homogeneous nature and is controlled by the melt cohesive forces [41].…”