Suppressed Cavitation in Die-Drawn Isotactic Polypropylene

Abstract

Cavitation is an important phenomenon in solidphase deformation of polymers, which either has potential adverse effects on physical properties or creates potential opportunities for new properties. In either case, it needs to be better understood to help achieve better control of cavitation and its effects. Cavitation associated with solid-phase deformation in a β-nucleated isotactic polypropylene was found to depend on the solid-phase deformation route employed. Compared with samples obtained by free tensile stretching, cavitation was suppressed in samples deformed via die-drawing, although an almost identical βto αphase transition was observed for both deformation routes. Even when die-drawn samples were subsequently deformed to large strains by free stretching, there was still no comparable cavitation compared with the single free tensile-stretching route. The die-drawing process appears to suppress cavitation by fundamentally diminishing the number of growable nuclei of cavities, rather than merely hindering the growth of cavities. A relationship between cavitation intensity and the fractions of lamellae along specific directions has been established. During subsequent free stretching of die-drawn samples, newly created cavities were suggested to be initiated within the crystalline layers. The reduction of the cavity nuclei in the die-drawing process originated from the stabilization of the connections between the crystalline blocks within the lamellae.

A Simple Way to Control Small-Strain Cavitation in Die-Drawn Isotactic Polypropylene

“…And it is quite challenging to alter only one of them and leave the other one untouched. On the basis of our previous work where the cavitation was related to the crystalline layer, and considering the barely changed crystallinity as shown in Figure S1, it seemed quite fair to attribute the observed cavitation intensity decrease to the evolution of the perpendicular lamellae. Hence, the physical essence of the proposed method to control the small-strain cavitation was interpreted in the aspect of perpendicular lamellae.…”

“…More recently, we revealed that the cavitation behaviors of β-nucleated polypropylene can be influenced by different elongation methods and the cavitation intensity is related to the β-lamellae with normal perpendicular to the elongation direction . This provides an underlying route to control small-strain cavitation.…”

“…31 More recently, we revealed that the cavitation behaviors of β-nucleated polypropylene can be influenced by different elongation methods and the cavitation intensity is related to the β-lamellae with normal perpendicular to the elongation direction. 32 This provides an underlying route to control smallstrain cavitation. In this work, we realized a direct adjustment of small-strain cavitation occurring in the deformed samples through the regulation of lamellae with normal perpendicular to the deformation direction.…”

Coupling effects of toughening modification and solid die-drawing process on the morphology and mechanical properties of PP/TMB-5 composites with POE

“…After SDD, both α (040) and β (300) crystal planes were orientated along the drawing direction and the orientation parameters of those two crystal planes were equivalent, indicating that the orientation of crystalline region is independent of the crystal form. The orientation parameter of α (040) in PP/ TMB-5 composites was lower than the orientation parameter of α (040) in T 0 , which might be caused by cavitation [31] in Figure 2 shows the melting behaviors of pure PP and PP/ TMB-5 composites with different TMB-5 content before and after SDD. For T 0 , only one obvious melting peak corresponding to α form appeared at around 165 °C.…”

Molecular Weight and Distribution Dependent Critical Stress of Fragmentation of Highly Oriented Amorphous Network in Stretched Isotactic Polypropylene

“…51 If the critical stress of plastic deformation is smaller than the stress for initiating the small strain cavitation, the sample will deform with plastic deformation rather than cavitation and vice versa. 52 The iPP blend with a more homogeneous distribution of chain lengths favored in small strain cavitation at low T d might be due to its larger lamellar thickness. The slippage of these lamellae was more difficult as compared to the ones with smaller thickness induced in iPP with a more heterogeneous distribution of molecular weight.…”