Crystal morphology and structure of the β‐form of isotactic polypropylene under supercooled extrusion

Abstract

A supercooled melt of isotactic polypropylene (iPP) was extruded through a capillary die. Polarized light microscopy (PLM), wide-angle X-ray diffraction (WAXD), and differential scanning calorimetry (DSC) were used to investigate the effects of the relatively weak wall shear stress (r w ), extrusion temperature (T e ), and crystallization temperature (T c ) on the structure and morphology of b-form isotactic polypropylene (b-iPP). b-cylindrites crystals could be observed by PLM in the extruded specimen even at a lower r w 's (0.020 MPa), and the b-iPP content increased with decreasing T e . Under a given T e of 150 C, the increase in r w positively influenced the b-iPP content. The DSC and WAXD results indicate that the total crystallinity and b-iPP content increased when T c was set from 105 to 125 C; the other experimental parameters were kept on the same level. Although T c was above 125 C, the b-iPP content obviously decreased, and the total crystallinity continued to increase. On the basis of the influences of r w , T e , and T c on the b-iPP crystal morphology and structure, a modified model is proposed to explain the growing of shearinduced b-iPP nucleation.

AgNPs polypropylene gel films–thermal study and antibacterial activity

“…The gel PP 12.5 kGy peak which appears at 158°C corresponds to the a-crystal PP form. The two peaks of AgNPGelPPs melting temperature were observed at 160 and 174°C, respectively, due to the melting of the b and a-phase similar to the values found in the literature [29]. Silver insertion caused the displacement of a-peak to higher temperature and induced the b-phase formation.…”

Influence of β nucleation agent on the dispersion of nano‐CaCO3 in isotactic polypropylene matrix

“…1 It has four modifications: a, b, c, and smectic, 2-5 among them the b-form is the most attractive one for its better impact resistance as well as higher heat distortion temperature than other forms. [13][14][15] Adding b-nucleation agent is the most effective and accessible method to get a high level of b-PP. [13][14][15] Adding b-nucleation agent is the most effective and accessible method to get a high level of b-PP.…”

“…6,7 The b-form is metastable thermodynamically and can be obtained under some special conditions, such as in the presence of specific heterogeneous nucleation agents, [8][9][10] by crystallization in a temperature gradient during processing, 11,12 or by shear-induced crystallization. [13][14][15] Adding b-nucleation agent is the most effective and accessible method to get a high level of b-PP. 16 However, the yield strength and stiffness of iPP parts is lowered by the presence of b crystals.…”

Fiber preparation and mechanical properties of recycled polypropylene for reinforcing concrete

“…Similar with other polymer fibers, the tensile strength and Young modulus of PP fibers are affected by their physical structure, which is normally controlled by both the choice of starting material and the fiber formation conditions . The various conditions for fiber formation during melt spinning and hot drawing caused different arrangement of the supermolecular structural elements, further leading to different fiber mechanical properties.…”