Crystallization and Melting of Oriented Parent - Daughter Lamellae in Sheared Isotactic Poly(propylene)

Abstract

Alpha isotactic poly(propylene) (α-iPP) exhibits a form of lamellar branching that is unique among semicrystalline polymers, where the branches have a distinct orientation relationship with the original crystalline lamellae. This is termed a parent–daughter relationship (PD). By allowing the structure to crystallize in an oriented form, a bimodal orientation of lamellae is developed and the individual contributions of PD lamellae can be observed using wide-angle X-ray scattering (WAXS). The present study investigated oriented PD lamellae during flow-induced crystallization and subsequent melting using time resolved rheo-WAXS. During crystallization the planes of the daughter lamellae were observed to curve towards the flow direction as they grew from their parent lamellae. This was explained by the influence of neighbouring daughter lamellae confining their growth direction. Oriented daughter lamellae were found to melt ~5°C lower than oriented parent lamellae, which provides a new explanation for the multiple melting behaviour observed in the melting thermograms of sheared α-iPP.

Crystalline structure and thermodynamic analysis of ultra‐low diameter VGCF‐polypropylene nanocomposite monofilaments

“…The monotonic decrease in the melting temperature of the VGCF loaded filaments correlates with a reduction of the inter-lamellar spacing (increase in LP 21 ), as shown in Fig. 7.…”

“…As in the case of the melting temperature, DH f also decreases, from 72, to 54 J g 21 . Using the heat of fusion for bulk, crystalline polypropylene as a reference the %v (crystallinity) was calculated and is presented in Fig.…”

“…For the preparation of extruded monofilament nanocomposites, we used iPP high flow nucleated homopolymer (Mw 5 135,000 g mol 21 , Capilen U77, Carmel Olefins, Israel) as the matrix. Acicular nano-fibers were used as the reinforcing phase: VGCF (graphitized up to 2,800 C, average diameter 150 nm, length 10-20 lm, density 2.0 g cm 21 , without surface treatment, i.e., as is), supplied by Showa Denko KK, Japan.…”

“…Acicular nano-fibers were used as the reinforcing phase: VGCF (graphitized up to 2,800 C, average diameter 150 nm, length 10-20 lm, density 2.0 g cm 21 , without surface treatment, i.e., as is), supplied by Showa Denko KK, Japan. In addition, 0.1 wt% of the antioxidant Irganox B-225 (Ciba) was added to prevent polymer degradation at high temperatures.…”

Everything Under the Sun: The 11th Pacific Polymer Conference

“…This very careful study examined the effect of molar mass and of copolymer composition on solution properties. The thermal and crystallization properties of α isotactic polypropylene have been reported by Phillips et al [14] The authors have used several techniques notably both small-angle X-ray scattering and rheo-WAXS to examine in exquisite detail the complex reorientation behaviour of the crystalline lamellae under shear. Marianne Gaborieau and her coworkers [15] have shown that coupling of capillary electrophoresis to electrospray ionization mass spectrometry provides a powerful tool for characterization of the small polymers and oligomers formed using the modern controlled radical polymerization methods.…”