Transmission electron microscope observations of fibrillar-to-lamellar transformations in melt-drawn polymers ? I. Isotactic polypropylene

Abstract

Abstract:The transformation during heat treatment from a fibrillar to a lamellar morphology in highly oriented polypropylene is followed by transmission electron microscopy (TEM) and small angle electron scattering (SAES). While the as drawn films exhibit long (up to 1/an) continuous fibrillar crystals, those crystals disintegrate into short crystalline blocks which finally aggregate into a lamellar morphology during the heat treatment. After even longer heat treatment the lamellar crystals start to thicken.

Crystal shapes and crystallization in continuum modeling

“…47,48 In this transition, several oriented partly crystalline fibrillar crystals merge to form a stack of lamellae, where the stacking direction is along the fibrillar direction and the lamellae themselves are oriented perpendicular. For simplification, we assume that the crystal morphology is described by one-dimensional growth of cylinders prior to the transition, and by two-dimensional (lateral) growth of cylinders thereafter.…”

Continuum model for the simulation of fiber spinning, with quiescent and flow-induced crystallization

“…In a small angle X-ray scattering study, Murthy et al [61,62] report that for as-spun nylon fibers the fibrils have a length of 100-300 nm and a diameter of 5-20 nm. Visual inspection of the TEM analysis of fast drawn PB-1 [63] and iPP [64,65] films from the melt reveal a fibril length of about 250 nm. Hence, based on the present experimental data, one finds that after (different) fast extensional flows the average length and diameter of the fibrils are approximately similar for different polymers.…”

“…The parameters A fibril , g n and g l are determined as follows. Based on experimental data of asspun fibers we consider for the cross-section of the fibrils a value of A fibril = 10 −16 m 2 , corresponding to a fibril diameter of about 11.3 nm, which is of the proper order compared to available experimental data [61][62][63][64][65]. To determine g n and g l it is convenient that φ only depends on the magnitude of g n g l , whereas the number density and average length of the fibrils follow from specifying g n and g l .…”

Morphology in Oriented Semicrystalline Polymers

“…After annealing, the needle crystals consist of periodic arrangements of defect-free and highly defective zones along the needle direction (see Figure 2(b)) [23]. With further annealing at elevated temperatures, an additional transformation from a needle crystal morphology into a stacked lamellar morphology may occur in some polymers, as depicted in Figure 11 [24].…”