Novel etching phenomena in poly(3‐hydroxy butyrate) and poly(oxymethylene) spherulites

Macro Chemistry & Physics

Mitchell

2005

Summary: We show that small quantities of dibenzylidene sorbitol dispersed in poly(ε‐caprolactone) coupled with shear flow provide a self‐assembling nanoscale framework to yield high levels of crystal orientation. During modest shear flow of the melt, the additive forms highly extended nanofibrils which adopt a preferred alignment with respect to the flow field, and on cooling polymer crystallisation is directed by these fibrils. We use in situ time‐resolving SAXS and WAXS techniques to explore how this behaviour can be modified by the composition, the shear rate and strain as well as the temperature at which the shear flow is imposed. SAXS studies show that the 3% DBS completely dissolves in the PCL melt at temperatures ≥120 °C and that any shear flow imposed at temperatures above such values is ineffective in directing crystallisation.

Section: Resultsmentioning

confidence: 99%

Directed Crystallisation of Poly(ε‐caprolactone) using a Low‐Molar‐Mass Self‐Assembled Template

Wangsoub

Macro Chemistry & Physics

Mitchell

2005

“…Small-angle X-ray scattering (SAXS) data in the range jQj % 0.01 to 0.12 Å À1 (jQj ¼ 4psiny/l, where l is the incident wavelength and 2y is the scattering angle) were recorded using a two-dimensional (2D) RAPID detector with a data accumulation times of 10 s. Wide-angle X-ray scattering (WAXS) data in the range jQj ¼ 0.2 to 1.7Å À1 were recorded on the same beam-line using a Photonic Science CCD system and an integration time of 1 s. Samples for microscopy were prepared by first abrading the surface with a grinding cloth to remove any remaining mica and then by etching with an alkaline alcoholic reagent similar to those used previously for etching polyesters. [7,8] The etched specimens were then shaken in a solution of 10 wt.-% potassium hydroxide in propan-2-ol for three hours and then washed several times with distilled water and dried. The etched surfaces were sputter-coated with gold and examined in a Cambridge 360 Stereoscan scanning electron microscope.…”

Section: Experimental Partmentioning

confidence: 99%

The Use of a Low‐Molar‐Mass Self‐Assembled Template to Direct the Crystallisation of Poly(ε‐caprolactone)

Siripitayananon

Wangsoub

Macromol. Rapid Commun.

et al. 2004

Summary: We show that small quantities of dibenzylidene sorbitol dispersed in poly(ε‐caprolactone) provide a self‐assembling nanoscale framework to yield high levels of crystal orientation. During modest shear flow of the melt, the additive forms highly extended nanoparticles which adopt a preferred alignment with respect to the flow field and, on cooling, polymer crystallisation is directed by these particles. We speculate that atomistic level epitaxy is unlikely to be the only directing influence.SAXS pattern of PCL/DBS in the melt at 80 °C and subjected to a shear flow of 10 s−1 for 1 000 shear units. The flow direction is vertical.magnified imageSAXS pattern of PCL/DBS in the melt at 80 °C and subjected to a shear flow of 10 s−1 for 1 000 shear units. The flow direction is vertical.

“…Also, all of the objects are surrounded by a featureless region known as a quench halo, formed when growth suddenly accelerates as the specimen temperature is rapidly reduced. These are characteristic not only of PP but also of poly(4‐methyl pentene‐1)19 and polyhydroxybutyrate and polyoxymethylene20 and, to a lesser extent, of polyethylene. This type of splaying cannot, by itself, lead to the development of a typical three‐dimensional spherulitic shape: without deviation from this plane, the objects will remain quasi‐two‐dimensional.…”

Section: Resultsmentioning

confidence: 99%

Crystallization of propylene–ethylene random copolymers

Weng

J Polym Sci B Polym Phys

Bassett

et al. 2004

Self Cite

Of the three melting peaks typical of a propylene-ethylene random copolymer (with 5.1 wt % ethylene) crystallized between 110 and 140°C, the two higher peaks result from primary and secondary isothermal crystallization, whereas the material crystallized on cooling gives the lowest peak. In contrast to polypropylene homopolymers, which show strong morphological changes developing from the center of a spherulite, copolymer specimens are uniformly crosshatched. The highest melting peak is related to an open crosshatched framework of primary lamellae, and the next lower peak is related to later forming subsidiary lamellae filling the intervening space. The origin and nature of these double peaks are discussed in terms of the fractional crystallization and the ensuing constraints placed on isothermal lamellar thickening as a result of the exclusion of the comonomer from the polypropylene lattice.