Lamellar Morphology of Poly(3-hydroxybutyrate)/Poly(ethylene oxide) Blends as Studied via Small Angle X-ray Scattering |
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Authors: | Hsiu-Jung Chiu Jiang-Wen You |
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Affiliation: | (1) Department of Chemical Engineering, Ta Hwa Institute of Technology, Chiunglin, Hsinchu, 30703 Taiwan, ROC |
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Abstract: | The lamellar morphology of a melt-miscible blend consisting of two crystalline constituents, poly(3-hydroxybutyrate) (PHB) and poly(ethylene oxide) (PEO) have been investigated by means of small angle X-ray scattering (SAXS). The blend was a crystalline/amorphous system when temperatures lay between the melting point of PEO (ca. T
m
PEO=60![thinsp](/content/k85l035g17v363r0/xxlarge8201.gif) C) and that of PHB (ca. T
m
PHB=170![thinsp](/content/k85l035g17v363r0/xxlarge8201.gif) C), while it became a crystalline/crystalline system below T
m
PEO. The crystalline microstructures of the blends were induced by two types of crystallization history, i.e. one-step and two-step crystallizations. In the one-step crystallization, the blends were directly quenched from the melt to room temperature to allow simultaneous PHB and PEO crystallization. The two-step crystallization involved first cooling to 70![thinsp](/content/k85l035g17v363r0/xxlarge8201.gif) C to allow PHB crystallization for 72 h followed by cooling to room temperature (ca. 19![thinsp](/content/k85l035g17v363r0/xxlarge8201.gif) C) to allow PEO crystallization. In the crystalline/crystalline state, two scattering peaks have been observed in the Lorentz-corrected SAXS profiles, irrespective of the crystallization histories, meaning that crystallization created separate PHB and PEO lamellar stack domains. One-step crystallization yielded lamellar stack domains containing almost pure PHB and PEO lamellae. Two-step crystallization generated almost pure PHB lamellar domains and the PEO lamellar domains with inserted PHB lamellae. In the crystalline/amorphous state, the composition dependence of the amorphous layer thickness (l
a), the presence of zero-angle scattering, and the volume fraction of the PHB lamellar stack ( s) revealed that both one-step and two-step crystallizations, generated the interfibrillar segregation morphology, where the extent of interfibrillar segregation of amorphous PEO increased with increasing PEO content. |
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Keywords: | interfibrillar segregation poly(ethylene oxide) poly(3-hydroxybutyrate) small angle X-ray scattering (SAXS) zero-angle scattering |
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