MeIt reaction in blends of immiscible PHB and ENR-50
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Date
2003
Authors
J., Ismail
Journal Title
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Abstract
Melt reaction at the interface of immiscible blends compnsmg a biopolymer, poly(3-
hydroxybutyrate )(PHB), and epoxidized natural rubber with 50 mol percent level of
epoxidation (ENR-50), prepared by solution casting technique has been studied. Differential
scanning calorimetry (DSC) technique was used to measure the enthalpy of reaction under
isothermal annealing. Morphologies upon melting of PHB are highly unstable as observed
using optical pol~rizing microscope. The enthalpy of reaction increases with PHB and ENR-
50 content respectively as long as they constitute the dispersed phases and· exhibits a
maximum at about 40-50 % PHB. Enthalpy also increases with temperature for PHB/ENR-50
blends comprising PHB below 50% while remains practically independent of temperature in
other compositions. The overall rate ofreaction expressed as the reciprocal ofthe half-time of
the reaction, Ilto. 5, exhibits an exponential increase with temperature and also increases with ..
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decreasing PHB content. A reaction mechanism comprising degradation of PHB chains to
shorter chains bearing carboxyl end groups that subsequently reacted with epoxide group of
the ENR-50 was proposed, providing the basis for kinetic analysis and determination of
parameters that characterize the melt reaction. While the glass transition teinperatures
observed at -18.4 and 1.2°C are associated with immiscible ENR-50 and PHB phases
respectively, a mutual shift towards each other after annealing at 190°C is observed,
increasing gradually with increasing annealing time, an indication of progressive
enhancement of compatibility of the blends. There is evidence that crystallization and melting
behavior of PHB in blends are affected by annealing. These observations are s~en as the
jirect effects of the melt reaction. FTIR spectrum provides further evidence that supports the
ing opening reaction of the epoxide group by the carboxyl group.
~eywords: Melt, blends, morphology, epoxidized natural rubber, poly(3-hydroxybutyrate).
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Keywords
Immiscible , ENR-50