Chemistry Reference
In-Depth Information
5.1 INTRODUCTION
This chapter is designed to be an informative source for biodegradable
poly(3-hydroxybutyrate) and its derivatives' research. We focuses on hy-
drolytic degradation kinetics at 37 °C and 70 °C in phosphate buffer to
compare PLA and PHB kinetic profiles. Besides, we reveal the kinetic
behavior for copolymer PHBV (20% of 3-hydroxyvalerate) and the blend
PHB-PLA. The intensity of biopolymer hydrolysis characterized by to-
tal weight lost and the viscosity-averaged molecular weight (MW) decre-
ment. The degradation is enhanced in the series PHBV < PHB < PHB-
PLA blend < PLA. Characterization of PHB and PHBV includes MW and
crystallinity evolution (X-ray diffraction) as well as AFM analysis of PHB
film surfaces before and after aggressive medium exposition. The impor-
tant impact of MW on the biopolymer hydrolysis is shown.
The bacterial polyhydroxyalkanoates (PHA)s and their principal rep-
resentative poly(3-R-hydroxybutyrate) (PHB) create a competitive option
to conventional synthetic polymers such as polypropylene, polyethylene,
polyesters, etc. These polymers are nontoxic and renewable. Their bio-
technology output does not depend on hydrocarbon production as well as
their biodegradation intermediates and resulting products (water and car-
bon dioxide) do not provoke the adverse actions in environmental media
or living systems [1-3]. Being friendly environmental [4], the PHB and
its derivatives are used as the alternative packaging materials, which are
biodegradable in the soil or different humid media [5, 6].
The copolymerization of 3-hydroxybutyrate entities with 3-hy-
droxyoctanoate (HO), 3-hydroxyheptanoate (HH) or 3-hydroxyvalerate
(HV) monomers modifies the physical and mechanical characteristics of
the parent PHB, such as ductility and toughness to depress its processing
temperature and embrittlement. Besides, copolymers PHB-HV [7], PHB-
HH [8] or PHB-HO [9], etc, have improved thermo physical and/or me-
chanical properties and hence they expand the spectrum of constructional
and medical materials/items. For predicting the behavior of PHB and its
copolymers in a aqueous media, for example, in vitro, in a living body or
in a wet soil, it is essential to study kinetics and mechanism of hydrolytic
destruction.
Despite the history of such-like investigations reckons about 25 years,
the problem of (bio)degradation in semicrystalline biopolymers is too far
from a final resolution. Moreover, in the literature the description of hy-
