O. Miguel et Jj. Iruin, Water transport properties in poly(3-hydroxybutyrate) and poly(3-hydroxybutyrate-co-3-hydroxyvalerate) biopolymers, J APPL POLY, 73(4), 1999, pp. 455-468
Water sorption and diffusion have been investigated in poly(3-hydroxybutyra
te) (PHB) and three poly(3-hydroxybutyrate-co-3-hydroxyvalerate) copolymers
[P(HB-KV)] by means of a Cahn electromicrobalance. Permeability of these s
amples have been determined using a gravimetric permeation cell. Two experi
mental setups were used for the gravimetric sorption measurements, under dy
namic and static conditions, respectively. The differences observed in the
results obtained using these techniques are discussed. The sorption measure
ments have evidenced the tendency of water molecules to form aggregates or
clusters in the polymer. In addition, the static sorption method revealed t
he potential of PHB and P(HB-HV) to undergo molecular relaxations, eventual
ly leading to a partial desorption of the previously sorbed water after an
induction period. The clustering effect was adequately described by the pol
ycondensation model. On the other hand, the interpretation of the diffusivi
ty in terms of mobility coefficients has revealed a competition between a p
lasticization effect and clustering. As a whole, water transport properties
in PHB and its copolymers can be considered to be very close in magnitude
to those of common thermoplastics such as PVC and PET. (C) 1999 John Wiley
& Sons, Inc.