Chemistry Reference
In-Depth Information
The variance of characteristics is related with solvent desorption con-
ditions during its evaporation for the cast film. During chloroform evapo-
ration from the surface faced to air, the flux forms additional channels (viz.
the pores), which are fixed as far as the film is solidified and crystallized.
Simultaneously, during evaporation the morphology and texture on the
opposite side of film exposed to the glass support are not subjected to the
impact of solvent transport. The morphology of the latter surface depends
on energy interaction conditions (interface glass-biopolymer tension) pre-
dominantly. The exposition of PHB films to the buffer for long time (83
days) lead to a threefold growth of roughness characteristics for glass-
exposed surface and practically does not affects the air-exposed surface.
It is interesting that temperature of film degradation does not influence on
the roughness change. The surface characteristics of film surface have the
same values after treatment at 37 °C and 70 °C.
Summarizing the AMF data we can conclude that during degradation
the air-exposed, rough surface remained stable that probably related with
the volume mechanism of degradation (V-mechanism [31, 32]). The pores
on the surface provide the fast water diffusion into the bulk of PHB. How-
ever, under the same environmental conditions, the change of surface po-
rosity (roughness) for glass-exposed surface is remarkable showing the
engagement of surface into degradation process (S-mechanism [31, 32]).
Last findings show that along with the volume processes of polymer deg-
radation the surface hydrolysis can proceed. Several authors [20, 21] have
recently reported on surface mechanism of PHB destruction but traditional
point of view states a volume mechanism of degradation [12]. Here, us-
ing an advanced method of surface investigation (AMF) we have shown
that for the same film under the same exterior conditions the mechanism
of degradation could be changed depending on the prehistory of polymer
preparation.
5.4 CONCLUSION
Analyzing all results related with hydrolytic degradation of PHB and its
derivatives, the consecutive stages of such complicated process are pre-
sented as follows. During the initial stage, the total weight is invariable and
the cleavage of bio-molecules resulting in the MW decrease is observed.
Within this time the PHB intermediates are too large and hydrophobic to
provide solubility in aqueous media. Because the PHB crystallites stay
