Chemistry Reference
In-Depth Information
5.3
RESULTS AND DISCUSSION
The in vitro degradation of PHB with different molecular weight (MW)
and its derivatives (PHBV, blend PHB/PLA) prepared as films was ob-
served by the changes of total weight loss, MW, and morphologies (AFM,
XRD) during the period of 91 days.
5.3.1 THE HYDROLYSIS KINETICS OF PLA, PHB, AND ITS
DERIVATIVES
The hydrolytic degradation of the biopolymer and the derivatives (the co-
polymer PHBV, and the blend PHB/PLA 1:1) has been monitored for three
months under condition, which is realistically approximated to physio-
logical conditions, namely, in vitro: phosphate buffer, pH=7.4, tempera-
ture 37 °C. The analysis of kinetic curves for all samples shows that the
highest rate of weight loss is observed for PLA with the smallest MW ≈
70 kDa and for PHB with relatively low MW ≈ 150 kDa (Fig. 5.1). On
the base of the data in this figure it is possible to compare the weight-loss
increment for the polymers with different initial MW. Here, we clearly see
that the samples with the higher MWs (300-1000 kDа) are much stabler
against hydrolytic degradation than the samples of the lowest MW. The
total weight of PHB films with MW=150 kDa decreases faster compared
to the weight reduction of the other PHB samples with higher MW's = 300
and 450 or 1000 kDa. Additionally, by the 91st day of buffer exposition
the residual weight of the low-MW sample reaches 10.5% weight loss that
it is essentially higher than the weight loss for the other PHB samples (Fig.
5.1).
After establishing the impact of MW upon the hydrolysis, we have
compared the weight-loss kinetic curves for PLA and PHB films with the
relatively comparative MW = 400 and 350 kDa, respectively and the same
film thickness. For the PLA films one can see the weight depletion with the
higher rate than the analogous samples of PHB. The results obtained here
are in line with the preceding literature data [8, 12, 19-21].
