Chemistry Reference
In-Depth Information
Having compare destruction behavior of the homopolymer PHB and
the copolymer PHBV, we can see that the introduction of hydrophobic
entity (HV) into the PHB molecule via copolymerization reveals the hy-
drolytic stability of PHBV molecules. For PHBV an hydrolysis induction
time is the longest among the other polymer systems and over a period
of 70 days its weight loss is minimal (<1% wt.) and possibly related with
desorption of low-molecular fraction of PHBV presented initially in the
samples after biosynthesis and isolation. The kinetic curves in Fig. 5.1
show also that the conversion the parent polymers to their blend PHB-
PLA decreases the hydrolysis rate compared to PHB (MW=1000 kDa)
even if the second component is a readily hydrolysable polymer: PLA
(MW=70 kDa).
For the sake of hydrolysis amplification and its exploration simultane-
ously, an polymer exposition in aqueous media has usually been carried
out at elevated temperature [11, 19]. To find out a temperature impact on
degradation and intensify this process, we have elevated the temperature
in phosphate buffer to 70 °C. This value of temperature is often used
as the standard in other publications see, for example Ref. [11]. As one
should expect, under such condition the hydrolysis acceleration is fairly
visible that is presented in Fig. 5.1b. By the 45th day of PLA incubation
its films turned into fine-grinding dust with the weight-loss equaled 50%
(MW=70 kDa) or 40% (MW=350 kDa). Simultaneously the PHB with
the lowest MW=170 kDa has the weight loss = 38 wt.% and the film was
markedly fragmented while the PHB samples with higher MWs 350, 500
and 1000 kDa have lost the less percent of the initial weight, namely 20,
15 and 10%, respectively. Additionally, for 83 days the weight drop in
the PHB-PLA blend films is about 51 wt.% and, hence, hydrolytic sta-
bility of the blend polymer system is essentially declined (cf. Figs. 5.1a
and 5.1b).
