New Trends in Polymers - Progress in Organic and Physical Chemistry: Structures and Mechanisms - page 189

TABLE 1 (Continued)

Type of device Initial

M w of
PHB,
kDa

Size/
Thickness,
—m

Conditions Relative

mass loss
of PHB,
%

Relative
decrease of
PHB M w ,
%

Time,
days

Links

film 279 - 37°C,

pH=10

100 - 28 31

film 279 - 37°C,

pH=13

100 - 19 31

film 650 50 55°C,

pH=7.4

0 68 150 20

plate 380 2000 55°C,

pH=7.4

0 61 98 32

film 640 100 70°C,

pH=7.4

- 55 28 11

film 150 40 70°C,

pH=7.4

39 96 84 24-25

film 450 40 70°C,

pH=7.4

12 92 84 24-25

micro-spheres 50 250-850 85°C, pH

= 7.4

50 68 150 36

micro-spheres 600 250-850 85°C,

pH=7.4

25 - 150 36

During degradation of PHB mono¿ lament threads, ¿ lms and plates in vitro, the
change of mechanical properties was observed under different conditions [17, 37].
It was shown that a number of mechanical indices of threads became worse: load at
break lost 36%, strain at break lost 33%, Young's modulus did not change, tensile
strength lost 42% after 182 days incubation in phosphate buffer (pH = 7.2) at 70°C.
But at 37°C the changes were more complicated: at ¿ rst load at break increased from
440 g to 510 g (16%) at 90 th day and then decreased to the initial value at 182 nd day,
strain at break increased rapidly from 60 to 70% (in 17%) at 20 th day and then gradu-
ally increased to 75% (in 25%) at 182 nd day, Young's modulus did not change [17].
For PHB ¿ lms demonstrated a gradual 32% decrease in Young's modulus and 77%
fall in tensile strength during 120 days incubation in phosphate buffer (pH = 7.4) at
37°C [37]. For PHB plates more complicated changes were observed: at ¿ rst tensile
strength dropped in 13% for 1 st day and then increased to the initial value at 28 th day,
Young's modulus dropped in 32% for 1 st day and then remain unchanged up to 28 th
day, stiffness decreased sharply also in 40% for 1 st day and then remain unchanged up
to 28 th day [38].