Chemical and Radiation Stability of PEEK - PEEK Biomaterials - page 75

Table 6.1 Mechanical Properties Before and After a 75-kGy Gamma Irradiation Dose

Results Before
Sterilization

Results After
Sterilization Test Test Method

Tensile strength ISO 527 100.69 MPa 99.77 MPa

Tensile elongation ISO 527 32.21% 34.30%

Flexural strength ISI 178 163.88 MPa 163.73 MPa

Flexural modulus ISO 178 3.99 GPa 4.09 GPa

7.0 kJ/m 2 7.3 kJ/m 2

Impact strength (Notched Izod) ISO 180

Density ASTM D792 1.30 g/cc 1.30 g/cc

T g (onset) DSC 146.77 C 144.33 C

Melt temperature DSC 341.30 C 339.49 C

Recrystallization temperature DSC 289.77 C 290.32 C

DSC, differential scanning calorimetry.

mobility of electrons along the molecular chain [16] .
In studies of free radical decay using electron spin
resonance(ESR),Lietal. [16] found no evidence of
residual free radicals in PEEK immediately after
exposure with up to 600 kGy of gamma radiation,
indicating that any free radicals produced by irradiation
of PEEK have a lifetime of less than 20 min, which
was the time needed to transfer the samples from the
irradiation chamber to the ESR instrument in their
experiment.
The radiation stability of crystalline and amor-
phous PEEK has been extensively studied for
the past two decades because of the interest in
spacecraft applications and nuclear fusion reactors,
where the total exposure to radiation ranges between
10 and 50 MGy (i.e., 10,000 e 50,000 kGy) [2,15,
17 e 25] . Although degradation and cross-linking of
PEEK occur at doses above 10 MGy, it should be
appreciated that the exposures of concern to the
aerospace and nuclear power industry exceed the
standard sterilization doses for medical devices
(25 e 40 kGy) by three orders of magnitude.
Table 6.1 demonstrates the mechanical properties of
PEEK-OPTIMA LT1 before and after a 75-kGy
gamma radiation dose.
Repeated sterilization, with up to four 25- to 40-
kGy doses of gamma radiation in air, has been
confirmed to result in no significant changes to the
mechanical behavior of PEEK and PEEK carbon

fiber composites [6] . This is demonstrated in Fig. 6.2 ,
which compares the oxidative gamma radiation dose
at which a slight (5%) deterioration of flexural
properties occurs in various polymers. Microstruc-
tural characterization of CFR-PEEK detected only
slight modification to the interphase region of the
composite, from 3 to 3.8 m m in width, following
radiation sterilization [5] .
Therefore, reported radiation stability data indi-
cate that PEEK components may be effectively
sterilized by gamma irradiation in air. Although it is
possible to gamma sterilize PEEK components in
a low-oxygen environment, unlike UHMWPE, such
advanced packaging would not be expected to
confer improved shelf life. Test methods have been

Figure 6.2 The oxidative gamma radiation dose (Rads)
at which a slight (5%) deterioration of flexural proper-
ties occurs.