Biomedical Engineering Reference
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hydrolysis. To determine sample crystallinity, the diffraction data was smoothed with a
Savitzky-Golay filter using a second-order polynomial regression with 10 points, decon-
voluted, and fit with Gaussian-Lorentzian line shapes, all performed in the Peak Fit V.4
software package. This method of peak fitting provided a reasonable overall curve fit
with a correlation coefficient of 0.95 for all samples. The six most intense crystalline
diffraction peaks were observed for 5
◦
≤
30
◦
, and were indexed as the
020, 021,
110, 120, 130
,and
013
reflections according to the unit cell of
α
-chitin as reported by
Minke and Blackwell (31). The deconvolution of the XRD data for the chitin nanocrys-
tals sample is presented in Figure 8.12 and assumed the 2
θ
values predicted by the
reported Minke and Blackwell unit cell as noted in Table 8.1.
The crystallinity was measured as the ratio of the sum of the areas under the crystalline
diffraction peaks to the total area under the curve for 5
◦
≤
2
θ
≤
30
◦
, based on a method
proposed for cellulose and used here for chitin (32). From this analysis we found the
percentage crystallinity of the pure shrimp shell chitin to be approximately 76%, and
2
θ
≤
1250
1250
1000
1000
750
500
250
750
500
250
19.4
1000
1000
9.368
750
750
23.72
26.648
20.888
500
250
0
500
250
0
22.472
29.672
28.232
17.864
12.824
5
15
2 Theta (Degrees)
25
35
Figure 8.12
Deconvolution of chitin nanocrystal X-ray diffraction data. Top: dotted line
represents smoothed data, and the solid line represents the overall fit. Bottom: individual
peakfits.Reprintedwithpermissionfrom(23).Copyright(2007),AmericanChemicalSociety.
Table8.1
Observedandliteraturereported
2
θ
valuesforthe6most intensecrystalline
diffractionpeaksobservedin
α
-chitin(31).
hkl
2
θ
literature
2
θ
Obs
020
9.39
9.37
021
12.72
12.82
110
19.30
19.40
120
20.95
20.88
130
23.54
22.47
013
26.37
26.65
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