Index of crystallinity

The highest yield of levoglucosenonc (29 %) has been obtained by pyrolysis of microcrystalline Munktell cellulose, which is characterized by the highest index of crystallinity, levelling-off DP and the lowest hydrophiliiy. 

Indexes of crystallinity can be obtained from these different experiments. It has to be noted that the crystalline structure generally corresponds to the crystalline structure of the starting homopolymers. The crystalline domains play a role as physical crosslinks. 

Since 0j is always less than equal to unity, the bulk crystallinity caimot be higher than the linear crystallinity. The volume fraction of the bulk crystallinity (0, ) can also be estimated from the index of crystallinity (xJ obtained from WAXD/XRD via [35]... 

Degree of Crystallinity The index of crystallinity (x ) is evaluated from WAXS data by taking the ratio of crystalline diffraction area to the total diffraction area of the diffraction profile, and is given by... 

To study the ratio between crystalline and non-crystalline fractions of cellulose, different experimental techniques can be used including IR or Raman spectroscopy, solid-state C-NMR, X-ray diffraction and some others (Park et al., 2010). In most cases, these experiments give so-called index of crystallinity (Crl) that shov the comparative content of crystalline fraction in several cellulose samples. Index of crystallinity may indicate which of the samples has greater crystallinity and which has less crystallinity, but it does not disclose the true degree of crystallinity, i.e., weight part of the crystalline fraction in cellulose. Besides, it was found that the value of Crl for the same sample varies significantly depending on the chosen measurement technique (Evans et al., 1995 Park etal., 2010). 

The index of crystallinity for the investigated cellulose sample or samples may be calculated from the system of the Eq. (7.2) as follows ... 

Due to these shortcomings, the method of Hermans-Weidinger gives only comparative index of crystallinity of cellulose, and therefore it should not be used for determination of the absolute content of crystalline and non-crystalline fractions in cellulose samples. For example, this method gives CrI of bacterial cellulose about 0.40 (Hermans, 1951] that is far from the later crystallinity measurements of the sample about 0.80-0.90 (Czaja et al., 2004]. 

The Segal method gives comparative index of crystallinity various natural celluloses, e.g., wood pulp, cotton, and flax fibers and celluloses, micro crystalline and powder celluloses, etc. However, this method is not intended for modified celluloses having CII, CHI, and CIV crystalline allomorphs. 

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