is that all of these CMC derivatives have Tm
values lower than the parent cellulose. In accordance with these data, the
carboxymethylation decreases the thermal stability of cellulose [18].

Second, Tm values for the earth
alkaline salts of CMC are greater than that of
the alkali one. In such way, the earth alkaline salts of CMC are thermally more
stable than the alkali counterpart. The reason for this behavior is probably due to the divalent character of the earth
alkaline counter-ion that may bond to more than one carboxylate anion,
providing additional stabilization. Other periodic properties noted here is
that the greater the ionic radius, the lower the thermal stability of a specific group alkali or earth alkaline
salts. The CMC
salts with transition metals as counter-ions show lower stability considering
the Tm value and a complex multi-steps
degradation pattern [18].

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The thermal stability of the CMC is strongly influenced by the initial solution
pH before precipitation. A sample of NaCMC recovered from an acid medium (pH
2.0 in HCl) show a TG curve very different from a NaCMC sample recovered from
an alkaline one (pH 12.0 in NaOH). In this case,
the degree of ionization is an important role in the stabilization of the CMC.
In acid condition, some carboxylate
groups are in the non-dissociate form, which is
noticeably less stable than the dissociated form. This finding confirms that
intermolecular forces acting between the cation and the anion dictated the
thermal stability of the CMC polyelectrolyte. This different degree of ionization may also affect the degree of humidity uptake [18].

Case study

Koh May Hong et al. (2013) study differential
scanning calorimetry analysis of sodium carboxymethyl cellulose obtained from
sugarcane bagasse. Melting temperature (Tm) and heat of fusion (?Hf)
of NaCMC found 136.67(ºC) and 198.64(J g-1) respectively [19].

Kunio Nakamur et
al. (2004) study thermal
properties of NaCMC and water-NaCMC systems and found that the functional
properties of NaCMC are affected by the presence of bound water. In
this study, CMC-PLys molecular complexes carboxymethylcellulose-polylysine (CMC-PLys)
with controlled PLys/CMC ratio prepared.
NaCMC is having various degrees of substitution (DS) and PLys with a molecular weight of about 5000 having random
coil structure were used. A thermal property of the complexes is measured by DSC in order to investigate the
higher order structure of CMC-PLys and its gelation mechanism.


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