Civil Engineering Reference
In-Depth Information
appeared as strongly dependent on polymer concentration, type of solvent and tem-
perature [120] . h e critical volume fraction decreases with increasing the acidity of the
given solvent and intrinsic viscosity of the polymer. Cellulose derivatives with posi-
tive birefringence (the light polarized parallel to the optical axis is larger than the light
polarized perpendicular to the optical axis) form negative spherulitic domains, besides
cellulose triacetate, in the case in which the negativity of the birefringent system (the
light polarized perpendicular to the optical axis is larger than the light polarized par-
allel to the optical axis) forms liquid crystalline domains with positive birefringent
spherulites.
Methyl cellulose is a derivative of cellulose soluble in water and widely used as a
binder or thickener in pharmaceutical products, food products, in the i eld of ceramics,
etc. Formation of the liquid crystal phase is dependent on molecular weight, concen-
tration and temperature, as evidenced in dif erent experimental studies employing dif-
ferential scanning calorimetry, polarized light microscopy, optical rotatory dispersion
[121] . h is cellulose derivative has two stages of thermoreversible gelation in aqueous
solution, as temperature rises, if concentration exceeds a certain critical value [117,
122]. Several studies [123] have revealed a crystal liquid phase in dilute solutions as
well.
14.1.6
Cellulose Derivatives/Polymers Systems
h e wide range of preparative and structure-analytical studies includes characteriza-
tion of the donor-acceptor properties of cellulose substrates and derivatives. Cellulose
derivatives are important due to new properties and applications, including their solu-
tion structure and design of supramolecular architectures. Progress in cellulose ester
(as i lm-forming materials, anionic polyelectrolytes, and biologically active polymers)
and cellulose ethers (with nonstatistical substituent distribution along the chains) leads
to dif erent materials [1] . h e importance of the cellulose derivatives biopolymers is
a result of its specii c structure determined by intermolecular interactions, crosslink-
ing reactions, chain lengths, chain-length distribution, and by the distribution of func-
tional groups on the repeating units and along the polymer chains. Cellulose dif ers
from synthetic polymers by its polyfunctionality, high chain stif ness, and sensitivity
toward the hydrolysis and oxidation of the chain-forming acetal groups, which deter-
mine its chemistry and handling.
Moreover, the structure of cellulose and cellulose derivatives in solution has great
practical importance as well. Examples include the shaping of cellulose from spin-
ning solutions, modii cation of the synthesis of cellulose derivatives and the properties
of water-soluble cellulose ethers, which are all dependent on the solution structure.
For this reason, questions regarding the structure of cellulose in solution have been
the subject of intense research and discussion. Literature presents dif erent cellulose
derivative blends containing low and high molar mass liquid crystals [124]. Low molar
mass liquid crystals have been used as plasticizers for thermoplastic polymers and in
applications such as electro-optics, optical recording media, and membranes, and high
molar mass liquid crystalline polymers have been primarily used in polymer blends as
processing aids and as an incipient reinforcing phase for “self-reinforced” materials.
