Cellulose derivative behavior

In this study, adsorption behavior of water soluble polymers and their effect on colloid stability have been studied using polystyrene latices plus cellulose derivatives. As the aqueous solution of hydroxy propyl cellulose(HPC) has a lower critical solution temperature(LCST), near 50 °C(6 ), an increased adsorption and strong protection can be expected by treating the latices with HPC at the LCST. 

The study of mesophases of cellulose and cellulose derivatives is an active field which has expanded rapidly since the initial observation of liquid crystms of hydroxy-propyl cellulose in 1976. There are two areas that warrant turther investigation recent observations regarding the influence of solvent and/or substituents on the cholesteric helicoidal twist await a theoretical explanation there is a lack of careful studies to permit a theoretical treatment of the behavior of ordered celltdose phases. To date, no applications have been developea where the unusual properties of cellulose derivatives are utilized. 

UHMWPE gels have been studied mainly for their processability into high modulus/strength products. The viscoelastic behavior of this polymer/solvent system, as well as others which are capable of forming a gel-like state at some suitable concentration, has received little attention. Previous studies have been carried out by Ferry et al. (6,7) with gel systems of cellulose derivatives and polyvinychloride... 

Quite recently, a series of N-alkyl substituted imidazolium salts has been evaluated for additive effects on the mesomorphic behavior and ensuing optical properties of HPC aqueous solutions, followed by characterization of the thermotropicity of novel cellulose derivatives with such an ionic liquid structure in the side-chains [193]. 

In summarizing the intrinsic viscosity relations presented in this section, it must be admitted that they represent nothing more than rather small semi-empirical refinements of the Flory excluded volume theory and the Flory-Fox viscosity theory. For a large fraction of the existing body of experimental data, they offer merely a slight improvement in curve-fitting. But for polymers in good solvents it is believed that a more transcendental result has been achieved. The new equations permit more reliable assessment of unperturbed chain dimensions in such cases, and in some instances (e. g., certain cellulose derivatives see Section III B) they offer possible explanations of heretofore paradoxical solution behavior. 

The lyotropic mesophases of cellulose and cellulose derivatives were first observed only relatively recendy (1-3). It is of interest to note that Flory in his now classical papers (44) i icted in 1956 that cellulose or cellulose derivatives should exhitnt liquid crystal behavior. Since Werbowyj and Gray (I) first reported mesophases of hydroxylpropyl cellulose in water, the field has expanded rapidly (for reviews see References 6 and 7). Undoubtedly, the activity in this area originates from a desire to prepare fibers or films of cellulose or cellulose derivatives with supoior properties as well as to understand the purely scientific aspects of the systems. 

Alkoxy fatty acid anhydrides show a behavior similar to that of the halogenated anhydrides and do not esterify cellulose in the presence of acid catalysts. In the presence of pyridine, however, methoxyacetic and ethoxyacetic anhydrides or their acid chlorides give soluble cellulose derivatives."... 

The more fundamental aspects of fiber constitution and behavior are dealt with in Astbury s Fundamentals of Fibre Structure 27) and Textile Fibres under the X-Rays 28), Hermans Contributions to the Physics of Cellulose Fibres 39), and Physics and Chemistry of Cellulose Fibres (40 Marsh s Textile Science (40 Preston s Fibre Science 59) and the High Polymers series of monographs, three of which are concerned with natural fibers—Volume IV, Natural and Synthetic High Polymers, by Kurt H. Meyer 53), Volume V, Cellulose and Cellulose Derivatives, edited by Emil Ott 56), and Volume VI, Mechanical Behavior of High Polymers, by Turner Alfrey, Jr. 21 ... 

A remarkable hysteresis between the compression and expansion cycles is apparent for the cellulose derivatives, with E4M the cellulose that showed the highest area within the compression and expansion cycles. This behavior is associated with the rearrangement and reorganization of the polymer... 

The cellulose derivatives E4M, E50LV, and F4M have shown different behavior at the air-water interface. E4M displayed the highest adsorption efficiency and surface activity, as could be determined from tensiometry and ir-A isotherms. E4M was found to adsorb fastest at the interface. The high hysteresis shown by E4M implies that it forms monolayers where molecules can be more compacted after compression and yet keep the acquired spatial conformation. 

As for every material, the behavior of cellulose derivatives is governed by equations in which solubility parameters or surface free energy terms are frequently included. For comparison purposes, it seemed opportune to collect recently published data (Table 8). Polarity is for most applications a relevant parameter and therefore fractional polarities xp were calculated from solubility parameters or surface free energies, Eq. (4) Sect. 2.3. 

One of the main features of nonionic water-soluble cellulose derivatives is that they exhibit, like some other polyethers, an inverse solubility-temperature behavior, i.e. there is phase separation on heating above the so-called lower critical solution temperature (LCST). The temperature at which a polymer-rich phase separates is normally referred to as the cloud point (CP). For ideal solutions, this temperature corresponds to the theta-temperature. Actually, for some derivatives, the cloud point may be preceded, if the concentration is not too low, by a sol-gel transformation with an increase in viscosity and possibly formation of liquid crystals (see Sect. 3.5). As it will be seen later, this reversible thermotropic behavior may be detrimental to the performance of the derivatives or can be advantageneously utilized to develop applications. 

Hydrophobically Associating Copolymers. Hydrophobically modified cellulose derivatives (28) and N-alkylacrylamido copolymers (24, 25, 27) were among the first nonionic associative thickeners reported in the patent literature. The concentration of hydrophobic units allowed for dissolution in aqueous solution is usually less than 1-2 mol %. Like conventional polymers, apparent viscosity is proportional to molecular weight and concentration. However, with associative copolymers, a very dramatic increase in apparent viscosity occurs at a critical concentration, C, which clearly is related to a phenomenon other than simple entanglement. Viscosity dependence on hydrophobe concentration, size, and distribution suggests mi-croheterogeneous phase formation. Surfactants enhance viscosity behavior in some instances (24), yet clearly reduce viscosity in others (i). 

Amphotropic behavior can be found for a large number of different chemical structures. Additional information is given in other chapters of this Handbook. Typical classes of amphotropic materials are for instance classical soaps (see lyotropics), transition metal soaps (see metallomesogens), viologens, quartemary amines and other ionic surfactants (see lyotropics), block copolymers (see polymer liquid crystals), cellulose derivatives (see cellulose liquid crystals) and partially fluorinated paraffines, diols, peptide surfactants, lecithins, lipids, alkylated sugars and inositols, naturally occurring glycosides and silanols, which are discussed in this chapter. 

It should be emphasized that the compensation of the twist and changes in the pitch for statistically trisubstituted LC deriva-tive/solvent system, e.g., 3C1-CTC-CTC/ TRIMM, occur when no full turn of the conformational helix with one kind of substituent group most probably exists. At present, a suitable explanation cannot be provided for this behavior of lyotropic LC cellulose derivatives. 

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