Mesophase formation and chain rigidity in cellulose and derivatives. 1. (Hydroxypropyl)cellulose in dimethylacetamide

Conio, G.; Bianchi, E.; Ciferri, A.; Tealdi, A.; Aden, M. A.

doi:10.1021/ma00242a004

Cited by 121 publications

(58 citation statements)

References 11 publications

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“…Presumably there is a mesogenic phase in the 0.6% solution so that already oriented structures exist before shear begins. This behavior supports the detection of a cholesteric mesophase via polarization microscopy [17,19] as well as a rise in elliptically polarized light shortly before the phase separation. [16] In contrast to this, supramolecular structures presumably exist in 1% solutions, which are not oriented until they enter the shear field.…”

Section: Influence Of Concentration and Temperature On The Physical Ssupporting

confidence: 78%

“…Here small orientation angles at low shear rates in the dichroism experiment give an indication of mesogenic structures, which could be supported by the detection of cholesteric mesophases by means of polarization microscopyl. [17,19] Presumably the hydrodynamic interactions at temperatures beyond T = 39 8C are reduced to such an extent that the molecular structure of the polymer chains becomes more compact. Therefore, due to the existing chirality of the repeating anhydroglucose units, helices are able to form (Fig.…”

Section: Influence Of Concentration and Temperature On The Physical Smentioning

confidence: 99%

“…Here was a biphasic solution for each different composition, with the size being dependent upon the temperature. [17,18] Furthermore, both characterization via ellipticity data and investigations using polarization microscopy suggest that mesogenic structures, which may be the primary cause in phase separation, are already present in the temperature range below the phase boundary. [19] The development of an ordered, oriented structure during this process is presumably delayed by kinetic effects.…”

Section: Introductionmentioning

confidence: 99%

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Rheological characterization of aqueous hydroxypropyl cellulose solutions close to phase separation

Roschinski

Kulicke

2000

Macromol. Chem. Phys.

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The influence of temperature, concentration, shear rate and degree of substitution on the molecular structure of aqueous hydroxypropyl cellulose solutions (HPC) was investigated by means of rheo‐mechanical and rheo‐optical methods. During the investigations, it was possible to demonstrate the formation of supramolecular structures, even before visual or rheo‐mechanical confirmation, through the detection of dichroism in the shear field at T = 39°C shortly before the flocculation temperature at TF = 40°C. In addition, birefringence experiments and mechanical oscillation investigations showed that this conformational change of the segments was dependent upon the polymer concentration and the shear rate. The aggregated structure of the 0.6% HPC was elastic and easily degradable under shear, whereas the 1.5% solution was less elastic and the aggregates could only be degraded at higher shear rates. At high shear rates it is presumed that a conformation change in the HPC segments for 0.6–1.5% solutions led to the development of a second shear‐stable aggregate structure. It was therefore not possible to perform a uniform normalization of the birefringence in the semi‐concentrated solutions and compare it with phenomenological theories for the temperature range at T = 39°C due to differences in conformation that were dependent upon concentration and shear stress. The influence of the molar substitution, MS, at T = 39°C on the formation of supramolecular HPC structures was significant for 1.5% solutions. Beyond a MS > 6, the birefringence increased by over a decade as a function of the shear rate.

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Section: Influence Of Concentration and Temperature On The Physical Ssupporting

confidence: 78%

Section: Influence Of Concentration and Temperature On The Physical Smentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Rheological characterization of aqueous hydroxypropyl cellulose solutions close to phase separation

Roschinski

Kulicke

2000

Macromol. Chem. Phys.

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“…These mesophases have been observed, by using cross-polarized light microscopy and viscometry, in various macromolecular systems e.g. aromatic polyamides [1][2][3][4], polyisocyanates [5,6], cellulosic polymers [7][8][9][10][11][12] and, more especially, polysaccharides [13 151.…”

Section: Introductionmentioning

confidence: 99%

Mesophase formation in high molecular-weight xanthan solutions

1988

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After a short review of theoretical background on mesophase formation in polymer solutions, this paper describes the liquid crystal phase transition and the corresponding rheological properties for aqueous solutions of a high-molecularweight xanthan sample (M w g 1.8.106). The formation of mesophases has been studied using polarizing microscopy and viscometry. The effects of the presence of salts, bacteria cells and proteins have been investigated. The variations in the viscosity, due to mesophase formation, are in qualitative agreement with the predictions of Matheson's theory, but the onset of the ordered phase occurs at very low polymer concentrations and the diphasic domain is much broader than predicted by thermodynamic models. These characteristics of the phase transition are related to the very high molecular weight of the sample studied and can be explained mainly by the effects of cooperative interactions between xanthan chains and of chain flexibility reducing translational entropy.

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“…109 At higher concentrations, the appearance of the precipitate changes from a white suspension to a semi-transparent gel. 111 Gel formation is favoured in cellulose derivatives rich in -OH groups, i.e. at low degrees of substitution, due to the strong hydrogen bonding between cellulose chains.…”

mentioning

confidence: 99%

New ways to enhance the functionality of paperboard by surface treatment – a review

2008

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This review summarizes recent development of functional materials to improve the barrier properties of paperboard with emphasis on bio-based polymers. Focus is directed to novel application techniques and water-borne, renewable coating materials. Some aspects on substrate properties and the requirements on food packaging are discussed as are the processability, convertability, recyclability and biodegradability of packaging materials. The functionality, advantages and disadvantages of several bio-based polymers are presented in detail. Among these are starch and cellulose derivatives, chitosan, alginate, wheat gluten, whey proteins, polycaprolactone, poly(lactic acid) and polyhydroxyalkanoates. Also discussed is the enhancement of barrier properties by incorporation of nanosized materials, by application of thin protective top coatings and local reinforcement by self-healing agents.

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Mesophase formation and chain rigidity in cellulose and derivatives. 1. (Hydroxypropyl)cellulose in dimethylacetamide

Cited by 121 publications

References 11 publications

Rheological characterization of aqueous hydroxypropyl cellulose solutions close to phase separation

Rheological characterization of aqueous hydroxypropyl cellulose solutions close to phase separation

Mesophase formation in high molecular-weight xanthan solutions

New ways to enhance the functionality of paperboard by surface treatment – a review

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