Hydroxypropyl Cellulose Derivatives Research Articles

Dominant Factors Affecting Rheological Properties of Cellulose Derivatives Forming Thermotropic Cholesteric Liquid Crystals with Visible Reflection.

Hydroxypropyl cellulose (HPC) derivatives with alkanoyl side chains are known to form thermotropic cholesteric liquid crystals (CLCs) with visible reflection. Although the widely investigated CLCs are requisite for tedious syntheses of chiral and mesogenic compounds from precious petroleum resources, the HPC derivatives easily prepared from biomass resources would contribute to the realization of environment-friendly CLC devices. In this study, we report the linear rheological behavior of thermotropic CLCs of HPC derivatives possessing alkanoyl side chains of different lengths. In addition, the HPC derivatives have been synthesized by the complete esterification of hydroxy groups in HPC. The master curves of these HPC derivatives were almost identical at reference temperatures, with their light reflection at 405 nm. The relaxation peaks appeared at an angular frequency of ~102 rad/s, suggesting the motion of the CLC helical axis. Moreover, the dominant factors affecting the rheological properties of HPC derivatives were strongly dependent on the CLC helical structures. Further, this study provides one of the most promising fabrication strategies for the highly oriented CLC helix by shearing force, which is indispensable to the development of advanced photonic devices with eco-friendliness.

Room-Temperature Cholesteric Liquid Crystals of Cellulose Derivatives with Visible Reflection.

Hydroxypropyl cellulose (HPC) derivatives with alkanoyl side chains have attracted attention as bio-based cholesteric liquid crystal (CLC) materials with reflection colors. By taking advantage of the ability to change the reflection color in response to external stimuli, the thermotropic CLCs can be applied to a wide variety of photonic devices for a sustainable society of future generations. However, the thermotropic CLCs of HPC derivatives substituted with only one kind of alkanoyl group are not suitable for such applications because they do not exhibit visible reflection at room temperature. In this report, we describe a promising strategy to control the reflection colors of HPC derivatives at room temperature by introducing two kinds of alkanoyl groups with different lengths into the side chains of HPCs, which also enables the fine control of temperature dependence on the reflection wavelength. By chemically optimizing the side chain, we successfully prepared room-temperature thermotropic CLCs of HPC derivatives with visible reflection. This report would contribute toward the development of versatile photonic applications by CLCs produced from biomass.

Rheological Properties of Cholesteric Liquid Crystal with Visible Reflection from an Etherified Hydroxypropyl Cellulose Derivative.

Optical properties of hydroxypropyl cellulose (HPC) derivatives have been widely investigated for their ability to exhibit cholesteric liquid crystal (CLC) phase. However, there are only a limited number of studies on their rheological properties even though they are quite important for the applications of such HPC derivatives to the versatile CLC photonic devices. In this article, we report on the optical and rheological properties of an HPC derivative possessing pentyl ether groups in the side-chains. The etherified HPC derivative exhibited thermotropic CLC phase with light reflection in the temperature range between 25 °C and 120 °C. After the HPC derivative was heated once at isotropic phase, followed by being cooled to the CLC phase, the reflection peak could not be observed, even at the CLC phase. At this stage, the HPC derivative exhibited solid-like rheological responses compared to that of sheared at a constant shear rate of 1.0 s−1. Such differences in the optical and rheological properties of the HPC derivative can be ascribed to the difference in CLC orientation state. From the rheological results, the etherified HPC derivative showed liquid-like behavior rather than the esterified HPC derivatives. This evidence provides a promising clue for fabricating high-quality CLC devices by the facile CLC orientation.

Development of electrospun mats based on hydrophobic hydroxypropyl cellulose derivatives

In this work, hydroxypropyl cellulose esters (HPCE) with long aliphatic chains were prepared and innovatively used in electrospinning to obtain hydroxypropyl cellulose (HPC)-based mats with enhanced resistance to moist environments. The described approach is very simple and does not require any post-treatment (e.g. cross-linking step) to overcome a major problem concerning the premature loss of properties of cellulose-based materials when in contact with moisture.HPCE-based electrospun mats were characterized in terms of their morphology, swelling ability and in vitro hydrolytic degradation. The mats exhibited a swelling capacity of over 115%, depending on the degree of substitution. The in vitro hydrolytic degradation tests showed the high structural integrity of the mats (< 5% weight loss) over a period of 30 days. The in vitro cytotoxicity tests showed that the mats of HPC esters are cytocompatible and promote the adhesion, proliferation and spreading of NIH3T3 fibroblast cells. These data suggest that the HPCE mats may be interesting materials for wound dressings, as well as for other tissue engineering applications.

Viscoelastic Properties of Cholesteric Liquid Crystals from Hydroxypropyl Cellulose Derivatives

Viscoelastic Properties of Cholesteric Liquid Crystals from Hydroxypropyl Cellulose Derivatives

Synthesis and Optical Properties of Completely Etherified Hydroxypropyl Cellulose Derivatives

Synthesis and Optical Properties of Completely Etherified Hydroxypropyl Cellulose Derivatives

Side Chain Effect of Hydroxypropyl Cellulose Derivatives on Reflection Properties.

Some cellulose derivatives are known to exhibit thermotropic and lyotropic cholesteric liquid crystal (CLC) phases with a visible reflection feature by changing the side chains and mixing with specific solvents, respectively. Although many studies have been reported so far, most of the derivatives have the side chains of linear alkyl groups, but not the bulky phenyl groups. In this report, we synthesized a series of hydroxypropyl cellulose (HPC) derivatives that possessed both linear propionyl esters and bulky (trifluoromethyl)phenyl carbamates in the side chains. The reflection peaks of HPC derivatives shifted to longer wavelengths upon heating due to an increase in the CLC helical pitch. Such thermally induced shifting behavior of the reflection peak was crucially dependent on not only the propionyl esterification degree, but also the substituents in the side chains of HPC derivatives. When the side chains of HPC were chemically modified with both propionyl esters and bulky substituents such as 3,5-bis(trifluoromethyl)phenyl carbamates, the reflection peaks emerged at longer wavelengths at the same temperature. This probably happened because of the steric hindrance of bulky side chains, as supported by the empirical molecular modeling calculation. Although the occupied volumes of (trifluoromethyl)phenyl groups were independent of the CLC phase temperature with visible Bragg reflection, the substituent position, i.e., substituent orientation of trifluoromethyl groups affected the CLC phase temperature. Moreover, we found that the hydrogen bonds between carbamate moieties in the HPC side chains play an important role in the thermally induced shift of reflection peaks.

Amphiphilic hydroxyalkyl cellulose derivatives for amorphous solid dispersion prepared by olefin cross-metathesis

Olefin CM followed by transfer hydrogenation is an efficient method for synthesizing amphiphilic hydroxypropyl cellulose derivatives.

Synthesis and photosensitivity of azobenzene functionalized hydroxypropylcellulose

Azobenzene functionalized hydroxypropyl cellulose derivatives (azo-HPCs) with different degrees of substitution with azobenzene moieties were synthesized and characterized. The degree of substitution with the azobenzene moieties (DSazo) can be adjusted by changing the feed ratio in the reaction mixture. The photosensitivity of the azo-HPCs in both solution and solution film was investigated. The azobenzene moieties of the azo-HPCs exhibited a reversible cis-to-trans isomerization transition upon irradiation with UV and visible light in both solution and the solid state. The reversible trans-to-cis photoisomerization led to a change of the wettability of the azo-HPC films. Surface energy estimations suggest that the tunable film wettability was attributed to the change of the dipole moment of the azobenzene moieties in the film surface. The variation of the contact angle depends on the DSazo of the azo-HPC derivatives. A higher DSazo corresponds to a larger variation of water contact angle upon UV irradiation under the same conditions. This work offers a versatile method to manipulate the surface properties of the eco-friendly cellulose derivatives.

Synthesis and characterization of novel liquid crystalline cholesteryl-modified hydroxypropyl cellulose derivatives

Two new series of cholesteryl-modified hydroxypropyl cellulose (HPC) derivatives were synthesized by performing reactions involving HPC, a cholesterol-based mesogenic dimer (HPC-G1-Chol), or cholesteryl chloroformate (HPC-Chol), all with different degrees of substitution (D Chol). All of the compounds obtained were characterized by conventional spectroscopic methods. The D Chol values of the modified HPCs was obtained using 1H NMR spectroscopy. Thermogravimetric analysis and differential scanning calorimetry (DSC) in combination with polarizing optical microscopy (POM) were used to investigate the thermal properties of the compounds obtained. The glass transitions of the modified HPCs occurred at lower temperatures than the glass transition temperature for HPC, but the glass transition temperatures increased with increasing D Chol. All of the synthesized polymers formed thermotropic liquid crystalline phases. Polymers with a mesogenic side chain (i.e., the HPC-G1-Chol series) had wider mesophases than HPC and polymers that were derived from HPC-Chol. These compounds were found to be soluble in a variety of organic solvents, so they formed lyotropic liquid crystal mesophases in acetone. The critical concentrations above which liquid crystalline order was observed were 20 and 25 wt% for a sample from each series (HPC-G1-Chol and HPC-Chol, respectively) in acetone. It can therefore be hypothesized that HPC-G1-Chol has a greater propensity to exhibit specific chain–chain association phenomena than HPC-Chol in acetone.

Synthesis of hydroxypropyl cellulose derivatives modified with amphiphilic diblock copolymer side-chains for the slow release of volatile molecules

Hydroxypropyl cellulose (HPC) was used as carrier material to prepare comb-like grafted block copolymers having an amphiphilic core–shell structure. The hydroxyl groups of HPC were partially protected with trimethylsilyl groups and the free OH groups used to initiate the ring opening polymerisation (ROP) of L-lactide. The end-chain of the grafted hydrophobic poly(L-lactide) (PLLA) chain was then functionalised with 2-bromopropionyl bromide which was used to polymerise the tert-butyl acrylate (tBA) monomer by atom transfer radical polymerisation (ATRP). The hydrophobic PtBA block was then hydrolysed to a hydrophilic poly(acrylic acid) (PAA) block. The resulting amphiphilic grafted copolymer HPC-g-(PLLA-b-PAA) was dissolved in an ethanol/water mixture (9 : 1), such as a typical Eau de Toilette (EdT) formulation. Atomic force microscopy (AFM) and size measurements confirmed the presence of core–shell structures in solution. A significant swelling of HPC-g-(PLLA-b-PAA) in the presence of a volatile bioactive molecule, methyl 2,2-dimethyl-6-methylene-1-cyclohexanecarboxylate (Romascone®), was observed by dynamic light scattering (DLS). Furthermore, the presence of HPC-g-(PLLA-b-PAA) significantly decreased the evaporation rate of Romascone®, thus serving as an efficient fragrance delivery system in formulations with high ethanol content.

Preparation and Characterization of Water-Soluble Single-Walled Carbon Nanotubes by Hybridization with Hydroxypropyl Cellulose Derivatives

Single-walled carbon nanotube (SWNT) hybrids were prepared through noncovalent functionalization with pyrene-containing hydroxypropyl cellulose derivatives (HPC-Py) that were synthesized by simple condensation and substitution reactions. The obtained SWNT hybrids were structurally characterized with UV−vis, fluorescence, ATR FT-IR, and Raman spectroscopies. The prepared SWNT hybrids were soluble in water with good storage stability, and their statistical average size was approximately 260 nm. The hybridization extent of the SWNTs was dependent on the content of pyrene moieties in HPC-Py. The hydroxypropyl cellulose attached to the surface of the SWNTs was hydrolyzable or removable by cellulases, whereas the SWNTs underwent no structural changes during the enzymatic treatment.

Hydroxypropyl–cellulose derivatives: phase behaviour of hydroxypropylcellulose methacrylate

Peculiar effects on the phase behaviour of hydroxypropylcellulose (HPC), obtained by the introduction of few methacrylic groups along the main chain, are discussed. In particular, the increase of mesophase stability in water, lowering the value of polymer concentration at which the anisotropic phase first appears with respect to underivatized HPC, as well as the decrease of stability of the anisotropic phase for neat polymers is illustrated and discussed in terms of substituent hydrophobicity.

Liquid crystallinity and side chain order in partially substituted semi-flexible polymers

A series of hydroxypropyl cellulose (HPC) derivatives with, on the average, 3, 2, 3/2, 1, 1/2, 1/3 alkyl side chains (18 carbons) on each anhydroglucose unit were synthesized. X-ray studies indicate that layered structures prevail in most of these HPC derivatives, even in the sample containing only one alkyl side chain per two rings, i.e. C18(1/6)HPC. The polymers were able to pack in better ordered arrays in the solvent-cast films than in as-made samples obtained by precipitation from a nonsolvent. Side chain melting endotherms were observed for C18(3/3), C18(2/3), C18(1/6), and C18(1/9)HPC's. In C18(1/2) and C18(1/3)HPC's, side chain melting enthalpies were negligible but isotropization enthalpies were unexpectedly large. The isotropization temperatures and the associated enthalpies remained almost constant in differential scanning calorimetry (DSC) heating/cooling cycles. Distinct morphological features were observed under the cross polarized optical microscope (POM) after shearing the samples in the molten state. The degree of side chain substitution has a profound influence on the polymer morphology.

Liquid crystallinity and side chain order in partially substituted semi-flexible polymers

A series of hydroxypropyl cellulose (HPC) derivatives with, on the average, 3, 2, 3/2, 1, 1/2, 1/3 alkyl side chains (18 carbons) on each anhydroglucose unit were synthesized. X-ray studies indicate that layered structures prevail in most of these HPC derivatives, even in the sample containing only one alkyl side chain per two rings, i.e. C18(1/6)HPC. The polymers were able to pack in better ordered arrays in the solvent-cast films than in as-made samples obtained by precipitation from a nonsolvent. Side chain melting endotherms were observed for C18(3/3), C18(2/3), C18(1/6), and C18(1/9)HPC's. In C18(1/2) and C18(1/3)HPC's, side chain melting enthalpies were negligible but isotropization enthalpies were unexpectedly large. The isotropization temperatures and the associated enthalpies remained almost constant in differential scanning calorimetry (DSC) heating/cooling cycles. Distinct morphological features were observed under the cross polarized optical microscope (POM) after shearing the samples in the molten state. The degree of side chain substitution has a profound influence on the polymer morphology.

Analysis of polymer heterogeneity by sedimentation transport: 3. Hydroxypropyl cellulose derivatives in organic solvents

Abstract The sedimentation velocity of hydroxypropyl cellulose acetate and cyanoethylhydroxypropyl cellulose molecules has been investigated in dilute solution in organic solvents. For these polymers, a linear dependence of the standard deviation of the displacement spectrum of macromolecules in an ultracentrifuge field on the sedimentation boundary shift was observed. The method of moments with linear approximations was used to exclude the concentration and diffusion effects and to determine the inhomogeneity parameter of the samples, Mz/Mw. They range from 1.4 to 7. The inhomogeneity of fractions and the initial unfractionated samples is compared.

In vitro evaluation of sustained-release matrix tablets prepared with new modified polymeric carbohydrates

The study of the rheological and compressional properties of sustained-release matrix tablets prepared with new polymers obtained by graft copolymerization of methyl methacrylate (MMA) on various carbohydrates is the main purpose of this work. All the mixtures had good flow properties, showing cellulose derivatives mixtures the best values. Powders without homopolymers showed a statistically significant lower flow rate than mixtures with homopolymers. All the mixtures with hydroxypropyl starch polymers showed better statistically significant compactibility and plasticity than the hydroxypropyl cellulose derivatives. Practically all the mixtures accomplished with the requirements of direct compression excipients in relation with lubrication coefficient. All the tablets elaborated with mixtures with homopolymers required a total work lower than the mixtures without homopolymers. Tablets from all products passed the test for weight uniformity, except the tablets of carboxymethyl starch (CS-MMA) without homopolymer. Only hydroxypropylcellulose tablets demonstrated an acceptable friability. Only standard tablets and CS-MMA without homopolymers exhibited disintegration times higher than 30 min. A clearly different behaviour between the new polymers and the standards was observed in relation with dissolution test.