Acetoxypropylcellulose Research Articles

Surface tailoring and design-driven prototyping of fabrics with 3D-printing: An all-cellulose approach

In this work, we present a new all-cellulose approach for modifying and functionalizing textiles. The use of 3D-printing and two acetylated cellulose derivatives, rigid cellulose acetate (CA) and flexible acetoxypropyl cellulose (APC), on cellulosic fabrics were studied. In addition, prototypes were generated using a design-driven approach. The interactions of cellulose derivatives with cellulose were assessed by quartz crystal microbalance with dissipation monitoring (QCM-D). 3D-printing of cellulosic materials on cellulosic fabrics was performed using a direct-write method by printing cellulose derivatives on woven and knitted cotton and woven viscose fabrics. The adhesion of the printed structures was evaluated via peeling and washability tests. The results indicated that although both cellulose derivatives had a positive attraction towards the cellulose substrate, CA had higher affinity and good adhesion properties, whereas the more branched molecular structure of APC was less firmly attached to cellulosic material. The applicability of 3D-printing cellulosic materials for textile modification and functionalization was assessed through iterative prototyping. Visual effects and functional surface structures were demonstrated. Utilization of 3D-printing of cellulosic materials for surface tailoring of cellulosic textiles, eliminates labour intensive processing or external glues and may enable new and simple customization processes with minimized material usage.

Rheo-optical characterization of liquid crystalline acetoxypropylcellulose melt undergoing large shear flow and relaxation after flow cessation

The rheological and structural characteristics of acetoxypropylcellulose (APC) nematic melt are studied at shear rates ranging from 10 s−1 to 1000 s−1 which are relevant to extrusion based processes. APC shows a monotonic shear thinning behavior over the range of shear rates tested. The negative extrudate-swell shows a minimum when a critical shear rate γ˙c is reached. For shear rates smaller than γ˙c, the flow-induced texture consists of two set of bands aligned parallel and normal to the flow direction. At shear rates larger than γ˙c, the flow induced texture is reminiscent of a 2 fluids structure. Close to the shearing walls, domains elongated along the flow direction and stacked along the vorticity are imaged with POM, whereas SALS patterns indicate that the bulk of the sheared APC is made of elliptical domains oriented along the vorticity. No full nematic alignment is achieved at the largest shear rate tested. Below γ˙c, the stress relaxation is described by a stretched exponential. Above γ˙c, the stress relaxation is described by a fast and a slow process. The latter coincides with the growth of normal bands thicknesses, as the APC texture after flow cessation consists of two types of bands with parallel and normal orientations relative to the flow direction. Both bands thicknesses do not depend on the applied shear rate, in contrast to their orientation.

Improved Mechanical Stability of Acetoxypropyl Cellulose upon Blending with Ultranarrow PbS Nanowires in Langmuir Monolayer Matrix

Cellulose and cellulose derivatives have long been used as membrane fabrication. Langmuir monolayer behavior, which naturally mimics membranes, of acetoxypropyl cellulose (APC) and lead sulfide (PbS) nanowire mixtures at different volume ratios is reported. Surface pressure (π)-area (A) isotherms of APC and PbS nanowires mixtures at different volume ratios show a gradual decrease in the monolayer area with increasing volume fraction of PbS nanowires. Change of surface potential with monolayer area at different volume ratios also reveals a gradual increase in the surface potential indicating incorporation of PbS nanowires within APC matrix. The compressibility and elastic constants measurements reveal an enhancement of the elasticity upon incorporation of PbS nanowires up to certain volume fractions. An enhancement in stability of the blend is observed upon PbS nanowire incorporation to the APC matrix. Rheological measurements also support the robustness of the mixture of APC and PbS nanowires in 3D bulk phase. Such robust ultrathin films of cellulose based-nanowire blend obtained by means of the Langmuir technique may lead to novel routes for designing cellulosic-based thin films and membranes.

Deuterium NMR Study of Orientational Order in Cellulosic Network Microfibers

Deuterium NMR was used to investigate the orientational order in a composite cellulosic formed by liquid crystalline acetoxypropylcellulose (APC) and deuterated nematic 4′-pentyl-4-cyanobiphenyl (5CB-αd2) with the percentage of 85% APC by weight. Three forms of the composite including electro spun microfibers, thin film and bulk samples were analyzed. The NMR results initially suggest two distinct scenarios, one where the 5CB-αd2 is confined to small droplets with dimensions smaller than the magnetic coherence length and the other where the 5CB-αd2 molecules are aligned with the APC network chains. Polarized optical microscopy (POM) from thin film samples along with all the NMR results show the presence of 5CB-αd2 droplets in the composite systems with a nematic wetting layer at the APC-5CB-αd2 interface that experiences an order−disorder transition driven by the polymer network N−I transition. The characterization of the APC network I−N transition shows a pronounced subcritical behavior within a heterogeneity scenario.

液晶性セルロース誘導体の凝集状態制御について

We have designed a new material with stable cholesteric structure by blending a cellulose derivative, (acetoxypropyl)cellulose (APC), with a thermoplastic polymer, poly(viny acetate) (PVAc). In the material obtained from THF solution, the compatibility between APC and PVAc was confirmed by differential scanning calorimetry (DSC) and infrared spectroscopy (IR). The materials showed colors arising from the selective reflection of circular polarized light. The colors depended on the composition of the materials. The material obtained from acetone solution showed phase separation into an APC rich phase and a PVAc rich phase, respectively. This indicated that the aggregation structure of APC/PVAc blends was affected by the preparation condition for materials. The FT IR results supported that the molecular aggregation structure was controlled by the hydrogen bonds between APC and PVAc polymer chains.

Deformation of isotropic and anisotropic liquid droplets dispersed in a cellulose liquid crystalline derivative

In this work we study the strain-induced deformation of both isotropic and anisotropic liquid droplets dispersed in a liquid crystalline cellulose matrix. We have produced two types of acetoxypropylcellulose (APC) solid films one with a droplet dispersion of the commercial liquid crystal E7 from Merck, and another with a droplet dispersion of silicone oil. To produce the solid films a solution of APC (60%wt) in dimethylacetamide (DMAc) with 15%wt of either the commercial nematic liquid crystal E7 or the silicone oil was prepared. After homogenization the phase separated solutions were submitted to a shear flow mechanical field and casted onto a Teflon plate. We performed mechanical uniaxial stress-strain tests in the free standing films recording continuously the strain and images of the deformed droplets. The mechanical tests were carried out using a mini stress-strain testing machine apparatus and an Olympus optical polarizing microscope with an attached CCD camera. The images obtained from the mechanical tests for each value of the imposed strain were then analyzed comparing the images of deformed droplets with those of the undeformed ones, extracting in this way the local strain field. The droplet deformation data obtained show, as expected, significant differences in the local strain field when stretching parallel and perpendicular to the initial shear direction. No significant differences were found in the local strain fields obtained from the silicone oil and the E7 droplets films. The local strain fields variation with the imposed strain are compared with the predictions of the theory developed for nematic elastomers by Warner and Terentjev (Liquid crystal elastomers. Clarendon Oxford Press, Oxford, 2003).

New cellulose derivatives composites for electro-optical sensors

In this work we used hydroxypropylcellulose (HPC) and acetoxypropylcellulose (APC) to produce free standing solid films (∼60 μm) for electro-optical devices. Cellulose derivatives films were prepared from crosslinked both HPC and APC isotropic and liquid crystalline solutions without and with a low molecular weight nematic liquid crystal mixture (LC) E7. Films prepared from anisotropic solutions presented a band texture and E7 droplets of micron and submicron size were found to coexist with the band texture in the films prepared with E7. The optical cells were composed by the cellulose derivatives films covered on both free surfaces by a layer of the LC E7 and placed between two transparent conducting substrates. All the electro-optical cells prepared showed switching times in the range of some milliseconds to hundreds of milliseconds. The on-voltage ( V on) is lowered for cells prepared with the ester derivative film obtained from isotropic solutions. The maximum transmission values show a clearly tendency to decrease for the cellulosic matrix prepared from anisotropic solutions with and without nematic liquid crystal droplets.

Tunable topographical cellulose matrices for electro-optical liquid crystal cells

AbstractIn this work we have used acetoxypropylcellulose (APC) to produce free standing solid films (∼60 μm) that were used for assembling electro-optical devices. Thin films were obtained from concentrated lyotropic solutions of cellulose derivatives. Induced by the cast and shearing preparation conditions wrinkles and band textures can be observed in their free-surface plane. In order to eliminate and control these textures we used a process similar to that introducted in literature [1] which consists of storing the films in the same solvent-vapour atmosphere as the solution system. Lyotropic APC liquid crystalline solutions in dymethylacetamide (DMA) with crosslinker were prepared, thin films were obtained by using a shear/casting technique and stored in the solvent-vapour atmosphere until a planar structure was achieved. The dried crosslinked films were analyzed by optical polarised microscopy (POM) and scanning electron microscopy (SEM). The films with different topographies were used to produce optical cells composed by the cellulose derivative film covered on both free surfaces by a layer of the nematic liquid crystal E7 and placed between two transparent conducting substrates. The electro-optical properties of these cells were obtained.

RHEOLOGICAL PROPERTIES OF LYOTROPIC SOLUTIONS OF ACETOXYPROPYLCELLULOSE IN DIMETHYLACETAMIDE. A COMPARISION WITH THE THERMOTROPIC CASE

The rheological properties of a thermotropic acetoxypropylcellulose (APC) were already described in previous works [1,2]. In this work we present the rheological properties, viscosity, η, and first normal stress difference, N1, of lyotropic solutions of APC in dimethylacetamide (DMAc).The flow curve of the lyotropic solution presents the typical behavior for this type of system (Onogi and Asada Curve) [3] however, contrary to what happens with that other lyotropic system [4–7], the APC/DMAc system presents a continuous increase of N1 in function of the shear rate, which we attribute to the fact that APC has higher flexibility than the other liquid crystalline polymers studied so far—namely hydroxypropylcellulose and poly-benzyl-L-glutamate—that present a negative N1 region, as well as a low molecular weight.We will also present some remarks concerning rheo-optical studies preformed with APC/DMAc, by comparison with previous studies on thermotropic APC [8,9].

Temperature Dependence of the Rheological Properties of Acetoxypropylcellulose in the Thermotropic Chiral Nematic Phase

The rheological behaviour of two different molecular weights of a thermotropic liquid crystalline cellulose derivative, acetoxypropylcellulose (APC), at T=120°C, has already been reported [1]. In this work we present the temperature dependence of the rheological properties of two molecular weights of APC.The shear viscosity, η, and first normal stress difference, N1, were measured at temperatures T=120, 130 and 140°C, for MW = 94000 g/mole, and T=120 and 140°C for MW = 129000 g/mole, and for shear rates, γ, between 0.01 and 10 s-1.The shear viscosity η(γ) decreases with increasing T, for both samples, showing a strong shear thinning behaviour at all temperatures and over the whole range of γ studied, except for shear rates between about 0.2 and 1 s-1 (depending on MW and T), where a quasi-Newtonian plateau is observed. The first normal stress difference N1 (γ) also decreases with increasing T at a given γ. It increases with shear rate over the whole γ range studied, and shows an inflection at γ values slightly above γ = 1/τ, where τ is the relaxation time of the polymer memory function.The temperature dependence of the shear viscosity was fitted to an Arrhenius law, giving an apparent activation energy (Ea) in the order of 8–15 kcal/mole, depending on molecular weight and shear rate. The activation energy was found to increase with molecular weight (at a given γ). The variation of Ea with γ, for MW = 94000 g/mole, shows a minimum at γ η 2 s-1.Using a continuum theory for nematic polymers, proposed by Martins [2], some fundamental parameters were obtained from the fit of the theory to the experimental data. Using these parameters it was possible to construct a ``master curve” for the viscosity, η(γ), in good agreement with the experimental data.

Rheological Properties of Acetoxypropylcellulose in the Thermotropic Chiral Nematic Phase

Abstract Experimental data for the rheological behavior of two thermotropic liquid crystalline (LC) samples of acetoxypropylcellulose (APC) with different molecular weights, at 120°C, and in shear rates between 0.01 and 10s −1, are presented and analyzed in the framework of the continuum theory for LC polymers recently proposed by Martins1. The viscosity η(γ.)shows a strong shear thinning in the range of shear rates γ. studied, with an hesitation at shear rates of about 0.1-0.2 s−1, depending on the molecular weight, and the first normal stress difference Nl(γ.) shows only positive values, increasing with shear rate γ., with an hesitation at shear rates of an order of magnitude higher, i.e. about 1-2 s−l, also depending on the molecular weight. The hesitation points of the flow functions are displaced towards lower values of the shear rate, with increasing molecular weight. For small and intermediate γ. the shear viscosity of the higher molecular weight sample is greater than the corresponding viscosity for the lower molecular weight sample, but this pattern is reversed at higher γ., the crossover point being at γ. = 1.5 s−1. The molecular weight dependence of the first normal stress difference follows a similar pattern. All these observations can be interpreted by Martins' theory. The expressions for η(γ.) and N1(γ.) derived from this theory fit very well to the experimental data, therefore allowing for some fundamental viscoelastic parameters to be estimated.

Miscibility of Liquid Crystalline Polymers; Mixtures of (Hydroxypropyl)cellulose and Ester Derivatives

Abstract Heavily substituted cellulosic polymers including (hydroxypropyl)cellulose (HPC), (acetoxypropyl)cellulose (APC), and the propionate ester of HPC (PPC) form both lyotropic and thermotropic liquid crystalline phases. The miscibility of binary mixtures of these cellulosics in methanol and in film form are examined by polarizing microscopy. In methanol all of the binary polymer systems demix and segregate into distinct regions. Decreasing the molar mass of HPC and APC polymers does not inhibit the demixion in solution, but facilitates the phenomenon. Ester-ether blends once heated above the isotropization temperature, , exhibit two co-existing phases. The segregated regions do not mix even when reheated to a temperature at which both regions are isotropic. The ester-ester blends are apparently miscible since segregation was not observed. The of the ester blends (with the esters in a 1:1 ratio) is an average of the of the two esters.

The liquid‐crystalline properties of (acetoxypropyl)cellulose: Effect of chain length and degree of acetylation

AbstractPartially degraded (hydroxypropyl)cellulose methanolysates were acetylated in an acetic anhydride/dioxane mixture with a perchloric acid catalyst, yielding (acetoxypropyl)cellulose (APC) samples with an unit ester content per anhydroglucose unit of three. Eight APC samples of molar masses from 10,000 to 1.8 × 105 g/mol were prepared. On heating, all the samples displayed biphasic behavior prior to isotropization. The isotropization temperature of the samples increased rapidly with molar mass, attaining a limiting value of 174°C. The substitution of hydroxyl groups of HPC by acetyl groups lowered the limiting value. Lyotropic mesophases of APC in dimethyl acetamide (DMAc) showed isotropization temperatures that increase nonlinearly with increasing APC concentration. For chains with contour lengths exceeding 72 nm, the critical concentration for mesophase formation, 0, does not depend on the chain length. However, for short chains the 0 value increases rapidly with decreasing chain length. The cholesteric reflection wavelength, λ0, of a thermotropic APC sample of low molar mass is greater than that of a higher molar mass sample at a given temperature and increases with increasing temperature for all samples. Partially acetylated (hydroxypropyl)cellulose displays reflection colors at lower temperatures than the fully acetylated APC.

Optical properties of (acetoxypropyl)cellulose mesophases: factors influencing the cholesteric pitch

(Acetoxypropyl)cellulose (APC) forms a thermotropic cholesteric liquid crystalline phase, and with dibutyl phthalate (DBP) it also forms a lyotropic cholesteric phase. The reflection bands for the mesophases occur in the visible region, at wavelengths which depend on concentration and temperatures. The pitch of the cholesteric helicoidal structure is derived from measurements of the mean refractive indices and of the reflection band wavelengths for mesophase samples containing from 0 to 30% diluent at temperatures from ambient to 170°C. The pitch of the thermotropic mesophase increases with increasing temperature and with decreasing molar mass. The pitch of the lyotropic mesophase increases with increasing temperature and diluent content. Pitch values approach infinity at temperatures close to the clearing temperature of the mesophase, and no reversal in the sense of the pitch with temperature or diluent content was detected. The experimentally observed changes in pitch with composition and temperature are in reasonable agreement with the predictions of a recent theory for cholesteric mesophases composed of helical rod-like species. The average distance between chains in the mesophase is estimated from X-ray diffraction measurements, and hence the average angle of twist between neighbouring APC molecules may be found. The angle decreased from 2.2° for pure APC to 0.9° for a volume fraction of 0.73 APC in DBP.