Hydroxypropylation of cellulose isolated from bamboo (Dendrocalamus strictus) with respect to hydroxypropoxyl content and rheological behavior of the hydroxypropyl cellulose

Bamboo, a lignocellulosic material, is a renewable source of interest as feedstock for production of cellulose derivatives by chemical functionalization. Optimization of hydroxypropylation of cellulosic material (average DP 816), isolated from bamboo (Dendrocalamus strictus) was, therefore, performed with respect to maximum percent hydroxylpropoxyl (% HP) contents under varying reaction conditions and studying their effect on the % HP. The optimized reaction conditions were aqueous NaOH concentration 22%, propylene oxide concentration 17.4 mol/AGU, temperature 50°C, duration of hydroxypropylation 4 h to yield hydroxypropyl cellulose of % HP 65.89. The η_app of 1 and 2% solutions of the optimized product showed it to be non‐Newtonian pseudoplastic. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Nonlinear rheological behavior of a novel oil displacing agent

In this work, the shear and elongational rheologies have been investigated for a newly developed oil displacing agent, polymeric surfactant‐PSf. It was found that the PSf solutions exhibited Newtonian, shear‐thinning, and shear‐thickening behavior, respectively, depending on the polymer concentration and shear rate, and Cox–Merz rule was not applicable to these systems. The first normal stress difference (N₁) versus shear rate plots for PSf were complicated, which varied with the composition of the solutions. The uniaxial elongation in capillary breakup experimental results indicated that Exponential model could be used to fit the experimental data of the PSf solutions at lower polymer concentrations. In addition, it was found that PSf was more effective in improving shear viscosity than partially hydrolyzed polyacrylamide, but not in the case of elongational viscosity. The experimental results indicated that the microstructural mechanisms are responsible for the rheological behavior of the polymers. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40813.     

Rheology of 1‐butyl‐3‐methylimidazolium chloride cellulose solutions. III. Elongational rheology

The elongational rheology of solutions of cellulose in the ionic liquid solvent 1‐butyl‐3‐methylimidazolium chloride ([Bmim]Cl) was measured at 80, 90, and 100°C; 8, 10, and 12 wt% cellulose; Hencky strains 5, 6, 7; and strain rates from 1 to 100 s^?1. Master curves were generated by shifting the elongational viscosity curves with respect to temperature and Hencky strain. Also, general master curves were generated by simultaneously shifting with respect to both temperatures and Hencky strain. From the Arrhenius plots of the temperature shift factors, the activation energy for elongational flow was determined. The elongational rheology of these solutions was elongational strain rate thinning similar to that of their shear behavior and polymer melts and they were also strain hardening. Both effects and the viscosity increased with cellulose concentration. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

The dependence of shear and elongational viscosity on the molecular weight of poly(vinylidene fluoride)

The dependence of shear and elongational viscosity on the molecular weight of poly(vinylidene fluoride) has been studied using a capillary rheometer. The elongational viscosity was evaluated based on Cogswell's method with two types of capillaries: capillary length (L)/capillary diameter (D) = 10 mm/1 mm and L/D = 0 mm/1 mm. We used the ratio P₀/P_L that indicates the contribution of elongational flow to the total flow involving both the shear and elongational flows. P_L and P₀ are the pressure losses in the capillary and the converging flows, respectively. P₀/P_L increased with molecular weight and shear rate. This corresponds to decreasing the number of entanglements of molecular chain under a large displacement, especially high shear. Thus, we suggest using P₀/P_L as the parameter of the entanglement interaction on the molecular chain under a large displacement. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 2381–2384, 1999     

Rheology of cellulosic N‐methylmorpholine oxide monohydrate solutions

Shear dynamic and elongational rheology of concentrated solutions of cellulose in N‐methylmorpholine oxide monohydrate (lyocell) were investigated at different temperatures and for two Hencky strains. Shear thinning and strain thinning behavior is characteristic for dynamic viscosity and effective elongational viscosity of lyocell solutions. Body forces, enthalpy, and entropy of orientation are high at low temperature and high deformation rates, showing a strong orientation effect. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 1369–1377, 2000     

Identifying breach mechanism during air-gap spinning of lignin–cellulose ionic-liquid solutions

To be able to produce highly oriented and strong fibers from polymer solutions, a high elongational rate during the fiber-forming process is necessary. In the air-gap spinning process, a high elongational rate is realized by employing a high draw ratio, the ratio between take-up and extrusion velocity. Air-gap spinning of lignin–cellulose ionic-liquid solutions renders fibers that are promising to use as carbon fiber precursors. To further improve their mechanical properties, the polymer orientation should be maximized. However, achieving high draw ratios is limited by spinning instabilities that occur at high elongational rates. The aim of this experimental study is to understand the link between solution properties and the critical draw ratio during air-gap spinning. A maximum critical draw ratio with respect to temperature is found. Two mechanisms that limit the critical draw ratio are proposed, cohesive breach and draw resonance, the latter identified from high-speed videos. The two mechanisms clearly correlate with different temperature regions. The results from this work are not only of value for future work within the studied system but also for the design of air-gap spinning processes in general. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47800.     

Rheological aspects of fiber spinning from cellulose solutions in N‐methylmorpholine‐N‐oxide

Based on rheological experiments with a cellulose solution in N‐methylmorpholine‐N‐oxide (NMMO), it was found that the shearing stress generated in the flowing viscoelastic fluid decreases with an l/d ratio in a rheometer capillary. This reduces the elastic response and the outflow of the fluid becomes more uniform. At constant temperature, the elongational viscosity of the solidified stream of the cellulose solution in NMMO is reduced with increase of the deformation rate, which makes it possible to increase the fiber‐formation velocity within the air zone. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 79: 1860–1868, 2001     

Influence of melt deformation history on orientation in vitrified polymers

An experimental study of the development of orientation in polystyrene melts during flow and its retention in vitrified parts is described. It is shown on the basis of elongational and shear flow experiments that orientation in vitrified polystyrenes may be predicted from a knowledge of the stress field at the time of vitrification and application of stress-optical laws. More generally a relationship between birefringence and principal stress difference is found which correlates (1) on-line isothermal shear flow, (2) on-line non-isothermal elongational flow (melt spinning), and (3) vitrified samples formed in both shear and elongational flow. It is further proposed that orientation in polymer chains in deforming melts is uniquely dependent on stress—specifically, that the ratio of the stress-optical constant C to the intrinsic birefringence Δ° is approximately a constant.     

A study of rheological properties of cellulose diacetate in acetone solution at low and high shear rates

The rheological properties of cellulose diacetate (CDA) with different intrinsic viscosity (IV) and different concentration in acetone solutions were studied at low and high shear rates. The zero-shear viscosity increased and the structural index increased, when the IV of CDA was increased or the acetone solution concentration was increased. Evidence suggested that a sulfate structure may be forming. It is shown that the increase of hemicellulose and sulfur content is associated with an increase of chain entanglements between CDA molecules and the abnormal increase of solution zero-shear viscosity. At a high shear rate, the correlation curve between inlet pressure drop and solution concentration obtained by Bagley method analysis shows an inflection point, which appears to be the critical concentration at which the cellulose diacetate molecular chains in the solution form a long range entangled elastic network. After the concentration exceeds a certain range of above critical points, the entanglement of the molecular chains in the solution is significantly enhanced. The zero shear viscosity inflection point concentration calculated by the rheological curve with low shear velocity and the inlet pressure drop inflection point concentration calculated by the capillary rheological calculation have good consistency.     

纤维素/NMMO·H_2O溶液体系流变性能的研究

利用 Brookfield DV-Ⅱ型粘度计对纤维素/NMMO·H2O 溶液体系的流变性能进行了研究,讨论了温度、纤维素浓度、浆粕聚合度及添加剂等对溶液粘度的影响。结果表明,纤维素/NMMO·H2O 溶液的流动活化能较低,因此其表观粘度随温度的变化不大;纤维素浓度和浆粕聚合度的增加都可使溶液粘度增大,但纤维素浓度对溶液粘度的影响更显著;抗氧化剂没食子酸丙酯(GPE)的加入减缓了加热时溶液粘度的下降,降低了纤维素的氧化降解;二甲亚砜(DMSO)的加入可有效地控制溶液粘度,改善溶液的加工性能。     

Rheological properties of poly(methyl methacrylate)/rigid ladderlike polyphenylsilsesquioxane blends

A series of poly(methyl methacrylate) (PMMA) blends with rigid ladderlike polyphenylsilsesquioxane (PPSQ) were prepared at weight ratios of 100/0, 95/5, 90/10, 85/15, and 80/20 by solution casting and then hot‐pressing. Their rheological properties have been studied under both dynamic shear and uniaxial elongation conditions. Their rheological properties depend on the compositions. The storage modulus, G′, loss modulus, G″, and dynamic shear viscosity, η*, of the PMMA/PPSQ 95/5 blend were slightly lower than those of pure PMMA. However, the values of G′, G″, and η* for the other PMMA/PPSQ blends are higher than those of PMMA. The G′ values increase with an increase in PPSQ content from 5% through 15% PPSQ at low frequencies and then drop as the PPSQ content increases to 20%. Uniaxial elongational viscosity (η_E) data demonstrate that PMMA/PPSQ blends exhibit slightly weaker (5% PPSQ) and much weaker (10% PPSQ) strain‐hardening than PMMA. In contrast, the PMMA/PPSQ 85/15 blend shows strain‐softening. Neither strain‐hardening nor strain‐softening was observed in the 80/20 blend. The special rheological properties for the 95/5 blend is probably due to a decrease in PMMA entanglements brought by the specific PMMA–PPSQ interactions. Rheological properties of PMMA/PPSQ blends with higher PPSQ content (≥10%) are mainly affected by formation of hard PPSQ particles. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 352–359, 2007     

Preparation,characterization, and properties of cellulose–polyacrylamide graft copolymers

Graft copolymers of acrylamide on cellulose materials (α‐cellulose 55.8%, DP 287.3) obtained from Terminalia superba wood meal and its carboxymethylated derivative (DS 0.438) were prepared using a ceric ion initiator and batch polymerization and modified batch polymerization processes. The extent of graft polymer formation was measured in graft level, grafting efficiency, molecular weight of grafted polymer chains, frequency of grafting as a function of the polymerization medium, and initiator and monomer concentrations. It was found that the modified batch polymerization process yielded greater graft polymer formation and that graft copolymerization in aqueous alcohol medium resulted in enhanced levels of grafting and formation of many short grafted polymer chains. Viscosity measurements in aqueous solutions of carboxymethyl cellulose‐g‐polyacrylamide copolymer samples showed that interpositioning of polyacrylamide chains markedly increased the specific viscosity and resistance to biodegradation of the graft copolymers. The flocculation characteristics of the graft copolymers were determined with kaolin suspension. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 913–923, 2003     

Rheology of polymeric solutions I. Zero shear conditions

Based on kinetic considerations, the following equation, connecting the zero‐shear viscosity of polymeric solutions with temperature and the molecular weight and concentration of the polymer was derived: RTln η_R = KBφMⁿ /(1 + BφMⁿ), where η_R is relative viscosity (i.e., the ratio of the solution viscosity to the solvent viscosity); K represents a change in enthalpy of viscous flow from a pure solvent to a pure polymer at the same temperature or from a polymer of low molecular weight (M) to one of higher molecular weight, and has the dimensions of energy (e.g., J/mol) because the ratio BφMⁿ/(1 + BφMⁿ) is dimensionless; φ is the volume or molar fraction of a polymer in solution (concentration units can be used in dilute solutions); B is a constant related to the stiffness of the chains of the polymer in a given solvent; and at BφMⁿ >> 1, ln η_R = K/RT. The equation describes published data on the zero‐shear viscosity of four polar and nonpolar polymers in nine solvents with R² > 0.98. This approach allows the use of solutions of moderate concentrations for the characterization of polymers and opens a way for a single‐point degree of polymerization (DP) determination of polymers at moderate concentrations if constants K, B, and n of the equation are known. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 2064–2073, 2002     

Steady shear and viscoelastic properties of a micro‐crosslinked acrylamide‐based terpolymer

A water‐soluble micro‐crosslinked associating polymer (PASA‐PL): poly (acrylamide/butyl styrene/sodium 2‐acrylamido‐2‐methylpropane sulphonate) (PASA)–phenolic aldehyde (PL) was prepared to reduce the critical associated concentration and enhance the thickening properties for the linear PASA polymer in aqueous and brine solutions. The consecutive steady shear and viscoelastic properties were investigated to explore the correlations between the rheologic performance and supramolecular structures for the PASA‐PL brine solutions. Upon consecutive steady shear, the intermolecular hydrophobic association is greatly reinforced because of the expansion of the coiled PASA‐PL chains at the suitable shear rate, and the brine solution exhibits obvious shear thickening behavior. The steady shear results show that the intermolecular hydrophobic association is reversible, and that the polymer chains do not degrade upon shearing. The PASA‐PL brine solutions with 50 g L⁻¹ NaCl have predominantly elastic character over the angular frequency range at the polymer concentration higher than 1.0 g L⁻¹, which is remarkably strengthened with a slight increase in polymer concentration. The PASA‐PL brine solutions display a salt‐thickening effect and predominantly exhibit elastic character over the angular frequency range at 10–50 g L⁻¹ NaCl. These results demonstrate that the viscoelastic behavior of the PASA‐PL solutions mainly depends on the formation of hydrophobically associated structures via the intermolecular association strengthened by the micro‐crosslink of PASA with PL. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Antibacterial activity against Escherichia coli of Cu‐BTC (MOF‐199) metal‐organic framework immobilized onto cellulosic fibers

A strong antimicrobial activity against Escherichia coli of Cu‐BTC metal‐organic frameworks immobilized over cellulosic fibers is hereby reported. The in situ synthesis of Cu‐BTC metal‐organic frameworks, aka MOF‐199 or HKUST‐1, onto cellulosic substrates was carried out by exposing carboxymethylated cellulosic substrates to Cu(OAC)₂, 1,3,5‐benzenetricarboxylic acid and triethylamine solutions following a very specific order. Using an in vitro model, in accordance to ASTM E2149‐13a, we observed that the cellulose‐MOF system was able to completely eliminate the growth of E. coli on agar plates and liquid cultures. The antibacterial activity of the comprising components of MOF‐199 and the cellulosic substrate was also evaluated and determined to be negligible. Since the method used to synthesize MOF‐199 crystals provides a strong bond between the crystals and the cellulosic substrates, the crystals not detach from the anionic cellulosic fibers allowing the modified textile to be washed and reused hence opening a new avenue to fabricate antibacterial clinical fabrics. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40815.     

Recoverable shear strain of liquid crystal‐forming concentrated hydroxypropyl cellulose solutions

The recoverable shear strain (S_R) for the liquid crystal‐forming hydroxypropyl cellulose solutions was determined by means of a concentric cylinder rotational apparatus as functions of shear stress prior to recovery and concentration of the solutions at 30°C. S_R greatly depended on shear stress and concentration; the phase of the solution (the single phase or biphase) governed the dependences of S_R on stress and concentration. S_R increased with increasing stress for the single phase and decreased for the biphase. S_R seemed to be related to the die swell (B): S_R ∝ Bⁿ. S_R exhibited a maximum and a minimum with respect to concentration. S_R for the cellulosic cholesteric liquid crystalline solutions was greater than that for the isotropic solutions. A model was proposed for explaining the greater S_R. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 865–872, 2002     

Influence of process parameters on the structure formation of man‐made cellulosic fibers from ionic liquid solution

The influence of dry‐jet wet spinning parameters on the production of man‐made cellulosic fibers from 13 wt % cellulose/1,5‐diazabicyclo[4.3.0]non‐5‐ene acetate solutions was investigated. The spinneret nozzle diameter, extrusion velocity, draw ratio, and coagulation bath temperature were the studied parameters. The production of highly oriented fibers was favored by selecting higher extrusion velocity and lower spinneret diameter. A spinneret size of 100 µm and a draw ratio of 6 were sufficient to highly orient the cellulose macromolecules and achieve tenacities above 40 cN/tex (600 MPa). Total orientation assessed via birefringence measurement, tenacity, and Young's modulus values reached a plateau at a draw of 6 and no further development in properties was observed. A temperature of the aqueous coagulation bath of 15 °C slightly promoted greater orientation of the fibers by hampering structural changes of the cellulose macromolecules in the nascent solid fibers. Furthermore, the determination of the elongational viscosity of the liquid thread via the measurement of radial force tensor was tested and showed promising results. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43718.     

Physicochemical characterization of celluloses extracted from Esparto “Stipa tenacissima” of Eastern Morocco

Increasing ecological concerns have given rise to renewed interest in the use of natural materials, considering their renewability and possibility of disposal at the end of their life cycle without damage to the environment. In this study, we examined the isolation of cellulose from Esparto “Stipa tenacissima” of Eastern Morocco by two different ways; the first one using an acetic acid solution catalyzed by nitric acid. The objective is to determine the optimum amount of this catalyst needed to the extraction. The second way consists to study the cellulose extraction with change of the alkaline solution concentration in order to choose the required value. The cellulosic samples were characterized by FT‐IR spectroscopy and X‐ray diffraction, the morphology of the isolated fibers was investigated by optical microscopy. Thermal analysis (DT‐TGA) were carried out to study the thermal behavior of the cellulose isolated compared with the control sample. The degree of polymerization (DP) of the samples extracted is estimated from the intrinsic viscosity value using the Mark‐Houwink equation in two different solutions (DMAc/9%LiCl) and (6%NaOH/4%urea/90%H₂O). We have demonstrated that the extraction using an acetic acid solution has been very successful by adding 2% in volume of nitric acid (HNO₃). However, the extraction process using an alkaline solution (NaOH; 1M) is preferable because of the absence of acetylating reaction and the high purity and the nondegradation of the resulted fibers. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

田菁水溶液的拉伸流动

用自制的Sridhar-Gupta拉伸粘度计测定了田菁水溶液的拉伸应力与拉伸粘度.结果表明,田菁水溶液的剪切流动和拉伸流动都可用改进的Williams-Bird四参数本构方程描述.     

Apparent elongational viscosity of dilute polymer solutions

Apparent elongational viscosity studies were made on dilute solutions of high molecular weight polymers using a fiber spinning apparatus designed for low shear viscosity liquids with substantial elongational effects. The experimental method involved the flow of solutions of polyacrylamide and poly(ethylene oxide) from a tube into an evacuated vessel. Experimental results showed that the apparent elongational viscosity obtained from the jet shape increased linearly with the stretch rate.