Swelling behavior of crosslinked hydroxypropylcellulose films retaining cholesteric liquid crystalline order,II. Effects of temperature,solvent, and pH

Crosslinked hydroxypropylcellulose (HPC) films were cast from the cholesteric liquid crystalline HPC solution in methanol. The films retained the cholesteric liquid crystalline order. The dependences of swelling behavior of our films in water and propanol on temperature and on pH of the solvent were determined. The response of our films to the changes in water, temperature and in pH was discussed. In water, the equilibrium swelling ratio (B_e) decreased with temperature whereas B_e increased with temperature in propanol. For a given composition of water and propanol, B_e was independent of temperature. B_e in the acidic solvents was higher than in the alkaline solvents. The response data to the stepwise change in temperature revealed that the deswelling behavior was more rapid than the swelling behavior in water, and the swelling-deswelling behavior was reversible. The response to the stepwise change in pH was almost the same as that of the change in temperature, but the surface of the film was attacked by the acid and became fluffy with increasing soaking time.     

Interpenetrating polymer networks based on poly(acrylic acid) and gelatin. I: Swelling and thermal behavior

This article describes the synthesis of full and semi-interpenetrating polymer networks (IPNs) based on poly(acrylic acid) and gelatin as polymers 1 and 2, which were crosslinked sequentially using N,N′-methylene bisacrylamide (B_Am) and glutaraldehyde, respectively. Various samples were prepared by taking varying amounts of acrylic acid and gelatin in the initial feed. Sequential IPNs were prepared by first polymerizing and crosslinking acrylic acid in the presence of gelatin using redox initiators (ammonium persulphate and sodium metabisulphite) and B_Am as a crosslinking agent. Gelatin present in the firm gels was then crosslinked using 4% glutaraldehyde. Characterization of these gels was done by measuring their swelling behavior as a function of pH, temperature, and time. Percent swelling increased with increasing amounts of acrylic acid. The swelling ratio was also determined in the pH range of 1 to 12. Acid/alkali or buffers were used for maintaining pH. A significant increase in the percent swelling was observed when pH of distilled water was above 10. On the other hand, in the case of buffer, the swelling ratio increased with increasing the pH, and a maxima was observed at pH 8.4. A further increase in pH resulted in a decrease in the swelling ratio. Thermal and morphological characterization was done using thermogravimetric analyzer and scanning electron microscopy, respectively. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 217–227, 2001     

Preparation and Swelling Properties of Temperature‐Sensitive Semi‐Interpenetrating Polymer Networks Composed of Poly[(N‐tert‐butylacrylamide)‐co‐acrylamide] and Hydroxypropyl Cellulose

Summary: Temperature‐responsive hydrogels based on linear HPC and crosslinked P(NTBA‐co‐AAm) were prepared by the semi‐IPN technique. The structure of these semi‐IPN hydrogels was investigated by FT‐IR spectroscopy. An increase in normalized band ratios (A₂₉₈₀/A₁₆₆₅) was observed with increasing HPC content in the initial mixture. The swelling kinetics and water transport mechanism of these semi‐IPN hydrogels were examined and their temperature responsive behaviors were also investigated by measuring equilibrium swelling ratios and pulsatile swelling experiments. The results showed that these semi‐IPN hydrogels underwent a volume phase transition between 18 and 22 °C irrespective of the amounts of MBAAm and HPC. However, below the volume phase transition temperature, their equilibrium swelling ratios were affected by the amount of MBAAm and HPC. The pulsatile swelling experiments indicated that the lower the MBAAm and the higher HPC contents in semi‐IPN hydrogels the faster the response rate temperature change.

Equilibrium swelling ratios of the semi‐IPN P(NTBA‐co‐AAm)/HPC hydrogels in water shown as a function of temperature.     

Swelling and mechanical properties of cellulose hydrogels. III. Temperature effects on the swelling and compliance levels studied by dilatometry and 1H-NMR spectroscopy

The temperature dependence of the swelling and the creep compliance has been investigated for swollen isotropic cellulose hydrogels. The measurements were performed in a high precision type of dilatometer between 5 and 65°C. The thermal expansion of the gels in silicone oil (closed system) and the temperature dependence of the equilibrium swelling in water (open system) were studied. The influence of compressive stress in these experiments was also evaluated. The swelling level in equilibrium with water diminishes slightly with increasing temperature due to migration of water from the gel phase to the surrounding water phase. A secondary transition was found at 35°C where the temperature dependence of the swelling level is changed. When measured at constant gel composition the creep compliance of a highly swollen gel decreases with increasing temperature. The decrease is not, however, large enough for entropy elasticity to dominate over energetic elasticity. The energetic contribution f_U/f was determined to be 0.61 for a gel swollen to 3.9 g water/g dry gel (g/g) and 1.24 for a gel swollen to 1.05 g/g. The swelling and compliance data have also been analyzed in terms of a model where the gels are assumed to behave as a filler-reinforced rubbery network. The amorphous parts of the hydrogels are thus assumed to be described by the statistical theory for polymeric networks. In proton magnetic resonance studies of a gel swollen to 4.4 g/g the spin-lattice relaxation time T₁ was determined to be considerably longer than the spin-spin relaxation time T₂. T₂ has a maximum at 30°C. This maximum marks the onset (on the NMR time scale) of an exchange process between two types of proton species. These species are suggested to be specific hydration water and free gel water, respectively.     

Study on the structure of nylon 6 films iodinated before forming. III. Fine structure variation of the amorphous film through deiodination

Amorphous nylon 6 film iodinated before forming with an aqueous solution of 1.0N iodine–potassium iodide (I₂/KI) was deiodinated by dipping in water/ethylene glycol (EG) solutions of sodium thiosulfate with various EG contents and temperatures, washed with water, and dried at ambient condition. Structural variation through deiodination and the effects of the deiodination conditions were investigated by X‐ray diffractometry and differential scanning calorimetry. The degree of swelling of the films immediately after deiodination and the time required to complete the deiodination were generally increased and decreased, respectively, with increasing temperature and EG content. The amorphous iodinated film was crystallized through deiodination. The α‐crystal formation became easier with increasing temperature and EG content in the solution. The crystallinity of the films was higher after drying than before drying, suggesting that the drying induced further crystallization without any significant conversion of crystal type. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Rheological properties of liquid crystalline solutions of ethyl celluloses with different molecular weight in m-cresol

Steady-state shear rheological properties of liquid crystalline solutions of four ethyl celluloses (ECs) were determined at a low shear rate (1 s^?1) and at relatively high shear rates by using two rheometers (cone-plate and capillary types), and were compared with those of liquid crystalline hydroxypropyl cellulose (HPC). The effect of molecular weight (MW) on the viscoelastic behavior was also determined. The viscoelastic behavior was also determined. The viscometric behavior of EC solutions was similar to that of HPC solutions: (1) with respect to temperature, the shear viscosity (η) at shear rate of 1 s^?1 exhibited a minimum (η_min) and a maximum (η_max), and the concentration–temperature superposition for η could be applied; (2) the behavior of η at relatively high shear rates as a function of shear rate or polymer concentration was typical of lyotropic liquid crystals. The MW dependence of η_min was greater than that of η_max for EC solutions. The behavior of the elastic parameters such as Bagley correction factor (v), entrance pressure drop (ΔP_ent), and die swell (B) at relatively high shear rates for EC solutions was essentially similar to that for HPC solutions: (1) the shear rate or stress dependence of the elastic parameters was greatly dependent on whether the polymer solution was in a single phase or biphase; (2) with respect to concentration the elastic parameters showed a maximum and a minimum and the maximum or minimum point for each parameter was not always identical to each other. η for the isotropic or fully anisotropic solutions at a given concentration (C) increased, whereas η for the solutions in the vicinity of the biphasic region showed a minimum, with respect to MW. The slope of η at a given shear rate vs. CM _w depended on shear rate, and this slope for the isotropic solutions appeared to be greater than that for fully anisotropic solutions. ΔP_ent and v at a given concentration showed either a monotonical increase or a maximum or minimum with MW, and this behavior was not fully consistent with that of η. B for the isotropic solutions increased and B's for both biphasic and fully anisotropic solutions were almost constant, with MW.     

Case II swelling of poly(ethylene terephthalate) in organic solvents

The swelling kinetics of crystalline PET films in chloroform–n-hexane mixtures were examined as a function of chloroform concentration. With increasing concentration, the swelling mechanism varied from Fickian to Case II behavior. The dependence of the swelling mechanism on the equilibrium uptake and activation energy for swelling were thoroughly compatible with those presented by other workers. From a viewpoint of superposition of Fickian and Case II swelling, the intermediate swelling between the above two limiting cases was analyzed by Kwei's equation. The magnitude of the diffusion coefficient obtained was remarkably smaller than that presented for the swollen amorphous polymer. The magnitude of the penetration velocity is also discussed in comparison with the data for amorphous polymer.     

Poly(L‐lactide): v. effects of storage in swelling solvents on physical properties and structure of poly(L‐lactide)

The effects of storage at 25°C in swelling solvents having different solubility parameter (δ_s) values of 16.8–26.0 J^0.5 cm^−1.5 on the physical properties and structure of as‐cast poly(L ‐lactide) (PLLA) films was investigated by the degree of swelling (DS), differential scanning calorimetry (DSC), and tensile tests. It was found that PLLA film shows durabity to swelling solvents having δ_s values much lower or higher than the value range of 19–20.5 J^0.5 cm^−1.5 and that the polymer solubility parameter (δ_p) for PLLA is in the value range of 19–20.5 J^0.5 cm^−1.5. The decrease in the glass transition temperature (T_g) and tensile properties and the increase in melting temperature (T_m) and crystallinity (x_c) were larger for PLLA films swollen in solvents having a high DS at 7 days (DS_7days). The slight increase in T_m and x_c for PLLA films after swelling in solvents with high DS_7days values was due to the crystallization of PLLA that occurred during swelling, while the small increase in T_g and elongation at break (ε_B) for PLLA films after immersion in the solvents having low DS_7days values was ascribed to stabilized chain packing in the amorphous region. The T_g, ε_B, and Young's modulus of the PLLA films after swelling in the solvents varied in the ranges of 47–57°C, 4–8%, and 55–77 kg/mm², depending on their DS_7days or δ_s values. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 1582–1589, 2001     

A comparative study of swelling properties of hydrogels based on poly(acrylamide‐co‐methyl methacrylate) containing physical and chemical crosslinks

Poly (acrylamide‐co‐methyl methacrylate) hydrogels of different ratios were prepared by using chemical and physical crosslinks to study the effect of nature of crosslinks on swelling behavior of hydrogels. The chemically crosslinked gels were prepared by using NN′‐methylene bis acrylamide, while physically crosslinked hydrogels were prepared by precipitation polymerization method, using dioxane as solvent. Detailed swelling kinetics such as swelling ratio, transport exponent n, diffusion coefficient D and the effect of pH on equilibrium swelling studies. The study revealed that the nature of crosslinks alter the swelling characteristics of the hydrogel. In chemically crosslinked hydrogels the water transport is Fickian in nature, while in the case of the physically crosslinked hydrogels the water transport mechanism is anomalous indicating major change in relaxation mechanism due to nature of crosslinks. The results also indicate that with increasing acrylamide content the swelling ratio of the hydrogels were also increased, but the transport exponent n remains nearly constant. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 779–786, 2003     

Effect of crosslinking on the surface free energy and surface reorganization of waterborne fluorinated polyurethane

To endow waterborne fluorinated polyurethanes (WFPUs), films with stable lower surface free energy and lower surface reorganization after the films contacted with water, a series of crosslinked WFPUs (CWFPUs) emulsions were prepared by adjusting the content of aziridine (AZ). The effect of crosslinking on the surface free energy, glass-transition temperature (T _g), water absorption, and surface composition of dry/hydrated WFPUs and CWFPUs films were studied by CAs test, dynamic mechanical analysis, water absorption measurements, and X-ray photoelectron spectroscopy. When the fluorine content was 0.5%, the surface free energy of the CWFPUs films modified by 0.4% AZ content (CWFPU-6-0.5-CK0.4) reached to the lowest value of 15.76 mN m⁻¹ which almost equaled to the surface free energy (15.45 mN m⁻¹) of the dry uncrosslinked films (WFPU-6-0.5). With the increasing of AZ content, the T _{g, hard} of hard segments of the CWFPUs films increased and the water absorption of the CWFPUs films decreased, which suggested the formation of the crosslinked network structures. The studies of the surface elements and groups composition of dry/hydrated WFPUs and CWFPUs both confirmed that the surface reorganization and the migration of fluorinated side chains were restricted by the crosslinked network structures. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47167.     

Swelling of hydrophilic polymers. IV

The swelling of five types of spherical crosslinked dextrans (Sephadex) that are either nonionic (G) or ionic [carboxymethyl (CM), sulphopropyl (SP), diethylaminoethyl (DEAE), and diethyl-(2-hydroxypropyl)aminoethyl (QAE)] in the same skeleton has been studied in water at different dissolved oxygen concentrations by microscopic observation and by dilatometry. The maximum specific volume, V_max/V₀ obtained by microscopic observation increased with the lowered dissolved oxygen concentration for each Sephadex. The change of the maximum specific volume was closely related to the changes of the dissolved oxygen concentrations. The maximum changes of the total volume took the larger negative values at the lower dissolved oxygen concentration. The effect of the difference in the dissolved oxygen on the change of the total volume with swelling was closely related to the viscosity B coefficient of the Jones-Dole equation. From these results, we conclude that the structure of water on the inside of the gel differs from that on the outside of the gel. © 1995 John Wiley & Sons, Inc.     

The rheological behavior and dynamic mechanical properties of syndiotactic 1,2‐polybutadiene

The rheological behavior and the dynamic mechanical properties of syndiotactic 1,2‐polybutadiene (sPB) were investigated by a rotational rheometer (MCR‐300) and a dynamic mechanical analyzer (DMA‐242C). Rheological behavior of sPB‐830, a sPB with crystalline degree of 20.1% and syndiotactic content of 65.1%, showed that storage modulus (G′) and loss modulus (G″) decreased, and the zero shear viscosity (η₀) decreased slightly with increasing temperature when measuring temperatures were lower than 160°C. However, G′ and G″ increased at the end region of relaxation curves with increasing temperature and η₀ increased with increasing temperature as the measuring temperatures were higher than 160°C. Furthermore, critical crosslinked reaction temperature was detected at about 160°C for sPB‐830. The crosslinked reaction was not detected when test temperature was lower than 150°C for measuring the dynamic mechanical properties of sample. The relationship between processing temperature and crosslinked reaction was proposed for the sPB‐830 sample. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Blends of aliphatic polyesters. IV. Morphology,swelling behavior,and surface and bulk properties of blends from hydrophobic poly(L-lactide) and hydrophilic poly(vinyl alcohol)

Blend films were prepared from hydrophobic poly(L -lactide) (PLLA) and hydrophilic poly(vinyl alcohol) (PVA) with different PLLA contents [X_PLLA (w/w) = PLLA/(PVA + PLLA)] by solution casting and melt quenching. Their morphology, swelling behavior, and surface and bulk properties were investigated. Polarizing optical microscopy, scanning electron microscopy, differential scanning calorimetry, X-ray diffractometry, and tensile testing revealed that PLLA and PVA were phase separated in these blend films and the PLLA-rich and PVA-rich phases both formed a continuous domain in the blend film of X_PLLA = 0.5. The water absorption of the blend films was higher for the blend films of low X_PLLA values when compared at the same immersion time, and it was larger than expected from those of nonblended PLLA and PVA films. The dynamic contact angles of the blend films were linearly increased with an increase in X_PLLA. The tensile strength and Young's modulus of the dry blend films decreased with a rise in X_PLLA, but this dependence was reversed because of the large decreases in tensile strength and Young's modulus for the blend films having high X_PLLA values after immersion in water. The elongation at break was higher for the wet blend film than for the dry blend film when compared at the same X_PLLA and that of the dry and wet blend films decreased with an increase in X_PLLA. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 2151–2160, 2001     

Properties of syndiotacticity-rich poly(vinyl alcohol) thin film in water. IV. Elastic behavior of untreated thin film by repeated elongation and contraction in water

The activation energy ΔE_a for diffusion of water molecules into untreated thin film of poly(vinyl alcohol) (PVA_VTFA) derived from vinyl trifluoroacetate was estimated as 30.3 kcal/mol from the temperature dependence of the initiation time of swelling. The degree of equilibrium swelling increases with the increase in temperature in the range of 10–70°C, passing through the constant range between 30 and 50°C. Under the forced, repeated elongation and contraction for swollen PVA_VTFA thin film in water, the perfect elastic behavior is kept up to higher elongation with the increase in temperature and especially up to about three times equilibrium swelling length at 70°C. Young's modulus of swollen PVA_VTFA thin film in water was 6.47 × 10⁶ to 1.60 × 10⁶ dyn/cm² at 25–70°C. The molecular weight between junctions M_c increased with the increase in temperature; M_c was nearly equal to about one-sixth of the molecular weight of raw polymer M at 25°C and about one-third of M at 70°C. The interaction parameter between PVA_VTFA and water X₁, was 0.493–0.497 at 25–70°C.     

Ionizable interpenetrating polymer networks of carboxymethyl cellulose and polyacrylic acid: Evaluation of water uptake

A semi interpenetrating polymer network (IPN) of carboxymethyl cellulose (CMC) and crosslinked polyacrylic acid (PAA) has been prepared and its water‐sorption capacity has been evaluated as a function of chemical architecture of the IPN, pH, and temperature of the swelling medium. The water uptake potential of the IPNs has also been investigated in inorganic salt containing aqueous solutions and simulated biological fluids. The IPN was characterized by IR spectral analysis, and the network parameters such as average molecular weight between crosslinks (M_c), crosslink density (q), and number of elastically effective chains (V_e) have been evaluated by water‐sorption measurements. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 2054–2065, 2004     

Thermal and dynamic mechanical properties of hydroxypropyl cellulose films

Differential scanning calorimetry (DSC) and dynamic mechanical thermal analysis (DMTA) were used to characterize the morphology of solvent cast hydroxypropyl cellulose (HPC) films. DSC results were indicative of a semicrystalline material with a melt at 220°C and a glass transition at 19°C (T₁), although an additional event was suggested by a baseline inflection at about 80°C (T₂). Corresponding relaxations were found by DMTA. A secondary relaxation at ?55°C was attributed to the interaction between hydroxyl groups of the polymer and residual diluent. The tan δ peak at T₂ was found to arise from an organized phase, presumably from a liquid-crystal mesophase formed while in solution. Crosslinking with a diisocyanate increased the peak temperature of the two primary relaxations, and resulted in a more clearly defined peak for the T₂ transition. From this behavior it was concluded that both T₁ and T₂ are similar to glass transitions (T_g's) associated with an amorphous component and a more highly ordered phase (due to a residual liquid crystal superstructure) in the HPC bulk.     

Static tensile and dynamic mechanical properties of hydroxypropylcellulose films prepared under various conditions

The films of hydroxypropyl cellulose (HPC), which is a lyotropic and thermotropic liquid crystal, were cast under various conditions of temperature and concentration. The effects of the casting conditions on the static tensile and dynamic mechanical properties of the cast films were determined, and the results were compared with those of films prepared by means of hot compression. The tensile properties of the films prepared by both processes (cast and hot compression) were unsatisfactory in comparison with other liquid crystalline polymers, and this was partly due to water absorbed during the test. In dynamic properties, two distinct transitions were detected. The higher one, around 110°C, was associated with the rotation of an unhydroglucose ring and the lower one, around 25°C, was associated with the T_g. There were no marked differences in the properties between cast films and hot-compressed films, except the disappearance of the T_g for hot-compressed film prepared at a relatively higher temperature. The basis for defining the liquid crystalline structure in cast and hot-compressed films are not directly given in this preliminary paper. However, judging from the dynamic mechanical properties and refractive index data for films prepared by both processes, it appears that dimethylacetamide-cast films and films compressed at 180 and 200°C may have some structures related to liquid crystalline phase and that inter- and intramolecular hydrogen bonding play an important role in lyotropic and thermotropic liquid crystalline behavior for HPC.     

Preparation and characterization of crosslinked and heat-treated PVA-MA films

Two kinds of water-insoluble PVA-MA hydrogel films were prepared from PVA-MA, an esterification product of poly(vinyl alcohol) and maleic anhydride, by heat treatment and a crosslinking reaction, respectively. Both films changed their dimensions upon environmental pH changes. The crosslinked gel expanded to approximately 230% of its original length, with most changes occurring in the pH range of 2–7. The heat-treated PVA-MA film swelled stepwisely, with about 45% of the total expansion occurring at pH 2–7 and the remaining 55% at pH 9–12. Results from IR spectra analysis and acid-base titration suggest that the ionization of carboxylic acid accounts for the pH-induced gel swelling irrespective of the differences in the swelling behavior of these two gels. The pK_a values of the heat-treated PVA-MA gel increased from 4 to 10 while the degree of dissociation varied from 0 to 80%, whereas that of the crosslinked PVA-MA film is limited in a range of 3.3–4.2. The permeability of glucose across the crosslinked PVA-MA film increased when pH was raised from 2 to 7. No significant change of permeability was noticed between pH 7 and 12. For the heat-treated PVA-MA film, glucose permeability increased when pH was changed from 2 to 7 and from 7 to 12. © 1996 John Wiley & Sons, Inc.     

Self assembled hydrophobic nanoclusters of poly(methyl methacrylate) embedded into polyvinyl alcohol based hydrophilic matrix: Preparation and water sorption study

Hydrophilic matrices containing nanosized clusters of hydrophilic moieties have demonstrated potential applications in biomedical field. A novel hydrogel containing nanosized domains (20–35 nm) of hydrophobic moieties of poly(methyl methacrylate) (PMMA) was prepared by grafting crosslinked poly(acrylic acid‐co‐methyl methacrylate) chains onto polyvinyl alcohol (PVA) backbone using an efficient redox system. The graft copolymerization process was investigated to observe the influence of gel components on the kinetic parameters of grafting such as rate of grafting (R_g), grafting yield (G_y) and grafting efficiency (G_e). The prepared graft nanohydrogel was evaluated for its water sorption potential under varying chemical composition of the gel and changing pH, temperature, and ionic strength of the swelling bath. The swelling process was also examined mechanistically and diffusion constants (D) of water molecules through the swellable nanohydrogel were also evaluated. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Studies on swelling behaviors,mechanical properties,network parameters and thermodynamic interaction of water sorption of 2-hydroxyethyl methacrylate/novolac epoxy vinyl ester resin copolymeric hydrogels

A series of the highly cross-linked hydrogels has been developed by the syntheses of bulk copolymers based on 2-hydroxyethyl methacrylate (HEMA) and novolac epoxy vinyl ester resin (NEVER). The resulting hydrogels were investigated on their equilibrium water content (EWC), swelling behaviors and tensile properties. Dynamic swelling behaviors of copolymeric hydrogels indicate that the swelling process of these polymers follows Fickian behavior. The EWC decreased and volume fraction of polymer in hydrogel (ϕ₂) increased with NEVER content increasing due to its hydrophobicity. The increase of ionic strength of swelling medium or temperature results in a decrease in EWC and an increase in values of ϕ₂. Young’s modulus and tensile strength of hydrogels, as well as effective cross-link density (v_e), increased as NEVER content increased or ionic strength of swelling medium increased, attributing to increasing interaction between hydrophobic groups and polymer–polymer interaction with an increase in NEVER content or in ionic strength. The polymer–solvent interaction parameter χ reflecting thermodynamic interaction was also studied. As NEVER content, ionic strength of swelling medium or temperature increased, the values of χ increased. The values of χ and its two components χ_H and χ_S varied with increasing T. The negative values and trend of the enthalpy and entropy of dilution derived from values of χ_H and χ_S, could be explained on the basis of structuring of water through improved hydrogen bonding and hydrophobic interaction.