Rheological properties and microstructures of cellulose acetate phthalate/hydroxypropyl cellulose blends

Cellulose acetate phthalate (CAP)/hydroxypropyl cellulose (HPC) blends were investigated by means of attenuated total reflection‐Fourier transform infrared spectroscopy, thermogravimetry/differential thermal analysis, shear viscosity, oscillatory shear tests, and atomic force microscopy (AFM). Effect of solution concentrations in 2‐methoxyethanol, blend compositions, and shear rate on the rheological functions reflects the mobility of the chain segments or their orientation—with thinning behavior in the shear field. Specific interactions, such as the hydrogen bonds between polymer components and 2‐methoxyethanol used in casting solutions of films, influence the resulting morphology. Supernodular aggregates with different intensities and dimensions, which involve the coexistence of an isotropic and an anisotropic phase, typical for lyotropic cellulosic derivative liquid crystals at low concentrations, are evidenced by AFM images. This study is useful for applications of CAP/HPC blends in pharmaceutical domains.POLYM. COMPOS., 33:2072–2083, 2012. © 2012 Society of Plastics Engineers     

Phase separation,cure kinetics,and morphology of epoxy/poly(vinyl acetate) blends

Epoxy based on diglycidyl ether of bisphenol A + 4,4′diaminodiphenylsulfone blended with poly(vinyl acetate) (PVAc) was investigated through differential scanning calorimetry (DSC), dynamic mechanical thermal analysis (DMTA) and environmental scanning electron microscopy (ESEM). The influence of PVAc content on reaction induced phase separation, cure kinetics, morphology and dynamic‐mechanical properties of cured blends at 180°C is reported. Epoxy/PVAc blends (5, 10 and 15 wt % of PVAc content) are initially miscible but phase separate upon curing. DMTA α‐relaxations of cured blends agree with T_g results by DSC. The conversion‐time data revealed the cure reaction was slower in the blends than in the neat system, although the autocatalytic cure mechanism was not affected by the addition of PVAc. ESEM showed the cured epoxy/PVAc blends had different morphologies as a function of PVAc content: an inversion in morphology took place for blends containing 15 wt % PVAc. The changes in the blend morphology with PVAc content had a clear effect on the DMTA behavior. Inverted morphology blends had low storage modulus values and a high capability to dissipate energy at temperatures higher than the PVAc glass‐transition temperature, in contrast to the behavior of neat epoxy and blends with a low PVAc content. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 1507–1516, 2007     

Phase separation behavior and morphology development of phenolic resin/PMMA/hexamethylenetetrarnine blends

Summary In order to obtain materials with nanopores which will be applicable for many fields, the structures of the cured blends of phenolic resin (PhN), poly(methyl methacrylate) (PMMA) and curing agent were studied. After PMMA was extracted from cured blends, the structures of cured phenolic resins were observed with SEM. As a results, it was found that nanosized continuous pore structures were formed in extremely wide composition region if curing temperature was high.     

Phase morphology of PP/COC blends

Phase morphology of polymer blends PP/COC, where PP is polypropylene and COC is a copolymer of ethene and norbornene, was characterized by means of scanning electron microscopy (SEM) and scanning transmission electron microscopy (STEM). PP/COC blends were prepared by injection molding and their morphology was studied for six different compositions (90/10, 80/20, 70/30, 60/40, 50/50, and 25/75 wt %). The intention was to improve PP properties by forming COC cocontinuous phase, which should impart to the PP matrix higher stiffness, yield stress, and barrier properties. Surprisingly enough, all studied blends were found to have fibrillar morphology. In the 90/10, 80/20, and 70/30 blends, the PP matrix contained fibers of COC, whose average diameter increased with increasing COC fraction. In the 60/40 blend, the COC component formed in the PP matrix both fibers and larger elongated entities with PP fibers inside. The 50/50 blend was formed by COC cocontinuous phase with PP fibers and PP cocontinuous phase with COC fibers. In the 25/75 blend, PP fibers were embedded in the COC matrix. In all blends, the fibers had an aspect ratio at least 20, were oriented in the injection direction, and acted as a reinforcing component, which was proven by stress–strain and creep measurements. According to the available literature, the fibrous morphology formed spontaneously in PP/COC is not common in polymer blends. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 253–259, 2004     

Phase separation induced morphology evolution andcorresponding impact fracture behavior of iPP/PEOc blends

In this study, the influence of phase separation on impact toughness of isotactic polypropylene (iPP)/poly(ethylene‐co‐octene) (PEOc) blends was investigated. For the typical toughened polymeric system, three iPP/PEOc compositions (80/20, 70/30, and 60/40) were selected. When the polymeric blends were annealed at 200°C, the coarsening of phase domains was more prominent for the blend containing higher content of PEOc, and the scale of its morphological evolution was increased as well. The impact test showed that the impact strength variation trend as a function of annealing time was closely related to morphological evolution. It was believed that the sharpening of phase boundary and coarsening of phase domains were responsible for the depression of impact toughness, and the probable fracture mode alteration from shear banding to crazing and voiding. Structure evolution induced by phase separation showed an important effect on impact toughness, and it was also affected by the environmental conditions. Proper temperature was required to catch the tough‐brittle transition induced by phase separation. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Mechanical properties of cellulose acetate propionate/aliphatic polyester blends

Useful blends of cellulose esters with other higher molecular weight polymers are generally unknown. Two aliphatic polyesters, poly(tetramethylene glutarate) (PTG) and poly(tetramethylene succinate) (PTS), have been thermally compounded with cellulose acetate propionate (CAP) in the range of 10–40 wt % polyester. These blends have been injection molded, and the mechanical properties of the molded bars were compared to bars molded from CAP plasticized with a low molecular weight diester, dioctyl adipate (DOA). The CAP/aliphatic polyester blends have significantly higher tensile strengths, flexural moduli, heat deflection temperatures, and greater hardness values than the corresponding CAP/DOA blends. © 1994 John Wiley & Sons, Inc.     

Preparation and properties of foamed cellulose acetate/polylactic acid blends

In order to improve the foaming performance of pure cellulose acetate (CA), blends were prepared by mixing polylactic acid (PLA) in CA and foamed by supercritical CO₂ (ScCO₂) in this study. The effect of PLA content (percentage by mass of blend) on structure, thermal properties, rheological properties, foaming properties and mechanical properties of the blends was investigated. The results showed that the addition of PLA destroyed the original hydrogen bonds of CA, while the blends had good crystallization properties. At the same time, compared with pure CA, the glass transition temperature (T_g) of the blends decreased, and the initial decomposition temperature (T₀) was reduced from 349.41°C (pure CA) to 334.68°C (CA/20%PLA). In addition, the rheological properties of the blends were improved, and the viscosity was reduced, which was obviously beneficial to foaming process. The pore size and density of the foamed blends both reached the maximum value at 20%PLA. The presence of PLA could degrade the mechanical properties of the blends. However, the overall drop (1.01 KJ/m²) of impact strength of the blends after foaming is much smaller than that before foaming (12.11 KJ/m²), indicating that the improvement of foaming performance was beneficial to improve its impact strength.     

Phase morphology and melt viscoelastic properties in blends of ethylene/vinyl acetate copolymer and metallocene-catalysed linear polyethylene

The aim of this study was to determine the linear viscoelastic properties of a series of ethylene/vinyl acetate copolymer/metallocene-catalysed polyethylene (mPEs) blends. Newtonian viscosity showed a pronounced positive deviation from the double reptation model, which assumes miscibility or, at least, cooperative relaxation between the mixed species. Enhanced values of steady-state compliance and elastic indices with respect to those of the pure components were also noted. These features are typical of emulsion-like polymer blends and are thought to arise from additional relaxation processes associated with dispersed phase deformability. Application of the Palierne model for emulsions of two viscoelastic liquids showed good agreement with our experimental dynamic results at both ends of the phase diagram. However, the model failed at intermediate compositions. Through the application of several rheological criteria we were able to locate the phase inversion concentration at a weight fraction of w=0.60 in the mPEs. It is suspected that, in this composition range, a fully co-continuous phase develops due to the phase inversion mechanism, which has considerable effects on the viscoelastic properties of the blends.     

Electrokinetics and stability of a cellulose acetate phthalate latex

An experimental investigation is described on the surface electric characterization of a commercially available latex, Aquateric, composed of cellulose acetate phthalate polymer particles, and used in enteric-controlled drug release. Since the surface charge of dispersed systems is an essential parameter governing most of their behavior, it is of fundamental importance to characterize how that quantity changes in the different environments in which the colloids could be used. The experimental method used in this work is electrophoresis; we report measurements of electrophoretic mobility of the latex as a function of pH and ionic concentration in the dispersion medium. It is shown that the zeta potential of the polymer particles is negative for the whole pH range studied and increases with pH as the dissociation of surface acetic acid groups proceeds. A plateau value is found for pH > 5, corresponding to complete dissociation of available ionizable sites. The values of the electrophoretic mobility (μ_e) and the zeta potential (ζ) of Aquateric are also analyzed as a function of the concentration of 1-1 (NaCl) and 2-1 (CaCl₂) concentration. The anomalous surface conductance (associated to the mobility of counterions adsorbed in the inner part of the electric double layer of the particles) manifests in a maximum in the |μ_e|-NaCl concentration plot for 10⁻³M concentration. No such behavior is observed in the presence of CaCl₂ solutions, where only a decrease of the mobility with ionic strength is observed. The effect of AlCl₃ concentration on the mobility is also considered; it is found that at pH 2 aluminum ions adsorb on the particles and render them positively charged. When the pH of the suspensions is not maintained constant, the hydrolysis of aluminum gives rise to a less efficient control of the charge of the particles and no positive mobilities are observed. Electrophoretic mobility measurements as a function of pH at constant AlCl₃ concentration show an abrupt change of μ_e from negative to positive, interpreted as due to surface precipitation of Al(OH)₃. When the pH is further increased, a second charge reversal is found, corresponding to the isoelectric point (pH of zero zeta potential) of Al(OH)₃. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65: 2721–2726, 1997     

The interactions and partitioning of low molecular weight polyethylene glycols and diethyl phthalate in ethylcellulose/hydroxypropyl methylcellulose blends

The interactions and partitioning of diethyl phthalate and low molecular weight polyethylene-glycols in blends of ethylcellulose/hydroxypropyl methylcellulose have been studied. Both plasticizers were shown to diffuse in both phases according to the overall volume composition. The plasticizers interacted preferentially with one polymer component of the blend as predicted from studies of the individual polymers. Diethyl phthalate, a preferential plasticizer for ethylcellulose, demonstrated increased partitioning in the ethylcellulose-rich phase only at 80/20 w/w ethylcellulose/hydroxypropyl methylcellulose compositions. Polyethylene glycols, PEG200 and PEG400, preferential plasticizers for hydroxypropyl methylcellulose, showed increased partitioning in the hydroxypropyl-methycellulose-rich phase also in blends containing 80% w/w ethylcellulose. The general effect of the mechanism and kinetics of the phase separation of the blend on the plasticizer partitioning has also been discussed.     

Hydrogen/carbon monoxide separation with cellulose acetate membranes

Hydrogen/carbon monoxide ratio adjustment is of fundamental interest to the petrochemical and energy industries for the production of C₁ chemicals. Cellulose acetate membranes have been found to be effective for this service and can offer improvements over other gas purification techniques in several respects including reduced capital and operating costs. Membrane and cryogenic processes are compared for the specific case of manufacture of a 1/1 H₂/CO syngas for oxoalcohol production. A particular advantage of the membrane process is its flexibility. This has benefited a recently installed facility for the Central Research Institute of the Electrical Power Institute of Japan for variable adjustment of the hydrogen to carbon monoxide ratio at a test facility demonstrating coal gasification/ gas turbine power production. Design and operating details of this facility are discussed. The membrane process may also be used to produce a pure CO product. The performance of polysulphone and cellulose acetate are compared for this application.     

Phase separation in polypropylene and metallocene polyethylene blends

Blends of a metallocene linear low density polyethylene (m‐LLDPE) and polypropylene random copolymer (PP) have been prepared using a twin screw extruder and characterized by thermal analysis, mechanical properties, and wide angle X‐ray scattering to determine their degree of compatibility. The blends were either directly quenched in water from the melt‐ or slow‐cooled to room temperature. In both cases, the two components formed separate phases and crystallized independently. The slow‐cooled specimens had higher yield stress, tensile modulus, and lower elongation at break consistent with higher degree of crystallinity. The elongation to break also varied with composition reaching a minimum at 50% consistent with the incompatible nature of the blends. Crystallization kinetics and melting studies confirm that the two components formed separate phases and crystallized independently. POLYM. ENG. SCI., 46:889–895, 2006. © 2006 Society of Plastics Engineers     

Miscible blends of cellulose acetate hydrogen phthalate and poly(vinyl pyrollidone) characterization by viscometry,ultrasound, and DSC

Miscibility characteristics of cellulose acetate hydrogen phthalate (CAP) and poly(vinyl pyrollidone) (PVP) have been investigated by solution viscometric, ultrasonic, and differential scanning calorimetric (DSC) methods. From viscosity measurements, Krigbaum and Wall polymer–polymer interaction parameter Δb was evaluated. Ultrasonic velocity and adiabatic compressibility have been plotted versus blend composition and are found to be linear. Variation of T_g with composition follows Gordon–Taylor equation. T_g values have also been calculated from the Fox equation. The results obtained reveal that CAP forms a miscible blend with PVP in the entire composition range. Compatibility may be due to the formation of hydrogen bonding between the carbonyl group of PVP and the free‐hydroxyl group of CAP. Compatibility has also been confirmed from dielectric measurements. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 859–867, 2000     

Phase morphology of as-molded and annealed blends of polyarylate/copolyester

The phase morphology of injection molded blends of polyarylate (PAR) and a copolyester (PCTG-5445) was studied by transmission electron microscopy (TEM) and X-ray diffraction (XRD). The use of ultramicrotomy to prepare ? 50 nm thin section TEM specimens and solvent etching to dissolve the PAR phase revealed PCTG as the matrix phase in the as-molded state which crystallized into PCTG spherulites upon annealing. The most consistent morphological information vs. concentration of PCTG and the highest structural integrity of the PCTG spherulites was obtained from thin sections treated with a mixture of 75% methylene chloride as the solvent for the PAR and 25% 2-propanol as the nonreactive diluent. XRD results from the annealed PCTG/PAR blends show crystalline reflections of 0.59, 0.53, 0.46, 0.38, and 0.35 nm, which disappear into the amorphous background below 50% PCTG.     

Phase separation and gelation of epoxy resin/hyperbranched polymer blends

The structural buildup during reticulation of thermoset systems containing reactive modifiers can strongly influence the final properties of such blends. This was studied by considering the rheological behavior during cure of an epoxy/amine thermoset system blended with reactive dendritic hyperbranched polymers (HBPs). Depending on the chemical structure of the HBP used in the blend, a phase separation could be observed. The onset and offset of the phase separation process could be detected by observing the evolution of the viscoelastic properties. The phase separation onsets obtained by rheological measurements were compared with the values obtained by traditional cloud point observations. Good agreement between the two techniques was observed. Hyperbranched polymers that did not phase separate during the curing process were used to study gelation phenomena and its dependence on the reactivity and functionality of the HBP. The gelation of the homogeneous blend system using the Flory‐Stockmayer theory was also modeled. This highlighted the influence of both functionality and reactivity of the components, and the appearance of co‐operative polymerization mechanisms in homogeneous blends.     

Phase separation behavior of cyanate ester resin/polysulfone blends

The composition of the blends and the curing temperature affect the morphology of the blends and the phase separation mechanism. The phase separation mechanism depends on the viscosity of medium at the initial stage of phase separation determined by the amount of thermoplastics and the curing temperature, and is closely related with the final morphology. When the homogeneous bisphenol A dicyanate (BADCy)/polysulfone (PSF) blends with low content of PSF (less than 10 wt %) were cured isothermally, the blends were phase separated by nucleation and growth (NG) mechanism to form the PSF particle structure. On the other hand, with more than 20 wt % of PSF content, the BADCy/PSF blends were phase separated by spinodal decomposition (SD) to form the BADCy particle structure. With about 15 wt % of PSF content, the blends were phase separated by SD and then NG to form a combined structure having both the PSF particle structure and the BADCy particle structure. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 33–45, 1999     

Modified polyacrylonitrile blends with cellulose acetate: Fibers' properties

Fiber forming polyacrylonitriles (PAN) were modified by copolymerizing acrylonitrile monomer with methyl acrylate (MA) and 2-acrylamido-2-methyl propane sulfonic acid (AP), respectively, and blended with collulose acetate (CA). Fibers of MA-PAN, AP-PAN, and their blends with CA were wet-spun in dimethylformamide in a broad range of coagulation bath concentrations (CBC). The effects of hydrophilic and hydrophobic modification of PAN and the CBC, as well as the coagulation behavior, were studied in terms of morphology, mechanical properties, and water regain property of the fibers. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 1937–1946, 1997