The solidification behavior of a PBT/PET blend over a wide range of cooling rate

In recent years, much attention has been paid to the development of high‐performance polyester blends, among which blends of polybutylene terephthalate/polyethylene terephthalate (PBT/PET) are expected to exhibit remarkable properties as far as their crystallization behavior is concerned. Through trial and error, appropriate commercial compositions have been chosen which could not be otherwise explained by a suitable interpretation of the mechanisms determining their solidification behavior. The solidification behavior of a 60/40 w/w PBT/PET blend was studied in a wide range of cooling conditions, according to a continuous cooling transformation (CCT) procedure developed previously, aiming at emulating the typical conditions encountered in polymer processing. Several samples characterized by a homogeneous structure were solidified from the melt at various cooling rates and the resulting structure and properties were subsequently evaluated by analyzing the density, microhardness (MH), and wide angle x‐ray diffraction (WAXD). The resulting solidification behavior was then compared to that exhibited by the individual constituents of the blend (i.e., PBT and PET). The blend displayed a unique solidification behavior, conversely to those of the pure components which showed characteristics not recognized in the blend except at certain restricted cooling rates ranges. The cooling rate dependence observed in the blend does not bring similarities to the crystallization behavior of individual constituents since the fall down of density with cooling rate should be related to the rate controlling demixing stage of the two moieties just before crystallization occurs. The kinetics observed is thus a measure of the kinetics of demixing. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 799–810, 2009     

Influence of migration of plasticizer during melt mixing on the transitions and properties of PC/CAB blends

Static and dynamic mechanical properties, morphology, and thermal behavior of polycarbonate (PC)/plasticized cellulose acetobutyrate (CAB) blends were investigated to determine whether the plasticizer of the CAB modifies the miscibility of the blend and the mechanical properties of this essentially incompatible blend. In spite of the lack of transparency of the blends, both dynamic mechanical and thermal analysis results show the presence, at all blend compositions studied, of a single glass transition temperature which varies with the composition of the blend. Considering the ternary nature of the blends, we propose that plasticizer migration and the difficulty of discerning the presence of one or two peaks in a narrow temperature range may account for the observed behavior. Scanning electron microscopy confirms the immiscibility of the blends. The blends show large positive deviations of the tensile moduli from linearity and very low ductility. The reported tensile strength data are discussed in terms of several different equations for composites. This mechanical behavior is explained as a consequence of the migration of the plasticizer and of its subsequent antiplasticizing effect on the properties of the blend.     

顺丁橡胶／低密度聚乙烯的共混

比较了未交联和动态交联不同组成PB/LDPE共混物的力学性能。共混物的T_g、T_m和T_d不随组成而变化,表明PB和LDPE不具有相容性。但共混物中PE的γ转变向高温方向位移,说明PE非晶部分的分子短链和PB有界面相互作用。形态研究表明,未交联体系中量多的组份形成连续相,动态交联体系在PB/LDPE≤70/30时,PE呈连续相,交联的PB为分散相。     

Thermal behavior of chitosan/natural rubber latex blends TG and DSC analysis

The thermal behavior of chitosan (CS)/natural rubber latex (NRL) blends has been studied by thermogravimetry (TG) and differential scanning calorimetry (DSC). Decomposition behavior of CS changes with the addition of NRL. The effect of blend composition on the amount of residue remaining at various temperatures has been studied. Activation energies of degradation have been calculated using Horowitz-Metzger equation. From the activation energy values, it is found that among the series of the blend compositions, CS₁₅NRL₈₅ exhibits better thermal stability. DSC studies reveals that the CS/NRL blends are thermodynamically incompatible. This is evident from the presence of two glass transitions, corresponding to CS and NRL phases in the blend.     

Toughening of highly crosslinked epoxy resins by reactive blending with bisphenol A polycarbonate. II. Yield and fracture behavior

The yield and fracture behavior of highly crosslinked epoxy resin modified by a reactive blending process carried out in the presence of bisphenol A polycarbonate has been studied. It was found that the fracture toughness of this blend system increases markedly with increasing PC content in the blend. Scanning electron microscopy of the fractured surfaces indicated a crack blunting mechanism as the main source of energy dissipation in the various investigated blend compositions. No evidence of phase separation of the minor component during the curing and postcuring steps was observed. The yield data were correlated with the fracture toughness data to evaluate the extent of crack-tip blunting. © 1994 John Wiley & Sons, Inc.     

Rheology and morphology of linear polyurethane and poly(methyl methacrylate) blends formed in situ

The rheological properties and morphology of flow during the in situ formation of linear polyurethane and poly(methyl methacrylate) blends of various compositions are studied. At a certain conversion of the components, the initial homogeneous blend undergoes phase separation, as evidenced by the nonadditive dependence of the logarithm of viscosity on blend composition. For individual components, the gel points correspond to appreciably different conversions. For components in blends of various compositions, this difference is less pronounced and associated with the kinetic conditions of blend formation. The morphology of flow of the reaction blend over the time (or conversion) between the onset of phase separation and gelation during flow with a high shear rate is determined by the blend composition and the ratio between the viscosity of the dispersion phase and the matrix.     

Phase behavior and its viscoelastic response of polylactide/poly(ε-caprolactone) blend

Polylactide (PLA)/polycaprolactone (PCL) blends with various blend ratios were prepared via melt mixing. The morphology, linear and non-linear viscoelastic properties of the blend were studied using scanning electron microscope (SEM) and cone-plate rheometer. Three typical immiscible morphologies, i.e., spherical droplet, fibrous and co-continuous structure can be observed at various compositions. The elasticity ratio was proposed to play an important role together with the viscosity on the phase inversion because PLA/PCL blend presents a high viscosity ratio between two components. Two emulsion models were used to predict the linear viscoelastic properties of the blend with various morphologies. The Palierne model gives better fit compared with the G–M model, but both fail to predict the viscoelastic properties of the co-continuous blend. The viscoelastic behavior of those blends shows different temperature dependence due to their different morphologies. The principle of time–temperature superposition (TTS) is only valid for the co-continuous blend while fails with the rheological data of those blends with discrete spherical and fibrous domain structure. Moreover, although the discrete phase is difficult to be broken up due to the high viscosity ratio of the systems, the change of viscoelastic responses of those blends before and after preshear shows large difference, indicating that different morphologies have different sensitivity to the steady shear flow.     

双酚A聚砜对PBT的结晶与多重熔化行为的影响

本文研究了PBT结晶的熔化行为及非晶性组分PSF的加入对PBT结晶度及熔化行为的影响。结果表明:PBT结晶熔化时的DSC双峰图为多重熔化行为而非多晶型的结果;PSF的加入对PBT结晶度影响不大,但对多重熔化行为有明显影响。此乃PSF无定形组分加入后,使PBT结晶速率减慢而形成更完善的PBT结晶之缘故。     

Effect of the liquid–liquid phase separation on the crystallization behavior and mechanical properties of poly(ethylene‐ran‐vinyl acetate) and paraffin wax blend

The effect of liquid–liquid phase‐separation (LLPS) on the crystallization behavior and mechanical properties of poly(ethylene‐ran‐vinyl acetate) (EVA) with various amounts of vinyl acetate and paraffin wax blend was investigated. The blend of EVA‐H (9.5% vinyl acetate) and the wax became homogeneous at temperatures greater than its upper critical solution temperature (UCST) (98°C), and an LLPS was observed between UCST and the melting point of 88°C for EVA‐H in the blend. The existence of the LLPS is attributed to the relatively large amount of the hydrophilic component of vinyl acetate in EVA, although the molecular weight of the wax was just 560. However, LLPS did not occur for the EVA/wax blend when the content of vinyl acetate in EVA was less than 3%. This behavior was explained by using the Flory–Huggins lattice model with an effective interaction parameter. The degree of crystallinity of EVA‐H in the EVA‐H/wax blend, judged from a melting endothermic peak in differential scanning calorimeter (DSC) thermograms obtained during heating runs, decreased with increasing duration time in the LLPS region. The flexural modulus of the EVA/wax blend became maximum at certain blend composition (about 30 ∼ 40 wt % EVA depending upon the amount of vinyl acetate). This behavior can be explained by the fact that this blend composition has the largest relative degree of crystallinity of EVA measured by DSC and wide‐angle X‐ray scattering method. We found that the flexural modulus of the binder itself is directly related to that of a feedstock consisting of larger amounts of metal powder and the binder, which can help someone to develop a suitable binder system for a powder injection molding process. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 1991–2005, 1999     

A closed-loop behavior of ternary polymer blends composed of three miscible binaries

Poly (methyl methacrylate) (PMMA) was known to be miscible with poly (vinyl phenol) (PVPh). According to literature, poly (vinyl cinnamate) (PVCN) was also miscible with PVPh. The miscibility between PMMA and PVCN was corroborated on the basis of preliminary experiments. Is a ternary blend consisting of PMMA, PVPh and PVCN miscible in all the blend compositions? To answer this question, the miscibility of this ternary was examined in different blend compositions mainly based on calorimetry data in this investigation. The results using two different molecular weights of PVPh demonstrated an interestingly closed-loop behavior of immiscibility. The reason is likely because of the “Δχ effect”.     

Cellulose acetate blends with acrylonitrile/N-phenyl maleimide copolymers morphological and thermal properties

Cellulose acetate (CA) was blended in different compositions with various acrylonitrile-N-halo phenyl maleimide (AN-XPhM) copolymers to improve the thermal and mechanical properties of cellulose acetate. The structure, morphology, thermal stability, and crystallinity of the blend films were characterized by infrared spectroscopy, scanning electron micrographs, thermogravimetry/differential thermal analysis, differential scanning calorimetry, and X-ray diffraction. The results revealed that the thermal stability was improved by the increase in AN-XPhM content, irrespective of the type of the N-halo phenyl maleimide. The CA/AN-4BrPhM blend films possessed the highest thermal stability compared to the other CA/AN-XPhM blend films. Blending CA with AN-4BrPhM yielded the most homogeneous blend films, irrespective of the composition ratio. The mechanical properties of various compositions of the CA/AN-4BrPhM blend films were also discussed.     

CELLULOSE ACETATE AND EPOXY RESIN BLEND ULTRAFILTRATION MEMBRANES: REPARATION,CHARACTERIZATION, AND APPLICATION

ABSTRACT

Membranes based on cellulose acetate used in ultrafiltration applications lack good, chemical, mechanical and thermal resistance. In order to prepare membranes with improved properties, modification of cellulose acetate with epoxy resin through solution blending was attempted. In the present work, the membrane casting solutions with different polymer blend compositions of cellulose acetate and diglycidyl ether of bisphenol-A (DGEBA) were prepared at 30±2°C. The maximum percent compatibility of the two polymers, cellulose acetate and diglycidyl ether of bisphenol-A, was estimated to be 60/40%. Ultrafiltration blend membranes based on various blend compositions were prepared, characterized in terms of compaction, pure water flux, water content, membrane hydraulic resistance and molecular weight cut-off. The application of these membranes, in rejection of proteins of various molecular weights, are discussed.     

Ternary upper-critical-solution-temperature behavior in a blend system comprising poly(2,6-dimethyl-1,4-phenylene oxide), poly(4-methyl styrene), and polystyrene

 Upper-critical-solution-temperature (UCST) behavior in a ternary blend of poly(2,6-dimethyl-1,4-phenylene oxide), poly(4-methyl styrene), and polystyrene is reported. The as-cast ternary blend is immiscible at ambient conditions and comprises two different phases, and, however, turns into a miscible system above the “clarity point” ranging from 160 to 300 °C for different ternary compositions. The maximum clarity point is labeled as the UCST for the ternary system, which is about 295 °C. Above the clarity point, the originally immiscible ternary blend turned into one miscible phase. Owing to the thermodynamic UCST behavior and kinetic hindrance, the immiscible ternary polymer blend can be locked into a pseudo-miscible state if it is heated to a temperature above the clarity point followed by a rapid-cooling processing scheme. The quenched ternary blend can remain in a pseudo-miscible state as long as the service temperature does not exceed the glass-transition temperature of the blend. Received: 17 July 2001 Accepted: 3 October 2001     

Viscosity of Blends of Pectins of Various Origins with Ethylene-Vinyl Acetate Copolymers

The rheological properties of ethylene-vinyl acetate copolymers of various compositions in blends with pectins of various origins (pectins recovered from apple pulp, watermelon peel, and citrus fruits) were studied. The degrees of swelling of blend films in water were measured.     

Photodegradation of polypropylene/polystyrene blends: Styrene-butadiene-styrene compatibilisation effect

The mutual influence between the PP/PS polymer blend components during UV photodegradation was studied. Polypropylene (PP) and polystyrene (PS) have different photodegradation mechanisms, due to the larger UV absorption of polystyrene and formation of more stable tertiary carbon radicals. To compare the stabilities the kinetics of carbonyl formation was measured in different blend compositions. The results show that polystyrene presented a faster carbonyl formation than polypropylene, while the blends display faster kinetics than the isolated components. The kinetics of carbonyl formation of the blends was a function of polypropylene content. This result is unexpected if one considers the behaviour of each component alone. The kinetics and mechanism of UV degradation can be only explained taking into account the interaction between the blend components. PS absorbs UV light and energy is transferred to PP, which produces more reactive tertiary carbon free radicals. The effect of the interaction between the domains is enhanced when a compatibiliser is used, corroborating the hypothesis of energy transfer.     

Phase behavior in mixtures of a homopolymer and a block copolymer. 4. SALS and SAXS studies

Phase behavior of blends of poly(vinyl methyl ether) (PVME) with four styrene-butadiene-styrene (SBS) triblock copolymers, being of various molecular weights, architecture, and compositions, was investigated by small-angle light scattering. Small-angle X-ray scattering investigation was accomplished for one blend. Low critical solution temperature (LCST) and a unique phase behavior, resembling upper critical solution temperature (UCST), were observed. It was found that the architecture of the copolymer greatly influenced the phase behavior of the blends. Random phase approximation theory was used to calculate the spinodal phase transition curves of the ABA/C and BAB/C systems; LCST and resembling UCST phase behavior were observed as the parameters of the system changed. Qualitatively, the experimental and the theoretical results are consistent with each other. © 1996 John Wiley & Sons, Inc.     

Cellulose acetate and polyetherimide blend ultrafiltration membranes: II. Effect of additive

Ultrafiltration membranes are largely applied in the separation of heavy metal ion and macromolecular solutes from aqueous streams. Studies are presented on ultrafiltration blend membranes, based on cellulose acetate (CA) and polyetherimide (PEI) in various blend compositions. Polyethylene glycol (PEG 600) was employed as a non‐solvent additive in various concentrations to the casting solution to improve the ultrafiltration performance of the resulting membranes. The blend membranes prepared were characterized in terms of compaction time, pure water flux (PWF), water content, membrane resistance, and scanning electron microscopy (SEM). The molecular weight cut‐off (MWCO) obtained from the protein separation studies is also reported. Applications of these membranes for separating toxic metal ions from aqueous streams are discussed. Copyright © 2007 John Wiley & Sons, Ltd.     

Studies on cellulose acetate-carboxylated polysulfone blend ultrafiltration membranes--Part I

Hydrophilic polysulfone ultrafiltration (UF) membranes were prepared from blends of cellulose acetate with carboxylated polysulfone of 0.14 degree of carboxylation. The effects of blend polymer composition on compaction, pure water flux, water content and membrane hydraulic resistance (R_m), have been investigated to evaluate the performance of the membranes. The performance of the blend membranes of various blend polymer compositions were compared with that of membranes prepared from pure cellulose acetate and blends of cellulose acetate and pure polysulfone. The hydrophilic cellulose acetate-carboxylated polysulfone blend UF membranes showed better performance compared to membranes prepared from pure cellulose acetate and blends of cellulose acetate and pure polysulfone.     

Tribochemical and thermal activation of α-c2s hydrate as precursor for cementitious binders

Co-pyrolysis characteristics of white pine and sub-bituminous coal blend were studied by thermogravimetric analysis (TG) and in a free fall reactor. The pyrolysis behavior of the blends at various biomass blending ratios was compared with that of the individual coal and biomass. The results from TG indicate that the interactions between the blends present an inhibitive effect on thermal decomposition, resulting in higher than expected char yields. In the free fall reactor, a positive synergy effect on tar production was observed under the higher biomass blending ratio. Moreover, the compositions of the gaseous products from the blends are not all in accordance with those of their parent fuels. The observed synergetic effects might be due to char-coal interactions in TG, while gas-coal interactions are preferred in free fall reactor.     

聚己内酯在聚己内酯/聚乙烯基甲基醚共混体系中的结晶研究

通过示差扫描量热(DSC)、广角X射线衍射(WAXD)、小角X射线散射(SAXS)研究了聚己内酯(PCL)/聚乙烯基甲基醚(PVME)共混体系中PCL的结晶行为.研究结果表明,共混聚合物中PCL的结晶度几乎不随体系的组成而发生变化.共混物中PVME的存在没有改变PCL的晶体结构,但是随着PVME含量的增加,片晶之间的距离则大,这主要是由于非晶层增厚引起的.