Improved fracture toughness of immiscible polypropylene/ethylene-co-vinyl acetate blends with multiwalled carbon nanotubes

Functionalized multiwalled carbon nanotubes (f-MWCNTs) have been introduced into immiscible polypropylene/ethylene-co-vinyl acetate (PP/EVA) blends. Two different compositions, one (PP/EVA = 80/20) exhibits the typical sea-island morphology and the other (PP/EVA = 60/40) exhibits the cocontinuous morphology, have been prepared with different contents of f-MWCNTs. The impact measurement shows that f-MWCNTs induce the great improvement of fracture toughness of cocontinuous PP/EVA blends. The results based on the morphologies and the rheological properties of the composites suggest that, a local “single-network structure” of f-MWCNTs exists in PP/EVA (80/20) system whereas a “dual-network structure” of f-MWCNTs and EVA phase exists in PP/EVA (60/40) system, and the latter structure accounts for the largely improved fracture toughness of the composites.     

Morphology development in immiscible polymer blends

This paper presents the results obtained using a new method for analyzing polymer blend morphologies. The method is based on the selective solubilization of the matrix followed by a separation of the dispersed phase in suspension by filtering. A suspension of the nodular part going through the filter is obtained and can be analyzed with a particle counter. The other part of the dispersed phase retained by the filter is constituted of fibers. The average droplet diameters were compared with those obtained using a Scanning Electron Microscope on fracture surfaces for different compositions and flow conditions. The average diameter obtained with the counter technique increases with the dispersed phase content up to an optimum where simultaneously a decrease in the mean diameter and an increase of the fibrillar part are observed, which means that there is a concentration range where these two types of morphologies are present in the blends. The results indicates that the stability of the fibrillar part seems to determine whether the blend morphology will evolve into nodules by the Rayleigh mechanism or into phase inversion by coalescence of stable fibers.     

Reverse osmosis characteristics of cellulose acetate butyrate membranes

Cellulose acetate butyrate membranes were cast from five different formulations. The pure water flux through the membrane increased with evaporation period. The separation of 4000 ppm NaCl aqueous solution remained unchanged until it reached a critical flux; at that point, separation decreased inversely proportional to the flux. Scanning electron microscope photography of the membranes corresponding to each evaporation period is reported.     

The dynamics of montmorillonite clay dispersion and morphology development in immiscible ethylene-propylene rubber/polypropylene blends

The evolution of morphology during the melt compounding of polypropylene (PP), maleated ethylene-propylene rubber (EPR-g-MAn) and onium-ion exchanged montmorillonite clay (NR₄⁺-MM) is described. Irrespective of the ratio of components, clay partitions into the EPR-g-MAn phase exclusively, with significant amounts of mineral exfoliation occurring in the very early stages of compounding. These changes in filler distribution and dispersion are accompanied by reductions in the size of the dispersed PP phase, as the rate of droplet coalescence falls in response to an elevated EPR-g-MAn matrix viscosity. However, when NR₄⁺-MM is localized in a dispersed EPR-g-MAn phase, coalescence increases as a result of hindered particle break-up.     

Physical aging and biaxial creep in cellulose acetate butyrate

Torsional and tension-torsion creep studies have been performed on cellulose acetate butyrate at 65°C. The aging shift factor, μ, at this temperature has been determined to be 0.85. This is somewhat higher than 0.75 which was suggested as a maximum value for cellulose acetate butyrate (5). Axial stresses cause the torsional retardation times to become shorter. The change in retardation time is mainly determined by the magnitude of the axial stress and not by the length of time during which the axial stress is applied. Torsional stresses cause the axial retardation times to shift in a similar manner. The shifting of retardation times follows a maximum shear stress criterion.     

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     

Effect of a low-molecular-weight compatibilizer on the immiscible blends of cellulose acetate propionate and poly(butylene terephthalate)

Blends of poly(butylene terephthalate) (PBT) and cellulose acetate propionate (CAP) were found to be immiscible. In order to improve the interfacial strength and miscibility of the PBT/CAP blends, a low-molecular-weight poly(ethylene glycol) (PEG) was thus pre-mixed with the CAP to form the P-CAP mixture. It was then blended with the PBT up to 15 wt% using a twin-screw extruder to prepare the PBT/P-CAP blends, and subsequently processed into the films and fibers by compression-molding and melt-spinning, respectively. The thermal and dynamic mechanical analyses suggested that the PBT and CAP became partially miscible and the interfacial strength was thus improved in the PBT/P-CAP blends, owing to the addition of PEG. The PEG was not only miscible with the CAP but also with the PBT, and it served as a plasticizer as well as a compatibilizer. From the observation of the fractured surface of the PBT/P-CAP films, the PBT component was present as dispersed particles in the P-CAP matrix with size ranging from 1.4 to 3.0 μm; yet it became nanofiber in the spun fibers. Successful fibers of the PBT/P-CAP blends with an average diameter of 20 μm could be spun, where the tensile strength and elongation at break were in the range of 0.6?0.7 g/denier and 12?16%, respectively. Finally, the ultra-fine PBT nanofibers with diameters in the range of 50?70 nm were observed after removing the P-CAP matrix with acetone from the fibers, owing to the formation of PBT nanofibers during spinning and orientation processes. This method thus could successfully produce nano-scale PBT fibers with fineness comparable with the nanofibers developed via electrospinning technology.     

醋酸丁酸纤维素与聚丙烯酸乙酯共混体系的研究

通过差热分析和拉伸试验研究了醋酸丁酸纤维素CAB－35－1与聚丙烯酸乙酯（PEA）物理共混、半一互穿网络共混体系的相容性和力学性能，并用扫描电镜观察了共混物的形态。     

Compatibilization and morphology development of immiscible ternary polymer blends

We report a novel and effective strategy that compatibilizes three immiscible polymers, polyolefins, styrene polymers, and engineering plastics, achieved by using a polyolefin-based multi-phase compatibilizer. Compatibilizing effect and morphology development are investigated in a model ternary immiscible polymer blends consisting of polypropylene (PP)/polystyrene(PS)/polyamide(PA6) and a multi-phase compatibilizer (PP-g-(MAH-co-St) as prepared by maleic anhydride (MAH) and styrene (St) dual monomers melt grafting PP. Scanning electron microscopy (SEM) results indicate that, as a multi-phase compatibilizer, PP-g-(MAH-co-St) shows effective compatibilization in the PP/PS/PA6 blends. The particle size of both PS and PA6 is greatly decreased due to the addition of multi-phase compatibilizer, while the interfacial adhesion in immiscible pairs is increased. This good compatibilizing effect is promising for developing a new, technologically attractive method for achieving compatibilization of immiscible multi-component polymer blends as well as for recycling and reusing of such blends. For phase morphology development, the morphology of PP/PS/PA6 (70/15/15) uncompatibilized blend reveals that the blend is constituted from PP matrix in which are dispersed composite droplets of PA6 core encapsulated by PS phase. Whereas, the compatibilized blend shows the three components strongly interact with each other, i.e. multi-phase compatibilizer has good compatibilization between the various immiscible pairs. For the 40/30/30 blend, the morphology changed from a three-phase co-continuous morphology (uncompatibilized) to the dispersed droplets of PA6 and PS in the PP matrix (compatibilized).     

Multiphase materials with lignin. XV. Blends of cellulose acetate butyrate with lignin esters

Commercially available cellulose acetate butyrate (CAB, unplasticized) was blended in melt and solution with lignin esters having different ester substituents—acetate (LA), butyrate (LB), hexanoate (LH), and laurate (LL). All lignin esters formed phase‐separated blends with CAB with domain size depending on processing conditions and the interaction between phases depending on blend components. CAB/LA and CAB/LB revealed the strongest interactions with domain sizes on the 15–30 nm scale as probed by dynamic mechanical thermal analysis and differential scanning calorimetry. The glass transitions (T_g) followed the Fox equation. Broader transitions corresponding to the T_gs of the two parent components were observed for CAB blends with LH and LL. Transmission electron micrographs revealed differences in the phase dimensions of the blends in accordance with chemical and processing (i.e., melt vs solvent) differences. Modest gains in modulus were observed for low contents (<20 wt %) of LA and LB. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 448–457, 1999     

Phase continuity detection and phase inversion phenomena in immiscible polypropylene/polystyrene blends with different viscosity ratios

Blends of polypropylene (PP) and polystyrene (PS) were prepared in a twin-screw extruder and studied in a wide range of compositions. Phase continuity was first determined using selective solvent extraction. Subsequently, dynamic stress rheometry and dynamic mechanical analysis were used to detect the co-continuity and phase inversion compositions in the melt and the solid states. It appears that the phase inversion occurs in a domain rather than at a single point. The evaluation of the storage modulus of PP/PS blends in the melt at a constant low frequency gives information about the co-continuity, as far as the onset of co-continuity and phase inversion composition of the PS phase are concerned. The evaluation of the storage modulus and mechanical loss factor at a constant high temperature, or the glass transition temperature intensity allowed to precisely detect the phase inversion composition. The fractionated or bulk crystallization behavior of the crystallizable PP phase in the PP/PS blends can also be used to identify the matrix/dispersed phase or co-continuous phase morphology. Several semi-empirical models using the dynamic viscoelastic properties of blend components have been applied to detect the phase inversion composition. An extensive data set presented, can also be used to guide future modeling.     

Review on morphology development of immiscible blends in confined shear flow

The bulk dynamics of immiscible polymer blends during flow is relatively well understood, especially when the system contains Newtonian components. Recently, a number of studies have focused on flow of immiscible blends in confined geometries. In that case, the morphology development is not only affected by the material characteristics and the type of flow, but also by the degree of confinement. Here, we present an overview on the morphology development in immiscible two-phase blends in confined shear flow. Firstly, we focus on the typical microstructures that are observed in confined dilute blends. Secondly, in order to understand those peculiar morphologies, the systematic studies on single droplets in confined shear flow are reviewed. In addition to the experimental work, theoretical, phenomenological, and numerical models that include the effects of confinement are discussed.     

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.     

Spinnability of chitosan butyrate/cellulose acetate for obtaining a blend fiber

The production of chitosan fibers has remained of interest over the last decade. However, the copolymer structure of partially deacetylated chitosan generally lowers the dry/wet strength properties of chitosan fibers. There are numerous methods available for improving the mechanical properties of chitosan fibers, that is, the strain and stress to failure. In this work, the blending of chitosan with cellulose acetate is described. The chitosan is in the form of the butyrate ester, which, like cellulose acetate, is easily transesterified to regenerate the polysaccharide. The fibers obtained from codissolving cellulose acetate with chitosan butyrate are described. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Synthesis and characterization of interpenetrating networks from polycarbonate and cellulose acetate butyrate

Polycarbonates (PC) are currently used for organic optical glass; nevertheless they show a poor impact resistance which may be increased by combination with cellulose acetate butyrate (CAB) into a PC/CAB interpenetrating polymer network (IPN), without altering the material transparency as we show here. A series of rigid IPNs based on an aliphatic polycarbonate and CAB was prepared through in situ polymerization techniques. The kinetics of the formation of two networks in the IPNs were studied by FTIR spectroscopy. Effects of the CAB cross-linking and weight proportions of the two components in the IPNs were investigated by dynamic mechanical thermal analysis.     

Morphological studies on the blends of polyethyleneoxide and cellulose ethers

Summary The blends of the water soluble polymers, PEO/HPC and PEO/CMC show crystallization of PEO over a wide composition range. The crystallinity of the PEO fraction decreases drastically beyond an HPC concentration of 70%, whereas it persists throughout the composition range in the case of the blend with CMC. This leads to the conclusion that at low concentrations, PEO is more compatible with HPC than with CMC. The films of the blends exhibit a skin as seen in the cross-sections of the films. Calorimetric studies show that annealing above T_m of PEO or prolonged annealing below T_m causes disorder of the PEO crystalline domains. Student from Concordia University, under the Co-Op program     

Phase separation and morphology in ethylcellulose/cellulose acetate phthalate blends

This article discusses the phase separation and morphology of ethylcellulose/cellulose acetate phthalate blended films cast from methanol/methylene chloride (50/50 v/v) solvent mixture. The solvent system has been shown to be a cosolvent for CAP and a solvent/nonsolvent for EC. The two polymers have been shown to phase separate for all blend compositions via nucleation and growth. The morphology of these systems consists of a dispersion of broad size distribution of the minor component in a matrix of the major one. The formation of two layers due to coalescence of the dispersed phases and their eventual precipitation has been observed for the middle blend compositions. Finally, the phase separation in this system is discussed in terms of the Flory–Huggins theory and changes in the solvency mechanism during film casting. Enrichment of the solvent system in methanol at relatively early stages of film casting leads to changes in the system viscosity, relative chain conformation in solution, and chain diffusion. The effect of these parameters on the final morphology are discussed in terms of deviations from the equilibrium binodal decomposition.     

Mechanical compatibilization of immiscible blends

The mechanical properties of a variety of immiscible binary blends, with and without third component polymeric compatibilizers, are reviewed and qualitatively related to the degree of adhesion between blend components as determined by lap shear testing. Generally, blends comprised of components which adhere well, one to the other, show improved ductility relative to blends of components which do not adhere, Similarly, polymeric compatibilizers are found to be more effective for improving the properties of a binary blend system if they adhere well to both primary components of the immiscible mixture. These results suggest that adhesion between phases in the mixture strongly influences the ultimate properties of the blend. Some evidence is presented which suggests that components which adhere well are partially miscible.     

Evidence for cholesteric morphology in films of cellulose acetate butyrate by transmission electron microscopy

Summary Transmission electron microscopy provides direct evidence of helicoidal cholesteric morphology in films of cellulose acetate butyrate prepared by solvent casting from liquid crystalline solutions in dimethylacetamide. We believe this is the first observation reported of cholesteric structure in a mixed cellulosic ester. Cholesteric morphology was also observed in solvent cast blended films of cellulose acetate butyrate and lignin from liquid crystalline solutions. There are indications that lignin particles may be serving as nucleating surfaces or sites of direct termination for some of the observed cholesteric fingerprint pattern.