Function Of Blend Composition Research Articles

Quantitative characterization of dispersed particle size, size distribution, and matrix ligament thickness in polypropylene blended with metallocene ethylene–octene copolymers

AbstractThe average rubber particle size, size distribution, and matrix ligament thickness between particles in polypropylene blends containing metallocene catalyzed ethylene–octene copolymers have been quantitatively analyzed, as functions of blend composition and phase viscosity ratio. Comparison has been made between experimental data and those predicted from a number of theoretical models. All blends showed two‐phase morphology, with interestingly a bimodal distribution of the rubber particle size. The ranges and averages of rubber particle size were mainly determined by blend composition and viscosity ratio between the phases, irrespective of comonomer content along the rubber chains. The logarithmic relationship between the matrix ligament thickness and rubber concentration was observed. The values of ligament thickness obtained from the experiments and theoretical models were not in agreement. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 2140–2149, 2001

Blends of AB/BC Diblock Copolymers with a Large Interaction Parameter χ

Blends of poly(styrene)-b-poly(isoprene) (PS−PI) and poly(isoprene)-b-poly(ethylene oxide) (PI−PEO) were investigated by small-angle X-ray scattering, photon correlation spectroscopy, light microscopy, and rheology. Blends were prepared in which both diblocks had the same PI composition, f, and were investigated as a function of blend composition, Φ. We generally found a disordered one-phase region at high temperatures and two macrophase-separated, ordered phases at low temperatures. At low temperatures the only appreciable miscibility was found for f = 0.7 in the PI−PEO-rich phase. At intermediate temperatures we generally observed macrophase separation before microphase separation upon cooling. The macrophase separation boundary compared to the microphase boundary is lowered upon increasing f. For f = 0.6 and 0.7 we observe an adjustment of the d spacing of the macrophase-separated, ordered phases. The general trend of the phase behavior is described by a theory using the random phase approximation.

Molecular, Nanostructural and Mechanical Characteristics of Lamellar Triblock Copolymer Blends: Effects of Molecular Weight and Constraint

While theoretical and experimental efforts have thoroughly addressed microphase-ordered AB diblock copolymer blends with a parent homopolymer (hA or hB) or a second block copolymer, surprisingly few studies have considered comparable ABA triblock copolymers in the presence of hB or an AB diblock copolymer. In this study, we elucidate the roles of additive molecular weight and constraint by examining three matched series of miscible ABA/hB and ABA/AB blends. Self-consistent field theory is employed to analyze molecular characteristics, e. g., segmental distributions, microdomain periods and midblock bridging fractions, as functions of blend composition. Predictions are compared to morphological characteristics discerned by transmission electron microscopy and small-angle X-ray scattering. The corresponding mechanical properties of these blends are measured by dynamic mechanical analysis. The results of this comprehensive work reveal that addition of hB swells the B-lamellae of the ABA copolymer and has a generally deleterious effect on both the dynamic elastic modulus and midblock bridging fraction. In contrast, addition of a lamellar or cylindrical AB copolymer to the same ABA copolymer can promote an increase or decrease in lamellar period and bridging fraction, depending on relative block sizes.

Investigation of the phase structure of poly(3-hydroxybutyrate)/poly(vinyl acetate) blends by dielectric relaxation spectroscopy

Blends of poly(3-hydroxybutyrate) (PHB) and poly(vinyl acetate) (PVAc) were isothermally cold crystallized from homogeneous samples obtained by quenching. Dielectric relaxation spectroscopy has been used to investigate the glass–rubber relaxation characteristics and corresponding phase separation in cold-crystallized PHB/PVAc blends as a function of blend composition and crystallization conditions. All isothermally cold-crystallized blends displayed two glass–rubber relaxations corresponding to the coexisting of a mixed amorphous interlamellar phase, and a pure PVAc phase residing in interfibrillar/interspherulitic regions. No PHB relaxation was observed, indicating the absence of a pure crystal–amorphous interphase. The composition of the interlamellar phase was enriched in PVAc with increasing overall PVAc content in the blend. Lowering the crystallization temperature led to an increase in the amount of PVAc trapped in the interlamellar regions, which was consistent with kinetic control of the evolving morphology: as crystallization temperature decreased, the crystallization rate increased and the diffusion of PVAc molecules decreased. Comparison of the relaxation characteristics of interfibrillar/interspherulitic phase with those of pure PVAc indicated a much broader spectrum of local relaxation environments of PVAc in the blend, consistent with PVAc segregation across a wide range of size scales.

Miscibility in blends of poly (4-vinylpyridine)/poly (4-vinylphenol) as studied by 13C solid-state NMR

The miscibility of poly (4-vinylpyridine) (P4VP) with poly (4-vinylphenol) (PVPh) blends was investigated over a wide range of compositions by differential scanning calorimeter (DSC), Fourier transform infrared spectroscopy (FTIR), and high-resolution solid-state nuclear magnetic resonance (NMR) spectroscopy. DSC results show that the Tgs of the P4VP/PVPh blends are much higher than those of the calculated weight-average values. The proton spin–lattice relaxation times in the laboratory frame, T1(H), and the rotating frame, T1ρ(H), were studied as a function of blend composition. T1(H) and T1ρ(H) results demonstrate that the spin diffusion can completely average out the entire relaxation process. It was also found that the intimate mixing of the polymer blends restricts the local chain mobility.

Miscibility of poly(ethyl oxazoline)/poly(4-vinylphenol) blends as investigated by the high-resolution solid-state 13C NMR

The miscibility of poly(ethyl oxazoline) (PEOx) and poly(4-vinylphenol) (PVPh) blends were investigated by differential scanning calorimeter (DSC), Fourier-transform infrared spectroscopy (FTIR), and high-resolution solid-state nuclear magnetic resonance (NMR) spectroscopy. It was found that PEOx was miscible with PVPh as shown by the existence of single composition-dependent glass transition temperature ( T g) in the whole composition range. FTIR results revealed strong hydrogen bonding between the carbonyl groups of PEOx and the hydroxyl groups of PVPh. 13C cross-polarization (CP)/magic angle spinning (MAS)/dipolar decoupling (DD) spectra of the blends showed significant chemical shift changes, which support the FTIR results. The proton spin–lattice relaxation times in both the laboratory frame, T 1(H), and the rotating frame, T 1 ρ (H), were studied as a function of blend composition, and blends gave values longer than pure polymers. The T 1(H) results are in good agreement with the thermal analysis; i.e. the blends are completely homogenous on the scale of 30–40 nm. The T 1 ρ (H) results further indicate that the blends were homogenous on the scale of 2–3 nm.

Dynamics and Morphology in Nanostructured Thermoset Network/Block Copolymer Blends during Network Formation

Molecular dynamics and morphology in the blends of a network-forming reactive polymer and an amphiphilic block copolymer were examined as a function of the advancement of chemical reactions. In the blends containing a triblock copolymer, both microscopic (domains of the order of micrometers) and nanoscopic (domains of the order of nanometers) phase separations were observed during network formation. Interestingly, only nanoscopic phase separation was found in the blends containing a diblock copolymer. The shape and the origin of these nanoscopic features were investigated by atomic force microscopy and were found to be a function of blend composition. A concept was advanced of the three-phase nanostructured morphology that begins to form with self-assembly of one block and continues to develop during network formation in the postassembly stage. The changes in relaxation dynamics that accompany network formation were monitored by broad-band dielectric relaxation spectroscopy (DRS) and were shown to represe...

Cure kinetics and properties of epoxy/dicyanate blends

The cure behavior and properties of epoxy/dicyanate blends containing a stoichiometric amount of an amine curing agent for epoxide groups were investigated as a function of blend composition. Differential scanning calorimetry (DSC) was used to investigate the dynamic and isothermal cure behavior of the blends. The cure rate of the blend increased with increasing dicyanate content. A second order autocatalytic reaction mechanism described the cure kinetics of the blends. The kinetic parameters were determined by fitting the dynamic DSC data to the model kinetic equation. The κ 10 and E 1 values were mainly affected by the change of dicyanate content. The glass transition temperature of the blend decreased with increasing dicyanate content. The thermal decomposition characteristics of the blends were investigated by thermogravimetric analysis (TGA). Dynamic mechanical analysis (DMA) and thermal mechanical analysis (TMA) were used to investigate the mechanical properties of the blends. With increasing dicyanate content, the cure rate increased but the thermal and mechanical properties of the cured blends were not improved.

Model acrylate-terminated urethane blends in toughened epoxies: a morphology and stress relaxation study

Improved toughness of heat-cured epoxies is readily achieved through chemical incorporation of a flexible moiety that phase-separates from the epoxy matrix during thermal cure. Many commercial flexibilizers are inherently polydisperse, which yields dispersions composed of flexibilizer chains of variable length. In this work, we examine the effect of flexibilizer polydispersity on the morphology and stress relaxation behavior of a commercial epoxy. This is achieved by systematically varying the composition of binary and ternary flexibilizer blends of monodisperse acrylate-terminated urethanes differing in molecular weight. Field-emission scanning electron micrographs of fracture surfaces permit quantification of dispersion sizes as a function of blend composition. Tensile stress relaxation data from three-point bend tests performed under isothermal conditions are analyzed in terms of a biexponential model to discern fast and slow characteristic relaxation times.

The semicrystalline morphology of aliphatic–aromatic polyamide blends

The morphology of a series of melt-miscible blends based on the combination of (crystalline) polyamide (PA) 4,6 and (amorphous) PA 6I has been investigated as a function of blend composition and thermal history. Wide-angle X-ray scattering (WAXS) was used to determine the unit cell structure and crystallinity index in PA 4,6 and the blends: the introduction of PA 6I resulted in no change in unit cell parameters and a monotonic decrease in bulk crystallinity. Dynamic mechanical studies revealed the coexistence of two amorphous phases in the crystallized blends: a mixed phase held between the crystal lamellae (interlamellar) and a PA 6I-rich phase excluded to interfibrillar and interspherulitic regions. There was no evidence of a separate crystal–amorphous interphase layer comprised of pure PA 4,6. Transamidation reactions over longer melt times led to the apparent homogenization of the two amorphous populations owing to the formation of increasingly random copolymers.

Miscibility and free volume behaviour of a number of polymer blends containing only thermotropic liquid crystalline polymers

An extensive study has been undertaken on a number of blends containing only thermotropic liquid crystalline polymers (TLCPs) as only components. The effect of the structure of the TLCPs on their miscibility and free volume properties (probed by positron annihilation lifetime spectroscopy) is presented in this work. Although all TLCPs studied are nematic and the experience with low molecular weight liquid crystals is that a common mesophase ensures miscibility, blends of TLCPs with each other show a wide range of miscibilities. The polymeric aspects of TLCPs such as their molecular chemistry, structure and conformation are also found to be important in determining miscibility in blends of such materials. Regardless of their various miscibilities, TLCP blends tend to display smaller, fewer free volume sites than expected from a weighted average. This is ascribed to the intrinsic affinity of nematic TLCPs. This differs from thermoplastic blends where it has been found that degree of blend miscibility alters free volume behaviour as a function of blend composition.

Morphological Characterization of Blends of Metal-Sulfonated Poly(styrene) and a Methylated Poly(amide) by Solid State NMR

Various blends of atactic, low-MW (4000), metal-sulfonated poly(styrene) (MSPS) and a higher-MW (25 000) poly(amide) (PA) were studied by solid-state 13C and proton NMR techniques which include multiple-pulse irradiation, cross-polarization, and magic angle spinning. This study is an investigation of the morphology of these MSPS(n)/PA blends (n ) 100 mole fraction sulfonate ) 2.3, 7.0, or 11.9) as functions of blend composition and sulfonation level. Unsulfonated PS and PA are incompatible and phase separate. Decoration with sulfonate groups promotes mixing of the blend components owing to strong, polar metal-sulfonate/amide interactions. Metal ions used were divalent Zn (diamagnetic) and Cu (paramagnetic), the latter ions having a significant influence on the protons. The PA, N,N'-dimethylethylene sebacamide, was N-methylated to weaken interactions between PA chains, thereby promoting mixing. Pure PA is semicrystalline, and intimate mixing prevents PA crystallization. 13 C CPMAS spectra were used to assay PA crystallinity. The stability of the blend morphology in the presence of water was also studied since water is expected to modify or compete with the polar interactions of the blend. Many of the experiments performed relied, for their interpretation, on the phenomenon of proton spin diffusion. For ZnSPS(11.9)/PA blends, mixing was quite intimate and PA crystallinity was suppressed for PA mass fractions of 0.5 and lower. PA crystallinity first appeared with a PA mass fraction of 0.65; however, this crystallinity was not the result of large-scale phase separation of the PA from the MSPS. Rather, PA crystallinity develops in the mixed MSPS/PA phase in such a way that each PA crystallite is surrounded by a mixed MSPS/PA phase. Larger PA mass fractions gave higher PA crystallinities. When PA crystallinity is present, there is an average periodicity of about 20-25 nm; moreover, the noncrystalline regions surrounding each crystallite have nonuniform composition in the sense that there is a buffer zone adjacent to the PA crystallites which is mainly PA in composition. A few blends involving ZnSPS(7.0) and ZnSPS(2.3) were also studied. Only the 75/25 ZnSPS(7.0)/PA blend seemed well mixed and noncrystalline. Compositional heterogeneities on scales larger than 20 nm were seen in the remaining blends. Certain CuSPS ionomers and blends, analogous to the Zn-containing materials, were studied in an attempt to resolve some ambiguities present in the interpretation of the data taken for the Zn-containing materials. Zn and Cu ions show similar affinities for the amide moieties; hence, the morphology for analogous Zn- and Cu-containing blends is expected to be similar. Mainly proton longitudinal relaxation was measured because it is sensitive to the presence of paramagnetic Cu. Two matters were pursued for the Cu-containing materials: First, the uniformity of Cu distribution was probed in pure CuSPS(11.9). Our T1 H analysis gave a variation by a factor of 1.3 in averaged Cu concentration, where the averaging was done over dimensions of 14 nm. Second, given that the 75/25 CuSPS(2.3)/PA blend exhibits large-scale phase separation, where one phase contains nearly all of the PA plus a small fraction of the SPS, we addressed the question whether the level of decorations for the SPS chains in this mixed phase was significantly above the 2.3% average. Our analysis did not support such a claim within the assumption that the morphologies of the Zn- and Cu-containing blends are the same. Toward an evaluation of paramagnetic Cu ions as aids for the elucidation of morphology in organic systems, several qualitative characteristics of the proton and 13 C relaxation are noted for these Cu-containing materials. Also, an estimate of the electron relaxation time, T1 e , in CuSPS(11.9) is given as is the fraction (0.95) of observable protons using multiple-pulse techniques. T1 e is shown to vary strongly with overall Cu concentration in the pure ionomers and with the amount of water absorbed in the pure ionomer. T1 e also changes when Cu is bound to the amide moiety of PA. One cannot simply assume that

Thermal analysis of single-site polymers in binary blends of low-molecular-weight linear polyethylene and high-molecular-weight branched polyethylene

The cocrystallization phenomenon has been studied by blending a low-molecular-weight linear polyethylene (LPE) with a high-molecular-weight lightly branched ethylene–hexene copolymer, as a function of blend composition and cooling rate. The materials are based on single-site catalysts. Differential scanning calorimetry indicates that the upper limit on the degree of branches for cocrystallization with LPE is lower than observed in blends with Ziegler–Natta based materials, in accordance with results obtained by other authors on different single-site blend systems. The effect of the cooling rate on blends with low LPE content is probed, and the observed behaviour is discussed in light of earlier observations on similar blends.

A thermodynamic model for thermoset polymer blends with reactive modifiers

A new quantitative thermodynamic model for the prediction of phase equilibrium behaviour of thermoset-reactive modifier polymer blends has been developed. The model combines the Flory–Huggins lattice theory with a group contribution theory for the prediction of the thermodynamics evolution. The model predicts the free energy of mixing as a function of blend composition, temperature, and degree of polymerisation. The evolution during polymerisation of both the entropy and enthalpy of mixing has been taken into account. Moreover, the reactions of both the thermoset and the modifier have been considered in the model. The model successfully interprets the trends observed in chemically induced phase separation (CIPS). Binodal and spinodal lines are calculated and the window available for phase separation is predicted. The model was evaluated using a diglycidyl ether bisphenol-A epoxy cured with isophorone diamine, blended with epoxy functionalised dendritic hyperbranched polymers (HBP). This system underwent chemically induced phase separation during cure as revealed by cloud point measurements. Excellent agreement was obtained between the model and the experimental data when entropy and enthalpy variations associated with both the thermoset and the modifier cure were taken into account. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 1893–1902, 2000

Blends of poly(p-oxybenzoate-co-p-phenylene isophthalate) and polycarbonate: Miscibility and free volume behaviors

Blends of a thermotropic liquid crystalline polymer [poly(p-oxybenzoate-co-p-phenylene isophthalate)] (HIQ45) and a polycarbonate (PC) are studied with regard to their miscibility and free volume behavior. The glass transition temperatures (Tgs) of the blends are found to be uncharacteristically higher than those of the pure components, even increasing with the addition of the low-Tg component, HIQ45. Based on the non-appearance of the Tg of HIQ45 in the tanδ spectra of the blends and the observed homogeneous morphology of the blend, mixtures of HIQ45 and PC are concluded to be a miscible blend system. The free volume properties determined by positron annihilation lifetime spectroscopy show that close packing does not occur in these miscible blends as indicated by positive deviations in size and number concentration of free volume cavities from average values as a function of blend composition. The increase in free volume is attributed to the loss of liquid crystalline alignment of HIQ45 and disturbed packing of PC molecules due to intimate miscibility between different molecules. The free volume fraction index of the blend correlates well with measured blend density.

Effect of NR and EPDM on the rheology of HDPE/PP blends

We studied melt-rheological properties of ternary blends of polypropylene and high-density polyethylene with an elastomer (natural rubber or ethylene-propylene-diene), at several blending ratios and shear rates. Measurements made on a cone-plate rheometer are presented and discussed as a function of blend composition. The effect of the shear rate on the viscosity and flow curve is discussed in terms of the exponent of the power low for a non-Newtonian liquid. The addition of an elastomer to the polyolefins blends changes the shape of the viscosity-composition curve; this change is discussed in terms of the possible morphology of the blend.

New polymeric blends from hydrogenated styrene–butadiene rubber and polyethylene

New thermoplastic elastomeric blends based on hydrogenated styrene–butadiene rubber (HSBR) and low-density polyethylene (LDPE) were prepared by the melt blending technique. The rheology, structural and mechanical properties were measured as a function of blend composition. The HSBR/LDPE blend had a higher tensile strength, modulus, and work-to-break with low elongation at break compared with those of pure HSBR. X-ray diffraction studies demonstrated co-crystallisation and a remarkable increase in the degree of crystallinity. The improvement in the mechanical properties and the uniform morphology were correlated with the interfacial adhesion and compatibilisation of the HSBR/LDPE blend through ethylene segments. The experimental results for the HSBR/LDPE blends were compared with those for HSBR/high-density polyethylene (HDPE) and SBR/LDPE blends. The mechanical properties of the HSBR/LDPE blend were found to be superior. The results were explained on the basis of morphology and interaction.

Compatibility studies of polymer–polymer systems by viscometric techniques: nitrile-rubber-based polymer blends

Interactions in binary polymer systems have been analysed from the viscosity behaviour. Dilute solution viscosity measurements were made on three different ternary polymer (1)/polymer (2)–solvent (3) systems, i.e. acrylonitrile–butadiene rubber (NBR)/polystyrene, NBR/poly(styrene– co–acrylonitrile), NBR/poly(acrylonitrile– co–butadiene–styrene) in chloroform, as a function of blend composition. The polymer–polymer interaction parameter χ i(p–p) and the corresponding polymer–solvent interaction parameter χ i(p–s) were determined for all the blend systems. In order to predict compatibility, the interaction parameter term Δ b, obtained from modified Krigbaum and Wall theory, and the difference in the intrinsic viscosities of the polymer mixtures and the weight-average intrinsic viscosities of the two polymer solutions taken separately are used. These results were correlated with the experimentally determined densities and were found to be in agreement. Finally, the results are correlated with spectroscopic evidence.

Surface studies of poly(methyl methacrylate)/poly(styrene-co-acrylonitrile) blends

The surface properties of blends of poly(methyl methacrylate) (PMMA) with statistical copolymer of styrene and acrylonitrile having 28 wt% of acrylonitrile (SAN) have been studied as a function of blend compositions. The surface enrichment of PMMA was shown at all compositions of blends. Presented theoretical calculations well correlate with experimental data. Spinodal decomposition of the PMMA/SAN blend did not result in significant change in the surface tension measured for these blends. This is due to the weak enthalpic interaction between the blend constituents.

Poly(3-D(-)hydroxybutyrate)/atactic poly(methylmethacrylate) blends: Morphology, miscibility and crystallization relationships

The morphology, the phase structure and the crystallization processes of poly(3-D(-)hydroxybutyrate)/atactic poly(methylmethacrylate) blends, (PHB/aPMMA), have been investigated as a function of blend composition and thermal treatments. The two-phase separation processes (liquid/liquid demixing and liquid/solid separation) are in competition between each other. In the melt at T≥185°C, the system was homogeneous. During crystallization from the melt, liquid/liquid phase separation occurred before crystallization. After crystallization, three phases were present: a crystalline PHB phase; and two amorphous phases, one formed by amorphous PHB and the other by aPMMA. From the homogeneous glass state, however, crystallization preserved the homogeneity. The system, after cold crystallization, was composed of two phases: a crystalline; and an amorphous homogeneous phase. The addition of aPMMA always caused a decrease of the spherulite radial growth and overall crystallization rates. These results are attributed to the increase of energy related to the transport of the macromolecules in the melt, and in the case of cold crystallized samples, also to the diluent effect of aPMMA on the growth of PHB crystals.