Studies on simultaneous crystallization of polypropylene/nylon 12 blends

The effect of the morphology of polypropylene (PP)/nylon 12 (PA12) blends on their crystallization behaviour is studied using differential scanning calorimetry and scanning electron microscopy. In PP/ maleated polypropylene (PP-MA)/PA12=65/10/25 blend, simultaneous phase (PA12) is smaller than 0.5 μm, PP crystallizes first and its crystals induce the crystallization of PA12. When some of the PA12 particles are larger than 0.5 μm, this part of PA12 crystallizes first. Then this part of the PA12 crystals induces the crystallization of PP, and PP crystals induced the crystallization of PA12 fine droplets in turn.     

Plasticizer effect on the melting and crystallization behavior of polyvinyl alcohol

The melting and crystallization behavior of polyvinyl alcohol (PVA) were examined as a function of plasticizer amount. The melting temperature (T_m) of PVA decreased with increasing the amount of glycerin. The effect of a plasticizer rapidly diminished when the phase separation of glycerin in PVA occurred. In addition, the crystallization peak temperature (T_c) of a fully hydrolysed PVA was reduced, and the maximum crystallization rate (K_max) was retarded, and the crystallite size distribution (ω_1/2) was widened. However, the crystallization behavior (T_c, K_max, ω_1/2) of a partially hydrolysed PVA could be disregarded compared with a fully hydrolysed PVA. The thermal history did not affect the crystallization behavior of a fully hydrolysed PVA, but largely affected that of a partially hydrolysed PVA. In a fully hydrolysed PVA / a partially hydrolysed PVA blend system, two T_m peaks appeared, and the concurrent crystallization occurred.     

Effects of annealing on the physico-chemical structure and permeation performance of novel hybrid membranes of poly(vinyl alcohol)/γ-aminopropyl-triethoxysilane

Novel organic–inorganic hybrid membranes of poly(vinyl alcohol) (PVA)/γ-aminopropyl-triethoxysilane (APTEOS) were prepared through a sol–gel approach in this study. The PVA/APTEOS hybrid membranes were characterized by a wide angle X-ray diffractometer (WXRD), scanning electronic microscope (SEM), themogravimetric analysis (TGA) and a contact angle meter to elucidate the effect of annealing temperature and time on the structure of the hybrid membranes. The swelling of the annealed hybrid membranes in an aqueous ethanol solution was investigated, and permeation performance of the annealed hybrid membranes was studied by pervaporation (PV) of 85 wt% ethanol aqueous solution. With annealing temperature or time increasing, both the swelling degree and the permeation flux of the hybrid membranes decreased, while water permselectivity increased. The interaction parameter of water with the membrane χ₁₃, and ethanol with the membrane χ₂₃ increased with annealing temperature and time increasing. The relation of the free volume with the permeation properties of the annealed hybrid membranes was studied by positron annihilation lifetime spectroscopy (PALS). And the diffusion behavior of water and ethanol in an aqueous ethanol solution through the hybrid membranes was analyzed by Maxwell–Stefan equation.     

Morphology investigation of transcrystallinity at polyamide 66/aramid fiber interface

The morphology of PA66/Kevlar‐129 fiber specimens was investigated by means of polarized optical microscopy and scanning electron microscopy. The results indicated that, at crystallization temperatures ranging from 100 to 220°C, the transcrystallinity (TC) interphase always occurs. Both the TC interphase and spherulite morphology were present under various crystallization conditions. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 91: 2980–2983, 2004     

Preparation of Portland Cement Components by Poly(vinyl alcohol) Solution Polymerization

The four components portland cement-dicalcium silicate, C₂S (Ca₂SiO₄); tricalcium silicate, C₃S (Ca₃SiO₅); tricalcium aluminate, C₃A (Ca₃Al₂O₆); and tetracalcium aluminate iron oxide, C₄AF (Ca₄Al₂Fe₃O₁₀)-were formed using a solution-polymerization route based on poly(vinyl alcohol) (PVA) as the polymer carrier. The powders were characterized using X-ray diffraction techniques, BET specific surface area measurements, and scanning electron microscopy. This method produced relatively pure, synthetic cement components of submicrometer or nanometer crystallite dimensions, high specific surface areas, as well as extremely high reactivity at relatively low calcining temperatures. The PVA content and its degree of polymerization had a significant influence on the homogeneity of the final powders. Two types of degree of polymerization (DP) PVA were used. Lower crystallization temperatures and smaller particle size powders were obtained from the low-DP-type PVA at optimum content.     

Thermal properties and phase morphology of melt‐mixed poly(trimethylene terephthalate)/poly(hexamethylene isophthalamide) blends

This work examines the thermal properties and phase morphology of melt‐mixed poly(trimethylene terephthalate) (PTT)/poly(hexamethylene isophthalamide) (PA 6I) blends. Two temperatures, i.e., 250 and 260°C, are used to prepare the blends, respectively. Differential scanning calorimetry results indicate the immiscible feature of the blends. It is thus concluded that the ester‐amide interchange reaction hardly occurred in the PTT/PA 6I blends. Depending on the composition and mixing temperature, the crystallization ability of PTT in the blends is either enhanced or hindered. Basically, a lower PA 6I content shifts the PTT melt crystallization to a higher temperature, whereas a higher PA 6I content causes an opposing outcome. The original complex melting behavior of neat PTT becomes more regular after the incorporation of 60 wt % or 80 wt % of PA 6I. Thermogravimetry analyses (TGA) show that the thermal stability of the blends improves as the PA 6I content increases. The two‐phased morphology of the blends is examined by scanning electron microscopy (SEM). Polarized light microscopy (PLM) results reveal that the PTT spherulites become coarser with the inclusion of PA 6I; only smaller/dispersed crystallites are observed in the blend with 20 wt % of PTT. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Miscibility behavior of polyamide 11/sulfonated polysulfone blends using thermal and spectroscopic techniques

Miscibility in a series of blends, derived from Polyamide 11 (PA 11) and sulfonated polysulfone (SPSF) with different sulfonation degrees, 20, 44 and 70% has been investigated using differential scanning calorimetry, dynamic mechanical analysis, Fourier transform infra-red (FT-IR) and Raman spectroscopy. The PA 11/SPSF(Na)_x blends were prepared by solution casting from dimethyl formamide (DMF). Differential scanning calorimetry has shown a melting point depression of the equilibrium melting point of PA 11. From the melting point data of the blends of PA 11 with the SPSF with a 70% degree of sulfonation, the value of the polymer–polymer interaction parameter χ₁₂ was found to be −1.1 at elevated temperatures where it was determined. Less negative values were obtained for the blends of SPSFs with lower degrees of sulfonation, indicating the role of the sodium sulfonate group to the observed miscibility. Dynamical mechanical analysis revealed a non single-phase system at lower temperatures, although the T_g of PA 11 phase is shifted to higher temperatures. FT-IR and FT-Raman spectroscopic techniques have been used to confirm the nature of the specific interactions involved.     

Effects of Poly(Vinyl Alcohol) Content and Calcination Temperature on the Characteristics of Unsupported Alumina Membrane

Abstract

Nonsupported alumina porous membranes without pinholes or cracks were prepared by the sol-gel process using aluminum sec-butoxide as the starting material. The effects of using different PVA contents at various calcination temperatures on the characteristics of the membrane were investigated by scanning electron microscopy and nitrogen sorption porosimetry. The results after calcining at 450°C for 5 hours showed that the range of pore size distributions increases with increasing PVA concentration. The active nucleus numbers of phase transition to α-alumina decreased as the content of PVA increased at about 1050°C. The morphology of unsupported alumina membranes was affected by the PVA concentration and calcination temperature.     

Study of the miscibility and crystallization behavior of poly(ethylene oxide)/poly(vinyl alcohol) blends

The miscibility and crystallization behavior of poly(ethylene oxide)/poly(vinyl alcohol) (PEO/PVA) blends were investigated by differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), and polarizing optical microscopy. Because the glass‐transition temperature of PVA was near the melting point of PEO crystalline, an uncommon DSC procedure was used to determine the glass‐transition temperature of the PVA‐rich phase. From the DSC and DMA results, two glass‐transition temperatures, which corresponded to the PEO‐rich phase and the PVA‐rich phase, were observed. It was an important criterion to indicate that a blend was immiscible. It was also found that the preparation method of samples influenced the morphology and crystallization behaviors of PEO/PVA blends. The domain size of the disperse phase (PVA‐rich) for the solution‐cast blends was much larger than that for the coprecipitated blends. The crystallinity, spherulitic morphology, and isothermal crystallization behavior of PEO in the solution‐cast blends were similar to those of the neat PEO. On the contrary, these properties in the coprecipitated blends were different from those of the neat PEO. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 1562–1568, 2004     

Synthesis of single-phase Ti3SiC2 powder

In this study, free 2Ti/2Si/3TiC powder mixture was heated at high temperatures in vacuum, in order to reveal the possibility for the synthesis of high Ti₃SiC₂ content powder. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used for the evaluation of phase identities and the morphology of the powder after different treatments. Results showed that almost single phase Ti₃SiC₂ powder (99.3 wt.%) can be synthesized by heat treatment with free 2Ti/2Si/3TiC powders in vacuum at 1210°C for about 3 h. The nucleation and growth of Ti₃SiC₂ within TiC particles was observed. The typical appearance of the formed Ti₃SiC₂ is equiaxed with particle size of 2–4 μm. Effects of temperature and heating time on the morphology and the particle sizes of the synthesized Ti₃SiC₂ powders are not obvious.     

原位增容PA6/PE-HD共混物的等温结晶动力学研究

采用差示扫描量热仪研究了原位增容聚酰胺6/高密度聚乙烯（PA6/PE-HD）共混物的等温结晶行为,采用Avrami方程分析了纯PA6和PA6/PE-HD共混物的等温结晶动力学,并通过Hoffman-Weeks方法计算出了共混物的平衡熔点。结果表明,二者的Avrami指数介于2.19~3.70之间,表明PA6晶体的生长方式为二维盘状生长和三维球晶生长并存,PE-HD的加入并没有影响PA6晶体的生长方式。偏光显微镜分析表明,纯PA6能够生成球晶,但加入PE-HD后,球晶尺寸明显变小,说明PE-HD的加入起到了异相成核的作用,加快了PA6的结晶过程。     

Structure and properties of polyamides‐epoxidized elastomers blends

Blends of aliphatic polyamides (PA6, PA66, and PA12), containing 0–15 wt % nonepoxidized or epoxidized elastomers (statistical copolymer butadiene–styrene BS/EBS or linear block copolymer styrene–butadiene–styrene SBS/ESBS) were investigated. For PA6‐elastomer blends, taken as an example, it was shown that with increasing blending time, mechanical properties of blends increase, especially, if ESBS copolymer is used. It can be treated as an indirect sign of reactions between components. It was also found that in blends considerable changes of glass temperatures of components occur. Polyamides in blends with elastomers have smaller heats of fusion in comparison with virgin polyamides. It testifies to hindering of PA crystallization by elastomers. In some cases, significant shifts of melting points are also observed. Measurements of water contact angle show that all blends have very similar values of contact angles, which are lower than those of virgin polyamides. Elastomer content does not also affect the blend water uptake. However, it depends on the polyamide and elastomer type contrary to contact angle. Highest water uptake changes are observed in blends of PA66, especially for epoxidized elastomers. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 1872–1879, 2006     

New high permeable polysulfone/ionic liquid membrane for gas separation

In this study, the effects of 1-Ethyl-3-methylimidazolium tetrafluoroborate ionic liquid on CO₂/CH₄ separation performance of symmetric polysulfone membranes are investigated. Pure polysulfone membrane and ionic liquid-containing membranes are characterized. Field emission scanning electron microscopy (FE-SEM) is used to analyze surface morphology and thickness of the fabricated membranes. Energy dispersive spectroscopy (EDS) and elemental mapping, Fourier transform infrared (FTIR), thermal gravimetric (TGA), X-ray diffraction (XRD) and Tensile strength analyses are also conducted to characterize the prepared membranes. CO₂/CH₄ separation performance of the membranes are measured twice at 0.3 MPa and room temperature (25 °C). Permeability measurements confirm that increasing ionic liquid content in polymer-ionic liquid membranes leads to a growth in CO₂ permeation and CO₂/CH₄ selectivity due to high affinity of the ionic liquid to carbon dioxide. CO₂ permeation significantly increases from 4.3 Barrer (1 Barrer=10^-10 cm³(STP)·cm·cm^-2·s^-1·cmHg^-1, 1cmHg=1.333kPa) for the pure polymer membrane to 601.9 Barrer for the 30 wt% ionic liquid membrane. Also, selectivity of this membrane is improved from 8.2 to 25.8. mixed gas tests are implemented to investigate gases interaction. The results showed, the disruptive effect of CH₄ molecules for CO₂ permeation lead to selectivity decrement compare to pure gas test. The fabricated membranes with high ionic liquid content in this study are promising materials for industrial CO₂/CH₄ separation membranes.     

Crystallization and morphological features of syndiotactic polystyrene induced from glassy state

Spherulitic growth rates and microstructure of syndiotactic polystyrene (sPS) cold-crystallized isothermally at various temperatures, T_c (115–240 °C), have been investigated by small-angle light scattering (SALS), optical microscopy and transmission electron microscopy. The derived activation energy for sPS chain mobility at the crystal growing front is 5.4 kJ/mol, which is relatively lower than that of isotactic polystyrene, 6.5 kJ/mol. In addition, the Hv scattering invariant (Q_Hv) measured by SALS on the crystallized sPS samples displays a pronounced minimum at 150 °C. Despite a wide range of T_c used, however, the sample crystallinity estimated by Fourier transformation infrared spectroscopy remains unchanged. Prior to crystallization, the correlation length derived from the Vv patterns on the basis of Debye–Bueche model is ca. 1.13 μm regardless of T_c used. Interconnected domains with a width of ca. 1.8±0.5 μm are readily observed in all the crystallized samples under phase contrast microscopy and the phase-separated structure is conserved within sPS spherulites whose diameters are increased with increasing T_c.

Based on the above facts, we conclude that the presence of a Q_Hv minimum is ascribed to the resultant events of the two competitive transitions i.e. liquid–solid crystallization, and liquid–liquid demixing resulting from the spinodal decomposition (SD). At lower T_c, the unstable SD transition overwhelms the crystallization. Despite the low chain mobility, the coarsening process driven by the interfacial energies has reached a certain level before crystalline nucleation takes place. At higher T_c, on the other hand, cold crystallization becomes the dominant process due to the enhanced chain mobility, leading to the suppression of ongoing SD coarsening process. At an intermediate T_c range, comparable competition of the phase separation and crystallization prohibits the development of ordered symmetry within spherulites, giving the presence of Q_Hv minimum.     

Novel polymer electrolyte membranes based on semi‐interpenetrating blends of poly(vinyl alcohol) and sulfonated poly(ether ether ketone)

In this work, the properties of novel ionic polymer blends of crosslinked and sulfonated poly(vinyl alcohol) (PVA) and sulfonated poly(ether ether ketone) (SPEEK) are investigated. Crosslinking and sulfonation of PVA were carried out using sulfosuccinic acid (SSA) in the presence of dispersed SPEEK to obtain semi‐interpenetrating network blends. PVA–SSA/SPEEK blend membranes of different compositions were studied for their ion‐exchange capacity, proton conductivity, water uptake, and thermal and mechanical properties. The hydrated blend membranes show good proton conductivities in the range of 10^?3 to 10^?2 S/cm. When compared with pure component membranes, the PVA–SSA/SPEEK blend membranes also exhibit improvement in tensile strength, tensile modulus, and delay in the onset of thermal and chemical degradation. Semi‐interpenetrating nature of the blends is established from morphology and dynamic mechanical analysis. Morphology of the membranes was studied using scanning electron microscopy after selective chemical treatment. The dynamic mechanical properties of the membranes are examined to understand the miscibility characteristics of the blends. The relative proportions of PVA and SPEEK and the degree of crosslinking of PVA–SSA are important factors in determining the optimum properties for the blend. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Mixed matrix membranes of sodium alginate and poly(vinyl alcohol) for pervaporation dehydration of isopropanol at different temperatures

Mixed matrix membranes of sodium alginate (NaAlg) and poly(vinyl alcohol) (PVA) containing 5 and 10 wt.% silicalite-1 particles were fabricated by solution casting method and the cured membranes were crosslinked with glutaraldehyde. These membranes were used in pervaporation (PV) dehydration of isopropanol at 30, 40, 50 and 60 °C. Membrane morphology was studied by scanning electron microscopy and universal testing machine to assess their mechanical strengths. Swelling results of the pristine and mixed matrix membranes were correlated with their PV performances. Selectivities of the mixed matrix membranes of NaAlg were 11,241 and 17,991 with the fluxes of 0.039 and 0.027 kg/m² h, respectively, for 5 and 10 wt.% silicalite-1 loadings. Corresponding values for mixed matrix membranes of PVA were 1295 and 2241, and 0.084 and 0.069 kg/m² h, respectively, for 10 wt.% water-containing feed at 30 °C. Pristine membranes of NaAlg and PVA exhibited lower selectivities of 653 and 77 with increased fluxes of 0.067 and 0.095 kg/m² h, respectively. From the temperature dependence of flux and diffusivity data with 10 wt.% water-containing feed, Arrhenius plots were constructed to compute heat of sorption, ΔH_s values. Mixed matrix membranes of NaAlg were better than PVA mixed matrix membranes at all compositions (10-40 wt.%) of water. Molecular dynamics (MD) simulation was employed to compute the interfacial interaction energies of NaAlg and PVA polymers with silicalite-1 filler; also sorption of liquid molecules was computed. Simulated diffusivities compared well with the experimental data. Thermodynamic treatment of sorption, diffusion and permeation processes was attempted based on the Flory-Huggins theory to explain the PV performances of the membranes.     

Morphology and mechanical property changes in compatibilized high density polyethylene/polyamide 6 nanocomposites induced by carbon nanotubes

Addition of carbon nanotubes to immiscible polymer blends with co‐continuous morphology features to improve the electrical conductivity has attracted much attention in recent years; however, less attention has been paid to the effect of carbon nanotubes on the morphology and corresponding physical properties of immiscible polymer blends with typical sea‐island morphology. In this work, therefore, functionalized multiwalled carbon nanotubes (FMWCNTs) were introduced into an immiscible high density polyethylene/polyamide 6 (HDPE/PA6) blend which was compatibilized by maleic anhydride grafted HDPE (HDPE‐MA). The distribution of FMWCNTs and the phase morphologies of the nanocomposites were characterized using scanning electron microscopy and transmission electron microscopy. The crystallization and melting behaviors of the components were analyzed by differential scanning calorimetry, which is thought to be favorable for an understanding of the distribution of FMWCNTs. It is interesting to observe that the morphology of PA6 particles is very dependent on the method of preparation of the nanocomposites. Correspondingly, FMWCNTs exhibit an apparent reinforcement effect and/or an excellent toughening effect for the compatibilized HDPE/PA6 blend, depending upon their distribution state and the variation of PA6 morphology. This work proves that FMWCNTs have a potential application in further improving the mechanical properties of compatibilized immiscible polymer blends. Copyright © 2012 Society of Chemical Industry     

Effects of Sn residue on the high temperature stability of the H_2-permeable palladium membranes prepared by electroless plating on Al_2O_3 substrate after SnCl_2–PdCl_2 process: A case study

The stability of composite palladium membranes is of key importance for their application in hydrogen energy systems. Most of these membranes are prepared by electroless plating, and beforehand the substrate surface is activated by a SnCl_2–PdCl_2 process, but this process leads to a residue of Sn, which has been reported to be harmful to the membrane stability. In this work, the Pd/Al_2O_3 membranes were prepared by electroless plating after the SnCl_2–PdCl_2 process. The amount of Sn residue was adjusted by the SnCl_2 concentration, activation times and additional Sn(OH)_2coating. The surface morphology, cross-sectional structure and elemental composition were analyzed by scanning electron microscopy(SEM), metallography and energy dispersive spectroscopy(EDS), respectively. Hydrogen permeation stability of the prepared palladium membranes were tested at450–600 °C for 400 h. It was found that the higher SnCl_2 concentration and activation times enlarged the Sn residue amount and led to a lower initial selectivity but a better membrane stability. Moreover, the additional Sn(OH)_2coating on the Al_2O_3 substrate surface also greatly improved the membrane selectivity and stability.Therefore, it can be concluded that the Sn residue from the SnCl_2–PdCl_2 process cannot be a main factor for the stability of the composite palladium membranes at high temperatures.     

Transient liquid phase bonding of alumina to alumina via boron oxide interlayer

Alumina bulks coated with 3 μm boron oxide layer were bonded at various temperatures and times in air. The joining strength, interfacial compounds and morphologies of cross-sections and fracture surfaces were investigated by means of four-point bending, X-ray diffraction and scanning electron microscopy. The maximum bending strength is 71 MPa for alumina bonded at 800 °C for 15 h. The layered metastable phase of 3Al₂O₃---B₃O₃ forms at the beginning of joining at temperature above 700 °C. This interlayer transforms into a whisker structure consisting of 2Al₂O₃---B₃O₃ and 9Al₂O₃---2B₃O₃ with increasing temperature and time. Models for the growth and morphology of these interfacial compounds are proposed.     

Isothermal crystallization kinetics and melting behavior of in situ compatibilized polyamide 6/Polyethylene-octene blends

We developed in situ compatibilization technology to improve the compatibility between polyamide 6 (PA 6) and polyethylene-octene (POE). In the present work, we investigated the isothermal crystallization and melting behavior of PA 6/POE blends using differential scanning calorimetry (DSC). All specimens exhibited double melting peaks at lower temperature and single melting peaks at higher temperature. The Avrami exponent and equilibrium melting temperature were obtained by analysis of DSC experimental data using the Avrami equation and Hoffman-Weeks theory, respectively. It has demonstrated that the crystallization model of PA 6 for all specimens might be a mixture with two-dimensional, circular, three-dimensional growth with thermal nucleation. We further calculated the nucleation parameter (K _g ) from the obtained crystallization kinetics data using Lauritzen-Hoffmann equation. It was found that the K _g values of the compatibilized PA 6 were lower than that of pure PA 6 whereas increased with the increase of POE content, which was related to the better dispersion of POE and the interaction between PA 6 and the in situ formed POE-g-MAH. Additionally, the spherulite morphology was observed by polarized optical microscopy (POM).