Oriented structure in stretched isotactic polypropylene melt and its unexpected recrystallization: optical and X‐ray studies

At an extremely small extrusion rate, an isotactic polypropylene melt was extruded through a slit die of an extruder. Simultaneously, the extruded melt was stretched at various stretching rates (SRs) at the die exit. The oriented structure and its subsequent recrystallization via self‐seeding were investigated using polarized optical microscopy, two‐dimensional wide‐angle X‐ray scattering and small‐angle X‐ray scattering. As expected, much slenderer and denser oriented structures were formed at larger SR, which indicates that orientation is preferably promoted with increasing SR. In the case of the crystalline morphology developed during recrystallization, a shish kebab‐like structure was retrieved via the surviving oriented structure after annealing. Unexpectedly, for the sheet stretched at higher SR, a mainly sparse and short shish kebab structure was observed. For the sheet stretched at lower SR, a dense and long shish kebab structure was observed. This suggests that the oriented structure in the sheet stretched at lower SR has a better thermal stability than that in the sheet stretched at higher SR. This is discussed based on the relaxation of entangled junctions in the stretched networks with respect to varying chain length. Copyright © 2011 Society of Chemical Industry     

Extrusion of polyethylene/polypropylene blends with microfibrillar‐phase morphology

Extrusion of immiscible polymers under special conditions can lead to creation of microfibrillar‐phase morphology, ensuring significant increase of mechanical properties of polymer profiles. Polyethylene/polypropylene blend extrudates with microfibrillar‐phase morphology (polypropylene microfibrils reinforcing polyethylene matrix phase) were prepared through continuous extrusion with semihyperbolic‐converging die enabling elongation and orientation of microfibrils in flow direction. Structure of extruded profiles was examined using electron microscopy and wide‐angle X‐ray scattering. Tensile tests proved that extrudates with microfibrillar‐phase morphology show significantly higher mechanical properties than the conventional extrudates. The presented concept offers possibility of replacing the existing expensive multi‐component medical devices with fully polymeric tools. POLYM. COMPOS., 31:1427–1433, 2010. © 2009 Society of Plastics Engineers     

Influence of cooling rate on the thermal behavior and solid‐state morphologies of polyhydroxyalkanoates

The influence of cooling rates on the thermal behavior and solid‐state morphologies of polyhydroxyalkanoates have been investigated. The thermal behavior was studied by differential scanning calorimetry (DSC). The crystal structures (～ Å), lamellar (tens of nanometers), fibrillar (several hundred nanometers), and spherulitic (～ μm) morphologies of poly (3‐hydroxybutyrate) (PHB) and the copolymers of poly (3‐hydroxybutyric acid‐co‐3‐hydroxyvaleric acid) (PHBV) and poly (3‐hydroxybutyric acid‐co‐3‐hydroxyhexanoic acid) (PHBHx) crystallized under different cooling rates were studied using simultaneous small angle X‐ray scattering (SAXS) and wide angle X‐ray scattering, simultaneous ultra small angle X‐ray scattering (USAXS) and SAXS, and polarized optical microscopy, respectively. The experimental results showed that the lamellar and spherulitic morphologies depended strongly on cooling rates. However, there was little influence of cooling rates on the crystal structures. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Tensile properties and morphological evolution of polypropylene and poly(ethylene‐co‐1‐octene) blends

Extruded sheet of isotactic polypropylene and poly(ethylene‐co‐1‐octene) blends extruded from a counterrotating twin‐screw extruder were studied by scanning electron microscopy, tensile test, and small‐angle X‐ray scattering. The average characteristic length (Λ_m) determined by the statistical computing from the SEM images increases linearly with increasing of dispersed phase concentration. When POE content is 50 wt% (double continuous phase), Λ_m is two or three times as big as that of other blends ratio. The analyses of SAXS data confirm this result. Comparison has been made between experimental data of tensile test and those predicted from several meso‐mechanical models such as parallel model, series model, Halpin's model, Mori‐Tanaka's model, and modified mixture model. The modified mixture model is an effective method for predicting Young's modulus in comparison with other models. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers     

Polyurethane/acrylate hybrids: Effects of the acrylic content and thermal treatment on the polymer properties

Polyurethane (PU)/acrylate hybrids with different acrylic contents (10, 30, 50, 70, and 90 wt %) were prepared by the polymerization of acrylic monomers in the presence of preformed PU chains with polymerizable terminal vinyl groups. Films obtained by the casting of polymer dispersions before and after thermal annealing were characterized by dynamic light scattering, Fourier transform infrared spectroscopy, transmission electron microscopy (TEM), TEM electron energy‐loss spectroscopy, differential scanning calorimetry, and gel fraction determination. Small‐angle X‐ray scattering (SAXS), wide‐angle X‐ray scattering, mechanical properties testing, atomic force microscopy, water contact angle testing, Buchholz hardness testing, and roughness testing of the films were also performed. The effects of the acrylic content and thermal treatment on the structure and properties were determined. TEM showed that a core–shell morphology was formed during polymerization. When the acrylic content increased, smaller particles without core–shell morphologies were observed. TEM energy‐loss spectroscopy studies confirmed this observation. Systems with up to 50 wt % acrylic component were homogeneous, as determined by SAXS, before and after thermal annealing. An attempt to incorporate a higher amount of acrylic component led to phase‐separated materials with a different morphology and, therefore, different properties. The relationship between the acrylic content and properties did not follow linear behavior. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Spray‐dried microspheres as a route to clay/polymer nanocomposites

A new strategy for the preparation of well‐dispersed clays in a polymer matrix by a spray‐drying method is presented. Scanning electron microscopy and transmission electron microscopy measurements show that the spray‐drying process produces clay/polymer microspheres in which the clay is trapped in a well‐dispersed state throughout the polymer matrix. The microspheres have been successfully extruded into clay/poly(methyl methacrylate) nanocomposite bulk structures without any perturbation of the well‐dispersed clay nanostructure in the original microspheres. Transmission electron microscopy and small‐angle X‐ray scattering show that the clay particles in the extruded materials range from single platelets to simple tactoids composed of a few stacked clay platelets, indicating an excellent degree of dispersion. The results show that sprayed microspheres are very good precursors for further processing such as extrusion or melt blending with other polymers for bulk nanocomposite fabrication. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Structure and characterization of poly[(vinylidene fluoride)‐co‐hexafluoropropene]–(dibutyl phthalate) blends

Blends of poly[(vinylidene fluoride)‐co‐hexafluoropropene] with dibutyl phthalate were examined by wide‐ and small‐angle X‐ray scattering, differential scanning calorimetry and dynamic mechanical spectroscopy, in order to study the influence of amount of plasticizer and the crystallization rate on the crystallinity and lamellar morphology of the copolymer. The dibutyl phthalate seems, at least for the cooling and heating rates used, simply to dilute the crystalline phase without affecting the amount of polymer that is able to crystallize. Furthermore, the small‐angle X‐ray scattering technique points out that the plasticizer mostly enters the amorphous phase either outside or inside the lamellar stacks. © 2001 Society of Chemical Industry     

The effects of crystallization condition on the microstructure and thermal stability of istactic polypropylene nucleated by β‐form nucleating agent

This article deals with the crystallization behaviors of original (prepared in a torque rheometer), DSC crystallization and mold crystallization (quenching and slow nonisothermal crystallization) of isotactic polypropylene (iPP) mixed with β‐form nucleating agent. The microstructure and thermal stability of these samples were investigated. The wide angle X‐ray diffraction (WAXD) results indicate that fast cooling is favorable for β‐form iPP formation. With slower cooling rate and higher concentration of nucleating agent, the lamellar thickness and stability of crystal0s were enhanced. Polarized optical microscopy (POM) and scanning electron microscopy (SEM) both showed that rapid crystallized samples gave rise to tiny spherulites, whereas under slow crystallization condition, nucleated samples could be fully developed in the form of dendritic or transcrystalline structures, depending on the nucleating agent concentration. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Spherical calcium phosphate nanoparticle fillers allow polymer processing of bone fixation devices with high bioactivity

Treatment of bone defects generally requires a fixation device. Biodegradable implants can often prevent second operations in contrast to metallic implants that are surgically removed after healing. In this study, we investigate the preparation of a bone fixation device with additional bioactivity by adding nanoparticulate amorphous tricalcium phosphate (ATCP) to improve bonding to bone. Medically approved poly(lactide‐co‐glycolide) (PLGA) and spherical (ATCP) nanoparticles were blended directly or through a two‐step approach, where ATCP was first dispersed in PLGA by solvent casting, extruded and hot pressed producing blocks and bone screws. The latter route yielded good particle dispersion while blending alone led to inhomogeneous mixtures. Samples were immersed in simulated body fluid and showed rapid formation of surface hydroxyapatite layers (examined by X‐ray diffraction and scanning electron microscopy) already after 3 days, thus confirming very high bioactivity. Polymer degradation during processing and upon simulated implantation conditions was followed by gel permeation chromatography. The elevated temperature during extrusion was the strongest single factor contributing to PLGA degradation. Screws could be machined out of extruded cylinders and demonstrated the ability to process PLGA/ATCP 90/10 composites with regular workshop tools. These properties suggest the use of such composites as improved, bioactive, and degradable bone fixation systems particularly in oral and maxillofacial surgery. POLYM. ENG. SCI., 2010. © 2009 Society of Plastics Engineers     

Effect of processing conditions on the yield and failure response of an aliphatic polyketone terpolymer

The effect of processing conditions on the yield and failure behavior of an aliphatic polyketone terpolymer was studied. Testing and characterization were performed on samples that were extruded in the form of hollow cylinders. We performed the extrusion process at different shear rates and at different cooling rates to assess the effect that process conditions had on the polymer properties. We performed biaxial testing on the samples to characterize the failure envelopes, including the ductile–brittle transition condition for each process condition. The effect of shear rate was negligible, whereas the cooling rate significantly affected the failure behavior. To explain these differences in behavior, we performed characterization via differential scanning calorimetry, wide‐angle X‐ray diffraction, attenuated total reflection IR spectroscopy, dynamic mechanical thermal analysis, scanning electron microscopy, and residual stress measurements. A broad glass transition was found for all samples at temperatures higher than previously reported for this material. Alteration of the processing conditions did not influence the crystalline phase (percentage crystallinity, crystalline orientation, crystallite size, etc.). A change in spherulitic structure was also observed with altered cooling rate and is suggested to have contributed to the change in failure behavior. Residual stresses also affected the behavior of all samples. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 318–334, 2002; DOI 10.1002/app.10334     

Synthesis and characterization of nanocomposites of silicon dioxide and polyurethane and epoxy resin interpenetrating network

Nanocomposites with varying concentrations of nanosized silicon dioxide particles were prepared by adding nanosilica to interpenetrating polymer networks (IPN)s of polyurethane and epoxy resin (PU/EP). The PU/EP IPNs and nanocomposites were studied by dynamic mechanical analysis, scanning electronic microscopy, wide‐angle X‐ray diffraction and small‐angle X‐ray scattering. The result showed that adding nanosize silicon dioxide can improve the properties of compatibility, damping and phase structure of IPN matrices. Copyright © 2003 Society of Chemical Industry     

Phase behavior and morphology in blends of poly(L‐lactic acid) and poly(butylene succinate)

Blends of poly(L ‐lactic acid) (PLA) and poly(butylene succinate) (PBS) were prepared with various compositions by a melt‐mixing method and the phase behavior, miscibility, and morphology were investigated using differential scanning calorimetry, wide‐angle X‐ray diffraction, small‐angle X‐ray scattering techniques, and polarized optical microscopy. The blend system exhibited a single glass transition over the entire composition range and its temperature decreased with an increasing weight fraction of the PBS component, but this depression was not significantly large. The DSC thermograms showed two distinct melting peaks over the entire composition range, indicating that these materials was classified as semicrystalline/semicrystalline blends. A depression of the equilibrium melting point of the PLA component was observed and the interaction parameter between PLA and PBS showed a negative value of ?0.15, which was derived using the Flory–Huggins equation. Small‐angle X‐ray scattering revealed that, in the blend system, the PBS component was expelled out of the interlamellar regions of PLA, which led to a significant decrease of a long‐period, amorphous layer thickness of PLA. For more than a 40% PBS content, significant crystallization‐induced phase separation was observed by polarized optical microscopy. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 647–655, 2002     

Structure and properties of composite antibacterial PET fibers

Poly(ethylene terephthalate) (PET) had been compounded with antibacterial materials for preparing antibacterial masterbatch using a twin‐screw extruder. Composite antibacterial PET fibers were prepared using the antibacterial masterbatch and pure PET resin by high‐speed melt‐spinning device, with spinning rate 3500 m/min. The antibacterial PET fibers of 5 wt % antibacterial materials were very effective against tested germs, with antibacterial ratios more than 90%, and had well mechanical properties. Scanning electron microscopy micrograph shows that antibacterial materials have been well dispersed in PET matrix. Microstructure of composite antibacterial fibers was studied by X‐ray diffraction, and the nucleating effect of antibacterial materials in the cooling crystallization process of PET was confirmed by differential scanning calorimetry (DSC). Result of thermogravimetry (TG) result shows that the addition of antibacterial materials accelerated the degradation of PET. The aged properties of antibacterial fibers were evaluated. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Structure of blown films of polyethylene/polybutene‐1 blends

The structure of blown films of blends of low‐density polyethylene (PE‐LD) and isotactic polybutene‐1 (iPB‐1) with different content of iPB‐1 was investigated using wide‐ and small‐angle X‐ray scattering (WAXS and SAXS), transmission electron microscopy (TEM), and polarizing optical microscopy (POM). TEM proves formation of a matrix–particle phase structure due to immiscibility of the blend components. Within the iPB‐1 particles, needle‐like crystals with c‐axis orientation were observed. The PE‐LD matrix showed two populations of crystals. WAXS data indicate that the majority of crystals were oriented with the c‐axis perpendicular to machine direction (MD), while SAXS data prove additional presence of stacks of lamellae, oriented parallel to MD. Quantitative birefringence measurements showed that the majority of molecule segments were oriented in the direction of the circumference of the film, confirming the WAXS data. The crystal orientation has direct impact on mechanical properties, which was demonstrated by measurement of the anisotropy of the modulus of elasticity. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers     

Studies on morphology and interphase of poly(butylene terephthalate)/carbon nanotubes nanocomposites

The microstructure of poly(butylene terephthalate) (PBT) nanocomposites was investigated by simultaneous small angle X‐ray scattering/wide angle X‐ray scattering (SAXS/WAXS) measurements at room temperature. The PBT was observed to crystallize in the α‐phase. The dispersion of single‐wall carbon nanotubes (SWCNTs) in PBT, using in situ polymerization, materials with higher degree of crystallinity than neat PBT were produced. SAXS results indicated that the SWCNT may be preferentially distributed in the amorphous phase of PBT, although WAXS results suggested a nucleation ability of SWCNT, which was supported by the DSC results. Much more complex changes were induced by the dispersion of multiwall carbon nanotubes (MWCNTs) in the PBT matrix. Evidence for the formation of an interphase with restricted chain mobility were found by dynamical mechanical thermal analysis (DMTA). Differential scanning calorimetry (DSC) and WAXS showed an increase of the crystallinity of the nanocomposites in comparison to neat PBT. POLYM. ENG. SCI., 50:1571–1576, 2010. © 2010 Society of Plastics Engineers     

Preparation and characterization of transparent poly(methyl methacrylate)/Na+‐MMT nanocomposite films by solution casting

Films of poly(methyl methacrylate) (PMMA)/sodium montmorillonite (Na⁺‐MMT) nanocomposites have been successfully prepared utilizing Na⁺‐MMT by N,N‐dimethylformamide solution casting. The nanocomposite films show high transparency, enhanced thermal resistance, and mechanical properties in comparison with the neat polymer film. The transparency of the films was investigated by UV‐vis spectra. The exfoliated dispersion of Na⁺‐MMT platelets in nanocomposites were investigated by X‐ray diffraction and transmission electron microscopy. The enhanced thermal resistance and mechanical properties of PMMA were studied by thermal gravimetric analysis and dynamic mechanical analysis, respectively. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Stereoselective Behavior of Nafion® Membranes towards (+)‐α‐Pinene and (−)‐α‐Pinene

α‐Pinene enantiomers were sorbed in Nafion® membranes. The membranes included a commercial extruded Nafion® 115 membrane as well as membranes prepared by casting a Nafion® solution, evaporating the solvent, and a thermal treatment at different temperatures. The microstructure of membranes was studied by small‐angle and wide‐angle X‐ray scattering, and magic‐angle spinning nuclear magnetic resonance spectroscopy. The change of membrane weight during the sorption process was determined with a sorption microbalance. Noticeable differences concerning the sorption behavior of the various membranes could be stated. The sorption of (+)‐α‐pinene and (?)‐α‐pinene in an extruded Nafion® membrane turned out to be rather low.     

Stress‐induced crystallization of biaxially oriented polypropylene

The hot stretching of thick, extruded sheets at high temperatures is a very important process in the production of finished biaxially oriented polypropylene (BOPP) films with special inner structures. Through a simulation of hot stretching in the machine direction (MD) of the processing of BOPP films, it was found that at high temperatures, the stretching ratio greatly influenced the obtained crystalline structure, as observed by differential scanning calorimetry (DSC). Also, in MD hot stretching, the crystallinity increased by an average of 20%. Wide‐angle X‐ray diffraction patterns of extruded sheet samples with and without stretching confirmed the structural changes shown by DSC, and the results proved that β‐crystal modification did not occur during the MD hot‐stretching process. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 686–690, 2003     

High‐pressure induced formation of isotactic polypropylene mesophase: Synergistic effect of pressure and pressurization rate

The crystallization induced by high pressures up to 2 GPa was studied for isotactic polypropylene (iPP) using wide angle X‐ray diffraction, small angle X‐ray scattering, and atomic force microscopy methods. The iPP mesophase can be induced at 200°C by high pressures with fast pressurization rate. A pressure–pressurization rate kinetic phase diagram of mesophase and γ‐phase was established to systematically analyze the influences of pressure and pressurization rate on crystallization polymorphism. Under pressure not higher than 0.75 GPa, only γ‐phase is formed, even the pressurization rate reaches 5 × 10³ MPa/s. With increasing pressure to 1.0 GPa, the mesophase is possible to be generated. As pressure further increases to 1.5 GPa and higher, the pure mesophase system can be obtained for pressurization rate above the critical values (about 10 MPa/s). Moreover, the structure of iPP mesophase obtained by rapid pressurization was analyzed and compared with that prepared by temperature quenching. Also interestingly, the pressure‐induced mesophase can transform into γ‐phase by annealing under pressure at 200°C, and the rate of this phase transition is slowed down with increasing annealing pressure. POLYM. ENG. SCI., 59:439–446, 2019. © 2018 Society of Plastics Engineers     

Polymorphism and crystallization in poly(vinylidene fluoride)/ poly(ϵ‐caprolactone)–block–poly(dimethylsiloxane)–block–poly(ϵ‐caprolactone) blends

The miscibility, crystallization kinetics and crystalline morphology of a new system of poly(vinylidene fluoride)/poly(?‐caprolactone)‐block‐poly(dimethylsiloxane)‐block‐poly(?‐caprolactone) (PVDF/PCL‐b‐PDMS‐b‐PCL) triblock copolymer were investigated by a variety of techniques. The miscibility and phase behaviour of PVDF/PCL‐b‐PDMS‐b‐PCL were studied by determination of the melting point temperature, crystallization kinetics and Fourier transform infrared (FTIR) mapping. Chemical imaging was used as a new technique to characterize the interaction of polymer blends in crystalline morphology. The results demonstrate the existence of characteristic peaks of both PVDF and PCL in the chosen crystalline area. The crystalline structures of PVDF were affected by the PCL‐b‐PDMS‐b‐PCL triblock copolymer and facilitate the formation of the β polymorph which was illustrated by FTIR analysis. The β crystal phase fraction increases significantly on increasing the composition of the PCL‐b‐PDMS‐b‐PCL triblock copolymer. In addition, confined crystallization of PCL within PVDF inter‐lamellar and/or inter‐fibrillar regions was confirmed through polarizing optical microscopy, wide‐angle X‐ray diffraction and small‐angle X‐ray scattering analysis. © 2019 Society of Chemical Industry