Effect of annealing on the microvoid formation and evolution during biaxial stretching of β nucleated isotactic polypropylene

ABSTRACT

Cast films, based on β-iPP, were prepared via melt extrusion, and, then annealed at different temperature. The effect of annealing on the properties of the cast films, as well as on microvoid formation and evolution was investigated. After annealing, the initial lamellar structure was improved, and more secondary crystals were formed which decreased the numbers of tie chains, which was beneficial to cavitation. And the stability of β-crystal and β lamellar thickness distribution was improved. Finally, the membrane obtained by unannealed film had inferior pore-size distribution, while the annealed sample had uniform pore-size distribution.     

Molecular weight dependency of β phase formation in injection-molded isotactic polypropylene

The influence of β-nucleating agents and the molecular weight of isotactic polypropylene (iPP) on the formation of β phase in the injection-molded iPP were explored using wide-angle X-ray diffraction technique. Without the β-nucleating agents, the molecular weight of iPP was the dominant factor controlling the production of β phase during injection. A higher molecular weight could promote the orientation of molecular chains in the skin layer of injected sample, bringing out a larger content of β phase in the corresponding region. Although the β-nucleating agents had a profound effect on the formation of β phase, it was only efficient for the iPP with moderate molecular weights. The systems of the lowest and highest molecular weight iPP samples compounded with β-nucleating agents still performed the same with the corresponding ones without β-nucleating agents. Such performances can be interpreted as a result of the competition between the β-nucleating agents and the orientation degree of molecular chains. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48555.     

Effect of calcination/rehydration treatments on the environment of V in β zeolite

A dealuminated zeolite β has been contacted with solutions of ammonium metavanadate to incorporate vanadium as tetrahedral V species which are not removed under treatment with aqueous solution of ammonium acetate. The effects of calcination and rehydration on the environment of the V species have been studied by diffuse reflectance UV-visible and ⁵¹V NMR. The reducibility of the V species has been followed by TPR and ESR. The dehydroxylation/rehydroxylation process occurring in the β framework upon dehydration/rehydration has been monitored by ²⁹Si MAS NMR and FT-IR spectroscopy. This revised version was published online in August 2006 with corrections to the Cover Date.     

Effect of intergranular phase chemistry on the sliding-wear resistance of pressureless liquid-phase-sintered α-SiC

The effect was investigated of the intergranular phase chemistry on the sliding-wear resistance of pressureless liquid-phase-sintered (PLPS) α-SiC densified with 10 vol.% 5Al₂O₃ + 3RE₂O₃ (RE = La, Nd, or Yb) additives. It was found that the sliding-wear behaviour of these ceramics is similar to what is observed in other polycrystalline ceramics: initial mild, plasticity-controlled wear followed by severe, fracture-controlled wear, with a well-defined wear transition. Most importantly, the sliding-wear resistance of PLPS SiC is found to increase with decreasing size of the RE³⁺ cation in the rare-earth oxide additive, with a lower susceptibility to mild and severe wear and a delayed transition to severe wear. Underlying this effect is likely the hardening of the intergranular phase resulting from the increase in the field strength of the RE³⁺-O²⁻ bonds as the size of the RE³⁺ cation decreases. Tailoring the intergranular phase chemistry via the selection of RE₂O₃ sintering additives with cations as small as possible thus emerges as a potentially interesting approach to improving the sliding-wear resistance of PLPS SiC ceramics.     

Effect of brookite phase on the anatase–rutile transition in titania nanoparticles

Nanosized TiO₂ powders were prepared from the precipitation in the TiCl₄ precursor under various pH values. The prepared titania existed in the form of nanocrystalline anatase with some brookite, which was evidenced by X-ray diffraction analysis and Raman spectroscopy. The average crystallite sizes of the TiO₂ particles heat treated at 450 °C for 2 h are in the range of 7–9 nm. The lattice constant c of anatase increased with increasing the synthesized pH value, whereas the volume fraction of the brookite phase increased with decreasing the synthesized pH value. The beginning and ending temperatures for the anatase–rutile transformation were found to decrease with increasing the volume fraction of the brookite phase. The brookite phase in the powder is responsible for enhancing the anatase–rutile transition.     

Influence of maleation of polypropylene on the interfacial properties between polypropylene and ethylene–vinyl alcohol copolymer

In order to improve the miscibility between the components of a blend, it is possible to modify the chemical structure by functionalizing one or more of the components. This results in better adhesion at the interface between the components and, consequently, in better mechanical properties. In this work, the influence of maleation of polypropylene on the interface between polypropylene and ethylene–vinyl alcohol copolymer was studied using the measurement of interfacial tension, surface analysis with electron spectroscopy for chemical analysis (ESCA), and morphological observation, using scanning electron microscopy (SEM). The interfacial tension between a 0.1-wt % maleated polypropylene and ethylene–vinyl alcohol copolymer was shown to be 25% lower than the interfacial tension between nonmaleated polypropylene and ethylene–vinyl alcohol copolymer. This resulted in better adhesion between maleated polypropylene and ethylene–vinyl alcohol copolymer. The surface analysis indicates that this decrease of interfacial tension is due to migration of the maleic groups of the maleated polypropylene to the interface between the 2 polymers and that, probably, a chemical interaction occurs at the interface between maleated polypropylene and ethylene–vinyl alcohol copolymer. It is also shown in this work that additives, such as SiO₂, found in commercial polymers, can influence the interfacial tension between 2 polymers. © 1998 John Wiley & Sons, Inc. J. Appl. Polym. Sci. 70: 75–87, 1998     

Effect of potassium-doping on the microstructure development in polyfurfuryl alcohol – derived activated carbon

Potassium-doped activated carbon was prepared by mixing potassium salt with polyfurfuryl alcohol precursor followed by carbonization and activation. Several experimental techniques, such as thermogravimetric analysis, gas adsorption, X-ray diffraction and Raman scattering spectroscopy were employed to understand the effects of potassium on the texture and pore structures of the activated carbon, which ultimately affects the hydrogen adsorption properties. After doping with potassium, the activated carbon exhibits higher surface area, higher micropore volume, and enhanced hydrogen adsorption capacity. Understanding of how alkali metals affect surface area and micropore development in activated carbon may help to clarify the hydrogen adsorption mechanism and improve the design of suitable carbon-based hydrogen storage materials.     

Exploring the roles of molecular structure on the β-crystallization of polypropylene random copolymer

To investigate effects of molecular structures on β-crystallization of polypropylene random copolymer (PPR), PPR-A and PPR-B with similar molecular weight and distribution but significantly different polymorphic behavior were used. Wide-angle X-ray diffraction (WAXD), Fourier transform infrared spectroscopy (FT-IR), solvent fractionation combined with successive self-nucleation and annealing (SSA) and Gel Permeation Chromatography (GPC) were applied. Results revealed that after addition of same amount of β-nucleating agent (β-NA), large amount of β-phase is obtained in PPR-A (K _β  = 0.603), while no β-phase can be seen from PPR-B; Structure characterizations revealed that they have similar molecular weight but different total amount and distribution of ethylene comonomer: the total content of ethylene comonomer of PPR-A is higher compared with PPR-B, but its ethylene comonomer distribution is less uniform. In this way, PPR-A possesses high molecular weight high isotactic fraction, which cannot be seen from PPR-B due to its more uniform comonomer distribution. Therefore, the presence of highly isotactic PP (HPP) is the key factor in β-crystallization of PPR. For verification, HPP with low or high molecular weights are respectively added into β-nucleated PPR-B. Results revealed that HPP was effective in enhancing β-crystallization of PPR-B; higher molecular weight of HPP was more favorable and more effective.     

Effect of titanium–magnesium catalyst morphology on the properties of polypropylene upon propylene polymerization in a liquid monomer

The effect of the particle size of an IK-8-21 domestic titanium-magnesium catalyst on the properties of polypropylene (PP) produced during the polymerization of propylene in a liquid monomer is studied. Catalysts with particle sizes of 20 to 64 μm are shown to have high activity and identical sensitivity to hydrogen and allow PP to be obtained with a narrow distribution of particles over size, high isotacticity, and close values of crystallinity, melting temperature, and physicomechanical properties. A slight decrease in the activity and bulk density of PP powder is observed when the average size of catalyst particles is increased from 20 to 43 μm. A more notable reduction in the activity and bulk density of PP powder is observed for catalyst with particle sizes of 62 to 64 μm. IK-8-21 catalyst is not inferior to its foreign analogues with respect to the properties of the resulting PP.     

Effects of ultrasound on the conformation and crystallization behavior of isotactic polypropylene and β-isotactic polypropylene

The effects of ultrasonic irradiation on conformation and crystalline structure of isotactic polypropylene (iPP) and β-isotactic polypropylene (β-iPP) were studied by means of Fourier transform infrared spectroscopy (FT-IR), differential scanning calorimetry (DSC) and wide-angle X-ray diffraction (WAXD). The results demonstrate that ultrasonic irradiation decreases the helical conformation order and changes the crystalline structures: for iPP, T_m and T_onset decrease, T_m − T_onset becomes larger; for β-iPP, the β_c, (1 − λ)_β and k_β increase, the intensities of α(040) plane and α(130) plane in WAXD profiles decrease evidently. For both iPP and β-iPP, the crystallinity decreases, d-spacing increases, the crystallite size L decreases and ultrasound shows a selective effect on the growth of β-crystal. Furthermore, DSC and WAXD were employed to observe the effect of ultrasound on the “melting memory effect” of β-iPP. The results indicate that ultrasonic irradiation destructs the existing “locally ordered structure” in β-iPP melt, as a result greatly inhibits the βα-recrystallization of β-iPP samples during heating.     

Effect of Calcium Salts of Glutaric Acid and Pimelic Acid on the Formation of β Crystalline Form in Isotactic Polypropylene

The effect of calcium glutarate (Cagt) and calcium pimelate (Capt) on the formation of β crystalline form in isotactic polypropylene (iPP) after isothermal crystallization at 130°C for 30 min has been investigated. The maximum K_WAXD and K_DSC values were 31.97% and 38.06%, respectively, for iPP doped with 0.2 wt.% Cagt. The maximum values of K_WAXD and K_DSC were 73.60% and 68.44% for iPP doped with 0.3 wt.% and 0.15 wt.% Capt, respectively. The crystal size of iPP doped with Capt is finer than that of iPP doped with Cagt. It is shown that the β nucleation ability of Capt is superior to that of Cagt. The difference in the β nucleation ability between Cagt and Capt is explained by the structural difference of the nucleators with β-iPP.     

Effect of tungsten doping on the dielectric response of PZN–PT–BT ceramics with the morphotropic phase boundary composition

In this paper, effect of tungsten doping on the dielectric property of the Pb(Zn_1/3Nb_2/3)O₃–BaTiO₃–PbTiO₃ system around morphotropic phase boundary(MPB) composition is presented. Samples were prepared according to the formula Pb_0.85−xBa_0.15[(Zn_1/3Nb_2/3)_0.7Ti_0.3]_1−xW_xO₃ assuming the compensation for W is achieved via the appearance of the lead vacancies. X-ray diffraction results show that a nearly complete perovskite phase was maintained as W was progressively added up to 5 wt.%. Introduction of W stabilizes the tetragonal phase against the rhombohedral one, resulting in the displacement of MPB composition region towards relaxor end. Moreover, lattice distortion of the tetragonal phase is enlarged, that of the rhombohedral phase is lowered. W- doping leads to an increase in the dielectric permittivity maximum and a decrease in the phase transition temperature (T_m). The frequency dispersion of T_m is succesively weakened as W ions are gradually incorporated, reflecting the strengthened couplings among ferroactive oxygen octahedra. A maximum on the degree of diffuse phase transition is observed at 1 mol% WO₃, which can be interpreted in terms of competing effects of chemical inhomogeneity and ferroelectric couplings. W-doping also induces an increase in the tendency towards Curie–Weiss behavior above T_m, which is associated with the growth of ferroelectric domains.     

Interfacial interactions in calcium carbonate–polypropylene composites. 2: Effect of compounding on the dispersion and the impact properties of surface-modified composites

This study was carried out to investigate the influences of compounding process and surface treatment on calcium carbonate (CaCO₃) filled polypropylene. The compounding process is discussed with reference to a twin-screw extruder and an internal mixer. The calcium carbonate filler was surface-treated with a liquid titanate coupling agent (LICA 12) and stearic acid. Composites of different weight fractions were prepared by both compounding processes, and their impact properties were evaluated. The notched Izod impact strength increased with CaCO₃ content up to a maximum at about 10 vol%, and then decreased. Surface treatment of CaCO₃ filler generally yielded composites of higher impact strength than untreated system. Though LICA 12 was more effective than stearic acid in modifying the filler, the low-cost stearic acid proved to be more effective when dealing with the impact properties of composites. Moreover, the composites from a Brabender Plasti-corder exhibited better gross uniformity than that from the twin-screw extruder. However, good filler dispersion and uniform microscopic morphology, as revealed by SEM microscopy, was observed in the samples from the twin-screw extruder. Polym. Compos. 25:451–460, 2004. © 2004 Society of Plastics Engineers.     

Effect of Self-Assemblies on the Dynamics of the Briggs–Rauscher Reaction

The study involves the dynamic evolution of the Briggs–Rauscher (BR) reaction in the presence of various surfactants—SDS (sodium dodecyl sulphate) as anionic, CTAB (cetyl trimethylammonium bromide) as cationic and TritonX‐100 [4‐(1,1,3,3‐(tetramethylbutyl) phenyl polyethylene glycol] as a neutral one in single as well as mixed mode conditions (SDS + TX‐100 and CTAB + TX‐100). The reaction has been monitored potentiometrically at 30 °C under CSTR conditions. These surfactants affect the reaction dynamics to an extent which depends on the nature and concentration of the surfactant and the formation of their self‐assemblies. The experimental findings indicate that the oscillatory behavior of the BR reaction in the presence of surfactants is due to the efficacy of organized surfactant assemblies to selectively distribute the key species involved in the reaction, and their interaction with the counter ions in cases of ionic micelles. The study reveals that the evolution of oscillatory behavior is a characteristic feature of the surfactant.     

Effect of the processing on the production of cordierite–mullite composite

In this study, effect of process on the production of cordierite–mullite composite was studied. For this reason two different processing methods were used in the production of cordierite–mullite composites. In first process, in situ cordierite–mullite composites were produced from cordierite and mullite layers which were formed by using aqueous tape casting method. In second one, composite was produced by addition of pre-produced mullite powders (in different weight percents, 0–30) into cordierite starting powders. The results show that the addition of pre-sintered mullite powders to the cordierite slip has more effect on densification behavior and mechanical properties of composites than layered production method.     

Comments on the mechanism of the vapour‐phase catalytic synthesis of thiophenes

A study of the synthesis of thiophene from the reaction of butanol and CS₂ over potassium‐promoted Cr₂O₃/γ‐Al₂O₃ has been performed by examination of the reactivity of model intermediates. This study indicates that the reaction path involves successive dehydrogenation, O/S exchange and dehydroheterocyclization. This revised version was published online in July 2006 with corrections to the Cover Date.     

Effect of Microsilica Addition on the Properties of Mullite-Corundum Ceramic

1IntroductionCorundum-mullite materials have been recognizedand adopted as important refractories because of theirexcellent properties,such as high refractoriness,highresistance to creep,good mechanical and chemical sta-bility at high temperatures,high th…