Morphology of water-blown flexible polyurethane foams

A series of four TDI–polypropylene oxide (PO) water-blown flexible polyurethane foams was produced in which the water content was varied from 2 to 5 pph at a constant isocyanate index of 110. A portion of each foam was thermally compression molded into a plaque. The morphology of both the foams and plaques was investigated using dynamic mechanical spectroscopy (DMS), differential scanning calorimetry (DSC), transmission electron microscopy (TEM), scanning electron microscopy (SEM), swelling, wide angle X-ray scattering (WAXS), and small angle X-ray scattering (SAXS). A high degree of microphase separation occurs in these foams, and its degree is nearly independent of water (hard segment) content. In the foam with the lowest water content the morphology possesses many similarities to that of typical linear segmented urethane elastomers. Small hard segment domains are present with a correlation distance of about 7.0 nm. When the water content is increased a binodal distribution of hard segment material appears. There are the small hard segment domains typical of segmented urethane elastomers as well as larger “hard aggregates” greater than 100 nm in size. The larger domains are thought to be aggregates of rich polyurea that develop by precipitation during the foaming reaction. WAXS patterns of the foams suggest urea and possibly hard segment ordering that may be of a paracrystalline nature but certainly lacking in true 3-dimensional crystallinity.     

Study on bisphenol-A polycarbonates samples crystallized by acetone vapor induction

Bisphenol-A polycarbonate (PC) is an important amorphous engineering polymer, which can have its crystallinity induced by special environmental conditions. Such crystallization can alter PC properties leading to flaws during its use or to new applications. Cast film samples of PC, prepared from chloroform solutions, were submitted to acetone vapor and characterized by polarized light microscopy (PLM), differential scanning calorimetry (DSC) and Fourier transform infrared spectroscopy (FTIR). PLM showed that the PC crystalline structure was presented as spherulites of different sizes. DSC analysis exhibited a multiple melting behavior for the crystalline structure. FTIR has presented bands shifting and intensity decrease, compared to the samples before treatment. Compression molded samples were characterized by scanning electron microscopy (SEM), DSC and mechanical properties tests. For those samples, DSC also showed the presence of a crystalline phase, with a little increase on surface rugosity observed through SEM. Stress–strain tests presented a decrease on samples performance after acetone exposure.     

Morphology and mechanical properties of injection molded poly(ethylene terephthalate)

This work reports on the relationships between processing, the morphology and the mechanical properties of an injection molded poly(ethylene terephthalate), PET. Specimens were injection molded with different mold temperatures of 30°C, 50°C, 80°C, 100°C, 120°C, 150°C, while maintaining constant the other operative processing parameters. The thermomechanical environment imposed during processing was estimated by computer simulations of the mold‐filling phase, which allow the calculation of two thermomechanical indices indicative of morphological development (degree of crystallinity and level of molecular orientation). The morphology of the moldings was characterized by differential scanning calorimetry (DSC) and by hot recoverable strain tests. The mechanical behavior was assessed in tensile testing at 5 mm/min and 23°C. A strong thermal and mechanical coupling is evidenced in the injection molding process, significantly influencing morphology development. An increase in the mold temperature induces a decrease of the level of molecular orientation (decrement in the hot recoverable strain) and an increment in the initial crystallinity of the moldings (decrement in the enthalpy of cold crystallization), also reflected in the variations of the computed thermomechanical indices. The initial modulus is mainly dependent upon the level of molecular orientation. The yield stress is influenced by both the degree of crystallinity and the level of molecular orientation of the moldings, but more significantly by the former. The strain at break was not satisfactorily linked directly to the initial morphological state because of the expected morphology changes occurring during deformation. Polym. Eng. Sci. 44:2174–2184, 2004. © 2004 Society of Plastics Engineers.     

Processing and structural optimization of PEEK composites

The objective of this experimental program was to understand how changes in processing conditions affect the morphology and ultimately, the performance of polyetheretherketone (PEEK)-based carbon fiber composites. Based on some initial differential scanning calorimetry (DSC) work, various molding and aging conditions were implemented on compression molded plaques made from PEEK APC-2 prepreg. These conditions included samples that were physically aged, annealed just below the melting point, slow cooled, prepared under low pressure, and under fast cooling. Using DSC, the crystallinity of plaques prepared according to the ICI procedure, low pressure, and physical aging conditions were found to be 31–33 percent, while the slow cooling and annealing conditions resulted in crystallinity of 42 percent, with slow cooling displaying a „shoulder”︁ on the primary melting endotherm. Optical and plasma etching/scanning electron microscopy on faster cooled plaques generally revealed a mixture of isolated and graphite fiber nucleated spherulites, while the slow-cooled condition revealed larger fiber nucleated spherulites exclusively. Fracture toughness and impact delamination as measured by ultrasonic C-scan indicates that slow cooling resulted in the lowest properties, while simultaneously resulting in the highest compression strength, all of which suggests reduced matrix toughness. The annealing condition, which allowed high crystallinity but in a matrix of smaller spherulites, resulted in properties intermediate between slow and fast cooling, suggesting that both spherulite size and degree of crystallinity are important in characterizing these materials. In contrast, physical aging resulted in no degradation in mechanical properties.     

Interrogation of “surface,” “skin,” and “core” orientation in thermotropic liquid‐crystalline copolyester moldings by near‐edge X‐ray absorption fine structure and wide‐angle X‐ray scattering

Injection molding thermotropic liquid‐crystalline polymers (TLCPs) usually results in the fabrication of molded articles that possess complex states of orientation that vary greatly as a function of thickness. “Skin‐core” morphologies are often observed in TLCP moldings. Given that both “core” and “skin” orientation states may often differ both in magnitude and direction, deconvolution of these complex orientation states requires a method to separately characterize molecular orientation in the surface region. A combination of two‐dimensional wide‐angle X‐ray scattering (WAXS) in transmission and near‐edge X‐ray absorption fine structure (NEXAFS) spectroscopy is used to probe the molecular orientation in injection molded plaques fabricated from a 4,4′‐dihydroxy‐α‐methylstilbene (DHαMS)‐based thermotropic liquid crystalline copolyester. Partial electron yield (PEY) mode NEXAFS is a noninvasive ex situ characterization tool with exquisite surface sensitivity that samples to a depth of 2 nm. The effects of plaque geometry and injection molding processing conditions on surface orientation in the regions on‐ and off‐ axis to the centerline of injection molded plaques are presented and discussed. Quantitative comparisons are made between orientation parameters obtained by NEXAFS and those from 2D WAXS in transmission, which are dominated by the microstructure in the skin and core regions. Some qualitative comparisons are also made with 2D WAXS results from the literature. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Structural development of HDPE in injection molding

This study investigated some relevant structure/properties relationships in shear‐controlled orientation in injection molding (SCORIM) of high‐density polyethylene (HDPE). SCORIM was used to deliberately induce a strong anisotropic character in the HDPE microstructure. Three grades with different molecular weight characteristics were molded into tensile test bars, which were subsequently characterized in terms of the mechanical behavior by tensile tests and microhardness measurements. The structure developed upon processing was also characterized by polarized light microscopy (PLM), scanning electron microscopy (SEM), differential scanning calorimetry (DSC), and wide‐angle X‐ray diffraction (WAXD). SCORIM allows the production of very stiff molded parts, exhibiting a very well‐defined laminated morphology. This morphology is associated with both an M‐shaped microhardness profile and a pronounced mechanical anisotropy. These characteristics are supported by an analogous variation in the crystallinity and a high level of molecular orientation, as indicated, respectively, by calorimetric measurements and X‐ray diffraction results. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 2079–2087, 2003     

Synthesis of PET-based Liquid Crystalline Copolyesters: Influence of the Overall Degree of Aromaticity on Phase Segregation

Abstract

Novel PET-based copolyesters have been synthesised by transesterification of PET with equimolar amounts of sebacic acid (S) and 4,4′-diacetoxybiphenyl (B) and with varying amounts of 4-acetoxybenzoic acid (H). The structure, the morphology, and the thermal properties of the PET-S-B-H copolyesters have been studied by scanning electron microscopy (SEM), polarized optical microscopy (POM), differential scanning calorimetry (DSC) and wide-angle X-ray diffraction (WAXS). It has been demonstrated that segregation of a liquid-crystalline phase, during polycondensation, provides the driving force for compositional differentiation, with the result that the final products are “synthetic polymer blends”. The characteristics of PET-S-B-H copolymers have been compared with those of PET-S-Q-H copolyesters having the same molar composition (Q-hydroquinone). It has been shown that the phase segregation is more prominent in PET-S-B-H copolyesters than in PET-S-Q-H polymers of similar molar composition. The influence of the overall degree of aromaticity of the copolyester on the segregation phenomenon has been discussed.     

The effects of thermal history on the structure/property relationship in polyphenylenesulfide/carbon fiber composites

The purpose of this investigation was to examine the effects of thermal history during cooling from the melt on the degree of crystallinity, morphology, and mechanical properties of polyphenylenesulfide (PPS)/carbon fiber composites. Three thermal treatments were employed in this tudy: isothermal crystallization from the melt at 140, 160, 180, 200, and 22O°C; quenching from 315°C and then annealing at 160 and 200°C; and nonisothermal crystallization from the melt at rates varying from 0.4°C/min to 38°C/s. The effect of varying the thermal history of the sample on the degree of crystallinity developed in the matrix polymer was determined using differential scanning calorimetry (DSC). The effect of thermal history on and the resulting matrix morphology was examined by scanning electron microscopy (SEM). The subsequent effects of the degree of crystallinity and the morphology on the mechanical behavior of the samples were monitored by transverse tensile tests and flexural tests. In all cases, the transverse tensile and flexural moduli increased as the amount of crystallinity in the samples increased. However, samples with greater amounts of crystallinity did not always yield higher transverse tensile or flexural strengths. Upon examination of the composite samples by electron miscroscopy, it was observed that large increases in the values of the transverse tensile and flexural strengths could be correlated with structural changes in the matrix.     

热拉伸比对熔融挤出拉伸法制备聚丙烯微孔膜的影响

通过固定冷拉伸比,改变热拉伸比制备了具有不同微孔结构的聚丙烯微孔膜,通过扫描电子显微镜(SEM)观测了微孔的形貌,通过差示扫描量热法(DSC)测试了微孔膜的片晶厚度,研究了热拉伸过程中微孔形成过程以及微孔尺寸和数量,微孔膜孔隙率随热拉伸比的变化情况.结果表明,冷拉伸过程主要是片晶间微裂纹的形成过程,微裂纹均匀的分布在试...     

Bulk functionalization of ethylene–propylene copolymers. III. Structural and superreticular order investigations

An ethylene-propylene copolymer (EPR) has been functionalized with dibutyl maleate (DBM) by means of a radical-initiated bulk process. Different degrees of grafting have been obtained by varying the overall composition of the reaction mixture as well as the processing procedures. The influence of the grafting degree on the structural and superreticular (or “long range”) order has been investigated by differential scanning calorimetry (DSC), Fourier transform infrared analysis (FTIR), and wide (WAXS) and small angle X-ray scattering (SAXS) techniques. The functionalization leads to a decrease of the “residual crystallinity” present in the parent copolymer. Linear relationships between the grafting degree and the crystallinity degree X_c evaluated by both DSC and WAXS have been obtained. The results of the structural investigations, in agreement with previously reported ones, suggest that the grafting preferentially occurs onto the longer or more perfect methylene sequences. SAXS investigations showed that the significant degree of structuration, i.e., crystalline and paracrystalline order, present in the parent elastomer, gradually disappears by increasing the degree of grafting.     

Effect of different film preparation procedures on the thermal,morphological and mechanical properties of pure and calcite‐filled HDPE films

The effect of different film preparation procedures on the thermal, morphological and mechanical properties of high density polyethylene (HDPE) films have been studied using differential scanning calorimetry (DSC), wide angle X‐ray diffraction (WAXRD), atomic force microscopy (AFM), scanning electron microscopy (SEM) and ultimate tensile testing. Film preparation procedures included variation in cooling methods, including quenching, forces (fanning) and natural cooling and techniques such as extrusion followed by melt squeezing and compression molding. The heat of fusion (from DSC), the degree of crystallinity (from WAXRD) and the crystallite size (from WAXRD and AFM) were found to be highest for naturally cooled specimens, followed by fan‐cooled and quenched ones. AFM images of surface topology exhibit stacked lamellar morphology for forcefully cooled (fan‐cooled and quenched) samples and spherulitic ‘lozenges’ for naturally cooled ones. The Young's modulus and yield stress [from the universal testing machine (UTM)] were highest for naturally cooled samples, followed by fan‐cooled and quenched ones. Among the calcite‐filled composites, the ‘base film,’ which was prepared by extrusion followed by melt squeezing and natural cooling, exhibited the lowest heat of fusion and degree of crystallinity and a similar crystallite size relative to compression‐molded films. Lower yield stress, tensile strength and Young's modulus and higher elongation at break were observed for the base film in comparison to the naturally cooled composite film. The low degree of crystallinity and crystallite size in the ‘base film’ explain all of its mechanical and morphological properties. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 1427–1434, 2004     

Correlation between morphological properties and thermal conductivity of injection‐molded polyamide 46

The morphology and thermal conductivity of injection‐molded polyamide 46 (PA46) samples were investigated in this study. It was found that injection molding parameters had no influence on the thermal conductivity. This was attributed to the high crystallization speed and therefore imperfect crystal structure of PA46. By annealing of some samples at 260°C for 24 h the thermal conductivity was increased by 30%. Polarization light microscopy revealed only minor changes of the visible morphological structure for the as molded and annealed samples. For the investigation of the sample crystallinity via Raman spectroscopy an analysis method was established and the term “Raman crystallinity” is introduced as the intensity ratio of characteristic Raman bands. Via Raman crystallinity it was possible to distinguish between different mold temperatures and the annealed PA46 samples showed a significantly increased Raman crystallinity. Our results show that the thermal conductivity of PA46 primarily depends on the crystal structure on a length scale of crystallites. The size of the visible spherulite‐like structures did not correlate with the change in thermal conductivity. A correlation of the Raman crystallinity with the thermal conductivity of PA46 was shown. POLYM. ENG. SCI., 55:2231–2236, 2015. © 2015 Society of Plastics Engineers     

Study on the Improvement of Crystallization in HDPE Induced by High–Molecular-Weight Polyethylene Through Dynamic Packing Injection Molding

The effect of high–molecular-weight polyethylene (HMWPE) on crystal morphology was investigated for high-density polyethylene (HDPE) through dynamic packing injection molding (DPIM). With the aid of differential scanning calorimetry (DSC), wide-angle x-ray diffraction (WAXD), and scanning electron microscopy (SEM) measurements, a typical web-like shish kebab morphology, which markedly increases stiffness and toughness, was found in HMWPE-induced samples through DPIM. The SEM results show that the much better web-like shish kebab structure, in which most of the lamellae connect different columns, compared with conventional shish kebab, was formed in HDPE blends with 4% HMWPE content (B4) through DPIM. The WAXD studies indicate that orientation degrees of crystallographic planes (110) and (200) in the B4 samples were much higher than those of samples molded by static packing injection molding and B0 samples molded by DPIM. A combination of the higher degree of crystal orientation and the formation of web-like shish kebab led to simultaneous great increments of stiffness and toughness, which overcomes the traditional limitation that stiffness and toughness cannot be greatly enhanced simultaneously. All these results show that HWMPE favored for great improvement of crystal structures in HDPE when its content is appropriate through DPIM.     

Mechanical properties and morphology of polyethylene–polypropylene blends with controlled thermal history

The effect of time–temperature treatment on the mechanical properties and morphology of polyethylene–polypropylene (PE–PP) blends was studied to establish a relationship among the thermal treatment, morphology, and mechanical properties. The experimental techniques used were polarized optical microscopy with hot‐stage, scanning electron microscopy (SEM), differential scanning calorimetry (DSC), and tensile testing. A PP homopolymer was used to blend with various PEs, including high‐density polyethylene (HDPE), low‐density polyethylene (LDPE), linear low‐density polyethylene (LLDPE), and very low density polyethylene (VLDPE). All the blends were made at a ratio of PE:PP = 80:20. Thermal treatment was carried out at temperatures between the crystallization temperatures of PP and PEs to allow PP to crystallize first from the blends. A very diffuse PP spherulite morphology in the PE matrix was formed in partially miscible blends of LLDPE–PP even though PP was present at only 20% by mass. Droplet‐matrix structures were developed in other blends with PP as dispersed domains in a continuous PE matrix. The SEM images displayed a fibrillar structure of PP spherulite in the LLDPE–PP blends and large droplets of PP in the HDPE–PP blend. The DSC results showed that the crystallinity of PP was increased in thermally treated samples. This special time–temperature treatment improved tensile properties for all PE–PP blends by improving the adhesion between PP and PE and increasing the overall crystallinity. In particular, in the LLDPE–PP blends, tensile properties were improved enormously because of a greater increase in the interfacial adhesion induced by the diffuse spherulite and fibrillar structure. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 1151–1164, 2000     

Nano‐sized silica supported Me2Si(Ind)2ZrCl2/MAO catalyst for ethylene polymerization

Nano‐sized and micro‐sized silica particles were used to support a zirconocene catalyst [racemic‐dimethylsilbis(1‐indenyl)zirconium dichloride], with methylaluminoxane as a cocatalyst. The resulting catalyst was used to catalyze the polymerization of ethylene in the temperature range of 40–70°C. Polyethylene samples produced were characterized with scanning electron microscopy (SEM), X‐ray diffraction (XRD), differential scanning calorimetry (DSC), and gel permeation chromatography (GPC). Nano‐sized catalyst exhibited better ethylene polymerization activity than micro‐sized catalyst. At the optimum temperature of 60°C, nano‐sized catalyst's activity was two times the micro‐sized catalyst's activity. Polymers obtained with nano‐sized catalyst had higher molecular weight (based on GPC measurements) and higher crystallinity (based on XRD and DSC measurements) than those obtained with micro‐sized catalyst. The better performances of nano‐sized catalyst were attributed to its large external surface area and its absence of internal diffusion resistance. SEM indicated that polymer morphology contained discrete tiny particles with thin long fiberous interlamellar links. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Lamellar morphology of high molecular weight poly(ether ether ketone) after rolltrusion

A rolltrusion technique has been applied to impose high molecule orientation in unreinforced poly(ether ether ketone). The relationships among processing, microstructure and properties were characterized. The morphology was controlled and investigated in the microstructural levels of crystallinity, chain orientation, lamellae and spherulite colony. The density measurements detected an increase in crystallinity after rolltrusion. Wide-angle X-ray scattering (WAXS) diffraction experiments showed the preferred c-axis chain orientation along the rolltrusion direction. The internal microstructure, revealed by permanganic etching and scanning electron microscopy (SEM), changed from randomly distributed lamellae to a row structure. The lamella thickness was estimated to be about 100 Å.     

Effects of liquid–liquid phase separation on crystallization kinetics and morphology of isotactic polypropylene/poly (ethylene-co-octene) in-reactor alloy

In this work, we investigated the effects of liquid–liquid phase separation (LLPS) on the crystallization kinetics and morphology of isotactic polypropylene/poly (ethylene-co-octene) (iPP/PEOc) in-reactor alloy with polarized optical microscopy (POM), differential scanning calorimeter (DSC), scanning electron microscopy (SEM), wide angle X-ray scattering (WAXS) and small angle X-ray scattering (SAXS) methods. Based on crystallization kinetics analysis by Avrami equation, we found that the overall crystallization rate was almost independent on LLPS time, whereas was strongly dependent on crystallization temperature. However, by combination with POM, we found that the LLPS played two opposite roles on the overall crystallization rate, i.e. the nucleation rate decreased and the spherulite growth rate increased as increasing LLPS time. It is due to the nucleation rate was dominated by fluctuation-assisted nucleation mechanism and the growth rate was dominated by diffusion-controlled growth. Furthermore, the spherulite size and PEOc domain size of iPP/PEOc in-reactor alloy were significantly dependent on LLPS time; however, the crystallinity was almost not dependent on LLPS time.     

Influence of processing on ethylene‐propylene block copolymers: Structure and mechanical behavior

Thin plaques (1, 2, and 3 mm) made of polypropylene homopolymer (iPP) and three ethylene propylene block copolymers (EPBC) with different ethylene content (5.5, 7.4, and 12% in weight) have been obtained by different processing methods (injection molding, injection and annealing, and compression molding). The morphology of the plaques has been studied using polarizing microscopy (PLM), differential scanning calorimetry (DSC), and wide‐angle X‐ray scattering (WAXS). The results have been related with the mechanical properties of the plaques (MD and TD directions) in tension loading tests. We show the influence of the ethylene content, thickness, and processing method and conditions in the final morphology and how they affect the mechanical behavior. This knowledge can be used to tailor the final properties of a piece. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 2866–2878, 2004     

Effect of annealing on the structure and properties of polyvinylidene fluoride hollow fiber by melt‐spinning

Polyvinylidene fluoride hollow fibers were prepared by melt‐spinning technique under three spinning temperatures. The effects of annealing treatment on the structure and properties of hollow fiber were studied by differential scanning calorimetry (DSC), wide‐angle X‐ray diffraction (WAXD), tensile test, and scanning electron microscopy (SEM) measurements. DSC and WAXD results indicated that the annealing not only produced secondary crystallization but also perfected primary crystallization, and spinning and annealing temperature influenced the crystallinity of hollow fiber: the crystallinity decreased with the increase of spinning temperature; 140°C annealing increased the crystallinity, and hardly influenced the orientation of hollow fiber; above 150°C annealing increased the crystallinity as well, and furthermore had a comparative effect on the orientation. The tensile tests showed that the annealed samples, which did not present the obvious yield point, exhibited characteristics of hard elasticity, and all the hollow fiber had no neck phenomenon. Compared with the annealed sample, the precursor presented a clear yield point. In addition, the annealed samples had a higher break strength and initial modulus by contrast with the precursor, and the 140°C annealed sample showed the smallest break elongation. SEM demonstrated the micro‐fiber structure appeared in surface of drawn sample. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 935–941, 2007