Miscibility,Crystallization, and Morphology of the Double-Crystalline Blends of Insulating Polyethylene and Semiconducting Poly(3-Butylthiophene)

A series of crystalline semiconducting poly(3-butylthiophene) (P3BT)/crystalline insulating polyethylene (PE) blends were prepared and the miscibility, crystallization, and structure/morphology were investigated. Even though phase separation was observed by transmission electron microscopy (TEM) and small-angle X-ray scattering (SAXS), several pieces of evidence indicated that limited miscibility should be present in PE/P3BT blends: small changes in both T_m and crystallinity of PE phase and a small portion of PE being dissolved in P3BT. The study of PE isothermal crystallization kinetics revealed that the introduction of P3BT significantly influenced the nucleation mechanism and growth geometry, i.e., PE was transformed from three-dimensional (3D) spherulitic to two-dimensional (2D) disc crystals. A striking reduction of nucleation density and an obvious ringed morphology of PE spherulites (2D) in PE/P3BT blends were also observed by polarized optical microscopy; it is proposed that the limited miscibility between PE and crystalline P3BT favors the formation of ringed PE spherulite in the blends. Additionally, preferred orientation of PE lamellae, with their b-axis largely constrained to the thin film plane, was observed by X-ray diffraction in PE/P3BT blend films. It is evidenced that the PE orientation was due to the b-axis being the crystal growth direction, which can only be in film plane.     

Structure and Properties of Ultradrawn Polylactide/Thermoplastic Polyurethane Elastomer Blends

Highly oriented self-reinforced 80/20 blends of polylactide (PLA)/thermoplastic polyurethane elastomer (TPU) were successfully fabricated through solid hot stretching technology. Different from the isotropic sample, stress rose rapidly in a low strain region, and exhibited strain hardening for the drawn samples of the PLA/TPU blend. Superior mechanical properties of the blend, with the notched Charpy impact strength 150 KJ/m², and tensile strength 197 MPa, were achieved. With increasing hot stretch ratio, the storage modulus increased, the glass transition temperatures of the PLA-rich phase and TPU-rich phase in the blends moved to higher temperatures, and the melting temperature and crystallinity of the blend increased, indicating the stress-induced crystallization of the blend during drawing. The longitudinal fracture surfaces of the blends at different stretch ratios exhibited orderly arranged fibrillar bundle structure, which contributed to the significantly higher strength and toughness of the blend.     

CRYSTALLIZATION IN PARTIALLY MOLTEN ORIENTED BLENDS OF POLYCONDENSATES AS REVEALED BY X-RAY STUDIES*

Oriented fibers or films of binary polymer blends from polycondensates were investigated by two-dimensional (2D) wide-angle X-ray scattering (WAXS) during the finishing process of microfibrillar reinforced composite (MFC) preparation, that is, heating to a temperature between the melting temperatures of the two components, isothermal annealing, and subsequent cooling. It is shown that the crystallization behavior in such MFC from polycondensates depends not only on the blend composition, but also on thermal treatment conditions. Poly(ethylene terephthalate)/polyamide 12 (PET/PA12), poly(butylene terephthalate)/poly(ether ester) (PBT/PEE), and PET/PA6 (polyamide 6) composites were prepared in various compositions from the components. Materials were investigated using rotating anode and synchrotron X-ray source facilities. The effect of the annealing time on the expected isotropization of the lower melting component was studied in the PET/PA6 blend. It was found that PA6 isotropization took place after 2 h; shorter (up to 30 min) and longer (up to 8 h) melt annealing results in oriented crystallization due to different reasons. In PET/PA12 composites, the effect of PA12 transcrystallization with reorientation was confirmed for various blend compositions. The relative strength of the effect decreases with progressing bulk crystallization. Earlier presumed coexistence of isotropic and highly oriented crystallites of the same kind with drawn PBT/PEE blend was confirmed by WAXS from a synchrotron source.

     

Effects of Blend Ratio on Rheology,Morphology, Mechanical and Oil-Resistant Properties in Chlorinated Polyethylene Rubber and Copolyamide Blends

The elastomeric chlorinated polyethylene (CPE) blended with a low melting point copolyamide (PA6/PA66/PA1010, PA) was prepared by a melt mixing technique. The mixing characteristics of the blends were analyzed from the rheographs. The influence of copolyamide (PA) content on the morphology, mechanical properties, crystallization and oil-resistance, and the addition of compatibilizers on the mechanical properties were also systematically investigated. Morphological examinations clearly revealed a two-phase system in which CPE/PA blends exhibit a cocontinuous morphology for 50/50 composition, and the continuous phase of PA turns into a disperse phase for 70/30, 80/20, and 90/10. There is a distinct interface between the two phases. The mechanical properties, crystallization, and oil-resistance have a strong dependence on the amount of PA. The blends with higher proportions of PA have superior mechanical properties; they are explained on the basis of the morphology of the blend and the cystallinity of PA. In addition, compatibilizers, including chlorinated polyethylene-graft-copolyamide (CPE-G-PA), chlorinated polyethylene-graft-maleic anhydride (CPE-G-MAH), ethylene-n-butyl acrylate-monoxide (EnBACO), and ethylene-n-butyl acrylate-monoxide-graft-maleic anhydride (EnBACO-g-MAH) were added into the blends. Tensile strength and elongation at break go through a maximum value at a compatibilizer resin content (on the basis of the total mass of the blend) of 20 wt% while the PA content is 30 wt%.     

Epitaxial crystallization of crystalline polymers on the surface of drawn polytetrafluoroethylene

Crystallization of crystalline polymers on the surface of drawn polytetrafluoroethylene (PTFE) was studied. Further, cold-drawn polyethylene (PE) was heat treated in contact with drawn PTFE, holding their drawing axes at right angles to each other, and then the morphological change of PE at the interface was studied. Molecular orientation in the surface layer of the PE was examined by observing the molecular orientation of polycaprolactone (PCLn) crystallized on the PE surface.

It was found that PE, PCLn, and nascent nylon 6 crystallize epitaxially on drawn PTFE, which is well known as a polymer having a low energy surface. Intermolecular interaction between PTFE and the overgrown crystalline polymers was explained on the basis of their crystal structures. The molecular orientation of PE in the interfacial region changes from the drawing direction of PE to the drawing direction of PTFE during annealing. It is proposed that PE partially melts during annealing, and nuclei of PE with their c-axis parallel to the molecular axis of PTFE are formed at the interface. Consequently, PE lamellar crystals with their c-axis perpendicular to the original drawing direction grow in the interfacial region between PE and PTFE.     

Phase Morphology and Mechanical Properties of Polyamide-6/Polyolefin Elastomer-g-Maleic Anhydride Blends

The effects of addition of varying amounts of polyolefin elastomers (POE) (with and/or without grafted maleic anhydride) on the morphology and mechanical properties of polyamide-6 (PA6)-based blends were studied. Scanning electron microscopy (SEM) was employed to obtain some detailed quantitative analyses of the morphology of the fracture behavior for the blends containing 80 wt% PA6 and 20 wt% total elastomer. Impact strength, tensile strength, and flexural strength were also measured for these blends. The results showed that POE and PA6 were an incompatible system, but the POE-g-MAH was compatible and had a toughening effect on PA6. PA6-g-POE was formed through the reaction between POE-g-MAH and PA6 during the melt extrusion process, which reduced the size of the dispersed phase and improved the impact and tensile strength of the blends. The impact strength was improved by nine times compared with the pure PA6 or the binary blend PA6/POE when the blend ratio of the ternary blend PA6/POE/POE-g-MAH was 80/16/4.     

Influence of Blend Composition on Crystallization of Poly(L-Lactic Acid)/Poly (Ethylene Oxide) Crystalline/Crystalline Blends

The effect of blend composition on crystallization morphology and behavior of a crystalline/crystalline blend, poly(l-lactic acid) (PLLA)/poly(ethylene oxide) (PEO), during slow, non-isothermal crystallization was studied by polarized light microscopy (PLM) connected with a hot-stage and differential scanning calorimetry (DSC). The results showed that all of the PLLA/PEO blends produced spherulites which gradually became bigger and looser, as well as coarser, with the increment of the PEO content, indicating that the PEO crystals was resided in the interlamellar or interfibrillar (between clusters of commonly oriented lamellae) regions of the PLLA spherulites. In the (25/75) and (10/90) blends, the nucleation and growth processes of the PEO spherulites could be clearly observed in the pre-existing PLLA spherulites. The onset crystallization temperature and the melting point of one component decreased with increasing the content of the other one owing to the good miscibility of the two components in the non-crystalline state and the interaction between their macromolecules, indicating that the crystallization of each component was influenced by the other one.     

PREPARATION OF a-AXIS ORIENTED YBa2Cu3Ox THIN FILMS

The a-axis oriented YBa₂Cu₃O_x(YBCO) thin films could be grown on (100) SrTiO₃(STO) substrates with STO buffer layers by dc and rf magnetron sputtering either by low-ering the deposition temperature, or by using a self-template technique. For the latter, the resistivity of the thin film at 290K along the substrate [001] direction is about four times larger than that in the [010] direction. The zero resistance temperatures T_c0 are 89 K in both directions. So high quality a-axis oriented YBCO thin films can be prepared by the self-template technique. Also the T_c0 increase monotonously with the reduction of the thickness of the YBCO seed layer.     

Isothermal lamellar thickening in blends of linear and low-density polyethylene

Polyethylene blends were studied by differential scanning calorimetry (DSC) and transmission electron microscopy (TEM). Binary blends of commercial linear polyethylene (LPE) with two low-density polyethylenes (LDPEs) of melt indexes, about 20 and about 0.27 g/10 minutes, were investigated. The blends, with 10% and 50% LPE contents, and the pure LPE were isothermally crystallized at 124°C for up to 48 h under solid-liquid phase segregation conditions. Double melting endotherms were obtained for the blends. Results show that, despite differences in crystallization kinetics between both types of blends, the same depression in the LPE melting temperature and approximately the same LPE crystal thicknesses were found for the blend compositions. In addition, the extent of occurrence of lamellar thickening in LPE during crystallization is a function of its content in the blend.     

Interfacial structure analysis of polymer laminate using SPring-8 X-ray microbeam

Interfacial structure of laminated polyethylene (PE)/polypropylene (PP) films was investigated by synchrotron X-ray microbeam. The X-ray microbeam (0.9 μm (vertical) × 1.7 μm (horizontal)) formed using a phase zone plate was irradiated on the cross-section of the laminated films. In order to irradiate X-ray microbeam in the direction perpendicular to the cross-section of the film sample, adjustment of the sample setting was performed by Thomson scattering method. The Thomson scattering intensity is proportional to the number of the irradiated electrons, so the irradiated position of the X-ray microbeam could be determined from the intensity profile with high spatial resolution. By changing the sample position, diffraction patterns could be obtained from the laminated films across the PE/PP interfacial region. The thickness of the interfacial region of the annealed laminate was estimated as 5 μm judging from the changes of the diffraction intensities from the PE crystallites to the PP ones. The interfacial thickness depended on the thermal treatment of the film. It was found that the adhesion strength of the PE/PP laminate increased with increasing the interfacial thickness. Both of PE and PP chains entangled each other during laminate processing. The entangled molecular chains play important role as anchoring effect at the PE/PP interdiffusion region. However, the phase separation progressed with further crystallization by annealing. Thus, the adhesion strength of the PE/PP laminate was considered to be influenced by the interfacial thickness.     

The Structure and Properties of Polyamide/Liquid Crystal Polymer Blends

Melt blended polyamide (PA)/liquid crystal polymer (LCP) blends were prepared and their structures and properties were studied. The tensile strength and impact strength of the PA/LCP blends increased with increasing small amount of LCP content. Compared with a pure PA sample, there was a 17.7% increase in the tensile strength and a 45.5% increase in the impact strength when the LCP content was less than 10%. On the other hand, the Vicat softening temperature decreased with increasing the LCP content. Differential scanning calorimetry (DSC) showed that small addition of LCP was beneficial to increase the crystallinity of PA component for PA/LCP blends and the melting peak for the PA component of PA/LCP blends shifted to lower temperature with increasing LCP content. Scanning electron microscopy (SEM) displayed a layered structure existing in the injection moldings of PA/LCP blends with the LCP crystals having a preferred orientation along the melt flow direction in the sub-skin, shearing layer, and core region. The increased crystallinity of PA component and preferred orientation structure of LCP phase were beneficial to increase the mechanical properties of the PA/LCP blends.     

Epitaxial Crystallization of Linear Polyethylene in Blends with Isotactic Polypropylene

The structure and morphology of extrusion-oriented ribbons of polypropylene/polyethylene blends is described. The blends with 20%, 30%, and 40% of oriented isotactic polypropylene fibrils show homo- and heteroepitaxial structures. Partial mutual solubility of the blend components influenced the melting and crystallization behavior.     

Effect of Organoclay Platelets on Crystallization of PTT/EPDM-g-MA Blends: Nonisothermal Melt Crystallization Kinetics

PTT/EPDM-g-MA (80/20 w/w) nanocomposites were prepared by melt mixing of poly(trimethylene terephthalate) (PTT), ethylene-propylene-diene copolymer grafted with maleic anhydride (EPDM-g-MA), and organoclay. The blend nanocomposites show typical sea-island morphologies. The nonisothermal crystallization kinetics of pure PTT and 80/20 (w/w) PTT/EPDM-g-MA blends with various amounts of the clay were extensively studied by differential scanning calorimetry (DSC). The Avrami, Ozawa, and Mo methods were used to describe the nonisothermal crystallization process of pure PTT and 80/20 (w/w) PTT/EPDM-g-MA blends with various amounts of the clay. Avrami analysis results show that the crystallization rates of 80/20 (w/w) PTT/EPDM-g-MA blends with the clay were faster than those of pure PTT or PTT/EPDM-g-MA blends without clay, which indicates that the clay particles promote crystallization effectively, in agreement with the Mo analysis results. Ozawa analysis can describe the nonisothermal crystallization of pure PTT very well but was rather inapplicable to the 80/20 (w/w) PTT/EPDM-g-MA blends with various amounts of the clay.     

CRYSTALLIZATION OF A LOW MOLECULAR WEIGHT POLYETHYLENE AND PARAFFINS UNDER A TEMPERATURE GRADIENT

A low molecular weight polyethylene (PE) and even-number paraffins were crystallized under a temperature gradient. Highly oriented crystalline textures were developed by the temperature slope crystallization. The in situ crystallizing surface was observed by an optical microscope and X-ray diffraction. Polyethylene has a b-axis orientation in which the lamellar normal and crystalline c-axis are perpendicular to the temperature gradient. On the contrary, in the even-number paraffins, both axes are parallel to the temperature gradient. The results of the in situ measurements and the crystalline orientation are compared and discussed for both cases.     

The study of compatibility of polyethylene and polypropylene by using irradiated polyethylene wax

The modification of the compatibility between polyethylene (PE) and polypropylene (PP) by using irradiated PE wax (PE wax) is the purpose of this study. In this part, polymer blends based on various ratios of PE and PP were blended with 2.5% PE wax in all the blend ratios to determine the optimum ratio of the blend to be compatabilized. The influence of PE wax as a compatibilizing agent for PE and PP blend was investigated through the measurements of thermal, mechanical and morphological properties. The PP/PE blends modified by this method showed higher mechanical properties than those of the unmodified blends. Also, stress and strain of the modified blend having ratio (60/40) PP/PE blend recorded the maximum mechanical behavior. Scanning electron microscopy (SEM) micrographs of modified blends showed an indication of strong interfacial adhesion and a smooth continuous surface in which giving a support to the effect of irradiated PE wax as a tool for improving the compatibility.     

在不同衬底上制备的ZnO薄膜透射率的研究

采用反应磁控溅射在不同结构衬底上生长ZnO薄膜,通过X-ray衍射(XRD)及透射光谱来分析薄膜的成膜情况,并得出在Al₂O₃/AlN复合基上溅射沉积的ZnO薄膜比单独在AlN薄膜衬底的结晶质量好且透过率也较高。而经不同的快速热退火温度验证,发现在400 ℃时,ZnO薄膜的结晶化及在(002)方向上的择优取向达到最好,并在可见光范围内的平均透过率达到88%以上。当退火温度超过450 ℃时,温度过高改变了ZnO薄膜的内部结构,使其氧原子和锌原子发生了较大距离的位移,导致薄膜内部缺陷的增多,从而存在过多的晶界,增加了其薄膜的散射机制,使光的透过性变差,退火温度为500 ℃时,薄膜的平均透过率为80%。     

Effect of PMMA on crystallization behavior and hydrophilicity of poly(vinylidene fluoride)/poly(methyl methacrylate) blend prepared in semi-dilute solutions

Films of poly(vinylidene fluoride) (PVDF)/poly(methyl methacrylate) (PMMA) blend were derived from a special procedure of casting semi-dilute solutions. Hydrophilic character and crystallization of PVDF were optimized by variation of PMMA concentration in PVDF/PMMA blends. It was found that a PVDF/PMMA blend containing 70 wt% PMMA has a good performance for the potential application of hydrophilic membranes via thermally induced phase separation. The films presented β crystalline phase regardless of PMMA content existed in the blends. Thermal analysis of the blends showed a promotion of crystallization of PVDF with small addition of PMMA which induced larger lamellar thickness of PVDF, leading to the largest spherulitic crystal of PVDF (10 wt% PMMA) is about 8 μm. SEM micrographs illustrated no phase separation occurred in blends, due to the high compatibility between PVDF and PMMA.     

PREPARATION OF a-AXIS ORIENTED YBa2Cu3Ox THIN FILMS

The a-axis oriented YBa₂Cu₃O_x(YBCO) thin films could be grown on (100) SrTiO₃(STO) substrates with STO buffer layers by dc and rf magnetron sputtering either by low-ering the deposition temperature, or by using a self-template technique. For the latter, the resistivity of the thin film at 290K along the substrate [001] direction is about four times larger than that in the [010] direction. The zero resistance temperatures T_c0 are 89 K in both directions. So high quality a-axis oriented YBCO thin films can be prepared by the self-template technique. Also the T_c0 increase monotonously with the reduction of the thickness of the YBCO seed layer.     

Phase Behavior of Rapidly Quenched PVDF/PMMA Blends as Characterized by Raman Spectroscopy,X‐Ray Diffraction and Thermal Techniques

Although PVDF/PMMA blends have been studied extensively, the phase behavior as a function of melt quenching conditions has not been examined in detail in the past. In this paper we report our results on the isotropic blends of PVDF/PMMA quenched into ice water as well as on a casting roll set at 30°C in all composition ranges. The results confirm the miscibility of this blend for all composition ranges, although at high PVDF (～85%) concentration micro heterogeneities were evidenced through thermal analysis. Though pure PVDF is observed to be mostly in the α crystalline form, the addition of PMMA favors the β crystal structure in composition range 85/15–60/40. Ice water quenching yields amorphous blends containing more than 40% PMMA and these films are deemed good candidates for rubbery state processes (between T _g and T _cc), including tenter frame biaxial stretching, where they can be oriented significantly at these low temperatures while undergoing strain induced crystallization.     

Interfacial morphology and friction properties of thin PEO and PEO/PAA blend films

The scanning force microscope (SFM) was used to investigate morphology of poly(ethylene oxide) (PEO) and poly(acrylic acid) (PAA) blend. The effect of solvent and dewetting in surface structure of PEO film was reported. The results manifested that the crystallization of PEO could be suppressed completely in ultrathin region via using chloroform as a solvent, and the branched-like crystallization was recovered after dewetting. Also, the effect of thickness, the ratio of PEO/PAA and dewetting in surface morphology of PEO-PAA blend films were investigated. These results showed that the crystallization was highly dependent on the ratio of PEO/PAA and the thickness of blend film. Furthermore, we assembled the PEO/PAA layer-by-layer film by spin-casting method for the first time, which exhibited highly efficiency. As a complementary tool, we also used lateral force microscopy (LFM) to explore surface information of these films. The result was indicative of interfacial constraints in ultrathin region, and also was supported by the results showing the spin-casting PEO/PAA blends rather than heterogeneous mixture.