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Star-shaped polystyrene-block-polybutadiene-block-polystyrene (SBS) block copolymer (BCP) was subjected to epoxidation reaction using m-chloroperoxy benzoic acid (MCPBA). The epoxidized SBS block copolymer (eSBS) was then blended with diglycidyl ether of bisphenol-A based epoxy resin (EP) and cross-linked with methylene dianiline (MDA). The materials were characterized by different techniques such as Fourier transform infrared (FTIR) spectroscopy, transmission electron microscopy (TEM), and thermogravimetric analysis (TGA). The FTIR spectrumwith the peak located at 890 cm−1 and 1230 cm−1 attested the occurrence of epoxidation reaction. The nanophase separated structures as demonstrated by transmission electron microscopy were induced in the eSBS/EP blends by epoxidized eSBS.

Multilayered composites of polypropylene (PP) and polystyrene (PS) fabricated by a layer-multiplying coextrusion technique are described. The aim of this investigation was to find a correlation between the morphology and the mechanical and micromechanical deformation behavior. The multilayered films had primarily continuous layers, exhibiting only few defects in layer construction and turning into an irregularly layered system when the calculated layer thickness was only 5 nm. The morphology and layer thickness of both the PP and PS layers affected the mechanical and the micromechanical behavior, which was brittle for the films having PS layers thicker than 75 nm and ductile when the PS layers were 50 nm and thinner. Transmission electron microscopy showed crazes in the thicker PS layers and homogeneous deformation in the thinner ones. The molecular orientation during deformation of the ductile films was calculated from rheo-optical measurements with Fourier transform infrared spectroscopy. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

The effectiveness of reinforcement of a polymer is known to depend on the strength of the interfaces between the reinforcement and the matrix. We have used polystyrene and a styrene–butadiene–styrene (SBS) copolymer as matrixes and ceramic boehmite γ-AlO(OH) as reinforcement. We have applied boehmite both untreated and treated with sulphonic acid based surfactants with different alkyl groups. As expected, the coupling agents improve the adhesion between the polymers and the ceramic filler. The presence of boehmite and treatments affect the glass transition temperatures determined by dynamic mechanical analysis, nanoindentation hardness hnanoindent as well as Vickers microhardness hVickers. For SBS and SBS containing composites, the hnanoindent/hVickers ratio is a constant.

Using electrospinning technique polystyrene (PS) nanofibers in the thickness range from 150 to 800 nm have been produced. Electron microscope inspections reveal the relatively uniform thickness of the obtained fibers. The me- chanical deformation mechanisms have been studied in ten- sion tests using micro-tensile devices for a scanning electron microscope (SEM) and a transmission electron microscope (TEM). A characteristic change in the deformation behavior from the typical craze formation of PS to a micro necking and cold drawing has been found with decreasing fiber thickness. There is a surprisingly sharp fiber thickness limit between both deformation types in the range of 220-225 nm: nanofibers thicker than � 225 nm deform with formation of crazes, nano- fibers thinner than � 225 nm show necking and cold drawing.

11 pags. ; 11 figs. ; 1 tab., The present work is concerned with the study of the crystalline morphology and the nanostructure of a multilayered system of two alternating immiscible semicrystalline polymers: isotactic polypropylene (iPP) and polyamide 6 (PA6). Films with a volume ratio of 70/30 were prepared by means of layer multiplying coextrusion. Contrary to previous experiments, performed with semicrystalline/amorphous and amorphous/amorphous nanolayered systems, the studied iPP/PA6 film does not exhibit a well defined maximum in the USAXS patterns. This result accounts for an irregular layered structure, as further confirmed by means of TEM images. Nevertheless, such a layered assembly still influences the crystallization behaviour of both constituent polymers. On the one hand, the crystallization of PA6 within the multilayered material is substantially hindered as evidenced by its weak scattering intensity. Real time studies as a function of temperature undoubtedly detect the presence of a WAXS peak and a SAXS maximum associated to PA6 above the melting temperature of iPP. Room temperature AFM studies also confirm the occurrence of crystalline structures within the PA6 layers., On the other hand, SAXS and WAXS measurements at room temperature reveal the occurrence of an oriented lamellar morphology within the iPP layers bearing uniaxial symmetry around an axis perpendicular to the layers surface. Results show that the crystalline molecular chains are placed mainly parallel to the layer surfaces forming edge-on lamellae. Moreover, X-ray scattering results are in agreement with the occurrence of two populations of lamellae, both edge-on and perpendicular to each other, in agreement with the crosshatched morphology observed by AFM., The authors gratefully acknowledge MICINN, Spain (grants FIS2007-60534 and FIS2010- 18069), USA NSF Science and Technology Center for Layered Polymeric Systems (Grant 0423914), German Research Foundation (DFG) and European Community contract RII3-CT- 2004-506008 (IA-SFS), DESY project II-20070031, for generous financial support.

To reveal the features of the structure of UHMWPE that depend on the catalytic system used for synthesis, a comparative study of the sets of laboratory and commercial powders of UHMWPE synthesized on different catalysts in the slurry process under different conditions is conducted. This study includes the use of various modern physical methods, such as transmission and scanning electron microscopy, X-ray analysis, Raman scattering spectroscopy, differential scanning calorimetry, nuclear magnetic resonance, and thermoluminescence. All nascent particles are shown to have a complex hierarchical structure. In all reactor powders, the elementary structural unit is crystalline lamellas, whose dimensions and mutual orientation are dependent on the type of catalytic system. In the synthesis on the supported catalysts, the character of the formed structure depends on the characteristics of the substrate. During the breakdown of the substrate in the course of the synthesis, fibrils form. The colloidal dimensions of the catalyst particles are responsible for a more uniform lamellar structure of the reactor powders. The conformational composition of the segments of molecules in the interlamellar regions of the reactor powders is characterized.

Using transmission electron microscopy (TEM) and tensile testing, we investigated the morphology and the micro-deformation processes in a new kind of highly asymmetric polystyrene/polybutadiene based triblock copolymer and its blends with general purpose polystyrene (GPPS). The emphasis has been put on the analysis of blends morphology evolved under extrusion conditions and the impact of the later on the micromechanical behaviour of the blends. It was found that the phase separated structures were strongly oriented along the extrusion direction leading to the anisotropic mechanical behaviour. The blends showed more ductile performance and lesser strength on loading the sample perpendicular to the extrusion direction. The ductile to brittle transition was observed when the morphology of the blends was dominated by the glassy phase for 60 wt.-% GPPS.

Nanocomposite scaffold materials based on biodegradable polymers, as there are poly(3-hydroxybutyrate (PHB), poly(hydroxybutyrate-co-hydroxyvalerate) (PHBHV) and polycaprolactone (PCL), and nanocrystalline hydroxyapatite (HA) have been developed for the application as biomimetic bone substitution materials and materials for the tissue engineering of bone. Parameters like pore size, shape and interconnectivity are optimized to facilitate the formation of new bone. In this paper we describe a manufacturing method for compact nanocomposite scaffolds as well as for 3 -dimesional porous scaffolds. Nanocomposite scaffolds consisting of PHB and HA needles or PHBHV and HA spheres, respectively, exhibit a very good filler dispersion even at 20 wt% loading. Smaller nanoparticles (needles) slightly tend to develop more agglomerates due to higher van der Waals forces of attraction compared to the larger spherical nanoparticles which were more uniformly dispersed. To produce porous structures, templates consisting of sugar and NaCl grains of varying grain size were used. In freeze-drying and particulate leaching processes smaller grain sizes resulted in pores with 46 to 70 μm, whereas grain sizes of more than 400 μm resulted in pores with 300 to 600 μm in diameter. The application of polymer solutions with a concentration of 5 % (w/v) resulted in larger pore sizes compared to solutions of 10% (w/v). By the application of the melt infiltration technique to PCL, the resulting pore size was less influenced by the concentration of the polymer solution. It can be demonstrated that these techniques are suitable for the fabrication of nanocomposite scaffolds with uniform filler dispersion and porosity up to 9 8%.

Electrospun micro- and nanofiber scaffolds have gained interest in biomedical applications, especially in tissue engineering, because they can be used to reproduce the structure of the extracellular matrix (ECM) of natural tissue. The selection of the solvent is an important factor which affects the diameter, the surface morphology and the crystallinity of the electrospun fibers, and, accordingly, their mechanical properties as well as their degradation kinetics. Furthermore, the surface morphology of the electrospun fibres can be controlled by solvent vapour pressure to produce porous structures which might be helpful for cell adhesion and proliferation. In the present work, poly (L-lactic acid) (PLLA) has been electrospun using solvents with different vapour pressures to investigate the influences of the solvent vapour pressure on morphology, diameter, crystallinity and mechanical properties of the electrospun fiber scaffolds. The results show that the vapour pressure of the solvents (or solvent mixtures) play an important role in the fiber diameter and crystallinity. Furthermore, the crystallinity of the fibers is increased by lowering the vapour pressure of the used solvent. In addition, the mechanical properties (e.g., tensile strength and Young's modulus) are strongly dependent on morphological features such average fibers diameter. The smaller the average diameter, the higher the tensile strength and Young's modulus.

This work reports on morphological, mechanical, and micromechanical properties of polyamide 6 (PA 6), a styrene-acrylonitrile copolymer (SAN), and their blends, which were reactively compatibilized using a styrene-acrylonitrile maleic anhydride (SANMA) terpolymer. Transmission electron microscopy (TEM) investigations revealed the phase morphology of the blends, which is characterized by inclusions of the minor component in the matrix of the major phase. The blend with 50% PA 6 and 50% SAN depicted a cocontinuous morphology. Using a microtensile device for TEM, the samples were deformed under uniaxial loading in the “dry” state (characterized by a zero water content in the PA 6 phase) and in a “wet” state (with water in the PA 6 phase). Whereas the dry blends behaved brittle, the wet blends showed a larger ductility with the formation of deformation bands in the matrix (PA 6 or SAN), which were initiated by stress concentration at the SAN and PA 6 particles, respectively. In the interface of blends with a PA 6 matrix and SAN inclusions, two phenomena were observed: partial cavitation and debonding on the one hand and partial fibrillation on the other hand. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

In this work, in situ investigations of the micromechanical properties of reactively compatibilized blends of polyamide 6 (PA6) and an acrylonitrile–butadiene–styrene copolymer (ABS) were performed with transmission electron microscopy. Three PA6/ABS blends were prepared with a disperse morphology (inclusions of PA6 or ABS) and with a cocontinuous structure. The objective of this work was to study the deformation of the inclusions and the interface between the PA6 phase and the ABS phase. Our transmission electron microscopy investigations revealed that the morphology of the blends was strongly influenced by the asymmetric nature of the interface between PA6 and ABS. In the blends with a PA6 matrix, the interface between PA6 and the ABS inclusions was deformed in tensile deformation under uniaxial loading. A strong influence of the PA6 water content on the (micro)mechanical behavior was observed. Although the “dry” blends behaved in a brittle fashion, the “wet” blends behaved in a ductile fashion with the formation of deformation bands in the matrix (PA6 or ABS), which were initiated by stress concentration at the particles (ABS or PA6, respectively). © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

Studies of thermal and fire-resistant properties of the polyethylene/organically modified montmorillonite (PE/MMT) nanocomposites prepared by means of melt intercalation are discussed. The sets of the data acquired with the aid of non-isothermal TG experiments have been treated by the model kinetic analysis. The extra acceleration of thermal-oxidative degradation of the nanocomposite which has been observed at the first stage of the overall process has been analyzed and is explained by the catalytic effect of the clay nanoparticles. The results of cone calorimetric tests lead to the conclusion that char formation plays a key role in the mechanism of flame retardation for nanocomposites.

Polymer/layered silicate nanocomposites, depending on the molecular weight of nylon 6 as the matrix, were prepared through melt blending with a twin-screw extruder to study their morphology and the role of layered silicates (i.e., montmorillonite) on local deformation processes. A thermal analysis of the nanocomposites was performed with differential scanning calorimetry. The dispersion of the layered silicates and nanocomposite morphology were investigated with wide-angle X-ray scattering and transmission electron microscopy. The results showed that the layered-silicate surfaces predominantly induced γ-form crystals of nylon 6, whereas α-form crystals were nucleated far away from the clay surface. The fraction of γ-form crystals and the degree of exfoliation increased with the molecular weight of the nylon 6 matrix. In a high-molecular-weight nanocomposite, a well-defined exfoliated nanomorphology was observed, in which fine nylon 6 lamellae were most likely to be oriented with their planes perpendicular to the injection-molding direction, although to a great extent the layered silicates were arranged on planes parallel to the injection-molding direction. On the contrary, a mixed nanomorphology appeared in a low-molecular-weight nanocomposite, intercalated and exfoliated nanomorphologies coexisting; the layered silicates were randomly dispersed in the nylon 6 matrix, and the nylon 6 lamellae grew in no preferential direction with respect to the layered-silicate surface. The dispersion of the layered silicates and the orientation of the layered silicates as well as the lamellae were directly reflected in the mechanical deformation processes. The results of in situ deformation experiments under a high-voltage electron microscope (1000 kV) indicated that the main deformation mechanism was microvoid formation either within the intercalated tactoids or in the vicinity of layered silicates in the matrix for intercalated and exfoliated nanomorphology systems, respectively. In the exfoliated nanocomposite, that is, the high-molecular-weight nanocomposite, the external applied stresses were much more effectively transferred from the polymer matrix to the layered silicates; furthermore, microvoid formation took place more uniformly and homogeneously throughout the deformed specimen, and thus a well-improved stiffness/strength/ toughness balance was achieved in comparison with the mixed nanomorphology system (the low-molecular-weight nanocomposite). © 2007 Wiley Periodicals, Inc. JAppl Polym Sci 105: 38–48, 2007

Different types of polymer nanocomposites on the base of polystyrene, polymethylmethacrylate, and polycarbonate with alumina and SiO2 nanoparticles and carbon nanotubes have been studied. Miniaturized, microdimensional samples were used, enabling a good control of morphology and distribution of particles by means of transmission and scanning electron microscopy. Special preparation techniques had been applied, which resulted in a very good dispersion of the nanoparticles. Using these materials with really nanosized particles of a few 10nm in size the effect on toughness enhancement could be studied without agglomerates as they often appear in the generally used large samples. Micromechanical mechanisms were studied in detail by TEM and SEM investigations of deformed samples. A “nanoparticle modulated crazing” could be detected as a toughness enhancing effect. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007

The influence of the extrusion process on the morphology and micromechanical behavior of an asymmetric polystyrene-block-(polystyrene-co-butadiene)-block-polystyrene (SBS) star block copolymer and its blends with general-purpose homopolystyrene (hPS) was studied with films prepared with a single-screw extruder. The techniques used were transmission electron microscopy and uniaxial tensile testing. Unlike the pure SBS block copolymer possessing a gyroid-like morphology, whose deformation was found to be insensitive to the processing conditions, the mechanical properties of the blends strongly depended on the extrusion temperature as well as the apparent shear rate. The deformation micromechanism was primarily dictated by the blend morphology. The yielding and cavitation of the nanostructures were the principal deformation mechanism for the blends having a droplet-like microphase-separated morphology, whereas cavitation dominated for the blends containing macrophase-separated layers of polystyrene. The mechanical properties of the blends were further examined with respect to the influence of the temperature and shear rate on the phase behavior of the blends. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007

The change in the crystalline structure of oriented melt-crystallised and gel-cast UHMPWPE (Stamylan) films of various draw ratios during creep upon constant load has been followed in real time using synchrotron X-ray diffraction techniques at the synchrotron radiation source ANKA (Angstroemquelle Karlsruhe) at Forschungszentrum Karlsruhe (Germany). The shift of (002) Bragg reflections with time of loading and change in their halfwidth are observed for all the samples investigated. The analysis of the data shows a difference in the behaviour of loaded gel-cast and melt-crystallised films. The longitudinal crystallite sizes in the former grow with time, while in the latter they become smaller. Besides, the splitting of a (002) profile in WAXS patterns of melt-crystallised samples (including unstressed samples) was revealed. Several possible causes of this splitting are suggested. One of them is the co-existence of strained crystallites in monoclinic and orthorhombic crystalline modifications. The observed phenomena is discussed in terms of coherent disposition of crystallites in microfibrils, one-dimensional diffraction on taut-tie molecules, probable pulling-out of the molecules from crystallites upon creep and inhomogeneity of stress distributions.

8 pags., 7 figs., 1 tab., The microindentation hardness, H (critical stress required to mechanically deform a material), of a series of homogeneous ethylene-1-octene copolymers with high comonomer content and low crystallinities (α, The authors acknowledge the Ministerio de Educacion y Ciencia (Grant No. FIS2004-01331), Spain, for the generous support of this investigation.

It is well known that coupling agents improve the adhesion between poly(propylene) and wood fillers leading to an incre ase of the composite mechanical properties. Above a certain concentration limit of the coupling agent, however deterioration of the mechanical properties often occurs, and little attention has been directed so far towards finding out the reasons for that behavior. Transmission electron microscopy and high-voltage electron microscopy were used in this work to study the morphology and microdeformation behavior of PP/wood-flour composites modified with high amounts of maleated poly(propylene) as a coupling agent. It was found that the coupling agent containing a higher concentration of grafted maleic anhydride forms a separate phase in the poly(propylene) matrix, influencing the mechanical properties of the composites.

The deformation behavior of rubber-toughened polymer, which was prepared by incorporating soft, core-shell rubbery particles into a glassy polymer such as poly (methyl methacrylate) (PMMA), has been investigated by means of mechanical tests, optical monitoring (OM), and scanning electron microscopy (SEM). By mechanical testing, the neat PMMA reveals a 2% strain with high yield stress. After inclusion of 17.5 and 35 vol%rubber particles, the softened-PMMA samples exhibit corresponding strain of 20% and 38%, showing an increase of strain along with the relative decrease of yield stress, resulting in a toughening behavior of PMMA. Clear shear bands and stress whitening develop in the rubber-toughened PMMA after deformation, as observed by OM. Investigation by SEM shows crazes/cracks in the stretched, rubber-softened PMMA samples in which the core-shell particles are found to be cavitated. The mechanism of this deformation has been explained based on the void formation in the rubbery shell as well as...

The influence of homopolymer molecular weight and compression moulding on morphology formation and deformation behaviour of binary blends of polystyrene-polybutadiene based star block copolymer and polystyrene (PS) homopolymer was investigated. The samples used were a polystyrene-(polystyrene-co-polybutadiene)-polystyrene (S-S/B-S) star block copolymer and anionically prepared polystyrene (aPS). The techniques used were transmission electron microscopy (TEM) and uniaxial tensile testing. A wide range of segregation behaviour was observed depending on the ratio of the length of aPS chains relative to that of corresponding outer blocks of the block copolymer. For the first time, the formation of macrophase-separated 'droplet-like' morphology has been reported, which endows the block copolymer/polystyrene blends with higher toughness. The mechanical properties of blends are discussed in the light of micromechanical processes of deformation. The micromechanical mechanisms and their dependence with inter domain distance are similar to the mechanisms found in rubber network toughened systems.

Relationships between phase morphology and mechanical deformation processes in various electrospun polymer nanocomposite nanofibres (PNCNFs) containing different types of one-, two- and three-dimensional nanofiller have been investigated by transmission electron microscopy using in situ tensile techniques. From the study of the phase structure of electrospun PNCNFs, two morphological standard types are classified for the analysis of deformation mechanisms: the binary system (polymer matrix and nanofillers), and the ternary system (polymer matrix, nanofillers and nanopores on the fibres surface). According to these categories, deformation processes have been characterized, and different schematic models for these processes are proposed. The finding of importance in the present work is a brittle-to-ductile transition in polymer nanocomposite fibres during in situ tensile deformation processes. This unique feature in the deformation behaviour of electrospun PNCNFs provides an optimal balance of stiffness, strength and toughness for use as reinforcing elements in a polymer based composite of a new kind.

Heterophasic copolymers comprised of polypropylene (PP) matrix and ethylene–propylene copolymer (EPC) dispersed phase were investigated with respect to the dispersed phase composition, i.e., ethylene/propylene ratio. The rheological properties, morphology, as well as thermal and mechanical relaxation behavior were studied to describe the structure evolution and phase interactions between the components of the PP copolymers. Decrease of the ethylene content of the EPC leads to a higher matrix-dispersed phase compatibility, as evaluated by the shift of the glass transition temperatures of EPC and PP towards each other. At ethylene content of EPC of 17 wt %, the glass transition temperatures of the both phases merged into a joint relaxation. The effect of the EPC composition on the internal structure of the dispersed domains and on the morphology development of the heterophasic copolymers was demonstrated. Decreasing ethylene content was found to induce a refinement of the dispersed phase with several orders of magnitude down to 0.18 μm for propylene-rich EPC. Optical microscopy observations showed that the dispersed propylene-rich phase is preferably rejected at the interlamellar regions of the spherulites and/or at the interspherulitic regions, while the ethylene-rich domains are engulfed within the PP spherulites. Both of these processes impose an additional energetic barrier and influence the spherulite growth rate of the heterophasic materials. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 2825–2837, 2006

The addition of inorganic filler into commodity plastics has a long history. Today, polymer composites based on nanosized filler are popular among polymer scientists from academia and industries due to their ability to enhance a number of physical properties. In this work, we investigate the dispersion and reinforcing effect of alumina nanoparticles using a polystyrene-polybutadiene based block copolymer (SBS) and organically modified alumina nanofiller. With the aid of solution casting procedures, polymer composites with good dispersion of nanoparticles could be produced. It has been demonstrated that with suitably coated nanoparticles, polymer composites with optimum dispersion of nanofiller ensuring marked reinforcement effect can be achieved.

Mechanical deformation processes of electrospun composite fibers based on polycarbonate with multiwalled carbon nanotubes (MWCNTs) were investigated by in situ tensile tests under transmission electron microscope (TEM) depending on morphology. Using chloroform as solvent and optimizing process conditions, uniform nanoporous composite fibers were generated by electrospinning process. TEM images indicate that the MWCNTs were embedded in the fibers as individual elements, highly aligned parallel to one another along the fiber axis, which makes the mechanical load transfer from the polymer matrix to the MWCNT more favorable. Due to the slippage of individual MWCNTs within the fibers the strain at break of composite fibers is significantly enhanced. In addition, the nanopores on the fiber surface provide the effective sites for stress concentration for the plastic deformation to form nanonecking of fibers under tensile load. Combination of these unique features makes the electrospun composite fibers extremely strong and tough. The results from present work may provide a feasible consideration of such electrospun composite fibers for use as the reinforcing elements in a polymer based composite of a new kind.

Cyclic olefin copolymers (COC) of ethylene and different types of cyclic monomers were investigated in detail. In particular, the influence of the type and the content of cyclic monomers on the micromechanical deformation behaviour was studied using electron microscopy. Several deformation modes as fibrillated crazes, homogeneous deformation zones, shear-bands, and occasionally a combination of some of these deformation structures were observed in these materials. The different deformation modes are correlated with the mechanical properties. A tendency to an increase in brittleness with increasing cyclic monomer content was observed. COC with larger side chains in the cyclic monomer show a more ductile behaviour with the corresponding deformation structures than COC with norbornene.

Using transmission electron microscopy (TEM) and scanning force microscopy (SFM), this work deals with morphology and micromechanical deformation behavior of coextruded multilayers comprising alternating layers of polycarbonate (PC) and polyethylene terephthalate (PET). The multilayered composites were found to consist of macroscopically aligned continuous layers of the constituents having nearly uniform thickness. On annealing the samples, the PET layers were found to undergo cold-crystallization and to form lamellar crystals independent of thickness of individual layers. Under the influence of tensile loading, mechanical properties of the composites was found to be intermediate between that of the constituent homopolymers. The components of the multilayered composites deformed in homogeneous manner at high strains without forming localized deformation zones. Copyright © 2005 John Wiley & Sons, Ltd.

8 pags. 9 figs., The relationship between morphology and deformation behavior of selected ethylene/1-octene copolymers (EOCs) and their blends with high density polyethylene (HDPE) was investigated. The copolymers showed, depending on the 1-octene content, different morphologies ranging from lamellar to worm-like crystalline domains. The binary HDPE/EOC blends studied, which showed well phase-separated structures consistent with individual melting and crystallization behavior of the blend components, were characterized by a wide range of mechanical and micromechanical properties. The study of strain induced structural changes in an HDPE/ EOC blend revealed that at large strains, the extensive stretching of the soft EOC phase is accompanied by rotation of lamellar stack along the strain axis and subsequent fragmentation of the crystals forming beaded-string-like structures. A significant depression in microhardness was observed in the copolymers. In their blends with HDPE, a deviation in microhardness behavior from the additivity law was observed. Copyright © 2005 John Wiley & Sons, Ltd.

10 pags. 7 figs., The microindentation hardness,H, of uniaxially deformed isotactic polypropylene samples was determined near the neck region, as a function of the draw ratio. The microhardness technique appears to be a valuable tool to describe mechanical properties in localized regions within a material and is capable of following changes in the semicrystalline structure during deformation. Differences in the microhardness behaviour of the two types of polymorphic forms, α and β, of isotactic polypropylene are discussed in terms of the two specific types of morphology, i.e. the cross-hatched arrangement of the crystalline lamellae for the α form and the parallel lamellar stacking for the β form. The changes of H as a function of λ are shown to be in accordance with the transformation in the neck from the spherulitic into the fibre structure. The steep H-decrease observed in the neck region is discussed in the light of the nanomechanical processes as revealed by scanning electron microscopy. These include lamellar separation, micro-void formation and fibrillation. Finally, microindentation experiments carried out in the neck allow an estimation of the local draw ratio at which the maximum pore content in the polypropylene samples occurs. © Springer-Verlag 2004.

Polymer blends comprising a polystyrene-block-polybutadiene-block-polystyrene (SBS) block copolymer and atactic homopolystyrene (hPS) were investigated using injection molded and solution cast samples. The morphology of the materials was studied by means of transmission electron microscopy (TEM) and scanning force microscopy (SFM). Dynamic mechanical analysis (DMA) was used to characterize the phase behavior and the morphology formation of the block copolymer as well as of the SBS/hPS blends. The glass transition temperatures seem to strongly depend on the homogeneity of the corresponding phases. A distinct difference was found between the morphologies of the blends prepared by different methods. While the SBS block copolymer always shows a lamellar morphology in injection molded or as-cast samples, the injection molded blends show a disturbance in the morphology consisting of alternating layers. In contrast, in the case of as-cast samples, added hPS forms polystyrene domains dispersed in a matrix of the pure block copolymer. Regarding the change in the glass transition temperature, in the effective volume and in the interfacial volume obtained from DMA curves, the morphology formation of the injection molded samples (pure SBS block copolymer and the corresponding blends) was investigated. Two different structural models for the blends are proposed. Polym. Eng. Sci. 44:1534–1542, 2004. © 2004 Society of Plastics Engineers.

By means of transmission electron microscopy (TEM) and uniaxial tensile testing, the connection between the morphology and the micromechanical properties of selected styrene-rich styrene/butadiene block copolymers was studied with respect to their molecular architecture. In particular, the structure-property correlation of a lamellae forming asymmetric linear SBS triblock copolymer was examined by systematically varying the sample preparation techniques and testing temperature. The molecular architecture was found to influence directly the morphology formation of the block copolymers. Different mechanisms such as drawing of the lamellae, shearing in the rubbery phase and rotation of the lamellar axis were observed. From room temperature down to the temperature close to glass transition temperature of the soft phase, a homogeneous plastic drawing of glassy lamellae was perceptible.

Two samples of isotactic polypropylene (iPP) representing the crystalline α- and (3- modifications are compared with regard to their semicrystalline morphology and the resulting micromechanical mechanisms. Processes at room temperature (23°C) and at -40°C have been investigated by means of different microscopic techniques. Good results can be achieved by the application of a chemical etching technique to the deformed samples prior to scanning electron microscopy inspection. The toughness enhancement that is measured for the β-iPP is attributed to micromechanical mechanisms initiated within the intercrystalline, amorphous phase. It is shown that the specific nanostructure (lamellar arrangement) causes significant changes in the mechanical behaviour of the materials.

The viscoelastic-plastic properties of various amorphous, glassy polymers [polystyrene (PS), poly(styrene-acrylonitrile) copolymer (SAN), poly(methyl methacrylate) (PMMA), poly(vinyl chloride) (PVC), polycarbonate (PC)] in the micron and submicron range were investigated by means of load-displacement analysis from depth-sensing experiments. Hardness and Young's modulus values decrease rapidly with increasing depth up to a few microns. New data on the glass transition temperature correlation with microhardness are presented. The influence of annealing below the glass transition temperature upon the microhardness for various glassy polymers is pointed out. For PS, the influence of the molecular weight variation and molecular weight distribution on the microhardness is reported. Results are discussed on the basis of an entanglement network model, recently developed to explain the fine structure of crazes in amorphous polymers. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 1951–1956, 2004

Fracture behavior of binary blends comprising styrene-butadiene block copolymers having star and triblock architectures was studied by instrumented Charpy impact test. The toughness of the ductile blends was characterized by the dynamic crack resistance concept (R curves). While the lamellar thermoplastic star block copolymer shows elastic behavior (small scale yielding and unstable crack growth), adding 20 wt% of a triblock copolymer (thermoplastic elastomer, TPE) leads to a strong increase in crack toughness. The stable crack propagation behavior of these blends was described by the crack resistance curve (R) concept of elastic-plastic fracture mechanics. This concept allows the determination of fracture mechanics parameters as resistance against stable crack initiation and propagation. Two brittle to tough transitions (BTT) are observed in the binary block copolymer blend: BTT1 at 20% TPE and BTT2 at about 60% TPE. The strong increase of toughness at 60 wt% TPE indicates a ‘tough/high-impact’ transition as a measure for the protection against stable crack initiation.

The effect of grafting level of maleic anhydride (MA) in the maleated polypropylene (PPMA) on the fracture, deformation mechanisms, and mechanical properties of polypropylene (PP) wood flour composites was studied. Tensile strength, elongation at break, and impact strength are noticeably improved with addition of interfacial modifiers as maximum values of the examined mechanical properties were detected when concentration of MA in the compatibilizer was 1 wt %. To explore the microstructure and deformation mechanisms, scanning electron microscopy was employed. It was found that low concentrations of MA up to 1 wt % led to the creation of a thin and irregular polymer layer assisted formation of fibrillated plastic deformation zone around the wood particles, while the bulk PP matrix experienced voiding and brittle fracture. Higher concentrations of MA fetch to stronger interaction between PP and wood flour, the reason for brittle fracture and reduced ductility of the matrix. The impact fracture behavior of the composites during Instrumented impact tests is also discussed with respect to the interfacial bond strength. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 1286–1292, 2004

The correlation between morphology, mechanical properties, and micromechanical deformation behavior of the blends consisting of an asymmetric styrene/butadiene star block copolymer (ST2-S74, total styrene volume content ΦPS = 0.74) and general-purpose polystyrene (GPPS) was investigated using transmission electron microscopy and uniaxial tensile testing. Addition of 20 wt % of GPPS to the block copolymer resulted in a drastic reduction in strain at break, indicating the existence of critical PS lamella thickness Dc. Above Dc lamellar block copolymers displayed a transition from ductile to brittle behavior, substantiating the mechanism of thin layer yielding proposed for lamellar star block copolymers. The blends showed a variety of deformation structures ranging from classical crazelike zones to those with internal shearlike components. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 1208–1218, 2004

The microhardness of transparent rubber‐toughened poly(methyl methacrylate) (RTPMMA) was investigated by means of the microindentation technique. Core‐shell particles (CSP) with a rubbery shell were used as reinforcing material for the production of RTPMMA. The increasing volume fraction of CSP within the poly(methyl methacrylate) (PMMA) matrix is shown to soften the material, diminishing the hardness (H) value of RTPMMA of about 40% of the initial value at 35 vol% CSP content. Creep experiments under the indenter are reported. The creep constant is found to increase by adding CSP up to a leveling‐off value. On the other hand, the thermal variation of the creep constant for the blends shows a maximum. Results reveal a good correlation of the glass transition temperature (T g) value deduced from microindentation, and the values obtained from differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA) techniques. Contrary to expectation H is shown to decrease with increasing glass...

The structure–property correlation in blends consisting of styrene/butadiene block copolymers forming alternating polystyrene (PS) and polybutadiene (PB) lamellae, and PS domains in rubbery matrix was investigated by different microscopic techniques (transmission electron microscopy, scanning force microscopy, and scanning electron microscopy), uniaxial tensile testing, and dynamic mechanical analysis. Unlike the pure lamellar block copolymer, the blends showed predominantly disordered wormlike morphology formed by the intermolecular mixing. These structures allowed a precise control of stiffness/toughness ratio of the blends over a wide range. The blends showed a gradual transition from predominantly viscoplastic to elastomeric behavior with increasing triblock copolymer content. The results demonstrated that the binary block copolymer blends provide the unique possibility of tailoring mechanical properties on the basis of nanostructured polymeric materials. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 1219–1230, 2004

Mechanical properties and deformation mechanisms of polypropylene (PP)/wood fiber (WFb) composites modified with maleated polypropylene as compatibilizer and styrene-butadiene rubber (SBR) as impact modifier have been studied. The addition of maleated polypropylene to the unmodified polypropylene/wood fiber composite enhances the tensile modulus and yield stress as well as the Charpy impact strength. SBR does not cause a drop in the tensile modulus and yield strength because of the interplay between decreasing stiffness and strength by rubber modification and increasing stiffness and strength by good interfacial adhesion between the matrix and fibers. The addition of both maleated polypropylene and rubber to the polypropylene/wood fiber composite does not result in an improvement of effects based on maleated polypropylene and rubber, which includes possible synergism. The deformation mechanisms in unmodified polypropylene/wood fiber composite are matrix brittle fracture, fiber debonding and pullout. A polymeric layer around the fibers created from maleated polypropylene may undergo debonding, initiating local plasticity. Rubber particle cavitation, fiber pullout and debonding were the basic failure mechanisms of rubber-toughened polypropylene/wood fiber composite. When maleated polypropylene was added to this composite, fiber breakage and matrix plastic deformation took place. Polym. Compos. 25:521–526, 2004. © 2004 Society of Plastics Engineers.

The influence of molecular architecture on the mechanical properties of styrene/butadiene block copol- ymers was investigated by means of the microhardness technique. It was found that the microhardness of the sty- rene/butadiene block copolymers is dictated by the nature of microphase separated morphology. In contrast to poly- mer blends and random copolymers, in which the micro- hardness generally follows the additivity rule, the behavior of the investigated block copolymers was found to signifi- cantly deviate depending on their molecular architecture. The glass-transition temperature of the polystyrene phase (Tg-PS), which practically remained constant and that of the polybutadiene phase (Tg-PB), which varied with the change in the block copolymer architecture, apparently do not in- fluence the microhardness values of the block copolymers. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 1670 -1677, 2003

The deformation behavior of blends consisting of a styrene–butadiene star block copolymer and a polystyrene homopolymer was studied by high-voltage electron microscopy with a tensile device. The mechanical properties and micromechanical deformation mechanisms in the star block copolymer/polystyrene blends were directly influenced by their morphology. Although the pure block copolymer deformed in a very unequal manner (because of a thin-layer-yielding mechanism) and revealed no local deformation zones, a transition to the formation of crazelike zones was observed in the blends. This transition in the deformation mechanisms was correlated to the abrupt change in the macroscopic strain at break of the injection-molded specimens. At lower contents of added polystyrene, a craze-stopping mechanism was observed, whereas the blends with higher polystyrene contents demonstrated crazing like that in pure polystyrene. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1157–1167, 2003

The craze structure of linear and long chain branched poly(styrene) (PS) was investigated as a function of temperature by means of in situ transmission electron microscopy (TEM). At room temperature, high entanglement density and a degree of molecular mobility result in homogeneous crazes for branched PS and fine fibrillated crazes for linear PS. With increasing temperature up to near (but still below) the glass transition temperature, the mobility of polymer chains increases, longer units of macromolecules are mobile, and disentanglement becomes more probable. This behavior results in a transition from the formation of homogeneous crazes to fibrillated crazes in long chain branched PS, and in the formation of coarser fibrils and greater distances between the fibrils in both linear and long chain branched PS. The increase in the deformation rate has the opposite effect on the craze structure compared to the temperature increase. After breaking the craze fibrils, a high stress concentration is suddenly pro...

Asymmetric styrene/butadiene block copolymers and their blends with polystyrene homopolymer are studied, using transmission electron microscopy and scanning force microscopy, to explore the influence of phase morphology on the microindentation hardness and the nano-mechanical deformation mechanisms. In contrast to polymer blends and random copolymers, in which microhardness generally follows the additivity law, the behaviour of the investigated block copolymer systems is found to significantly deviate from the hardness additivity behaviour. Owing to the modified architecture, the asymmetric star block copolymer having 74 vol% polystyrene possesses a lamellar morphology, which partly explains the observed low hardness values. An additional explanation is found in the large plastic homogeneous deformation of the polystyrene (PS) lamellae by means of a new micromechanical mechanism called thin layer yielding. In the blends of a star block copolymer with polystyrene homopolymer, a rapid change in the micromechanical deformation behaviour is found to cause a shift in the observed microhardness to larger values. A major conclusion of our investigations is that microhardness of the triblock and star block copolymers can only be explained in the light of the morphology and nano-mechanical deformation mechanisms involved.

Polystyrene-b-n-butyl methacrylate, PS-b-PBMA, star block copolymers having different strengths of segregation are investigated with respect to their deformation behavior. Disordered block copolyme...

Lamellae-forming styrene/butadiene star block copolymers are studied to investigate the influence of morphology on micromechanical deformation mechanisms and mechanical properties by using transmission electron microscopy and tensile testing. A large homogeneous plastic deformation of polystyrene (PS) lamellae is found in styrene/butadiene star block copolymers on the basis of the new mechanism called thin-layer yielding. This mechanism depends strongly on the thickness of the PS lamellae. At a critical thickness of PS lamellae of about 20 nm, a transition from thin-layer yielding mechanism to a crazelike deformation was observed. These new deformation zones are similar to crazes with respect to their propagation perpendicular to direction of external stress and similar to shear bands with respect to an internal shear deformation component of the lamellae in the deformation zones. As a result of our investigations, the mechanical properties of star block copolymers can be understood in correlation with morphology and micromechanical deformation mechanisms. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 683–700, 2002

The influence of molecular architecture on morphology, mechanical properties, and micromechanical deformation behavior of asymmetric styrene/butadiene star block copolymers is investigated by transmission electron microscopy (TEM) and uniaxial tensile testing. In contrast to diblock copolymers, star block copolymers having 74% polystyrene (PS) show a lamellar morphology. Furthermore, tapered asymmetric star block copolymers having a PS core reveal additional PS domains inside the PB lamellae not observed in untapered star block copolymers. The introduction of tapered sequences in star block copolymers results in a significant improvement of tensile properties due to the increased interfacial width between the phases as well as differences in morphology. The investigated star block copolymers show a homogeneous plastic deformation of PS lamellae. This mechanism is called thin-layer yielding of PS lamellae. The lamellae are locally deformed via inhomogeneous necking and drawing. Lamellae which are not oriented parallel to the load direction are twisted to the deformation direction. Neat star block copolymers (without tapered chains) exhibit a premature failure of PS lamellae arising from the decreased interfacial width, which results in a decrease of their ultimate strain. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 701–713, 2002

Fracture behavior of binary blends comprising of styrene–butadiene block copolymers having star and triblock architectures was studied via instrumented Charpy impact test. The toughness of the ductile blends was characterized by dynamic crack resistance curves (R-curves). This study represents a systematic investigation of crack resistance behavior of nanometer structured binary block copolymer blends and the development of a new material with a combination of high toughness and transparency, usually not observed in incompatible polymer blends. While the lamellar star block copolymer shows an elastic behavior (small-scale yielding and unstable crack growth), adding of 20 wt% of the triblock copolymer leads to a stable crack growth and at 60 wt% of the triblock copolymer the strong increase of toughness values indicate a tough/high-impact transition, demonstrating the existence of novel toughening concepts for polymers based on nanometer structured materials.

International audience; The values of the fragility index of polycarbonate/poly(methylmetacrylate) multilayer films have been determined for materials having thicknesses varying from micro- to nano-scales. The influence of the layer thickness reduction down to 12 nm has been shown to have very different influence on the glass transition parameters of the two polymers. Polycarbonate has exhibited a huge sensitivity to such geometric scale modifications while no modification has been observed for PMMA. A large decrease of the fragility index m, has been observed for PC. This modification is proportional to length scale variations of molecular cooperative motions at Tg, ξ(Tg). In regard to the molecular structure of each polymer, these results show that this correlation between fragility index and ξ(Tg) is mainly associated to modifications of intermolecular interactions and local density. These material parameters are influencing the activation volume ΔV# which plays a role on the modification of the fragility index.

The morphology of different styrene/butadiene (SB) block copolymers with triblock architectures was investigated using tapping mode scanning force microscopy (SFM). Comparative analysis of the morphology of the samples at the polymer/substrate interface of solution-cast films and in bulk was performed. It was found that, besides the total phase volume ratio, the interfacial structure between the incompatible chains determines the phase morphology and mechanical properties of the investigated block copolymers. The asymmetric SBS triblock copolymer (φps( 74 vol%) forms, as expected, a cylindrical morphology with hexagonally packed polybutadiene (PB) cylinders in the polystyrene (PS) matrix. Depending on the interfacial structure, block configuration, and the hard/soft phase ratio, other triblock copolymers (φps( 74 vol% and 65 vol%) show lamellae and randomly distributed PS cylinders in a random styrene/butadiene copolymer S/B matrix, respectively. *Dedicated to Prof. Francisco J. Balta Calleja on the occas...

Block copolymers having different strengths of segregation are investigated with respect to their deformation behavior. Disordered block copolymers are deformed by the mechanism which corresponds to a glassy homopolymer. A crazing mechanism is observed for block copolymers with polystyrene as matrix. At the order−disorder transition (ODT), a change from crazing to cavitation mechanism is observed, confirming the change of deformation mechanism at the ODT. For intermediately and strongly segregated block copolymers, observed mechanisms of termination and diversion of crazes are caused by both the increased long-range order and larger grain size with increasing incompatibility. A novel scheme is proposed which summarizes the deformation behavior of block copolymers depending on strength of segregation, χN. It is now possible to predict the deformation mechanism of a diblock copolymer system only from strength of segregation. Since the mechanical properties are also influenced by strength of segregation, it ...

The deformation behavior of poly(styrene-b-butyl methacrylate) diblock copolymers, PS-b-PBMA, is studied by high-voltage electron microscopy (HVEM) with an in-situ tensile device. While in the first part the phase behavior of PS-b-PBMA diblock copolymers is investigated via small-angle neutron scattering (SANS), in the second part the deformation behavior depending on composition and molecular weight is discussed. Disordered block copolymers have the same deformation mechanism as the corresponding homopolymers, while microphase-separated block copolymers undergo a cavitation mechanism. At the order−disorder transition, ODT, a transition from crazing to cavitation mechanism is found via HVEM. Moreover, a sharp increase of the diameter of craze fibrils occurs at the ODT, demonstrating that the craze microstructure is strongly influenced by phase behavior. As the incompatibility increases with increasing molecular weight, deformation mechanisms such as diversion and termination of crazes are observed for int...