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The final structure of molten syndiotactic polypropylene (sPP) sheared under different conditions was investigated by synchrotron small-angle x-ray scattering (SAXS) and wide-angle x-ray diffraction (WAXD) techniques to elucidate the shear effects on sPP crystalline structure. The results obtained from the WAXD show that there is no variation on crystalline form but a little difference on the orientation of the 200 reflection. The SAXS data indicate that the lamellar thickness and long period have not been affected by shear but the lamellar orientation is dependent on shear. The experimental data of sPP crystallization from sheared melt may indicate a mesophase structure that is crucial to the shear effects on the final polymer multiscale crystalline structures. [ABSTRACT FROM AUTHOR]

ABSTRACT Two pure impact copolymer polypropylenes (ICP), one pure homo-polypropylene (HPP) and their compounds with different type and fraction of Vistamaxx™ propylene-based elastomer ('Vistamaxx') were used to investigate the stress whitening activated in the impact processes via ultra-small-angle X-ray scattering technique. The whitening presented in ICP is confirmed to be caused by the interfaces existed between ethylene-propylene (EP) rubber and polypropylene matrix, such kind whitening is apparently unlike the one initiated in the crystal phase of HPP. In this study, Vistamaxx with high crystallinity can adjust the compatibility of EP rubber and PP matrix which results in a reduction of interfaces, thus, a phenomenon of reduced stress whitening can be observed in blends of ICP with Vistamaxx. However, the enhancement of stress whitening can be found in blends of ICP with Vistamaxx which occupied low crystallinity. Such behaviors can be assigned to the poor compatibility between Vistamaxx and PP matrix. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 44747. [ABSTRACT FROM AUTHOR]

ABSTRACT Cavitation behavior in poly(4-methyl-1-pentene) upon stretching below glass transition temperature was investigated by in situ ultra-small angle X-ray scattering technique. Strong stress-whitening was observed indicating an extensive occurrence of cavitation in the material during tensile deformation below Tg. The X-ray scattering patterns suggest oriented disc-shaped cavities with normal mostly parallel to the stretching direction occurred. Structural parameters of such cavities such as thickness, radius, and tilting angle of the normal of the disc with respect to the stretching direction have been successfully calculated using a model fitting procedure. The results exhibited a two-step process of cavitation that small amount of large cavities appeared first and then small cavities were triggered extensively in the samples at larger strains. This two-step cavitation phenomenon can be weakened after the quenched sample was annealed or the sample was prepared by slow cooling. This peculiar two-step cavitation process can be understood as a result of high frozen in internal stress in quenched sample that led to local failure of the materials. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016, 54, 2007-2014 [ABSTRACT FROM AUTHOR]

ABSTRACT The reinforcement of mechanical properties of polymeric materials is often important for widening their applications; however, it remains a technical challenge to effectively increase toughness without degrading stiffness and strength of the polymers. In this work, by a facile methodology combining solution mixing and melt blending, poly(vinylidene fluoride)/multi-walled carbon nanotubes (PVDF/MWCNTs) composite with exceptionally enhanced ductility and toughness are prepared. With only 0.2 wt % CNT loading, the elongation at break has increased from originally 138% to almost 500%, while toughness improved by as much as 386%, without compromising the stiffness and strength. Note that raw CNTs are directly dispersed in the matrix without any surface modification. In order to elucidate this novel enhancement of ductility of PVDF/MWCNTs composites, we carried out detailed analyses based on results from ultra-small-angle X-ray scattering (USAXS), cryo-fractured surface morphology, differential scanning calorimetry (DSC), and Fourier transform infrared spectroscopy (FTIR). It is proposed that the enhanced ductility are contributed by a synergistic combination of 'void pinning effect' of CNT, as well as the formation of γ phase polymorph as the interphase in the PVDF/CNTs composites. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43610. [ABSTRACT FROM AUTHOR]

Polybutene-1 (PB-1), a typical semicrystalline polymer, in its stable form I shows a peculiar temperature dependent strain-whitening behavior when being stretched at temperatures in between room temperature and melting temperature of the crystallites where the extent of strain-whitening weakens with the increasing of stretching temperature reaching a minima value followed by an increase at higher stretching temperatures. Correspondingly, a stronger strain-hardening phenomenon was observed at higher temperatures. The strain-whitening phenomenon in semicrystalline polymers has its origin of cavitation process during stretching. In this work, the effect of crystalline lamellar thickness and stretching temperature on the cavitation process in PB-1 has been investigated by means of combined synchrotron ultrasmall-angle and wide-angle X-ray scattering techniques. Three modes of cavitation during the stretching process can be identified, namely “no cavitation” for the quenched sample with the thinnest lamellae where only shear yielding occurred, “cavitation with reorientation” for the samples stretched at lower temperatures and samples with thicker lamellae, and “cavitation without reorientation” for samples with thinner lamellae stretched at higher temperatures. The mode “cavitation with reorientation” occurs before yield point where the plate-like cavities start to be generated within the lamellar stacks with normal perpendicular to the stretching direction due to the blocky substructure of the crystalline lamellae and reorient gradually to the stretching direction after strain-hardening. The mode of “cavitation without reorientation” appears after yield point where ellipsoidal shaped cavities are generated in those lamellae stacks with normal parallel to the stretching direction followed by an improvement of their orientation at larger strains. X-ray diffraction results reveal a much improved crystalline orientation for samples with thinner lamellae stretched at higher temperatures. The observed behavior of microscopic structural evolution in PB-1 stretched at different temperatures explains above mentioned changes in macroscopic strain-whitening phenomenon with increasing in stretching temperature and stress-strain curves. [ABSTRACT FROM AUTHOR]

We report on the confined crystallization and polymorphism behavior of a series of comb-like polymers (CS(n)Cs), which were prepared viaan N-alkylation reaction between chitosan and n-alkyl bromides (n= 14–20). Analysis by temperature-dependent synchrotron X-ray scattering, Fourier transform infrared spectroscopy (FTIR), solid-state nuclear magnetic resonance spectroscopy (NMR) and differential scanning calorimetry (DSC) revealed that the phase transition and crystalline structure were sensitively controlled by the length scale and the confinement state of alkyl groups, which could induce different packing structures and conformational variation behavior. Remarkably, phase transition from orthorhombic-hexagonal to monoclinic structure was observed for these side-chain polymers, demonstrating that the length scales of alkyl groups and the microstructure of polymeric backbones play an important role in the evolution of packing mode of nano-crystallites. [ABSTRACT FROM AUTHOR]

Tensile deformation behavior of amorphous Poly (1,4-cyclohexylenedimethylene Terephthalate) (PCT) at 25 °C–108 °C was investigated by means of in situ synchrotron wide-angle X-ray scattering (WAXS). WAXS patterns were processed in a way that the scatterings from isotropic and anisotropic structures were separated. It turned out that the influences of temperature during deformation can be divided into three zones: below 80 °C, only molecular chains oriented; between 80 °C to 90 °C, very few imperfect crystals were induced by strain; above glass transition temperature (92 °C), the triclinic PCT crystalline structure began to form during deformation process. It was found that the Gaussian model of Haward and Thackray described the stress-strain behavior of the tensile stretched amorphous PCT very well. However, when being stretched above 80 °C, the system showed two characteristic network moduli because of strain-induced crystallization. The onset of change in network modulus occurred immediately after the formation of unoriented crystallites which served as physical cross-linking points to reinforce the material. Image 1 • In-situ WAXS measurements were performed during stretching of PCT at different temperatures. • Gaussian network stretching of Haward-Thackray model describes the mechanical data very well. • Change in network modulus was observed when unoriented crystals were generated during stretching. [ABSTRACT FROM AUTHOR]

Abstract: Synchrotron small angle X-ray scattering was used to study the deformation mechanism of high-density polyethylene that was stretched beyond the natural draw ratio. New insight into the cooperative deformational behavior being mediated via slippage of micro-fibrils was gained. The scattering data confirm on the one hand the model proposed by Peterlin on the static structure of oriented polyethylene being composed of oriented fibrils, which are built by bundles of micro-fibrils. On the other hand it was found that deformation is mediated by the slippage of the micro-fibrils and not the slippage of the fibrils. In the micro-fibrils, the polymer chains are highly oriented both in the crystalline and in the amorphous regions. When stretching beyond the natural draw ratio mainly slippage of micro-fibrils past each other takes place. The thickness of the interlamellar amorphous layers increases only slightly. The coupling force between micro-fibrils increases during stretching due to inter-microfibrillar polymer segments being stretched taut thus increasingly impeding further sliding of the micro-fibrils leading finally to slippage of the fibrils. [Copyright &y& Elsevier]

The step-cycle tensile experiments were carried out on syndiotactic polypropylene to explore the crystallization and deformation temperature dependency of cavitation via the wide and small angle scattering X-ray techniques. The development of cavitation process exhibited a dependency on the original crystallites. The cavities appeared around the yield point could be healed after releasing the tensile force before a specific strain, while the ones occurred beyond this point are permanent. This phenomenon was in accord with the process of the recoverable lamellar thickness within one stretching and relaxation cycle. After reaching the critical point of fragmentation and recrystallization of lamellae, the growth rate of cavities started to decrease due to the destruction of the original crystallites. Moreover, the crystallites formed at higher crystallization temperature could be preserved to a larger strain and thus more intense cavitation could be expected. The high deformation temperature could weaken the intensity of cavitation, then, the weakest cavitation phenomenon was observed in the sample crystallized at low temperature but drawn at high temperature. [Display omitted] • The cavitation behavior of sPP is linked to the original crystallites. • The cavities produced in sPP could be healed at early deformation stage. • The development of cavities in sPP began to slow down beyond the critical point C. [ABSTRACT FROM AUTHOR]

Morphological variation of thermoplastic polyurethanes (TPUs) with different hard segment contents (HSCs) stretched at 100 °C higher than the T g of hard domain was monitored by in-situ wide-angle X-ray scattering (WAXS) and small-angle X-ray scattering (SAXS) techniques. WAXS patterns reveal that the crystalline modification of TPUs with high HSCs transforms from paracrystal (termed as form I) to form III of 4,4′-methylene diphenyl diisocyanate/1,4-butanediol (MDI/BD) segment, and TPUs with low HSCs show the direct transition from amorphous MDI/BD packing to form III packing. The form III crystals are fibrillar hard domains. Chord distribution functions (CDFs) computed from the SAXS patterns were employed to illustrate the domain topology. The streak-like CDF peaks off the meridian indicate the existence of cylindrical microfibrils which are composed of very low inhomogeneities between the destructured hard domains and stretched soft domains along the straining direction. These microfibrils of TPUs with low HSCs present a periodically lateral correlation. Interface distribution function (IDF) and chord length distribution (CLD) were computed from Bonart's longitudinal and transverse projection to quantify the domain stacking and microfibril arrangement respectively. The average size of hard domains increases up to a constant size with the increasing macroscopic strain which may be related to the maximal sequence length of hard segment. The average size of soft domain also reaches up to a constant size at large strain that is smaller than the fully-extended length of soft segment. The variation of domain size is different from deformation at room temperature. The HSC affects the behaviors of morphological evolution significantly. [ABSTRACT FROM AUTHOR]

The deformation behavior and structural evolution of the quenched ethylene-butene copolymer under uniaxial loading and unloading were investigated as a function of stretching temperature using step-cycle tests, in situ small angle X-ray scattering (SAXS), and wide angle X-ray diffraction (WAXD) measurements. The true stress-strain curves together with detailed analysis of SAXS results indicated that the irreversible plastic strain set in quite early at small strains as the drawing temperature was increased. The critical strain, at which the recoverable elastic strain reached the plateau region and the long period started to keep essentially constant upon stretching, was found to increase distinctly from about 0.65 at room temperature to 1.00 at 100 °C. This dependence of critical strain on the stretching temperature was directly related to the effective entanglement density of the amorphous network as derived from the Gaussian model of Haward-Thackray. Despite the considerable changes of the long period and the crystallite dimensions at identical strains upon stretching and unloading, there existed a one-to-one correspondence between the strain and the orientational order parameter of polymeric chains in the crystalline phase, irrespective of mechanical stress state. This work yielded new insight into the relationship between mechanical stability and operation temperature in industrial application of crystalline polymers. [ABSTRACT FROM AUTHOR]

The differences in side chain crystallization behavior between cellulose esters (CEs) and hydroxypropyl cellulose esters (HPCEs) were systematically investigated by a combination of differential scanning calorimetry (DSC) and small and wide-angle X-ray scattering techniques. DSC investigation indicated that under the same side chain length, the fusion enthalpy and the number of crystallized CH 2 of CEs were smaller than HPCEs. At the same time, their d-spacing and molecular arrangements were also different from each other. For the CEs, the side chains are perpendicular to the main chain, while the side chains most probably tend to tilt to main chain in the HPCEs as was evidenced by X-ray scattering results. The phenomenon can be understood as a consequence of different flexibility of attachment bridges in both kinds of side chain polymers and the steric hindrance of methyl group in the hydroxypropyl group in HPCEs. In addition, the added hydroxypropyl substituents make the side chain length increasing. [ABSTRACT FROM AUTHOR]

Thecrystallization behavior of a butene-1/ethylene random copolymer with9.88 mol % ethylene counits was investigated by means of differentialscanning calorimetry, wide- and small-angle X-ray scattering, andpolarized optical microscopy. Unlike in its homopolymer counterpartwhich crystallizes always into a metastable form II from the meltstate, the random copolymer was found to crystallize either into formII or stable form I′ directly from its melt state after beingcooled down. The occurrence of either crystalline form only dependedon the temperature where the crystalline material was molten beforecooling down. Even though the material was brought to temperatureshigher than the equilibrium melting temperature, heterogeneities ofsegmental segregation character were preserved which promoted massivenucleation of form I′ crystallites, which makes it possiblethat the material is able to crystallize into pure form I′.Only if when the melt temperature was high enough where all heterogeneitiesof the above-mentioned character were erased can the material be crystallizedinto pure form II. The effect is found independent of the previouscrystalline form, meaning that the helical conformation of chainsin the heterogeneous melt does not affect the nucleation of stableform I′. [ABSTRACT FROM AUTHOR]

Thestructural parameters such as long spacing and thicknessesof crystalline lamellae and amorphous layers of polybutene-1 crystallizedfrom quiescent melt at different isothermal temperatures and establishedby tensile stretching the isothermally crystallized samples at differenttemperatures via a stress induced localized melting and recrystallizationprocess were determined by small-angle X-ray scattering experiments.In the two cases, almost parallel crystallization lines where reciprocallamellar thickness and temperature at which the structure formed arein linear relationship were observed. As it turns out, the samplescrystallized from the quiescent melt possess much thicker crystallinelamellae than those obtained via stretching at same temperature. Theresults yield two limiting temperatures for the formation of lamellaewith infinite thickness in the two cases which can be understood byconsidering the influence of the stress on the thermodynamic parametersin the melt and thus the crystallization process. [ABSTRACT FROM AUTHOR]

Structural evolution of two ethylene–octene copolymerswith different octene content during tensile deformation and recoverywas investigated using the in-situ synchrotron small-angle X-ray scatteringtechnique. Sample containing 4 mol % octene shows similar deformationmechanism as observed previously that the whole process of deformationcan be regarded as a stretching of two interpenetrating networks ofcrystalline rigid network and entangled amorphous phase. A transitionfrom a crystalline rigid network dominating behavior at small deformationsto a stretching-induced crystalline block disaggregation–recrystallizationprocess occurs at a critical strain where stress generated by thestretched amorphous network reaches a critical value leading to thedestruction of crystalline blocks. In sample containing 8 mol % octene,this critical strain is much larger than observed in the other sample.Such a phenomenon is attributed to the fact that only crystallinelamellar stacks and bundle-like crystals with much weakened couplingcan be developed in the sample. The weakened coupling between crystallinelamellar stacks is due to the existence of interstack amorphous phasewhich also leads to an inhomogeneous strain distribution in the system. [ABSTRACT FROM AUTHOR]

Abstract: In this work, we investigated the epitaxial crystallization and its determinant factor in the blends of high density polyethylene (HDPE) and a low crystallizable propylene-ethylene random copolymer (PPR) during injection molding. For PPR dominated blend (blended with 30 wt.% HDPE), epitaxial growth of HDPE on the PPR crystals can be achieved, as demonstrated by two-dimensional wide-angle X-ray diffraction and small-angle X-ray scattering measurements, though the crystallization of PPR was far behind that of HDPE component under quiescent conditions. In-situ shear infrared experiments indicated that PPR crystallized in advance mainly due to larger crystallization window and flow-induced crystallization acceleration. As for the blend with 70 wt.% HDPE, however, one could not observe epitaxy. Shear-induced crystallization of HDPE hindered its epitaxial growth. Once the formation of shish-kebab of HDPE was activated, the epitaxial growth would be suppressed to a large extent. [Copyright &y& Elsevier]

Cavitation in the impact copolymer polypropylene (ICP) and its corresponding homo-isotactic polypropylene (homo-iPP) during stretching was investigated using ultra-small angle X-ray scattering technique. Different from the iPP showing a suppressed cavitation around yielding at high deformation temperature (T d), the ICP presented a more intensive cavitation at elevated T d. This unusual T d dependency of cavitation around yielding observed in ICP was suggested to be caused by the changes of the stability of the rubber particles dispersed in iPP matrix. The rubber particles exhibit a multi-phase core-shell structure which contains crystallizable polyethylene segments in the core layer, the amorphous polymer of ethylene-propylene random copolymer in the inner shell layer, and the crystallizable polypropylene segments in the outer shell layer. The softening and melting from the inner shell to the core and the outer shell took place as the T d increased. It can be envisaged that the fraction of unstable regions inside the rubber particles and the debonding between the iPP matrix and the dispersed phase gradually increased providing more nucleation sites for cavities at high T d , a more intensive cavitation was thus observed. Image 1 • The cavitation in ICP was determined by the stability of rubber particles embedded in the iPP matrix. • The cavities were generated in the rubber particles and the interfaces between iPP matrix and dispersed phases at high Td. • The melting of crystallites in the rubber particles provided more nucleation sites for cavities in ICP. [ABSTRACT FROM AUTHOR]

Based on results of small and wide angle X-ray scattering measurements, we report a new microstructural feature in bottlebrush poly (n-alkyl methacrylate)s larger than side chain packing. Temperature dependent X-ray experiments confirmed that such large scale aggregation structure is originated from the crystallization of the side chains. Two-dimensional X-ray scattering patterns revealed that the structure is due to the formation of disordered regions locate on average two layers of well crystallized side chains apart. Crystallization of the side chains rejected backbone entanglements to the surrounding area forming regions of high entanglement density so that restricting the crystallization of side chains. As such a density contrast is created between the crystallized regions and the disordered ones which results in strong small angle X-ray scattering signals. Image 1 • Amorphous regions exists in poly (n-alkyl methacrylate)s with scale larger than the side chain packing. • The amorphous regions are correlated with a distance over two layers of well crystallized side chains on average. • Enriched entanglements and backbone-backbone expansion lead to the formation of amorphous regions. [ABSTRACT FROM AUTHOR]

Microstructural development of poly(ε-caprolactone) (PCL) and its miscible blends with poly(vinyl methyl ether) (PVME) and poly(styrene-co-acrylonitrile) (SAN) were investigated as a function of strain in the process of uniaxial stretching using in situ synchrotron ultrasmall- and small-angle X-ray scattering (USAXS and SAXS) techniques. The addition of amorphous polymer SAN gives rise to a distinct reduction in the entanglement density of the amorphous phase of PCL, whereas an introduction of PVME does not affect the entanglement density in the blend. At small strains, the initial cavities in pure PCL are oriented perpendicular to the drawing direction, while the cavities at the onset of their formation are oriented along the extensional direction for the PCL/PVME blend. Nevertheless, no cavity scattering is observed in PCL/SAN blend during the process of tensile deformation. These results confirm that the cavitation is directly linked to the lamellar crystallites with their orientation parallel to the drawing direction at small extension ratios. For the two cavitated samples, the volume fraction of cavities was assessed from the integrated scattering intensity based on a three phase model. A critical stress value, above which the lamellar mosaic blocks begin to be pulled apart and the cavitation just sets in, was found to be nearly constant at around 15 MPa. Furthermore, the dimensions of cavities were evaluated at different deformations via direct cylinder model fitting to the USAXS patterns. The height of cavities is much larger than the long spacing of lamellar stacks even at the early stages of cavity formation, which indicates the cavities emanating from the lamellae into several amorphous phases at small elongations. Analysis of the SAXS patterns shows an independence of lamellar long spacing on the sample composition at large strains, which strongly supports the deformation scheme of stress-induced fragmentation and recrystallization. Image 1 • Cavitation and plastic deformation of lamellae were studied under tensile stretching. • Cavitation was related to the crystallites with their orientation along the drawing direction. • The volume fraction of cavities was calculated from the scattering invariant based on a three phase model. • The dimensions of cavities were evaluated at different deformations via direct cylinder model fitting to USAXS patterns. [ABSTRACT FROM AUTHOR]