Influence of Annealing on Microstructure and Mechanical Properties of Isotactic Polypropylene with beta-Phase Nucleating Agent

The microstructure and mechanical properties of beta-nucleated iPP before and after being annealed at different temperatures (90-160 degrees C) have been analyzed, Annealing induced different degrees of variation in fracture toughness of beta-nucleated iPP samples. namely, slight enhancement at relatively low annealing temperatures (< 110 degrees C) and great improvement at moderate temperatures (120-130 degrees C), whereas dramatic deterioration at relatively high temperatures ( > 140 degrees C) has been observed. The variation of fracture toughness of beta-nucleated iPP is observed to be dependent on the content of beta-NA. Experiments, including scanning electronic microscope (SEM), wide-angle X-ray diffraction (WAXD), differential scanning calorimetry (DSC), small-angle X-ray scattering (SAXS), and dynamic mechanical analysis (DMA), are performed to study the variations of microstructures as well as the toughening mechanism of the beta-nucleated iPP after being annealed.

Probing structural changes of spin-coated polystyrene film after swelling and precipitation by synchrotron GIUSAXS and AFM

Polystyrenc film of about 50 nm in thickness on silicon wafer was obtained by spin-coating in tetrahydrofuran solution.The film exhibits a rough surface as shown by atomic force microscopy images and ellipsometry data.

Confined intra-molecular clustering in orientated polyethylene after annealing

Deuterated polyethylene tracer molecules with small amount of branches (12 C2H5- branches per 1000 backbone carbon atoms) were blended with a hydrogenated polyethylene matrix to form a homogenous mixture. The conformational evolution of the deuterated chains in a stretched semi-cry stall me film was observed via online small angle neutron scattering measurements during annealing at high temperatures close to the melting point. Because the sample was annealed at a temperature closely below its melting point, the crystalline lamellae were only partially molten and the system could not fully relax. The global chain dimensions were preserved during annealing. Recrystallization of released polymeric chain segments allows for local phase separation thus driving the deuterated chain segments into the confining interlamellar amorphous layers giving rise to an interesting intra-molecular clustering effect of the long deuterated chain. This clustering is deduced from characteristic small angle neutron scattering patterns. The confined phase separation has its origin in primarily the small amount of the branches on the deuterated polymers which impede the crystallization of the deuterated chain segments.

Shear-enhanced crystallization of a thermoplastic polyimide derived from 3,3 ',4,4 '-oxydiphthalic dianhydride and 4,4 '-oxydianiline

The aim of this work is to investigate the effect of consecutive shear on the crystallization of an amorphous aromatic polyimide (PI) derived from 3,3',4,4'oxydiphthalic dianhydride (3,3',4,4'-ODPA) and 4,4-oxydianiline (ODA). At 260 degrees C, the increase of shear rate or shear time leads to the increase of crystallinity. Indeed, increasing shear rate can also accelerate the crystallization behavior. Moreover, it was found that a new melting peak appeared at higher temperature for long time or high rate sheared sample. The enhancement of crystallization behavior appears directly linked to the increase of crystal thickness. Particularly, the effect of shear temperature was investigated, and the results revealed that the crystallization of the PI was more sensitive to shear at 260 degrees C, which was 10 degrees above the glass transition temperature (250 degrees C) of the PI. Possible mechanism was proposed to illustrate the effect of consecutive shear on the crystallization of the PI polymer.

Thermal and crystallization behaviors of polyethylene blends synthesized by binary late transition metal catalysts combinations

A series of reactor blends of linear and branched polyethylenes have been prepared, in the presence of modified methylaluminoxane, using a combination of 2,6-bis[1(2,6-dimethyphenylimino) pyridyl]-cobalt(II) dichloride (1), known as an active catalyst for producing linear polyethylene, and [1,4-bis(2,6-diidopropylphenyl)] acenaphthene diimine nickel(II) dibromide (2), which is active for the production of branched polyethylene. The polymerizations were performed at various levels of catalyst feed ratio at 10 bar. The linear correlation between catalyst activity and concentration of catalyst 2 suggested that the catalysts performed independently from each other. The weight-average molecular weights ((M) over bar (w)), crystalline structures, and phase structures of the blends were investigated, using a combination of gel permeation chromatography, differential scanning calorimetry, wide-angle X-ray diffraction, and small angle X-ray scattering techniques. It was found that the polymerization activities and MWs and crystallization rate of the polymers took decreasing tendency with the increase of the catalyst 2 ratios, while melting temperatures (T-m), crystalline temperatures (T,), and crystalline degrees took decreasing tendency. Long period was distinctly influenced by the amorphous component concentration.

The influence of hard-segments on two-phase structure and shape memory properties of PCL-based segmented polyurethanes

Poly(epsilon-caprolactone)-based segmented polyurethanes (PCLUs) were prepared from poly(epsilon-caprolactone) diol, diisocyanates (DI), and 1,4-butanediol. The DIs used were 4,4'-diphenylmethane diisocyanate (MDI), 2,4-toluenediisocyanate (TDI), iso-phorone diisocyanate (IPDI), and hexamethylene diisocyanate (HDI). Differential scanning calorimetry, small-angle X-ray scattering, and dynamic mechanical analysis were employed to characterize the two-phase structures of all PCLUs. It was found that HDI- and MDI-based PCLUs had higher degree of microphase separation than did IPDI- and TDI-based PCLUs, which was primarily due to the crystallization of HDI- and MDI-based hard-segments. As a result, the HDI-based PCLU exhibited the highest recovery force up to 6 MPa and slowest stress relaxation with increasing temperature. Besides, it was found that the partial damage in hard-segment domains during the sample deformation was responsible for the incomplete shape-recovery of PCLUs after the first deformation, but the damage did not develop during the subsequent deformation.

Structural analysis of PEKEKK(T/I) using WAXD, imaging plates and SAXS

Structures and crystal form transition of the novel aryl ether ketone polymer containing meta-phenylene linkage: PEKEKK(T/I) were investigated by wide angle X-ray diffraction (WAXD), imaging plates (IPs) and small angle X-ray scattering (SAXS). The energy of activation of the decomposition reaction and degree of crystallinity of PEKEKK(T/I) were determined by WAXD and thermo-gravimetric analysis (TGA), respectively. Results obtained from WAXD and IPs show that crystal forms I and II coexist in the PEKEKK(T/I) samples isothermally cold crystallized in the temperature range from 180degreesC to 240degreesC and only form I occurs in PEKEKK(T/I) samples isothermally cold crystallized at 270degreesC. The radius of gyration (Rg), thickness of microregions with electron-density fluctuations (E) and distribution of particle sizes were investigated by SAXS.

Effect of annealing on the viscoelastic and viscoplastic responses of low-density polyethylene

Two series of tensile tests with constant crosshead speeds (ranging from 5 to 200 mm/min) and tensile relaxation tests (at strains from 0.03 to 0.09) were performed on low-density polyethylene in the subyield region of deformations at room temperature. Mechanical tests were carried out on nonannealed specimens and on samples annealed for 24 h at the temperatures T = 50, 60, 70, 80, and 100 degreesC. Constitutive equations were derived for the time-dependent response of semicrystalline polymers at isothermal deformations with small strains. A polymer is treated as an equivalent heterogeneous network of chains bridged by temporary junctions (entanglements, physical crosslinks, and lamellar blocks). The network is thought of as an ensemble of mesoregions linked with each other. The viscoelastic behavior of a polymer is modeled as a thermally induced rearrangement of strands (separation of active strands from temporary junctions and merging of dangling strands with the network). The viscoplastic response reflects sliding of junctions in the network with respect to their reference positions driven by macrostrains. Stress-strain relations involve five material constants that were found by fitting the observations.

Effect of crystallization on the lamellar orientation in thin films of symmetric poly(styrene)-b-poly(L-lactide) diblock copolymer

The effect of crystallization on the lamellar orientation of poly( styrene)-b-poly(L-lactide) (PS-PLLA) semicrystalline diblock copolymer in thin films has been investigated by atomic force microscopy (AFM), transmission electronic microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). In the melt state, microphase separation leads to a symmetric wetting structure with PLLA blocks located at both polymer/substrate and polymer/air interfaces. The lamellar period is equal to the long period L in bulk determined by small-angle X-ray scattering (SAXS). Symmetric wetting structure formed in the melt state provides a model structure to study the crystallization of PLLA monolayer tethered on glassy (T-c < T-g,T-PS) or rubber (T-c > T-g,T-PS) PS substrate. In both cases, it is found that the crystallization of PLLA results in a "sandwich" structure with amorphous PS layer located at both folding surfaces. For T-c <= T-g,T- PS, the crystallization induces a transition of the lamellar orientation from parallel to perpendicular to substrate in between and front of the crystals. In addition, the depletion of materials around the crystals leads to the formation of holes of 1/2 L, leaving the adsorbed monolayer exposure at the bottom of the holes.

Non-affine structural evolution of soft colloidal crystalline latex films under stretching as observed via synchrotron X-ray scattering

A polymer dispersion consisting of soft latex spheres with a diameter of 135 nm was used to produce a crystalline film with face-centered cubic (fcc) packing of the spheres. Different from conventional small-molecule and hardsphere colloidal crystals, the crystalline latex film in the present case is soft (i.e., easily deformable). The structural evolution of this soft colloidal latex film under stretching was investigated by in-situ synchrotron ultra-small-angle X-ray scattering. The film exhibits polycrystalline scattering behavior corresponding to fcc structure. Stretching results not only in a large deformation of the crystallographic structure but also in considerable nonaffine deformation at high draw ratios. The unexpected nonaffine deformation was attributed to slippage between rows of particles and crystalline grain boundaries. The crystalline structure remains intact even at high deformation, suggesting that directional anisotropic colloidal crystallites can be easily produced.

Composition dependence of the crystallization behavior and morphology of the poly(ethylene oxide)-poly(epsilon-caprolactone) diblock copolymer

The crystallization behavior and morphology of the crystalline-crystalline poly(ethylene oxide)-poly(epsilon-caprolactone) diblock copolymer (PEO-b-PCL) was studied by differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD), Fourier transform infrared spectroscopy (FTIR), small-angle X-ray scattering (SAXS), and hot-stage polarized optical microscope (POM). The mutual effects between the PEO and PCL blocks were significant, leading to the obvious composition dependence of the crystallization behavior and morphology of PEO-b-PCL. In this study, the PEO block length was fixed (M-n = 5000) and the weight ratio of PCL/PEO was tailored by changing the PCL block length. Both blocks could crystallize in PEO-b-PCL with the PCL weight fraction (WFPCL) of 0.23-0.87. For the sample with the WFPCL of 0.36 or less, the PEO block crystallized first, resulting in the obvious confinement of the PCL block and vice versa for the sample with WFPCL of 0.43 or more. With increasing WFPCL, the crystallinity of PEO reduced continuously while the variation of the PCL crystallinity exhibited a maximum. The long period of PEO-b-PCL increased with increasing WFPCL from 0.16 to 0.50 but then decreased with the further increase of WFPCL due to the interaction of the respective variation of the thicknesses of the PEO and PCL crystalline lamellae.

Investigation on isothermal and non-isothermal crystallization kinetics of poly (epsilon-caprolactone)

The crystallization kinetics and the development of lamellar structure during the isothermal crystallization of poly (epsilon-caprolactone) (PCL) were investigated by means of differential scanning calorimetry (DSC) and real-time synchrotron small angle X-ray scattering (SR-SAXS) techniques, respectively. The Avrami analysis was performed to obtain the kinetics parameters. The value of Avrami index, n, is about 3, demonstrating a three-dimensional spherulitic growth on heterogeneous nuclei in the process of isothermal crystallization. The activation energy and the surface free energy of chain folding for isothermal crystallization were determined according to the Arrhenius equation and Hoffman-Lauritzen theory, respectively. In the process of nonisothermal crystallization of PCL, the value of Avrami index, n, is about 4, which demonstrates a three-dimensional spherulitic growth on homogeneous nuclei. In addition, lamellar parameters were obtained from the analysis of SR-SAXS data.

Miscibility and crystallization behavior of poly(3-hydroxyvalerate-co-3-hydroxyvalerate)/poly(propylene carbonate) blends

Blends of synthetic poly(propylene carbonate) (PPC) with a natural bacterial copolymer of 3-hydroxybutyrate with 3-hydroxyvalerate (PHBV) containing 8 mol % 3-hydroxyvalerate units were prepared with a simple casting procedure. PPC was thermally stabilized by end-capping before use. The miscibility, morphology, and crystallization behavior of the blends were investigated by differential scanning calorimetry, polarized optical microscopy, wide-angle X-ray diffraction (WAXD), and small-angle Xray scattering (SAXS). PHBV/PPC blends showed weak miscibility in the melt, but the miscibility was very low. The effect of PPC on the crystallization of PHBV was evident. The addition of PPC decreased the rate of spherulite growth of PHBV, and with increasing PPC content in the PHBV/PPC blends, the PHBV spherulites became more and more open. However, the crystalline structure of PHBV did not change with increasing PPC in the PHBV/PPC blends, as shown from WAXD analysis. The long period obtained from SAXS showed a small increase with the addition of PPC.

In situ study of nanostructure and morphological development during the crystal-mesophase transition of poly(di-n-hexylsilane) and poly(di-n-butylsilane) by X-ray and hot-stage AFM

Nanostructure and morphology and their development of poly(di-n-hexylsilane) (PDHS) and poly(di-n-butylsilane) (PDBS) during the crystal-mesophase transition are investigated using small angle X-ray scattering (SAXS), wide angle X-ray diffraction and hot-stage atomic force microscopy. At room temperature, PDHS consists of stacks of lamellae separated by mesophase layers, which can be well accounted using an ideal two-phase model. During the crystal-mesophase transition, obvious morphological changes are observed due to the marked changes in main chain conformation and intermolecular distances between crystalline phase and mesophase. In contrast to PDHS, the lamellae in PDBS barely show anisotropy in dimensions at room temperature. The nonperiodic structure and rather small electronic density fluctuation in PDBS lead to the much weak SAXS. The nonperiodic structure is preserved during the crystal-mesophase transition because of the similarity of main chain conformation and intermolecular distances between crystalline phase and mesophase.

Microstructure analysis of nylon 66 by WAXD and SAXS

The analysis of the small angle X-ray scattering (SAXS) data was based upon particle characteristic function, one-dimensional electron-density correlation function and particle distribution function. The microstructure of nylon 66 with different degrees of crystallinity was studied by means of X-ray scattering method. The radius of gyration R-g, the Porod radius R-p, the thickness of crystalline region L-c the thickness of non-crystalline region L-n, the thickness of interphase region d(tr), the long period L, the semiaxises of particles (a, a, b), the distribution of the particle sizes and the scattering invariant were calculated. The results indicate that there was a significant interphase region between the crystalline region and the non-crystalline region. and its content (W-t,W-x) should not be neglected in comparison with that of crystalline region W-c,W-x. The morphology of nylon 66 prepared by isothermal crystallization at a high temperature was mainly a lamellar structure, while the spherical crystals dominated in the quenched sample. The size of the particles in the quenched sample was smaller than that of those in the isothermally crystallized sample. and the distribution of the particle sizes in the isothermally crystallized sample was wider.