Real-time X-ray scattering study during heating of oriented injection-molded polyethylene

Highly oriented linear polyethylene was prepared by elongational flow injection molding. The changes in crystal orientation were investigated as a function of temperature by real-time wide-angle X-ray diffraction. Additionally, the influence of molecular weight upon the microstructure and the changes in orientation, during heating near the melting point, and after cooling have been examined. A shish-kebab structure is inferred for the high molecular weight samples (M_w≥10⁵) from SAXS observations, while for samples with M_w<10⁵ only an oriented lamellar structure is found. Consequently, a higher thermal stability is shown by the higher molecular weight samples. Furthermore, a recovery of crystal orientation on rapid cooling of the samples from the melt is only observed for samples with M_w≥10⁵. The results are discussed in terms of a preferential recrystallization of chain-folded lamellae, on cooling, onto the shish fibrils which survive at high temperature.     

Crystal orientation in a semicrystalline polymer in relation to deformation of polymer spherulites. II. Orientation distribution function of crystallites within crystal lamella as a function of lamellar orientation

A model relating crystal orientation in a semicrystalline polymer to the deformation of polymer spherulites is proposed. The distribution function for orientation of crystallites within crystal lamellae is assumed to be a function of lamellar orientation. In addition to the orientation of crystal lamellae in affine fashion, several parameters are introduced to characterize the untwisting of the crystal lamellae and the four different types of orientations of the crystallites within the crystal lamellae in the undeformed and deformed states of the spherulite. The model was tested by experiments in uniaxial stretching of a low-density polyethylene. The theoretical distributions of orientation of given reciprocal lattice vectors of the crystallites, such as the reciprocal lattice vectors of the (110) and (200) crystal planes, are compared with the results of x-ray diffraction experiments. It was found that the most important factors in fitting the model to experimental results are: (a) the fraction of crystallites having random orientation within lamella and, in turn, representing the degree of imperfection of the lamella in the undeformed state; (b) the ease of transition of crystal orientation within lamella from b-axis orientation parallel to the lamellar axis to two types of c-axis orientations (type C_a and type C_r) parallel to the stretching direction; and (c) the fraction of crystallites having orientation in type C_r (unfolding mechanism) rather than type C_a (rotation mechanism).     

Deformation and structure of doubly oriented polyethylene

Doubly oriented low-density polyethylene with parallel lamellae was compressed along the initial draw direction (i.e., at right angles to the lamellar surfaces) at 20°C. Wide- and low-angle x-ray diffraction were used to determine the changes in the molecular orientation and in the texture. During the compression, specimens previously annealed at or near 102°C were found to undergo changes in length, in long spacing, and in molecular orientation which were consistent with an (001) chain slip mechanism. In specimens annealed at higher temperatures x-ray diffraction indicated that during compression some series component of the long spacing was compressed by a much smaller amount than the remainder of the long spacing, which deformed by chain slip; in these cases it was found that the macroscopic strain along the compression axis (ε_y) was greater than the strain in the long spacing along that axis (ε_d). It is suggested that the missing strain which makes ε_y greater than ε_d is due to partial melting and the consequent development of amorphous regions between the stacks of lamellae.     

Study of crystalline orientation in drawn ultra-high–molecular weight polyethylene films

A wide-angle x-ray diffraction (WAXD) study of the development of molecular orientation in the crystalline phase of ultra-high–molecular weight polyethylene films prepared by the gelation–crystallization method is presented. WAXD scans of the undrawn films show that the lamellae are oriented in the plane of the films. Upon drawing at 130°C, the orientation of the molecular chains changes from the direction normal to the film surface (ND) to the elongation direction. The decrease of the 200/020 intensity ratio at low draw ration (λ <10) indicates that double orientation develops during the transformation from the lamellar to the fibrillar morphology, with the a-axis oriented parallel to ND. The orientation distributions of the 110, 200, 020, and 002 planes of the orthorhombic unit cell of polyethylene were studied and characterized by the coefficients of a Legendre polynomial series. At a draw ratio of 4.5, the second-order coefficient, 〈P₂(cos χ〉, already gets close to its limiting value, but it is shown that higher order coefficients of the polynomial series can be used to describe the evolution of the orentation, even up to λ = 50. The coefficients relative to the molecular chain orientation, 〈P_n(cos χ)〉_c, can be calculated from different crystalline reflections. Curve-fitting calculations were made in order to improve the correlation between the results obtained from the orientation distribution of the 110, 020, and 002 planes. A Person VII function was found to give a better fit of the experimental curves than Gaussian or Lorentzian equations. © 1993 John Wiley & Sons, Inc.     

Crystal orientation in a semicrystalline polymer in relation to deformation of polymer spherulites. IV. Crystal orientation mechanism of nylon-6 under uniaxial stretching

A model relating crystal orientation to the deformation of nylon-6 spherulites under uniaxial stretching is discussed in terms of the orientation distribution functions of reciprocal lattice vectors of crystal planes, such as the (002) and (200) planes. The distribution functions calculated from the model are compared with those obtained from x-ray diffraction experiments. It is found that the crystal a axis and, consequently, the direction of hydrogen bonds within the crystal (α modification) orient parallel to the lamellar axis in the undeformed state, and that the crystal orientation behavior of nylon-6 is much different from that of low-density polyethylene, being characterized by much smaller values of the reorientation parameters of crystallites within orienting lamellae. Moreover, small-angle light scattering for H_v and V_v polarization is also calculated on the basis of the spherulite deformation model by taking the nylon-6 crystal as having orthogonal–biaxial symmetry in optical anisotropy. It is concluded that the H_v scattering can be realized in terms of the proposed model for spherulite deformation by taking into account a considerable contribution of hydrogen bonds to the molecular polarizability, so as to make the polarizability along the crystal a axis larger than that along the b axis. In other words, this conclusion suggests positively birefringent spherulites in the nylon-6 samples studied.     

Oscillatory shear‐induced alignment of ketjen black conductive particles in polylactic acid and its effect on the electrical anisotropy

This study aligned Ketjen black (KB) particles along one preferred direction in a polylactic acid (PLA) matrix using an oscillatory shear flow and investigated the effect of aligned KB on the electrical anisotropy. Under the oscillatory shear, the KB particles are aligned along the flow direction in the PLA matrix, resulting in an oriented conductive network. When the concentration of KB is in the range of 0.88–1.56 vol %, the electrical volume resistivity along the flow direction (ρ_∥) decreases to ～3 × 10⁴ Ω m and that perpendicular to the flow direction (ρ_⊥) remains at ～1 × 10¹⁰ Ω m, showing an extremely large electrical anisotropy, and the ρ_⊥/ρ_∥ value is 3–4 orders of magnitude higher than that of previously reported carbon‐nanotube‐based electrical anisotropic composites. This strong anisotropy is attributed to the preferential alignment of KB particles with lower percolation threshold for conductive path along the flow direction. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 369–373     

Grafting onto carbon black by the reaction of reactive carbon black having masked isocyanate or acyl azide group with functional polymers

Although isocyanate group (NCO) introduced onto carbon black surface was inactivated rapidly upon storage, it could be stabilized by masking the NCO group with active hydrogen compounds such as acetylacetone, diethyl malonate, and sodium hydrogensulfite. Upon heating these carbon blacks having masked NCO group at 150°C, the NCO group was regenerated on carbon black by the decomposition of the masked NCO group. On the other hand, acyl azide (CON₃) group introduced onto carbon black was stable at below 20°C, but readily decomposed to NCO group by heating. By means of the reaction of NCO group on carbon black with functional polymers having hydroxyl, amino, and carboxyl group, these polymers were effectively grafted onto carbon black surface. When carbon black having CON₃ group was used as reactive carbon black, the grafting ratio of diol-type polyethylene glycol (M_n = 8.2 × 10³), polyethyleneimine (M_n = 2.0 × 10⁴), polyvinyl alcohol (M_n = 2.2 × 10⁴), and bifunctional carboxyl-terminated polystyrene (M_n = 1.1 × 10⁵) was determined to be 29.7, 81.7, 32.2, and 50.4%, respectively. The number of grafted polymer chain decreases with an increase in molecular weight of the polymers, because the shielding effect of NCO group by grafted polymer chain is enhanced with an increase in molecular weight of the polymer.     

Structural changes on hot-rolling of polyethylene. I. Crystallite orientation and lamellar deformation

The crystallite orientation and lamellar deformation produced by hot-rolling in polyethylene have been investigated. In the lightly rolled stage, the [110]^* axis of polyethylene crystals orientates in the plane perpendicular to the rolling direction and the c axis becomes aligned with the rolling direction. In the heavily rolled stage the a, b, and c axes coincide with the macroscopic directions in the sample. These orientational changes are interpreted in terms of a slip mechanism. Small-angle x-ray scattering (SAXS) investigations of hot-rolled polyethylene show the following. (1) There are two kinds of lamellar structures; one in which inclined lamellae give a four-point diagram in the SAXS photograph and another in which lamellar normals are oriented around the rolling direction even at the lightly rolled stage. The latter structure is attributed to the mechanism of unfolding and recrystallization. (2) The chain-fold length in the original structure remains unchanged in the lamellae up to a roll ratio of four although the apparent long period decreases. This is explained by inclination of polymer chains in the lamellae. Further rolling aligns the polymer chains with the rolling direction and the fold length decreases.     

Thermal expansion,free volume,and molecular mobility in a carbon black-filled elastomer

The thermal expansion of a butadiene–styrene copolymer filled with carbon blacks differing tenfold in mean particle size (HAF and MT) was investigated. The glass transition was unaffected by MT and was raised only 0.2°C for every 10 parts per hundred by weight of polymer of HAF black added. The coefficient of expansion of the polymer component of the composite in the rubbery region was substantially unaffected by either carbon black, but decreased markedly with increasing black loading in the glassy state. These results suggest that free volume is not altered appreciably by the presence of the filler in the rubbery state, but expands with decreasing temperature below T_g. The latter effect is explained by dilatation due to stresses set up around filler particles, arising from differences in the expansion coefficients of filler and polymer, which are not relieved in the glassy state. The near invariability of T_g and of the rubbery fected by adsorption of polymer segments on the carbon black surface. A conservative rough estimate indicates that restriction of segmental motion is confined to a 30 Å layer around the particles in which T_g is elevated by only 10°C.     

A study of the mechanical anisotropy of high-draw,low-draw,and voided PVDF

The mechanical anisotropy of oriented PVDF sheet is examined using a variety of experimental techniques. The mechanical behavior is similar to that observed previously for low-density polyethylene and nylon and consistent with a parallel lamellar crystalline structure. The s₃₁ compliance is reduced in magnitude by drawing to higher draw ratio, but the reduction in the piezoelectric coefficient d₃₁ is less marked, suggesting that the piezoelectric response cannot be related solely to dimensional changes under stress. Drawing to high draw ratio increases the s₃₃ compliance, and this is further increased by introducing voids. The corresponding d₃₃ piezoelectric coefficient is not changed significantly by drawing to high draw ratio, or by the introduction of voids, again indicating that the piezoelectric behavior relates to factors other than dimensional changes.     

Influence of Carbon Black on Conductivity and Structure of Polyethylene Oxide Based Polymer Electrolyte Film

The potential applications of carbon black are expected to grow as science and technology improve offering up new possibilities for innovation throughout disciplines included in the field of energy storage. The present work shows the influence of carbon black to improve the ionic conductivity of the polymer electrolyte. The synthesis of polyethylene oxide: ammonium iodide based polymer electrolyte incorporated with carbon black varying from 0.01 to 0.06 wt% with respect to PEO: NH4I system by solution casting method. Different characterizations like polarized optical microscopy (POM), impedance spectroscopy, and ionic transference number (t_ion) are studied in detail. The maximum ionic conductivity is achieved at 0.05 wt% carbon black shows 1.20 × 10⁻⁵ S cm⁻¹ at ambient temperature. In accordance with POM data, the amorphous region has increased whereas the crystalline region has shrunk which further indicated the increase in ionic conductivity . The value of (t_ion) is calculated to be 0.97 which shows the system is ionic in nature. PEO based polymer electrolyte doped carbon black can be used for the fabrication of energy storage devices.     

The mechanical moduli of lamellar semicrystalline polymers

Bounds on the elastic constants are derived for semicrystalline polymers whose local morphology is lamellar. Local response matrices (stiffness and compliance) are formulated in three dimensions that simultaneously incorporate uniform in-plane strain and additive forces from layer to layer of crystalline and amorphous phases and uniform stress and additive displacements normal to the lamellar surfaces. Spatial averaging of the stiffness and compliance matrices under the assumption of axially symmetric orientation gives the upper and lower bounds on the longitudinal and transverse tensile moduli and the axial and transverse shear moduli as functions of the separate phase elastic constants, the volume percent crystallinity, and the moments of the orientation 〈cos²θ〉 and 〈cos⁴θ〉. The bounds are much tighter than the Voight upper and Reuss lower bounds that do not recognize phase geometry. Using the known crystal elastic constants of polyethylene, sample calculations on isotropic unoriented materials show that the divergence of bounds at high crystallinity necessitated by the extreme crystal anisotropy shows up only at very high crystallinity. At low temperature the bounds are tight enough to specify G₁, the amorphous modulus, from the measured G and the known crystal elastic constants. At higher temperatures and lower G, the bounds are not tight enough for this purpose but the shear modulus versus crystallinity and temperature data are well fitted by the lamellar lower bound using a temperature-dependent, crystallinity-independent G₁.     

Quantitative characterization of deformation in drawn polypropylene films

The submicroscopic morphology of uniaxially deformed isotactic polypropylene films has been examined by small-angle light scattering (SALS), electron microscopy, optical microscopy, small-angle x-ray scattering (SAXS), wide-angle x-ray diffraction, birefringence, sonic modulus, and density methods. Several new interpretations and extensions of existing theories are developed and verified experimentally as follows. (1) The V_v SALS pattern is shown to be a new tool for the identification of the sign of the birefringence of spherulites too small to be seen in the optical microscope. The theoretical dependence of the V_v SALS pattern is developed and verified experimentally with patterns from isotactic polypropylene, polyethylene, Penton, nylon 6,6, poly(ethylene terephthalate), and nylon 6,10. (2) Intraspherulitic lamellar behavior during deformation can be identified from the SAXS pattern. This includes quantitative evaluation of the long spacing between lamellae and their average orientation. (3) The two-phase sonic modulus theory is valid over the wide range of deformations, crystallinities, processing temperatures, and molecular weights used in this study. The deformation of isotactic polypropylene films drawn at 110 and 135°C. has been characterized quantitatively in terms of an integrated picture of mass movement on all morphological levels: the molecular, the interlamellar, and the spherulitic. At both temperatures, the spherulites deform affinely with extension, whereas the deformation mechanisms within the spherulite depend on the location of the radii with respect to the applied load. During spherulite deformation, lamellar orientation and separation processes predominate, whereas at high extensions, fibrillation occurs and crystal cleavage processes predominate. The noncrystalline region orients throughout the draw region. At 135°C. non-orienting relaxation processes appear in the noncrystalline region which retard the rate of molecular orientation with extension.     

Hardness of nitric acid treated polyethylene followed by recrystallization

The hardness variation of melt crystallized polyethylene as a consequence of controlled fuming nitric exposure has been investigated using the microindentation technique. This study complements previous results obtained using other reagents (H₂SO₄, ClHSO₃). After HNO₃ exposure the microhardness of polyethylene decreases very rapidly, instead of increasing after the first hours of treatment. The hardness decrease is correlated to the volume fraction of interlamellar microvoids arising through selective acid digestion. For longer treatment times (t>40 h) the fragility of the material increases and the sample collapses under the indenter. The hardening of the degraded material after recrystallization from the melt is followed as a function of treatment time. The results are discussed in the light of the molecular mechanisms involved. Comparison of the experimental data with hardness calculations for ideal PE lamellar structures and chain extended dicarboxylic crystals implies that the major contribution to hardening is due to electron dense groups attachment at the surface of a mixed lamellar structure.     

Rheo-optical studies on the deformation mechanism of semicrystalline polymers. XIV. Alpha and beta mechanical dispersions of spherulitic high-density polyethylene and the dynamic orientation distribution function of crystallites

The dynamic tensile deformation mechanism of spherulitic high-density polyethylene was investigated by dynamic x-ray diffraction at various temperatures and frequencies in order to assign the α and β mechanical dispersions explicity. The uniaxial orientation distribution function q(ζ_j,0) of the jth crystal plane and its dynamic response Δq′_j(ζ_j,0) in phase with dynamic strain were observed for the (110), (200), (210) and (020) crystal planes. Then the orientation distribution function w(ζ,0,η) of crystallites (crystal grains) and its dynamic response Δw′(ζ,0,η), also in phase with the dynamic strain, were determined by a mathematical transformation procedure proposed by Roe and Krigbaum on the basis of the Legendre addition theorem. The temperature and frequency dependences of w′(ζ,0,η) were analyzed in terms of the model parameters for dynamic spherulite deformation combining affine orientation of crystal lamellae with several types of preferential reorientation of the crystal grains within the orienting lamellae. The following assignments are made: (i) The α mechanical dispersion must be assigned to the dynamic orientation dispersion of crystal grains within the crystal lamellae, involving two types of preferential rotations of the grains about their own crystal b and a axes. The rotation about the b axis is associated with lamellar detwisting, mostly in the equatorial zone of uniaxially deformed spherulites; the rotation about the a axis is associated with intralamellar shearing, mostly in the polar zone of the spherulites. Thus both rotations are intralamellar grain-boundary phenomena. (ii) The β mechanical dispersion must be assigned to the dynamic orientation dispersion of the crystal lamellae behaving as rigid bodies. It is not accompanied by reorientation of the crystal grains, but is associated with orientation dispersion of noncrystalline material between the lamellae. Thus it is an interlamellar grain-boundary phenomena.     

Thermal annealing of doubly oriented nylon 11 in contact with formic acid

The most striking feature of the mechanism of thermal annealing of doubly oriented samples of low-density polyethylene (LDPE) and probably of high-density polyethylene (HDPE) is a progressive tilt of lamellar crystals around their crystallographic b axis. Such a rotation does not occur on thermal annealing in doubly oriented nylons. However, this rotation mechanism occurs during the thermal annealing of doubly oriented samples of nylon 11 in contact with a solvent below its dissolution temperature. As for oriented samples of polyethylene (PE), a correlation between the changes of macroscopic dimensions and long spacing obtained from the small-angle x-ray pattern is difficult to establish. In doubly oriented samples of nylon 11, the basal faces of the lamellar crystals are parallel to the a axis of the unit cell. Nevertheless, simple Miller indices cannot be assigned to the basal planes of the lamellae. On thermal annealing in formic acid, the basal planes of the lamellar crystals are, in some cases, parallel to (00l) planes. Annealing in formic acid at room temperature induces a phase transition: the chain c axis remains oriented along the rolling direction and the (00l) planes become parallel to the limiting planes of the lamellar crystals. Bulk doubly oriented samples of nylon 11 annealed in formic acid just below the “dissolution temperature” have the same texture of orientation as filter mats of single crystals grown from dilute solution; moreover, as these bulk specimens remain doubly oriented, they can be used for further physicochemical investigations. The usual interpretation of the small-angle x-ray pattern is also discussed on the basis of the results reported in this paper.     

Gas transport and diffusive resistance in highly oriented high-density polyethylene

High density polyethylene was biaxially oriented by high-pressure forging and subsequently low-pressure thermal forming. The permeability of O₂, CO₂, and CH₄ was reduced slightly by biaxial orientation, the diffusivity of the gases was found to increase with the degree of orientation. The solubility decreased markedly with orientation. Density measurements indicated that crystallinity increases with the extent of biaxial deformation. Based on the concept of particle flow in viscous media, the variation of gas diffusivity with orientation is viewed as a frictional resistance effect. The diffusivity is inversely proportional to a phenomenological friction coefficient; which can be related to orientation by a shape factor s. The diffusivity for the oriented state, D, is then related to that of the nonoriented state, D₀, as D = D₀/(1 + s?). The variation of diffusivity selectivity with orientation is also formulated based on this consideration. Results on both biaxially and uniaxially oriented HDPE are examined in light of this model.     

Polymérisation “basse pression” de l'ethylène en préasence de noir de carbone

The polymerization of ethylene with Ziegler-Natta catalysts in the presence of carbon black has shown three characteristic features both with a heterogeneous catalyst, AlBu₃? TiCl₄, and with a soluble catalyst, Cl₂Ti(C₅H₅)₂? AlEt₂Cl. They are, in order of increasing importance: reactivity of the organoaluminum derivatives with surface chemical groups of the carbon black, adsorption of a certain amount of organoaluminum compounds on the carbon black surface, and influence of the specific surface of carbon black, which controls the dispersion degree of the catalytic system. Furthermore, it was possible to obtain polyethylene by this procedure, containing different amounts and different types of carbon black.     

MOLECULAR AND SUPRAMOLECULAR ORDERING IN CONFINED ENVIRONMENTS

Crystal and phase morphologies and structures determined by self-organization of crystalline-amorphous diblockcopolymers, crystallization of the crystallizable blocks, and vitrification of the amorphous blocks are reviewed through asystematic study on a series of poly(ethylene oxide)-b-polystyrene (PEO-b-PS) diblock copolymers. On the base ofcompetitions among these three processes, molecular and supramolecular ordering in confined environments can beinvestigated. In a concentration-fluctuation-induced disordered (D_(CF)) diblock copolymer, the competition between crystalli-zation of the PEO blocks and vitrification of the PS blocks is momtored by time-resolved simultaneous small angle X-rayscattering (SAXS) and wide angle X-ray diffraction (WAXD) techniques. In the case of T_c相似文献   

Effect of solvent and carbon black species on the rubber–carbon black interactions studied by pulsed NMR

The spin–spin relaxation time T₂ and the fraction of short T₂ component for composites of natural rubber with carbon black prepared under various conditions have been measured by pulsed NMR. Effect of swelling with a solvent (CCl₄), carbon black species (SAF, HAF, SRF) with different surface areas, and different initial carbon black loadings (35, 50, 70 phr) have been determined. Molecular motion in the rubber phase not in the immediate vicinity of the carbon black surface increases rapidly with increasing solvent concentration, yet it is still slightly restricted compared to rubber with solvent alone. On the other hand, molecular motion in the immobilized layer around carbon black and the fraction rubber in that layer are not affected by the solvent. This indicates strong restriction of molecular motion of polymers at the surface. For estimation of the thickness of the immobilized layer, the necessity of using an appropriate measure of surface area accessible to polymer molecules is pointed out. The degree of immobilization in the layer and the thickness of the layer do not vary appreciably with the nature of carbon black or the initial loading of carbon black.