The use of etching techniques to investigate the morphology of mechanically induced transformations in an aliphatic polyketone

Existing permanganic etching techniques have been adapted for an aliphatic polyketone terpolymer to examine its spherulitic and lamellar morphology by Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM). A spherulitic morphology was observed consisting of irregularly shaped spherulites with an average diameter of 5–7 μm and poorly defined spherulite boundaries. Crystalline lamellae were found to be oriented radially within the spherulites. The morphology associated with mechanically induced transformations in a number of deformation systems has been studied and compared to that arising in other common polymeric systems. Changes in morphology through the neck region of drawn samples revealed the elongation of the spherulites as the morphology is transformed from a spherulitic to a fibrillar structure. In samples tested between 23°C and 120°C, radial flaws were observed within the spherulites prior to and within the neck transformation zone. These radial flaws were not observed for samples tested at higher temperatures. Four-point bend tests were conducted on double notched and pre-cracked aliphatic polyketone samples. Examination of the process zone around the crack at the core of the sample revealed crazes characteristic of semicrystalline polymers subjected to a highly constrained stress state. However, the process zone around the crack at the surface of the sample was found to consist of shear bands, suggesting a less constrained damage regime. High cycle fatigue loading also induced flaws oriented radially within the spherulites. Examination of the region around the failure surface in samples fatigue cycled until failure revealed a process consisting of an array of crazes reminiscent to that found in the four-point bend tests. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 3246–3255, 1999     

DSC experiments on gel-spun polyethylene fibers

The tensile strength of gel-spun polyethylene fibers obtained after hot-drawing depends on spinning conditions such as spinning speed, spinning temperature, spinline stretching, polymer concentration, and molecular weight/molecular weight distribution. High deformation rates in the spinline result in shish-kebab structures which after hot-drawing lead to fibers with poor properties. This is in contrast to hot-drawn fibers obtained from gel-spun fibers with a lamellar structure. Lamellar or shish-kebab structures in the gel-spun fibers can be distinguished by means of DSC experiments on strained fibers. On the basis of these experiments a qualitative prediction of the final tensile properties can be made. DSC experiments on (un)strained hot-drawn fibers show that in the case of shish-kebab structures an incomplete transformation into a fibrillar structure takes place which partly explains the low tensile strength. Chain slippage which becomes possible after the orthorhombic-hexagonal phase transition is involved in the fracture mechanism. The shift of the orthorhombic-hexagonal phase transition to higher temperatures with increasing tensile strength indicates that the increase in strength corresponds to an increase in length of the crystal blocks. Consequently, creep failure also occurs at higher stresses. The melting behavior of cold-drawn and hot-drawn fibers is qualitatively similar, but the transformation into a fibrillar structure is more complete in the latter case.     

SAXS experiments on gel-spun polyethylene fibers

The properties of gel-spun polyethylene fibers hot-drawn to the maximum draw ratio depend on the spinning conditions. Different spinning conditions result in two types of structure in the paraffin oil containing fibers: an isotropic lamellar structure or a shish-kebab structure. Meridional SAXS experiments can identify the structure present. After extraction, these structures are still present but can be detected only in a more indirect way by SAXS experiments because of an excessive contribution of void scattering. During hot-drawing both structures are transformed into a more fibrillar structure. The shish-kebab structures can be drawn only to relatively low hot-draw ratios with an incomplete transformation of the lamellar overgrowth into the fibrils, as demonstrated by the presence of a meridional SAXS maximum/shoulder. This leads to relatively weak fibers. Lamellar structures can be drawn to high draw ratios by chain unfolding. A nearly complete transformation of the lamellae into fibrils is obtained and the fibers have excellent properties. The information about the morphology obtained by SAXS, DSC, WAXS, and SEM can be used to establish a relation between morphology and properties.     

The lamellar phase of the sodium dodecylsulfate/decanol/toluene/formamide system: NMR and phase studies of solubilization

The phase behavior of the system sodium dodecylsulfate/decanol/toluene/ formamide was investigated and pseudo-ternary diagrams established. In particular, the effect of varying the amount of toluene in the system on the stability of the lamellar phase region was studied in detail. Deuterium NMR and low-angle x-ray diffraction measurements showed that more toluene was distributed between the surfactant chains as the amount of decanol in the system is reduced, resulting in a more disordered dynamic structure in the bilayers. Similarly, increased formamide content lead to greater penetration of the toluene into the bilayer and more disorder. Both factors were found to be instrumental in decreasing the stability of the lamellar structure.     

Surfactant association structures in the system water,sorbitol, sodium dodecyl sulfate,and hexanol

The phase regions in the system hexanol, sodium dodecyl sulfate, and concentrated aqueous solutions of sorbitol were similar to the corresponding system with glycerol.In addition to the expected phase regions of a water/sugar micellar solution, a lamellar liquid crystalline phase, and the alcohol solution with solubilized sugar and water, a small region was found with an extremely stable emulsion, which could be separated by ultracentrifugation at 108,000 g. This emulsion consisted of micron sized droplets separated by layers of a lamellar liquid crystal.     

Deformation of elastomeric polyolefin spherulites

The ethylene‐octene block copolymers in this study consist of long crystallizable sequences with low comonomer content alternating with rubbery amorphous blocks with high comonomer content. The crystallizable blocks form lamellae that organize into space‐filling spherulites even when the fraction of crystallizable block is so low that the crystallinity is only 7%. These unusual spherulites are highly elastic and recover from strains as high as 300%. This new class of thermoplastic elastomers is fundamentally different from conventional elastomeric olefin copolymers that depend on isolated, fringed micellar‐like crystals to provide the junctions for the elastomeric network. The elastomeric block copolymers are shown to be unique in that a hierarchical organization of space‐filling lamellar spherulites provides the junctions for the elastomeric network. The deformation of the elastic spherulites is readily studied with small angle light scattering, wide angle X‐ray diffractograms, and atomic force microscopy. At strains in excess of 300%, the spherulites break up into a fibrillar structure following lamellar deformation processes that are similar to those established for high density ethylenic polymers. The crystalline transformation produces a stiffer elastomer that exhibits complete recovery on subsequent loadings. Similar experiments on elastomeric random ethylene‐octene copolymers where fringed micellar crystals provide the physical crosslinks that connect the rubbery, amorphous chain segments reveal significant differences. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 1313–1330, 2009     

Effects of thermal history on the rigid amorphous phase in poly(phenylene sulfide)

The rigid amorphous phase of semicrystalline poly(phenylene sulfide) (PPS) has been studied as a function of thermal history using scanning calorimetry, dielectric relaxation, density, and small-angle x-ray scattering (SAXS). Based on the new heat of fusion of perfect crystalline PPS, which is 26.7±0.8 cal/gram, the weight fraction of rigid amorphous phase is shown to be nearly twice as large as previously reported [1]. The mass fraction of the rigid amorphous phase ranges from 0.24 to 0.42 and is dependent upon thermal treatment. We have taken the approach of assuming a three-phase model for the morphology of semicrystalline PPS consisting of crystalline lamellae, mobile amorphous, and rigid amorphous components. Using this three-phase model, we determine that the average density of the rigid amorphous fraction is 1.325 g/cc, which is slightly larger than the density of the mobile amorphous phase fraction and was insensitive to thermal history. From the SAXS long period, the layer thicknesses of the mobile amorphous phase, rigid amorphous phase, and crystal lamellae were estimated. Only the lamellar thickness shows a systematic variation with thermal history, increasing with melt or cold crystallization temperature, or with decreasing cooling rate.     

Classification of homogeneous ethylene-octene copolymers based on comonomer content

Ethylene-octene copolymers prepared by Dow's INSITE™ constrained geometry catalyst technology present a broad range of solid-state structures from highly crystalline, lamellar morphologies to the granular morphology of low crystallinity copolymers. As the comonomer content increases, the accompanying tensile behavior changes from necking and cold drawing typical of a semicrystalline thermoplastic to uniform drawing and high recovery characteristic of an elastomer. Although changes in morphological features and tensile properties occur gradually with increasing comonomer content, the combined body of observations from melting behavior, morphology, dynamic mechanical response, yielding, and large-scale deformation suggest a classification scheme with four distinct categories. Materials with densities higher than 0.93 g/cc, type IV, exhibit a lamellar morphology with well-developed spherulitic superstructure. Type III polymers with densities between 0.93 and 0.91 g/cc have thinner lamellae and smaller spherulites. Type II materials with densities between 0.91 and 0.89 g/cc have a mixed morphology of small lamellae and bundled crystals. These materials can form very small spherulites. Type I copolymers with densities less than 0.89 g/cc have no lamellae or spherulites. Fringed micellar or bundled crystals are inferred from the low degree of crystallinity, the low melting temperature, and the granular, nonlamellar morphology. © 1996 John Wiley & Sons, Inc.     

Drawing and extrusion of semi-crystalline polymers

This review treats mainly the initial transformation of the starting unoriented lamellar material into the final oriented microfibrillar structure and its drawing. If the starting material has partially oriented shish-kebab structure the drawing is a combination of transformation of lamellae into the microfibrils and the drawing of microfibrils. The review article is based on the literature from the last ten years and relys heavily on recent reviewing [1–3]. Older articles are only included if they have contributed to the basic ideas and experiments of drawing.     

Spherulitic morphology in polyethylene and isotactic polystyrene: Influence of diffusion of segregated species

Morphological consequences of a localized diffusion of segregated species at crystal growth fronts have been studied in two specific contexts: (1) variation of texture in spherulites grown in unfractionated polyethylene over a range of crystallization temperatures mostly in regime II, and (2) development of elongated lamellar habits in spherulites of a polymer (isotactic polystyrene) whose native crystal habit is regularly polygonal. In relation to (1) it is shown that, as crystallization temperature is varied, there is a correlation between mean thickness of stacks of lamellae and an averaged diffusion range of segregated molecules of lower molecular weight. It is noted that lamellar organization appears to be significantly different in polyethylene fractions. In relation to (2) it is shown that principal contributors to the evolution of spherulitic texture from hedritic precursors are fragmentation of lamellae by screw dislocations and radially biased growth under the influence of concentration gradients of segregated species.     

静高压下邻苯二甲酸二辛酯增塑双酚A型聚碳酸酯体系中立体开放球晶的生长

通过加入增塑剂邻苯二甲酸二辛酯(DOP), 改变高分子链在压力作用下的运动能力, 培养出具有独特形貌、亚结构为折叠链晶体和三维立体的开放聚合物球晶.     

Classification of homogeneous copolymers of propylene and 1‐octene based on comonomer content

The solid‐state structure and properties of homogeneous copolymers of propylene and 1‐octene were examined. Based on the combined observations from melting behavior, dynamic mechanical response, morphology with primarily atomic force microscopy, X‐ray diffraction, and tensile deformation, a classification scheme with four distinct categories is proposed. The homopolymer constitutes Type IV. It is characterized by large α‐positive spherulites with thick lamellae, good lamellar organization, and considerable secondary crystallization. Copolymers with up to 5 mol % octene, with at least 28 wt % crystallinity, are classified as Type III. Like the homopolymer, these copolymers crystallize as α‐positive spherulites, however, they have smaller spherulites and thinner lamellae. Both Type IV and Type III materials exhibit thermoplastic behavior characterized by yielding with formation of a sharp neck, cold drawing, strong strain hardening, and small recovery. Copolymers classified as Type II have between 5 and 10 mol % octene with crystallinity in the range of 15–28%. Type II materials have smaller impinging spherulites and thinner lamellae than Type III copolymers. Moreover, the spherulites are α‐negative, meaning that they exhibit very little crystallographic branching. These copolymers also contain predominately α‐phase crystallinity. The materials in this category have plastomeric behavior. They form a diffuse neck upon yielding and exhibit some recovery. Type I copolymers have more than 10 mol % octene and less than 15% crystallinity. They exhibit a granular texture with the granules often assembled into beaded strings that resemble poorly developed lamellae. Type I copolymers crystallize predominantly in the mesophase. Materials belonging to this class deform with a very diffuse neck and also exhibit some recovery. They are identified as elastoplastomers. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 4357–4370, 2004     

Craze fibril extension ratio measurements in glassy block copolymers

The extension ratios of crazes in triblock copolymer films of poly(2-vinylpyridine)-polystyrene-poly(2-vinylpyridine) [PVP-PS-PVP] which had lamellar microphase domain structure were measured by transmission electron microscopy. The extension ratio when the lamellae were oriented parallel to the craze fibril direction was always greater than that when the lamellae were oriented perpendicular to this direction, reflecting the stretching of the chains of the block copolymer in a direction normal to the interfaces of the lamellar domains.     

X-ray scattering study of molecular order in a liquid crystal-side group polysiloxane

The molecular structure of a polysiloxane with phenyl benzoate mesogenic side groups was investigated in an x-ray scattering study in the partially crystalline, smectic and nematic phase, and in the melt. In the crystalline phase polymer molecules have the form of straight ribbons with a double-comb-conformation. A bilayer structure is built up by regular stacking. Layers are the dominating structure element not only in the crystalline and smectic phase, but also in the nematic phase, and even in the isotropic melt. Layers are planar in the smectic phase and curved in the nematic phase, with an asymmetric distribution of the normal vectors about the director. In the isotropic melt there is evidence for the occurrence of clusters with layer-like short-range order.     

Further electron microscope observations on polyethylene III. Smectic intermediate state during melting and crystallization

While it was possible to demonstrate in the first part of this paper [1] that the granular structure in an LPE melt created by short-time staining with chlorosulfonic acid is an artifact, it was demonstrated in the second part [2] that an artifact can actually be useful. It makes it possible to differentiate between the mobile melt and a very thin layer of fixed melt on the crystalline lamellae which corresponds to the switchboard model.This third part reports the discovery of a smectic type of liquid crystal intermediate state both in the melting and in the crystallization processes, which many authors regarded as impossible because of the flexibility of the molecules in polyethylene.Extracts presented at the 32nd Hauptversammlung der Kolloid-Gesellschaft und Berliner Polymeren Tage 1985, 2–4 October 1985 in Berlin     

SAXS study of core-shell colloids

Polymeric core-shell systems were produced by a two-stage emulsion polymerization technique under fixed conditions: i) monodisperse seed latex with a sufficiently high particle number; ii) starved monomer-II addition; iii) water-soluble initiator; iv) incompatibility of core and shell polymer. From electron micrographs, it is not possible to determine where the second polymer is located within these two-stage emulsion polymers. The internal structure of the particles can be detected by small-angle x-ray scattering. The results indicate that; i) the emulsion polymerization process takes place in a small surface layer region of the seed particles, and ii) a small interfacial layer exists between the core and shell polymer.Part 6 of Polymerizations in the Presence of Seeds     

Structural factors controlling tensile yield deformation of semi‐crystalline polymers

In this work, a molecular model is proposed to account for the stress‐strain relationships of spherulitic polymers. To describe the yielding behavior of spherulitic polymers, we introduced a new structural unit, i.e. the lamellar cluster, which is represented by several stacked lamellae bound by some tie molecules. It was shown that the tie molecules between the adjacent lamellar clusters produce the concentrated load acting on the cluster surface, leading to bending deformation of the lamellar cluster. The yielding behavior was explained by the disintegration of lamellar cluster due to the bending deformation.     

Effect of random copolymerization on growth transition and morphology change in polypropylene

The growth rate of an ethylene-propylene random copolymer with a 2.8% w/w ethylene content was studied in a similar manner to polypropylene. A growth regime transition associated with a birefringence change was observed at 130C, while the same phenomena appeared at 138C in isotactic polypropylene. In both polymers positive birefringence corresponds to Regime III, whereas negative birefringence of spherulites is associated with Regime II. The birefringence change is attributed to a change in the organization of crystalline lamellae: quadritic arrays of intercrossing lamellae at low temperature (Regime III) and preferentially radiating lamellae at higher temperature (Regime II). We confirm that such a morphological change can be interpreted using the concept of non-adjacent re-entry introduced in Hoffman's kinetic theory. Thus, quadritic morphology seems to have a partly kinetic origin. The shift of the transition temperature in the copolymer is due to the rejection of ethylene segments at the surface of crystalline lamellae of polypropylene.     

Novel etching phenomena in poly(3‐hydroxy butyrate) and poly(oxymethylene) spherulites

Poly‐3‐hydroxy butyrate has been etched and studied under scanning and transmission electron microscopes. It displays three of the following unusual features: (1) spherulites develop in a loose spiral rather than radial structure, which appears to reflect the chiral nature of the polymer; (2) in the banded spherulitic structure, lamellae oriented flat‐on to the surface are etched more deeply in relation to edge‐on lamellae; and (3) material crystallized at high temperature is less resistant to etching than that crystallized at low temperature, whereas the most rapid rate of etching appears to be where growth occurred at an intermediate temperature where the growth rate was at its maximum. The second and third phenomena are contrary to what is found in polymers such as polyethylene and polyethylene terephthalate and are attributed to excess free volume in the material located between the main lamellar bundles. Polyoxymethylene also displays the same unusual relationship of etching rate with crystallization temperature. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 40: 124–133, 2002     

The morphology of the spherulitic surface in polyethylene

Studies of lamellar shapes and profiles in linear polyethylene have often been implemented by microscopic examination of appropriately etched random slices through spherulitic specimens. However, since a spherulite crystallized from a bulk specimen is a three-dimensional assembly of radially oriented lamellae with a twisting orientation (except for very high T_cs), it may be difficult to draw appropriate conclusions from a random slice. A technique has been developed that allows one to prepare spherulitic surfaces such that their distance relative to the geometric center can be well characterized. A computer-based graphical representation is also presented which suggests that the projection of lamellae on such surfaces is adequately represented by a radially oriented assembly of helicoidally twisted lamellae. Based on the agreement between the experimental results and the computer model, it is suggested that the C and S shapes previously observed by other researchers are not necessarily intrinsic to the lamellar profile but may arise due to geometrical effects as the lameliae project onto a surface at various angles. From these results it is also evident that in ringed spherulites lamellae undergo continuous twisting rather than successive misalignment of essentially untwisted segments.