Intercrystalline Links Research Articles

High-temperature relaxation promoting form II-to-form I phase transition of Polybutene-1

Amorphous coils between crystalline layers of polybutene-1, especially intercrystalline links within, were thought to play a critical role in form I nucleation, but recent experiments found that it actually played a negative role in form II to form I phase transition, that is, obstructing form I growth by hindering translational movements of form II stems. To reexamine the role of amorphous coils, a high molecular weight PB-1 sample was annealed at a high temperature ranging from 40 to 100 °C after low-temperature nucleation. Results indicated that high-temperature annealing after low-temperature nucleation facilitated disentanglement of amorphous coils, promoting subsequent form I growth. The growth rate of form I doubled after relaxation at 100 °C for 5 min. We also explored nucleation mechanism of form I by moving the relaxation process before nucleation of form I. Results indicated that the form I nuclei were highly fragile crystals on the ends of form II lamellae, suggesting critical role of internal stress in form I nucleation. With this study, we assume that the role of amorphous coils in form II to form I phase transition is indispensable. The seemingly conflicting roles of amorphous coils in form I nucleation and growth can be relieved partly by addition of a high-temperature relaxation process. We suggest addition of a high-temperature relaxation process between nucleation and growth to further expedite phase transition in a high molecular weight PB-1 sample. This study is beneficial to further understand form II to form I phase transition.

Microstructure and Tensile Properties of Melt-Spun Filaments of Polybutene-1 and Butene-1/Ethylene Copolymer.

Polybutene-1 with form I crystals exhibits excellent creep resistance and environmental stress crack resistance. The filaments of polybutene-1 and its random copolymer with 4 mol% ethylene co-units were produced via extrusion melt spinning, which are expected to be in form I states and show outstanding mechanical properties. The variances in microstructure, crystallization-melting behavior, and mechanical properties between homopolymer and copolymer filaments were analyzed using SEM, SAXS/WAXD, DSC, and tensile tests. The crystallization of form II and subsequent phase transition into form I finished after the melt-spinning process in the copolymer sample while small amounts of form II crystals remained in homopolymer filaments. Surprisingly, copolymer filaments exhibited higher tensile strength and Young's modulus than homopolymer filaments, while the homopolymer films showed better mechanical properties than copolymer films. The high degree of orientation and long fibrous crystals play a critical role in the superior properties of copolymer filaments. The results indicate that the existence of ethylene increases the chain flexibility and benefits the formation of intercrystalline links during spinning, which contributes to an enhancement of mechanical properties. The structure-property correlation of melt-spun PB-1 filaments provides a reference for the development of polymer fibers with excellent creep resistance.

Molar mass dependent spatial distribution of form II to I transition inside spherulites of disentangled isotactic Polybutene revealed by scanning Confocal Raman microscopy

Form II to I transition in isotactic polybutene-1 (PB-1) is known to depend on the molar mass due to complicated interplays between crystalline phase and the amorphous inter-crystalline links. In general, higher molar mass favored the transition at the early stage as more inter-crystalline links result in more form I nuclei. At the late stage, it was observed that the low molar mass samples possess higher transition rate because of an easy relaxation of the unfavored stress generated during the transition. In this work, form II to I transition at room temperature in spherulites with few inter-crystalline links between adjacent lamellae, which were obtained by isothermally crystallizing two commercial PB-1 of different molar mass at sufficiently high temperature, were investigated using confocal Raman microscope scanning along the radii. Surprisingly, the spherulite of the higher molar mass PB-1 showed a higher gross transition rate at late stage than that of the lower molar mass one. Considering the impacts from the thermal stress, exterior stress, the neighbor effect of form I as well as the coordination of thermal fluctuation driven transition and retarding effect by nearest form I, a detailed analysis of the spatial distribution of the transition within the spherulites revealed that the lamellae inside the higher molar mass sample led to a higher form II to I transition in the late stage through its preponderance of abundant long-chain ends, numerous folding parts and more effective lateral connectivity along the radial arms.

Macromolecular Insights into the Altered Mechanical Deformation Mechanisms of Non-Polyolefin Contaminated Polyolefins

Current recycling technologies rarely achieve 100% pure plastic fractions from a single polymer type. Often, sorted bales marked as containing a single polymer type in fact contain small amounts of other polymers as contaminants. Inevitably, this will affect the properties of the recycled plastic. This work focuses on understanding the changes in tensile deformation mechanism and the related mechanical properties of the four dominant types of polyolefin (PO) (linear low-density polyethylene (LLDPE), low-density polyethylene (LDPE), high-density polyethylene (HDPE), and polypropylene (PP)), contaminated with three different non-polyolefin (NPO) polymers (polyamide-6 (PA-6), polyethylene terephthalate (PET), and polystyrene (PS)). Under the locally elevated stress state induced by the NPO phase, the weak interfacial adhesion typically provokes decohesion. The resulting microvoids, in turn, initiate shear yielding of the PO matrix. LLDPE, due to the linear structure and intercrystalline links, is well able to maintain high ductility when contaminated. LDPE shows deformation similar to the pure material, but with decreasing ductility as the amount of NPO increases. Addition of 20 wt% PA-6, PET, and PS causes a drop in strain at break of 79%, 63%, and 84%, respectively. The typical ductile necking of the high-crystalline HDPE and PP is strongly disturbed by the NPO phase, with a transition even to full brittle failure at high NPO concentration.

Phase transition of polybutene-1 ionomers: Influences of ion content and branch length

The phase transition behaviors from the tetragonal form II to the trigonal form I of polybutene-1 ionomers with various ion contents and branch lengths were studied by means of differential scanning calorimetry. In the ionomers studied, ionic functional groups were located at the end of the branches incorporated, so ion content was varied with the incorporation ratio and, branch length was tuned by the distinct co-monomers of 6-iodo-1-hexene and 18-iodo-1-octadecene. The results show that although the branches introduced retard the II-I phase transition in reference copolymers, after introduction of ions, the ionomers exhibit the largely accelerated kinetics of the solid II-I phase transition. Interestingly, it was found that the phase transition exhibits a non-monotonic dependence on the ion content and for the ionomers with 4-carbon branches, the optimal ion content to obtain the maximum transition degree is around 2.6 mol%. This is probably due to the cooperative effects of the formation of intercrystalline links by the ion aggregates in ionomers, 1) the enhanced transfer of internal stress for nucleation and 2) the restricted chain mobility for adjusting segmental packing. Furthermore, the II-I phase transition can be further accelerated by increasing the 4-carbon branch to the 16-carbon branch via copolymerizing 18-iodo-1-octadecene as the comonomers. These results provide the helpful guide to the molecular design of polybutene-1 ionomer materials.

Reexamining the role of intercrystalline links in the II-I phase transition of Poly(1-butene)

Despite being studied extensively, the role of intercrystalline links has not been elucidated completely. To clarify its role, two kinds of different lengths of poly (1-butene) chains were blended with different proportions, among which only the long chain was able to form intercrystalline links. Phase transitions of these blends were monitored with time-resolved FTIR. Surprisingly, when the content of long chains reached 30% or 40%, phase transition rates were even slower than they existed alone, indicating phase transition was suppressed greatly by long chains. Adding a minority of short chains actually would also slow down the phase transition, though the effect was not as obvious as long chains. Estimation indicates that the change of enthalpy cannot compensate for the loss in conformational entropy in II-I phase transition. To ensure continuous proceeding of II-I phase transition, the role of amorphous chains is indispensable in the quiescent phase transition. Nevertheless, the role of intercrystalline links should not be undue stressed either. Analysis indicates that a transient amorphous network exists in the blends, consisting of different sizes of amorphous coils. Long chains can form larger coils because of intercrystalline links, while small coils are most likely from individual short chains. Entanglements exist between these amorphous coils, stabilizing the transient network, which would also affect phase transition significantly. When a minority of short chains are added, stress on one side of some big coils reduces. The big coils deviate from previous mass centers, slowing down its internal stress on form II crystal and thus its phase transition rate. Conversely, when a minority of long chains are added, big coils not only would lead small coils deviating from their previous mass centers, but also slow down contraction of the small coils through the entanglement, leading to a larger decrease in form I nuclei. The roles of intercrystalline links and entanglement should be considered simultaneously.

Glass-Transition-Temperature-Independent Form II to I Phase Transition of Low-Molar-Mass Isotactic Polybutene-1

Temperature-dependent form II to I transition in isothermally crystallized low-molar-mass polybutene-1 has been investigated by means of fast scanning calorimetry. The as-crystallized sample possesses metastable form II crystals with a wide distribution of lamellar thickness and thus a wide distribution of the density of intercrystalline links between adjacent lamellae due to the high mobility of the chain segments within form II crystals and a limited chain length (low molar mass). Upon annealing the as-crystallized sample at different temperatures, the form II to I transition was found to occur in a wide temperature range irrespective of the glass transition temperature. The form I crystals transformed below glass transition possess a higher melting point than those transformed at a temperature close to the crystallization temperature. The results indicate that those lamellae with less or no intercrystalline links are not restricted by the vitrified amorphous phase. The mobility of chain segments in those well-crystallized form II crystals remains even at a temperature few tens of kelvin below the glass transition.

Spontaneous Form II to I Transition in Low Molar Mass Polybutene-1 at Crystallization Temperature Reveals Stabilization Role of Intercrystalline Links and Entanglements for Metastable Form II Crystals

As for the solid–solid transformation from form II to form I in polybutene-1, the intercrystalline links in amorphous phase and the temperature difference between crystallization and phase transiti...

Intercrystalline Links Determined Kinetics of Form II to I Polymorphic Transition in Polybutene-1

The effect of intercrystalline links containing tie molecules and entangled loops on polymorphic transition from form II to form I in polybutene-1 (PB-1) of different molecular weights has been investigated by differential scanning calorimetry and small-angle X-ray scattering techniques. The PB-1 samples were isothermally crystallized at a range of temperatures to develop metastable form II crystalline modification of different lamellar thickness, long spacing, and number of intercrystalline links in the amorphous phase. Tammann’s two-stage crystal nuclei development method was applied to promote a faster polymorphic transition from form II to I; that is, form I nuclei were developed at the early low temperature stage, and form I crystals were formed at the later high temperature stage. At a given annealing condition, the transition rate in the high molecular weight sample is found to increase with the increase of the prior form II crystallization temperature, while it shows a negative correlation between...

Ентропійно-енергетичнА моделЬ розвиткУ втомниХ дефектіВ

The dependence is deduced on the basis of the maximum entropy method, to distribute the number of fatigue microcracks according to the category of absorbed energy. The ratio obtained is non-Gaussian and is called “The ultimately hyperbolic distribution law”, which becomes asymptotically hyperbolic with the growth of argument. That plot allows the microcracks to “distribute” the absorbed energy in the most reasonable way. The energy balance for the microcrack’s absorbed energy is made out, proceeding from the supposition that the increase of its area is in proportion to the gap energy of intercrystalline links, and the dissipation energy in the plasticity area is in proportion to the size of its borders. This gave an opportunity to obtain the ratios for the growth indicators of microcrack’s area. These results and taking account of microcracks’ distribution according to the categories of absorbed energy, help to get the evaluation formula for the fatigue plot.

Superdrawing of polytetrafluoroethylene nascent powder by solid-state coextrusion

A film of nascent powder of polytetrafluoroethylene (PTFE), compacted below the ambient melting temperature (Tm, 335 °C), was drawn by two-stage draw techniques consisting of a first-stage solid-state coextrusion followed by a second-stage solid-state coextrusion or tensile draw. Although the ductility of extrudates was lost for the second-stage tensile draw at temperatures above 150 °C due to the rapid decrease in strength, as previously reported, the ductility of extrudates increased with temperature even above 150 °C when the second-stage draw was made by solid-state coextrusion, reflecting the different deformation flow fields in a free space for the former and in an extrusion die for the latter. Thus, a powder film initially coextruded to a low extrusion draw ratio (EDR) of 6–20 at 325 °C was further drawn by coextrusion to EDRs up to ∼︁400 at 325–340 °C, near the Tm. Extremely high chain orientation (fc = 0.998 ± 0.001), crystallinity (96.5 ± 0.5)%, and tensile modulus (115 ± 5 GPa at 24 °C, corresponding to 73% of the X-ray crystal modulus) were achieved at high EDRs. Despite such a morphological perfection and a high modulus, the tensile strength of a superdrawn tape, 0.48 ± 0.03 GPa, was significantly low when compared with those (1.4–2.3 GPa) previously reported by tensile drawing above the Tm. Such a low strength of a superdrawn, high-modulus PTFE tape was ascribed to the low intermolecular interaction of PTFE and the lack of intercrystalline links along the fiber axis, reflecting the initial chain-extended morphology of the nascent powder combined with the fairly high chain mobility associated with the crystal/crystal transitions at around room temperature. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 3369–3377, 2006

Application of an interpenetrating network model to the solid deformation of a quenched isotactic polypropylene film

The molecular orientation and deformation mechanisms of a quenched isotactic polypropylene (iPP) film deformed at temperatures between 303 K and the melting point are studied. At draw temperature T E less than 400 K where the degree of crystallinity does not change markedly, a linear relationship between molecular orientations of the crystalline and the amorphous phases is revealed and the slope is estimated about 1.82. The interpenetrating network (IPN) model, that takes into account the plastic response of the crystalline (C) network formed by a small portion of crystallites adhered through intercrystalline links and the pseudo-affine deformation of the crystallite enhanced amorphous matrix (CEAM) network, is able to account for inhomogeneous deformation behavior on the mesoscale accompanied with the localized necking in this T E range. Meanwhile, the initial Young's modulus and the true yield stress exerted by the deformation of the rigid C network exhibit the Arrhenius type of dependence on T E. The apparent shear modulus of the CEAM network as a function of T E is discussed in relation to variations in numbers and average molecular weights of the crystalline and the amorphous sequences being manifested by small consecutive endothermic and exothermic peaks in the DSC curve. The IPN model becomes invalid for deformations above T E=400 K where morphological changes are induced due to melting of crystallites as proved from the DSC measurement.

H. Douglas Keith

For more than four decades, H. Douglas Keith was a leading figure in polymer physics. He died at his home in South Windsor, Connecticut, on 9 February 2003, following a yearlong battle with cancer. Keith was born in Belfast, Northern Ireland, on 10 March 1927. He received a BSc from Queen’s University Belfast in 1948 and a PhD in physics from the University of Bristol in England in 1951.For the next five years, he taught as a lecturer at Bristol, where he specialized in optics. During that time, Keith was influenced by and collaborated with Peter Paul Ewald, Nevill Mott, and Charles Frank. He emigrated to the US in 1956 after accepting a position at the American Viscose Corp in Marcus Hook, Pennsylvania. There, Keith became interested in the complex structures and morphologies exhibited by macromolecules, a class of condensed matter that was emerging as an important category of materials. Along with Frank J. Padden Jr, he began evaluating the optical properties of spherulites, entities that form during solidification of most crystalline polymers from the melt.Keith, along with Padden, joined Bell Telephone Laboratories in Murray Hill, New Jersey, in 1960 and soon thereafter published a highly influential paper on spherulitic crystallization, subsequently known as the Keith and Padden theory. Over the next three decades, Keith interacted with a host of individuals to explain many of the mysteries surrounding the solidification of long-chain molecules.In the early 1960s, he and Padden provided one of the first morphological descriptions of melt-crystallized isotactic polypropylene, a polymeric material that today is superseded only by polyethylene in commercial importance. Their systematic experimental methods and insightful analyses were applied to many systems, including polyesters, various poly-peptides, and other crystallizable polymers. In 1965, Keith and his colleagues discovered intercrystalline links in polymers, which helped explain their mechanical strength. Four years later, he led a group that produced the first chain-folded single crystals of DNA. That work established an important bridge between synthetic and naturally occurring macromolecules. Keith was instrumental in expanding polymer science and engineering at Bell Laboratories during the 1970s. He headed the analytical chemistry research department and later the organic materials research department, from which a generation of young scientists and engineers began their research careers blending chemistry, physics, and engineering. A superb mentor, Keith combined a sophisticated understanding of physics with a deep appreciation for collaborative and interdisciplinary research. His encouragement and helpfulness to young scientists is legendary, particularly his unparalleled willingness to evaluate and debate new ideas and review manuscripts.On retiring from what was then called AT&T Bell Laboratories in 1988, Keith moved to the University of Connecticut in Storrs, where he taught and continued his research with polymers until he became professor emeritus in 1996. He remained active in research and his last publication appeared just a couple of weeks before his death. His impact on the field of polymer science and engineering continues to be felt today.Keith was a leader in the American Physical Society. He chaired the polymer physics division (1965–66) and was a divisional councillor (1977–85). He also headed the committee on applications of physics before it became the forum on industrial and applied physics. In 1973, Keith, with Padden, received APS’s Polymer Physics Prize. He was also a fellow of the American Association for the Advancement of Science.Outside of his profession, Keith maintained many interests. He was an accomplished choral singer and a passionate golfer, and was broadly knowledgeable in history, biography, literature, and music.Those who knew Keith were impressed by his wisdom, common sense, erudition, and humor. He enriched the lives of many and served as a role model and mentor to a number of younger scientists worldwide who have gone on to make a name for themselves in polymer physics. He was universally recognized as a scholar and gentleman, and those who knew him remember him with great fondness.H. Douglas KeithPPT|High resolution© 2004 American Institute of Physics.

Molecular Orientations and True Stress−Strain Relationship in Isotactic Polypropylene Film

The microscopic infrared dichroism measurement is made on a quenched iPP thin film during the stepwise elongation to obtain the molecular orientation functions, fam and fc, in the amorphous and the crystalline phases, respectively. Results reveal that the pseudo-affine deformation of the amorphous phase occurs for fam < 0.45 with fc = 1.85fam, and concurrent structure alternation of a small portion of crystallites is evidenced from a limited change in the degree of crystallinity Vc. The true stress−strain relationship on the mesoscale is discussed on the basis of an interpenetrating network model, in which thin threadlike strands composed of crystallites firmly connected through intercrystalline links (C network) penetrate through an elastic network composed of amorphous chains interconnected to each other with lamellae at cross-linking sites (CEAM network). Combining the Matsuoka viscoelastic constitutive equation and the Takayanagi model for the C network below and above the yielding point, respectively, and the affine deformation equation for the CEAM network, we are allowed to give a straightforward description of the local deformation upon necking.

Application of Lamellar Clustering Theory to Isotactic Polypropylene and Direct Observation of Lamellar Cluster Morphology by Electron Microscopy

In this work the lamellar cluster model was found to be applicable to the explanation of the mechanical yield behavior in polypropylene materials. According to the lamellar clustering theory, a spherulite is composed of radiating arms, each arm is composed of lamellar clusters, and each lamellar cluster is an aggregate of structural units of the cluster, including several crystalline lamellae and amorphous layers. The intercluster links capable of supporting external force play a role in the destruction of lamellar clusters at the yield point. These morphological features were directly confirmed from TEM observation on two-dimensional polypropylene spherulites that were crystallized from mixtures of isotactic polypropylene and atactic polypropylene, with the latter being removed later by a solvent. In addition, the structural parameters, such as the distance between intercrystalline links and the lamellar cluster thickness, which were determined by applying the mechanical yielding data to the lamellar cluster theory, were confirmed to be in agreement with the quantitative estimations from the TEM images of the polypropylene spherulites.

Novel Proposal of Lamellar Clustering Process for Elucidation of Tensile Yield Behavior of Linear Polyethylenes

We propose a new solidification process in crystallizable polymers in which lamellar clustering takes place in the crystallization process under high supercoolings. Clustering of lamellae is a two-step process: the first step is the exclusion process of chain ends from the space of a single Gaussian chain accompanied by the cooperative alignment of stiffened segments. This leads to anisotropic cylindrical units including several intertwined chains and is followed by the two-dimensional development of the partially solidified units into the final lamellar cluster. Using a series of polyethylenes with different molecular weights we show that the use of the lamellar cluster model makes it possible to provide a consistent understanding of both the solidification process and tensile yielding behavior in semicrystalline solids. The present model well explains the intercrystalline links found by Keith et al. (J. Polym. Sci. A2 1966, 4, 267–282) and the results which show that the calculation of the strength of the links agree with that of ultra-high-modulus fibers.

Origin of intercrystalline links

Journal of Polymer Science: Polymer Physics EditionVolume 18, Issue 11 p. 2307-2309 Note Origin of intercrystalline links H. D. Keith, H. D. Keith Bell Laboratories, Murray Hill, New Jersey 07974Search for more papers by this authorF. J. Padden Jr., F. J. Padden Jr. Bell Laboratories, Murray Hill, New Jersey 07974Search for more papers by this authorR. G. Vadimsky, R. G. Vadimsky Bell Laboratories, Murray Hill, New Jersey 07974Search for more papers by this author H. D. Keith, H. D. Keith Bell Laboratories, Murray Hill, New Jersey 07974Search for more papers by this authorF. J. Padden Jr., F. J. Padden Jr. Bell Laboratories, Murray Hill, New Jersey 07974Search for more papers by this authorR. G. Vadimsky, R. G. Vadimsky Bell Laboratories, Murray Hill, New Jersey 07974Search for more papers by this author First published: November 1980 https://doi.org/10.1002/pol.1980.180181117Citations: 16AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Citing Literature Volume18, Issue11November 1980Pages 2307-2309 RelatedInformation

Tensile properties and morphology of blends of polyethylene and polypropylene

AbstractThe tensile behavior of blends of linear polyethylene (PE) and isotactic polypropylene (PP) was examined in relation to their morphology. Yield stress increases monotonically with increasing PP content, while true ultimate strength is much lower in all blends than in the pure polymers as a result of early fracture. The blends fail at low elongation because of their two‐phase structure, consisting of interpenetrating networks or of islands of PE in a PP matrix, as shown by scanning electron microscopy of fracture surfaces and transmission electron microscopy of thin films. While spherulites in PP are very large (∼100 μm in diameter), addition of 10% or more of PE drastically reduces their average size. This, together with the profusion of intercrystalline links introduced by PE, may be associated with maximization of tensile modulus in blends containing ∼80% PP. Introduction of special nucleating agents to PP reduces average spherulite size and is accompanied by slight improvements in modulus. Thin films of blends strained in the electron microscope neck and fibrillate in their PE regions, but fracture cleanly with little fibrillation in areas of PP.

The role of intercrystalline links in the environmental stress cracking of high density polyethylene

AbstractResults of dynamic mechanical spectroscopy, infrared spectroscopy, and tensile stress‐strain data show that the non‐ionic surfactant Igepal CO‐630, often used as a stress cracking agent, and water are absorbed by high density polyethylene to cause an internal stress relaxation of the intercrystalline tie molecules. The resulting molecular rearrangements produce changes in both the crystalline and amorphous regions. Thus, a molecular mechanism is proposed for the long‐term aging process based on the results of accelerated aging in the presence of an environmental stress cracking agent.

The influence of structure and processing conditions on engineering mechanical properties in bulk crystallized isotactic polypropylene

AbstractA study of the influence of processing conditions and structure on engineering mechanical properties was conducted in bulk isotactic polypropylene. The influence of one processing parameter, undercooling, defined so as to account for both pressure and temperature effects, was particularly studied.Improved mechanical properties were found with increased undercooling. At low undercoolings, brittle failure without yield occurred, presumably the result of a sparsity of intercrystalline links under these conditions. As undercooling was increased, failure occurred after yielding as failure stress elevated dramatically, apparently because of greater link density. A modest improvement in yield stress with increased undercooling was attributed to the increasingly crosshatched lamellar structure produced at higher undercoolings, a structural trend confirmed by electron microscopy.Spherulite size, varied by altering melt history (melt temperature and time at melt temperature) at constant undercooling, was found to have no effect on engineering yield stress. This result indicates that apparent yield stress–spherulite size effects found by several earlier investigators were probably caused by structural variations other than spherulite size.