Crystallization Of Polybutene-1 Research Articles

Accelerated crystallization and crystal-crystal transition of PB induced by PP with optimized content

Isotactic polybutene-1 (PB)/isotactic polypropylene (PP) blends, typical crystalline/crystalline polymer blends with low-melting-temperature (Tm) PB and high-Tm PP, exhibit complicated interactions between their components in both molten and solid states. However, the intrinsic influences of PP component on crystallization of PB form II, form II-I transformation, and the dependence of these phase transitions on PP content are unclear. In this work, the influences of PP content ranged from 5 wt% to 40 wt% on PB crystallization were investigated. It was found that the content of PP played significant roles on the phase morphologies of the blends in molten state and then the subsequent crystallization of PB whatever in form II or form I. The PP components with ≤20 wt% addition acting as heterogeneous nucleation sites promoted crystallization nucleation, increased the crystallinity and lamellar thickness of PB, accelerated PB form II-I transformation and increased transformation degree with the increase in PP content. Whereas, the PP components with ≥30 wt% incorporation reduced the crystallinity and lamellar thickness of PB, retarded PB form II-I transformation and transformation degree with the increase in PP content. Interestingly, the PB/PP (80/20) blend presented the fastest II-I transformation rate as well as the highest transformation degree of PB. The dependence of crystallization and crystal structures of PB form II, form I, and form II-I transformation kinetics on PP concentration was discussed. PB form I′ was not observed in the present study. This work provides a theoretical and practical guide for the preparation of novel PB materials with desired structures and excellent performance, especially with anxiously accelerated crystal-crystal transition and transition degree of PB.

Equilibrium Melting Temperature of the Hexagonal Crystals of Polybutene-1 and Its Copolymer

TheLamellar structures of form I in polymorphic isotactic polybutene-1 (iPB-1) and forms I and I′ in butene-1/ethylene random copolymer (iPB-1/C2) were investigated by studying their melting behavior using the combination of small-angle X-ray scattering (SAXS) and fast scanning chip calorimetry (FSC) techniques. Hexagonal form I was transformed from tetragonal form II obtained by crystallization of a homogeneous melt of iPB-1 and iPB-1/C2. Hexagonal form I′ was crystallized directly from a heterogeneous melt of iPB-1/C2. Despite the same hexagonal crystallographic structure, forms I and I′ have obviously distinct melting behaviors due to different ways of crystal formation. Well-defined linear dependences of the melting temperature against the reciprocal lamellar thickness were observed for forms I and I′ with frozen chain mobility in crystals. The slopes of the thus obtained melting lines for forms I and I′ are different. Their extrapolations to imaginary infinitely large lamellar thickness provide the equilibrium melting temperature Tm∞ for forms I and I′, which is associated with the stability of the lamellar crystals. In spite of crystal defects in form I′, a higher Tm∞ is observed for this form in iPB-1/C2 than Tm∞ for form I in both iPB-1 and iPB-1/C2. The difference in Tm∞ indicates a less perfect structure of form I crystal lamellae that is caused by the fragmentation of form II crystal lamellae during the polymorphic phase transition from form II to I. The lamellae broke into crystal blocks along the lamellar direction. The smaller lateral sizes of the fragmented lamellae clearly induce a decrease in the stability of crystals, as expressed in a lower Tm∞ for form I.

Mpemba effect in crystallization of polybutene-1.

The Mpemba effect and its inverse can be understood as a result of nonequilibrium thermodynamics. In polymers, changes of state are generally non-equilibrium processes. However, the Mpemba effect has been rarely reported in the crystallization of polymers. In the melt, polybutene-1 (PB-1) has the lowest critical cooling rate in polyolefins and tends to maintain its original structure and properties with thermal history. A nascent PB-1 sample was prepared by using metallocene catalysis at low temperature, and the crystallization behavior and crystalline structure of the PB-1 were characterized by DSC and WAXS. Experimentally, a clear Mpemba effect is observed not only in the crystallization of the nascent PB-1 melt in form II but also in form I obtained from the nascent PB-1 at low melting temperature. It is proposed that this is due to the differences in the chain conformational entropy in the lattice which influence conformational relaxation times. The entropy and the relaxation time can be predicted using the Adam-Gibbs equations, whereas non-equilibrium thermodynamics is required to describe the crystallization with the Mpemba effect.

Crystallization of Polybutene-1 into Forms I′, II, and III Under High Pressure CO2: In situ Synchrotron X-Ray Diffraction, WAXD Mapping, and DSC Investigations

Crystallization of Polybutene-1 into Forms I′, II, and III Under High Pressure CO₂: In situ Synchrotron X-Ray Diffraction, WAXD Mapping, and DSC Investigations

Melt pre-shear induced orientation crystallization of PB and PB/HMwPB blend

Shear flow is important to understand the relationship between processing and properties of polymer products. In this work, the influences of shearing and high-molecular-weight polybutene-1 (HMwPB) on the evolution of oriented crystal's morphologies of isotactic polybutene-1 (PB) were investigated by shearing at a temperature slightly above the nominal melting temperature under different shear rate and shear duration. The shear thickening presented in primary normal stress revealed the presence of a gel-like network of shish-precursors, in which a birefringence region was observed in polarized optical microscopy (POM) images after crystallization in both PB and PB/HMwPB blend. Those shish-precursors enhanced the crystallization temperature and directly influenced the crystal structures of PB form II, and these crystal structures could be preserved from the form Ⅱ to form Ⅰ. The rheological, one-dimensional scattering, and DSC data reach a plateau with the shear duration, indicating that all the PB chains achieve their ultimate oriented state. The addition of a small amount of HMwPB caused the earlier formation of shish-precursors, the higher crystallization temperature of PB form Ⅱ, thicker lamellae, higher melting temperature, and degree of orientation of PB form Ⅰ. • Shear conditions for different crystal structures formation were given. • Shish-precursors formation and oriented crystal evolution were investigated using rheology methods combining optical microscopy and scattering technology. • The effect of HMwPB on shish-precursors formation and oriented crystal evolution was investigated.

Mechanism of form I′ formation in polybutene-1/polypropylene blends

Isotactic polybutene-1 (PB) can crystallize into form I′ polymorph directly in its blends with isotactic polypropylene (iPP), but the mechanism remains controversial. In this work, by using Fourier-transform infrared spectroscopy (FTIR), wide-angle X-ray diffraction (WAXD) and differential scanning calorimetry (DSC), we investigated systematically cold crystallization of PB in its blends with iPP and with atactic polypropylene (aPP), one crystallizable and the other amorphous. It was found that form I′ was produced in both PB/iPP and PB/aPP blends, the higher the PP content, the greater the form I′ fraction, and iPP was found to be more effective in promoting form I'. However, in a PB/iPP blend containing 10 wt% iPP with the iPP fully crystallized at 120 °C, the PB crystallized into form II exclusively in the cold crystallization, at a faster rate than in neat PB. These experimental results indicate that in PB/iPP blends both confined nucleation mechanism and surface nucleation mechanism operate, but the former governs the PB polymorph formed. Under the confinement only the smaller form I′ nuclei are allowed, and the PP crystals then expedite the process via the surface nucleation mechanism.

Nucleation Mechanism for Form II to I Polymorphic Transformation in Polybutene-1

By means of in situ small-/wide-angle X-ray scattering (SAXS/WAXS) techniques, nucleation mechanism for Form I crystals of polybutene-1 (PB-1) has been investigated by heating the early-stage polym...

Fractionated and Confined Crystallization of Polybutene-1 in Immiscible Polypropylene/Polybutene-1 Blends

In this work, the crystallization of immiscible polypropylene (PP)/polybutene-1 (PB) blends, in particular the effect of crystal morphology of PP (HTC, high Tm component) on the subsequent crystallization behavior of PB (LTC, low Tm component) was studied. Herein, we firstly indicated that PP/PB blends were not completely compatible but characterized as the LCST-like phase diagram above the melting temperature of PP. Crystallization of PP at different crystallization temperatures brought about different PP crystal morphologies and PB was segregated and confined at different locations. Much larger-sized domain of PB component appeared in PP spherulites resulting from the effects of non-negligible phase separation and the slower PP crystallization rate as PP crystallized at high temperature. As temperature continued to fall below Tm of PB, the fractionated and confined crystallization of PB occurred in the framework of PP spherulites, reflected by the decreased crystallization temperature (Tc) of PB and the formation of form I′ beside form II. Notably, if PP previously crystallized at high Tc, fractionated crystallization of PB became predominant and confined crystallization of PB became weak due to the much wider droplet-size distribution of PB domains.

Interfacial nucleation in iPP/PB-1 blends promotes the formation of polybutene-1 trigonal crystals

The formation of trigonal Form I′ crystals of polybutene-1 (PB-1) directly from melt has drawn much attention in past decades. In this study, we investigate the fractionated crystallization behavior of PB-1 within droplets formed by blending PB-1 with an excess of isotactic polypropylene (iPP) employing DSC, SEM, in situ synchrotron WAXD and FT-IR. When PB-1 is dispersed into a large number of small size droplets, the heterogeneous nucleation of Form II crystals can be inhibited because the number of droplets is larger than that of active nucleation sites for Form II (i.e., active heterogeneities originally present in bulk PB-1). The nucleation of the finely dispersed PB-1 droplets does not occur homogenously, but at the interface with the iPP matrix, which induces the crystallization of the droplets into Form I′. The crystallization rate of Form I′ at different temperatures was determined by Fourier transform infrared spectroscopy. It was found that trigonal Form I′ crystallizes faster when the content of PB-1 in the blend is lower, and the specific interfacial surface area is larger. The opposite effect has been observed for the kinetics of the metastable Form II formation. It is therefore suggested that Form I′ crystallization is driven by the nucleation of PB-1 at the crystalline iPP surface, which competes with the crystallization of Form II induced by nucleating heterogeneities present in PB-1 droplets.

Control of Chain Orientation in Blends of Polypropylene and Polybutene‐1

An extruded sheet having unique molecular orientation is developed using a miscible blend of isotactic polypropylene (PP) and isotactic polybutene‐1 (PB). Blends containing a small amount of N,N′‐dicyclohexyl‐2,6‐naphthalenedicarboxamide are extruded from a ribbon‐shaped die onto a chill roll at various temperatures. It is found that form‐I crystals of PB become oriented in the flow direction, whereas β‐form crystals of PP become oriented perpendicular to the flow direction. The molecular orientation is the most obvious for the blend containing 60 wt% of PB extruded at a chill roll temperature of 80 °C. The anisotropy in the tensile modulus of the obtained extruded sheet is reduced by its extraordinary molecular orientation. image

Morphology of Form I′ crystals of polybutene-1 formed on melt-crystallization

It is known that presence of both constitutional chain defects and stereodefects in butene-1 macromolecules may lead to the formation of the trigonal Form-I′ crystal polymorph on cooling the melt. In this study, Form I′ crystals were prepared by slow cooling of the melt of a specific random copolymer of butene-1 containing about 18 mol% propylene, and analyzed for the first time regarding their morphology by atomic force microscopy. It has been found that Form I′ crystals which develop on slow cooling of the isotropic melt exhibit a lamellar crystal shape, with a thickness and lateral width of less than 10 and 500 nm, respectively. In addition, there was proven that at the particular crystallization conditions the lamellae form stacks. Though crystallization seems non-spherulitic, the irregularly oriented stacks of lamellae are then also detected by polarizing optical microscopy.

Additive effects of tripalmitin and low-density polyethylene on morphologies and tensile properties of polybutene-1/micro fibrous cellulose composite

Effects of tripalmitin (TP) and low-density polyethylene (LDPE) loading on morphologies and tensile properties of polybutene-1 (PB)/micro fibrous cellulose (MFC)/composite were studied. The scanning electron microscope (SEM) observation showed that the 10 % TP loading brought about good dispersity of the MFC in PB matrix. The TP worked as a good compatibilizer for the composite. The Young’s moduli of the PB/TP (10 %)/MFC (10 and 20 %) content were slightly lower than those of the corresponding PB/MFC under 0, 48 and 96 h aging treatments at r. t., and that of the PB/TP (10 %)/MFC (50 %) specifically decreased up to 73 %. The TP loading increased the PB crystal phase transformation rate, and its behavior suggested that there existed TP in the interface between the PB and MFC. The elongation at break values increased up to 281 % of the corresponding PB/MFC ones. The 30 % TP loading little improved the tensile properties of the composite as compared with the 10 % one. The 10 % LDPE loading brought about 5–51 % higher Young’s moduli than those of the corresponding PB/MFC without the aging treatment although the composite rapidly became embrittlement by the higher MFC content and aging. It was found that the LDPE loading highly improved the interface strength, in particular, without the aging treatment.

Additive effects of tripalmitin on morphologies and tensile properties of polybutene-1 and its composite with micro fibrous cellulose

Morphologies and tensile properties of polybutene-1 (PB)/tripalmitin (TP) blend and PB/micro fibrous cellulose (MFC)/TP composite were studied. The scanning electron microscope observation showed that the PB(70 %)/TP(30 %) had a microphase-separated structure. The DSC measurement showed that the crystallization of the PB part was affected by the TP existence. A new crystal structure was observed in the X-ray diffraction pattern of the PB(70 %)/TP(30 %). Quicker saturation of the PB crystal phase transformation from the metastable tetragonal (II) to the stable hexagonal (I) phase was observed in the PB(70 %)/TP(30 %) under the aging at r.t. The saturation controlled the Young’s modulus increment of the PB(70 %)/TP(30 %) in the aging process. The elongation at break value of the PB/TP increased by the loading of the TP, suggesting that the TP worked as the plasticizer. The thermogravimetry measurement of the PB(70 %)/TP(30 %) suggested that there existed an interaction between them. The TP addition provided a good dispersibility and ductility enhancement for PB/MFC composite. It was found that the TP worked as a good compatibilizer for the composite.

Effects of crystal phase transformation on tensile properties of polybutene‐1/cellulose composites

AbstractMorphologies and tensile properties of polybutene‐1 (PB), PB/fibrous cellulose (FC), and the PB/silanized FC with 3‐aminopropyltrimethoxysilane (APTMS) composites were studied. The scanning electron microscope micrographs exhibited the adherent PB parts on the FC and the silanized FC, suggesting that there was a certain affinity of PB to them. The spherulite observation suggested that there existed a secondary bonding between the PB and the FC or the silanized FC. These tensile properties were remarkably affected by the PB crystal phase transformation from the metastable tetragonal (II) to the stable hexagonal (I) phase. The transformation caused the ageing embrittlement even at r.t. In particular, the ageing embrittlement rate of the PB/silanized FC was much higher than other samples. Because the silanized FC became the excellent nucleating agent for the PB crystallization, the PB/silanized FC was found to easily form the thicker lamella having a higher probability of containing a crystal defect to serve as a starting point of the transformation. The higher transformation rate depended on the thicker lamella formation rate and its amount. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

ポリブテン‐１の結晶化過程のレオロジー挙動に与えるひずみの効果

Effects of strains on rheological properties in the course of isothermal crystallization of polybutene-1 have been investigated. Dynamic viscoelasticity measurements made as a preliminary experiment showed that an induction period emerged on the plots of dynamic storage and loss moduli against time. The induction period was affected by the strain amplitude (γ) in the region of γ>0.03, but was independent of γ at γ≤0.03. The induction time for the dynamic measurement was independent from the frequency, but that for the steady shear measurement depended on the shear rate: the larger the shear rate, the shorter the induction time. This induction period was not governed by the total strain.

Direct Observation of Crystallization of Polybutene-1 Under Low Shear Rate Flow

The isothermal crystallization process of polybutene-1 melt under shear flow was investigated with an optical microscope and a device (shear flow direct observation system, SF-DOS) newly developed by our group. The nucleation rate and growth rate of polybutene-1 were studied under slow shear rates (0–0.1 s−1) at high crystallization temperature (102–108°C) with the SF-DOS. The nucleation remains heterogeneous. The number of nuclei after long times increased and induction time decreased by increasing the shear rate. Anisotropic and distorted spherulites were observed under shear flow, while the spherulites in the static condition were isotropic. It was clearly observed that the spherulites were rotating under shear. The average growth rates were enhanced by increasing shear rates, which acts as the main factor affecting the overall crystallization kinetics. Finally, the crystallization kinetics were analyzed on the basis of the secondary nucleation theory of Hoffman and Lauritzen. Even under very low shear rates, the product of lateral‐surface free energy σ s and fold-surface free energy σ e was found to be reduced as shear rate increased.

Direct observation of polymer crystallization process under shear by a shear flow observation system

Isothermal crystallization of polybutene-1 melt under shear flow was observed with an optical microscope by using a device newly developed by our group. Firstly, our coaxial cylinder-type apparatus (shear flow direct observation system (SF-DOS)) to observe crystallization directly under shear flow is explained in detail. Secondly to examine the accuracy of the measurement with the new device and to establish an appropriate procedure for the elimination of overshoot in temperature profiles, various examinations were performed in terms of temperature distribution, stability, and the velocity gradient by comparing the results from isothermal DSC measurements. The precise investigation suggested that the temperature distribution was proved to be very small (within 0.5°C) and the establishment of the procedure eliminated the overshooting of temperature profiles. Finally, we observed isothermal crystallization of polybutene-1 with the new device at various temperatures between 102°C and 140°C under shear rates of up to 0.7 s –1. When the shear strain became higher and the temperature became lower, narrow bands of oriented region formed after a certain time along the flow direction even at high temperature. This tendency was also observed in a polystyrene melt; therefore, it was interpreted that the narrow bands were considered to be the highly deformed region, which was generated by high shear stress. In the narrow bands, spherulites nucleated. After a certain amount of time, spherulites were also generated randomly outside of the narrow bands. Under very low shear rate, where the narrow bands did not exist, the spherulites appeared randomly.

High-Resolution Transmission Electron Microscopy of Crystal Transformation in Solution-Grown Lamellae of Isotactic Polybutene-1

The crystal transformation in lamellar crystals of polybutene-1 grown from an amyl acetate solution was studied by cryogenic high-resolution transmission electron microscopy. The shape of the transformed trigonal (form-1) crystal domains in the surrounding tetragonal (form-2) crystal was successfully revealed. Along with the nucleation of the “untwinned” form-1, the existence of another nucleation mechanism which creates the “twinned” form-1 was suspected. Each crystallite of form-1 was comparatively large, and accordingly, the growth of the form-1 crystal was thought to progress not stem by stem but by pulling in the molecular chains from the surrounding form-2, creating new stems of form-1. Once form-1 has nucleated, mutual orientation between the form-1 and the form-2 domains appeared to be insignificant for further growth. The shape of the form-1 domain was irregular, and no specific crystallographic direction along which the form-1 domain tends to grow was found.

Crystallization behaviour of polyethylene and i-polybutene-1 blends

The mutual influence of the components on the crystallization behaviour of polyblends, namely, isotactic polybutene-1 (PB) with low-density and high-density polyethylene (LDPE and HDPE), has been studied using techniques such as differential scanning calorimetry, infra-red spectroscopy, wide-angle X-ray diffraction, scanning electron microscopy, etc. Each component in the blend is observed to crystallize independently. There is phase separation and incompatibility, as shown from tensile properties and scanning electron microscopic observation of the fracture surface of the blend. For HDPE-PE blends (<30% HDPE), unusual form I′ crystals of PB are observed along with the usual form II.

The effect of certain processing variables on the form ii to form i phase transformation in polybutene‐1

AbstractDensity and wide angle x‐ray scattering techniques were used to study the form II to form I phase transformation in polybutene‐1. The influence of deformation by cold rolling, orientation produced by melt processing (film blowing), and certain additives blended with the homopolymer on the phase transformation behavior were examined. A new technique based on a combination of wide angle X‐ray diffraction and density measurements was devised to determine the relative fractions of form I, form II, and amorphous phases present. Small reductions in thickness by cold rolling cause a rapid partial transformation to form I followed by further transformation at enhanced rates. The enhancement of crystal transformation by cold rolling is primarily the result of the stresses or strains applied rather than the orientation produced. The introduction of molecular orientation by melt processing also enhances the rate of the form II to form I phase transformation, but it is rather less effective than small amounts of cold rolling which themselves produce comparatively little change in molecular orientation. The mechanical blending of polypropylene with polybutene‐1 was found to accelerate the form II to form I phase transformation, while another additive (1‐naphtylacetamide) known to be a good nucleating agent for crystallization of polybutene‐1 did not increase the rate of phase transformation when added at concentration levels needed to nucleate crystallization from the melt.