Radial Growth Rate Of Spherulites Research Articles

Synthesis of biodegradable polyhydroxyalcanoate copolymer from a renewable source by alternate feeding

AbstractPolyhydroxyalcanoates copolymers with 3‐hydroxybutirate (3HB) and 3‐hydroxyvalerate (3HV) co‐monomers, P3(HB‐co‐x%HV), were produced in fed‐batch culture by Ralstonia eutropha DSM428 using fructose as a single carbon source in the first step and adding propionic acid in the second step by alternating feeding. Polymer yield was 0.18 g/L with a content of 24 mol% of the 3HV fraction determined by 1H NMR. NMR measurements indicated that the polymer obtained is isotactic. The copolymer attained 35% of crystallinity according to X‐ray diffraction measurements, and two (020) planes were observed. Thermal behavior presented melting temperature at 154°C and the crystallization temperature was 65°C. A glass transition temperature was observed at −10°C. Average molecular weight measured by GPC was 4.9 × 105 Dalton. Isothermal radial growth rates of spherulites of P3(HB‐co‐24%HV) were studied. All experimental facts and the analysis of the sequence distribution of diads and triads of 3HB and 3HV units led to the conclusion that it is not a completely statistical random copolymer once it contains different types of segments. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers.

Crystallization kinetics of linear polyethylene: The maximum in crystal growth rate–temperature dependence

This rapid communication reports a summary of the key findings of crystallization kinetics studies of unfractionated high density (linear) polyethylene at extremely large supercoolings. We report, for the first time, the maximum in crystal growth rate–crystallization temperature data for linear polyethylene, which has been sought by many researchers since the 1950s. The maximum growth rate was found to occur in the range of 70–75 °C with two separate methods. The kinetics studies were performed using a newly developed quench-crystallization technique based on depolarized reflection light microscopy that is capable of achieving enormously higher quench rates than existing methods. Typical onset crystallization temperatures accessed with this technique range from 40 to 90 °C. Bulk growth rates of crystals were obtained as the reciprocal of crystallization half times measured from the change in the depolarized light intensity upon direct crystallization from the melt. Separately, radial growth rates of spherulites were measured over a wide range of supercoolings. Secondary nucleation analysis of the crystal growth rates resulted in single linear fits extending into deep regime III, suggesting no change in mechanism of formation of the crystals at the largest supercoolings. The deeply quenched films, crystallized at temperatures below the maximum, contain non-impinged spherulites, capable of further crystallization.

Role of multi-wall carbon nanotube network in composites to crystallization of isotactic polypropylene matrix

The composites (iPP/CNTs) made of isotactic polypropylene (iPP) and multi-wall carbon nanotubes (CNTs) were prepared by solution blending. To improve compatibility between CNTs and iPP and to enhance dispersion of CNTs in iPP matrix, CNTs were chemically modified by grafting alkyl chains. The chemically modified CNTs had about 6wt% grafted alkyl chains. Rheological measurements indicated that CNTs caused gelation in iPP/CNTs due to CNT network formation and the critical gelation CNT concentration was about 7.4wt%, which was considered to be high due to the low CNT aspect ratio in this study. Crystallization behaviors of iPP/CNTs were studied by using optical microscopy (OM) and differential scanning calorimetry (DSC). Radial growth rates of spherulites during isothermal crystallization of iPP/CNTs with CNT concentrations less than 2.0wt% measured by using OM showed decreasing trends with increasing CNT concentration. Avrami analysis of the exothermic heat flow curves during isothermal crystallization of iPP/CNTs measured by DSC indicated that crystallization rates were accelerated when CNT concentrations were lower than the critical gelation concentration, because CNTs mainly functioned as nucleating agents for crystallization, while crystallization rates did not change obviously when CNT concentrations were higher than the critical gelation concentration, because CNT network could form and mainly functioned to provide restriction to mobility and diffusion of iPP chains to crystal growth fronts.

Crystallisation of polypropylene containing nucleators

The crystallisation of polypropylene in the presence of sodium benzoate, graphite powders, Millad 3988 (1,3:2,4- bis(3,4-dimethyl-benzylidene sorbitol)) and NA-11 (sodium 2,2′-methylene bis-(4,6-di- tert-butylphenyl)phosphate) was studied. As a parameter for the effectiveness of nucleators, a free-energy parameter for the nucleation was estimated, on the basis of a theory, from the nucleation temperature during cooling at various rates. The density of actual nuclei was estimated from the radial growth rate of spherulites and the bulk growth rate, the latter obtained by the analysis of crystallisation isotherms. The dispersibility of nucleator particles calculated with reference to the mean volume of particles was various, the cluster size being ranged between unity to several hundred. The Young's modulus of films prepared from the polymer–nucleator mixtures has been found to correlate with the nucleus density without respect to the kind of nucleator.

Morphology and spherulitic growth kinetics in poly(ethylene oxide)/poly(n‐butyl methacrylate) blends

AbstractResults of a study concerning the morphology and the spherulite growth rates of poly(ethylene oxide) (PEO) in binary blends with poly(n‐butyl methacrylate) (PnBMA) are reported. Microscopic observations show that blending causes the spherulite structure to become coarser and less birefringent and confirms that the spherulitic growth rates of PEO were reduced by the addition of PnBMA. X‐ray diffraction studies show no change in the unit cell dimensions and a decrease in the degree of crystallinity upon blending. Analysis of the spherulite radial growth rate data by using Lauritzen–Hoffman theory indicates that crystallization in the range of 300 to 330 K occurs solely within regime III. The calculated surface free energy of folding, σe, for pure PEO is 57 erg cm−2 and decreases with increasing the content of PnBMA in the blend. Copyright © 2004 Society of Chemical Industry

Radial growth rate of spherulites in polypropylene/barium sulfate composites

The effect of barium sulfate (BaSO 4) on the spherulite radial growth rates of isotactic polypropylene (PP) was studied by means of optical microscopy. The PP–BaSO 4 interface was modified by treating the fillers with different couple agents. The addition of BaSO 4 depresses the spherulite growth rate, and the effect is more dramatic when the interfacial interaction between the PP and BaSO 4 was enhanced. The data were analyzed with the Lauritzen–Hoffmann secondary nucleation theory, and the results demonstrated that the enhanced PP–BaSO 4 interaction promotes the particles to serve as physical crosslinking points, which hinder the movement of the polymer chains and results in a decrease of the pre-exponential factor, G 0.

Thermal properties and phase structure of PP + oligopinene blends

Blends of polypropylene (PP) and β-oligo-pinene, a synthetic low molar mass resin, were prepared by melt mixing in a Haake Rheocord at 473 K, 30 rpm during 600 s. The influence of the terpenic resin on the thermal properties, phase structure and crystallization of PP was evaluated. The DSC results indicated the presence of phase separation. The SEM analysis shows that the oligopinene was extracted along the whole surface and it was observed entities as cut cylinder atributted to low molar mass PP. The isothermal crystallization of blends was conducted at 396, 398 and 403 K. The mixtures did not show phase separation in molten, during crystallization and after solidification. The spherulite radial growth rate of PP decreased and was dependent on the temperature and composition. The results indicated that the system is an immiscible blend with at least three phases: a fine dispersion of the oligopinene in the amorphous PP, some boundary solubility of PP in oligopinene and a crystalline PP.

High temperature internal friction of engineering ceramics

Poly(l-lactide) (PLLA) polymers having terminal n-alkyl groups with a wide variety of lengths (C0–C22) were synthesized by ring-opening polymerization of l-lactide in the presence of coinitiators of l-lactic acid (C0), 1-hexanol (C6), 1-dodecanol (C12), and 1-docosanol (C22) and their segmental mobility and non-isothermal and isothermal crystallization behavior were investigated by differential scanning calorimetry (DSC) and wide-angle X-ray diffractometry (WAXD). Glass transition and cold crystallization temperatures of melt-quenched samples during heating decreased with an increase in the length of terminal n-alkyl groups. The enhanced PLLA segmental mobility and hydrophobic interaction-based accelerated PLLA nucleation by the presence of terminal long n-alkyl groups should have caused the accelerated non-isothermal and isothermal crystallization of PLLA segments traced by cold crystallization temperature during heating and by radial growth rate of spherulites, respectively. The crystallization accelerating effect became higher with the length of terminal n-alkyl groups. The effects of the length of terminal n-alkyl group on the crystalline growth mechanism of PLLA at the lowest crystallizable temperature was insignificant, whereas the effects of the length of terminal n-alkyl group on the nucleation mechanism of PLLA chains were significant and insignificant for PLLA having Mn of 6–7 × 103 of 2 × 104 g mol−1, respectively. WAXD measurements revealed that the transition crystallization temperature at which crystalline modification changes from δ-form to α-form was affected by the length of terminal n-alkyl group for PLLA having Mn of 6–7 × 103 g mol−1, but was not altered by the length of terminal n-alkyl group for PLLA having Mn of 2 × 104 g mol−1.

PP/ROSIN Blends: Isothermal Crystallization

The isothermal crystallization of polypropylene (PP) melt blended with a glycerpl ester of hydrogenated rosin (ester gum) (PP/ROSIN) were prepared under select conditions using up to 50% of rosin revealed phase separation. The presence of rosin changed the radial growth rate and size of PP spherulites. The rosin-separated domains were noticed in the intraspherulitic and interspherulitic regions and increased in size when the oligomer enriched the blends. Up to 30% of rosin, samples isothermally crystallized at 125°C showed a decrease of spherulite radial growth rate and above that amount an increase was observed.

Miscibility, crystallization kinetics, and morphology of poly(β‐hydroxybutyrate) and poly(methyl acrylate) blends

The miscibility, spherulite growth kinetics, and morphology of binary blends of poly(β-hydroxybutyrate) (PHB) and poly(methyl acrylate) (PMA) were studied with differential scanning calorimetry, optical microscopy, and small-angle X-ray scattering (SAXS). As the PMA content increases in the blends, the glass-transition temperature and cold-crystallization temperature increase, but the melting point decreases. The interaction parameter between PHB and PMA, obtained from an analysis of the equilibrium-melting-point depression, is −0.074. The presence of an amorphous PMA component results in a reduction in the rate of spherulite growth of PHB. The radial growth rates of spherulites were analyzed with the Lauritzen–Hoffman model. The spherulites of PHB were volume-filled, indicating the inclusion of PMA within the spherulites. The long period obtained from SAXS increases with increased PMA content, implying that the amorphous PMA is entrapped in the interlamellar region of PHB during the crystallization process of PHB. All the results presented show that PHB and PMA are miscible in the melt. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 1860–1867, 2000

Polymer blends of poly( ϵ-caprolactone) and poly(vinyl methyl ether) – thermal properties and morphology

We report on thermal properties and the phase behaviour of polymer blends comprising poly( ϵ-caprolactone) (PCL) and poly(vinyl methyl ether) (PVME). The blends were subjected to different thermal histories. In all cases, the fraction of PCL, that crystallizes in the blends, increases slightly up to 30% content of PVME. Crystallization rates of PCL are found markedly reduced in blends as compared to neat PCL. Ring-banded spherulites develop during isothermal crystallization. Radial growth rates of spherulites decrease exponentially with increasing PVME content up to approximately 40% of PVME. At higher PVME contents non-exponential decrease was observed. Melting points of PCL in blends were determined applying a step-wise annealing procedure. The glass transition temperatures of the blends reveal formation of PVME-rich phases even after rapid quenching of the homogeneous melt owing to crystallization of PCL. Lower critical solution temperature behaviour of the melts could be determined tentatively by optical inspection. The homogeneous melt phase-separates above approximately 190°C.

Poly(3-D(-)hydroxybutyrate)/atactic poly(methylmethacrylate) blends: Morphology, miscibility and crystallization relationships

The morphology, the phase structure and the crystallization processes of poly(3-D(-)hydroxybutyrate)/atactic poly(methylmethacrylate) blends, (PHB/aPMMA), have been investigated as a function of blend composition and thermal treatments. The two-phase separation processes (liquid/liquid demixing and liquid/solid separation) are in competition between each other. In the melt at T≥185°C, the system was homogeneous. During crystallization from the melt, liquid/liquid phase separation occurred before crystallization. After crystallization, three phases were present: a crystalline PHB phase; and two amorphous phases, one formed by amorphous PHB and the other by aPMMA. From the homogeneous glass state, however, crystallization preserved the homogeneity. The system, after cold crystallization, was composed of two phases: a crystalline; and an amorphous homogeneous phase. The addition of aPMMA always caused a decrease of the spherulite radial growth and overall crystallization rates. These results are attributed to the increase of energy related to the transport of the macromolecules in the melt, and in the case of cold crystallized samples, also to the diluent effect of aPMMA on the growth of PHB crystals.

The crystallization of poly(ethylene oxide) in blends with neat and plasticized poly(vinyl chloride)

This study concerns the morphology and spherulite growth rates of poly(ethylene oxide) (PEO), a semicrystalline polymer, in binary blends with poly(vinyl chloride) (PVC), an amorphous polymer, and in ternary mixtures containing (i) the amorphous polymer and (ii) tricresyl phosphate (TCP), a plasticizer for PVC. It is shown that the determining factor in the slight melting temperature depression observed in PEO/PVC blends by differential scanning calorimetry is the influence of PVC on the crystalline structure of PEO. PVC does not influence the spherulite radial growth rates of PEO, measured using polarized light videomicroscopy, in the accessible temperature range; however, TCP causes a substantial depression in the growth rates. Both additives cause the spherulite structure to become coarser and less birefringent. Unusual radial extinction bands indicate that TCP is incorporated within amorphous fold surfaces of PEO lamellae. Studies using polarized infrared microspectroscopy demonstrate that PVC causes a disordering of the orientation of the crystalline stems of PEO, and induces a higher incidence of the trans planar zig-zag conformation of the PEO chains within spherulites grown in PEO/ PVC blends. Epitaxial interaction between PEO and PVC also leads to an increased incidence of the planar zig-zag conformation of the PVC. In contrast, TCP has a minimal effect on the orientation and conformation of PEO. In ternary mixtures containing PEO, PVC and TCP, the plasticization of PVC by TCP drastically reduces the effects of PVC on the microstructure of PEO.

Solubility of erucamide (13-cis docosenamide) in isotactic poly(propylene) and thermal behaviour of their blends

Differential scanning calorimetry studies, made on blends prepared by mixing in the melt, have demonstrated that crystallization of erucamide (13- cis-docosenamide) [H 3C-(-CH 2-) 7-HC=CH-(-CH 2-) 11-CO-NH 2]/ isotactic poly(propylene (i-PP) blends results in separate crystals of the two components, rather than cocrystallization. For low content erucamide blends (less than 29%), two melting peaks for erucamide have been observed. They have been assigned to: i) erucamide crystals situated in the external surfaces of the i-PP and located forming globules, droplets or inclusions whose melting point appears at the higher temperature (Erucamide I); ii) erucamide crystals forming crystalline microdomains of erucamide, located either within the amorphous region of spherulites and/or in the amorphous regions which surround the spherulites (Erucamide II). The enthalpy of these crystals located in these regions, i.e. in the amorphous region of the spherulites and/or their surroundings, has been estimated. A good linear correlation has been found between the solubility of erucamide crystals in the amorphous region of i-PP spherulites and/or the surrounding region of the spherulites and their apparent melting enthalpy. Spherulite radial growth rates, G, for the different blends are lower than for the pure i-PP. They show a characteristic dependence on the erucamide content in the blend. This behaviour is in agreement with theoretical predictions for crystallization in immiscible blends. An additional feature, as an unambiguous test of the incompatibility, is the poor interfacial adhesion, which has been made clear from the large voids left on the fracture surface where the erucamide globules have separated from the matrix and from the smooth surfaces of the exposed erucamide globules. A model is proposed for erucamide/i-PP blends, which is able to explain quantitatively in detail all the thermal and morphological experimental data.

Miscibility and Biodegradation Behavior of Melt-Processed Blends of Bacterial Poly(3-Hydroxybutyrate) with Poly(Epichlorohydrin)

The miscibility of melt processed blends of bacterial poly(3-hydroxybutyrate) (PHB) with poly(epichlorohydrin) (PEC) is investigated over the whole range of compositions by means of differential scanning calorimetry, dynamic-mechanical analysis, and hot-stage optical microscopy. PHB and PEC are miscible in the melt in all proportions. After melt quenching, PHB/PEC blends show a single glass transition that linearly changes with composition between the T gs of the pure components (PHB = 2°C, PEC = −21°C). At room temperature all PHB/PEC blends are partially crystalline, owing to crystallization of a constant fraction (58%) of the PHB present in each blend. A spacefilling spherulitic morphology develops upon blend crystallization from the melt. Isothermal crystallization measurements show that over the range of crystallization temperatures (40°C < T e < 130°C) and compositions (20% < PEC < 80%) explored, the spherulite radial growth rate (G) decreases with increasing PEC content. Biodegradation experiments, carried out in activated sludge and in enzymatic solution (PHB-depolymerase from Aureobacterium saperdae) on the blend containing 80% PHB, show both weight loss and surface erosion. The biodegradation results are discussed in terms of PHB chain-mobility.

Structure and properties of poly(3-hydroxybutyrate-co-4-hydroxybutyrate) produced by Alcaligenes latus

Random copolymers of 3-hydroxybutyrate (3HB) and 4-hydroxybutyrate (4HB) with a wide range of compositions varying from 0 to 83 mol% 4HB were produced by Alcaligenes latus from the mixed carbon substrates of 3-hydroxybutyric and 4-hydroxybutyric acids. The structure and physical properties of P(3HB-co-4HB) were characterized by1H and13C NMR spectroscopy, gel-permeation chromatography, and differential scanning calorimetry. The isothermal radial growth rates of spherulites of P(3HB-co-4HB) were much slower than the rate of P(3HB) homopolymer. The enzymatic degradation rates of P(3HB-co-4HB) films by a PHB depolymerase were strongly influenced by the copolymer composition.

Optically Active Polyethers. 1. Studies of the Crystallization in Blends of the Enantiomers and the Stereoblock Form of Poly(epichlorohydrin)

The isothermal crystallization kinetics and morphology of the melt-crystallized optically active polyenantiomers, their blends, and the stereoblock form of poly(epichlorohydrin) have been investigated using polarized light video microscopy. The optically active polyenantiomers develop regularly banded spherulites, while the equimolar blend and the stereoblock polymer form nonbanded, coarser spherulites. The apparent morphological differences among the polymers suggest a stereospecific segregation at the growth front in an attempt to produce optically pure lamellae. The equilibrium melting temperature as determined by the classical Hoffman-Weeks method was found to be 411 ± 1 K for all of the polymers. Over the range of crystallization temperatures from the T g (247 K) to T m °, the spherulite radial growth rates of the 50 :50 blend of the polyenantiomers are depressed relative to those of either of the optically pure components. A further marked reduction in growth rates is recorded for the stereoblock polymer. An analysis of the linear spherulite radial growth rates in terms of the Hoffman-Lauritzen treatment gave evidence of the development of larger folds, hence a rougher lamellar surface in the stereoblock polymer than in the polyenantiomers.

Effects of soft segments and hydrolysis on the crystallization behavior of degradable poly(oxyethylene)/poly(L‐lactide) block copolymers

AbstractThe crystallization behavior of poly(oxyethylene) (PEG)/poly(L‐lactide) (PLLA) block copolymers with PEG (number‐average molecular weights Mn = 1000–6000) contents ≦ 18,3 wt.‐% has been studied under different isothermal temperature and linear cooling conditions. A differential scanning calorimeter was used to monitor the energetics of the crystallization process from the melt state. The influence of copolymer composition and hydrolysis on radial growth rates of spherulites, G, in PEG/PLLA copolymer was investigated using polarized light video‐microscopy. The data were analyzed in terms of a model describing two processes, namely crystal nucleation and growth which were observed experimentally in a typical Avrami plot for the isothermal data. At a given crystallization temperature, G's are increased with increasing PEG content and with decreasing PEG segment length in PEG/PLLA copolymer spherulites. The Avrami exponent n and rate coefficient k of PEG/PLLA copolymers decrease with increasing hydrolysis time up to 200 h. The spherulite morphology appeared to be a complex function of copolymer composition, hydrolysis time and crystallization temperature.

Crystallization of polypropylene I. Isothermal kinetics

With the aid of differential scanning calorimetry (DSC), we first analyzed the isothermal crystallization kinetics of polypropylene (PP) on the basis of the Avrami equation, the Turnbull-Fisher nucleation theory and the Hoffman-Lauritzen growth theory. It is shown that the nucleation rate, the average radial growth rate of spherulites and the overall crystallization rate constant first increase and then decrease as the supercooling temperature increases.

Crystallization of isotactic (D,L) poly(propylene oxide) in the presence of fine‐particle silica. I: Radial growth rates of spherulites

AbstractThe effect of added silica on the spherulite radial growth rates of isotactic poly(propylene oxide) (i‐PPrO) has been investigated by optical photomicroscopy. Two different i‐PPrO samples were used of different molecular weights and isotacticity, 87 and 100% as determined by 13C NMR. The addition of fine particle silica, an effective nucleating agent, depresses the spherulite growth rates throughout the entire temperature range, but the effect is more dramatic for the i‐PPrO of lower isotacticity. For a given sample, the retardation increases as the quantity of filler increases. The growth rate‐temperature behavior is analyzed in terms of the classical Hoffman‐Lauritzen equation, modified to take into account the polymer‐filler interaction.