Melting and crystallization behavior of aliphatic polyketones

The basic crystallization and melting behavior of three aliphatic polyketones were studied using differential scanning calorimetry (DSC), wide‐angle X‐ray diffraction (WAXD), small‐angle X‐ray scattering (SAXS), and optical microscopy. One resin was a perfectly alternating copolymer of ethylene and carbon monoxide, while the other two resins were terpolymers in which 6 mol % propylene was substituted for ethylene. Small decreases in the melting point and percent crystallinity of these materials were displayed with repeated melting. This behavior was attributed to light crosslinking as a result of condensation reactions occurring at temperatures in the melting range. WAXS showed that, after cooling to room temperature, the crystalline form in the copolymer was the α‐phase, while that in the terpolymers was the β‐phase. Optical microscopy revealed that the materials produce both negative and mixed birefringence spherulites under the conditions studied. SAXS measurements showed that the lamella thickness was largely a function of the temperature of crystallization. Attempts were made to measure the equilibrium melting temperature of these resins using several available techniques. The best value of the equilibrium melting temperature was concluded to be 278 ± 2°C for the copolymer. The results varied over a wide range for the terpolymers, but it is suggested that appropriate values are of order 252°C for the terpolymers. Crystallization kinetics studies, carried out under isothermal conditions using DSC, were evaluated using the Avrami equation. Results showed the Avrami exponent to lie in the range of 2–3. Spherulite growth rates were interpreted in terms of the secondary nucleation theory of Lauritzen and Hoffman. A transition from regime II to regime III was discovered. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 2124–2142, 2002     

Cocrystallization behavior of poly(n‐docosyl acrylate) with n‐docosanoic acid by X‐ray and differential scanning calorimetry studies

Cocrystallization behavior of comb‐like poly(n‐docosyl acrylate) (PDA) with n‐docosanoic acid (C₂₂) has been studied by means of differential scanning calorimetry (DSC) and X‐ray diffraction (XRD) methods. The DSC curves of blended samples of neat PDA with C₂₂ show the characteristic melting endotherms that correspond to the melting of the crystallites. DSC measurements of PDA/C₂₂ blends also suggest the existence of another crystalline form induced by the addition of the C₂₂. From the XRD measurements, the existence of hexagonally‐packed crystalline lattice and the phase behavior of PDA/C₂₂ blends at different mole percent are confirmed. Thermal degradation behavior of PDA and its corresponding blends with C₂₂ is studied by thermogravimetric analysis. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 2140–2146, 2005     

Structure of blown films of polyethylene/polybutene‐1 blends

The structure of blown films of blends of low‐density polyethylene (PE‐LD) and isotactic polybutene‐1 (iPB‐1) with different content of iPB‐1 was investigated using wide‐ and small‐angle X‐ray scattering (WAXS and SAXS), transmission electron microscopy (TEM), and polarizing optical microscopy (POM). TEM proves formation of a matrix–particle phase structure due to immiscibility of the blend components. Within the iPB‐1 particles, needle‐like crystals with c‐axis orientation were observed. The PE‐LD matrix showed two populations of crystals. WAXS data indicate that the majority of crystals were oriented with the c‐axis perpendicular to machine direction (MD), while SAXS data prove additional presence of stacks of lamellae, oriented parallel to MD. Quantitative birefringence measurements showed that the majority of molecule segments were oriented in the direction of the circumference of the film, confirming the WAXS data. The crystal orientation has direct impact on mechanical properties, which was demonstrated by measurement of the anisotropy of the modulus of elasticity. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers     

Structure development during crystallization and solid‐state processing of poly(glycolic acid)

DSC and time‐resolved WAXS and SAXS are used to study the structure development during isothermal crystallization of poly(glycolic acid) (PGA) in the temperature range 180–195°C. It is shown that the crystallization rate increases with degree of supercooling in the temperature range of consideration. WAXS and DSC crystallinity measurements agree well and a final crystallinity of 50% is found independently of the crystallization temperature. In‐situ SAXS measurements indicate that for PGA the final crystal thickness approaches a limiting value of 70 Å independent of the crystallization temperature in the range 195–180°C. The material develops a well‐defined lamellar structure during crystallization at the highest crystallization temperature under study (195°C). We show that by increasing the degree of supercooling it is possible to hinder the formation of the lamellar structure and crystals, resulting in a less ordered structure. We report that PGA fibers with elastic modulus in the range 20–25 GPa can be prepared by adequate control of the structure before solid‐state plastic deformation. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Synthesis and Properties of some ε‐Caprolactone‐Based Di‐ and Triblock Polymers by Anionic Polymerization

Block copolymers containing ε‐caprolactone were synthesized. Mechanical properties as a function of chemical composition and domain structure as a function of elongation were studied. Based on previous optimal conditions determination by factorial design of experiments of ε‐caprolactone anionic polymerization, polystyrene‐block‐poly(ε‐caprolactone), polyisoprene‐block‐poly(ε‐caprolactone), polystyrene‐block‐polybutadiene‐block‐poly(ε‐caprolactone) (SBCL), and polystyrene‐block‐polyisoprene‐block‐poly(ε‐caprolactone) (SICL) with different compositions where synthesized, and characterized by GPC and DSC. Both the SICL and SBCL materials are thermoplastic elastomers, from which spin‐cast films were prepared. Their mechanical properties were determined, small angle X‐ray scattering (SAXS) measurements were carried out during straining, and dynamic mechanical analysis (DMA) was performed. All diblock polymers separate into a two‐phase structure, but the melting point of crystalline poly(ε‐caprolactone) domains in the block polymer is higher than in the case of the homopolymer. According to DMA data, some of the SICL and SBCL materials are three‐phase systems, but others are only two‐phase systems. The two‐phase materials show a considerable depression of the composite hard domain glass transition and, consequently, turn out to be very soft. It appears peculiar that the transition from three‐phase to two‐phase material is accomplished by decreasing the soft block length. For the soft material SAXS exhibits a lamellar stack nanoscale structure and several reflections of colloidal crystals. As a function of increasing elongation, the crystal reflections broaden, whereas lamellar stacks rotate as a whole.     

Thermal properties,structure and morphology of PEEK/thermotropic liquid crystalline polymer blends

The dynamic crystallization and subsequent melting behaviour of poly(aryl ether ether ketone), PEEK, and its blends with a thermotropic liquid crystalline polymer, Vectra^®, have been studied using differential scanning calorimetry, optical microscopy and wide‐angle and small‐angle X‐ray diffraction (WAXS and SAXS) techniques in a wide compositional range. Differences in crystallization rates and crystallinities were related to the structural and morphological characteristics of the blends measured by simultaneous real‐time WAXS and SAXS experiments using synchrotron radiation and optical microscopy. The crystallization process of PEEK in the blends takes place in the presence of the nematic phase of Vectra and leads to the formation of two different crystalline families. The addition of Vectra reduces the crystallization rate of PEEK, depending on composition, and more perfect crystals are formed. An increase in the long period of PEEK during heating was generally observed in the blends at all cooling rates. Copyright © 2003 Society of Chemical Industry     

Novel Self‐Reinforced Films Based on Poly (3‐Hydroxybutyrate‐Co‐3‐Hydroxyvalerate) (PHBV) and PHBV Microparticles

Biodegradable self‐reinforced films of poly (3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) (PHBV) and PHBV microparticles were prepared through the solvent casting method (srPHBV). Differential scanning calorimetry (DSC), wide angle X‐ray scattering (WAXS) and polarized optical microscopy results confirmed the nucleating effect of PHBV microparticles. WAXS proved that diffractograms of PHBV and srPHBV‐6 films at room temperature contain the main characteristic diffraction peaks of an orthorhombic α‐type crystalline structure. Small angle X‐ray scattering (SAXS) showed a similar decrement rate of long spacing in PHBV and srPHBV films. SAXS/WAXS data revealed that when the amount of filler was increased, lamellae thickness grew. Transmission electron microscopy images illustrated well filler dispersion in the srPHBV films. Scanning electron microscopy results exhibited a significant reduction in porosity for srPHBV films once the PHBV microparticles were added. Atomic force microscopy analysis showed higher surface roughness after filler incorporation. Samples of srPHBV films showed higher barrier properties against water vapor, oxygen, and carbon dioxide. Combined properties of srPHBV films revealed the possibility of being suitable candidates for food packaging applications. POLYM. ENG. SCI., 59:E120–E128, 2019. © 2018 Society of Plastics Engineers     

Manipulating the microstructure and rheology in polymer‐organoclay composites

A series of nanocomposites prepared by melt‐blending of cloisite‐based organoclays with poly(ethylene‐vinylacetate) (EVA) and neutralized poly (ethylene‐methacrylic acid) (EMA) copolymers were investigated via DSC, small‐angle X‐ray scattering (SAXS), and rheological techniques. SAXS results indicated partial clay exfoliation in all samples. In both EMA and EVA systems, the nominal melting temperature T_m and bulk crystallinity are not significantly affected by the presence of organoclays, suggesting that clay particles are predominantly confined in the amorphous phase. In rheological measurements (above T_m), the EVA‐clay system demonstrated a solid‐like rheological behavior under the small‐strain oscillatory shear, yet it was able to yield and flow under a steady shear, which is the characteristic of physical crosslinking. In contrast, the EMA‐clay system exhibited a melt‐like rheological behavior, where the influence of organoclay on the thermorheological behavior of the EMA composite was quite minimal. We propose that the carbonyl groups of vinylacetate in EVA interact with the clay surface, resulting in a strong physically crosslinking like interaction in the melt. On the other hand, the interaction between EMA and clay is weak because of repulsion between carboxyl anions and negatively charged clay surface.     

Synthesis and thermotropic liquid‐crystalline behavior of novel main‐chain poly(aryl ether ketones)

Novel aromatic poly(ether ketones) containing bulky lateral groups were synthesized via nucleophilic substitution reactions of 4,4′‐biphenol and (4‐chloro‐3‐trifluoromethyl)phenylhydroquinone (CF‐PH) with 1,4‐bis(p‐fluorobenzoyl)benzene. The copolymers were characterized by differential scanning calorimetry (DSC), wide‐angle X‐ray diffraction, and polarized light microscopy observation. Thermotropic liquid‐crystalline behavior was observed in the copolymers containing 40, 50, 60, and 70 mol % CF‐PH. The crystalline–liquid‐crystalline transition [melting temperature (T_m)] and the liquid‐crystalline–isotropic phase transition appeared in the DSC thermograms, whereas the biphenol‐based homopolymer had only a melting transition. The novel poly(aryl ether ketones) had glass‐transition temperatures that ranged from 143 to 151°C and lower T_m's that ranged from 279 to 291°C, due to the copolymerization. The polymers showed high thermal stability, and some exhibited a large range in mesophase stability. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 1347–1350, 2003     

Poly(trimethylene terephthalate‐block‐tetramethylene oxide) elastomer/single‐walled carbon nanotubes nanocomposites: Synthesis,structure, and properties

Nanocomposites based on poly(trimethylene terephthalate)‐block‐poly(tetramethylene oxide) (PTT‐PTMO)‐segmented copolymer and COOH‐functionalized single‐walled carbon nanotubes (SWCNTs) were prepared by in situ polymerization method. The obtained nanocomposites were characterized by thermogravimetric analysis, scanning electron microscopy, differential scanning calorimetry (DSC), DMTA, wide‐angle x‐ray scattering (WAXS), small‐angle X‐ray scattering, and tensile testing. The nanocomposites with low SWCNTs loading (<0.5 wt %) shows uniform dispersion of CNT in polymer matrix. As the SWCNTs loading in the nanocomposites increase, the significant improvement of thermo‐oxidative stability was observed. It was found that the nanocomposites have slightly higher degree of crystallinity (determined by DSC and WAXS) of poly(trimethylene terephthalate) (PTT) hard phase than neat PTT‐PTMO copolymer. The melting point of PTT hard phase and glass transition temperature of poly(tetramethylene oxide)‐rich phase were not affected by the presence of CNTs in polymer matrix. The SWCNTs played a role as nucleating agent in PTT‐PTMO matrix, which led to increase in the crystallization rate. Tensile tests showed that the tensile strength of the nanocomposites with 0.05–0.3 wt % loading of SWCNTs have improved tensile strength in comparison to the neat PTT‐PTMO copolymer without reduction elongation at break. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Phase stability and melting behavior of the α and γ phases of nylon 6

The phase stability and melting behavior of nylon 6 were studied by high‐temperature wide‐angle X‐ray diffraction and differential scanning calorimetry (DSC). The results show that most of the α phase obtained by a solution‐precipitation process [nylon 6 powder (Sol‐Ny6)] was thermodynamically stable and mainly melted at 221°C; the double melting peaks were related to the melt of α crystals with different degrees of perfection. The γ phase formed by liquid nitrogen quenching (sample LN‐Ny6) melted within the range 193–225°C. The amorphous phase converted into the γ phase below 180°C but into the high‐temperature α phase at 180–200°C. Both were stable over 220°C. α‐ and γ*‐crystalline structures were formed by annealing but were not so stable upon heating. Typical double melting peaks were shown on the DSC curve; melt recrystallization happened within the range 100–200°C. The peak at 210°C was mainly due to the melting of the less perfect crystalline structure of the γ phase and a fraction of the α phase; the one at 219°C was due to the high‐temperature α‐ and γ‐phase crystals. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Studies on morphology and interphase of poly(butylene terephthalate)/carbon nanotubes nanocomposites

The microstructure of poly(butylene terephthalate) (PBT) nanocomposites was investigated by simultaneous small angle X‐ray scattering/wide angle X‐ray scattering (SAXS/WAXS) measurements at room temperature. The PBT was observed to crystallize in the α‐phase. The dispersion of single‐wall carbon nanotubes (SWCNTs) in PBT, using in situ polymerization, materials with higher degree of crystallinity than neat PBT were produced. SAXS results indicated that the SWCNT may be preferentially distributed in the amorphous phase of PBT, although WAXS results suggested a nucleation ability of SWCNT, which was supported by the DSC results. Much more complex changes were induced by the dispersion of multiwall carbon nanotubes (MWCNTs) in the PBT matrix. Evidence for the formation of an interphase with restricted chain mobility were found by dynamical mechanical thermal analysis (DMTA). Differential scanning calorimetry (DSC) and WAXS showed an increase of the crystallinity of the nanocomposites in comparison to neat PBT. POLYM. ENG. SCI., 50:1571–1576, 2010. © 2010 Society of Plastics Engineers     

Solvent‐induced modifications in polyester yarns. II. Structural and thermal behavior

The structural and thermal behaviors of polyester yarns treated with trichloroacetic acid–chloroform (TCAC) mixture were investigated by differential scanning calorimetric analysis (DSC), wide‐angle X‐ray scattering (WAXS), infrared spectroscopy (IR), and scanning electron microscopy (SEM). The effects of TCAC treatment on original fine filament (FFP) and microdenier (MDP) polyester yarns and on heat‐set polyester yarns were studied. It was found that the glass transition temperature of TCAC‐treated polyester yarns decreases with an increase in treatment concentration due to the plasticization effect, which is remarkable even at lower treatment concentration. The TCAC treatment on polyester yarns resulted in the formation of new crystallites in the extended noncrystalline domains of PET as well as growth and perfection of these new crystallites and the preexisting crystals. Further, the DSC thermograms revealed that TCAC treatment with 3% concentration could be able to overcome the structural changes in PET produced by heat setting at 180°C. The substantial changes in noncrystalline and crystalline domains observed were related to the mechanical properties of yarns. From the WAXS studies, an increase in crystal size and lateral order of TCAC‐treated polyester yarns was noted. The most distinct changes brought about by TCAC treatment include overall orientation determined by the trans–gauche ratio from IR measurements. The removal of oligomers and smoothening out of the fiber surface by TCAC treatment were observed from SEM studies. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 1555–1566, 2003     

On the effect of the nature of the side chain over the crystalline structure in aliphatic polyketones

The crystalline structure of a number of random polymers of perfectly alternating l-olefins/carbon monoxide aliphatic polyketones has been studied by wide angle X-ray scattering (WAXS), small-angle X-ray scattering (SAXS), differential scanning calorimetry (DSC) and Raman spectroscopy. From previous studies, WAXS, Raman and DSC have shown to be suitable techniques for the characterisation of the two crystalline polymorphs, α (denser) and β, detected in ethene/carbon monoxide (ECO) and in ethene/propene/carbon monoxide (EPCO) polymers. In this paper for the first time, polyketones with butene and hexene as the second olefin are reported. It was found that the ethene/propene/carbon monoxide polymers and ethene/butene/carbon monoxide (EBCO) polymers, predominately contain the β-rich crystalline phase. The crystalline density of this phase drops with increasing second olefin content, albeit at a faster pace for propene polymers. From the latter results, and from the behaviour of the melting point, crystallinity, and crystal thickness across composition, inclusion of methyl and ethyl side chains into the crystals as defects was inferred. Ethene/hexene/carbon monoxide (EHCO) polymers do seem to behave differently: they show lower crystallinity, the presence of a larger quantity of the denser α crystals and a relatively high and constant crystalline density for the β phase throughout composition; observations that unambiguously support the exclusion argument for the butyl branches. The above behaviour is surprising since for instance in polyethylene copolymers it is considered that only methyl branches can enter the crystal lattice. The relative presence of α crystals was found to decrease with increasing the concentration of branches and in the order EHCO>EBCO>EPCO.     

On the fractal character of polymer spherulites: an ultra‐small‐angle X‐ray scattering study of poly[(R)‐3‐hydroxybutyrate]

Ultra‐small‐angle X‐ray scattering (USAXS) and small‐angle X‐ray scattering (SAXS) measurements are presented for poly[(R)‐3‐hydroxybutyrate] (PHB) crystallized at room temperature. The USAXS patterns indicated that the spherulites had a radially orientated fibrillar nanostructure with fractal geometry over a length scale ranging from 12 nm up to at least 300 nm, with a mass fractal dimension of approximately 2.7 in aged samples. The SAXS patterns indicated that the fibrils themselves were built up of bundles of crystalline lamellae separated by layers of disordered material, with a period length of approximately 6 nm. The SAXS measurements during primary crystallization gave an initial fractal dimension of 4 during spherulite growth, due to the sharp phase boundary between the spherulites and the melt. Copyright © 2004 Society of Chemical Industry     

Isotactic polypropylene/ethylene‐co‐propylene blends: Influence of the copolymer microstructure on rheology,morphology, and properties of injection‐molded samples

Meltrheological behavior, phase morphology, and impact properties of isotactic‐polypropylene (iPP)‐based blends containing ethylene–propylene copolymer (EPR) synthesized by means of a titanium‐based catalyst with very high stereospecific activity (EPR_Ti) were compared to those of iPP/EPR blends containing EPR copolymers synthesized by using a traditional vanadium‐based catalyst (EPR_V). The samples of EPR copolymers were synthesized ad hoc. They were characterized by comparable propylene content, average molecular masses, and molecular mass distribution in order to assess the effects of distribution of composition and sequence lengths of the structural units on the structure–properties correlations established in the melt and in the solid state while studying different iPP/EPR pairs.^1–5 Differential scanning calorimetry, (DSC), wide‐angle X‐ray spectroscopy (WAXS), small‐angle X‐ray (SAXS), and scanning electron microscopy (SEM) investigations showed that the EPR_Ti chain is characterized by the presence of long ethylenic sequences with constitutional and configurational regularity required for crystallization of the polyethylene (PE) phase occurring, whereas a microstructure typical of a random ethylene–propylene copolymer was exhibited by the EPR_V copolymer. The different intra‐ and intermolecular homogeneity shown by such EPR phases was found to affect their melt rheological behavior at the temperatures of 200 and 250°C; all the EPR_Ti dynamic–viscoelastic properties resulting were lower than that shown by the EPR_V copolymer. As far as the melt rheological behavior of the iPP/EPR_V and iPP/EPR_Ti blends was concerned, both the iPP/EPR pairs are to be classified as “negative deviation blends” with G′ and G" values higher than that shown by the plain components. The extent of the observed deviation in the viscosity values and of the increase in the amounts of stored and dissipated energy shown by such iPP/EPR pairs was found to be dependent on copolymer microstructure, being larger for the melts containing the EPR_Ti copolymer. The application of the Cross–Bueche equation also confirmed that, in absence of shear, the melt phase viscosity ratio is the main factor in determining the viscosity of iPP/EPR blends and their viscoelastic parameters. The general correlation established between EPR dispersion degree (range of particle size and number‐average particle size), as determined in injection‐molded samples, and melt phase viscosity ratio (μ) was ratified; the type of dependence of EPR size upon μ value was in qualitative agreement with the prediction of the Taylor–Tomotika theory. Contrary to expectation,^1–5 for test temperature close to iPP T_g, EPR_V particles ranging in size between 0.75 and 1.25 μm resulted and were more effective than EPR_Ti particles, ranging in size between 0.25 and 0.75 μm, in promoting multiple craze formation. Also taking into account the SAXS results, revealed that the molecular superstructure (i.e., crystalline lamellar thickness and amorphous interlayer) of the iPP matrix is unaffected by both the presence of EPR_Ti and EPR_V phase. The above finding was related to the ethylenic crystallinity degree shown by the EPR_Ti copolymer. In particular, such a degree of crystallinity was supposed to deteriorate toughening by decreasing the tie molecules density in the EPR_Ti domains, notwithstanding the beneficial effect of the ethylenic lamellar buildup. For test temperature close to room temperature, the ductile behavior exhibited by the iPP/EPR_Ti blends was accounted for by a predominant shear yielding fracture mechanism probably promoted by a high concentration of interlamellar tie molecules among iPP crystallites in agreement with DSC results. Nonisothermal crystallization experiments showed, in fact, that the crystallization peak of the iPP phase from iPP/EPR_Ti melt is shifted to higher temperatures noticeably, thus indicating a material characterized by a comparatively higher number of spherulites per unit value grown at lower apparent undercooling values. Accordingly, WAXS analysis revealed comparatively higher iPP crystal growth in the directions perpendicular to the crystallographic planes (110) and (040) of the iPP. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 701–719, 1999     

Crystallization and melting behavior of multi‐walled carbon nanotube‐reinforced nylon‐6 composites

The crystallization and melting behavior of neat nylon‐6 (PA6) and multi‐walled carbon nanotubes (MWNTs)/PA6 composites prepared by simple melt‐compounding was comparatively studied. Differential scanning calorimetry (DSC) results show two crystallization exotherms (T_{CC, 1} and T_{CC, 2}) for PA6/MWNTs composites instead of a single exotherm (T_{CC, 1}) for the neat matrix. The formation of the higher‐temperature exotherm T_{CC, 2} is closely related to the addition of MWNTs. X‐ray diffraction (XRD) results indicate that only the α‐phase crystalline structure is formed upon incorporating MWNTs into PA6 matrix, independently of the cooling rate and annealing conditions. These observations are significantly different from those for PA6 matrix, where the increase in cooling rate or decrease in annealing temperature results in the crystal transformation from α‐phase to γ‐phase. The crystallization behavior of PA6/MWNTs composites is also significantly different from those reported in PA6/nanoclay systems, probably due to the difference in nanofiller geometry between one‐dimensional MWNTs and two‐dimensional nanoclay platelets. The nucleation sites provided by carbon nanotubes seem to be favorable to the formation of thermodynamically stable α‐phase crystals of PA6. The dominant α‐phase crystals in PA6/MWNTs composites may play an important role in the remarkable enhancement of mechanical properties. Copyright © 2005 Society of Chemical Industry     

Multiple melting and partial miscibility of ethylene‐vinyl acetate copolymer/low density polyethylene blends

Multiple melting behaviors and partial miscibility of ethylene‐vinyl acetate (EVA) copolymer/low density polyethylene (LDPE) binary blend via isothermal crystallization are investigated by differential scanning calorimetry (DSC) and wide angle X‐ray diffraction (WAXD). Crystallization temperature T (°C) is designed as 30, 50, 70, 80°C with different crystallization times t (min) of 10, 30, 60, 300, 600 min. The increase of crystallization temperature and time can facilitate the growth in lateral crystal size, and also the shift of melting peak, which means the completion of defective secondary crystallization. For blends of various fractions, sequence distribution of ethylene segments results in complex multiple melting behaviors during isothermal crystallization process. Overlapping endothermic peaks and drops of equilibrium melting points of LDPE component extrapolated from Hoffman–Weeks plots clarify the existence of partial miscibility in crystalline region between EVA and LDPE. WAXD results show that variables have no perceptible influence on the predominant existence of orthorhombic crystalline phase structure. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Morphological changes of poly(ethylene terephthalate‐co‐isophthalate) during solid state polymerization

Poly(ethylene terephthalate‐co‐isophthalate) (PETI) prepolymer was submitted to solid state polymerization (SSP) at 184–230°C in a fixed bed reactor, to study the evolution of morphological changes during the process. Short reaction times were selected to investigate crystallization phenomena during nonisothermal (heating) and isothermal SSP phases. More specifically, multiple PETI melting behavior was observed and attributed to secondary crystallization, the rate of which increased significantly with SSP temperature. Reaction time was also found to exert a positive effect on solid‐phase perfection of secondary crystals, leading at each temperature to melting points close to the value of bottle‐grade poly(ethylene terephthalate). Finally, the mass fraction crystallinity of the SSP grades was found to comply with the crystal morphology encountered. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Effect of diluents on the crystallization behavior of poly(4‐methyl‐1‐pentene) and membrane morphology via thermally induced phase separation

The effect of diluents on polymer crystallization and membrane morphology via thermally induced phase separation(TIPS) were studied by changing the composition of the mixed‐diluents systematically, in the system of poly(4‐methyl‐1‐pentene) (TPX)/dibutyl‐phthalate (DBP)/di‐n‐octyl‐phthalate (D‐n‐OP) with TPX concentration of 30 wt %. The TPX crystallization was observed with differential scanning calorimetry (DSC) and wide angle X‐ray diffraction (WAXD). The membranes were characterized with scanning electron microscopy (SEM), porosity, and pore size measurement. As the content of D‐n‐OP increased in mixed‐diluents, the solubility with TPX increased, inducing the phase separation changing from liquid–liquid phase separation into solid–liquid phase separation, which changed the membrane morphology and structure. When the ratios of DBP to D‐n‐OP were 10 : 0, 7 : 3; 5 : 5, and 3 : 7, membranes were formed with cellular structure and well connected pores, while the ratio was 0 : 10, discernable spherulities were found with not well‐formed pore structure. The effect of composition of the mixed‐diluents on membrane morphology was more remarkable in TPX/dioctyl‐sebacate (DOS)/dimethyl‐phthalate (DMP) system, since good cellular structure was formed when the ratios of DOS to DMP were 10 : 0, 7 : 3, while spherulites were observed when 5 : 5. Dual endotherm peaks behavior on DSC melting curves emerged for all the samples in this study, which was attributed to the special polymer crystallization behavior, primary crystallization, and secondary crystallization occurred when quenching the samples. As the content of D‐n‐OP increased, the secondary crystallization enhanced which induced the first endotherm peak on DSC melting curves moving to a lower temperature and the broadening of the overall melting peak, as well as the increasing of the overall crystallinity. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008