Non-isothermal crystallization of a vinyl alcohol-ethylene copolymer studied by DSC and real time WAXS/SAXS scattering

Time resolved SAXS/WAXS experiments, employing synchrotron radiation, together with DSC studies have been carried out on a vinyl alcohol-ethylene copolymer in order to clarify the morphological changes occurring during the non-isothermal crystallization of that copolymer from the melt. It was found that the SAXS long spacing and the WAXS diffraction peaks appear at the same temperature, revealing that the predominant growth mechanism of this process is nucleation and crystal growth but not density fluctuations. Moreover, the temperature variation of different structural parameters (peaks intensity, degree of crystallinity, long period, lamellar thickness) was comprehensively analyzed. Three temperature intervals are observed in this analysis, which have been interpreted as ‘high-temperature crystallization’, ‘low temperature crystallization’ and sub-glass region in order of decreasing temperatures.     

Melt Functionalization of Ethylene-Propylene Copolymer: Structural Investigation

An ethylene-propylene copolymer (EPM) has been functionalized with acrylic acid (AA) by means of a radical-initiated melt process. Different degrees of grafting have been obtained by varying the overall composition of the reaction mixture. The influence of the grafting degree on the structure has been investigated by differential scanning calorimetry (DSC), Fourier-transform infrared analysis (FTIR), and wide-angle x-ray scattering (WAXS) techniques. The results of the structural investigations suggest that the grafting preferentially occurs onto the ethylene sequences of EPM. After acrylic acid was grafted onto EPM, the grafted AA acted as nucleation agent; it caused an increase of crystallization temperature of propylene sequences of EPM-g-AA.     

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     

Cold Crystallization of PLLA Studied by Simultaneous SAXS and WAXS

Summary: The cold crystallization process of initially amorphous poly(L ‐lactic acid), PLLA, with two different molecular weights, during a heating at 2 °C/min, was investigated by DSC and time‐resolved simultaneous SAXS and WAXS, using synchrotron radiation. Equatorial scans of the isotropic 2D‐SAXS patterns showed that the average Bragg long period (L_B) of PLLA samples was approximately constant with the development of cold crystallization up to a temperature that corresponded to a melt/re‐crystallization process that took place before the nominal melting peak seen by DSC. L_B values were found to be higher for the high molecular weight material. This was in accordance with the higher melting temperature observed in the high molecular weight PLLA that implied the existence of thicker lamellae. WAXS results showed that the molecular weight did not apparently affect the crystal form and the final degree of crystallinity of PLLA. The Avrami parameters from WAXS and DSC were consistent, showing that the non‐isothermal cold crystallization of the two PLLA samples corresponded mainly to a three‐dimensional growth, although an imperfect crystallization process was involved at early times. The crystallization rate of PLLA, observed both by WAXS and DSC, decreased with increasing molecular weight.

SAXS profiles of PLLA2 as a function of temperature. The inset shows the 2D‐SAXS pattern obtained at 180 °C.     

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     

Crystallization of itaconic anhydride grafted poly(lactic acid) during annealing

The effect of annealing poly(lactic acid) (PLA) and PLA grafted with itaconic anhydride (IA) at different temperatures was studied using differential scanning calorimetry (DSC) and wide angle X‐ray scattering (WAXS). For PLA, two crystal forms were obtained when annealed between 110 and 120 °C, transforming into only the α‐form at 130 °C while a mixture of α′ and α‐form were obtained in grafted PLA. Grafting increased the percentage crystallinity of PLA, but it was mostly unaffected by the degree of grafting. The rate of crystallization was strongly dependent on the degree of grafting; when annealed at 100 °C, the crystallinity increased from 27.7 to 43.1% while the crystallization halftime reduced from 10.7 to 4.4 min at the lowest degree of grafting. It was thought that the increase in crystallization rate was likely due heterogeneous nucleation in the presence of grafted chains. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44614.     

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     

Structural investigations of poly(ethylene terephthalate)‐graft‐polystyrene copolymer films

Structural investigations of poly(ethylene terephthalate)‐graft‐polystyrene (PET‐g‐PS) films prepared by radiation‐induced grafting of styrene onto commercial poly(ethylene terephthalate) (PET) films were carried out by FTIR, X‐ray diffraction (XRD), and differential scanning calorimetry (DSC). The variation in the degree of crystallinity and the thermal characteristics of PET films was correlated with the amount of polystyrene grafted therein (i.e., the degree of grafting). The heat of melting was found to be a function of PET crystalline fraction in the grafted films. The grafting is found to take place by incorporation of amorphous polystyrene grafts in the entire noncrystalline (amorphous) region of the PET films and at the surface of the crystallites. This results in a decrease in the degree of crystallinity with the increase in the degree of grafting, attributed to the dilution of PET crystalline structure with the amorphous polystyrene, without almost any disruption in the inherent crystallinity. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 1949–1955, 2002; DOI 10.1002/app.10515     

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     

The structure and morphology of syndiotactic polystyrene injection molded coupons

The structure and morphology of syndiotactic polystyrene (sPS) injection molded coupons have been investigated using wide angle X-ray scattering (WAXS), differential scanning calorimetry (DSC), scanning electron microscopy (SEM), light microscopy, and laser Raman spectroscopy (LRS). By sectioning the samples at approximately 200 μm increments, profiles across “hot molded” (oil heated to 140°C) and “cold molded” (water heated to 104°C) coupons, could be built up. Using DSC and WAXS, variations in crystallinity and polymorphic phases were observed. The crystallinity was found to remain fairly constant in the “hot molded” samples, whereas the cold molded samples had a pronounced “amorphous” skin, before becoming more uniform towards the center of the specimen. Characterization of the polymers' microstructure, in the molded plaques, was achieved by optical birefringence. The surface of the plaques were successfully etched with an acid/permanganate solution, prior to SEM studies, to reveal their morphology. Overall, the coupons showed very little orientation effects and the structure appeared to be consistent with that of a semicrystalline polymer, crystallized under relaxed conditions.     

Structural changes of injection molded starch during heat treatment in water atmosphere: Simultaneous wide and small‐angle X‐ray scattering study

Native starches with wide varying amylose content were processed by injection molding. The injection‐molded materials were conditioned in water for 20 days and sealed in glass capillaries. Simultaneous wide‐ and small‐angle X‐ray scattering (WAXS and SAXS, respectively) were recorded during thermal heating using a synchrotron source. Crystallinity, SAXS invariant, Q, and long period, L, were measured as a function of heating temperature. The injection‐molding process provokes a destruction of the crystal forms A (cereal starch) and B (tubercle starch) but favors a development of the crystal form V_h. After wet conditioning, WAXS of the injection‐molded samples shows again the appearance of the crystal forms A or B, and crystallinity reaches values similar or larger than those of native starch. A constant heating rate (5°C/min) was particularly used for a comparison of potato and corn starch with a similar amylose content. While the crystallinity associated to forms A and B slowly decreases below 55°C and then rapidly decreases until its disappearance at 85–90°C, the invariant shows a maximum around 40°C and rapidly decreases thereafter. The total nanostructure disappearance occurs at temperatures about 10°C higher for the case of potato starch. In addition, a recovery of the WAXS and SAXS maxima during the subsequent cooling process before reaching room temperature was observed only for potato starch. Analysis of WAXS and SAXS for the rest of the starch materials reveals clear differences in the structural parameters of the samples that cannot be easily explained solely on the basis of the amylose content. Thus, for Cerestar and Roquette, it is noteworthy that there was a continuous decrease of L until its total disappearance as well as the persistence of crystallinity (form B), presumably stabilized by the presence of the V_h structure (12–15%). Real‐time crystallization experiments on two amorphous injection molded samples, waxy maize (free amylose starch) and potato starch, are also discussed. It is shown that the absence of amylose delays the recrystallization of amylopectine during the experiment. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 301–309, 2004     

Relationships between crystalline structure and the thermal behavior of poly(ethylene 2,5‐furandicarboxylate): An in situ simultaneous SAXS‐WAXS study

Poly(ethylene 2,5‐furandicarboxylate) (PEF) is an emerging bio‐based polymer with interesting thermal and barrier properties. In this study, the melting behavior of PEF was investigated in situ by means of simultaneous wide and small angle X‐ray scattering (WAXS and SAXS) measurements coupled with DSC measurements. This study gives the first evidence of what happens from a structural point of view during the multiple melting behavior of PEF, which is composed of three distinct events, taking into account the nature of the initial crystalline phase present. The first result is that the α′ form, induced at low crystallization temperature, does not undergo any phase transformation upon heating revealing its stable character. Second, the comparison of the SAXS and WAXS results with the DSC ones showed that the multiple melting behavior observed is attributed to a melting–recrystallization–melting process. Third, this work also definitely shows that the low amplitude melting endotherm observed in the DSC thermograms is ascribed to the melting of secondary crystals. Finally, SAXS‐WAXS results led to the conclusion that the secondary crystals cannot be depicted by the commonly accepted lamellar insertion model. Another microstructural representation of these secondary crystals is proposed. In this model, the secondary crystals consist of bundles of macromolecules, which formed small crystalline entities located between the primary crystalline lamellae stacks. POLYM. ENG. SCI., 59:1667–1677 2019. © 2019 Society of Plastics Engineers     

Isotactic polypropylene/polymethylmethacrylate blends: Effects of addition of propylene-graft-methylmethacrylate copolymer

A novel graft copolymer of unsaturated propylene with methyl methacrylate (uPP-g-PMMA) was added to binary blends of isotactic polypropylene (iPP) and atactic poly(methyl methacrylate) (aPMMA) with a view to using such a copolymer as a compatibilizer for iPP/aPMMA materials. Optical microscopy (OM), scanning electron microscopy, wide angle X-ray scattering (WAXS), and small angle X-ray scattering (SAXS) techniques showed that, contrary to expectation, the uPP-g-PMMA addition does not provide iPP/aPMMA compatibilized materials, irrespective of composition. As a matter of fact the degree of dispersion of the minor component achieved following the addition of uPP-g-PMMA copolymer remained quite comparable to that exhibited by binary blends of iPP and aPMMA with no relevant evidence of adhesion or interconnection between the phases. On the other hand the crystalline texture was deeply modified by the copolymer presence. With increasing uPP-g-PMMA content (w/w) the iPP spherulites were found to become more open and coarse and the dimensions and number per unit area of the amorphous interspherulitic contact regions were found to increase. According to such OM results the copolymer uncrystallizable sequences were assumed to be mainly located in interfibrillar and interspherulitic amorphous contact regions. SAXS analysis demonstrated that the phase structure developed in the iPP/aPMMA/uPP-g-PMMA blends is characterized by values of the long period increasing linearly with increasing copolymer content (w/w). Assuming a two phase model for the iPP spherulite fibrillae, constituted of alternating parallel crystalline lamellae and amorphous layers, the lamellar structure of the iPP phase in the ternary blends is characterized by crystalline lamellar thickness (L_c) and an interlamellar amorphous layer (L_a) higher than that shown by plain iPP and L_c and L_a values both increased with increasing uPP-g-PMMA content (w/w). Such SAXS results have been accounted for by assuming that a cocrystallization phenomenon between propylenic sequences of the uPP-g-PMMA copolymer and iPP occurs. The development of the iPP lamellar structure in the iPP/aPMMA/uPP-g-PMMA blends was thus modeled hypothesizing that during such a cocrystallization process copolymer PMMA chains with comparatively lower molecular mass remain entrapped into the iPP interlamellar amorphous layer forming their own domains. Moreover, evidence of strong correlations between the crystallization process of the uPP-g-PMMA copolymer and the iPP crystallization process was shown also by differential scanning calorimetry and WAXS experiments. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 2377–2393, 1997     

Structure-property Relationships in Radiation Grafted Poly(tetrafluoroethylene)-<Emphasis Type="Italic">graft</Emphasis>-polystyrene Sulfonic Acid Membranes

Structure-property relationships in poly(tetrafluoroethylene)-graft-polystyrene sulfonic acid (PTFE-g-PSSA) membranes prepared by radiation-induced grafting of styrene onto poly(tetrafluoroethylene) (PTFE) films using simultaneous radiation-induced grafting followed by sulfonation reaction were established. The physico-chemical properties of the membranes such as ion exchange capacity, swelling and ionic conductivity were correlated with the degree of grafting and the structural changes taking place in the membrane matrix during the preparation procedure. The variation in the crystallinity of membranes was studied by differential scanning calorimetry (DSC). The membranes thermal stability was evaluated using thermogravimetric analysis (TGA) and the effect of the heat treatment on the ion exchange capacity and the water uptake was investigated. The membranes were found to undergo substantial structural changes in the form of ionic sites increase, hydrophilicity enhancement, hydrophobicity reduction and crystallinity decrease with the increase in the degree of grafting. These structural changes were found to have a collective effect on the physico-chemical properties of the membranes but their relative contribution depends on the degree of grafting.     

On the physical behavior of isotactic polypropylene fibers extruded at different draw‐down ratios: II. Structure and properties

Microinterferometry (MIF), wide‐angle X‐ray scattering (WAXS), differential scanning calorimetry (DSC), and an Instron tensile tester (ITT) were used to determine the correlation between optical and structural properties of polypropylene (PP) fibers. For the purpose of the study a set of as‐spun isotactic PP fibers were extruded by melt spinning at different draw‐down ratios (DDR). The birefringence (Δn), degrees of orientation, degree of crystallinity (χ), Young's modulus (E_e), and tenacity (τ) were determined for PP fibers at the different DDR. An equiangular orientation of PP fibers at particular DDR was predicted experimentally, and the transverse modulus (E_t) was estimated for the tested fibers. Empirical formulae were developed for correlating the fiber birefringence with some of the studied structural properties of PP fibers. POLYM. ENG. SCI., 2010. © 2009 Society of Plastics Engineers     

Modification of natural rubber tubes for biomaterials I. Radiation-induced grafting of N,N-dimethyl acrylamide onto natural rubber tubes

Radiation-induced simultaneous grafting of N,N-dimethyl-acrylamide (DMAA) onto natural rubber (NR) tubes has been studied to improve blood compatibility of the NR tubes. Concerning grafting of DMAA onto NR tubes, it was found that the grafting proceeds effectively in the presence of carbon tetrachloride (CCl₄) as a solvent. The degree of grafting was found to be saturated at about 26 wt%, but a higher degree of grafting can be obtained by either “so called two-step grafting” or “putting a standing time for a while before irradiation.” The initial grafting rate was proportional to 0.85 power of dose rate. The apparent activation energy of the graft-copolymerization was 7.42 kcal/mol. Evaluation of blood compatibility of DMAA-grafted NR tubes has been carried out by ex vivo test. According to the results, significant improvement of blood compatibility was obtained for the samples in which degree of grafting is higher than 30 wt%.     

X-ray scattering investigations of acrylonitrileethylene oxide block copolymers

Wide angle (WAXS) and small angle (SAXS) X-ray scattering studies are reported on block copolymers of acrylonitrile with ethylene oxide. A distinct structural similarity between the copolymers and acrylonitrile homopolymer has been found. Considerable porosity of the copolymers has been shown. The porosity very largely governs the scattering power. It was found that the pores are three dimensional “particles” (scattering exponent α = 4), probably with smooth surfaces (surface fractal dimension d_s = 2).     

Deformation behaviour during cold drawing of nanocomposites based on single wall carbon nanotubes and poly(ether ester) copolymers

Relationships between the macroscopic deformation behaviour and microstructure of a pure (PBT-b-PTMO) block copolymer and a polymer nanocomposite (PBT-b-PTMO + 0.2 wt% SWCNT) were investigated by simultaneous small- and wide-angle X-ray scattering (SAXS and WAXS) during tensile deformation using synchrotron radiation. The Young's modulus was found to be 15% higher for the nanocomposite than for the pure block copolymer as well as the yield strength, while the elongation-to-break was less than a half. This different behaviour can be explained by taking into account the different structural features revealed by SAXS and WAXS and thus considering that SWCNT act as anchors in the nanocomposite, sharing the applied stress with the PBT crystals and partially preventing the flexible, non-crystallisable PTMO chains to elongate.     

Crystallization Study of Glassy PET/PEN Blends by Means of Real Time X-ray Scattering

Abstract

The crystallization of several blends of poly(ethylene terephthalate) (PET) and poly(ethylene 2,6 naphthalene dicarboxylate) (PEN) has been investigated by wide angle- (WAXS) and small angle X-ray scattering (SAXS) using synchrotron radiation. The role of transesterification reactions, giving rise to a fully amorphous non-crystal-lizable material (copolyester) is brought up. For the blends rich in PET, crystallization temperatures (T_c ) of 105 and 117°C were used. For blends rich in PEN, crystaffization was performed at T_c =150 and 165°C, respectively. The time variation of the degree of crystallinity was fitted into an Avrami equation considering the induction time prior to the beginning of crystallization. The Avrami parameters, the half times of crystallization, as well as the nanostructure development (SAXS invariant and long period) for the blends, are discussed in relation to blend composition and are compared to the parameters observed for the homopolymers PET and PEN.     

Development of crystallinity in NEW-TPI polyimide

Development of crystallinity in NEW-TPI semicrystalline polyimide has been studied using differential scanning calorimetry (DSC), wide (WAXS), and small angle X-ray scattering (SAXS). Crystallinity of the fully imidized powder, pellet, or film processed NEW-TPI can occur from the melt, and depends upon the holding temperature of the melt. Repetitive exposure to elevated temperatures supresses the development of crystallinity from the melt state. In amorphous pellets and film, crystallinity can also develop by cold crystallization from the rubbery amorphous state. SAXS results show that during cold crystallization, NEW-TPI develops a periodic structure consistent with formation of alternating crystalamorphous stacks, but with crystals only a few molecular repeat units thick. Kinetics of nonisothermal crystallization were studied as a function of heating rate and could be described using the Ozawa analysis. Non-isothermal crystallization proceeds at a slower rate in NEW-TPI than in other high temperature thermoplastics such as PEEK, and with a much narrower processing window. The maximum degree of crystallinity that could develop during heating was 0.34, which occurred at a rate of 5°C/min. Similar degrees of crystallinity could be introduced by heating amorphous NEW-TPI film in N-methylpyrrolidone.