Rigid Amorphous Fraction Research Articles

New insight on the annealing induced microstructural changes and their roles in the toughening of β-form polypropylene

Large amount of work has been reported on the annealing of polypropylene (PP) and the related changes in mechanical properties. However, the structure–property correlations and the physical origin of annealing induced microstructural evolution are still not very clear. In this work, taking β-form PP (β-PP) as example, the microstructural changes induced by annealing were investigated from macromolecular to crystalline lamellae level with Fourier transform infrared (FTIR) spectroscopy, conventional differential scanning calorimetry (DSC), temperature-modulated DSC (TMDSC), wide-angle X-ray diffraction (WAXD), small-angle X-ray scattering (SAXS) and dynamic mechanical analysis (DMA). Besides mobile amorphous fraction (MAF), the role of rigid amorphous fraction (RAF) in toughening PP is particularly taken into consideration. It is shown that annealing increases the chain mobility in MAF and decreases it in RAF. Such an effect is believed to be mainly associated with the formation of looser MAF and more RAF by the microstructural re-arrangement involving conformational ordering of partial amorphous chain segments and a significant interlamellae thickening. A thorough analysis of structure–property relationship through observing plastic deformation behaviors by scanning electron microscope (SEM) and estimating stress transmission between crystalline and amorphous phases, suggests that both MAF and RAF play important role on toughening β-PP. They can promote the initiation of microvoids effectively upon deformation by reducing the stress transmission. As a result, large-scale plastic deformation is triggered. This work is important and provides a new insight into the mechanisms of microstructural evolution and subsequent improvement in impact toughness during annealing.

Kinetics of nucleation and crystallization in poly(ɛ-caprolactone) (PCL)

The recently developed differential fast scanning calorimetry (DFSC) is used for a new look at the crystal growth of poly(ɛ-caprolactone) (PCL) from 185 K, below the glass transition temperature, to 330 K, close to the equilibrium melting temperature. The DFSC allows temperature control of the sample and determination of its heat capacity using heating rates from 50 to 50,000 K/s. The crystal nucleation and crystallization halftimes were determined simultaneously. The obtained halftimes cover a range from 3 × 10 −2 s (nucleation at 215 K) to 3 × 10 9 s (crystallization at 185 K). After attempting to analyze the experiments with the classical nucleation and growth model, developed for systems consisting of small molecules, a new methodology is described which addresses the specific problems of crystallization of flexible linear macromolecules. The key problems which are attempted to be resolved concern the differences between the structures of the various entities identified and their specific role in the mechanism of growth. The structures range from configurations having practically unmeasurable latent heats of ordering (nuclei) to being clearly-recognizable, ordered species with rather sharp disordering endotherms in the temperature range from the glass transition to equilibrium melting for increasingly perfect and larger crystals. The mechanisms and kinetics of growth involve also a detailed understanding of the interaction with the surrounding rigid-amorphous fraction (RAF) in dependence of crystal size and perfection.

Small strain mechanical properties of latex-based acrylic nanocomposite films

A waterborne latex-based technique has been used to prepare acrylic films with laponite contents up to about 25 vol%. The laponite was attached to the surfaces of the latex particles, giving a cellular arrangement of laponite-rich regions at high laponite contents. Two regimes of reinforcement were observed, depending on whether T was above or below T-g, reinforcement at T > T-g being significantly greater than predicted by micromechanical models. Modulated differential scanning calorimetry and dynamic mechanical analysis showed part of the organic content of the films not to contribute to the glass transition. This rigid amorphous fraction (RAF) was argued to correspond to intercalated regions of the matrix. However, the RAF alone was insufficient to account for the observed increases in stiffness at T > T-g. The mechanical response is therefore discussed in terms of a four-phase model, in which intercalated laponite stacks are embedded in a matrix with reduced mobility, forming a foam-like structure, in turn embedded in a matrix with the properties of the bulk polymer. (C) 2011 Elsevier Ltd. All rights reserved.

Isotropization, perfection and reorganization of the mesophase of isotactic polypropylene

The perfection, reorganization, and isotropization of the mesophase of isotactic polypropylene were investigated by fast scanning calorimetry (FSC). The analysis was made at different heating rates, to evaluate the isotropization temperature of the initially grown mesophase and of mesophase which has been perfected or even reorganized into crystals. Mesophase formation is paralleled by formation of a rigid–amorphous fraction which was about twice the mesophase content. While the isotropization temperature of the initially grown mesophase is controlled by the temperature of its formation, the isotropization temperature of perfected or reorganized mesophase was independent on the condition of prior formation. Absence of exothermic heat flow during heating suggests that the mesophase converted gradually into crystals due to the fast heating rate. The discussion of data includes new ideas about nucleation, growth, and perfection of the mesophase, involving nanophase to microphase and rigid–amorphous fraction to mesophase transitions.

Crystalline, mobile amorphous and rigid amorphous fractions in poly(L-lactic acid) by TMDSC

A detailed analysis of the three-phase structure of poly(L-lactic acid) was performed by temperature-modulated differential scanning calorimetry upon quasi-isothermal and non-isothermal crystallizations. The TMDSC analyses revealed that the relative amounts of the three fractions of poly(L-lactic acid) depend on the temperature at which crystallization occurs. It was found that rigid amorphous fraction grows in parallel with crystalline phase during quasi-isothermal crystallization at 90 °C, whereas at T c = 130 °C it starts to appear approximately in correspondence with secondary crystallization. At T c = 135 °C RAF practically does not develop. The results prove that RAF development during crystallization depends on the mobility of the chains. The temperature of complete devitrification at 10 °C min −1 seems to be 130 °C: this temperature could be the limit for the formation and the disappearance of rigid amorphous fraction in the PLLA sample analyzed in the present study.

The influence of the liquid-to-solid transitions on the changes of macromolecules from disorder to order

When crystallizing macromolecules, one needs to recognize that they are sufficiently long to connect neighboring phases. This coupling between the phases is the reason that on ordering, practically all polymers develop a globally metastable, semicrystalline structure, consisting of multiple phases with different degrees of mobility. The ordered and amorphous phases are separated by nanophases of strained segments of molecule of nanometer dimensions, consisting of rigid-amorphous fractions, RAFs, which soften, above, within, or below the often very broad melting range of the ordered phases. Thus, ordering of a melt of macromolecules causes significant changes in the remaining amorphous phases. A summary of the various phases is given in terms of their structures, molecular vibrations, and large-amplitude motion as they influence the glass and order-disorder transitions. This is followed by a description of the limits of the classical nucleation theory of crystals when applied to macromolecules. Discussed in detail are the problems in primary and secondary nucleation which arise from the presence of RAFs. Special macromolecular nucleation processes that needed to be considered are the self-nucleation on cooling from above the melting temperature or on heating from above the glass transition temperature, and the molecular nucleation causing molar mass segregation on ordering. Finally, the glass transitions of the phases of various sizes and degree of order are discussed on hand of selected, pertinent examples.

Coupling between Crystal Melting and Rigid Amorphous Fraction Mobilization in Poly(ethylene terephthalate)

A thorough analysis of the melting behavior of poly(ethylene terephthalate) (PET) is detailed in this contribution. Isothermal crystallization at 190 °C followed by cooling to room temperature provides a three-phase structure composed of a mobile amorphous, a crystalline, and a rigid amorphous fraction. A close connection between multiple melting and devitrification of the rigid amorphous fraction in PET is revealed by conventional and temperature-modulated calorimetry. Rearrangements of PET crystals at high temperatures involve recrystallization/annealing/crystal perfection following partial melting, which can occur only if the amorphous chain portions coupled to the crystal/melt phase boundary have sufficient mobility. Such mobility can be achieved above the glass transition of the amorphous chain segments coupled with the just-melted crystals. Combined analysis of the reversing heat capacity monitored during quasi-isothermal modulation with the thermal properties of the resulting structure suggests tha...

Phase structure of electrospun poly(trimethylene terephthalate) composite nanofibers containing carbon nanotubes

Nanofibrous composite mats were prepared by electrospinning of poly(trimethylene terephthalate), PTT, with multi-walled carbon nanotubes (PTT/MWCNT). Tri- fluoroacetic acid (TFA) and methylene chloride (MC) with volume ratio of 50/50 is a good solvent for PTT and was used as the electrospining solution. Scanning electron microscopy was used to investigate the morphology of electrospun (ES) nanofibers with 0, 0.2, 1.0, or 2.0 wt% of MWCNTs. Crystal structure of the ES mats was deter- mined from wide angle X-ray diffraction. Thermal prop- erties were investigated using heat capacity measurements from differential scanning calorimetry (DSC) using the three-runs method for baseline correction, heat flow amplitude calibration, and sample heat capacity determi- nation. A model comprising three phases, a mobile amor- phous fraction (MAF), rigid amorphous fraction (RAF), and crystalline fraction (C), is appropriate for ES PTT/ MWCNT fibers. The phase fractions, Wi (for i = RAF, MAF or C) were determined by DSC. Crystallinity decreases very slightly with the amount of MWCNT. At the same time, a large increase in RAF was observed: WRAF of PTT fiber with 2% MWCNT is twice that of neat PTT fiber. The addition of MWCNTs enhanced the PTT chain alignment and increased RAF as a result. Changes of vibrational band absorbance at 1358 and 1385 cm -1 , cor- responding to characteristic groups, were obtained with infrared spectroscopy. The increased absorbance at 1358 cm -1 and decreased absorbance at 1385 cm -1 , with the addition of MWCNTs, strongly supports the three- phase model for ES PTT/MWCNT nanocomposites.

A comparison of crystallization behavior for melt and cold crystallized poly ( l-Lactide) using rapid scanning rate calorimetry

A unique rapid scanning rate differential scanning calorimeter is used to examine the differences in melt and cold crystallized poly ( l-Lactide) (PLLA), a biodegradable semi-crystalline polymer. After isothermal melt and cold crystallization at various temperatures, both melt and cold crystallized PLLA are characterized by similar melting temperatures ( T m) and exhibit multiple melting behavior on heating at 500 °C/min. However, cold crystallization results in a higher degree of crystallinity ( w c) compared to melt crystallization. While the overall amorphous fraction is higher for melt crystallization, the mobile amorphous fraction ( w a) is found to be higher for cold crystallization. The rigid amorphous fraction ( w raf) in PLLA is determined to be higher for melt crystallization than for cold crystallization at almost all temperatures. The higher values of w raf also appear to result in higher values of the glass transition temperature ( T g) for melt crystallized samples due to a reduction in mobility of amorphous phase. These dramatic differences depending on whether the material is brought to the crystallization temperature from the melt or the glassy state, could have profound implications for processing and optimizing the properties of PLLA.

Vitrification and devitrification of the rigid amorphous fraction in poly(ethylene terephthalate)

AbstractVitrification and devitrification of the rigid amorphous fraction (RAF) of poly(ethylene terephthalate) (PET), analyzed during development and disappearance of the three phase structure, are detailed in this contribution. Upon cooling from the melt at a constant rate, the rigid amorphous fraction starts to vitrify when the crystallization process is almost finished, and continues on further cooling. The rigid amorphous fraction is formed in the same temperature range of the secondary crystal growth. Analysis of the low melting endotherm that is observed in isothermally crystallized PET a few degrees above the crystallization temperature reveals a joint contribution of melting and devitrification of the rigid amorphous fraction. The results confirm a link between secondary crystallization and vitrification of the rigid amorphous fraction in semicrystalline polymers. Secondary crystallization takes place in geometrically restricted areas, in which the polymer chains undergo large constraints, so that the mobility of the amorphous chain portions coupled with the crystal phase is reduced. Similarly, the gain in mobility upon partial melting of thinner and/or more defective crystals allows an increase in mobility of the coupled amorphous regions, which results in concurrent mobilization of the rigid amorphous fraction.

Effect of a Nanodispersed Clay Fillers on Glass Transition of Thermosetting Polyurethane

AbstractIn this work polyurethane (PU) matrix nanocomposite, obtained using an organically modified montmorillonite (OMM), was synthesized and characterized. An amount of organoclay ranging from 2% up to 6% by volume was added to the polyol component of the resin before mixing with isocyanate. The microstructure of the composites was investigated by X‐ray diffraction. The glass transition temperature (Tg) of PU nanocomposites, measured using differential scanning calorimeter, increases with increasing the volume fraction of OMM. On the other hand, the heat capacity increment, ΔCp, decreases from that the unfilled PU to that of the sample with 5.7% vol of OMM. Therefore a corresponding increase of the rigid amorphous fraction of PU nanocomposites with nanoclay was observed. Finally, the definition of molecular cooperativity was discussed for this system and the characteristic length of the cooperative region was determined, using the approach proposed by Donth.

Structure versus properties relationship of poly(lactic acid). I. Effect of crystallinity on barrier properties

AbstractPoly(lactic acid) is at present the most promising and commercially available bio‐based and biocompostable (bio)plastic. The properties of PLA, however, are rather poor, notably its low glass transition temperature Tg of ∼55 °C, its intrinsic low crystallization rate and the limited barrier properties with respect to water, oxygen and carbon dioxide in comparison with to oil‐based counterparts, notably polyesters (PET). In this manuscript we address the question of what could ultimately be achieved in terms of barrier properties when PLA is crystallized fully. In fact, this question is rather academic in view of the long crystallization/annealing times needed to obtain maximum crystallinity but serves the purpose of better understanding current limits and notably a better understanding of the role of crystallinity on the barrier properties. A correlation is made between crystallization, various morphological parameters and the barrier properties of PLA. Crystallization of PLA causes a decrease of the oxygen permeability, but not in linear proportion with the decrease in amorphous volume. We explain this in terms of influence of the space filling and the inner crystalline structure on gas transport properties. Furthermore we suggest that the presence of a rigid amorphous fraction with lower density can have strong impact on PLA gas permeability, in particular on the gas solubility coefficient of PLA. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 2247–2258, 2009

Quasi-isothermal temperature-modulated differential scanning calorimetry (TMDSC) for the separation of reversible and irreversible thermodynamic changes in glass transition and melting ranges of flexible macromolecules

Abstract With standard differential scanning calorimetry (DSC), it is possible to derive calorimetric data for equilibrium or metastable samples. The introduction of temperature-modulated DSC (TMDSC) permits in its quasi-isothermal (non-scanning) mode (TMDC), long-time apparent heat capacity measurements of high precision (±1 %). For flexible molecules, heat capacity measurements from the various calorimetric methods could be combined in the ATHAS Data Bank, which now contains experimental data for over 200 materials. These data were linked to the vibrational and large-amplitude motion of the constituent atoms and molecules, to provide a base for the judgement of the thermal analyses, extending outside the range of equilibrium or metastability with an error of only 2-5 %. The TMDC together with DSC is now able to quantitatively assess the reversibility of thermal processes. A sufficient number of systems have been analyzed in this fashion to develop better understanding of macro-, micro-, and nanophases of flexible macromolecules. The new concepts discussed are: (1) multiple glass transitions due to possible rigid-amorphous fractions (RAFs) and glass transitions within crystals, both observed in semicrystalline macromolecules, and (2) locally reversibly melting on the surface of chain-folded crystals. The locally reversible melting decreases with crystal perfection and also disappears when the chains become rigid.

Relationship between free volume properties and structure of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) membranes via various crystallization conditions

The relationship between the crystalline structure and the free volume properties within the amorphous phase of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) membranes, which were prepared via isothermal crystallization processes at various crystallization temperatures, was investigated. From the data of positron annihilation lifetime (PAL) spectroscopy over a temperature range of 25–90°C, the temperature dependence of free volume size, amount, distribution, and relative fractional free volume and thermal expansion behaviors of free volume were discussed. The existence of a rigid-amorphous fraction (RAF) which constrained long-range motions in the semi-crystalline polymer was demonstrated by DSC trace and considered to interpret the temperature dependence of those free volume properties. Based on the crystallization conditions, the effect of the crystallization rate of PHBV polymer was proposed to explain the thermal expansion coefficients of free volume size. The membranes crystallized at faster crystallization rate would accompany higher thermal expansion coefficients of free volume size and the larger free volume size at higher temperatures. Larger distribution of the free volume size and higher thermal expansivity of o-Ps lifetime dispersion (dσ/dt) of isothermally melt-crystallized membranes were observed as a result of the bimodal distribution of the lamellar periodicity, which was obtained by small-angle X-ray scattering (SAXS), and less amount of RAF than that of a cold-crystallized membrane. Conclusively, free volume size and thermal expansion of the free volume in PHBV membranes were affected by the kinetics of crystallization; comparatively, the total amount of free volume and fractional free volume were determined by the final crystallinity. The size distribution of free volume was associated with the crystalline lamellar structure which was dominated by the crystallization conditions.

Polymer nanocomposites with a uniform distribution of nanoparticles in a polymer matrix synthesized by the frontal polymerization technique

The use of frontal polymerization as an efficient technological method for synthesizing polymeric nanocomposites based on polyacrylamide/FeO, SiO2, YBa2Cu3O7 − x, polymethylmethakrylate/SiO2 is offered. The advantages of frontal polymerization (which promotes the deagglomeration of nanoparticles, as well as the uniform distribution and preservation of the nanoparticle sizes in the obtained nanocomposites) are shown. The influence of the size of the SiO2 particles (10 nm, 0.6 mkm, and 30 mkm) on the macrokinetic laws of methylmethacrylate’s frontal polymerization is investigated. It is shown that, during the poly-merization process, the interaction between methylmethacrylate macromolecules and the surface of nanoparticles is observed. As a result a rigid amorphous fraction of polymer is formed on the phase boundary, which leads to an appreciable change in the relative heat capacity, glass transition temperature, and dynamicmechanical properties of nanocomposites, depending on filling degree.

Novel polypropylene microporous membranes via spherulitic deformation – Processing perspectives

Abstract The processing boundaries for initiating intra-/inter-spherulitic deformation to create microporous polypropylene membranes by lamellar separation are delineated. The processing parameters are: annealing temperature, extension ratio, stretching rate, and stretching temperature. A fixed set of extrusion conditions was chosen for producing precursor films having similar spherulitic morphologies. The morphological changes indicating the occurrence of intra-/inter-spherulitic transition on a spherulitic scale can also be detected on a lamellar scale by WAXS examination via analysis of the α-form orientation index. Membrane porosity measurements showed a consistent correlation with the observed values of the α-form orientation index. Increasing the extension ratio did not change the microstructure in the non-annealed sample; however, the lamellae can be further oriented in the annealed samples. Inter-spherulitic deformation became obvious at slow stretching rates; intra-spherulitic deformation was favored at fast stretching rates. The DSC thermal analysis of the precursor films showed two significant endothermic discontinuities ( T 1 at 0 °C and T 2 at 40 °C) in both non-annealed and annealed precursor films; T 1 is believed to be the conventional T g of polypropylene whereas T 2 appears to originate from the rigid-amorphous fraction trapped within the lamellar “wells” where the amorphous phase is surrounded by the R-lamellae and the T-lamellae. The lamellae could break down or slip from the lamellar knots as stretching temperatures are high enough to minimize the influence of the rigid-amorphous fraction, and the annealed lamellae can still be oriented without a catastrophic cold-drawn deformation.

Study of crystalline and amorphous phases of biodegradable poly(lactic acid) by advanced thermal analysis

Abstract The qualitative and quantitative thermal analysis of biodegradable poly(lactic acid) PLA is presented. The glass transition, melting process, and heat capacity of a semi-crystalline poly(lactic acid) are studied utilizing the differential scanning calorimetry and temperature-modulated DSC. The mobile amorphous fraction, W a degree of crystallinity, W c and rigid-amorphous fraction, W RAF were estimated depending on the thermal history of semi-crystalline PLA. From qualitative thermal analysis, the glass transition of rigid-amorphous phase was observed as a broadening from the changes of heat-flow-rate between mobile glass transition temperature and melting temperature. The amount of the rigid-amorphous fraction (RAF) was evaluated from W RAF = 1− W c − W a and graphically was presented as the result of a deflection from the linearity of the dependence of the change of degree of mobile amorphous phase ( W a ) vs. the degree of crystalline fraction ( W c ) for semi-crystalline PLA with different thermal history. The degree of crystallinity of semi-crystalline samples of PLA can be discussed in terms of a two- or three-phase model. In contrast, the quantitative thermal analysis of the experimental apparent heat capacity of semi-crystalline PLA did not show any appearance of RAF in the examples of analyzed samples. The experimental heat capacity of PLA was analyzed in reference to the solid and liquid equilibrium heat capacities of poly(lactic acid) found in the ATHAS Data Bank.

Non-isothermal crystallization of PET/PLA blends

Binary blends of poly(ethylene terephthalate) with poly(lactic acid), PET/PLA, were studied by differential scanning calorimetry and X-ray scattering. The PET/PLA blends, prepared by solution casting, were found to be miscible in the melt over the entire composition range. Both quenched amorphous and semicrystalline blends exhibit a single, composition dependent glass transition temperature. We report the non-isothermal crystallization of (a) PET, with and without the presence of PLA crystals and (b) PLA, with and without the presence of PET crystals. PET can crystallize in all blends, regardless of whether PLA is amorphous or crystalline, and degree of crystallinity of PET decreases as PLA content increases. In contrast, PLA crystallization is strongly affected by the mobility of the PET fraction. When PET is wholly amorphous, PLA can crystallize even in 70/30 blends, albeit weakly. But when PET is crystalline, PLA cannot crystallize when its own content drops below 0.90. These different behaviors may possibly be related to the tendency of each polymer to form constrained chains, i.e., to form the rigid amorphous fraction, or RAF. PET is capable of forming a large amount of RAF, whereas relatively smaller amount of RAF forms in PLA. Like the crystals, the rigid amorphous fraction of one polymer component may inhibit the growth of crystals of the other blend partner.

Effect of thermal history on the free volume properties of semi‐crystalline poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) membranes by positron annihilation lifetime spectroscopy

AbstractFree volume properties of a series of poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) (PHBV) membranes, which were produced by various nonisothermal crystallization processes (rapid‐, step‐, and slow‐cooling processes), were investigated using positron annihilation lifetime (PAL) spectroscopy over a temperature range of 25–90 °C. From the annihilation lifetime parameters, the temperature dependence of free volume size, amount, size distribution, and fractional free volume and thermal expansion properties of free volume were discussed. A model which assumed that amorphous phase was subdivided into mobile and rigid amorphous fractions (MAF and RAF) in the semicrystalline polymer was considered to interpret the temperature dependence of those free volume properties. Morphological observation of the semicrystalline polymer by small‐angle X‐ray scattering (SAXS) indicated that the rapid‐cooled (cold‐crystallized) membranes showed a much thinner thickness of the repeating lamellar/amorphous layers and most likely higher amount of RAF, which restrained the chain motion, than the step‐ and slow‐cooled (melt‐crystallized) membranes. The difference of free volume properties among various PHBV membranes was created according to the crystalline structure of the polymer from different thermal history. The polymer crystallized with slower cooling rate induced higher crystallinity and resulted in less free volume amount and lower fractional free volume. In addition, the thermal expansion coefficients of free volume size were affected by the crystallization rate of PHBV polymer. Larger distribution of the free volume size of melt‐crystallized membranes was observed as a result of the bimodal distribution of the lamellar periodicity and less amount of RAF than that of the cold‐crystallized membranes. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 855–865, 2009

Chain confinement in electrospun nanofibers of PET with carbon nanotubes

Composite nanofibers of poly(ethylene terephthalate), PET, with multiwalled carbon nanotubes (PET/MWCNT) were prepared by the electrospinning method. Confinement, chain conformation, and crystallization of PET electrospun (ES) fibers were analyzed as a function of the weight fraction of MWCNTs. For the first time, we have characterized the rigid amorphous fraction (RAF) in polymer electrospun fibers, with and without MWCNTs. The addition of MWCNTs causes polymer chains in the ES fibers to become more extended, impeding cold crystallization of the fibers, resulting in more confinement of PET chains and an increase in the RAF. The fraction of rigid amorphous chains greatly increased with a small amount of MWCNT loading: with addition of 2% MWCNTs, RAF increased to 0.64, compared to 0.23 in homopolymer PET ES fibers. Spatial constraints also inhibit the folding of polymer chains, resulting in a decrease in crystallinity of PET. For fully amorphous PET/MWCNT composites, MWCNTs do not affect the chain conformation of PET in the ES fibers. For cold crystallized PET/MWCNT composite nanofibers, more trans conformers were formed with the addition of MWCNTs. The increase of RAF (chain confinement) is associated with an increase of the concentration of the trans conformers in the amorphous region as the MWCNT concentration increases in the semicrystalline nanofibers.