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     

An in-situ simultaneous SAXS and WAXS survey of PEBAX® nanocomposites reinforced with organoclay and POSS during uniaxial deformation

Poly(ether-block-amide) (PEBA), commercially known as PEBAX^®, nanocomposites filled with organically modified clay (Cloisite 30B) and trisilinolphenyl-polyhedral oligomeric silsesquioxane (tsp-POSS) were prepared by a melt mixing method, respectively. The structures of the nanocomposites were investigated using differential scanning calorimetry (DSC), Fourier transform infrared (FT-IR) spectroscopy, and in-situ simultaneous small and wide angle X-ray scatterings (SAXS and WAXS) during uniaxial deformation. The FT-IR spectra showed the hydrogen bonding between the fillers and the PEBA which helped to disperse the fillers in the polymer matrix. The crystallinities and mechanical properties of the nanocomposites were improved compared to the neat polymer. Their origins were studied with an in-situ simultaneous SAXS and WAXS technique during the uniaxial deformation.     

A Globule in a Stretching Field. The Role of Partial Melting During Drawing of Crystalline Polymers

Abstract

The statistical theory of solid polymers (without a solvent) is presented. Such problems as the neck formation, the α-relaxation transition, the calculation of the scale critical exponents are considered. The experimental data obtained are in excellent agreement with the theory. It is found that the dynamic properties of dilute polymer solutions in a good solvent are influenced by entanglement interactions. Therefore it is not necessary to introduce a new dynamic critical exponent. Ethylene-acrylic acids copolymers with the co-unit content ca 0.1 mol % and linear polyethylenes are studied by WAXS, SAXS, and infrared spectroscopy. Drawing and shrinkage behavior of these materials are also investigated. It is shown that the copolymer branches can be aggregated through intramolecular attraction. The entanglement concentration as revealed by SAXS and from shrinkage data is 0.07–0.08 mol % in high-oriented polyethylene.     

Relaxation behavior of layered double hydroxides filled dangling chain-based polyurethane/polymethyl methacrylate nanocomposites

A series of dangling chain based-polyurethane/poly(methyl methacrylate) (DPU/PMMA) filled with exfoliated layered double hydroxides (LDH) were synthesized by methyl methacrylate in-situ intercalative polymerization. The dangling chains were introduced by using vegetable oils as chain extender. The effect of dangling chain and the contents of LDH on the molecular dynamics of DPU/PMMA was investigated by a combination of dynamic mechanical analysis and broadband dielectric relaxation spectroscopy. Compared with polyurethane/poly(methyl methacrylate) (PU/PMMA) without dangling chain, the glass transition temperature (T_g) of DPU/PMMA shifts to lower temperature and the segmental dynamics becomes faster. A plateau with a high loss factor value above T_g significantly broadens the damping temperature range due to the synergy effect between the dangling chains and LDH layers. In DPU/PMMA/LDH nanocomposites, the α-relaxation associated with the glass transition of the polymer matrix becomes slower with the increase of LDH content, which indicates a restricted molecular mobility in the interfacial regions between polymer and LDH. However, the local relaxations at relatively low temperature remain unaffected by dangling chain or the addition of LDH. When the LDH content increases, Maxwell–Wagner–Sillars (MWS) interfacial polarization process caused by charge accumulation at interfaces becomes faster because of the smaller mean distance d between the exfoliated LDH layers.     

In situ polymerization of polyethylene/clay nanocomposites using a novel clay‐supported Ziegler‐Natta catalyst

Polyethylene/clay nanocomposites (PECNC) were synthesized via in situ Ziegler‐Natta catalyst polymerization. Activated catalyst for polymerization of ethylene monomer has been prepared at first by supporting of the cocatalyst on the montmorillonite (MMT) smectite type clay and then active complex for polymerization formed by reaction of TiCl₄ and aluminum oxide compound on the clay. Acid wash treatment has been used for increasing hydroxyl group and porosity of the clay and subsequently activity of the catalyst. The nanostructure of composites was investigated by X‐ray diffraction (XRD) and transmission electron microscopy (TEM). Obtained results show that silica layers of the mineral clay in these polyethylene/nanocomposites were exfoliated, intercalated, and uniformly dispersed in the polyethylene matrix even at very high concentration of the clay. Thermogravimetric analysis (TGA) shows good thermal stability of the PECNCs. Differential scanning calorimeter (DSC) results reveal considerable decrease in the crystalline phase of the PECNC samples. Results of permeability analysis show an increase in barrier properties of PECNC films. POLYM. COMPOS., 2009. © 2009 Society of Plastics Engineers     

Dynamic interplay between phase separation and crystallization in a poly(?-caprolactone)/poly(ethylene glycol) oligomer blend

We have investigated the crystallization effect on the phase separation of a poly(?-caprolactone) and poly(ethylene glycol) oligomer (PCL/PEGo) blending system using simultaneous small-angle light scattering and differential scanning calorimetry (SALS/DSC) as well as simultaneous small-angle X-ray scattering (SAXS), wide-angle X-ray scattering (WAXS), and DSC (SAXS/WAXS/DSC). When the PCL/PEGo system, of a weight ratio of 7/3, is quenched from a melt state (160 °C) to temperatures below the spinodal point and the melting temperature of PCL (63 °C), the structural evolution observed exhibits characteristics of (I) early stage of spinodal decomposition (SD), (II) transient pinning, (III) crystallization-induced depinning, and (IV) diffusion-limited crystallization. The time-dependent scattering data of SALS, SAXS and WAXS, covering a wide range of length scale, clearly show that the crystallization of PCL intervenes significantly in the ongoing viscoelastic phase separation of the system, only after the early stage of SD. The effect of preordering before crystallization revives the structural evolution pinned by the viscoelastic phase separation. The growth of SAXS intensity during the preordering period conforms to the Cahn-Hilliard theory. In the later stage of the phase separation, the PCL-rich matrix, of spherulite crystalline domains developed due to the faster crystallization kinetics, traps the isolated PEGo-rich domains of a slower viscoelastic separation.     

Wide-angle X-ray scattering study of crystalline orientation in reticulate-doped polymer composites

Reticulate doping consists of casting a composite film from a solution containing both a polymer and a charge-transfer complex (CTC) and allowing the conductive free radical salt to recrystallize as the solvent is removed from the polymer. In this study, a highly branched, low molecular weight polyethylene (PE) was doped with the CTC tetrathiafulvalene–tetracyanoquinodimethane (TTF–TCNQ). Wide-angle X-ray scattering (WAXS), conductivity, optical microscopy, stress relaxation, and differential scanning calorimetry (DSC) measurements were used to show the effect of the addition of filler and uniaxial orientation on the mechanical and electrical properties of the composites. It has been shown that increasing TTF–TCNQ concentration shifts the preferential orientation of the crystalline phase of the PE from slightly perpendicular to slightly parallel to the casting surface. WAXS measurements were made on samples that were uniaxially stretched at 80°C and cooled to room temperature. These experiments showed a smaller incremental increase in crystalline orientation with increasing TTF–TCNQ. This observation was consistent with a drop in initial relaxation times calculated from room temperature stress relaxation experiments. In the unoriented composites, increasing TTF–TCNQ loading had no effect on PE crystallinity; however, the increase in crystallinity caused by uniaxial stretching was decreased by the presence of TTF–TCNQ. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 70: 1785–1794, 1998     

Dielectric relaxation of monoesters based poly(styrene-co-maleic anhydride) copolymer

A series of alkyl-grafted copolymers based on styrene-maleic anhydride (SMA) copolymers were synthesized by esterification of SMA with several long chain normal aliphatic alcohols. The prepared copolymers were characterized by FT-IR and ¹H NMR and DSC. The dielectric behavior of these copolymers was investigated in the frequency 20–10⁵ Hz and temperature −40 to 180 °C ranges. Two relaxation processes were observed, α, and β-relaxation. The former is associated with the glass-rubber transition and is characterized by the Vogel–Fulcher–Tammann temperature dependence and the latter relaxation is related to the local motion of the ester side groups attached to the polymer backbone. The apparent activation energy for the β-relaxation was found to depend significantly on the alkyl chain length. The dielectric analysis of the β-relaxation process detected is discussed.     

Dielectric and thermal behavior of liquid crystalline comb-like polybutadiene-diols with mesogenic groups in side chains

Ordered polybutadiene-diols (LCPBDs) with the comb-like architecture were prepared by radical reaction of a 5-(4-{[4-(octyloxy)phenyl]azo}phenoxy)pentane-1-thiol with double bonds of telechelic HO-terminated polybutadiene (PBD); several polymers with various initial molar ratios of thiol to double bonds of PBD, R₀, in the range from 0 to 1 were prepared. DSC, polarizing microscopy, WAXS and dielectric relaxation spectroscopy (DRS) were employed to investigate their thermal and dielectric behavior in relation to morphology. DRS of the LCPBDs have revealed both collective and individual dynamic motions of molecules. Secondary β- and segmental α-relaxation were observed in unmodified PBD. In the LCPBDs, two secondary γ- and β- and two high-temperature α- and δ-relaxations were observed and assigned to specific molecular motions; all relaxations were analyzed and discussed in terms of time scale (Arrhenius diagram), magnitude (relaxation strength) and shape of the response.     

Calorimetric and dielectric study on poly(trimethylene terephthalate)/polycarbonate blends

Poly(trimethylene terephthalate) (PTT)/polycarbonate (PC) blends with different compositions were prepared by melt blending. The miscibility and phase behavior of melt-quenched and cold-crystallized blends were studied using differential scanning calorimetry (DSC) and dielectric relaxation spectroscopy. The blends of all compositions display only one glass transition (T _g ) in both states. The melting temperature and the crystallinity of PTT in the blend decrease with increasing PC content. The dielectric results for the melt-quenched blends, for PC content up to 60 wt.%, exhibited two merged relaxation peaks during the heating scan; the lower temperature relaxation peak represent the normal glass-transition (α) relaxation of the mixed amorphous phase and the higher temperature relaxation due to the new-constrained mixed amorphous phase after crystallization. Cold-crystallized blends displayed only one glass transition α-relaxation whose temperatures varied with composition in manner similar to that observed by DSC. The dielectric α-relaxation of cold crystallized blends has been analyzed. Parameters relating to relaxation broadening, dielectric relaxation strength, and activation energy were quantified and were found to be composition dependent. The PTT/PC blends could be considered as two-phase system, a crystalline PTT phase and a mixed amorphous phase consisting of a miscible mixture of the two polymers. However, the crystallinity was only detected for blends containing greater than 40 wt.% PTT.     

Time-electric field superposition in electrically activated polypropylene/layered silicate nanocomposites

This study investigated the microstructural evolution of PP/clay nanocomposites under electric field. The storage modulus, which is a kind of mirror of the microstructure, increases while an electric field (both AC and DC) is applied. It was found that time and the electric field strength can be superposed to yield a single mastercurve that is independent of the type and strength of the electric field. In addition, the shift factor scaled differently according to the field type. The SAXS and TEM data revealed that the AC field induces the microstructural evolution of the nanocomposites toward an exfoliated structure, while the DC field induces the alignment of silicate layers. In a DC field, the alignment process occurs as a result of dielectrophoretic motion. However, in an AC field, dielectric relaxation analysis showed that an exfoliation process arises as a result of the breakup of the charge balance.     

Dielectric Relaxation Dynamics of Clay-Containing Low-Density polyethylene Blends and Nanocomposites

Series of clay-containing nanocomposites have been prepared and investigated using frequency-domain dielectric spectroscopy at different temperatures. Different matrix materials have been used: neat low-density polyethylene (LDPE) with and without compatibilizer and co-continuous blends of LDPE with two grades of polystyrene-b-poly(ethylene-co-butylene)-b-polystyrene (SEBS) copolymers. Two major relaxation modes were detected in the dielectric losses of all the nanocomposites and associated with Maxwell–Wagner–Sillars interfacial polarization and dipolar relaxation, respectively. Characteristic relaxation rates, activation energies, dielectric strength, and shape parameters of these relaxation mechanismes were calculated and discussed for the LDPE/clay nanocomposites. The addition of compatibilizer was found to slightly increase the dielectric loss of the nanocomposites while slowing the dynamics due to an improved dispersion. When combined with a high loading of nanofiller (15%), the compatibilizer addition led to low-frequency dispersion. A new relaxation process was then observed for the nanocomposites with the blend matrix. Several speculations were made as to the origin of this phenomenon, all of which were related to the SEBS phase. POLYM. ENG. SCI., 60:968–978, 2020. © 2020 Society of Plastics Engineers     

Nanostructure and crystallisation kinetics of poly(ethylene oxide)/poly(4-vinylphenol-co-2-hydroxyethyl methacrylate) blends

Blends of poly(ethylene oxide) (PEO) and poly(4-vinylphenol-co-2-hydroxyethyl methacrylate) (PVPh-HEM) were studied by means of synchrotron small and wide angle X-ray scattering (SAXS and WAXS, respectively) and by differential scanning calorimetry (DSC). The DSC measurements were used in the determination of the Flory–Huggins interaction parameter and also to study the isothermal and non-isothermal crystallisation kinetics of the PEO/PVPh-HEM blend. The interaction parameter, χ₁₂, was found to be negative (between −0.5 and −2.5, approximately) and presented a significant dependence on the blend composition, which is expected for a system with specific interactions such as hydrogen bonding. From the kinetic studies with Kissinger, Friedman and Avrami models, it was shown that crystallisation of PEO chains is slower in the blend than in the pure polymer, despite the decrease in the energy barrier to the crystallisation with the increase in PVPh-HEM concentration.

From the SAXS and WAXS profiles, the nanostructure of the blend was elucidated, exhibiting the formation of PEO lamellae even in the blends containing high concentrations of PVPh-HEM, which are non-crystalline (as observed by the WAXS profiles). The thickness of the PEO lamellae (R_c, approximately 8 nm) remains almost unchanged with the blend composition, while the crystalline peaks, observed at 19.78 and 23.98°, vanish, and the WAXS profile exhibits only a non-crystalline halo. For the non-crystalline blends with high concentrations of PVPh-HEM, PEO chains keep their crystalline structural memory.     

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.     

Annealing of poly(trimethylene terephthalate)/polycarbonate blends

A blend of poly(trimethylene terephthalate) (PTT) and polycarbonate with a weight ratio of 50/50 was studied by means of differential scanning calorimetry (DSC) and dielectric spectroscopy (DS) after melt annealing that enables transesterification. The DSC results show that with increasing the residence time in the melt, the melting temperature and the heat of fusion of PTT crystals decrease. Prolonged thermal treatment at 300 °C gives rise to a copolymer that no longer reveals melting or crystallization. Additional annealing of such samples below the melting temperature of PTT results in restoration of the crystallization ability. The amorphous phase dynamics is studied by means of DS demonstrating that the glass transition relaxations are very sensitive to the crystallinity changes. The random copolymer is characterized by only one α-relaxation indicating a more or less homogeneous amorphous phase. In contrast to this, the physical blend and the block copolymers show two α-relaxation processes attributed to the existence of two amorphous fractions. Analysis of the relaxation process in terms of Vogel–Fucher–Tammann–Hesse model reveals a correlation between the fragility parameter and the extent of trans-reaction. The crystallization kinetics of the blocky copolymer determined from the changes of the dielectric constant with time are discussed and compared with pure PTT.     

In situ WAXS/SAXS structural evolution study during uniaxial stretching of poly(ethylene therephthalate) nanocomposites in solid state: Poly(ethylene therephthalate)/montmorillonite nanocomposites

This work investigates the solid state uniaxial stretching of neat polyethylene therephthalate, PET, and its montmorillonite, MMT, nanocomposites (0.3 wt % of MMT particles with different initial agglomerate sizes) showing intercalated and tactoid morphologies, followed by in situ WAXS and SAXS experiments under an X‐ray synchrotron source. The distinct nanocomposite morphologies were assessed by WAXS and transmission electron microscopy. The in situ WAXS experiments during stretching evaluated the evolution of phase's mass fractions and the average level of molecular orientation upon uniaxial deformation, and the in situ SAXS experiments assessed the evolution of craze‐like structures and void sizes. Multiscale structure evolution models are proposed and compared for neat PET and its nanocomposites. Main global mechanisms are identical although with distinct evolutions of phase mass fractions. Also craze‐like/voids structures evolve with distinct sizes. Intercalated MMT morphology induces an earlier formation of periodical mesophase, a retarded widening of craze‐like structures and the smallest void sizes.© 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Shish and its relaxation dependence of re-crystallization of isotactic polypropylene from an oriented melt in the blends with high-density polyethylene

Shish structure and its relaxation dependence of re-crystallization of isotactic polypropylene (iPP) from an oriented melt, caused by melting of shish kebab in original samples (indicated by 2D SAXS and 2D-wide-angle X-ray scattering experiments (2D WAXS) measurements), has been investigated by differential scanning calorimetry (DSC) and optical microscopy (OM). Shish was obtained by dynamic packing injection molding and its size was controlled by addition of high-density polyethylene (HDPE). An increase in shish size was observed with increasing of HDPE content, as indicated by an increase in the crystallization temperature for iPP during re-crystallization. This is understood as, on one hand, the overall decrease in viscosity by addition of HDPE, thus an increase in shear rate. Higher shear rate can promote larger orientation of molecules and continuous growth of shish structure. On the other hand, the relaxation mode of shish in the melt while re-crystallization is also dominated by its size. Shish with larger size has higher thermal stability and can endure more duration time in the melt. Even more, shish with a larger size cannot be transformed to random coil entirely even subjected to annealing at 200 °C for 60 min, and thus re-crystallization via self-seeding is always observed on primary nuclei originated from shish structure. A permanent ordered structure, most likely with chain helical conformation, is proposed for iPP with large shish size. However, shish with smaller size can only maintain for a short time and then relax into random coil completely, resulting in almost absence of self-seeding in re-crystallization. Re-crystallization of isotactic polypropylene was discussed based on: (1) self-seeding with respect to size of shish structure and (2) relaxation of shish with different size.     

Thermoplastic apparent interpenetrating polymer networks of polyurethane and styrene/acrylic acid copolymer obtained by melt mixing. Structure‐property relationships

Thermoplastic apparent interpenetrating polymer networks (thermoplastic‐AIPNs) were prepared at several compositions by melting and pressing of crystallizable polyurethane (CPU), based on butylene adipate glycol (BAG), and styrene/acrylic acid random copolymer (S/AA). Structure‐property relationships in the thermoplastic‐AIPNs were investigated by means of wide‐angle and small‐angle X‐ray scattering (WAXS, SAXS), differential scanning calorimetry (DSC), dynamic mechanical thermal analysis (DMTA), thermally stimulated depolarization currents (TSDC) techniques, dielectric relaxation spectroscopy (DRS) and several physico‐mechanical characterization techniques. The results obtained by the various techniques were critically compared to each other. They suggest that the two components show weak affinity to each other and that the thermoplastic‐AIPNs can be classified into two groups with high and low contents of CPU, showing essentially the behavior of CPU and S/AA, respectively. However, deviations from additivity and significant changes for several properties on addition of small amounts of either of the components suggest partial miscibility. Most of the results are explained by physical interactions of COOH‐groups of AA in S/AA with the ester groups of the flexible CPU blocks, which promote microphase separation in both the CPU and the S/AA components.     

Intercalation of Mg–Al layered double hydroxide by anionic surfactants: Preparation and characterization

The preparation and the characterization of intercalation compounds of Mg–Al layered double hydroxide (Mg–Al LDH) and various organic surfactants have been studied in detail. The preparation has been carried out following regeneration method. The aim of such organic modification is to prepare LDHs suitable for application in polymer-LDH nanocomposites. The LDH-surfactant hybrids have been characterized by wide angle X-ray scattering (WAXS) and Fourier transform infrared (FTIR) spectroscopy. The modified Mg–Al LDH materials show an increase in interlayer distance as compared to the unmodified Mg–Al LDH depending on the length of the surfactant anions. Thermal decomposition changed significantly after organic modification. The particle morphology was investigated by scanning electron microscopy (SEM).     

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