Amorphous PS Research Articles

Visualizing the selective localization of carbon nanotubes in immiscible polymer blends

AbstractThis paper examines the migration mechanisms of multiwalled carbon nanotubes (MWCNTs) in 80/20 polyvinylidenefloride/polystyrene (PVDF/PS) and 80/20 polyvinylidenefloride /polycaprolactone (PVDF/PCL) blends. We contrasted the migration of MWCNTs in a low‐viscosity, semi‐crystalline PCL phase versus that in a high‐viscosity, amorphous PS phase. With a 1 vol% loading of MWCNTs, the PVDF/PCL system required 54% higher processing work relative to the neat blend, while the PVDF/PS system required 360% higher work. A visualization system was used to capture the changes in the structure of the blend throughout the mixing process. The structural changes in the blend were correlated with the processing Work and the morphology through electron microscopy. Using the Young equation, for the PVDF/PCL blend, MWCNT is predicted to have a thermodynamic affinity to migrate to the interface, while preferring to remain in the PVDF phase for the PVDF/PS system. However, in practice, for the PVDF/PCL system, the MWCNTs are localized in the PCL phase, while the MWCNTs remained scattered between the PS and PVDF phases for the PVDF/PS system. The viscoelastic properties of the polymers, specifically the viscosity of the minor component, played a crucial role in the migration mechanism. Due to a better dispersion of MWCNTs, the rheological and electromagnetic properties of the PVDF/PCL system are significantly higher.Highlights In‐situ visualization of carbon nanotubes migration during blending. Examining the influence of viscosity of the blend on the migration of nanofiller. Correlating the torque of mixing to the morphology of blends.

Regression analysis for the determination of microplastics in sediments using differential scanning calorimetry

This research addresses the growing need for fast and cost-efficient methods for microplastic (MP) analysis. We present a thermo-analytical method that enables the identification and quantification of different polymer types in sediment and sand composite samples based on their phase transition behavior. Differential scanning calorimetry (DSC) was performed, and the results were evaluated by using different regression models. The melting and crystallization enthalpies or the change in heat capacity at the glass transition point were measured as regression analysis data. Ten milligrams of sea sand was spiked with 0.05 to 1.5 mg of microplastic particles (size: 100 to 200 µm) of the semi-crystalline polymers LD-PE, HD-PE, PP, PA6, and PET, and the amorphous polymers PS and PVC. The results showed that a two-factorial regression enabled the unambiguous identification and robust quantification of different polymer types. The limits of quantification were 0.13 to 0.33 mg and 0.40 to 1.84 mg per measurement for semi-crystalline and amorphous polymers, respectively. Moreover, DSC is robust with regard to natural organic matrices and allows the fast and non-destructive analysis of microplastic within the analytical limits. Hence, DSC could expand the range of analytical methods for microplastics and compete with perturbation-prone chemical analyses such as thermal extraction–desorption gas chromatography–mass spectrometry or spectroscopic methods. Further work should focus on potential changes in phase transition behavior in more complex matrices and the application of DSC for MP analysis in environmental samples.

Approach to quantify the resistance of polymeric foams against thermal load under compression

Abstract Nowadays, numerous techniques are used to quantify the resistance of cellular polymers against a thermal load. These techniques differ in significance and reproducibility and are all dependent on foam density, structure (i.e., cell size and -distribution) and sample geometry. Very different behaviors are expected for extrusion- and bead foams, as well as for amorphous and semi-crystalline polymers. Moreover, established tests use temperature ramps which would lead to temperature gradients within the sample and thus to faulty results. In this study, we developed a new approach from an engineering perspective to minimize these influences. In this approach, the resistance against the thermal load is derived from a steady creep test with defined temperature steps under a mechanical load, which is specifically set for each foam sample depending on its static compression behavior at room temperature. The two-stage test therefore combines (i) a standard quasi-static compression test at room temperature and (ii) a creep test with stepwise increased thermal loading. For each foam type, a rather low mechanical load (stress) is determined from the quasi-static compression test at room temperature; low enough to remain below the collapse strength and avoid irreversible deformation (i.e., buckling and/or breaking of the cell walls). This load is then applied in a creep test where the temperature is increased in defined steps from room temperature to a temperature close to T g or T m . The stepwise increase and holding of the temperature for a defined time enables a homogeneous temperature in the test specimen. The approach was applied to (i) polystyrene extrusion and bead foams (i.e., XPS and EPS), which have different foam structure, (ii) amorphous and semi-crystalline bead foams of polystyrene (EPS) and polypropylene (EPP), (iii) bead foams with different densities (30, 60, 120, and 210 kg/m3) and (iv) to a new type of bead foam made of the engineering polymer polybutylene terephthalate (E-PBT). The termination criterion for the test is defined as the temperature at which a relative compression of 10% is reached in the creep test with temperature steps. We suggest calling it the heat stability temperature T HS. For the studied foams, the procedure delivers characteristic T HS values that allow a good comparison between different polymer matrices and densities. The heat stability temperature T HS of amorphous PS foams (i.e., XPS and EPS) was determined to be 98 °C, which is close to the glass transition temperature T g . Using the same approach, values of 99–107 °C were determined for EPP and 186 °C for the semi-crystalline bead foam E-PBT.

Disperse-within-disperse patterning on ternary/binary mixed-brush single crystals using polyaniline, polystyrene and poly(methyl methacrylate) grafts

Novel binary rod-coil and ternary rod-coil-coil mixed-brushes were designed using poly(ethylene glycol) (PEG)-b-poly(styrene) (PS), PEG-b-poly(methyl methacrylate) (PMMA), and PEG-b-polyaniline (PANI) block copolymers. In the current rod-coil mixed-brushes, the brush osmotic pressure did not absolutely affect the surface morphology, instead, the rigidity or flexibility of brushes was a dominant factor. The flexibility of coily PS brushes caused them to be easily entered into the system compared to the rod brushes with higher osmotic pressure, thereby they composed the matrix phase. In a similar growth condition but with packed pancake PMMA brushes, a more faise osmotic pressure was detected for PANI nanorods in the vicinity of PMMA brushes compared to PS ones. A higher faise osmotic pressure for PANI nanorods reflected the lower diameter dispersity and population of PANI nanorods in PEG-b-PMMA/PEG-b-PANI compared to PEG-b-PS/PEG-b-PANI. Via enhancing the amorphous brushes molecular weight, in a constant PANI nanorods molecular weight, the diameter dispersity and population of PANI nanorods increased. The PANI nanorods diameter in binary PS/PANI and PMMA/PANI mixed-brushes ranged in 6–10 nm. With elevating the crystallization temperature, no changes were detected in the morphology of rod-coil mixed-brush single crystals. In the novel ternary mixed-brushes with the amorphous PS and PMMA brushes and the PANI nanorods, the PANI nanorods were dispersed within both matrix (PS) and disperse (PMMA) phases. In these systems, the PANI diameters were 6 and 7 nm in PMMA disperses and 6–9 nm in PS matrix phase. The overall PANI nanorods population was in the range of 594–1392 for binary mixed-brushes. Furthermore, in ternary structures, the PANI overall populations were about 222 and 316 in PMMA and PS phases, respectively. Generally, in all binary and ternary mixed-brush systems, the amorphous brushes (PS and PMMA), due to their flexibility could be arranged in the vicinity of each other in a more facile manner compared to the PANI nanorods, they thus developed matrix phase.

Electrical percolation and crystallization kinetics of semi-crystalline polystyrene composites filled with graphene nanosheets

Syndiotactic polystyrene (sPS) is a semi-crystalline polymer with high melting temperature and good mechanical strength. Composites of sPS filled with different contents of graphene nanosheets (GNS) are prepared by coagulation method. Two types of GNS with different thicknesses (denoted as G1 and G10) are studied to unveil the effect of aspect ratio on electrical conductivity and crystallization kinetics of the composite. Atomic force microscopy and transmission electron microscopy (TEM) show that G1 is a wrinkled sheet with an average thickness of ∼2 nm and that G10 is a smooth flake with a thickness of ∼50 nm; both possess a similar basal dimension of ∼5 μm. The percolation thresholds for electrical conductivity (φc) of the G1-filled and G10-filled composites are 0.46 and 3.84 vol%, respectively. At a given GNS content, the electrical conductivity of the G1-filled composites is higher than that of the G10-filled composites. Both findings are attributed to the larger GNS aspect ratio of G1 compared with G10. The deduced φc of the G1-filled composites is significantly larger than that of GNS-filled amorphous atactic PS composites, indicating that the crystallizability of the matrix has an important influence on formation of GNS networks. Both G1 and G10 nanofillers are found to be good nucleating agents for the heterogeneous nucleation of sPS. Because of its wrinkled surface, G1 is less effective than G10 in inducing sPS crystallization. Compared with 2D sheet-like GNS, 1D CNTs are more effective in enhancing sPS crystallization through surface-induced nucleation as well as the chain-tube wrapping behavior in the sPS/CNT composites.

Phase morphology, thermomechanical, and crystallization behavior of uncompatibilized and PP‐g‐MAH compatibilized polypropylene/polystyrene blends

ABSTRACTIn this article, we discuss the phase morphology, thermal, mechanical, and crystallization properties of uncompatibilized and compatibilized polypropylene/polystyrene (PP/PS) blends. It is observed that the Young's modulus increases, but other mechanical properties such as tensile strength, flexural strength, elongation at break, and impact strength decrease by blending PS to PP. The tensile strength and Young's modulus of PP/PS blends were compared with various theoretical models. The thermal stability, melting, and crystallization temperatures and percentage crystallinity of semicrystalline PP in the blends were marginally decreased by the addition of amorphous PS. The presence of maleic anhydride‐grafted polypropylene (compatibilizer) increases the phase stability of 90/10 and 80/20 blends by preventing the coalescence. Hence, finer and more uniform droplets of PS dispersed phases are observed. The compatibilizer induced some improvement in impact strength for the blends with PP matrix phase, however fluctuations in modulus, strength and ductility were observed with respect to the uncompatibilized blend. The thermal stability was not much affected by the addition of the compatibilizer for the PP rich blends but shows some decrease in the thermal stability of the blends, where PS forms the matrix. On the other hand, the % crystallinity was increased by the addition of compatibilizer, irrespective of the blend concentration. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42100.

A study on the morphology of polystyrene-grafted poly(ethylene-alt-tetrafluoroethylene) (ETFE) films prepared using a simultaneous radiation grafting method

The morphology of polystyrene-grafted poly(ethylene-alt-tetrafluoroethylene) (ETFE) films prepared using a simultaneous radiation grafting method was investigated using DMA, DSC, XRD, and SAXS instruments. The DMA study indicates that the ETFE amorphous phase and PS amorphous phase are mixed well in the PS-grafted ETFE films while the ETFE crystalline phase and the PS amorphous phase are separated, suggesting that the PS chains are grafted mainly on the ETFE amorphous regions. The DSC and XRD data showed that the natural crystalline structures of ETFE in the grafted ETFE films are not affected by the degree of grafting. The SAXS profiles displayed that the inter-crystalline distance of the ETFE films increases with an increasing degree of grafting, which further implies that the PS graft chains formed by the simultaneous irradiation has a significant impact on the amorphous morphology of the resulting grafted ETFE film. Thus, these results indicate that the styrene monomers are mainly grafted on the ETFE amorphous regions during the simultaneous radiation grafting process.

Linear and nonlinear rheological behavior and crystallization of semicrystalline poly(styrene)–poly(l-lactide) block copolymers

The rheological behavior of a poly(styrene)–poly(l-lactide) (PS–PLLA) block copolymer was investigated in the viscoelastic linear and nonlinear regime. Large amplitude oscillatory shear (LAOS) experiments in the nonlinear regime led to an exponential decay of the G moduli and the nonlinearity parameter I3/1. During LAOS, the lamellar microstructure of a low molecular weight PS–PLLA copolymer was orientated parallel to the shear field to achieve a macroscopically ordered material. The degree of orientation was analyzed via small angle X-ray scattering (SAXS) measurements. The crystallization kinetics could be accurately described by the Avrami equation as determined by DSC and rheology. These experiments revealed that the crystallization process was slower for the PS–PLLA copolymers than for the PLLA homopolymers. SAXS was also used to monitor the crystallization of the PS–PLLA copolymers. When the temperature of the crystallization experiments, Tc, was lower than the glass transition temperature of the amorphous PS block, Tga (hard confinement), the lamellar microstructure of the low molecular weight PS–PLLA was maintained apart from a small increase in the domain spacing. When Tc was higher than Tga of PS (soft confinement), the block copolymer also retained its lamellar structure, but the increase in the domain spacing was unexpectedly increased compared to what occurred for crystallization under hard confinement conditions. In addition, two-dimensional (2-D) SAXS diffractograms indicated a loss of the structure periodicity during crystallization under soft confinement.

Elaboration of highly hydrophobic polymeric surface — a potential strategy to reduce the adhesion of pathogenic bacteria?

Different polymeric surfaces have been modified in order to reach a high hydrophobic character, indeed the superhydrophobicity property. For this purpose, polypropylene and polystyrene have been treated by RF or μwaves CF4 plasma with different volumes, the results were compared according to the density of injected power. The effect of pretreatment such as mechanical abrasion or plasma activation was also studied. The modified surfaces were shown as hydrophobic, or even superhydrophobic depending of defects density. They were characterized by measurement of wettability and roughness at different scales, i.e. macroscopic, mesoscopic and atomic. It has been shown that a homogeneous surface at the macroscopic scale could be heterogeneous at lower mesoscopic scale. This was associated with the crystallinity of the material. The bioadhesion tests were performed with Gram positive and negative pathogenic strains: Listeria monocytogenes, Pseudomonas aeruginosa and Hafnia alvei. They have demonstrated an antibacterial efficiency of very hydrophobic and amorphous PS treated for all strains tested and a strain-dependent efficiency with modified PP surface being very heterogeneous at the mesoscopic scale. Thus, these biological results pointed out not only the respective role of the surface chemistry and topography in bacterial adhesion, but also the dependence on the peaks and valley distribution at bacteria dimension scale.

Adopting the Experimental Pressure Evolution to Monitor Online the Shrinkage in Injection Molding

In this work, a procedure is reported which is suitable to analyze online the quality of molded parts in terms of shrinkage. The procedure is based on the evaluation of the average solidification pressure, namely the average along the thickness of the pressure at which each layer solidifies, a parameter which is known to correlate well with shrinkage. The calculation of this parameter normally requires the estimation of the solidification history, information which is currently not reachable experimentally. The procedure reported in this work allows adoption of the pressure evolution measured by a piezoelectric pressure transducer to make an estimation of the solidification profile and thus of the average solidification pressure. The procedure is applied to the data of shrinkage measured on an amorphous PS and a semicrystalline iPP in a wide range of processing conditions.

Orientation distribution in injection molding: a further step toward more accurate simulations

In this work, a viscoelastic model was applied to describe the evolution of molecular orientation in injection molding. This model is an evolution of a previously applied nonlinear Maxwell model, in which the relaxation time was allowed to depend on a structural parameter rather than on shear rate as considered in our previous works. The parameter chosen was the difference between the two main eigenvalues of the molecular conformation tensor. The model was applied to some injection molding tests carried out on an amorphous PS. The results in terms of orientation were discussed, also in comparison with the results of the previous model in which relaxation time depended on shear rate. It was found that, apart from being much sounder on a physical basis, the model also introduces improvements on the description of experimental data.

A Novel Crystallization Scheme in Poly[styrene‐block‐(ferrocenyl dimethylsilane)] Diblock Copolymers

AbstractIsothermal crystallization of the poly(ferrocenyl dimethylsilane) (PFDMS) segments in a poly[styrene‐block‐(ferrocenyl dimethylsilane)] (PS‐b‐PFDMS) diblock copolymer of lamellar micro‐morphology has been investigated. The PFDMS is shown to crystallize in a confined and grain‐by‐grain fashion. Here a ‘grain’ is defined as an ensemble of stacked lamellae wherein the PFDMS crystallization spreads quickly but stops at its surroundings. Such crystallization propagates not only along the PFDMS lamellae but across the amorphous PS layers as well. We suggest that conformational changes in the PS as induced by the PFDMS crystallization (‘squeezing transfer’) are responsible for the latter pathway of the crystallization's spread.magnified image

Block copolymers as dispersants and migration inhibitors: incorporation of fluorescent dyes in polyethylene

AbstractThe problem of dye migration in PE which is of importance for coating and packaging applications was examined with fluorescent colorant C.I. Solvent Yellow 43 as a model of fluorescent dye poorly soluble in PE. These types of dyes are soluble in the PE melt, they show however a strong tendency to crystallize on cooling and to migrate on the surface giving rise to the typical blooming effect. It could be demonstrated by different migration tests that on addition of P(EB)-b-PEO or SEBS block copolymers, having one sequence selectively miscible with PE, the other with the dye, prevent to a very large extent the dye migration and thus its surface crystallization (blooming). This improvement is attributed to the formation, in the PE amorphous phase, of PEO and PS microdomains respectively that are able to solubilize selectively the dye. By fluorescence spectroscopy it could be demonstrated that the dye is selectively solubilized in the PEO microdomains of the P(EB)-b-PEO block copolymer, as well for micelles formed in heptane, as for the blends with PE.

Crystallization-induced order in polystyrene-poly(ethylene oxide) metallo-supramolecular diblock copolymer

The solid-state morphology of polystyrene-poly(ethylene oxide) metallo-supramolecular diblock copolymer PS20-[Ru]-PEO70, has been investigated by small-and wide-angle X-ray scattering and atomic force microscopy. Above the melting point of PEO the metal–ligand complexes and their associated counter ions are known to form aggregates within the still disordered polymer matrix of PS and PEO. Crystallization of PEO induces microphase separation between the PS and the PEO blocks. In addition, the metal–ligand aggregates are forced out of the crystalline PEO part and subsequently order at the interface in the amorphous PS block into a (short-range) square lattice.

Phase Transitions in Thin Films of a Diblock Copolymer Composed of a Linear Polymer Block and a Brush Polymer Block with Mesogenic Oligothiophenyl Bristles

In this study, we quantitatively investigated the temperature-dependent phase transition behaviors in thin films of an interesting semirod−coil diblock copolymer, poly(styrene)-b-poly(oligothiophene side chain modified isoprene) (PS-b-POTI), and the resulting morphological structures using synchrotron grazing incidence X-ray scattering combined with differential scanning calorimetry. These analyses provided detailed information about the morphologies of the phase-separated domains and the molecular structures formed in each domain. At room temperature, the diblock copolymer molecules in thin films were found to form an alternately stacked structure comprised of amorphous PS and smectic-A POTI microdomains whose stacking direction is parallel to the film plane. On heating, the films underwent a phase transformation to a hexagonal cylinder structure with cylindrical POTI domains in the PS matrix oriented normal to the film plane. This phase conversion is induced by the transformation of the POTI domains fro...

Solid‐state blending of poly(ethylene terephthalate) with polystyrene: Extent of compatibilization and its dependence on blend composition

AbstractPolystyrene (PS) and poly(ethylene terephthalate) (PET) were blended together in the solid state via cryogenic mechanical attrition (CMA) and in the melt through conventional twin‐screw extrusion. Consecutive modulated differential scanning calorimetry (MDSC) and thermogravitometric analysis (TGA) investigations allowed for the quantitative estimation of the extent of blend compatibility through the accurate determination of sample composition. The extent of blend compatibility, i.e., the amount of PET calculated to have been removed from the bulk and into interphase entanglements with PS, was found to be higher for milled blends than for extruded blends. This compatibility enhancement was the most pronounced for PET‐rich blends. The other benefits of CMA are more precise compositional homogeneity through intimate mixing and the ability for more amorphous PET chains to be entangled with the amorphous PS phase at the interphase. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers

On the measurement and modeling of viscosity of polymers at low temperatures

Viscosity was measured for three amorphous polymers, PS, PMMA and PC, down to temperatures well below those normally available. Measurements were made in the dynamic mode and the Cox–Merz rule was applied to obtain the shear viscosity versus shear rate data. The Carreau–Yasuda viscosity model with WLF-type temperature dependence was found to provide good fits to the measured data over a wide range of temperatures.

Synthesis and crystallization behaviors of poly(styrene- b-isoprene- b- ε-caprolactone) triblock copolymers

The triblock copolymers, poly(styrene- b-isoprene- b- ε-caprolactone)s (PS- b-PI- b-PCL) have been synthesized successfully by combination of anionic polymerization and ring-opening polymerization. Diblock copolymer capped with hydroxyl group, PS- b-PI-OH was synthesized by sequential anionic polymerization of styrene and isoprene and following end-capping reaction of EO, and then it was used as macro initiator in the ring-opening polymerization of CL. The results of DSC and WAXD show big effect of amorphous PS- b-PI on the thermal behaviors of PCL block in the triblock copolymers and the lower degree of crystalline in the triblock copolymer with higher molecular weight of PS- b-PI was observed. The real-time observation on the polarized optical microscopy shows the spherulite growth rates of PCL 27, PCL 328 and PS- b-PI- b-PCL 344 are 0.71, 0.46 and 0.07 μm s −1, respectively. The atomic force microscopy (AFM) images of the PS 90- b-PI 66- b-PCL 28 show the columns morphology formed by it’s self-assembling.

Effect of Crystallization on the Lamellar Orientation in Thin Films of Symmetric Poly(styrene)-b-poly(l-lactide) Diblock Copolymer

The effect of crystallization on the lamellar orientation of poly(styrene)-b-poly(l-lactide) (PS−PLLA) semicrystalline diblock copolymer in thin films has been investigated by atomic force microscopy (AFM), transmission electronic microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). In the melt state, microphase separation leads to a symmetric wetting structure with PLLA blocks located at both polymer/substrate and polymer/air interfaces. The lamellar period is equal to the long period L in bulk determined by small-angle X-ray scattering (SAXS). Symmetric wetting structure formed in the melt state provides a model structure to study the crystallization of PLLA monolayer tethered on glassy (Tc < Tg,PS) or rubber (Tc > Tg,PS) PS substrate. In both cases, it is found that the crystallization of PLLA results in a “sandwich” structure with amorphous PS layer located at both folding surfaces. For Tc ≤ Tg,PS, the crystallization induces a transition of the lamellar orientation from parallel to perpendicular to substrate in between and front of the crystals. In addition, the depletion of materials around the crystals leads to the formation of holes of 1/2L, leaving the adsorbed monolayer exposure at the bottom of the holes. In contrast, the adsorbed monolayer on the substrate with thickness of 1/2L does not change in parallel orientation and thickness upon crystallization. When Tc > Tg,PS, no perpendicular lamellae and holes could be observed due to the high mobility of molecules.

Toward Reconciling STEM and SAXS Data from Ionomers by Investigating Gold Nanoparticles

To date, the sizes of the nanoscale ionic aggregates present in ionomers as determined by scanning transmission electron microscopy (STEM) experiments are inconsistent with small-angle X-ray scattering (SAXS) data interpreted by the Yarusso−Cooper model. To address this discrepancy, we have investigated a pair of model nanoparticles (11- and 55-atom Au clusters) with both STEM and SAXS. To mimic ionic aggregates, these nanoparticles were supported by amorphous PS films of predetermined thickness. While the size of the STEM probe was inconsequential to the resolution and measurement of the particles, the optimal specimen thickness was determined to be less than 50 nm. SAXS was performed on dilute solutions of the nanoparticles and fit using a monodisperse, noninteracting hard-sphere form factor model. For Au 11, STEM finds a diameter of 1.3 ± 0.14 nm and SAXS finds a diameter of 1.4 nm. Similarly, both STEM and SAXS determine a diameter of 1.7 nm for Au 55. For a combined system of Au 11 and Au 55, STEM data suggests a bimodal distribution of particle sizes consistent with those of the individual particles while SAXS data indicate hard spheres with diameter of 1.6 nm. Analysis of this model system has allowed us to optimize several experimental conditions of potential importance in reconciling STEM and SAXS data from ionomers.