Small Amount Of Polystyrene Research Articles

Effect of polystyrene on poly(ethylene terephthalate) crystallization

Blends of poly(ethylene terephthalate) (PET) and polystyrene (PS) with PS content ranging from 0% to 60% by weight, were compounded in a laboratory internal mixer, followed by quenching into iced water, resulting in substantially amorphous compounds. Blend morphology was analyzed by scanning electron microscopy (SEM). Standard differential scanning calorimetry (DSC) was used to study the cold crystallization and melting behavior of PET and PET/PS blends. SEM micrographs show a two-phase structure made up with spherical PS particles dispersed in a PET matrix. DSC scans showed that crystallization of PET is affected by the heating rate and by the addition of even small amounts of PS. In particular, the rate of cold crystallization of PET is significantly reduced by the incorporation of 1% of PS, attributed to the anti-nucleating effect of PS on PET. The amount of PET crystallized and the melting characteristics (temperature, rate) are not significantly affected by either PS content or heating rate.

Inter-particle correlations in a hard-sphere colloidal suspension with polymer additives investigated by Spin Echo Small Angle Neutron Scattering (SESANS)

Using a neutron scattering technique that measures a statistically-averaged density correlation function in real space rather than the conventional reciprocal-space structure factor, we have measured correlations between poly(methyl-methacrylate) (PMMA) colloidal particles of several sizes suspended in decalin. The new method, called Spin Echo Small Angle Neutron Scattering (SESANS) provides accurate information about particle composition, including the degree of solvent penetration into the polymer brush grafted on to the PMMA spheres to prevent aggregation. It confirms for particles, between 85 nm and 150 nm in radius that inter-particle correlations closely follow the Percus-Yevick hard-sphere model when the colloidal volume-fraction is between 30% and 50% provided the volume-fraction is used as a fitted parameter. No particle aggregation occurs in these systems. When small amounts of polystyrene are added as a depletant to a concentrated suspension of PMMA particles, short-range clustering of the particles occurs and there is an increase in the frequency of near-neighbor contacts. Within a small range of depletant concentration, near-neighbor correlations saturate and large aggregates with power law density correlations are formed. SESANS clearly separates the short- and long-range correlations and shows that, in this case, the power-law correlations are visible for inter-particle distances larger than roughly two particle diameters. In some cases, aggregate sizes are within our measurement window, which can extend out to 16 microns in favorable cases. We discuss the advantages of SESANS for measurements of the structure of concentrated colloidal systems and conclude that the method offers several important advantages.

Particle-based transcutaneous administration of HIV-1 p24 protein to human skin explants and targeting of epidermal antigen presenting cells

Transcutaneous immunization is a promising vaccination strategy for the treatment of infectious diseases and cancer. In this study, we investigate the combination of cyanoacrylate skin surface stripping (CSSS) and particle-based antigen delivery to target the HIV-1 p24 protein to skin antigen presenting cells (APC). The CSSS treatment pre-activates skin APC and opens hair follicles, where protein-loaded particles accumulate and allow for sustained delivery of the loaded antigen to perifollicular APC. We found that poly-lactic acid (PLA) and polystyrene (PS) particles targeted the adsorbed HIV-1 p24 protein to the hair follicles. Small amounts of PS and PLA particles were found to translocate to the epidermis and be internalized by skin cells, whereas most of the particles aggregated in the hair follicle canal, where they released the loaded antigen. The p24 protein diffused to the epidermis and dermis and was detected in skin cells, especially in Langerhans cells and dermal dendritic cells. Furthermore, the combination of CSSS and particle-based delivery resulted in activation and maturation of Langerhans cells (HLA-DR, CD80 and CD83). We conclude that particle-based antigen delivery across partially disrupted skin barrier is a feasible and effective approach to needle-free transcutaneous vaccination.

A simple way of improving graphite nanoplatelets (GNP) for their incorporation into a polymer matrix

A simple method of solvent exfoliation/refining of direct-graphite nanoplatelets for their better incorporation into a polymer matrix is presented. We demonstrate the method for polystyrene. The method relies on sonication in N-methyl-2-pyrrolidone solvent, with surfactant assistance. A small amount of polystyrene is added to the solvent in order to increase the viscosity, this enhancing the exfoliation process and resulting in formation of a polymeric layer on graphene for its better incorporation in the polymer matrix. Polystyrene-coated thin graphene stacks form a stable dispersion, while thicker graphite nanoplatelets settle out. Thus bulk separation of thin and thick graphene stacks takes place. The polystyrene-coated thin graphene stacks are studied using Transmission Electron Microscopy in two ways: (i) we calculate the number of graphene layers forming thin graphene stacks, and (ii) we employ Selected Area Diffraction to confirm our image analysis results by checking the intensity ratio (1100) and (2100) deflections in the diffraction patterns. Five layers is found to be the cut-off number, that is there are no stacks >5 layers, and 3 layer stacks are dominantly present. The average largest in-plane dimension is found to be approximately 2.5 mu m (reduction by 50%).

Revisiting the Morphology Development of Solvent-Swollen Composite Polymer Particles at Thermodynamic Equilibrium†

Morphology of polystyrene (PS)/poly(methyl methacrylate) (PMMA)/toluene droplets, in which phase separation proceeds, dispersed in SDS aqueous solution was examined. It changed from ex-centered PS-core/PMMA-shell to hemisphere with increasing SDS concentration. At low polymer weight fraction (wp), PS and PMMA phases contained non-negligible amount of PMMA and PS, respectively. The small amount of PS and PMMA in PMMA and PS phases, respectively, affected significantly the interfacial tension between polymer/toluene and aqueous solutions. Interfacial tension between PS and PMMA phases at low wp was measured by the spinning drop method, showing a quite low value ( approximately 10-2 mN/m). Predicted morphology obtained from calculation of minimum total interfacial free energy of the droplets using the interfacial tensions agreed well with the experimental observation.

Strategies for Achieving Microcellular LDPE Foams in Extrusion

This paper describes the fundamental process design for achieving microcellular foams using low-density polyethylene (LDPE) in extrusion. Microcellular foams are classified as foams with cell densities larger than 109 cells/cm3 and cell sizes in the order of 10 micrometers. Supercritical CO2 was used as a blowing agent in microcellular foaming due to its high volatility, which greatly increases thermodynamic instability. Our previous studies have indicated that microcellular foams cannot be produced from pure LDPE in a conventional microcellular extrusion system because of the high activation energy for cell nucleation. To increase the cell-nuclei density, an attempt was made at reducing the free energy for bubble nucleation by heterogeneous cell-nucleation. LDPE blends, with a small amount of polystyrene (PS) and/or a nucleating agent, were employed to induce heterogeneous cell-nucleating spots. The amount of the PS phase was varied to determine the optimum content. Furthermore, the melt strength of LDPE was increased by crosslinking. Microcellular LDPE foams have been successfully obtained in extrusion and the materials and processing windows have been clearly identified. The amount of injected CO2 was varied in order to investigate its effect on the cell-population density.

Application of Fourier Transform Infrared Spectrometry and Chemometrics to Analysis of Polystyrene and Copolymerized Styrene in Ethylene-Styrene Copolymers

The physical properties of ethylene-styrene (ES) copolymers, like many other copolymers, are determined primarily by copolymer composition. ES copolymers may also contain a small amount of polystyrene. It is important to quantify the copolymerized styrene and polystyrene in ES copolymers. The difficulty associated with this analysis, however, arises from the fact that copolymerized styrene and polystyrene have a similar infrared spectrum. The quantitative analysis of ethylene-styrene copolymers by the Fourier transform infrared (FT-IR) technique, combined with the partial least squares (PLS) method, is described. The use of the PLS method facilitates the analysis. The PLS factors, which are calculated iteratively to maximize the covariance between the independent variable and the dependent variable in PLS, remove the collinearity problem present in the original spectral data, and make this analysis possible. The standard error of calibration (SEC) for 60 samples included in the calibration is 0.19% for polystyrene and 0.48% for copolymerized styrene. The standard error of prediction (SEP) for polystyrene and copolymerized styrene, calculated from 120 samples that were excluded from the calibration, is 0.25 and 0.51%, respectively.

Characterization and CO 2 sorption behaviour of polystyrene/polycarbonate blend system

The CO 2 sorption isotherms of samples of polystyrene/polycarbonate blends with different compositions which were prepared by casting from 1,4-dioxane solutions were obtained as a function of composition of the polymer blend at 25°C using a Cahn-sorption apparatus. The characterization of the polymer blend system was obtained from the point of thermal behaviour such as differential scanning calorimetry, X-ray diffraction, and 13C CP/MAS n.m.r. From the characterization of the polymer blend, it was confirmed that there was a small amount of crystallinity of polycarbonate. Basically the polymer blend system studied here is heterogeneous (i.e. phase-separated) but it was found that a small amount of polystyrene is partly miscible with polycarbonate and this probably disrupts the crystallization of polycarbonate especially at the higher polystyrene content. CO 2 sorption isotherms of the blend system including two homopolymers appeared to obey the dual mode sorption isotherm, which is a characteristic of the glassy state. The change of the CO 2 sorption amount for the polymer blend was mainly explained by the amount of the crystallite of polycarbonate, indicating that the effect of the partly miscible region on the CO 2 sorption behaviour is very small.

Processability and properties of yarns made from polypropylene containing small amounts of polystyrene

The effect of the addition of 2–8% by weight of commercial atactic polystyrene to fiber-grade polypropylene on the drawability of the multifilament yarn spun from the blends and on the mechanical properties and thermal shrinkage of the drawn yarns was studied. In the as-spun state, polystyrene is present in the form of near-spherical particles and improves the drawability and plastic deformation characteristics of the yarn. In the drawn state, with higher molecular orientation and more compact structure, the intrinsic rigidity of the polystyrene molecule manifests itself in the form of enhanced stiffness and greater creep resistance. © 1996 John Wiley & Sons, Inc.

Processability and properties of yarns made from polypropylene containing small amounts of polystyrene

The effect of the addition of 2–8% by weight of commercial atactic polystyrene to fiber-grade polypropylene on the drawability of the multifilament yarn spun from the blends and on the mechanical properties and thermal shrinkage of the drawn yarns was studied. In the as-spun state, polystyrene is present in the form of near-spherical particles and improves the drawability and plastic deformation characteristics of the yarn. In the drawn state, with higher molecular orientation and more compact structure, the intrinsic rigidity of the polystyrene molecule manifests itself in the form of enhanced stiffness and greater creep resistance. © 1996 John Wiley & Sons, Inc.

Effect of copolymers modifying PVC on its physical and mechanical properties and its UV‐radiation resistance. VIII. Thermal and photochemical stability of PVC films containing polystyrene and their permeability

AbstractThe influence of a polystyrene (PS) content of 1–5% in PVC films on their thermal stability, permeability of air and photooxidation, crosslinking, and photodehydrochlorination induced by 253.7 nm wavelength radiation was investigated.It was found that a small amount of PS in PVC films causes an increase of the permeability of air through these films and does not affect their thermal stability, but evidently improves their photochemical resistance hampering the photodehydrochlorination, crosslinking and photooxidation of PVC.These degradation processes change the thermal stability of the samples. Smaller changes observed in samples containing PS confirm its photostabilizing effect on PVC. Visible differences between the values of thermal parameters depending on the efficiency of photochemical reaction point out the sensitivity of derivatographic measurements on conversion of PVC caused by UV‐radiation.

Morphology-property relationships in polycarbonate-based blends. II. Tensile and impact strength

Abstract The tensile and Izod impact strength of polycarbonate (PC) based polyethylene (PE) and polystyrene (PS) blends has been examined. The tensile strength can best be described as being proportional to an exponential function of the volume fraction of PE and the first power of volume fraction of PS. The variation of Izod impact strength with composition also differs considerably for the two blends, a small amount of PS causing a marked drop in impact strength. The impact strength of the PE/PC blend is related to the area under the tensile stress-strain curve, whereas for PS/PC blends no correspondence is found. The variation in properties is related to the composition, morphology, interfacial adhesion at the phase boundary and failure surfaces of the various blends.

Preparation of Block Copolymer of ε-Caprolactone with Living Polystyrene

Abstract ε-Caprolactone was polymerized by using living polystyrene prepared by means of an anionic polymerization technique. A gross polymer was elution-fractionated into four fractions which were methanol-soluble low-molecular-weight polyester, high-molecular-weight polyester, a small amount of polystyrene and polystyrene-polyester block copolymer. Both yields and molecular weights of block copolymers were observed to be higher in benzene than in tetrahydrofuran. Formation of block copolymers was concluded from the results of an elementary- and infrared analyses and turbidometry. Polymerization mechanism of ε-caprolactone is discussed.