Temperature dependent elastic-plastic behaviour of polystyrene studied using AFM force-distance curves

Force-displacement curves have been obtained on two polystyrene samples, having different molecular weight, at various temperatures and probe rates using an atomic force microscope. The force-displacement curves have been analysed using a novel method, which extends continuum elastic contact theories also to the plastic deformations. The Young's modulus and the yielding force of the two polystyrene samples have been determined as a function of temperature and frequency. It was also possible to calculate the Williams-Landel-Ferry coefficients for measurements above the glass transition temperature, and the viscoelastic activation energy for measurements below the glass transition temperature using the Arrhenius equation. All the calculated coefficients were in very good agreement with the literature values. The measured quantities span a wide range of temperature (85 °C) and frequency (eight decades) and the shifts of all the quantities calculated from force-displacement curves obey the Williams-Landel-Ferry and Arrhenius equation with the same parameters. Quantitative and qualitative comparison of the Young's modulus, of the stiffness in the plastic region and of the yielding force of the two polystyrene samples revealed different viscoelastic behaviour because of the variation in glass transition temperature of the two samples, due to their difference in the molecular weight.     

Thermal decomposition of polystyrene

Kinetic studies on the decomposition of polystyrene samples with molecular weights ranging from 900 to 1.8 × 10⁶ have been carried out making use of the differential thermogravimetric and differential scanning calorimetric techniques. Changes in molecular weight distributions with decomposition, at different temperatures or times, have been studied by gel permeation chromatography. This technique was likewise used to carry out component splitting of the undecomposed polymer samples. These components have been shown to break down statistically primarily by a process of random scissions yielding lower molecular weight products. The major portion of the observed weight loss, by the volatilization of small chain segments, is attributed to a rapid and complete depolymerization of chains. These interpretations are based on changes in polydispersity occurring during the decompositions. Similar components, decomposing in a different manner but under identical operating conditions, are suspected of being different stereoregular forms of the polymer. The order of reaction as computed from the method of Freeman and Carroll has been found to be zero for random scissions and one for the process of depolymerization. The activation energy computed by the method of Coats and Redfern was found to increase with molecular weight reaching a maximum value in the 10⁵ molecular weight range.     

Molecular dynamics simulation of diffusion of hydrogen and its isotopic molecule in polystyrene

Polystyrene is one of the target materials used in Inertial Confinement Fusion (ICF). Molecular dynamics simulations are performed in this report to study the diffusion of gases, including hydrogen and its isotopic molecule under normal temperature and pressure. According to the Mean Square Displacement (MSD) of the gas moving in polystyrene, the diffusion coefficient of hydrogen, deuterium and tritium in different molecular weight polystyrene were obtained. The calculated diffusion coefficients agree well with the results of former simulation studies. The diffusion coefficients of polystyrene of the same molecular weight gradually decrease along with the increase of mass fraction of hydrogen isotopes (hydrogen, deuterium and tritium). The study also finds that diffusion coefficients will decrease along with the increasing of polystyrene molecular weight. Moreover, the pair correlation functions, cohesive energy density and fractional free volume were studied corresponding to hydrogen isotopes diffusion coefficients.     

Influence of microstructure on dynamic mechanical behaviour of polymeric composites with complex inclusions

The dynamic mechanical properties of polymeric composites composed of crosslinked poly(n-butyl methacrylate) continuous-phase and crosslinked polystyrene dispersed phase with poly(n-butyl methacrylate) occlusion have been examined. The composite samples were prepared by mixing and swelling of the crosslinked polystyrene particles obtained by emulsifier-free emulsion polymerization, with n-butyl methacrylate and crosslinker, then photopolymerizing at the desired temperature. The composite microstructure was varied by either changing the crosslink density of polystyrene, and temperature of swelling and polymerization, or using different sizes and contents of polystyrene particles. The tan δ peak positions of composite samples are found to be dependent on morphological characteristics as well as the properties of the dispersed phase while the peak height seems to be dependent on the effective volume of dispersed phase composed of polystyrene and poly(n-butyl methacrylate) occlusions. Special attention has been paid to the comparison among composite, homonetworks, and bulk IPN samples that are expected to have the identical structure with the complex dispersed phase of the composite samples. © 1993 John Wiley & Sons, Inc.     

原位乳液聚合法制备改性蒙脱土及其表征

通过原位乳液聚合的方法制备改性蒙脱土,在聚合之前,可聚合的小分子先接枝到蒙脱土的表面或层间,然后加入苯乙烯单体引发聚合,使聚合物大分子接枝到蒙脱土的表面和层间。十六烷基三甲基溴化铵(CTAB)在乳液聚合改性蒙脱土的过程中既是插层剂又是乳化剂。X射线衍射分析表明,经过处理引入了CTA+和PS大分子使得层间距扩大;红外、热重法分析表明,小分子和大分子已接枝到蒙脱土上。蒙脱土的存在影响了聚合反应动力学,并就小分子的影响作了简单的讨论。     

Surface composition of polystyrene

The physical and chemical properties of bulk polymers are well understood and have been measured exhaustively for numerous systems, but the properties of polymer surfaces are quite often different from those observed in the bulk and are usually not as easily measurable. Since many polymer properties vary with molecular weight, it is of interest to determine whether or not there is any segregation in a homopolymer system based on molecular weight. In particular, does the surface of a polymer sample have the same molecular weight composition as the bulk? The current work answers this question for a polystyrene system. Through the use of secondary ion mass spectrometry and tagged polystyrene, it has been shown that surface and bulk molecular weight composition are indistinguishable within the limits of the experimental method's sensitivity. The sensitivity of the technique is documented using samples artificially created with different surface and bulk molecular weight compositions.     

Mass loss and flammability of insulation materials used in sandwich panels during the pre‐flashover phase of fire

Nowadays, buildings contain more and more synthetic insulation materials in order to meet the increasing energy‐performance demands. These synthetic insulation materials have a different response to fire. In this study, the mass loss and flammability limits of different sandwich panels and their cores (polyurethane (PUR), polyisocyanurate (PIR) and stone wool) are studied separately by using a specially designed furnace. Expanded polystyrene and extruded polystyrene are tested on their cores only. The research has shown that the actual mass loss of synthetic and stone wool‐based cores is comparable up to 300 °C. From 300 °C onwards, the mass loss of PUR panels is significant higher. The mass losses up to 350 °C are 7%, 29% and 83% for stone wool, PIR and PUR respectively, for the influenced area. Furthermore, delamination can be observed at exposure to temperatures above 250 °C for the synthetic and 350 °C for the mineral wool panels. Delamination occurs due to the degradation of the resin between core and metal panels and the gasification of the (PUR) core. The lower flammability limits have been established experimentally at 9.2% m/m (PUR) and 3.1% m/m (PS). For PUR, an upper limit of 74% was found. For PIR and mineral wool, no flammability limits could be established. Copyright © 2017 John Wiley & Sons, Ltd.     

Nanoclay Addition and Core Materials Effect on Impact and Damage Tolerance Capability of Glass Fiber Skin Sandwich Laminates

This study explores the effects of modified (OMMT) nanoclay and core material on low velocity impact behavior and damage tolerance capability of glass fiber reinforced (FRP) polyester resin – polystyrene foam (PS) sandwich laminates. The FRP and sandwich laminates are prepared by a compression molding technique for investigation. Low velocity impacts are carried out on all the fabricated laminates by using a instrumented drop weight impact tower with the energy level of 30 J and load–energy–time plots were recorded using data acquisition software. Post impact flexural tests have been conducted to evaluate the damage tolerance capability of the fabricated composite laminates. X-ray Diffraction (XRD) results have been obtained for the samples, where the nanoclay has indicated that intergallery spacing of the layered clay increases with the matrix. Scanning Electron Microscopy (SEM) has given the morphological picture of the nanoclay dispersion in the polymer fracture samples. The results of the study show that the impact properties and damage tolerance capability of the 4% nanoclay polyester sandwich have been greatly increased.     

Smoke formation from burning polystyrene and its suppression

Studies have been made of the influence on smoke generation from polystyrene of the incorporation of a number of apparently inert solids, the smoke-producing tendency being expressed in terms of the maximum specific optical density of smoke per unit weight of polymer consumed. Of the compounds investigated, by far the most efficient smoke suppressant is pyrogenic silica, the effect of which is, over a wide range, directly proportional to the total surface area of the material introduced. Examination of partially burned polystyrene-pyrogenic silica composites reveals the presence at the surface of a hard rigid skin, which is not observer with polystyrene alone of with polymer samples containing other additives. The formation of a protective skin is also indicated by the kinetics of forced burning of these composites where the weight loss is a linear function of log time and by measurements of the rate of change of thickness of polymer samples during combustion. Thermogravimetric experiments in which polystyrene and pyrogenic silica are heated in contact with one another show that the silica encourages the formation of a carbon residue from the polymer. A mechanism of skin production is proposed which involves the build-up of layers of tangential spherical silica particles cemented together by cross-linked polystyrene.     

Study on dyeable polypropylene fiber and its properties

A disperse dyeable polypropylene fiber has been prepared by admixing polystyrene to the polymer prior to extrusion. Polystyrene has been synthesized at suitable molecule weight and narrow mol wt distribution. The dyeability, mechanical properties, shrinkage, degree of crystallinity, and orientation of pure polypropylene or the blend fibers with different amount of polystyrene were investigated. In addition, the structure of the blend containing 4 and 6% polystyrene was also studied to explain the interesting dyeing behavior of the blend fibers. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 3172–3176, 2001     

Gas sorption and transport in syndiotactic polystyrene with nanoporous crystalline phase

In this contribution we analyse sorption and transport of several gases in semicrystalline syndiotactic polystyrene with nanoporous crystalline δ form. Investigation was performed on amorphous samples and on samples characterized by different degrees of crystallinity. Sorption isotherms of carbon dioxide, nitrogen and oxygen in the crystalline phase have been determined starting from experimental results obtained for semicrystalline and amorphous samples. Corresponding isosteric heats of sorption were evaluated for the crystalline and amorphous phase. Permeation tests were also performed to gather information on mass transport properties of semicrystalline samples, evaluating average diffusivities of carbon dioxide and oxygen, in the limit of small concentrations as function of degree of crystallinity.     

The influence of charge density and steric factor of aminated chloromethyl polystyrene homologs in bilirubin adsorption

Bilirubin, a bile pigment, was studied for its extent of adsorption on substituted aminechloromethyl polystyrene by UV spectrophotometry. By performing simple displacement reactions on chloromethyl polystyrene with secondary and tertiary amines, the amount of charge density and steric factor on substituted nitrogen atom have been varied. Adsorption isotherms of bilirubin at 0°C by different amine–chloromethyl polystyrene homologs suggest the existence of electrostatic interaction of polymeric resin with bilirubin moiety. Results of adsorption of bilirubin to polymeric resin have shown that the extent of adsorption of bilirubin depends on the unit charge, and on the structure of the substituted amine–chloromethyl polystyrene. The effects of porosity of resin on bilirubin adsorption have also been discussed.     

Dynamic mechanical and thermal properties of fire-retardant high-impact polystyrene

The interaction of a series of fire-retardant additives with high-impact polystyrene (HIPS) has been inferred from their dynamic mechanical and thermal properties. High-melting additives phase separate and act as inert filler in both the rubber and polystyrene phases, while low-melting additives raise the T_g of the rubber phase and plasticize the polystyrene phase. Antimony oxide antiplasticizes the grafted rubber phase but acts as inert filler in the polystyrene phase. The impact strength of these fire-retardant HIPS's shows good correlation with the integrated loss tangent of the rubber T_g peak indicative of large energy dissipation in the rubbery region during impact causing the matrix to craze or flow. It is also suggested that additives which are compatible with, and localized in, the polystyrene phase help retain the impact strength of HIPS.     

Molecular weight distributions of standard polystyrene samples by GPC and by sedimentation velocity analysis

In precision gel permeation chromatographic (GPC) work, the spreading (zone spreading) characteristics of the instrument must be calibrated. Standard samples of anionic polystyrene have been used for this purpose. The molecular weight distributions of these standard samples, nevertheless, have not been determined carefully. In this work, several standard polystyrene samples obtained from Pressure Chemical Company were examined by GPC and by sedimentation velocity analysis. The results show that (1) the high molecular weight polystyrene samples have skewed molecular weight distributions as has been suspected and that (2) the present data treatment technique for GPC is effective for these very narrow-distribution samples.     

Effect of ceramic binders on microwave dielectric loss of alumina

Abstract

Several binders have been evaluated to determine their effect on high frequency dielectric loss. Alumina ceramics have been powder pressed with different binder levels, sintered, and then the dielectric loss (tan δ = Q^-1) has been measured at approximately 9·5 GHz. The quality factor Q was determined and significant differences were observed between samples made with different binders. The differences are caused by the different levels of residual porosity left by the different binders. In addition, differences in levels of impurities in the binders may also influence Q. Selected samples were measured for green body strength as a function of binder content.     

间规聚苯乙烯的热分解行为分析

利用热重分析（TG—DTA）法研究了间规聚苯乙烯（sPS）在不同气氛（空气和氮气）下的热分解行为机理。研究表明,sPS在两种气氛下都是只有一个主要的热分解过程。结果表明,用Kissinger最大失重速率法求得空气气氛下的表观活化能为133．86kJ／mol,而在氮气气氛下的表观活化能为158．96kJ／mol;用Ozawa等失重百分率法求得空气气氛（10％～30％的失重率）下的表观活化能为92．05～105．88kJ／mol,而在氮气气氛下的表观活化能为149．00—175．38kJ／mol;sPS的热裂解和热氧分解过程均为一级反应。     

Polystyrene encapsulation of manganese porphyrins: highly efficient catalysts for oxidation of olefins

Metalloporphyrins (MPs) of manganese have been successfully encapsulated for the first time in polystyrene matrix. The manganese porphyrins have been anchored onto polymer on the basis of physical envelopment by the polystyrene fibers, rendering them highly dispersible in common organic solvents. These polystyrene supported catalysts are characterized by UV–Vis and diffuse reflectance FT-IR spectroscopy. These encapsulated catalysts (MCMPs) exhibit enhanced activity for oxidation of alkenes in the presence of NaIO₄, KHSO₅ and NaOCl as oxidants. These catalysts not only possess high turnover frequencies but they are found to be quite stable and could be recovered quantitatively by simple filtration and reused without loss of activity.     

Photooxidation of polystyrene: Irradiation at 254 and 365 nm

Studies have been made of the near surface photooxidation of atactic polystyrene films prepared in the absence of air. The samples were photooxidized on exposure to air at two frequencies, 254 and 365 nm, using a calibrated mercury irradiation source with filters. Most studies were made at 40°C and as a function of irradition time with the reactions characterized by changes in molecular weight and composition. The former was evaluated by gel permeation chromatography and the latter by transmission Fourier transform infrared spectroscopy and by multiple-internal-reflectance infrared spectra using different angles and different crystals to evaluate compositions as a function of film depth. Species identified in photooxidation include the generation of hydroperoxides and the appearance of carbonyl bands with the latter identified by the spectral shift asociated with the exposure of the photooxidized polystyrene surface to ammonia. These results suggest that principal products of near-surface oxidation of polystyrene are carboxylic acids.     

On the application of a damped model to the falling weight impact characterization of glass beads–polystyrene composites

Instrumented falling weight impact tests were carried out to characterize the mechanical behavior of a material pattern formed by polystyrene and different amounts of glass beads. This characterization was performed at high strain rate using two different impact arrangements: the first uses high impact energy at the striker, whereas the second uses a low‐impact energy. Starting from a conservative model, a nonconservative one has been proposed for the low‐energy impact configuration as a better approach to the material behavior. In this latter model, the energy losses were quantified through the restitution coefficient. Two alternative methods for its calculation are described. The results shows good agreement between the flexural modulus and break stresses calculated in either the low‐ or the high‐energy arrangement; however, the low‐energy impact method yields more confidence results. Using the proposed model, the composites' fracture onset was determined, and also in the samples with low content of glass beads, it was possible to assess the micromechanism of failure, given the estimation for the stress to produce crazing. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 1271–1284, 2004     

Thermal and photochemical degradation of PPO/HIPS blends

In general, polymer blends show a degradation behavior different from a simple combination of the individual components, making any forecast difficult without experiments. Interactions between polymers can sensibilize or stabilize the blend against degradation. In this work, the thermal and photooxidative degradation of blends of poly(2,6‐dimethyl‐1,4‐phenylene oxide) (PPO) and high impact polystyrene (HIPS) have been studied under accelerated conditions. The extent of degradation was accompanied by infrared spectroscopy (FTIR) and Raman spectroscopy (FT‐Raman) and impact resistance and strain–stress testing followed its influence on the macroscopic properties of the blends. The results showed that HIPS and the blend containing 60 wt % of PPO are more susceptible to thermal and photochemical degradation, while the blends containing 40 and 50 wt % of PPO are more stable. Infrared and Raman spectroscopic analyses showed that the degradation of HIPS and its blends is caused not only by degradation of the polybutadiene phase. Effects of interactions, such as exchange of energy in excited state between the PPO and PS components of the polymeric matrix may also be responsible for the degradation and loss of mechanical properties of the PPO/HIPS blends. The chemical degradation directly affects the mechanical properties of the samples with photodegradation being more harmful than the thermal degradation at 75°C. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007