Time-dependent capillary flow of polystyrene

The nonsteady flow behavior of a characterized commercial polystyrene has been examined in a compressed-nitrogen-gas piston viscometer. Nonsteady flow data were erratic with virgin polymer at 173.9°C. Pretreatment of the polystyrene by subjecting the melt to a higher temperature, with or without shear, changed the nature of the time-dependent flow to that which is generally characteristic of polymers in experiments of this type. The pretreatment had no significant effect on the equilibrium flow curve at the same temperature nor on the molecular weight of the polystyrene. The results are interpreted in terms of changes in the size or nature of supermolecular flow units.     

Cold flow in high-impact polystyrene

Eyring's theory of viscous flow has been applied to some mechanical properties of rubber-modified polystyrenes. Yield strength as a function of orientation, temperature, of transition from ductile to strain have been shown to be consistent with the theory. The temperature of transition from ductile to brittle fracture as a function of orientation has also been measured and found to be consistent with theoretical predictions.     

Viscoelastic characteristics of pentane-swollen polystyrene beads

Expansion of pentane-swollen polystyrene beads was followed at and above the glass transition by using a very simple optical technique. Measurements allowed a suitable determination of the glass transition temperature and of the viscoelastic characteristics of the pentane-plasticized polystyrene chains inside the beads, at different pentane contents. This was achieved by combining the well-known Williams, Landel, and Ferry approach and some calculations derived from a recent micromechanical modeling of the expanded polystyrene microstructure. The results, analyzed in terms of free volume characteristics, revealed the peculiar plasticizing character of pentane, as compared to the usual polymer diluents. A value of 42°C was found as the lowest temperature for which the dimensional variation of the beads could result from glass transition motions. The relevance of these conclusions was discussed, not just in terms of the changes in dimensions of the individual beads at zero expansion time but also in terms of the dimensional evolution observed in the expanded polystyrene structures. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 2463–2472, 1999     

Effect of structure on impact strength of rubber-reinforced polystyrene

The influence of the quantity (gel-%), the degree of crosslinking (swelling index), and the particle size (mean cord) of the elastomeric phase on Izod impact strength of rubber-reinforced polystyrene has been investigated. It has been observed that (particle size being 2–3 μ) impact strength increases almost linearly with gel content and the slope of the curves increases with decreasing degree of crosslinking. This relation proved to be no more linear for different particle sizes: small particles prove more effective than other particles in the high gel-% range and less in the low gel-% range. These results are discussed in the light of theories of rubber toughening in polystyrene and on the basis of data from Izod tests with recorded stress–time curve as well as of electron micrographs of fracture surfaces.     

Factors influencing the impact strength of high impact polystyrene

The relationship between synthesis factors and the impact resistance of high impact polystyrene (HIPS) is investigated in the light of its morphology and dynamic mechanical properties. A decrease in polymerization temperature results in an increase in T_g, melt viscosity and molecular weight of the continuous polystyrene phase as characterized by gel permeation chromatography. The separated, occluded polystyrene phase however shows an invariant T_g suggesting that the grafting and/or crosslinking effect overweighs the molecular weight effect. The observed high impact strength has been correlated with the homogeneous 1-2 μ rubber particle size distribution, a comparatively sharp rubber T_g transition at lower temperature, and a much lower occluded polystyrene content in the dispersed phase.     

Ultrasonic improvement of weld line strength of injection‐molded polystyrene and polystyrene/polyethylene blend parts

The effect of melt temperature, ultrasonic oscillations, and induced ultrasonic oscillations modes on weld line strength of polystyrene (PS) and polystyrene/polyethylene (PS/HDPE) (90/10) blend was investigated. The results show that the increase of melt temperature is beneficial to the increase of weld line strength of PS and PS/HDPE blend. Compared with PS, the increase of melt temperature can greatly enhance the strength of PS/HDPE blends. For PS, the presence of ultrasonic oscillations can enhance the weld line strength of PS at different melt temperatures. But for PS/HDPE blends, the presence of ultrasonic oscillations can improve the weld line strength when the melt temperature is 230°C, but when the melt temperature is 195°C, the induced ultrasonic oscillations hardly enhance the weld line strength. Compared with Mode I (ultrasonic oscillations were induced into the mold at the whole process of injection molding), the induced ultrasonic oscillations as Mode II (ultrasonic oscillations were induced into the mold after injection mold filling) is more effective at increasing the weld line strength of PS and PS/HDPE blends. The mechanism for ultrasonic improvement of weld line strength was also studied. POLYM. ENG. SCI., 45:1666–1672, 2005. © 2005 Society of Plastics Engineers     

Effects of adhesive type and polystyrene concentration on the shear strength of bonded polystyrene/high-density polyethylene blends

The lap-shear strengths of adhesively bonded polystyrene (PS), high-density polyethylene (HDPE), and their blends, were studied as a function of adhesive type and blend composition. The performance of virgin and recycled polymer systems was examined. The lap-shear strength depended strongly on the amount of PS in the blend and the type of adhesive, and the acrylic adhesives demonstrated the best performance for all compositions. Bonded strengths of HDPE increased by approximately 50% when HDPE was blended with 34% PS, the co-continuous composition. The results indicate that structural elements made from PS/HDPE immiscible blends may be effectively bonded with adhesives without expensive surface treatments.     

Impact strength improvement of polystyrene by dispersion of rigid particulate

We have discovered that the impact strength of polystyrene is increased by the addition of rigid particles several microns in diameter and at concentrations of 0.01 ∼ 1 wt%. As examples, we used barium sulfate particles and crosslinked polystyrene beads. From the observation of real-time deformation of polystyrene incorporating the rigid particles, and from finite element analysis, it is clear that the impact improvement mechanism is related to the formation of voids or peeling layers, and successive extension of crazes from the voids or peeling layers.     

高分子量聚苯乙烯的生产特点

介绍了高分子量聚苯乙烯生产中原料的配制、引发剂的使用 ,反应停留时间、强放热、反应温度梯度、转化率及产品质量等方面的工艺特点。针对高分子量聚苯乙烯生产较难控制的特点提出了一些建议     

The particle flow of polystyrene during capillary extrusion

The melt flow of emulsion polymerized polystyrene has been investigated in accordance with the particle flow concepts developed by Berens and Folt. Particles were found to be present in the extrudate up to 210°C and resins with larger particles were found to have lower viscosities. The molecular weight appears to have no significant effect on the melt viscosity above a certain molecular weight. The energy of activation for viscous flow at 190°C and at shear stress of 5 × 10⁵ dynes/cm² was found to be 29–33 kcal/mol depending on type of resin.     

Relationship between rheological properties and impact strength in high impact polystyrene

Two batches of a commercially available high-impact polystyrene having different impact strengths were investigated. The steady-shear flow properties, dynamic shear properties, and elongational flow properties of the two were measured. Transmission electron microscopy (TEM) was used to study the microstructure. It is suggested that melt rheology can be a sensitive tool in the characterization of final product properties of rubber-modified polymers: the zero-shear-rate viscosity and the dynamic storage modulus G′, at low frequencies, were experimentally shown to correlate directly with the impact strength, despite the fact that TEM revealed no gross differences in the morphology of the two batches.     

The fracture of polystyrene: some observations on strength and cracking phenomena

Tensile tests have shown that crazes formed in stressed polystyrene are regions of unimpaired strength. The study of fracture surfaces with the aid of carbon replicas in the transmission electron microscope has revealed that at the onset of fracture the material has a sponge-like character and a great deal of fibrous structure. Investigation of the changing surface detail produced as the crack propagates has given new information, particularly on slow secondary fracture features.     

Wall slip and melt-fracture of polystyrene melts in capillary flow

We investigated slip and unstable flow phenomena of polystyrene melts in capillaries from the view of the effects of temperature and molecular weight by using three polystyrene samples with different molecular weights (M_w = 192,000, M_w = 258,000, and M_w = 321,000). The slip velocities are estimated by the Mooney method and the modified Mooney method. We found that the slip velocity increases and the critical slip stress above which a slip starts to occur decreases with the temperature. We also observed the melt-fracture at above a critical melt-fracture stress higher than . We found that the onset of melt fracture is affected by the extensional stress near the entry region to the capillary in the barrel and the melt-fracture tends to easily occur with increase of the molecular weight, but is not sensitive to the temperature.     

Shear flow rheological properties,fiber damage,and mastication characteristics of aramid-, glass-, and cellulose-fiber-reinforced polystyrene melts

An experimental study of the viscosity and principal normal stress difference of a polystyrene melt filled with aramid (Kevlar), glass, and cellulose fibers is reported. The influence of loading level and mastication on the rheological properties is discussed. The effects of mixing and mastication on fiber damage are considered. Glass fibers break down rapidly to very small aspect ratios, while aramid shows a “kinked” structure, with kinks occurring every 100 μm. A mechanism is proposed for fiber breakage based on buckling during rotation in shear flow. It is found that addition of fibers increases the viscosity in the same manner as a reduction in temperature, and data may be superposed by reduced plotting. This indicates that the viscosity increase is due solely to enhanced viscous dissipation in the matrix and not to interparticle forces as is the case with smaller particles. The principal normal stress difference increases at fixed shear stress with fiber loading. The extent of increase depends upon fiber loading, aspect ratio, and modulus.     

Velocity characteristics of beams of spherical polystyrene particles

Detailed measurements of the velocity characteristics of particle beams have not been previously reported. Since such information will be necessary in many uses of particle beams, a systematic study of the velocity characteristics of beams of spherical polystyrene particles was undertaken. The beams were generated by expansion of an aerosol through a capillary into a vacuum chamber. Beam velocities ranged up to the apparent carrier gas exit velocity of 316 m/sec, depending on source pressure and particle size. It was possible to adjust beam velocity by setting vacuum chamber pressure, thus regulating deceleration of the beam. A theoretical model describing the beam deceleration is presented. Velocity spread in the beam was relatively small for large velocities but substantial for low velocities. The velocity distribution function for particles in the beam was determined. The effect of condensation and subsequent evaporation of water on particle motion is discussed.     

Photon-correlation velocimetry of polystyrene solutions in extensional flow fields

A cross slot device has been used to produce elongational flow fields in dilute solutions of narrow fractions of high molecular weight ($\text{M}\text{?}{}_{\mathrm{w}}$ between 2.8 × 10⁶ and 2 × 10⁷) atactic polystyrene. Strainrates obtainable were sufficient to extend individual molecules. Photon-correlation microvelocimetry has been used to measure velocity profiles in a channel of the cross slot as a function of distance from the centre of the cross, polymer concentration and flow rate. It has been found that in solutions of concentration about or greater than $\text{c1}$ and at flow rates sufficient to extend the polymer molecules a minimum in velocity is observed at the centre of the channel. This minimum sets in at flow rates around that at which extension of the polymer molecules is first observed through birefringence observations, but the depth of the minimum decreases rapidly with decreasing polymer concentration below $\text{c1}$. The velocity profile evolves into the usual parabolic profile away from the region of elongational flow. At higher strain rates a birefringence in the solution near the channel walls was also observed and preliminary measurements indicate that two symmetrical minima or shoulders in the velocity profile may be associated with this observation.     

Precursor of shish-kebab in isotactic polystyrene under shear flow

We performed polarized optical microscope (POM), depolarized light scattering (DPLS) and small- and wide-angle X-ray scattering measurements on the structure formation process or the crystallization process of isotactic polystyrene (iPS) under shear flow below and above the nominal melting temperature T_m. It was found that an anisotropic oriented structure termed here as a string-like object was formed in μm scale even above the nominal melting temperature and stable for more than 24 h, but melted at around 270 °C far above the nominal melting temperature. The string-like object acts as a nucleation agent for the folded chain lamella crystal (or the kebab), and was assigned to a precursor of the shish-kebab. We also examined the shear rate dependence of the structure formation to find a critical shear rate for the formation of the string-like object, suggesting the relaxation of the chains plays an important role in the formation of the structure. Based on the results we have discussed the inner structure of the string-like object.     

Polydispersity effect on transient flow behavior of polystyrene solution

Summary The transient flow behavior of the binary blend of monodisperse polystyrene fractions is measured by a flow birefringence method. Both of the shear stress and first normal stress difference are obtained simultaneously in time by using a PMFB technique. The entanglements of the polymer chains significantly affect the rheological property of the binary blend in flow region. Especially, the entanglements of the high molecular weight fractions with themselves is proven to be the main source to the growth of first normal stress differences.