Modification of polystyrene by reactive extrusion with peroxide and trimethylolpropane triacrylate

Polystyrene (PS) was modified by reactive extrusion with trimethylolpropane triacrylate (TMPTA) and dicumyl peroxide (DCP). The coupling reaction caused by TMPTA increased the molecular weight of PS, and this coupling reaction was enhanced in the presence of DCP at high TMPTA/DCP ratio. The rheological properties of the extrudate were examined. The impact strength of PS improved as the molecular weight increased by the coupling reaction. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 1672–1679, 2004     

A unifying approach for melt rheology of linear polystyrene

Several studies of melt rheological properties of polystyrene have been conducted over the past 50 years. Several approaches, including empirical models, have been developed to understand the behavior of materials using simple equations. The existing melt rheology models are best suited for high‐molecular‐weight polymers whose T_g does not vary. In this work, a semiempirical viscosity equation has been derived, including the effect of T_g dependence on molecular weight, to describe the melt rheology of low‐molecular‐weight polymers. The equation is derived based on a combination of well‐known concepts, such as the effects of free volume and molecular dynamics on polymer rheology. This provides a better understanding of the rheological behavior in the low‐molecular‐weight regime with respect to temperature and molecular weight. Because of the industrial trend towards lower molecular weight materials for applications such as high solids coatings, this unifying approach, based on the free volume theory with a simple expression, is of extreme practical significance. This equation can predict the zero shear viscosity behavior for different molecular weights, including low‐molecular‐weight regions, and temperatures. Viscosity calculations using the empirical equation agree with published experimental data. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 2597–2607, 2007     

Thermodynamic theory of the viscoelasticity and yield of glassy polymers: Internal time theory

A nonlinear viscoelastic constitutive equation of glassy polymers has been developed on the basis of the internal time and irreversible thermodynamics of internal variables. The constitutive equation is a generalization of spring–dashpot models and describes the yield behavior of glassy polymers. With this constitutive equation, the rate of entropy production has been determined to show a peak near the yield. We propose a new yield criterion, that yield occurs at the maximum rate of entropy production. The yield criterion is almost equivalent to that of peak stress and a thermodynamic interpretation of yield. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 2400–2411, 2003     

Enhancement of the surface and bulk mechanical properties of polystyrene through the incorporation of raw multiwalled nanotubes with the twin‐screw mixing technique

In this article, we present the effects of incorporated multiwalled nanotubes (MWNTs) on a metal surface and the bulk mechanical properties of as‐synthesized polystyrene (PS)–MWNT composites prepared with the twin‐screw mixing technique. The MWNTs used for preparing the composites were raw compounds that were not treated with any surface modifications. The morphology for the dispersion capability of the MWNTs in the PS matrix was subsequently characterized with transmission electron microscopy. Surface mechanical property studies (i.e., wear resistance and hardness) showed that the integration of MWNTs led to a distinct increase in the wear resistance and also the micro/nanohardness with up to a 5 wt % MWNT loading in the composites. Moreover, the enhancement of the wear resistance of the as‐prepared composites, in comparison with pure PS, was further identified with scanning electron microscopy observations of the surface morphology after testing. On the other hand, for bulk mechanical property studies (i.e., the tensile strength and flexural strength), the composites containing a 3 wt % concentration of MWNTs in the PS matrix exhibited the best performance with respect to the tensile strength and flexural strength. This means that this composition of MWNTs exhibited good compatibility with the PS matrix, and this can be attributed to the π–π interacting forces existing between the aromaticity of the MWNTs and PS matrix. Furthermore, at higher MWNT loadings (e.g., 5 wt %), raw MWNTs were aggregated in the polymer matrix, as observed by transmission electron microscopy. Also, this led to an obvious decrease in the tensile strength and flexural strength. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Effect of clay dispersion on the synergism between clay and intumescent flame retardants in polystyrene

Different formulations were designed to evaluate the effect of organically modified clay (DK4) on the combustion behavior of polystyrene (PS) containing an intumescent flame retardant, poly(4,4‐diaminodiphenyl methane spirocyclic pentaerythritol bisphosphonate) (PDSPB). The results of transmission electron microscopy reveal that DK4 selectively dispersed in the PDSPB phase. An investigation of thermogravimetric analysis revealed that the thermal stability of PS resin showed no obvious change with the addition of PDSPB and DK4, but the residue increased. From the results of cone calorimetry, we observed that there were two steps during combustion. The dispersion of DK4 played an important role in improving the thermal stability and the flammability of the PS/PDSPB/DK4 nanocomposites. In the first step, DK4 was restricted in the PDSPB phase; there was no synergistic effect. A synergistic effect occurred in the second step when clay had a homogeneous distribution, in which the peak heat release rates were reduced by about 40 and 61% compared to the pure PS. A model of combustion behavior was developed according to these results. The synergistic mechanism was caused by the formation of the silicoaluminophosphate (SAPO) structure formed by reactions between PDSPB and DK4. Field emission scanning electron microscopy characterization showed that such an SAPO structure led to a ceramic‐like residue after burning. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Effects of functional groups on the thermal properties of modified polystyrene

Polystyrene is, after polyolefins, the most widespread polymer in both industry and everyday life, successfully replacing some raw natural materials. In this study, the chemical modification of polystyrenes of different molecular weights was performed with various functional group modifiers (epichlorohydrin, maleic anhydride, and acetic anhydride) in one stage and in the medium of the cationic catalyst BF₃·O(C₂H₅)₂ according to previous studies. The concentration of the functional groups bonded to the aromatic ring of the polymer as a result of the chemical modification of polystyrenes of different molecular weights depended on the molecular weight of the polymer, and more functional groups were bonded to lower molecular weight polystyrene. The effects of the functional groups bonded to the structure of the polymer on the thermal properties of modified polystyrene were investigated. The polystyrene that was modified by maleic anhydride was more stable against thermal destruction at high temperatures. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 2549–2553, 2007     

Interrelation between long‐term viscoelasticity and viscoplastic responses of semicrystalline polymers

Two types of linear low‐density polyethylenes, prepared by metallocene catalysts were studied experimentally in terms of differential scanning calorimetry, dynamic mechanical analysis (DMA), and tensile testing. The different comonomer content and the small amounts of long branching in one of the materials studied strongly affect the crystalline distribution and morphology and, consequently, the DMA and tensile experimental data. From the experimental DMA data, the function of relaxation modulus, treated as a material property, is used to describe the corresponding tensile experimental results. A constitutive analysis that considers the viscoelastic path at small strains and the viscoplastic one at high strains proved to be capable of describing the tensile behavior of the materials. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 1942–1950, 2003     

压缩条件下发泡PS黏弹塑性力学模型研究

为提高发泡聚苯乙烯(EPS)工程应用的长期稳定性,分析了压缩条件下EPS的力学性能。实验中EPS块体的受压变形呈现出黏弹塑性特征,并可分为3个阶段。随着加载速率的增大,屈服应变略微增大,但对切线弹性模量影响较小,在实验的基础上建立了表观密度与3个EPS压缩实验参数的关系。构造EPS块体的压缩黏弹塑性模型与实验结果的误差为0.37%。比较模型预测值与现场实测的压缩变形结果,结果表明两者图形趋势较为一致,用该模型可预测EPS块体的压缩变形。     

Effect of shielding rates on upward flame spread over extruded polystyrene foam in vertical channel and heat transfer mechanism

Fire hazard of extruded polystyrene (XPS) thermal insulation materials has aroused public concern. In order to develop flame spread theory and the guideline for fire risk assessment of XPS, an experimental study on upward flame spread behavior and heat transfer mechanism of XPS in a vertical channel with different frontal shielding rates was conducted. Maximum temperature at the place 2 cm from XPS surface and at the center of channel first increase and then decrease as the shielding rate rises. The former is higher than the latter. Experimental value of average flame height rises as the shielding rate increases. A model for predicting the flame height is built, and the predicted results are consistent with the experimental results. Moreover, the relation between flame height and pyrolysis height under different shielding rates is obtained. The flame spread rate rises as the shielding rate increases. A prediction model of flame spread rate is established, and its prediction results are more accurate compared with those from previous models. The model also predicts that radiative heat transfer is the dominant heat transfer mode, accounting for 93% of the total heat transfer. This work is beneficial for fire risk assessment and fire safety design of building façade.     

Charge density effects on polyelectrolyte dynamic rheology

The dynamic rheological properties of an uncharged polymer and charged polyelectrolytes were evaluated in salt‐free water at various concentrations above the entanglement concentration. A poly(acrylic acid) homopolymer was used as the uncharged polymer and was ionized to anionic poly(acrylic acid‐co‐sodium acrylate) at five levels of ionization (0.05, 0.10, 0.15, 0.30, and 0.50). The polymers exhibited a terminal region at a low frequency and a plateau region at a high frequency. The dynamic data for the nonionic parent and all charged polymers could be reduced to a master curve, which indicated a similar distribution of relaxation times for the nonionic and charged polymers. The shear modulus, relaxation time, and zero shear viscosity properties exhibited a concentration and charge density dependence. Higher power‐law exponents for the rheological properties were noted for the nonionic polymer versus the charged derivatives. The number of mechanically active entanglements per number of chains increased with the polymer concentration and charge density. The total number of mechanically active entanglements per number of chains that occurred because of imposing a charge to the nonionic parent did not change with increased concentration, and this indicated a different entanglement mechanism for charged polymers in comparison with their nonionic parent. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Polymorphism and mechanical properties of syndiotactic polystyrene films

The dynamic-mechanical behaviour and the tensile moduli of unstretched and stretched semicrystalline s-PS films, presenting different polymorphic forms (α, γ, δ and clathrate) but similar crystallinity and orientation, have been compared. The main aim is to elucidate the possible influence of different crystalline phases, being largely different in chain conformation and density, on mechanical properties of s-PS semicrystalline samples. For unstretched films presenting a preferential perpendicular orientation of the chain axes, the highest elastic modulus is observed for films with the high density γ phase while for uniaxially oriented films the highest modulus is observed for films with the trans-planar α phase. As for the clathrate films, the guest molecules when only included into the crystalline clathrate phase, have no plasticizing effect.     

Preparation and rheological characterization of intercalated polystyrene/organophilic montmorillonite nanocomposite

Polystyrene (PS)/organophilic montmorillonite (OMMT) clay nanocomposites were prepared by a solvent casting method using chloroform as a cosolvent. Intercalation of the OMMT in the PS matrix was achieved as revealed by X‐ray diffraction. The IR spectra of the products indicated that the OMMT is homogeneously dispersed in the PS matrix. A thermogravimetric analysis (TGA) showed that the onset temperature increases linearly with the clay content. The glass‐transition temperature of the PS, examined using differential scanning calorimetry, had a trend similar to that from the TGA. The rheological properties of the PS/OMMT nanocomposites were also investigated via a rotational rheometer with a parallel plate geometry, and they exhibited sharper shear thinning and increased storage and loss modulus with clay content. Furthermore, the shear viscosity obtained from the steady shear experiment was well correlated with the complex viscosity obtained from the oscillatory experiment via the Cox and Merz relation. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 87: 2106–2112, 2003     

Effect of size,surface charge,and hydrophobicity on the translocation of polystyrene microspheres through gastrointestinal mucin

Microspheres (MS) have been proposed for use as oral vaccine delivery vehicles (VDV); however, due to poor and variable absorption their clinical utility is limited. The effects of size, ζ-potential, and surface hydrophobicity on the translocation (P_T) permeabilities of polystyrene (PS) MS with varying surface functional groups (amidine, carboxyl, carboxylate-modified [CML], and sulfate) were determined through gastrointestinal (GI) mucin. P_T were determined, under steady-state conditions, using a modified Ussing-type diffusion chamber and a mucin packet developed for use with the Transwell-Snapwell system. P_T followed the Stokes-Einstein relationship, demonstrating the limited ability of larger MS (>0.5 μm) to diffuse through the mucin layer. P_T also varied according to the surface characteristics. Even though the ζ-potential did not correlate with the transport of MS through mucin, surface ionization appears to be important in MS translocation. The PS-amidine MS were significantly less hydrophobic and had a higher P_T than that of the other MS, suggesting that hydrophobicity is also a significant factor in MS transport through mucin. While these results suggest that mucin may be a significant barrier to the oral absorption of vaccines and VDVs in vivo, the rate-limiting barrier for the absorption of MS will be the intestinal mucosa. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 63: 1481–1492, 1997     

超声振动对PS熔体流变及黏弹行为的影响

采用Bagley入口校正等理论计算方法与实验结果相结合，讨论了超声振动对PS熔体流变及黏弹行为的影响。在口模入口处施加超声振动，降低了聚合物熔体的非牛顿性，改变其黏弹行为，使其在毛细管口模中流动时弹性形变及储能减小，形变松弛加快，黏度降低，从而使挤出加工中流动阻力变小，挤出效率得到提高。     

Examination of the time–water content superposition on the dynamic viscoelasticity of moistened polyamide 6 and epoxy

We have investigated the behavior of moisture absorption by the polyamide 6 and epoxy samples in various humid environments at constant temperature and also examined the effect of absorbed moisture on their dynamic viscoelastic properties. The moisture absorption was revealed to show the Fickian type of diffusion and to shift the dynamic viscoelastic properties of the specimen to those at lower temperature, as an effect of plasticization. Anti‐plasticization taken with an increase in the storage modulus was also observed in a low‐temperature range below ?50°C. The time–water content superposition was confirmed to hold at various equilibrium water contents at constant temperature for both polyamide 6 and epoxy. The relation of the shift factor, log a_H, to the equilibrium water content for polyamide 6 has a form similar to WLF equation of time–temperature superposition, whereas the log a_H for epoxy does not have such a form. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 560–567, 2004     

Enhanced permittivity by the adhesion of conducting and low‐loss insulating ceramics in polystyrene

Ca[(Li_1/3Nb_2/3)_0.8Ti_0.2]O_3?δ (CLNT)–polystyrene–La_0.5Sr_0.5CoO_3?δ (LSCO) three‐phase composites were prepared by a two‐step mixing and hot‐molding method. The dielectric properties of polystyrene–CLNT composites were in agreement with the theoretical predictions. The dielectric properties of the three‐phase composites were investigated in terms of the volume fraction of LSCO and the frequency. The relative permittivity of the composites increased with LSCO loading. These composites with low processing temperatures showed a maximum relative permittivity of the order of 10⁴. These composites, with a giant permittivity with a broad smearing region, can find application in electrostrictive, decoupling capacitors and embedded passive devices. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

二乙烯基苯对低密度聚苯乙烯密度及尺寸的影响

研究了悬浮聚合法合成氏密度聚苯乙烯（LDPS）微粒子过程中，二乙烯基苯（DVB）的加入对树脂粒径及密度的影响。结果表明，二乙烯基苯从单体分散阶段开始影响单体液滴的分散尺寸，加入DVB后，单体液滴尺寸变小，最终产物粒径变小。且在实验条件下，随DVB量增加，最终LDPS粒径减小，当用明胶做分散剂，二乙烯基苯与苯乙烯之比（DVB／St）大于1时，粒径减小变化趋于平缓；当有致孔剂存在时，LDPS的密度随DVB量增加而减小。     

Melt rheology of compatibilized polystyrene/low density polyethylene blends

Investigations have been made on the melt rheological behaviors of compatibilized blends composed of polystyrene, low density polyethylene and hydrogenated (styrene‐butadiene‐styrene) triblock copolymer used as a compatibilizer. The experiments were carried out on a capillary rheometer. The effects of shear stress, temperature and blending ratio on the activation energy for viscous flow and melt viscosity of the blends are described. The study shows that the viscosity of the blends exhibits a maximum or minimum value at a certain blending ratio. The activation energy for viscous flow decreases with increasing LDPE content. Furthermore, the concept of equal‐viscosity temperature is presented and its role in the processing of the blend is discussed. In addition, the morphology of the extrudate sample of the blends was observed by scanning electron microscopy and the correlation between the morphology and the rheological properties is explored. © 1999 Society of Chemical Industry     

Chain-scission and yellowing in high impact polystyrene

Different grades of impact-modified polystyrene were studied by viscometry, tensile impact test and colour change upon exposure to polychromatic irradiation at 55°C in air. The samples underwent extensive reduction in intrinsic viscosity [η] and tensile impact strength, and yellowed upon polychromatic irradiation (λ ≥ 290 nm). Chain-scission during photo-oxidative degradation was also studied under conditions where evolution of volatiles was negligible. Tristimulus values were calculated for unirradiated and irradiated samples. The rate of oxidative degradation was maximum in the sample possessing higher unsaturation content.     

Effect of reaction conditions on grafting ratio and properties of starch nanocrystals‐g‐polystyrene

Starch nanocrystals‐g‐polystyrene (StN‐g‐PS) was synthesized by free radical emulsion copolymerization of starch nanocrystals with styrene. The effect of polymerization conditions on grafting efficiency (GE) and grafting ratio (GR) were investigated. It was found that during graft copolymerization procedure both GE and GR increase with increasing monomer concentration and reaction time. As a result the high GE and high GR can be achieved. The good linear fit of the GR with A_St/A_OH (the absorption strength ratio of aromatic ring peaks and hydroxyl group peaks) confirmed that during graft copolymerization, FTIR spectra can be used as a simple method for determining GR. X‐ray diffraction showed that the crystallinity of StN‐g‐PS decreased slightly with increasing GR. Grafted polystyrene side chains can improve the interface compatibility of starch nanocrystals with the hydrophobic polymer matrix. The mechanical properties of StN‐g‐PS/rubber nanocomposites can be obviously enhanced. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40571.