Effect of aging on the mechanical properties of cold-crystallized poly(trimethylene terephthalate)

The changes in the mechanical and thermal properties of cold-crystallized poly(trimethylene terephthalate) during aging at 60 and 80 °C were investigated. A significant increase in the tensile modulus and stress at yield and a decrease in strain at yield were observed for both aging temperatures. Differential scanning calorimetry (DSC) scans of the aged sample showed an endothermic annealing peak 10-20 °C above the previous aging temperature, the maximum temperature and enthalpic content of these peaks increased with aging time. Dynamic mechanical measurements indicated a relaxation process starting at about 20 °C above the aging temperature and correlate with the annealing peak detected by DSC. Density measurements and wide-angle X-ray scattering investigation revealed that neither the crystallinity increased significantly nor did the crystal structure changed. These results were explained by the existence of a third phase besides the crystalline and the ‘classical amorphous’ which involves oriented and constrained ‘non-crystalline’ polymer chain sequences close to the crystalline lamellae.     

Thermorheological properties of asphalt binders

The rheological properties of different types of asphalt binders were studied and compared considering their constituents and physical characteristics. The saturate, aromatic, resin, and asphaltene (SARA) analysis and differential scanning calorimetry (DSC) have shown their individual constituents and two distinct glass transition temperatures, indicating the phase changes of the two main components of the asphalt binders, namely asphaltenes and maltenes. Rheological characterization was performed over a wide range of temperatures (−10°C-60°C) showing that these materials may exhibit viscoelastic solid to viscous liquid behaviour. Master curves of complex viscosity, storage modulus, and loss modulus were constructed by applying the time-temperature superposition principle, which was found applicable over the temperature range considered. Stress relaxation and steady-shear test were applied to the samples in order to determine their rheological behaviour in the nonlinear viscoelastic regime (viscosity and nonlinear relaxation modulus). The rheological results were modelled and revealed that the Kaye-Bernstein-Kearsley-Zappas (K-BKZ) constitutive equation is suitable in representing the rheological behaviour of asphalts. The SARA analysis and rheological measurements were found to be compatible.     

Study on percolation phenomena and mechanism of enhanced asphalt by polymers

Abstract

The properties of asphalt modified by styrene–butadiene–styrene, polyvinyl acetate and waste crumb rubber separately in a wide range of polymer loadings were studied in this paper. In analysing the relationship between polymer loading and modified asphalt properties, we found that the ductility of polymer modified asphalt measured at 5°C exhibited a percolation phenomenon, that is, as the loading of polymer exceeded a critical value, the ductility of modified asphalt changed abruptly. Furthermore, a percolation threshold differential existed. A rubber processing analyser, an optical microscope and a fluorescence microscope were used to characterise the microstructure of polymer modified asphalt and validate the occurrence of a polymer network in modified asphalt as a function of polymer loading. The percolation phenomenon of polymer modified asphalt was found to be associated with the polymer network in modified asphalt and can be well explained by the percolation mechanism of rubber toughened plastics.     

The effect of moisture on the dielectric behavior of poly(vinyl acetate)–natural rubber blend

Dynamic dielectric analysis was used to analyze the miscibility of poly(vinyl acetate) and natural rubber and the effect of moisture on the dielectric properties of the polymer blend. Two separate dielectric relaxations were observed within the temperature range studied. The high-temperature relaxation was a result of the glass transition of poly(vinyl acetate), whereas the low-temperature relaxation was attributed to that of natural rubber. The peak temperatures of ε″ of the high-temperature relaxation decreased with increasing aging time, while the magnitudes of the ε″ peaks increased with increasing days of aging. The peak temperatures of ε″ of the low-temperature relaxation stayed constant, while the magnitudes of the ε″ peaks increased with increasing days of aging. This indicates that both polymers are responsible for the sorption of moisture; however, water is an effective plasticizer only for poly(vinyl acetate). Anomalous increases in the magnitudes of ε″, especially in the low frequency sides, of the Argand diagrams were explained by Maxwell–Wagner–Sillar (MWS) polarization at component interfaces. The oscillator strength, relaxation time, and the two distribution parameters, A and B, calculated from the skewed circular are equation, were affected with days of aging.     

Mechanical properties of polyketone terpolymer/rubber blends

Blends of aliphatic polyketone terpolymer and a core-shell rubber (CSR) were melt processed with varying CSR concentration of 0-40 wt%. The obtained morphology was of finely dispersed CSR particles in the polyketone matrix. The thermal properties of the matrix polymer remained unaffected by the addition of the CSR phase. The crystallinity remained constant at 35 wt% and the melting temperature was not changed. The tensile modulus and yield stress were decreased by the addition of the rubber phase to the aliphatic polyketone polymer. The deformation was strongly delocalised with increasing CSR content. The temperature development during fracture was also strongly reduced with increasing rubber concentration. The CSR phase was found to toughen the aliphatic polyketone matrix very effectively, the brittle to ductile transition temperature was lowered from 90 to −40 °C with the highest rubber concentration (40 wt%). Cavitation experiments revealed that the macroscopic cavitation strain remained constant with increasing rubber content. A study of the deformation zone below the fracture surface showed that voids were produced by cavitation of the rubber phase. The voids were strongly deformed by the plastic deformation of the matrix polymer. At high strain rates a relaxation layer was found below the fracture surface, where the voids were no longer present. This relaxation zone was found to be due to the adiabatic temperature rise of the material during fracture at high strain rates.     

Elevated temperature aging of HIPS

The effects of aging at 85°C on a rubber-modified polystyrene (HIPS) have been studied as a function of aging time in both air and nitrogen. Four different types of physical measurements were carried out on the aged samples. These included mechanical relaxation measurements, tensile stress–strain measurements, creep measurements at several stresses, and measurements of fatigue lifetime under applied tension–compression stress. Aging in nitrogen is largely a physical aging process and results in higher modulus, higher tensile strength, and longer delay times to the onset of accelerating creep deformation. But tensile ductility and fatigue lifetime tend to reduce, and there is no change in location of T_g of the rubber phase. Aging in air involves both chemical and physical aging, and the changes that occur depend on which process dominates. For long-time aging of 150 h or more, the rubber-phase T_g is shifted to higher temperatures and the associated loss peak is broadened due to crosslinking. Also, the tensile strength, tensile ductility, creep delay time, and fatigue life all reduce. These effects are attributed to oxidative attack and embrittlement. SEM micrographs reveal variations in fracture surface morphology due to the mode of testing and to the aging medium.     

纳米有机膨润土/丁苯橡胶复合改性沥青的制备及性能

以纳米有机膨润土和丁苯橡胶(SBR)制备复合改性沥青,并考察了复合改性沥青的针入度、软化点、延度、储存稳定性及流变性能,同时对比了液体SBR和粉末SBR对复合改性沥青性能的影响.结果表明,复合改性沥青中,纳米有机膨润土的最佳质量分数为4％.随着SBR用量的增加,沥青的针入度降低,软化点升高,延度先增大后减小.粉末SBR...     

Artificial aging of polymer modified bitumens

This paper presents an investigation of artificial aging of polymer modified binders, prepared from three base bitumens and six polymers. Aging of the binders was performed using the Thin Film Oven Test (TFOT), the Rolling Thin Film Oven Test (RTFOT), and modified RTFOT (MRTFOT). The binders were characterized by means of infrared spectroscopy, different types of chromatography, and dynamic mechanical analysis. It was found that the effect of aging on the chemistry and rheology of the modified binders was influenced by the nature of the base bitumens and was strongly dependent on the characteristics of the polymers. For styrene–butadiene–styrene (SBS) and styrene–ethylene–butylene–styrene (SEBS) modified binders, aging decreased the complex modulus and increased the phase angle. Aging also increased the temperature susceptibility of these modified binders. The rheological changes of SBS modified bitumens were attributed to polymer degradation and bitumen oxidation. However, for SEBS modified bitumens, the mechanisms of aging are unclear. In the case of ethylene vinyl acetate (EVA) and ethylene butyl acrylate (EBA) modified binders, the process of aging increased the complex modulus and elastic response (decreased phase angle), and reduced temperature susceptibility. These changes were mainly due to the oxidative hardening of the base bitumens. The study also showed statistically significant correlation between TFOT, RTFOT, and MRTFOT. However, no definite conclusions could be drawn regarding the difference in severity of aging between these methods. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 1811–1824, 2000     

苯乙烯-丁二烯-苯乙烯嵌段共聚物改性沥青的老化性能

考察了苯乙烯-丁二烯-苯乙烯嵌段共聚物(SBS)和加入含硫稳定剂的SBS改性沥青老化后的动态力学性能、黏度变化和低温物理性能。结果表明,SBS与含硫稳定剂的加入改善了老化后沥青的高温性能;老化后的改性沥青表现出更好的高温刚性,蠕变劲度降低,蠕变速率增大,老化后沥青的低温性能提高,且长期使用性能良好。     

Monitoring the degradation of a thermally aged EPDM terpolymer by H NMR relaxation measurements of solvent swelled samples

¹H nuclear magnetic resonance (NMR) relaxation times were investigated as a method for monitoring the degradation of polymeric materials. The properties of an ethylene-propylene-diene (EPDM) terpolymer, oven aged at 140°C, were first characterized by traditional mechanical and solution measurements including ultimate tensile elongation, tensile strength, tensile modulus, gel fraction, solvent uptake and density. The elongation and density results provided a characteristic lifetime for this material at 140°C. The other measurements demonstrated that the EPDM terpolymer undergoes predominately chain scission during the early stages of the degradation process and predominately cross-linking during the latter stages. ¹H NMR spin-spin relaxation times, T₂, of the solid polymer were insensitive to the degree of aging until the polymer was very heavily cross-linked after long exposure times. The ¹H NMR T₂s of the polymer swelled in deutero-chloroform were as sensitive to aging as any of the classical measurements cited above. The NMR measurements have the advantage of being rapid, requiring minimal amounts of sample and being applicable for unconventional sample forms such as films, foams and powders.     

Dielectric relaxation due to interfacial polarization for heat-treated wood

The dielectric properties of totally dried sugi (Cryptomeria japonica) wood block and powder specimens treated at various temperatures up to 800 °C were measured in the range from 20 Hz to 1 MHz and from −150 to 20 °C. Relaxation ascribed to the motion of methylol groups was detected in specimens treated at temperatures below 300 °C and its magnitude decreased with increasing temperature. The electric conductivity decreased with increasing temperature up to 400 °C. Another form of relaxation was recognized for block specimens treated at temperatures between 500 and 600 °C. Cole-Cole’s circular arc law was applied to the experimental results. The relaxation magnitude was 60-75 and 24-28 in the longitudinal and radial directions of the block specimens, respectively. Identical relaxation was also observed in the powder specimen. The electric conductivity began to increase remarkably from 500 °C. These results suggested that a small volume fraction of particles with large conductivity is formed at microscopic levels in the cell walls. It is considered that this relaxation is due to interfacial polarization.     

Polymer blends for enhanced asphalt binders

Straight asphalt binders have been modified by addition of both high-density polyethylene (HDPE) and a blend of HDPE and ethylene-propylene-diene-monomer (EPDM). The blend composition was fixed to 90/10 HDPE/EPDM to illustrate the possibility of adapting the polymer to be added to the asphalt binder for specific end-use applications. Linear viscoelastic properties of unmodified and polymer modified asphalts at concentrations ranging from 1 to 5 wt% were studied before and after Thin-Film Oven Test (TFOT) aging. Temperatures ranging from −15°C to 60°C were considered. Standard tests such as Ring-and-Ball softening point, Fraass breaking point and TFOT aging were also performed on the whole set of samples. It was found that addition of rubber-modified polyethylene (HDPE/EPDM) to the straight asphalt results in materials with enhanced overall properties, and most important, dispersed phase much more stable than the equivalent HDPE modified asphalt, mainly before TFOT aging. Good results were obtained for 1% HDPE/EPDM samples. Optimum design is, however, required for the desired properties to be obtained.     

Infrared spectroscopy study of photodegradation of polymer modified asphalt binder

The effect of solar radiation in the aging of the asphalt binder can be considered relevant in several countries due to the high level of insulation. This article deals with the comparative aging of a conventional asphalt binder and styrene-butadiene-styrene modified asphalt binder samples under the effect of weathering. The samples were exposed to cycles of xenon radiation, moisture, and temperature. The degradation of binders was analyzed by using the technique of Fourier transform infrared spectroscopy. The C H/CO ratio decreased 92.5% for the conventional asphalt cement and 74% for the polymer modified asphalt after 150 h of exposure in a weathering chamber. The oxidation resistance of styrene-butadiene-styrene modified asphalt binder was higher than the conventional asphalt cement evaluated by using the weathering test and infrared spectroscopy analysis. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Sublinear dispersive conductivity in polymethyl methacrylate at temperatures above the glass transition

Dynamic electrical analysis shows that conductivity conditions the electrical properties of a polymer at high temperatures and low frequencies. In this paper we show the possibilities of the electric modulus formalism to study the properties of carrier transport and space charge relaxation processes in polymethyl methacrylate. Asymmetric Argand's plots are observed in the temperature range between 150 and 210 °C. This asymmetry is related to power-law dependencies in the real part of the conductivity, of the form ωⁿ with n<1, as a result of correlated ion hopping. The complex part of the electric modulus exhibits a peak in the low frequency range that can be associated with these conductive processes. In the case of the relaxation time related to conductive processes, it has been observed that Maxwell time is higher than the characteristic time associated with the crossover frequency which determines the transition from dc to ac regime. This fact is explained by the presence of deep traps. Finally, a maximum in the value of n is observed between 180 and 190 °C which may be related to coupling between charge transport and chain segment motions.     

Molecular Dynamics Simulations of Polymer‐Bonded Explosives (PBXs): Modeling,Mechanical Properties and their Dependence on Temperatures and Concentrations of Binders

Two models, i.e. “covering” and “cutting” models, for the polymer‐bonded explosives (PBXs) were proposed for different researching aspects. Used for choosing polymeric binders, the “covering” models are mainly applied to find the relations of temperatures and concentrations respectively with elastic properties of the PBXs. The “cutting” model is especially used to describe the highly anisotropic behavior of 1,3,5‐triamino‐2,4,6‐trinitrobenzene crystals (TATB). These models were realized by using molecular dynamics methods. It is found that the ductility of crystalline TATB can be effectively improved by blending fluorine‐containing polymers in small amounts. The moduli for the PBXs decrease with increase in temperature and concentration of binders. Different crystalline surfaces interacting with the same polymer binder have different modulus‐decreasing effects due to the highly anisotropic behavior of TATB. The modulus‐decreasing effect for different crystalline surfaces ranking order is (010)≈(100)>(001).     

Influence of Paint Baking Exposure on the Lap-Shear Properties of a Polymer-Cored Laminated Steel

Effect of thermal aging on the lap-shear properties of an acrylic-cored laminated steel was investigated by shear testing of specimens following exposure in air to the paint bake temperature of 180°C. The laminated steel consists of two thin steel layers bonded to a polymer core. It was found that thermal aging caused an increase in shear modulus and a decrease in ductility. Shear strength initially decreased, but then increased with aging time. Fractographic, thermal gravimetric, and differential scanning calorimetric analyses indicated that the decrease in shear strength and ductility is likely caused by void formation resulting from evaporation of the volatiles in the acrylic. These voids increased the local stresses. The subsequent increase in shear strength is attributed to the increase in adhesive cross-linking from thermal curing which hardens the adhesive. The increase in shear modulus with increase in aging time is ascribed primarily to thermal curing.     

Ring-opening polymerization of macrocyclic(aromatic disulfide) oligomer derived from 4,4′-oxybis(benzenethiol)

Ring-opening polymerization of macrocyclic(aromatic disulfide) oligomer derived from 4,4′-oxybis(benzenethiol) was studied. Ring-opening reactions were carried out in nitrogen and oxygen atmosphere, respectively. Oxidation reaction and cross-linking reaction took place in oxygen atmosphere. The melt copolymerization between cyclic 1 and elemental sulfur was studied using DSC, and TGA techniques. With increasing the contents of sulfur in the polymer, the T_g values, and 5% weight loss temperatures decreased. When the ratio of sulfur to cyclic reached 5, the polymer appeared as a rubber with a T_g of 23.0 °C and a 5% weight loss temperature of 269.4 °C. A series of poly(thiol aromatic)s were prepared from cyclic 1 and dibromo aromatic compounds in diphenyl ether at 260 °C. The dibromo aromatic compounds can be bis(4-bromophenyl) ether, 4,4′-dibromobiphenyl, and 1,4-dibromobenzene. 4,4′-Dibromobiphenyl gave poly(thiol aromatic) with a T_g of 122.2 °C and a T_m of 221.3 °C by reacting with the cyclic 1.     

Outdoor aging of road asphalt and SBS modified asphalt

The process of performance degradation of road asphalt (RA) is regarded as aging. At present, better understanding of the thermal-oxidative aging of asphalt is achieved and the corresponding method to evaluate this process is developed; meanwhile, photo-oxidative aging (aging in an atmospheric environment, which is referred to as “outdoor aging” in this paper) of asphalt remains at the initial stages of scientific exploration. The outdoor natural ultraviolet (UV) aging of RA and SBS modified asphalt (SBSMA) are investigated in this study. The experimental results show that the basic performances of RA and SBSMA present similar change tendencies. The softening point increased, while the penetration and ductility decreased as the outdoor aging time passed by, and the 5°C ductility (ductility measured at 5°C) of SBSMA decreased very quickly. The group components of RA and SBSMA also change during UV aging. The content of asphaltene rose and that of aromatics and saturates decreased, while the content of resins changed insignificantly. Moreover, the Fourier transform infrared (FTIR) graphs show that the content of sulfoxide and carbonyl groups in RA and SBSMA increased significantly during the outdoor aging process.     

Effect of temperature on sulfur prevulcanization of natural rubber latex

Sulfur prevulcanization of natural rubber latex was conducted at 60, 70, 80, and 90°C for different periods. The extent of crosslinking was assessed. Tensile properties, water absorption, leaching, and stress-relaxation characteristics of the films were also evaluated. The volume fraction of rubber (Vr), which is a measure of crosslink density of the films, showed a maximum when prevulcanization was conducted at 80°C for 2 h or at 90°C for 1 h. At lower temperatures, the rate of reaction was slow. At each temperature, tensile strength and elongation at break decreased when the prevulcanization time increased, whereas the modulus increased up to a maximum crosslinking and thereafter decreased. Water absorption and leaching were more rapid in prevulcanized film than in postvulcanized film. The rate of stress relaxation slightly increased as the extent of prevulcanization increased. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65: 1913–1920, 1997