Applications of rheological torque–time curves to the study of thermooxidative degradation of polypropylene powder

The torque–time curves of polypropylene (PP) powder treated under various thermooxidative degradation conditions were obtained through processing in the mixing chamber of a rheometer. Meanwhile, the Fourier transform infrared (FTIR) spectra of the corresponding samples were determined, and the quantitative analysis of the carbonyl indices of the FTIR spectra of the samples of the PP powder was carried out to provide evidence for the rheological characterization. PP granules, to which an antideteriorant was added before they were commercially supplied so good antidegradation could be achieved, was investigated for the sake of contrast. The analysis of the experimental results showed that the height of the torque–time curve of the PP powder and the corresponding value of the equilibrium torque could be used to characterize or evaluate the variations of the thermooxidative degradation of the PP powder. Under the same processing conditions, the heights of the torque–time curves of the PP powder and the corresponding values of the equilibrium torque decreased with the enhancement of the thermooxidative degradation treatment before mixing; on the contrary, the heights and areas of the characteristic bands of the carbonyl groups in the FTIR spectra of the PP powder and the corresponding values of the carbonyl index increased. The quantitative analysis of the FTIR spectra provided evidence for the conclusion that the heights of the torque–time curves of the PP powder and the corresponding values of the equilibrium torque could be used to characterize or evaluate the thermooxidative degradation of the PP powder. If the treatment under thermooxidative degradation conditions weakened or the degradation of the PP powder just began (i.e., in the viscosity range for processability), the evaluation method using the heights of the torque–time curves of the PP powder or the corresponding values of the equilibrium torque could provide more sensitivity than the method using the values of the carbonyl index. Consequently, the method using the heights of the torque–time curves to evaluate the thermooxidative degradation of the PP powder had its advantages. The application of the torque–time curves could be used to evaluate not only the variation of the thermooxidative degradation of the PP powder treated under aging conditions before mixing but also the variation of the degradation, including the mechanochemical degradation, of the PP powder during the period of mixing. The dependence of the variation of the degradation of the polymer on the processing time during mixing could be evaluated by the study of the variation of the torque–time curves. It can be concluded that the application of torque–time curves to the evaluation of degradation of PP powder has the advantages of being convenient, real‐time, in situ, online, and production‐oriented. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

葡萄花黑帝庙浅层含蜡原油流变性研究

原油含蜡会导致地下原油流动的复杂性,原油在管道运输过程中会堵塞管道.葡萄花黑帝庙浅层油藏是典型的低温含蜡油藏,原油在原始地层温度下已经失去流动性,从原油流变性的角度研究这类油藏的开发,分析原油随温度及剪切速率变化的物性特点,对原油开发方案的编制、原油的集输和分析地下原油渗流机理等提供参考.     

CR composites with improved processing safety crosslinked via Heck's reaction

The aim of this study was to optimize the composition of the chloroprene rubber (CR) composites crosslinked via the Heck-type reaction to ensure their safe processing at elevated temperature. The developed curing system consisting of iron (III) acetylacetonate (Fe(acac)) and triethanolamine (TEOA) demonstrates high activity and more eco-friendly composition in comparison with metal oxide system, commercially used for CR crosslinking. However, the high activity of Fe(acac)/TEOA system results in a short scorch time, which is the greatest disadvantage regarding the safe processing of CR rubber and thus, must be improved. Therefore, CR compounds with Fe(acac) in the presence of different additives were studied. The longest scorch times (t₀₂) were observed for rubber compounds with urotropine (U), N-cyclohexyl-2-benzothiazole sulfenamide (CBS) or salicylic acid. Moreover, vulcanizates containing these additives exhibited higher tensile strengths and elongation at breaks compared to CR crosslinked with Fe(acac)/TEOA system.     

Effect of electric field on storage modulus of dielectric composites

DCs composed by dielectric particles and elastomer matrix present electric field dependent deformation. Viscoelasticity dominates their electric field response, which has to be considered in their applications. Although the influence of strain amplitude and oscillation frequency on the viscoelasticity of DCs has been investigated, the effect of electric field has been seldom studied. In this study, DCs were prepared by dispersing TiO₂ particles with different concentrations and different distributions within silicone rubbers. The areal strain and the storage modulus of the DCs under different electric fields were tested. The results indicated the electric field has significant influence on the storage modulus of the DCs. Such an electric field dependent storage modulus is more significant for the DCs with higher particle fraction, or with aligned distributed particles. The enhanced electrostatic interaction between the adjacent particles by applying electric field is responsible for the phenomena.     

Rheological,thermal and morphological properties of polyethylene terephthalate/polyamide 6/rice husk ash composites

This work deals with the rheological, morphological, and thermal properties of composites having poly(ethylene terephthalate) (PET), polyamide-6 (PA6), and their blends as matrices, and rice husk ash (RHA) as a filler. The study determines the effect of composition on the change in viscosity and rate of degradation during processing in a torque rheometer. Our data indicates that thermal stability and degradation during processing depend on matrix composition and filler concentration. SEM micrographs show both partial adhesion of the filler to the matrices and filler pullout. Optical microscopy shows particle agglomeration and that agglomerate size increased with filler content. FTIR investigates the shifting of absorption bands of PET/PA6 composite after the addition of RHA and attributes the selective dispersion of RHA to the formation of hydrogen bonds. Our data supports the idea that filler employed here is an option to develop polymer composites with improved properties.     

Effects of polyphosphoric acid (PPA), styrene-butadiene-styrene (SBS), or rock asphalt on the performance of desulfurized rubber modified asphalt

To improve the performance of desulfurized rubber modified asphalt (DRMA), especially its high-temperature performance, three modifiers (including polyphosphoric acid [PPA], styrene-butadiene-styrene [SBS], and rock asphalt) were selected to modify DRMA respectively. The conventional performance, rheological properties, chemical composition, and thermal decomposition were characterized to analyze the performance and modification mechanism of DRMA and its composites. Test results show that, the addition of PPA, SBS, and rock asphalt can all improve the high temperature of DRMA, among which the desulfurized rubber/rock asphalt compound modified asphalt (DRMA-ROCK) has the best high-temperature performance; however, its construction workability, storage stability, and low-temperature performance are poor. In contrast, desulfurized rubber/PPA compound modified asphalt (DRMA-PPA) not only has better high-temperature performance, but also has excellent low-temperature performance, storage stability, and fatigue performance. Fourier infrared spectroscopy (FTIR) test confirms that the modification process of DRMA by these modifiers is chemical modification, and the characteristic peak indexes obtained from FTIR also prove that DRMA-ROCK has better high-temperature performance but poor construction workability from the microscopic point of view. Furthermore, thermogravimetric analysis-differential scanning calorimetry test shows that the addition of rock asphalt improves the thermal stability of DRMA, while PPA and SBS decrease its thermal stability. From the above results, it can be concluded that DRMA-PPA has excellent comprehensive properties.     

The challenge of predicting spinnability: Investigating benefits of adding lignin to cellulose solutions in air-gap spinning

In this study, the underlying mechanism for improved spinnability when mixing lignin and cellulose in solution was investigated. Co-processing of lignin and cellulose has previously been identified as a potential route for production of inexpensive and bio-based carbon fibers. The molecular order of cellulose contributes to the strength of the fibers and the high carbon content of lignin improves the yield during conversion to carbon fibers. The current work presents an additional benefit of combining lignin and cellulose; solutions that contain both lignin and cellulose could be air-gap spun at substantially higher draw ratios than pure cellulose solutions, that is, lignin improved the spinnability. Fibers were spun from solutions containing different ratios of lignin, from 0 to 70 wt%, and the critical draw ratio was determined at various temperatures of solution. The observations were followed by characterization of the solutions with shear and elongational viscosity and surface tension, but none of these methods could explain the beneficial effect of lignin on the spinnability. However, by measuring the take-up force it was found that lignin seems to stabilize against diameter fluctuations during spinning, and plausible explanations are discussed.     

Upcycling of polypropylene with various concentrations of peroxydicarbonate and dilauroyl peroxide and two processing steps

The influence of two peroxides (peroxydicarbonate/dilauroyl peroxide) with various concentrations (10–200 mmol/kg PP) and their effective opportunity to introduce long chain branched (LCB) were investigated. The dependence of a single and double extrusion step and the changes of the properties were studied. Experiments were carried out in a single screw extruder at 180°C for the first extrusion step (modification) and at 240°C for the second extrusion step (processing simulation). Melt flow rate and dynamic rheological properties were studied at a measuring temperature of 230°C. For the definitive determination of long chain branched polypropylene (LCB-PP) served the extensional rheology measurements. The mechanical properties were examined via tensile test and impact tensile test. Summarized, LCB (melt strength) could be observed via extensional rheology for all modified specimens and the mechanical properties were maintained or even improved for the modified samples. Particularly, samples containing dilauroyl peroxide display excellent mechanical properties in this study.     

Torrefied agro-industrial residue as filler in natural rubber compounds

This study explored the feasibility of using torrefied biomass as a reinforcing filler in natural rubber compounds. Carbon black was then replaced with the torrefied biomass in elastomer formulations for concentrations varying from 0% to 100% (60 parts per hundred rubber or phr total). Their influence on the curing process, dynamic properties, and mechanical properties was investigated. Results were compared with the properties of vulcanizates containing solely carbon black fillers. Time to cure (t₉₀) for compounds with torrefied biomass fillers increased, while filler-filler interactions (ΔG') decreased, compared to carbon black controls. At low strains, the tan δ values of the torrefied fillers vulcanizates were similar to the controls. Incorporation of torrefied biomass into natural rubber decreased compound tensile strength and modulus but increased elongation. Replacement with torrefied fillers resulted in a weaker filler network in the matrix. Still, results showed that moderate substitution concentrations (~20 phr) could be feasible for some natural rubber applications.     

工业纯铝高温流变行为的实验研究

为了深入了解连续铸轧这一融合了“铸造”和“轧制”两个工艺过程条件下的流变行为与简单铸造+热加工(热轧)组合条件下流变行为的差异,在Gleeble-1500热模拟机上对铸造工业纯铝高温压缩流变行为及其影响因素进行了系列的模拟实验研究,得到了不同变形条件下铸造工业纯铝高温压缩成形过程中的流变曲线;通过多元线性回归分析得到了其应力-应变本构方程;并与铸轧过程物理模拟实验研究的结果进行了对比分析,结果表明:在相同变形条件下铸造工业纯铝高温压缩变形流变应力小于铸轧过程的流变应力,且随着应变速率的增大,它们之间的差值更大。