几种塑料的太赫兹光谱检测

利用太赫兹时域光谱技术测量了聚乙烯、聚丙烯、聚氯乙烯、聚四氟乙烯和丙烯腈-丁二烯-苯乙烯的太赫兹透射谱,研究其在0.2~2.6 THz频段的光谱特性,得到了在室温氮气环境下这些材料的太赫兹吸收谱和折射率色散特性.发现这五种塑料在太赫兹波段的折射率和吸收系数差异显著,折射率分别在1.35~1.85之间,聚乙烯、聚丙烯、聚四氟乙烯吸收很小,相比之下聚氯乙烯、丙烯腈-丁二烯-苯乙烯吸收很大,这为塑料种类的鉴别及高太赫兹透过率塑料衬底选择提供了依据.     

Rheological and Mechanical Characterization of Multi-Walled Carbon Nanotubes/Polypropylene Nanocomposites

The rheology and morphology of multi-walled carbon nanotube (MWNT)/polypropylene (PP) nanocomposites prepared via melt blending was investigated. The minor phase content of MWNT varied between 0.25 and 8 wt%. From morphological studies using a scanning electron microscopy technique a good dispersion of carbon nanotubes in the PP matrix was observed. The rheological studies were performed by a capillary rheometer, and mechanical properties of the nanocomposites were studied using a tensile and flexural tester. Both PP and its nanocomposites showed non-Newtonian behavior. At low shear rates the addition of MWNT content causes an increase in viscosity; however, viscosity is less sensitive to addition of MWNT content at higher shear rates. Flow activation energy for the nanocomposites was calculated using an Arrhenius type equation. From this calculation it was concluded that the temperature sensitivity of nanocomposites was increased by increasing of nanotube content. An increase in tensile and flexural moduli and Izod impact strength was also observed by increasing the MWNT content. From rheological and mechanical tests it was concluded that the mechanical and rheological percolation threshold is at 1.5 wt%.     

The effect of slip in the flow of a branched PP melt: experiments and simulations

In this paper visualisation and direct velocity profile measurement experiments for a branched polypropylene melt in a 10:1 axisymmetric contraction demonstrate the onset of wall slip. Video processing of the flow shows the formation of vortices and their diminution with increasing flow rate. Numerical simulations using a multimode K-BKZ viscoelastic and a purely viscous (Cross) model—both of them incorporating a nonlinear slip law—were used to predict the flow kinematics and dynamics as well as to deduce the slip velocity function by performing fitting to the velocity profiles. It was found that the numerical predictions agree well with the experimental results for the velocity profiles, and vortex formation, growth and reduction. It is suggested that such experiments (visualisation of entrance flow and direct velocity profile measurement) can be useful in evaluating the validity of constitutive equations and slip laws in the flow of polymer melts through processing equipment.     

The effect of 1,3:2,4-<Emphasis Type="Italic">bis</Emphasis>-<Emphasis Type="Italic">O</Emphasis>-(<Emphasis Type="Italic">p</Emphasis>-methylbenzylidene)-<Emphasis Type="SmallCaps">d</Emphasis>-sorbitol (PDTS) on uniaxial elongational viscosity of polypropylene

We investigated the dynamic viscoelasticity and elongational viscosity of polypropylene (PP) containing 0.5 wt% of 1,3:2,4-bis-O-(p-methylbenzylidene)-d-sorbitol (PDTS). The PP/PDTS system exhibited a sol–gel transition (T _gel) at 193 °C. The critical exponent n was nearly equal to 2/3, in agreement with the value predicted by a percolation theory. This critical gel is due to a three-dimensional network structure of PDTS crystals. The elongational viscosity behavior of neat PP followed the linear viscosity growth function 3η ⁺ (t), where η ⁺ (t) is the shear stress growth function in the linear viscoelastic region. The elongational viscosity of the PP/PDTS system also followed the 3η ⁺ (t) above T _gel but did not follow the 3η ⁺ (t) and exhibited strong strain-softening behavior below T _gel. This strain softening can be attributed to breakage of the network structure of PDTS with a critical stress (σ _c) of about 10⁴ Pa.     

Investigation on Properties of Polypropylene/Multi-walled Carbon Nanotubes Nanocomposites Prepared by a Novel Eccentric Rotor Extruder Based on Elongational Rheology

The properties of polymer matrix composites are related not only to the chemical composition of the materials but also to the processing equipment used for their preparation which has a direct influence on the microstructure of the composites. In this paper polypropylene (PP)/multi-walled carbon nanotubes (MWCNTs) nanocomposites were prepared by melt blending through a self-developed, eccentric rotor extruder (ERE). The structure and elongational deformation mechanism of an ERE were described in detail. The morphological, rheological, thermal and mechanical properties of the resulting PP/MWCNTs nanocomposites were investigated. Scanning electron microscopy (SEM) and rheological analysis showed that the MWCNTs were well dispersed in the PP matrix. The thermal stability was investigated by thermogravimetric analysis (TGA) and indicated that the addition of MWCNTs could effectively improve the thermal stability of pure PP. The percentage of crystallinity and tensile strength of the composites were improved as a result of the heterogeneous nucleation effect of the MWCNTs in the PP matrix. The research results revealed that the enhancement of the properties of PP/MWCNTs composites could be attributed to a better dispersion of the MWCNTs in the matrix as compared to samples prepared by conventional extrusion.     

Magnetic fluids stabilized by polypropylene glycol

A series of samples of magnetic fluids stabilized with low-molecular weight polypropylene glycol (PPG) of different molecular masses were synthesized. The use of PPG allowed the maximum extension of the carrier fluid range to include ethyl- and butyl-acetate, ethanol, butanol, acetone, carbon tetrachloride, toluene, kerosene and PPG itself. Magnetic and rheological properties of the samples were investigated. Based on the results of investigation it has been concluded that magnetic nanoparticles are covered by a monolayer of surfactant molecules. At low temperatures the propanol-based sample preserves fluidity up to −115 °C. Measurement of critical temperatures of other base fluids showed that alcohols are the best carrier medium. Coagulation stability of the ethanol-based ferrocolloid with respect to water and kerosene was explored. It has been found that kerosene, whose fraction by weight exceeds 22.5%, does not mix with the colloid. This effect can be used to produce magneto-controllable extractors of ethyl alcohol. Under the action of water the colloid coagulates, which allows one to substitute the carrier fluid and to separate the colloid into fractions.     

The use of synchrotron X-ray scattering coupled with in situ mechanical testing for studying deformation and structural change in isotactic polypropylene

The mechanical behaviour of semi-crystalline polymers is greatly influenced by the properties of the crystalline and the amorphous phases. As a result this topic has been the subject of extensive research. However, to date, a comprehensive relationship between the structure and mechanical properties for semi-crystalline polymers has yet to be established. This present study concerns the commissioning of a novel method for in situ data collection during the deformation of polymers. This involves the combination of three different techniques into a single experiment, namely tensile testing, synchrotron radiation wide angle X-ray scattering, and optical microscopy. For this current investigation, three isotactic polypropylene samples have been studied, produced using different thermal treatments. This enables the influence of thermal treatment on the mechanical properties and crystallographic structure to be assessed. The results indicate that tensile properties are influenced by thermal treatment via the relative fraction of -phase material in the sample. As the temperature increases at which thermal treatment takes place, iPP ductility decreases due to the greater rigidity of the increasing -phase content. Differences in crystal strain between the different iPP crystal phases are also observed although the reasons for such differences remain unclear.     

Methods for correlating T1rho and FID components in wideline 1H NMR studies of motionally heterogeneous polymer systems

We address the problem of correlating the observed FID and T_1ρ components in wideline ¹H relaxation measurements of motionally heterogeneous polymers, and show that different methods of data treatment can highlight different aspects of the correlations present. For a sample of polypropylene we find that the T_1ρ relaxation behaviour is driven by relaxation associated with the intermediate FID component, which strongly suggests a motionally inhomogeneous amorphous region in the sample.     

Polypropylene ionic thermoplastic elastomers: Synthesis and properties

Polypropylene ionic thermoplastic elastomers have been prepared by melt radical grafting of maleic anhydride onto polypropylene in the presence of N-bromosuccinimide followed by neutralization of the resulting elastomeric grafted polypropylene using sodium salts. Sodium hydroxide and sodium acetate were compared in aqueous solution, as anhydrous or hydrated powders. The neutralization reaction was followed by Fourier transform infrared spectroscopy, allowing the development of a method to determine the effective neutralization degree. Important physical changes were recorded upon neutralization. Especially thermal stability, shear storage modulus and complex viscosity in the flow region were largely increased as a function of the neutralization degree.     

Investigation of water absorption in clay-reinforced polypropylene nanocomposites

The behaviour of polypropylene nanocomposites containing different amounts of commercial nanoclay upon exposure to distilled water and sea water at different temperatures was investigated and compared with that of neat polypropylene. In the initial stages, the weight gain (moisture absorption) follows Fick's second law, but at longer times deviations are observed owing to physical degradation and in some cases a loss of mass. Distilled water diffuses more rapidly than sea water. As the nanoclay content increases, both the rate of moisture absorption and the maximum moisture content increase, owing to the hydrophilic nature of the nanoclay and the added compatibilizing agent. Although the moisture absorption decreases the flexural properties of both the nanocomposites and neat PP, because the unexposed (as-moulded) nanocomposites are significantly superior to the neat PP they remain so even after prolonged exposure.