Jean-Louis Costa

Shear-induced crystallization of polypropylene: Influence of molecular weight

Three series of isotactic polypropylene characterized by different molecular weights and the same isotactic index have been studied during crystallization under static and shearing conditions. The shear is induced by the displacement of a glass fiber in the molten polymer. The monoclinic α-phase is here formed under shear with a columnar organization at the surface of the glass fiber, and does not appear under static condition. The growth-rate, constant during the shear-induced crystallization experiment, is compared with the result obtained from static crystallization. An important increase of the growth-rate due to the shear flow is observed. This increase depends on the molecular structure. The average molecular weights ―Mw and ―Mz seem to be the most important molecular parameters, for which an excellent correlation is obtained. The increase of these parameters ―Mw and ―Mz leads to a significant enhancement of the growth-rate, which can be multiplied by a factor of 10 in the present conditions.

Shear-induced crystallization of polypropylene : influence of molecular structure

The isothermal crystallization of isotactic polypropylenes has been studied under static conditions and under shear flow. The shear was induced by displacement of a glass fibre in the molten polymer. An α-monoclinic crystalline phase was formed with a columnar organization at the surface of the glass fibre, which did not appear under static conditions. The growth rate, constant during shear-induced crystallization experiments, is compared with the results obtained from static crystallizations. An important increase of the growth rate due to the shear flow is observed. This increase depends on the molecular weight and the tacticity of the polypropylene. Actually, the molecular weight and the isotactic index seem to be the most important molecular parameters. Their augmentation leads to a significant increase of the growth rate, which can be increased by a factor of seven, under the present conditions.

Shear-induced Crystallization of polypropylene. Growth enhancement and rheology in the Crystallization range

Crystallization under shear of many different polypropylenes has been studied using a fiber pull-out device. It appears that growth can be considerably enhanced by flow. The best correlation is obtained with weight average molecular weight. Modeling the flow pattern gives access to the mechanical parameters at the growth front (shear rate and shear stress) as well as to the total strain applied to the polymer. The residual strain can be calculated taking into account relaxation processes.

Atomic force microscopy imaging of viscoelastic properties in toughened polypropylene resins

The bulk morphology of two toughened polypropylene/(ethylene propylene)copolymer resins (PP/EP) presenting different impact resistances has been studied by means of different atomic force microscopy techniques: contact atomic force microscopy, lateral force microscopy (LFM), and force modulation microscopy (FMM). The three techniques reveal two different morphologies as observed in transmission electronic microscopy. In LFM, a higher friction force is observed on the rubbery phase which has the lower Young’s modulus confirming the relationship between friction force and elastic properties. In force modulation, the elastic moduli is found to be much lower on the EP nodules in both resins. FMM also reveals that the difference of viscous response between the PP matrix and the EP nodules is much lower in the resin which is less impact resistant.

Influence of EP/PP viscosity ratio on the surface morphology and elasticity of injection moulded PP/EP

The influence of the viscosity ratio between (ethylene-propylene) copolymer (EP) and polypropylene (PP) on the EP surface distribution in injection moulded disks of PP/EP resins has been investigated by transmission electron microscopy (TEM) and by atomic force and force modulation microscopies (AFM and FMM). TEM images taken on transverse sections parallel to the injection direction reveal that, for high EP/PP viscosity ratios, large (>1 mu m) undeformed EP nodules are observed up to the surface. The AFM and FMM observations performed on the surface reveal soft regions of the same size embedded in a more rigid matrix (undeformed EP nodules present at or just below the surface). For low viscosity ratios, EP rubber nodules, strongly elongated parallel to the surface, are observed by TEM. From FMM measurements, the elastic modulus is found to be homogeneous across the surface and is comparable to that measured above EP nodules on the high viscosity ratio resin

Characterization of ethylene in EP and in iPP/EP systems by deconvolution of IR spectra

The purpose of this study is to propose a correlation between IR spectra and molecular structure of ethylene-propylene (EP) copolymers possibly blended with isotactic polypropylene (iPP). The method is based on the deconvolution of the spectrum in the CH2-rocking range, i.e., 800-680 cm(-1), where the bands of interest overlap. The six bands present in this region were signal averaged in position and width. The spectra were then deconvoluted (curve fitted) assuming a Lorentzian shape for the bands. The band at 1167 cm(-1) (with a shoulder at 1156 cm(-1)) corresponding to a CH3 vibration is considered as an internal standard. The method was checked by varying some fitting parameters. In order to realize some quantitative measurements, calibration curves were established with some EP samples, characterized by C-13 NMR, which were used as standards. The amounts of total -(CH2-CH2)- units (ethylene units), isolated ethylene and structural defaults in PP were determined for different iPP/EP blends. Ethylene crystallinity has also been determined. A good correlation was evidenced between infrared and C-13 NMR measurements

NMR, differential scanning calorimetry, and Fourier transform infrared characterization of the crystalline degree and crystallite dimensions of ethylene runs in isotactic polypropylene/ethylene–propylene copolymer blends (iPP/EP)

High-resolution solid-state C-13-NMR, differential scanning calorimetry, and Fourier transform infrared spectroscopy were used to compare the very low crystalline degree and crystallite dimensions of ethylene runs in a series of isotactic polypropylene/ethylene-propylene copolymer blends exhibiting a range of properties. Results obtained from the three techniques on samples with the same thermal history are in a satisfying qualitative agreement. They show that the morphology of the polyethylene domains is only very slightly dependent on the viscosity ratio of the two blend components. On the opposite, it is largely governed by the ethylene content of the ethylene-propylene copolymer