José G. Fatou

Sulphuric acid etching of polyethylene surfaces

The sulphuric acid etching of polyethylene results in the formation of sulphonic groups, varying the surface properties. The study of the groups formed during the etching has been carried out by means of frustrated multiple internal reflection infrared spectroscopy (FMIR). Densities, thermal properties, superficial resistances and resistivities have been correlated with the content of sulphonic groups and treatment time. Moreover, the critical surface tension and platelet adhesion have been examined and related with the change in those properties. Direct sulphonation of polyethylene is a suitable method to change its surface properties, improving the application of this polymer as a biomaterial.

Fourier transform Raman spectroscopic study of main-chain thermotropic liquid crystalline polyesters

Abstract The Fourier transform infrared and Raman spectra of the semi-flexible main-chain thermotropic liquid crystal polyester, poly(heptamethylene terephthaloyl-bis-4-oxybenzoate) are presented, and tentative band assignments given. The polymer is investigated as a function of its thermal history, and Fourier transform Raman spectra are recorded with temperature using a high-temperature cell. The results are discussed along with calorimetric and X-ray scattering data. Spectral evidence is presented which is related to both the sample crystallinity, and the crystal-to-liquid crystal phase transition.

Delayed elastic recovery of hardness indentations in polyethylene

The depth of Vickers microindentations in high density, low density and linear low density polyethylenes has been studied by two wave interferometry. The evolution of the delayed depth recovery is explained in terms of the Burgers model of viscoelastic behaviour and the numerical parameters associated with the model are related to the crystallinity, elastic modulus and yield stress of the polyethylenes studied.

The influence of the deformation temperature on the tensile properties of polyethylenes

The force–elongation curves and key tensile parameters of a set of polyethylenes were studied over the temperature range from − 100°C to their respective melting temperatures, at a fixed strain rate. The polymers chosen possessed a diverse molecular architecture and constitution. They were crystallized in such a manner as to generate a wide range in crystallinity levels and supermolecular structures. Unique to this work are accompanying dilatometric studies. These enabled the changing level of crystallinity with temperature to be monitored. The force–elongation curves that were obtained varied in a systematic manner with the chain structure and deformation temperature. The yield stresses of all the polymers were very similar to one another in the region of the glass transition temperature. However, they diverged at elevated temperatures, depending on the chain structure, linear or branched, and the level of crystallinity. The change in the ultimate properties, the draw ratio, λB, after break and the true ultimate tensile strength, with deformation temperature could be correlated with the changing level of crystallinity. The temperature dependence of these properties are strongly dependent on molecular weight and, except for the very highest molecular weights, a maximum is observed. Possible mechanisms that govern the ultimate properties are presented and discussed. The temperature dependence of the yield stress could not be correlated with the dislocation theory that has been developed to describe yielding.

Raman spectroscopy studies on structural modifications in poly(3,3-dimethyl oxetane)

Abstract Monoclinic(II) and orthorhombic(III) modifications of poly(3,3-dimethyl oxetane) can be obtained from the relaxed melt state depending on crystallization temperature. However, if the crystallization of a given modification is not completed, the other modification can be obtained from the amorphous phase. Raman spectroscopy has been used to study the influence of the temperatures and times of crystallization on the structural modifications of this polymer. The influence of the annealing process on the crystalline amount is also examined.

Mechanical properties of ethylene-α-olefin copolymers

The stress-strain behaviour at ambient temperature has been studied for a set of commercial polyethylenes. High density polyethylenes, HDPE, and linear low density polyethylenes, LLDPE, have been considered. In the first group, the linear structure is slightly modified by random copolymerization with the α-olefins, 1-propene, 1-butene and 1-hexene, at a concentration lower than 1% molar. In the second group, the comonomers employed were 1-propene, 1-butene, 1-hexene and 1-octene at a concentration lower than 3% molar. The structural variables, the level of crystallinity, the structure and amount of the interfacial and amorphous regions, and the size of the lamellar crystallites, have been correlated with the chemical structure of the ethylene-α-olefin copolymers and with the main characteristics of the deformation, the initial modulus, the yield stress and the ultimate properties, draw ratio and strength at break. The small deformation properties, modulus and yield, depend on the branch content but do not depend on the branch type. Consequently, these parameters were found to depend on the core crystallinity. On the other hand, the draw ratio at break was found to be invariant with the co-unit content and the core crystallinity. The ultimate tensile strength decreases when the mol % branch content increases. The final properties are found to depend on molecular weight.

Raman spectroscopic study of a substituted poly(phosphazene)

SummaryPolyphosphazenes present a range of unique and fascinating physical properties, including thermotropic behaviour, which are highly dependent both on the type of substitution at the P atom in the inorganic backbone, and the thermal history of the material. Recent technological advances have allowed us to study this group of polymers using vibrational spectroscopy. Fourier transform (FT) Raman spectra have been recorded from samples of poly[bis(4-methoxy-phenoxy)phosphazene] with different thermal histories. With the aid of spectral subtraction methods, differences observed between the spectra have been related to the crystalline and mesophase content of the materials.

Anionic synthesis and thermal properties of poly(3,3-diethylthietane)

Summary3,3-Diethylthietane has been polymerized by means of the anionic initiators butyl lithium and naphthalene sodium. Linear poly (3,3-diethylthietane) samples have been obtained. The molecular weight of these polymers, measured by GPC, ranges from 70,000 to 241,000. The molecular weight distribution is quite narrow. Calorimetric measurements show a glass transition temperature, extrapolated to zero heating rate, of 236.7 K. The melting curves of a sample isothermally crystallized from the melt at 303 K show two different melting peaks located at 326 and 334 K, respectively. The wide angle X-ray diffractograms for poly (3,3-diethylthietane) crystallized at 303 and 330 K gave identical patterns. Microscopy and small angle light scattering observations show that the supermolecular structure corresponds to ordered spherulites.

Morphology of poly(3,3'diethyloxetane)

Abstract The morphology of poly(3,3′diethyloxetane) fractions crystallized from the melt has been analyzed by polarized light microscopy and small angle light scattering. The superstructures that can be developed have been studied for a wide range of isothermal and non-isothermal crystallization conditions and molecular weights. The crystallization of the polymer in two different crystalline modifications (monoclinic and orthorhombic, depending on the temperature) has also been considered in relation with the morphology. Spherulites have been observed for fractions ranging in molecular weight from 10,000 to 800,000 for all crystallization conditions. Only for the lowest molecular weight and lowest undercoolings, other forms have been found. In the crystallization region in which the crystalline modifications co-exist, spherulites have been observed to deteriorate.