Study of the morphology of semicrystalline poly(ethylene terephthalate) by hydrolysis etching

Semicrystalline poly(ethylene terephthalate) was hydrolysed in water at 180°C under elevated pressure and subsequently treated with ethanol, following the etching process first developed by Miyagi and Wunderlich. The weight loss, the wide-angle X-ray scattering and the molecular weight were measured as a function of etching time. It was found that even at the end of the etching process not all the amorphous material could be removed by the hydrolysis treatment. By comparing the obtained results with those derived from an elaborate small-angle X-ray scattering study and with wide-angle X-ray scattering measurements, it was concluded that only those amorphous regions lying outside of the lamellar stacks were removed. Subsequently, the lamellar stacks themselves were attacked. It was also found that at the very beginning of the hydrolysis process additional crystals were formed in the material.Peer reviewe

Micromechanical studies of styrene/butadiene block copolymer blends

The microhardness behavior of binary blends comprising a star block and a triblock copolymer, both consisting of polystyrene (PB) and polybutadiene (PB), was investigated over a wide composition range. In particular, a correlation between the microhardness H, the yield stress a y and the Young's modulus Ε was examined. The hardness was found to correlate with the mechanical parameters obtained by uniaxial tensile testing as follows: H/ay ~ 2 and Ε/Η ~ 30. In agreement with the studies performed in case of the pure microphase separated block copolymers, the microhardness behavior was found to be strongly dependent on the morphology of the blends. The glass transition temperature of the hard phase (Tg.PS) is shown to remain nearly constant in the blends with lower LN4 content. The glass transition temperature of the soft phase (Tg.PB), which varies with blend composition, is not related to the microhardness variation in the blends.Peer reviewe

Role of a Compatibilizer in the Structure and Micromechanical Properties of Recycled Poly(ethylene terephthalate)/Polyolefin Blends with Clay

The comparison of the degree of crystallinity and the micromechanical properties in the blends of recycled amorphous poly(ethylene terephthalate) (PET)with isotactic polypropylene (iPP) and high-density polyethylene (HDPE) with a compatibilizer in different proportions is reported. The physical study of the composites of the compatibilized blends and clay is also discussed. The analysis, performed by means of wide-angle X-ray scattering and differential scanning calorimetry techniques, permits us to describe, at microscale level, the role of the compatibilizer on the structure and microhardness of the polymer blends that we studied. The results reveal that PET was incompatible with both iPP and HDPE. However, the presence of the compatibilizer, a styrene–ethylene/butylene–styrene block copolymer grafted with maleic anhydride, allowed the compatibilization of these polymers. In the PET/iPP blends, the clay seemed to have a nucleating effect on the iPP and also induced a hardness increase in the compatibilized blends. On the other hand, in case of PET/HDPE, the crystallinity of these samples (pure blends,blends with compatibilizer, and blends with compatibilizer plus clay) only depended on their composition. Similarly to the PET/iPP blends, the addition of clay induced an increase in the hardness of the ompatibilized blends.Peer reviewe

Aromatic polymers obtained by precipitation polycondensation: 4*. Synthesis of poly(ether ketone ketone)s

High molecular weight aromatic poly(ether ketone ketone)s were synthesized by the Friedel-Crafts polyacylation condensation of iso- and terephthaloyl chlorides with diphenyl ether, 1,4- and 1,3-bis(4- phenoxybenzoyl)benzenes. Depending on the monomers used for polycondensation, polyketones of regular structure with different iso-/tereisomer repeating unit ratio (100/0, 50/50, 0/100) in the main chain were obtained. Polymers of each repeating isomer unit were prepared in two different ways. All the polymer syntheses were performed as precipitation polycondensations and the resulting polymers were obtained in particle form. The influence of reaction conditions and preparation route on the polymer properties were examined. The monomer concentration and monomer stoichiometric ratio were found to affect the polymer viscosity. The size and shape of the polyketone particles obtained were also found to be governed by reaction conditions and preparation route.Peer reviewe

Relationship between Nanostructure and Deformation Behavior of Microphase-Separated Styrene/Butadiene Systems

The relationship between the morphology and the mechanical properties of nanostructured blends,comprising an asymmetric styrene/butadiene star block copolymer,exhibiting cocontinuous-like morphology and low molar mass homopolymers, was studied by electron microscopy, microindentation hardness, and tensile testing methods. Results show that the deformation behavior of these systems is significantly modified by the presence of unentangled homopolymer chains, leading partly to a decrease in mechanical properties. In contrast to common polymer blends, in which usually, the hardness values do not markedly deviate from the additivity law, the H-values in the system investigated show large deviations from the linear additivity behavior. The observed anomalous behavior is discussed in terms of the enhanced local flow processes induced by the phase-separated morphology at a nanometer scale.Peer reviewe

X-ray diffraction study of poly-p-phenylene doped with SbFs and SbCls

X-ray diffraction experiments have been performed on SbFs and SbCls doped PPP prepared by the Kovacic method. Results are discussed in terms of two structural models which account for the regular intercalation of dopants within the polymer crystal lattice.Peer reviewe

Diamagnetism and Strucure of Nitric Acid-Treated Bulk Polyethylene

An alternative procedure to examine the nature of the end product of nitric-acid-treated bulk polyethylene involving the measurement of the diamagnetic susceptibility is reported. This simple non-destructive method complements previous results obtained by means of IR spectroscopy. Thus after selectively removing the surface layer of the polyethylene lamellae with nitric acid (t > 50h) the diamagnetic susceptibility substantially decreases to values wich are consistent with tilted paraffinic chains terminated by carboxyl groups including -NO2 groups in a 4:1 ratio tially decreases to values which are consistent with tilted paraffinic chains terminated by carboxyl groups including -NO 2 groups in a 4:1 ratio.Peer reviewe

Gelatin films with very high surface hardness

Microhardness (H) of gelatin dry cast films was measured in the 100-250°C range. A strong H increase with temperature from 330 MPa up to 450 MPa was observed in the first cycle. The H values reached in the subsequent cycles are higher than those obtained in the preceding ones, surpassing the hardness of all commercial synthetic polymers and soft metals. Results are discussed in terms of crosslinking between side-chain reactive groups.Peer reviewe

Degradation of Nitric Acid-Treated Bulk Polyethylene. III. Melting Behavior

LDPE samples with differing branching content were treated with fuming nitric acid for times up to 180 h at 60~ The samples were examined by differential scanning calorimetry and small angle X-ray diffraction. While the crystal thickness derived from the X-ray long period remains practically constant throughout treatment time t, a conspicuous sharpening and shifting of the melting curves to higher temperatures with t is observed. It is suggested that the shift in melting peak is caused by the contribution of the dicarboxylic groups attached to the crystal surface after treatment. It is further shown that the shift depends inversely on the crystal thickness. The comparison of melting points for long time nitric acid treated PE samples with data from dicarboxylic acids has permitted the derivation of an expression for the melting temperature of longer molecular diacids.Peer reviewe

Degradation of Nitric Acid-Treated Bulk Polyethylene. 2. Selective Removal of Chain Defects

The selective removal of Chain defects (branches, unsaturations)by nitric acid from melt crystallized polyethylene is examined with reference to the questionof the distribution of defects between crystalline and "amorphous" domains. The results obtained using the IR methyl band at 1376 cm-1 together with weight-loss measurements support the view that the majority of defects, which are situated in the non-crystalline regions, are selectively digested by the nitric acid attack. After removal of the non-crystalline phase the small remaining branch contentlocated within the crystal cores confirms the level of defects inclusion previously derived from unit cell expansion data.Peer reviewe