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Composites of LDPE filled with different amounts of alumina Al 2 O 3 were prepared using co-mixing technique and melt-mixing. This technique, which is easy, non-toxic and inexpensive, has been successfully used in our laboratory for different polyolefins/metal oxides nanocomposites elaboration. Samples containing 0.5, 1 and 2 wt% of alumina, were prepared by melt-mixing at 190 °C without any chemical treatment or coupling agent. The effect of alumina treatment was studied. The Al 2 O 3 was first co-mixed with the stearic acid then added to the polymer. The stearic acid melts at 70 °C, thus ensuring the dispersion of the covered filler particles into the polymeric matrix, which leads to better experimental results. The morphological characterization was carried out by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The thermal properties were investigated by thermogravimetric analysis (TGA). The electrical conductivity was also studied. The microstructure-properties relationships were also investigated. The composites prepared with the co-mixed Al 2 O 3 were compared to those prepared with the neat Al 2 O 3 . The thermogravimetric (TGA) results showed an enhancement of 55 °C in the thermal stability for the LDPE/Al 2 O 3 composition containing 1 wt% of treated Al 2 O 3 . The electrical conductivity results showed also an optimum value of 6.6.10–7 U –1 cm –1 for the same composition. Keywords: Composites, LDPE, Al 2 O 3 nanoparticles, stearic acid, co-mixing method

11 pags., 7 figs., 2 tabs., Nanocomposites based on poly(vinylidene fluoride) (PVDF)/poly(methyl methacrylate) (PMMA) with untreated clay were prepared in one step by reactive melt extrusion. Chemical reactions took place between the polymer matrices, the inorganic clay particles, and three reactive agents, leading to the PVDF/PMMA/clay nanocomposites. The microstructure characterizations were carried out by differential scanning calorimetry and wide-angle X-ray scattering (WAXS). The mechanical behavior was investigated by tensile experiments, impact tests, and microhardness measurements. The morphological characterization was carried out by optical and atomic force microscopy (AFM). The decrease of the melting and crystallization temperatures of the PVDF with the increasing PMMA content is attributed to the interactions between the oxygen of the PMMA carbonyl group and the PVDF’s hydrogen atom. WAXS analysis shows that there is neither an intercalation step nor total exfoliation in any composition. As the PMMA content increases, WAXS diagrams show either the PVDF α-crystallographic form, both, α- and β-forms, or only the β-form. For PMMA contents higher than 40 wt%, the materials became amorphous. The microhardness of the samples decrease for a PMMA content up to 20 wt%. The study by optical microscopy and AFM illustrates the significant effect in the presence of clay on the film’s surface morphology., FJBC gratefully acknowledges the MINECO, Spain (Grant MAT 2013–47898-C2-1-R) for the generous support of this work.

9 pags., 11 figs., 2 tabs., The effects of various compatibilizers on thermal, mechanical and morphological properties of 50/50 polypropylene/polystyrene blends were investigated. Various compatibilizers, polystyrene-(ethylene/butylenes/ styrene) (SEBS), ethylene vinyl acetate (EVA), polystyrene-butylene rubber (SBR) and blend of compatibilizers SEBS/PP-g-MAH, EVA/PP-g-MAH, and SBR/PP-g-MAH were used. Differential scanning calorimetry, thermogravimetric analysis, wide-angle X-ray scattering, scanning electron microscopy, microhardness, and Izod impact strength were adopted. It was found that the influence of various compatibilizers was appeared on all the properties studied. The properties of the blends compatibilized with SEBS, EVA, and SBR are very distinct from those of blends compatibilized with blend of compatibilizers. Results show that compatibilized blends with the blend of compatibilizers EVA/PP-g-MAH, SBR/PP-g-MAH, and SEBS/PP-g-MAH or SBR were relatively more stable than the uncompatibilized blend and blend compatibilized with SEBS or EVA. The compatibilizer does not only reduce the interfacial tension or increase the phase interfacial adhesion between the immiscible polymers, but greatly affects the degree of crystallinity of blends.© Pleiades Publishing, Ltd. 2016, Authors gratefully acknowledge the “University Ferhat Abbas, Setif. 1 UFAS. 19000. Algeria” for the financial support of the investigation and thank the Spanish LMICINN (Grant FIS2010-18069) for the generous support of the investigation.

Reversibly crosslinked isotactic polypropylene (iPP) was prepared in the presence of dicumyl peroxide. The effects of the peroxide oxy-radicals in the melt were investigated in relation to the modification of the polymer. The dynamic rheology analysis of the crosslinking process was carried out by using a plastograph. The crosslinking reaction was evaluated by the Monsanto method. The resulting structure of the modified samples was studied by means of differential scanning calorimetry (DSC), wide-angle X-ray scattering (WAXS), microhardness, and mechanical properties. The degree of crystallinity of the modified iPP, derived from DSC and WAXS, remains almost unchanged, i.e., the crystalline structure is unaffected, though the lamellar thickness slightly decreases. The impact strength of the crosslinked iPP is greatly improved with reference to that of the unmodified material. A transition from brittle to ductile behavior appears in the modified iPP for all the crosslinking agents studied.

The evolution of the amorphous structure of starch was characterized during the drying process by real time X-ray wide-angle scattering. The X-ray diffractograms of injection-molded starch show two superposed, rather broad, scattering maxima indicative of noncrystalline structures. The location of the two peaks has been associated to disordered starch single helices. A third maximum that arises upon drying the material in vacuum is associated to the scattering emerging from regions containing double helices. A model for the starch network is proposed, assuming a primary and a secondary component. The wider, temperature stable component appearing first, is correlated to the entanglement network of the melt. The narrower network component, which is created later, at lower temperature (secondary network), is explained by the formation of double helix regions that densify the wider primary network. The secondary network is increased strongly by the drying process. X-ray experiments performed during the penetration of water, provoking a higher molecular mobility, reveal a better-packed helical structure that becomes the precursor of a double helix crystalline formation. When temperature increases, the secondary network is dissolved and water molecules arrange themselves in better-organized crystals as strongly bound crystal water.

Native starches with wide varying amylose content were processed by injection molding. The injection- molded materials were conditioned in water for 20 days and sealed in glass capillaries. Simultaneous wide- and small- angle X-ray scattering (WAXS and SAXS, respectively) were recorded during thermal heating using a synchrotron source. Crystallinity, SAXS invariant, Q, and long period, L, were measured as a function of heating temperature. The injection-molding process provokes a destruction of the crystal forms A (cereal starch) and B (tubercle starch) but favors a development of the crystal form Vh. After wet conditioning, WAXS of the injection-molded samples shows again the appearance of the crystal forms A or B, and crys- tallinity reaches values similar or larger than those of native starch. A constant heating rate (5°C/min) was particularly used for a comparison of potato and corn starch with a similar amylose content. While the crystallinity associated to forms A and B slowly decreases below 55°C and then rap- idly decreases until its disappearance at 85-90°C, the invari- ant shows a maximum around 40°C and rapidly decreases thereafter. The total nanostructure disappearance occurs at temperatures about 10°C higher for the case of potato starch. In addition, a recovery of the WAXS and SAXS maxima during the subsequent cooling process before reaching room temperature was observed only for potato starch. Analysis of WAXS and SAXS for the rest of the starch materials reveals clear differences in the structural parameters of the samples that cannot be easily explained solely on the basis of the amylose content. Thus, for Cerestar and Roquette, it is noteworthy that there was a continuous decrease of L until its total disappearance as well as the persistence of crystal- linity (form B), presumably stabilized by the presence of the Vh structure (12-15%). Real-time crystallization experiments on two amorphous injection molded samples, waxy maize (free amylose starch) and potato starch, are also discussed. It is shown that the absence of amylose delays the recrystalli- zation of amylopectine during the experiment. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 301-309, 2004

The influence of molecular architecture on the mechanical properties of styrene/butadiene block copol- ymers was investigated by means of the microhardness technique. It was found that the microhardness of the sty- rene/butadiene block copolymers is dictated by the nature of microphase separated morphology. In contrast to poly- mer blends and random copolymers, in which the micro- hardness generally follows the additivity rule, the behavior of the investigated block copolymers was found to signifi- cantly deviate depending on their molecular architecture. The glass-transition temperature of the polystyrene phase (Tg-PS), which practically remained constant and that of the polybutadiene phase (Tg-PB), which varied with the change in the block copolymer architecture, apparently do not in- fluence the microhardness values of the block copolymers. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 1670 -1677, 2003

The microhardness H of PE/PP/PA blends prepared by one-Step and two-step mixing processes was determined. The microhardness of the blends was markedly affected by the composition. Results reveal that the presence of compatibilizers induces a remarkable decrease in the H of the blends. It is shown that the large deviation of H from the additivity law of the single components is mainly due to the depression of the crystal hardness values of polymer crystals. However, the decrease in crystallinity of the individual components in each blend also has to be considered. Comparison of experimental and calculated H data and analysis of DSC results in all the blends suggest that the surface free energy of the crystals increases as a consequence of the blending process. Results are discussed in light ofthe changes occurring in the defective boundary surface of the crystals. Finally, a linear relationship between the hardness H and the yield stress † y , as well as between H and the Young's modulus E, are found. The ...

Native potato starch has been processed without the use of any additive. Moldings of initial high strength and ductility have been achieved. However, mechanical properties change with time. Thermogravimetric experiments at different temperatures show that aging takes place in three different steps. The first is characterized by a strong formation of double helices (as revealed by wide-angle X-ray scattering [WAXS]) in parallel with strong water loss. Hardness, strength, and elongation at break increase in this time range: Double helices act as reinforcing elements. When the yield elongation is surpassed, double helices are unraveled, providing a higher elongation at break. With further aging (drying), due to a shrinking process, a temporary reduction of double helices, causing a resoftening, seems to take place. In a third step, the starch moldings become quite brittle due to the lack of molecular mobility. At room conditions, it takes approximately 1 year (beginning of range 3) to lose the good mechanica...

Aromatic poly(ether ketone ketone)s (PEKKs) of regular structure, containing 1,3- and 1,4-substituted phthalic acid units in a 1-to-1 ratio, were prepared by two methods: electrophilic and nucleophilic aromatic substitutions. Electrophilic preparations were performed as low-temperature precipitation polycondensations, and resulting polymers were obtained in the form of particles. Nucleophilic syntheses were carried out in N-cyclohexyl-pyrrolidone and diphenyl sulfone at 260°C and 290°C, respectively, in the presence of sodium and potassium carbonates. Differential scanning calorimetry (DSC) curves of the polyketones “as obtained” and “reprecipitated” revealed differences in their thermal behavior depending on the polymerization method, the synthetic route, and the reaction conditions used. The ability of samples to undergo molecular reorganization during heating, affected by polymerization conditions, is responsible for the diversity of DSC curves observed. A parallel X-ray study of the samples revealed s...

The microstructure (crystallinity, long spacing) and the micromechanical properties (microhardness H) of two series of nylon 6 and nylon 66 monofilaments and their blends were investigated as a function of annealing temperature TA and uniaxial deformation in a wide composition range. In case of the homopolymers, the gradual rise of microhardness with TA is interpreted in the light of the increasing values of the crystallinity a and the hardness of the crystals Hc. The depression of the hardness values of the blends from the additive behavior of the hardness of individual compo- nents is discussed in the basis of the crystallinity depression of one component by the second one and viceversa. Finally, the influence of drawing and pressing the blends at 130°C which leads to a hardness increase is also explained in the light of an increase in the Hc value of nylon 66 due to orientation. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 636 - 643, 2000

SUMMARY: A high molecular weight, linear aromatic poly(ether ketone ether ketone ketone) (PEKEKK) has been synthesized by electrophilic Friedel-Crafts acylation condensation of 1,4-diphenoxybenzophenone with terephthaloyl chloride. The syntheses were performed as precipitation polycondensations, and the polyketones were obtained in particle form. The viscosity (molecular weight), shape and size of these particles were found to be strongly dependent on the reaction conditions. For low monomer concentration, highly ordered needle-like particles were also obtained. The chemical structure of the polymers obtained was confirmed by 'H and 13C NMR spectroscopy, and para-substitution in aryl fragments of the main chain was identified. Analysis of the expanded 'H NMR spectra for the ring proton resonances reveals defect mefa- and ortho-structures. The amount and isomer ratio of these defect structures depend on the monomer concentration used.

High molecular weight, linear aromatic poly(ether ketone ketone)s with different iso-/tere-isomer repeating unit ratio ( 100 0 , 50 50 , 0 100 ) have been studied by 1 H and 13 C n.m.r. spectroscopy. The polymers were obtained in particle form by precipitation electrophilic Friedel-Crafts acylation condensation of iso- and terephthaloyl chlorides with diphenyl ether, 1,4- and 1,3-bis(4-phenoxybenzoyl)benzenes. Conventional 1 H and 13 C n.m.r. spectroscopy shows para -substitution in the diphenyl ether fragments of the main chain. Analysis of the expanded 1 H n.m.r. spectra for the ring proton resonances reveals defect meta - and ortho -structures. The amount and isomer ratio of these defect structures depend on the polymer structure and preparation path. The low field of 1 H n.m.r. spectra of polyketones based on ‘small monomers’ (diphenyl ether and iso- and terephthaloyl chlorides) were found to show additional minor signals corresponding to a different type of defect structure. A possible mechanism of formation of these defect structures is discussed. © 1997 Elsevier Science Ltd.

6 pags., 8 figs., 5 tabs., In the second part of this series the influence of monomer concentration on the chemical structure and the shape and size of poly(aryl ether ketone ether ketone ketone) (PEKEKK) particles was reported. The present study of the thermal behavior and microstructure of aromatic polyketone samples in the form of particles has been carried out by means of differential scanning calorimetry (DSC) and wide angle X-ray diffraction (WAXD). Samples before and after reprecipitation and annealing were investigated. Similar to other polyketones, PEKEKK shows two polymorphic forms: form II, less stable, is currently observed in the samples, while the reprecipitated polymer preferentially shows form I. Form II is partially converted into form I upon short annealing treatment of the material. The semicrystalline materials show melting points and glass transition temperatures which are higher for the samples with higher molecular weight and more regular chain structure. A comparison of thermal properties of “as obtained” and “reprecipitated” samples reveals the influence of the particle architecture on the chain mobility. The latter determines the ability of polyketone chains to crystallize. Infrared dichroism was also used to characterize the arrangement of polymer chains inside the polyketone particles showing crystal habits., Grateful acknowledgment is due to DGICYT, Spain, for the support of this investigation (grant PB94-0049). M.G.Z. also thanks DGICYT for the tenure of a sabbatical grant during his research work in Madrid

The crosslinking of isotactic polypropylene (iPP) using crosslinking agents (CAs) based on a peroxide/sulfur/accelerator system is a very attractive new method that has been reported recently. The present work deals with the study of the dynamic rheological behavior of iPP during and after the crosslinking process. The influence of the CA concentration and the processing temperature T on the rheological behavior of the iPP was analyzed. The kinetics of the crosslinking reaction was established using the technique described by G. A. Harpell and D. H. Walrod. This reaction is found to be of order one. At T = 180 ºC, the crosslinking reaction was faster. By varying the crosslinking agent content, different crosslinking degrees of iPP, expressed by the corresponding gel content, are achieved. On the other hand, the modified polypropylene exhibits an unexpected viscosity shear rate pattern, which describes the reverse crosslinking reaction mainly occurring by the opening of the bridges of the new interpenetrating network (IPN) formed.

Nanocomposites based on polyamide 6,6 and carbon nanofiber have been obtained following a new procedure. It consists of the physical mixing of the polymer matrix, in the form of powder, and the corresponding amount of additive. Then, samples were prepared by compression molding and their structural characteristics, as well as their thermal and electrical properties were determined. The materials present good electrical conductivity at lower percolation thresholds than those corresponding to systems prepared by melt mixing. The study was carried out with two different grain sizes, and the findings are discussed in terms of the different size ratios of polymer to carbon nanofiber.

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.

A new route based on reversibly crosslinking reactive extrusion is applied for the development of iPP/clay nanocomposites. Analysis of small-angle X-ray scattering (SAXS) reflections of isotactic polypropylene (iPP)/clay nanocomposites, prepared by two different mixing and chemical crosslinking methods (i.e., conventional and in situ), is presented and results are compared with preceding wide-angle X-ray diffraction (WAXD) results. It is shown that the presence of clay significantly affects the value of long spacing in iPP, as well as the coherence length of lamellar stacks. Results show that the size of the coherently diffracting nanodomains decreases in two stages, first rapidly and then slowly as a function of increasing clay content. This can be attributed to the influence of confined iPP lamellae under the effect of rising number of clay particles. The appearance of the gamma-crystalline form in the crosslinked iPP/clay nanocomposites is related with the difficulty in chain folding of iPP chains introduced by the chemical crosslinking process, as well as by the presence of clay particles.

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.

A line profile analysis of the (hk0) reflections of sintered poly(p-phenylene) is presented. The wide angle X-ray diffraction maxima were analyzed to study the average size of the coherently diffracting domains as a function of annealing temperature TA. The results show that the lateral size of the coherently diffracting domains increase first slightly for TA 300°C. This is related to a rearrangement of rigid chains from disordered into the crystalline regions. The absence of SAXS supports the view of a nematic frozen-in liquid crystalline structure contributing to about 40% of the material. Eine Linienprofilanalyse der (hk0)-Reflexe von gesintertem Poly(p-phenylen) wird vorgestellt. Die Maxima der Weitwinkelrontgenbeugung wurden analysiert, um die mittlere Grose der koharent streuenden Bereiche in Abhangigkeit von der Temperatur TA zu untersuchen. Die Ergebnisse zeigen, das die Querabmessung der koharent streuenden Bereiche bis TA = 300°C zuerst leicht zunimmt und dann fur TA > 300°C stark anwachst. Dies hangt mit der Umordnung starrer Ketten aus den ungeordneten in kristalline Bereiche zusammen. Das Fehlen einer Rontgenkleinwinkelstreuung stutzt die Annahme einer eingefrorenen nematischen flussig-kristallinen Struktur, die etwa 40% des Materials umfast.

The nanostructure formation in polyimide–fullerene composites during thermal treatment was investigated ‘‘in situ’’, by means of wide-angle (WAXS) and small-angle X-ray scattering techniques. The WAXS patterns of the PI composites do not reveal the presence of C60 reflections. However, the PI/C60 composite, obtained by adding the C60 solution to the diamines-solution during the first step of the reaction (preparation of the polyamic acid, PAA), shows a maximum at small X-ray scattering angles. Results show that this intensity maximum is markedly affected by thermal treatment of the PI/C60 composite, disappearing at high temperature. From ‘‘in situ’’ X-ray scattering experiments, the ‘‘manner’’ in which the C60 nanoparticles are added to the other reactants and influences the properties of the final polymer is discussed.

The micromechanical properties of injection molded starch–wood particle composites were investigated as a function of particle content and humidity conditions. The composite materials were characterized by scanning electron microscopy and X-ray diffraction methods. The microhardness of the composites was shown to increase notably with the concentration of the wood particles. In addition,creep behavior under the indenter and temperature dependence were evaluated in terms of the independent contribution of the starch matrix and the wood microparticles to the hardness value. The influence of drying time on the density and weight uptake of the injection-molded composites was highlighted. The results revealed the role of the mechanism of water evaporation, showing that the dependence of water uptake and temperature was greater for the starch–wood composites than for the pure starch sample. Experiments performed during the drying process at 70°C indicated that the wood in the starch composites did not prevent water loss from the samples.

The microhardness behaviour of binary blends comprising a styrene/butadiene star block copolymer and polystyrene homopolymer (hPS) over a wide composition range is investigated. In particular, the interrelation between the morphology, tensile properties (such as yield stress sY and the Young’s modulus, E) and the microhardness H is explored. As in the case of microphase separated block copolymers and binary block copolymer blends, as reported in preceding publications, a clear deviation in the microhardness behaviour from the additivity law is observed. The lamellar block copolymer system is compared with the nanostructure of semicrystalline polymers having a lamellar morphology. A dependence of H upon PS lamellar thickness is found. For the samples with lamellar morphology the hardness value was found to correlate with the mechanical parameters obtained by uni-axial tensile testing according to: H/sY approx. equal to 2.2 and E/H approx. equal to 22.

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.

6 pags. 4 figs, The microhardness, H, of carbon black-polycarbonate and carbon black-low-density polyethylene composites was investigated. Two types of microadditives with different average particle sizes were employed. It has been shown that the morphology of the polymeric matrix conspicuously influences the hardness dependence of the composites with volume concentration of filler, φ. The microhardness of the carbon black-polycarbonate composites shows a steplike behavior with respect to carbon black content, while the H value of the carbon black-low-density polyethylene composite linearly increases with increasing φ. The influence of filler structure on the microhardness of the carbon black-polymer composites is also discussed. Results favor the concept that a smaller carbon black particle size (smaller aggregate diameters and interaggregate distances) enhances the microhardness of the composites.

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.

The microhardness of injection-moulded i-polypropylene/polyamide (iPP/PA) blends prepared by reactive compounding was determined. The formulation rules and processing technology for the preparation of these alloys was reported previously, iPP/PA compositions between 100/0 and 50/50 using functionalized PP with various degrees of mainchain grafting,were investigated. It is shown that the deviation of microhardness from the additivity law of the single components is mainly due to a decrease in the crystallinity of the iPP phase. The results are discussed in the light of the microstructural variations as revealed by X-ray diffraction methods.

LDPE samples with differing branching content were treated with fuming nitric acid for times up to 180 h at 60°C. 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 timet, a conspicuous sharpening and shifting of the melting curves to higher temperatures witht 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.

An exploratory study on the distribution and location of chain defects (mainly butyl and longer branches) in melt-crystallized polyethylene by means of selective nitric acid degradation is reported. The data presented here complement earlier studies of Holdsworth and Keller on copolymers and extend our previous results regarding the evaluation of the level of defect inclusion within the lattice in the light of a model involving the penetration of chain defects (branches) at interstitial crystal sites by means of generation of step-chain defects (kinks). The concentration of chain defects incorporated as point defects in the crystal lattice is compared with the total concentration of defects, as derived from the methyl infrared absorption band throughout the stages of the degradation process. The reported experiments reveal, in consonance With preceding studies, that a large fraction of chain defects (60–95%, depending on the degree of branching) accumulate in the amorphous layer and consequently ...

The hardness variation of mek crystallized polyethylene as a consequence of controlled fuming nitric exposure has been investigated using the microindentation technique. This study complements previous results obtained using other reagents (H2SO4, C1HSO3). After HNO3 exposure the microhardness of polyethylene decreases very rapidly, instead of increasing after the first hours of treatment. The hardness decrease is correlated to the volume fraction of interlamellar microvoids arising through selective acid digestion. For longer treatment times (t > 40 h) the fragility of the material increases and the sample collapses under the indenter. The hardening of the degraded material after recrystallization from the melt is followed as a function of treatment time. The results are discussed in the light of the molecular mechanisms involved. Comparison of the experimental data with hardness calculations for ideal PE lamellar structures and chain extended dicarboxylic crystals implies that the major contribution to hardening is due to electron dense gfroups attachment at the surface of a mixed lamellar structure.

The investigation of representative details in the lamellar microstructure of LDPE observed after controlled chlorosulfonation using both EM and SAXD is reported. For this purpose melt crystallized PE with two branch contents (e=0.28 and 2.53 branches per 102CH2) has been prepared using Kanig's technique over a range of temperatures and treatment times. During the first treatment hours the selective incorporation of electron-dense atoms at the lamellar surface produces a macroscopic weight increase, swelling of the sample and a concurrent decrease of the SAXS intensity. The main result, however, is that the thickness of the lamellar structure does not vary with treatment time. After long chlorosulfonation times a saturation of electron-dense atoms within the surface layer and a reduction in the lateral dimensions of the lamellae take place. Optimum conditions for revealing the representative morphology are such as to lead to a weight increase of 50% for PE withe=0.28 of branches and only to an increase of 10% for material of branch content represented by ane value of 2.53.

4 pags.3 figs., Poly-p-phenilene, prepared in laboratory, commercial poly-p-phenylene sulphide and two new high temperature thermoplastic polymers (polyarylethersulphone and polyaryletter ketone) have been doped by means of SbCl5. Measurements of electrical conductivity at room temperature carried out in situ as a function of doping time are reported.

Augmentation rotable de la conductivite de 10 a 11 ordres de grandeur par dopage; on suggere que la formation d'un complexe de transfert de charge est responsable de l'augmentation de la conductivite

The hardening of lamellar polyethylene (PE) as a consequence of a controlled chlorosulfonation treatment has been studied using the microindentation technique. The hardness of the polymer turns out to be a linear function of the density of treated PE. The rate of increase is larger for samples with higher crystallinity. This increase is related to the hardening of crystal lamellae due to the surface attachment of electron dense groups. The latter impede the slippage of crystals and substantially reduce the rate of creep of the material under the contact pressure applied.

4 pags., 7 figs., The present report is part of a general study aiming to investigate the possible evidence of electron density fluctuations as precursors of crystallization in polymers with different chain stiffness. The present experiments on the thermoplastic polyimide (New-TPI) with varying induction times, studied by small- and wide-angle X-ray scattering (SAXS and WAXS), reveal the onset of long-range ordering prior to crystal growth. Slow crystallization, slightly above Tg indicates the development of well resolved SAXS patterns associated with long range order before the development of crystalline peaks in the WAXS region. The experimental results suggest that density fluctuations control at sufficiently low temperatures the precrystallization mechanisms during the embryonic period., Grateful acknowledgment is due to the International Research Grant NEDO and to the DGICYT, Spain (Grant PB94-0049) for the support of this investigation. Synchrotron radiation experiments were performed thanks to the support of the TMR Contract ERBFMGECT 950059 of the European Community. We wish to thank Prof. James C. Seferis, PCL (University of Washington) for the supply of the New-TPI films.