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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.

Recent developments concerning the meth- odology used to prepare composites of iPP and nanoclays are reported. Conventional (reactive melt mixing) and in situ preparations were performed, and the structural prop- erties exhibited by the composites are discussed. Results suggest that the nanoclay could exhibit partial and, maybe, total exfoliation within the composites. Adhe- sion between the polymeric matrix and the nanoclay layers is similar to that obtained after grafting. The ex- perimental procedure used and the analysis performed by means of the wide-angle X-ray scattering and differ- ential scanning calorimetry techniques permit to describe, at nanoscale level, the contribution of the nanoclay to the polymer composite system. The micro- hardness values of the iPP-clay composites depend on the clay content and on the preparation method, and linearly correlate, according to the additivity law, with the degree of crystallinity. V C 2009 Wiley Periodicals, Inc. J Appl Polym Sci 115: 2654-2662, 2010

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.

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...

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

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.

The degradation of samples of amorphous and semicrystalline PET with different molecular weights by means of hydrolysis at 180°C has been investigated by measuring the weight loss and the x-ray crystallinity as a function of etching time. It is shown that during the first hours of etching, a concurrent crystallization of the amorphous samples takes place. It is found that weight loss values of amorphous samples after long etching times are higher than the weight loss of the crystallized materials. Results also indicate that weight loss depends to some extent on the initial degree of crystallinity of the material. It is emphasized that the lateral size of the crystallites is a major parameter in determining the total amount of etched material. Analysis of results further confirms that mainly the amorphous regions lying outside of the lamellar stacks are removed by hydrolysis. However, the crystals formed during annealing of the amorphous samples at 180°C are less perfect and the lamellar stacks in...

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 microhardness of a series of biodegradable polyesters was determined. The nanostructural features of these materials were studied by wide-angle X-ray scattering (WAXS), small-angle X-ray scattering (SAXS), and differential scanning calorimetry. Analysis of the SAXS and WAXS patterns allowed direct derivation of the degree of crystallinity and crystal thickness values, and correlations of the micromechanical properties are presented. The differences in the thermal and mechanical properties exhibited by the studied systems and the ones found in other aromatic polyesters are explained as due to the different chemical natures of the monomeric units.

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.

Reversibly crosslinked blends of isotactic polypropylene and low density polyethylene (iPP/LDPE)were prepared in the presence of crosslinking agents using reactive extrusion. The structure and properties of the modified blends were investigated by means of wide-angle X-ray scattering (WAXS), differential scanning calorimetry (DSC), and macro- and micro-mechanical measurements. The crystallinity of the modified samples (LDPE, iPP, and their blends) does not seem to be so much affected by the crosslinking process. Results show that the microhardness of the iPP/LDPE blends notably increases with the iPP content. The micromechanical properties of the modified blends only improve slightly as a consequence of the crosslinking process. In the iPP samples, and also in the iPP/LDPE blends, this process gives rise to the appearance of new, crystalline ethylenic chains, as evidenced by the calorimetric measurements. Furthermore, the impact strength of the modified materials is improved as compared with that of the original ones, while some of the crosslinked blends show a ductile fracture behavior.

A study is presented of the electrical properties of a series of nanocomposites based on high density polyethylene (HDPE) as a matrix and either carbon nanofiber (CNF) or multiwall carbon nanotube (MWCNT) as a nanoadditive. The measurements of the electrical conductivity over a broad-band of frequencies (102 > F/Hz > 109) allow improvement of the description of the electrical properties of polymer nanocomposites based on either carbon nanofibers or carbon nanotubes. Despite the lack of a continuous conducting network between particles at low concentrations, the nanocomposites exhibit a significant dc electrical conductivity due to tunnel conduction. At low nanoadditive concentrations, the frequency dependence of the electrical conductivity is mainly caused by the influence of large polymeric gaps between conducting clusters. As nanoadditive concentration increases, the size of the finitesize cluster tends to increase and the frequency dependence of the conductivity reflects the features of anomalous diffusion in fractal structures, as expected according to percolation theory. A master curve for the electrical conductivity as a function of frequency can be constructed although, for the investigated nanocomposites, this behavior should be contemplated as a working, rather than as a universal, law. © 2008 American Chemical Society., Support from the MCYT (grant MAT2005-01768) UE, Spain

15 pags., 6 fgs., 'In situ' wide angle (WAXS) and small angle X-ray scattering (SAXS) studies were carried out to characterize the structural changes occurring during the conversion of a polyamic acid into the polyimide in the presence of fullerene, C60. The variations in crystallinity, long period, and the SAXS invariant of the samples are discussed in the light of the various temperature ranges studied. The conversion of the polyamic acid into the polyimide is analyzed according to the different structural steps. Results reveal that C60 affects the degree of order of the composite in the molecular direction, giving rise to slightly smaller crystals than those found in pure polyamic acid. The difference in the SAXS data between the pure PAA and the composite are discussed through the interaction of C60 molecules with the polyamic acid, which seems to hinder the imidization reaction up to 185°C. © 2007 VSP.

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.

12 pags., 2 figs., In the present paper the effect of crystallization conditions on the melting temperature (Tm) of chemically cross-linked gelatin is studied by means of differential scanning calorimetry (DSC) and microhardness (H) measurements as extension of our recent findings (Ref. [11]). A rather unusual situation when polymer crystals melt below the glass transition temperature (Tg) is confirmed by DSC. This is highlighted on dry gelatin which is characterized by relatively high, and close to each other, Tg and Tm values (217 and 230°C, respectively). By depressing Tg, using water as plasticizer, rather imperfect crystallites are obtained which melt well below the Tm of dry gelatin. It is shown that H increases with temperature mostly due to the drying out of the room-conditioned gelatin. In the 160-180°C range H reaches values of about 390 MPa. In this temperature range the imperfect crystallites melt (according to DSC), however without formation of a typical liquid phase (since H remains constant). It is expected that this direct crystal-glass transition can be used to obtain highly ordered polymer glasses. The unusual high H values as well as the low coefficient of thermal softening of gelatin, in contrast to those common for synthetic polymers, makes this material attractive for practical applications., DGICYT (Grant PB94-0049), Spain. It is a pleasure to acknowledge the partial financial support provided by the National Science Foundation (USA) through Grant INT-95 14149 (Division of International Programme), as well as by the Bulgarian Ministry of Education, Science and Technology (Contract TH-7 14). We also wish to thank NEDO’s International Joint Research Programme, Japan, for the generous support of this investigation. One of us (S. F.) wishes to acknowledge the tenure of a sabbatical grant from DGICYT, Spain

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.

Microindentation hardness is used to characterize the surface mechanical behaviour of two series of sintered PPP/PPS composites in a wide range of compositions. This work complements a previous electrical conductivity study carried out to determine the insulator-conductor transition within these materials. The influence of annealing the PPP-phase at 400° C before sintering the composites is discussed with reference to the additivity of hardness values of the single components PPP and PPS. The hardening of these composites upon doping with SbCl5 is investigated in the light of the morphology of sintered materials. The elastic release of the material and the creep behaviour under the indenter are examined in terms of the porosity of the samples and of the dopant penetration within the material. In the case of compact materials, the hardness is found to increase due to a doping-induced surface-hardening effect. The hardness increase in porous materials responds to an inclusion of the dopant species within the material volume.

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

A combined X-ray diffraction and DSC investigation of the crystalline phase in lamellar low density polyethylene after conventional chlorosulfonation treatment has been carried out. Our results indicate that the acid attack does not involve any heavy group penetration within the lattice. The location of these groups at the basal crystal surface contributes, however, to an enhancement of the melting temperature of the modified lamellae. It turns out that the destruction level of crystalline material at 45 ºC, after 15-20 h is of the order of 20% and progressively increases for longer periods of time.

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.

8 pags., 10 figs., 7 tabs., The isothermal `cold crystallization' of the thermoplastic polyimide (New TPI) has been studied using the microhardness technique to examine the property-microstructure correlation. By using wide- and small-angle X-ray diffraction and differential scanning calorimetry, the influence of the experimental parameters, i.e., treatment temperature Tc and time tc on the micromechanical properties of the `cold crystallized' samples has been examined. It is shown that both macroscopic hardness H and volume crystallinity xc increase with Tc and tc. For the samples prepared in the secondary crystallization range, it is demonstrated that H values strongly depend on the hardness of the crystalline units Hc. In this range, long spacing L, crystal thickness lc and crystallinity (both linear xCL, and derived from density xc) slightly increase with Tc. From the DSC study, it is demonstrated that the proportion of `liquid-like' and `rigid' amorphous fraction present in each sample is directly related with the crystallization conditions. Finally, from the SAXS and DSC combined study, information concerning the secondary crystallization mechanism has been obtained., The authors are indebted to DGICYT (Grant PB94-0049), Madrid (Spain). We wish also to thank NEDO's International Joint Research Programme, Japan, for the generous support of this investigation. Partial financial support was provided by the Polymeric Composites Laboratory Consortium at the University of Washington.

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.