bluuebunny/crossref_metadata_2025_split huggingface dataset:
Comprehensive fire behaviour assessment of polymeric materials based on cone calorimeter investigations
Authors: Schartel Bernhard , Braun Ulrike 
Published: August 2014

Abstract Bench scale performance based cone calorimeter investigations were conducted on glass fibre reinforced polyamide 66 (PA-66) and high impact polystyrene (HIPS) materials. Red phosphorus and magnesium hydroxide were used as fire retardants. Dilution, heat sink, barrier and charring mechanisms are considered to be active in the condensed phase. Dilution, cooling and flame poisoning mechanisms are discussed for the gas phase. Cone calorimeter data are used to give a comprehensive fire behaviour assessment in terms of the propensity to cause a quick growing fire and of the propensity to cause a fire of long duration. The external heat flux is varied between 30 and 75 kW/m2 so that the results for combustion behaviour and flame retardancy, respectively, are valid for different fire scenarios and fire tests. Results on the intrinsic contribution of the steady heat release rate per unit area reveal information about the flammability behaviour. UL 94 results are predicted in close correspondence to UL 94 experiments.
Effect of composition on the properties of PMMAPTEGDMA shrinkage-controlled copolymers
Authors: Velázquez Rodrigo , Reyes Julio , Castaño Victor M. 
Published: August 2014

Abstract Acrylic copolymers made of a casting syrup (prepared from poly(methyl methacrylate) (PMMA) dissolved in methyl methacrylate) and triethylene glycol dimethacrylate (TEGDMA) were synthesized by promoting the decomposition of benzoyl peroxide (BP) with dimethyl-p-toluidine. In addition, conventional copolymers, made of methyl methacrylate and triethylene glycol dimethacrylate monomers, were synthesized via thermal decomposition of BP. The two types of reaction were carried out as bulk polymerizations. Both types of copolymers were studied applying scanning electron microscopy, IR and micro-Raman spectroscopy, differential scanning calorimetry, and dilatometry. It was found that the conventional polymer is a MMA-TEGDMA copolymer without phase separation, while the phase-separated polymer contains microdomains. The shrinkage of the polymers, as well as their morphology, can be easily controlled through the chemical composition.
Novel polyelectrolyte complex between chitosan and poly(2-acryloylamido-2-methylpropanesulfonic acid-coacrylic acid)
Authors: Paneva Dilyana , Stoilova Olya , Manolova Nevena , Rashkov Iliya 
Published: August 2014

Abstract A novel polyelectrolyte complex between chitosan and copolymers of 2- acryloylamido-2-methylpropanesulfonic acid (AMPS) and acrylic acid (AA) has been prepared. The formation of the complex has been studied viscometrically, gravimetrically and turbidimetrically in the pH range from 1.2 to 5.8. The stoichiometry and the yield of the complex depend on the copolymer composition and on the pH value of the medium. In the case of copolymers with low content of AMPS units the complexes are enriched in copolymer when formed in the pH range from 1.2 to 4.8. In this pH region mainly AMPS units take part in complex formation. A stoichiometric complex forms only at higher pH values due to the increased number of complexable carboxylate ions of AA units. The stoichiometry of the complexes prepared from copolymers with higher content of AMPS units is close to equimolar and is less sensitive to pH. The obtained complexes are stable up to pH 8. It has been shown that chitosan once included in the complexes remains degradable under the action of a crude enzyme complex produced by the soil fungus Trichoderma viride. The rate of the enzymatic hydrolysis decreases in the order chitosan/PAA > chitosan/P(AMPS-co-AA) > chitosan/PAMPS. Tests on the proliferation of T. viride embedded in chitosan beads have shown that coating the beads with chitosan/P(AMPS-co-AA) complex does not hamper the development of the microorganisms.
Structure and dielectric properties of polymeric composites with ferroelectric fillers
Authors: Tchmyreva Viktoria V. , Ponomarenko Anatoliy T. , Shevchenko Vitaliy G. 
Published: August 2014

Abstract Dielectric properties of composite materials, polymer - ferroelectric filler, were investigated in wide frequency and temperature ranges. It has been shown that dielectric properties of polymer composites are a function of the size and concentration of ferroelectric filler particles, since these particles contain a defective outer surface layer with dielectric properties significantly different from those of the ferroelectric bulk. Dielectric properties of composites were found to depend on the type and properties of the polymer matrix, as well as on the method and conditions of composite preparation. Composites cured in the measurement cell possess a more porous structure, their dielectric constant ε' being lower compared to compression molded samples. ε' of polypropylene composites in the ferroelectric phase is higher than that of epoxy resin composites.
On the key role of the interface in the cationic polymerisation of p-methoxystyrene in miniemulsion
Authors: Cauvin Séverine , Dos Santos Rosalina , Ganachaud François 
Published: August 2014

Abstract This paper presents the latest improvements, in terms of reactivity and molar masses, of the process of cationic polymerisation of p-methoxystyrene in miniemulsion, which was published previously [Cauvin et al., Macromolecules 2002, 35, 7919]. The formulation was adapted to change dramatically the specific surface and the polarity of the interface where the polymerisation takes place. Adding hexadecane permits to significantly decrease the particle diameter and thus to favour a faster polymerisation rate. In addition, droplets generated by sonication are ideally covered by the INISURF (initiator/surfactant) dodecylbenzenesulfonic acid and nucleate quantitatively (true miniemulsion polymerisation). Hexadecane addition finally ensures a better stability of the polymerised dispersion. A more hydrophobic acidic surfactant, though used at much smaller concentrations, again allowed increasing the polymerisation rate. Both systems, however, show no improvements in terms of molar masses compared to those observed previously. By separating the initiating agent (a super acid such as triflic acid) from the surfactant (a non-ionic one) an increase of molar masses is obtained but accompanied by an important drop of the polymerisation rate.
Copolymers of 2-acryloylamido-2-methylpropanesulfonic acid and acrylic acid with anticoagulant activity
Authors: Paneva Dilyana , Stoilova Olya , Manolova Nevena , Danchev Dobri , Lazarov Zdravko , Rashkov Iliya 
Published: August 2014

Abstract Copolymers of 2-acryloylamido-2-methylpropanesulfonic acid (AMPS) and acrylic acid (AA), as well as the corresponding homopolymers PAMPS and PAA, were studied in vitro on human pool plasma for their anticoagulant activity. The values of the haemostatic parameters - prothrombin time, activated partial thromboplastin time and thrombin time - depend on the composition and the concentration of the (co)polymers. Reptilase time remains unchanged on adding the (co)polymers. A broad concentration range from 16 μg/ml to 3 mg/ml was studied. The copolymers possess anticoagulant activity, which is higher at higher content of AMPS units. It was found that, at certain concentrations, the haemostatic parameters of PAMPS are close to that of heparin. PAA has the lowest anticoagulant activity.
Controlled grafting of poly(styrene-ran-n-butyl methacrylate) to isotactic polypropylene with nitroxidemediated polymerization
Authors: Sugino Yusuke , Yamamoto Katsuhiro , Miwa Youhei , Sakaguchi Masato , Shimada Shigetaka 
Published: August 2014

Abstract A nitroxide (2,2,6,6-tetramethylpiperidin-1-oxyl, TEMPO) mediated polymerization method was applied to the graft polymerization of styrene (ST)/ n-butyl methacrylate (BMA) to isotactic polypropylene (PP). PP peroxides produced by γ-irradiation in air were used as macroinitiator for grafting. The molecular characteristics of grafted and free poly(ST-r-BMA) chains were analysed by gel permeation chromatography, NMR and IR measurements. The molecular weight of grafted poly(ST-r-BMA) cleaved from PP was slightly higher than that of free poly(ST-r-BMA) generated simultaneously in the reaction system. Polydispersities of these polymers were narrow, indicating that grafting proceeded in a living fashion. The incorporated amount of BMA into grafted poly(ST-r-BMA) was smaller than that of free poly(ST-r-BMA). It is considered that the local concentration of BMA around propagating ends of graft poly(ST-r-BMA) was lower than that around free poly(ST-r-BMA) because PP cannot be dissolved in BMA monomer but in ST monomer at the polymerization temperature.
Permeability of multi-layer structures
Authors: Solovyov Stanislav E. , Goldman Anatoliy Ya. 
Published: August 2014

Abstract In this paper we show that ‘permeability’ of a heterogeneous structure with mass transport and thermodynamic properties varying across its thickness is a misleading concept leading to incorrect results and design decisions while two structural transmission rate equations are recommended for practical applications. The notion of structural identity of multi-layer films is introduced to explain the apparent failure of the ‘permeability’ concept. Structural identity of two or more films means the same material sequence in the structure relative to separated environments with constant relative thickness of each corresponding layer. Structurally identical films indeed have the same ‘permeability’, however the notion of identity is shown to contradict the practical goals of multi-layer film design. Engineering examples are provided to demonstrate potential misuses of the ‘permeability’ concept in practical multi-layer design decisions. Correct problem statements and calculation procedures are included. Some general limitations of transmission rate equations are also discussed. These include the role of boundary conditions, temperature and concentration dependence of permeant diffusivity and solubility in a polymer matrix, the presence of co-permeants, surface sorption effects, film thickness, homogeneity of polymer matrix for permeation purposes and correct utilization of available data for predicting gas transport properties of multilayer films.
Effect of styrene/ethylene/butylene/styrene block copolymer on the dynamic mechanical behaviour and processability of high-impact polystyrene
Authors: Rek Vesna , Holjevac Grgurić Tamara , Jelčić Želimir , Hace Drago 
Published: August 2014

Abstract Blends of high-impact polystyrene (PS-HI) and styrene/ethylene/butylene/ styrene block copolymer (SEBS) were investigated to determine the effects of rubber on the polymer properties. The processing behaviour of the PS-HI + SEBS blends was analyzed and the dynamic mechanical behaviour of the processed blends was examined. The rheological behaviour of the prepared blends during processing was followed by measuring the torque, output and melt pressure in a twin extruder. Dynamical mechanical analysis was performed in the temperature range of -150 to 160°C. The blends were also investigated in the creep fatigue regime and relaxations were determined at 25 - 65°C. Master curves for the reference temperature 25°C were created using the time-temperature superposition principle. With increasing SEBS content there was not significant increase of the torque value for blends below a rubber content of 70 wt.-% with respect to neat PSHI. An influence of SEBS content on the increase of the apparent viscosity was observed above 40 wt.-% of SEBS. The curves of storage modulus E’, loss modulus E’’ and loss tangent tan δ vs. temperature are affected by lowering the hard phase (PS) content: tan δ of the soft phase ethylene/butylene (EB) increases, while tan δ for the hard phase and storage modulus decrease. All samples exhibit a single glass transition of the hard phase. At constant load the creep of PS-HI, SEBS and PS-HI + SEBS blends increases and the creep modulus decreases over a period of time for all samples examined. These effects are more pronounced in samples with lower hard phase content. The energy-time-temperature correspondence principle was applied to create master curves for the reference temperature 25°C for the creep modulus of PS-HI, SEBS and PS-HI + SEBS blends. Microscopic morphology results confirm the main conclusions obtained from the processing and dynamic mechanical behaviour of the blends. The phase-separated microstructure is more pronounced in PS-HI + SEBS blends. The rise in fracture energy with SEBS introduction appears in the whiteness of the SEM microphotographs, first as white crests, and in PS-HI + SEBS blends with higher SEBS content as globular structures.
Rheological behaviour of urea-formaldehyde adhesive resins
Authors: Christjanson Peep , Suurpere Aime , Siimer Kadri 
Published: August 2014

Abstract An attempt is made to describe the complicated rheokinetic behaviour of urea-formaldehyde resins during storage, in close connection with the changes in their chemical structure. The alkali-promoted non-linear polycondensation during resin storage is evaluated by pre-gel viscosity measurements. Viscosity changes are described by a power law function using extrapolation to zero shear and infinitely high shear rates. During most of the period of viscosity increase, the rheological behaviour of studied resins is similar. The deviation from the power law dependence occurring in the initial low-rate growth of viscosity takes place because of formaldehyde redistribution, which does not lead to covalent network build-up. In the presence of methanol this period is extended due to the formation of stable methoxymethylene groups.
Metastable state of amphiphilic polysaccharide solutions
Authors: Simon Sébastien , Mocanu Georgeta , Picton Luc , Le Cerf Didier , Muller Guy 
Published: August 2014

Abstract This communication reports the time-dependent viscometric behaviour of amphiphilic pullulan (with varied amount of grafted octyl groups, C8) solutions as a function of age and temperature. For lower C8 amount, no ageing effects were observed. With high amount of octyl-bearing groups, the solution exhibits a strong increase of viscosity caused by an increase of intermolecular associations and the simultaneous decrease of intramolecular associations. After longer time, a collapse of chains has been observed. This behaviour is favoured with concentration and temperature. These results evidence the metastable character of amphiphilic polymers in aqueous solution.
Comparative dielectric studies of segmental mobility in novel polyurethanes
Authors: Roussos Michalis , Konstantopoulou Anna , Kalogeras Ioannis M. , Kanapitsas Athanassios , Pissis Polycarpos , Savelyev Yuri , Vassilikou-Dova Aglaia 
Published: August 2014

Abstract Molecular dynamics in selected novel linear/low-branched polyurethanes (PUs), based on oligo(oxytetramethylene glycol), 4,4'-diphenylmethanediisocyanate (MDI) or 2,6-toluenediisocyanate (TDI), and unsymmetrical dimethylhydrazine (I) and a derivative of that (II) as chain extenders (CE), were studied by dielectric techniques. Special attention was paid to the investigation of the α relaxation, associated to the glass transition, by dielectric relaxation spectroscopy (DRS) and thermally stimulated depolarization currents (TSDC). The TSDC method was used to study the interfacial Maxwell-Wagner-Sillars (MWS) relaxation, related to the accumulation of charges at the interfaces between soft-segment and hardsegment microdomains. The results obtained by DRS and TSDC were in good agreement with each other and in reasonable agreement with results for the microphase separation (MS) obtained by small-angle X-ray scattering and differential scanning calorimetry. TSDC proved to be an attractive complementary technique to DRS for the study of MS in PUs. The results suggest that the position of the MWS band, as well as its separation from the α band, is a good measure of the degree of MS. As regards the PUs studied here, the degree of MS enhances by increasing the mole ratio of CE, and by replacing MDI by TDI or CE I by CE II.
Effects of a pulsatile magnetic field on the atom transfer radical polymerization of 2-hydroxyethyl methacrylate in methanol
Authors: Iliev Stefko B. , Georgiev George S. 
Published: August 2014

Abstract A more than twofold increase in the rate of 2-hydroxyethyl methacrylate atom transfer radical polymerization in methanol at 20°C was observed under the action of a pulsatile magnetic field. At the same time, the average molecular weight of the produced polymers decreased while the polydispersity increased slightly. The results are explained by assuming a shift of the equilibrium from the dormant species to the active propagating radicals under the action of the magnetic field.
Gel formation in frontal polymerization of 2-hydroxyethyl methacrylate
Authors: Pujari Narahari S. , Vishwakarma Avinash R. , Vishwakarma Avinash R. , Kelkar Mayuresh K. , Ponrathnam Surendra 
Published: August 2014

Abstract Frontal polymerization of 2-hydroxyethyl methacrylate was investigated to study the effect of type and concentration of initiator, solvent and diluent on the existence of a front, on front velocity as well as front temperature. A significant effect of the type of initiator and its concentration was recorded. Poly(2-hydroxyethyl methacrylate) (PHEMA) was obtained predominantly as a gel. The different gels were evaluated for water and cyclohexane gain and porosity, and the mechanism of gel formation is discussed. Amongst the three diluents used (silica gel, β- cyclodextrin and silica sol), gel formation was highest in the presence of silica sol (≈ 42%). Pore dimensions were less than 15 nm and pore size distribution was narrow. PHEMA networks showed significantly higher water regain due to swelling than attributed to the pore volume as estimated by mercury porosimetry or cyclohexane regain. Kinetics of the equilibrium swelling ratio was studied.
Polymerization of styrene using 1,1,2,2-tetraphenyl-1,2- ethanediol as initiator in the presence of 2,2,6,6-tetramethyl- 1-piperidinyloxy
Authors: Wang Gang , Zhu Xiulin , Hu Dijun , Cheng Zhengping , Zhu Jian 
Published: August 2014

Abstract The bulk polymerization of styrene using 1,1,2,2-tetraphenyl-1,2-ethanediol as initiator in the presence of 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) was investigated. The results show that polymerization proceeded in a controlled/ ’living’ way, i.e., polymerization rate is first order with respect to monomer concentration. Molecular weights increase linearly with conversion and molecular weight distributions are relatively low (Mw/Mn = 1.10 - 1.35). Well-defined polystyrenes with α-hydrogen and TEMPO end groups were obtained.
Deformation of the lamellar structure in semi-crystalline polymers studied by computer simulations
Authors: Viana Júlio C. , Ribeiro Carlos J. , Dias Gustavo R. 
Published: August 2014

Abstract Yield in a semi-crystalline polymer involves the disruption of the crystalline phase in an irreversible deformation process. In a semi-crystalline polymer, the crystalline lamellar regions are bridged together by inter-lamellar amorphous layers, which act as a loading transfer medium. The deformation of both phases is, therefore, to some extent inter-related. In this work we adopted a continuous mechanic approach (neglecting atomic/molecular interactions) of the lamellar deformation of semi-crystalline polymers in the sense that we simulated the mechanical response of a lamellar structure (two lamellae interconnected by amorphous regions) in a finite element analysis. The use of computer simulations allows studying independently the effect of each relevant morphological parameter on the mechanical response. Several simulations were performed considering isolated variations of the following morphological parameters: i) mechanical behaviour of the amorphous material; ii) thickness of the crystalline regions; iii) length of the amorphous regions; iv) number of amorphous regions connected with a crystalline lamella; v) relative angle between the crystalline and the amorphous regions; vi) mode of loading (tension and compression). The thickness of the crystalline lamellae is evidenced as the most significant factor affecting the tensile response of the lamellar structure, followed by the mechanical behaviour of the amorphous phase. The connection angle between amorphous and crystalline regions and the number of amorphous regions bridging adjacent crystalline lamellae play only a minor role. The length of the amorphous regions has a negligible influence. As expected, the lamellar structure shows also distinct behaviours under distinct loading modes, tensile loading showing the highest stresses.
Synthesis and electrooptical characterization of polysiloxanes containing indolyl groups acting as photoconductive substrates for photorefractive materials
Authors: Angelone Rocco , Castè Claudia , Castelvetro Valter , Ciardelli Francesco , Colligiani Arturo , Greco Francesco , Mazzotta Alessandro , Ruggeri Giacomo 
Published: August 2014

Abstract Synthesis and electrooptical analysis of polysiloxane and poly-N-vinyl derivatives containing indolyl groups are reported. The indole group and some of its methyl derivatives have been taken into account in order to evaluate their behaviour, with respect to that of the widely employed carbazole group, when used as photoconductive centres attached to a polymer chain. The obtained data show that photoconductivity and traps formation mechanism can be inferred as functions of the physico-chemical parameters (electric dipole moment and ionization potential) of the different groups and polymers involved. To this end such parameters have been carefully computed for a series of pyrrole, indole and carbazole derivatives. The 2,3-dimethylindole derivative appears to be particularly promising due to its electrooptical behaviour in the red absorption region where measurements have been accomplished and are shown to be consistent with the theoretical predictions.
Interfacial studies of carbon fibre / polycarbonate composites using dynamic mechanical analysis
Authors: Paiva Maria C. , Mano João F. 
Published: August 2014

AbstractUnidirectional composite material samples with ultrahigh modulus carbon fibres, treated and untreated by oxygen plasma, and a polycarbonate matrix were prepared and tested. Dynamic mechanical analysis (DMA) was used to study interfacial fibre/matrix interaction and the fragmentation test method was applied to determine interfacial shear strength. For the composite samples with treated carbon fibres, analyzed by DMA, a consistent shift of the loss modulus peak toward higher temperature was observed. The damping ratio was highly affected by residual stresses along the carbon fibre direction due to the large difference of thermal expansion coefficients of matrix and fibres. Critical fibre length and interfacial shear strength, obtained from the fragmentation test, showed substantial improvement for treated fibres as compared to the untreated ones. Plasma oxidation of the fibre surface improved considerably the fibre-matrix interaction. Care must be taken interpreting the DMA results, due to specific characteristics of the system studied.