1,721,112 research outputs found
Investigating the degradation phenomena of Teflon exposed to acidic environment
No full textThis study provides an overview of the effects of prolonged acid attack on the surface of PTFE gaskets, assessed using Fourier Transform Infrared Spectroscopy (FT-IR), Thermogravimetric Analysis (TGA) and Differential Scanning Calorimetry (DSC). The PTFE analysed originates from two manufacturers in form of Teflon adhesive tapes, used as gaskets in an ultrasonic tyre moulds cleaning plant (UMCS). The gaskets were exposed to various acid baths, temperature and ultrasonic waves, and shown anomalous damage and surface degradation in a relatively short operation time. The analyses here reported have been aimed at investigating this unusual behaviour. PTFE samples have been treated with different acid mixes to evaluate possible different aging effects. Both surface and core have been analysed after aging, providing evidence of the degradation phenomena. In particular, different acid treatments have highlighted different response of PTFE and differences among manufacturers
Crosslinked resins functionalized with triorganotin carboxylate: a promisin transesterification catalyst
No full textStraightforward synthesis of well-defined poly(vinyl acetate) and its block copolymers by atom transfer radical polymerization
No full textA facile Atom Transfer Radical Polymerization (ATRP) method based on the use of the complex obtained with CuCl, CuCl2 and the very active ligand 5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane (Me6CyClam) as catalytic system, was successfully employed for the first time to polymerize vinyl acetate (VAc) with a good control over the polymerization, which showed a living character and monomer conversion up to 90%. The use of such an active ligand allows to maintain a particularly low concentration of propagating species once very reactive radicals, from such monomers, are formed, hence establishing a fast and dynamic ATRP equilibrium. Several kinetic studies on the ATRP of VAc were carried out with the aim to identify the optimized conditions allowing a good control over the process attaining materials with well-defined structure and low polydispersity. The livingness of the macromolecular system was confirmed, among the others, by using the obtained PVAc as ATRP macroinitiator for the synthesis of several block copolymers. Furthermore, the possibility to hydrolyse the VAc block thus attaining amphiphilic materials was studied
Morphology, thermal, mechanical properties and ageing of nylon 6,6/graphene nanofibers as Nano2 materials
Full text linkNylon 6,6 nanofibers loaded with different Graphene (G) amounts were successfully produced with stable process and good fiber quality, using an optimized solvent system suitable both for electrospinning and for G-suspension. G addition is found to significantly affect diameter but not thermal behaviour. A new phenomenological model is proposed for the interpretation of mechanical behaviour of nanofibrous mat, trying to take into account the nanofibrous morphology. The model highlights a G contribution to mechanical properties that mainly affects the initial steps of deformation where fibers stretch, slide, twist and re-orient. Finally, the nanofibers were analysed after 20 months ageing, showing no significant alteration with respect to the pristine ones, thus the lack of detrimental ageing-effects due to G addition
Chirality on Amorphous High-Tg Polymeric Nanofilms: Optical Activity Amplification by Thermal Annealing
No full textThe chiroptical properties of amorphous chiral polymers functionalized with conjugated trans-azoaromatic chromophore linked to the backbone through a chiral cyclic pyrrolidine moiety of one single configuration at the solid state, as thin films, were investigated. For the first time nanometric thin films of amorphous polymers (not liquid crystals) showed a remarkable chiral amplification upon thermal treatment at a temperature close to their Tg. The side-chain azobenzene chromophores rearrangement driven by the enhanced chain mobility seems to favor the formation of nanodomains of conformationally ordered macromolecular chains with one prevailing helical handedness whose optical activity depends on the configuration of the intrinsic chirality of the monomeric units and which as a result are stable at room temperature for a long time
Evaluation of Tryptophan - Late curing agent systems as hardener for epoxy resin
No full textIn order to obtain a low-toxic and environmentally friendly epoxy system, the novel green curing agent L-Triptophan was used, in combination with the two commercial late curing agents 2-Undecyl-1H-imidazole and 3,3'-(4-Methyl-1,3-phenylene)bis(1,1-dimethylurea), as hardener system for the cross-link of Diglycidyl Ether of Bisphenol A (DGEBA). The thermal behavior of the precursors mixtures was evaluated by dynamic and isothermal Differential Scanning Calorimetry (DSC) and confirmed L-Tryptophan as a possible novel green curing agent for DGEBA. These encouraging results pave the way for a further study of a new class of low-toxic and sustainable curing agent systems for the production of fully bio-based epoxy resins
Dispersion and evaluation of organically modified nanoclays as performance enabling fillers for pPVC synthetic leathers
No full textNanoclays (NCs), both organically modified (OMNCs) and purely inorganic, have been evaluated as performance enabling fillers for innovative and high-performance plasticized PVC (pPVC) synthetic leathers (SLs). First, a novel dispersion technology for nanoclays in plastisols has been developed and tuned, modifying and improving different procedures used in Vulcaflex SpA. Secondly, pPVC foils containing three different NCs have been prepared and tested for mechanical, thermal and flame, and anti-migration properties using both standard and internal methods. Results have been compared to those of a neat pPVC foil and, due to the expected flame retardancy improvements, of a foil containing 2 phr of antimony trioxide (ATO). Even though certain properties appear to be slightly improved, the overall performance of these NCs are not completely satisfying
Evaluation of antimony-free flame retardants for pPVC synthetic leathers intended for safer automotive interiors
No full textAntimony-based compounds have been the state-of-the-art flame retardants (FRs) for plasticized PVC (pPVC) due to their superior efficiency at very low loading. However, the use of antimony compounds poses more than an issue, for both human health and the environment, related to their extraction, processing and use. In order to follow the consequent need to phase out antimony compounds, different FRs for high-performance plasticized PVC (pPVC) synthetic leathers (SLs), intended for automotive interiors applications, have been selected amongst readily available on the market additives and tested in highly plasticized formulations. These FRs have been evaluated either alone or in combination in order to ascertain possible synergistic effects. The samples have been obtained with standard procedures used in the R&D laboratory of Vulcaflex S.p.A., and tested for thermal stability, mechanical and flame resistance, following standard and internal methods. Results have been then compared to those of a neat pPVC foil (DUP) and of a foil containing 2 phr of antimony trioxide (ATO). Amongst the alternatives tested, various combinations proved effective in improve flame retardancy without negatively affecting mechanical properties, and proving to be, thus, promising candidates to substitute ATO as FRs in pPVC materials
Multicomponent reinforcing system for poly(butylene succinate): Composites containing poly(l-lactide) electrospun mats loaded with graphene
No full textGiven the increasing relevance of poly(butylene succinate) (PBS) and poly(l-lactide) (PLLA) as bio-based thermoplastics, and the need to improve the properties of such polymers, a novel multicomponent reinforcing system was devised. Nanofibrous electrospun mats of PLLA containing graphene were incorporated into the PBS matrix via the conventional thermo-pressed molding technique. The final biocomposites were characterized in terms of morphological characteristics via SEM and STEM; TGA and DSC were used to investigate the thermal properties and tensile testing used to assess the mechanical properties. The results showed that PBS matrix does not have modified thermal behaviour in the presence of PLLA and graphene. On the contrary, the tensile strength of the composites was gradually enhanced with the addition of PLLA mats, and the improvement was found to be proportional to the number of PLLA layers and to the amount of graphene added. The huge potential of this multicomponent reinforcing system is highlighted by the 21% increment in tensile strength
Novel porphyrin-containing regioregular poly(alkylthiophene) copolymers tested as polymeric solar cells
No full textRegioregular polyalkylthiophene copolymers were prepared by oxidative copolymerization of known amounts of brominated alkylthiophene monomers possessing or not a reactive bromide group linked at the end of the alkyl chain. Subsequent post-polymerization functionalization with tetraphenylporphyrin led to products with differing dye content in the side chain. Due to their chemical structure, the copolymeric precursors, as well as the porphyrin functionalized derivatives, were fully soluble in common organic solvents and could be used as active layers, in combination with PCBM, for the preparation of polymeric solar cells (PSC) with bulk heterojunction architecture. The power conversion efficiency of the cells containing porphyrin resulted remarkably higher with respect to the cells containing the precursor bromoalkyl moiety in the side chain and one order of magnitude higher with respect to similar previously investigated PSC produced with lower porphyrin content
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