43 research outputs found
Macrocyclic oligomers as compatibilizing agent for hemp fibres/biodegradable polyester eco-composites
No full textRing:chain equilibria (RCE), existing under appropriate reaction conditions, between a linear polyester and the corresponding family of macrocyclic oligomers (MCOs), were exploited to develop an original compatibilizing pathway for preparing eco-composites based on hemp fibres and a biodegradable random co-polyester, namely poly(1,4-butylene adipate-co-terephthalate) (PBAT) with 50:50 adipate:therephthalate proportion.Cyclo-depolymerization (CDP) of PBAT was successfully carried out at high dilution using various solvents, catalysts, and reaction times. The reconversion of MCOs into linear chains by entropically-driven ring-opening polymerization (ED-ROP) occurs by simple heating in the bulk. This reaction, after optimization of catalyst amount, temperature, and reaction time, was used for the surface modification of hemp fibres. PBAT-based eco-composites containing hemp fibres as such or pre-modified by treatment with the MCOs were then prepared and characterized by morphological, mechanical and dynamic-mechanical analysis
Double-step moulding: An effective method to induce the formation of β-phase in PVDF
No full textNowadays, the investigation of smart methods promoting PVDF β phase has become an important research topic in many energy related fields. In this work, compression moulding was proposed as an effective, simple and easy-scalable technique to tune PVDF polymorphism and obtain the desired crystalline form, exploiting a procedure in two steps. After a preliminary principal component analysis of the infrared spectra, the different moulding conditions tested were correlated with the electroactive phase amount, obtaining a non-monotonous trend. Finally, dielectric and dynamic-mechanical measurements were carried out on selected samples. Experimental evidence indicates that the double-step moulding induces the β phase formation due to the orienting effect generated by the shear stresses in the not completely molten polymer. Moreover, this method determines an increase in permittivity, a reduction of the dielectric losses and a change of PVDF molecular relaxations with respect to the reference film moulded through a simple single-step moulding
Estudios inmunológicos, físicos, químicos y biológicos de antígenos cancerosos
No full textFil: Díaz Primerano, Ana María L.. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina
Estudios inmunológicos, físicos, químicos y biológicos de antígenos cancerosos
No full textFil: Díaz Primerano, Ana María L.. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina
Improved dielectric properties of poly(vinylidene fluoride)–BaTiO3 composites by solvent-free processing
No full textComposites of poly(vinylidene fluoride) (PVDF) and BaTiO3 nanoparticles (average diameter ca. 125 nm) are fabricated by a solvent-free and industrially scalable technique, that is, melt blending, followed by compression molding. The effect of processing parameters on the spectroscopic, microstructural, thermal, mechanical and dielectric properties are evaluated as a function of composition (loading up to 30 vol%). The presence of nanoparticle inclusions as well as specific compression molding parameters demonstrate both to affect the molecular relaxations of the PVDF matrix, studied by correlating the results of different techniques, and to induce the PVDF crystallization as β phase. Processing parameters also play a key role for optimizing the dielectric properties. An improved dielectric behavior of the composites is obtained in terms of both permittivity, whose value increases up to four times that of neat PVDF, and dielectric losses, lower than 5% between 10 and 3·104 Hz. The obtained performances resulted enhanced compared to analogous composites prepared with the use of solvents
