1,721,111 research outputs found
Linea di condotta della ricerca che si svolge presso l'Istituto di Chimica Industriale ed Applicata dell'Università di Pisa
No full textCinetica di idrolisi della emicellulosa in residui vegetali: effetto della granulometria
No full textSicurezza e insicurezza nella società contemporanea
No full textLa sicurezza, bisogno primario della specie umana, abbraccia secondo R. Castel sia la dimensione "civile", affidata in età contemporanea allo Stato di diritto come garante dell'incolumità dei cittadini e della tutela dei loro beni, sia quella sociale, come garante del loro benessere mediante le provvidenze dello Stato sociale. Nel presente saggio la diffusa insicurezza rilevata attualmente in molte società occidentali viene ricondotta a una serie di fattori in grado di mettere a repentaglio l'equilibrio raggiunto nell'uno e nell'altro ambito: criminalità, guerre, terrorismo, così come crisi economiche, disoccupazione, indebolimento del Welfare. Allo scopo di sistematizzare e distinguere i differenti fenomeni, così come di immaginare possibili soluzioni, si propone di distinguere tra i fattori dell'insicurezza separando i PERICOLI (fonti di danni inintenzionali ed esterne in quanto naturali) dai RISCHI (conseguenze disfunzionali di processi interni intenzionalmente funzionali) dalle MINACCE (fonti intenzionali, esterne e talora interne, di danni). Evitare di confondere le tre categorie permette di elaborare misure di prevenzione e di gestione degli stati critici più eque ed efficaci di quelle talora evocate nel discorso pubblico - mediatico e politico
Competition between degradation and chain extension during processing of reclaimed poly(ethylene terephthalate)
No full textDuring processing of poly(ethylene terephthalate) (PET) hydrolytic chain scission, induced by the presence of small amounts of water, is the main cause of degradation. During repeated reprocessing chain scission can also occur because of the presence of other polymeric contaminants like PVC. In order to avoid or to limit hydrolytic chain cleavage adequate drying of PET before melt processing is necessary. Of course this practice is even more recommended when repeated processing steps are used, as for PET recycling. The behavior of recycling PET obtained from post-consumer water bottles when treated in a melt mixer under different conditions has been investigated in order to better understand the processing conditions that can reduce or avoid the hydrolytic chain scission. During processing both degradation (chain scission) and chain extension occur. When the processing is carried out under a nitrogen atmosphere the latter mechanism prevails leading to a polymer having larger molecular weight. (C) 1998 Elsevier Science Limited. All rights reserved
Inquinamento da produzione di cartapaglia. Possibilità di revisione del processo di produzione e trattamento degli effluenti
No full textPREPARATION AND CHARACTERIZATION OF COMB-SHAPED POLYESTERS FROM 2,2-DIOCTADECYL-1,3-PROPANEDIOL AND PHTHALIC ACIDS
No full textNew types of comb-shaped polyesters have been prepared by transesterification of 2,2-dioctadecyl-1,3-propanediol and the three isomeric diphenyl phthalates. Intrinsic viscosity and SEC analyses allowed determination of DPs (60-89) and molar masses; results compare well with absolute average weight molar masses (56,000-118,000) determined by low-angle laser light scattering. High-resolution C-13 NMR reveals the characteristic aromatic and glycol polyester patterns; it resolves many side-chain methylene carbons, but shows no evidence of end-groups. All the polyesters are crystalline as shown by X-ray diffractometry and DSC, the crystallinity being exclusively due to the octadecyl side-group crystallization in the hexagonal form. The results indicate that the crystallinity decreases substantially when going from the ortho- to the terephthalate polyester
Calorimetric Study of the Polymorphism of a Novel Polyester Containing Cyanoazobenzene Side Groups
No full textThe phase behavior of a novel comb-shaped polyester (P8a12), synthesized from 2-[8-(4-(4-cyanophenylazo)-phenoxy)-octyl]-1,3-propanediol and tetradecanedioic acid, has been studied by differential scanning calorimetry. It has been shown that the phase behavior of this polymer is strongly dependent of the thermal history. Up to four, partially overlapped endothermic effects have been found in the DSC heating scans, whose relative intensities markedly change with the conditions of the previous thermal treatment, as well as with the scanning rate. These effects have been tentatively associated with the transitions of as many different polymer structures. The thermal treatments needed for selectively developing the different structures in P8a12 specimens have been determined. The structures have been preliminarily studied by X-ray diffraction and optical microscopy
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