191 research outputs found
Studio strutturale e conformazionale del copolimero esafluoropropilene-tetrafluoroetilene
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A structural investigation on poly(glycolic acid)
No full textPowder X-ray diffraction patterns were recorded of the orthorhombic form of poly(glycolic acid) and the peak profiles were investigated in order to obtain the best fit with proposed structural models. The optimized unit cell parameters are in a good agreement with those reported from fibre X-ray diffraction patterns; moreover, the peak analysis allowed to evaluate the average crystallite dimensions along the three main crystallographic directions and in particular to observe a smaller size along the c axis. The R factors indicating the agreement between calculated and experimental patterns are satisfactory
From Biomass to Bio-Based Polymers: Exploitation of Vanillic Acid for the Design of New Copolymers with Tunable Properties
No full textVanillic acid represents a potentially interesting bio-based building block for the production of new aliphatic-aromatic polymers, characterized by thermal properties similar to those of the analogous terephthalic polyesters. However, poly(ethylene vanillate) proved to be a very brittle material, probably due to a very high degree of crystallinity, and, then, not suitable for melt processing. Therefore, the synthesis of copolymers, based on vanillic acid and pentadecalactone is considered as a strategy to obtain new polymeric materials with a low degree of crystallinity, tunable properties, and better performances. The synthesis of these fully bio-based random copolymers is successful. The thermal properties have been studied in order to correlate chemical structure and final performances. The polymers proved to be processable and films are obtained, suggesting possible applications of the copolymers in a new sustainable flexible packaging
Reading Japanese Documents from the Marega Collection: An Introductory Manual with Selected Texts
No full textThe volume, authored by Naohiro Ōta, and edited by Silvio Vita, Chiara Ghidini, and Luca Milasi, introduces the Mario Marega (1902-1978) collection of manuscripts at the Vatican Library. The complete collection comprises over 14,000 documents from Kyushu spanning the 17th-20th centuries recently cataloged and digitized and available through NIJL. The manual details a selection of documents specifically selected for the purpose of learning to read, transcribe, and translate komonjo. The book comprises an introduction, followed by, chapter 1, which includes four explanatory essays: “Documents as Material Objects,” “The Texts: Cursive Script and Language,” “The Historical Context of the Marega Documents,” and “Reference Tools and Suggested Readings.” The next two chapters cover “Reading Models” and “Texts for Practice.” Several appendices include information helpful to understanding komonjo, especially the documents related to Christianity in the Marega Collection. The author and editors compiled the volume mainly as a useful resource for students of sōrōbun and komonjo, and with the hope to provide up-to-date information about Japanese paleography and diplomatics of the Pre- and Early Modern period which will prove of interest for more advanced specialists, also
Poly (1-butene-ran-ethylene) monomodal copolymers from metallocene catalysts: Structural and morphological differences with increasing ethylene content
No full textSamples of random poly(butene-ran-ethylene) copolymers produced with metallocene catalysts were studied in order to elucidate the different behaviors of this particular class of materials as a function of increasing ethylene (C2) content. The samples cooled down from the melt are semi-crystalline or amorphous and crystallize in different crystal modifications, depending on the amount of C2. Thermal analysis, X-ray diffraction, and microscopic techniques were used to follow the changes of the materials with aging time and to understand the structural and morphological behavior with the aim of highlighting possible peculiar properties, which may be of great interest in the application of such materials in the field of Hot Melt adhesives
Aliphatic poly(alkylene dithiocarbonate)s: Thermal properties and structural characteristics of poly(hexamethylene dithiocarbonate)
No full textAliphatic poly(alkylene dithiocarbonate)s are an interesting class of potentially biodegradable and biocompatible materials in analogy with their homologous poly(alkylene carbonate)s. In this paper, the properties of poly(hexamethylene dithiocarbonate) (SSR6) are compared to those of poly(hexamethylene carbonate) (HMC) in order to study the effect of the substitution of oxygen atoms with sulphur atoms in the polymer backbone. SSR6 presents a higher level of crystallinity and a faster crystallisation rate with respect to HMC. The melting temperature in SSR6 is about 60 °C higher, due to a solid–solid transition between phase I, stable at room temperature, and phase II, present at high temperature. HMC crystallises only in phase I and melts at a relatively low temperature (30 °C). The capacity of SSR6 to crystallise in phase II has been attributed to the higher flexibility and mobility of the chains containing –S–CO–S– groups with respect to the chains containing –O–CO–O– groups. The pure phase II in SSR6 has been obtained in isothermal conditions and its crystallisation rate and mechanism have been analysed
Bio-based semi-crystalline PEF: Temperature dependence of the constrained amorphous interphase and amorphous chain mobility in relation to crystallization
No full textThe temperature dependence of the constrained amorphous interphase or rigid amorphous fraction (RAF) in bio-based semi-crystalline poly(ethylene 2,5-furandicarboxylate) (PEF) was assessed. RAF, which is located in proximity of the basal crystal planes, was found to develop in parallel with the crystal phase during crystallization at the lowest investigated Tcs, i.e. 130 and 140 °C, at which the less stable α′-crystal phase grows. At higher Tcs, RAF does not vitrify during crystallization, but only upon the subsequent cooling down to Tg. The rigid amorphous fraction at Tg increases by decreasing the crystallization temperature, ranging approximately from 15 to 25%. This information is useful for the development of PEF products, since many RAF physical properties, for example mechanical and barrier properties, are different from those of the amorphous fraction far from the crystals. RAF decreases with increasing temperature, and becomes zero around 150 °C. The same temperature limit of 150 °C was found to influence the reversing crystallization/melting process at the lateral crystal surfaces, as well as the crystallization rate, which reaches its maximum at temperatures above 150 °C. In addition, singularly, the more ordered crystalline α-form was found to grow only at temperatures higher than 150 °C. The total absence of constraints on the amorphous segments mobility, identified at temperatures higher than 150 °C, also favors additional crystallization upon heating in the PEF samples crystallized at low Tcs, with also α-crystals development. The densities of the RAF connected to α′- and α-crystals were estimated at room temperature
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