Lara Finelli

Physical properties of poly(ester-urethanes) prepared from different molar mass polycaprolactone-diols

Abstract Segmented poly(ester-urethanes) (PEUs) based on poly(ϵ-caprolactone) (PCL) as a soft segment and a non-aromatic diisocyanate in the hard segment were synthesized. The soft segment crystallinity and other physical properties of the PEUs were studied. It was found that the crystallinity and rate of crystallization of the PCL continuous phase in the PEUs decreases and the glass transition temperature of PEUs increases in comparison with the PCL prepolymers. The restriction of the crystallization of the PCL soft segment depends on the hard segment concentration, length of the soft segment, and total molecular weight of the PEUs.

Crystallization kinetics and melting behavior of poly(butylene isophthalate/terephthalate) random copolyesters

Abstract The melting behavior of a series of random poly(butylene isophthalate/terephthalate) (PBIPBT) copolymers of various compositions was investigated. In the DSC scan performed after isothermal crystallization, multiple endotherms were experimentally evidenced in the case of the samples containing the highest amounts of butylene terephthalate units, due to melting and recrystallization processes. Wide-angle X-ray diffraction measurements permitted to identify the crystalline structure of PBT in all the copolymers, except in the case of the sample containing the lowest amount of PBT units, where the PBI lattice was detected. The heat of fusion (ΔHm) was evaluated and correlated to the specific heat increment (Δcp) for samples with different degree of crystallinity, in an attempt to calculate ΔHm∘ for PBI and PBT. The observed trend was interpreted on the basis of the existence, besides the crystal and amorphous phases, of an interphase due to polymeric amorphous chains linked to the crystal surface. As concern the crystallizaton kinetics, the Avrami equation was applied and the values of the exponent n, nonintegral and lower than 3 in all cases, indicate an irregular spherulitic growth, which was confirmed by optical microscopy investigations. The dependence of the crystallization half-time t1/2 on the crystallization temperature was found to be characterized by a minimum for the 40PBI60PBT copolymer, the crystallization kinetics being controlled by the nucleation or by the polymer chain diffusion, depending on the value of Tc adopted.

Miscibility and Biodegradation Behavior of Melt-Processed Blends of Bacterial Poly(3-Hydroxybutyrate) with Poly(Epichlorohydrin)

Abstract The miscibility of melt processed blends of bacterial poly(3-hydroxybutyrate) (PHB) with poly(epichlorohydrin) (PEC) is investigated over the whole range of compositions by means of differential scanning calorimetry, dynamic-mechanical analysis, and hot-stage optical microscopy. PHB and PEC are miscible in the melt in all proportions. After melt quenching, PHB/PEC blends show a single glass transition that linearly changes with composition between the T gs of the pure components (PHB = 2°C, PEC = −21°C). At room temperature all PHB/PEC blends are partially crystalline, owing to crystallization of a constant fraction (58%) of the PHB present in each blend. A spacefilling spherulitic morphology develops upon blend crystallization from the melt. Isothermal crystallization measurements show that over the range of crystallization temperatures (40°C < T e < 130°C) and compositions (20% < PEC < 80%) explored, the spherulite radial growth rate (G) decreases with increasing PEC content. Biodegradation exp...

Synthesis and characterization of poly(butylene terephthalate-co-diethylene terephthalate) copolyesters

Abstract Poly(butylene terephthalate-co-diethylene terephthalate) random copolymers of various compositions and molecular weights were synthesized in bulk and characterized in terms of chemical structure and thermal and rheological properties. All copolymers are partially crystalline and thermally stable up to about 300°C. The main effect of copolymerization is a decrease in melting and glass transition temperatures with respect to PBT homopolymer. The fusion temperatures are well correlated to composition by Baurs equation and the Tm° and ΔHm° extrapolated values for PBT are in good agreement with those reported elsewhere. The presence of diethylene terephthalate units was found to influence slightly the rheological behaviour in the melt.

Thermal properties of poly(butylene oxalate) copolymerized with azelaic acid

Abstract Poly(butylene oxalate) (PBO) and poly(butylene oxalate/butylene azelate) random copolymers (PBOBAz) of various compositions were synthesized in bulk and characterized in terms of chemical structure and thermal properties. The thermal behavior was examined by thermogravimetric analysis and differential scanning calorimetry. All copolymers were found to be partially crystalline and thermally stable up to about 290 °C. The main effect of copolymerization was a decrease in melting and glass transition temperatures with respect to PBO homopolymer. The pure crystalline phase characteristic of PBO was evidenced by means of X-ray measurements in all the copolymers under investigation. The fusion temperatures appeared to be well correlated to composition by Baurs equation. Amorphous samples were obtained after melt quenching and showed a monotonic decrease of glass transition temperatures as the content of the flexible butylene azelate units is increased. Fox equation described well the T g –composition data. Lastly, the overall crystallization rate of PBO was found to decrease regularly with increasing butylene azelate unit content.

Preparation and thermal behavior of random copolyesters of thiodipropionic acid

Abstract Poly(butylene terephthalate/thiodipropionate) and poly(butylene terephthalate/azelate/thiodipropionate) random copolymers of various compositions were synthesized in bulk and characterized in terms of chemical structure and molecular weight. The thermal behavior was examined by thermogravimetric analysis and differential scanning calorimetry. The copolymers containing low amounts of thiodipropionate units showed a good thermal stability, similar to that of PBT, however decreasing with increasing sulfur atom content. All the samples synthesized appear as semicrystalline materials, with fusion temperatures well correlated to composition by Flory’s equation. The T0m and ΔHu values for the completely crystalline homopolymers poly(butylene terephthalate) and poly(butylene azelate) derived using Flory’s treatment are in good agreement with those reported elsewhere. Due to the high crystallization rate, the glass transition phenomenon can be detected only for some copolymers with intermediate compositions. As the introduction of S-atoms in the polymeric chain gives rise to a more flexible structure, a decrease of Tg was observed.

Biodegradation of a starch containing thermoplastic in standardized test systems

ABSTRACT Biodegradation of the commercial starch-based thermoplastic Mater Bi (MB) ZI01U was investigated in six different test systems: (1) aqueous aerobic (AQ-AE), (2) aqueous anaerobic (AQ-ANA), (3) in vitro in the presence of the microorganism Acidovorax avenae avenae (MICRO), (4) controlled compost (COCO), (5) composting bins (COBI) and (6) high solids anaerobic digestion (HSAD). MB ZI01U was found to biodegrade in all test systems. Samples in the form of pellets, films and ASTM-D638 test bars were used. The composition of MB ZI01U in the course and at the end of the biodegradation experiments was monitored by thermogravimetric analysis. Rapid loss from MB ZI01U of the water-soluble plasticizer (glycerin) was invariably observed. In the anaerobic tests (AQ-ANA and HSAD), the ratio of the two polymeric components of MB ZI01U (starch and Poly-ϵ-caprolactone, PCL) strongly changed with increasing exposure time, indicating preferential degradation of starch. During the aerobic tests AQ-AE and MICRO the s...

Synthesis and thermal behavior of poly(2-hydroxyethoxybenzoate) and its copolyesters with ε-caprolactone

Poly(2-hydroxyethoxybenzoate), poly(ε-caprolactone), and random poly(2-hydroxyethoxybenzoate/e-caprolactone) copolymers were synthesized and characterized in terms of chemical structure and molecular mass. The thermal behavior was examined by DSC. All the samples appear as semicrystalline materials; the main effect of copolymerization was lowering in the amount of crystallinity and a decrease of melting temperature with respect to homopolymers. Florys equation described well the Tm-composition data. Amorphous samples (in the 20–100%2-hydroxyethoxybenzoate unit concentration range) obtained by quenching showed amonotonic decrease of the glass transition temperature Tg as the content of caprolactone units is increased. The Woods equation described the Tg-composition data well.

Memory effect in melting behaviour, crystallization kinetics and morphology of poly(propylene terephthalate)

Abstract Crystallization kinetics and melting behaviour of poly(propylene terephthalate) (PPT) were investigated by means of differential scanning calorimetry and hot-stage optical microscopy. Isothermal crystallization kinetics was analysed according to the Avrami treatment. The effects of temperature and duration of melting on the overall rate of isothermal crystallization were studied: the rate was found to decrease with increasing melting temperature and melting time. This result was discussed on the basis of the gradual destruction of predetermined athermal nuclei. Values of the Avrami exponent close to 3 were obtained, regardless of the adopted thermal treatment and the crystallization temperature, Tc, in agreement with a crystallization process originating from predetermined nuclei and characterized by three-dimensional spherulitic growth. As a matter of fact, spacefilling spherulites were observed by optical microscopy at all Tc’s, independent of the applied thermal treatments. For each of them, the rate of crystallization became lower as Tc increased, as usual at low undercooling where the crystallization process is controlled by nucleation. The observed multiple endotherms, which are commonly displayed by polyesters, were influenced by Tc and ascribed to melting and recrystallization processes. Linear and non-linear treatments were applied in order to estimate the equilibrium melting temperature for PPT, by using the corrected melting temperatures. The non-linear estimation yielded an about 33°C higher value with respect to the one obtained by means of the linear approach. Through the analysis of secondary nucleation theory, the classical II→III transition was found to occur at a temperature of 194°C. The average work of chain folding for nucleation was determined to be c. 5.2 kcal/mol. The heat of fusion was correlated to the specific heat increment for samples with different degree of crystallinity and the results were interpreted on the basis of the existence of an interphase, whose amount was found to depend on the thermal treatment the polymer was subjected to.

Preparation and thermal behavior of random poly(butylene terephthalate/azelate) copolyesters

Poly(butylene terephthalate), poly(butylene azelate), and poly(butylene terephthalate/butylene azelate) random copolymers of various compositions were synthesized in bulk using the well-known two-stage polycondensation procedure, and characterized in terms of chemical structure and molecular weight. The thermal behavior was examined by thermogravimetric analysis and differential scanning calorimetry. As far as the thermal stability is concerned, it was found to be rather similar for all copolymers and homopolymers investigated. All the copolymers were found to be partially crystalline, and the main effect of copolymerization was a lowering in the amount of crystallinity and a decrease of melting temperature with respect to pure homopolymers. Florys equation was found to describe the Tm–composition data and permitted to calculate the melting temperatures (T°m ) and the heats of fusion (ΔHu) of both the completely crystalline homopolymers. Owing to the high crystallization rate, the glass transition was observable only for the copolymers containing from 30 to 70 mol % of the terephthalate units; even though the samples cannot be frozen in a completely amorphous state, the data obtained confirmed that the introduction of the aromatic units gave rise to an increase of Tg, due to a chain stiffening.