Nadia Lotti

Binary blends of microbial poly(3-hydroxybutyrate) with polymethacrylates

Abstract Blends of bacterial poly(3-hydroxybutyrate) (PHB) with poly(methyl methacrylate) (PMMA) and poly(cyclohexyl methacrylate) (PCHMA) were prepared by melt compounding followed by quenching to room temperature. PHB/PMMA blends containing up to 20 wt% PHB are single-phase amorphous glasses with a composition dependent glass transition temperature ( T g ). When the concentration of PHB exceeds 20 wt%, partially crystalline pure PHB coexists with a constant-composition PHB/PMMA ( 20 80 ) mixture, which represents the solubility limit of PHB in PMMA. In such blends crystallization of PHB, both isothermally from the melt and with heating from the rubbery state, is retarded by increasing amounts of PMMA in the blend. PHB shows no miscibility at all with PCHMA. In the PHB/PCHMA blends, two phases, consisting of the pure polymer components, are present over the whole composition range and PHB crystallization is unaffected by the presence of the methacrylate polymer.

Miscibility of bacterial poly(3-hydroxybutyrate-co-3-hydroxyvalerate) with ester substituted celluloses

SummaryBlends of bacterial Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) with cellulose acetate butyrate (CAB) and cellulose acetate propionate (CAP) were prepared by melt blending. When CAB or CAP content in the blends is ≥ 50%, the blends are stable, homogeneous mixed glasses, characterized by a glass transition that follows the Fox equation. When the cellulose ester content is lower than 50%, PHBV crystallizes upon room storage and the blends are partially crystalline. Besides the strongly composition dependent glass transition, another slightly composition dependent relaxation is observed by both DMTA and DSC measurements in the vicinity of the glass transition of PHBV. It is suggested that both blend components partake in both mobilization processes.

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.

Crystallization kinetics and melting behavior of poly(butylene adipate), poly(butylene isophthalate) and their copolymers

The melting behavior and the isothermal crystallization kinetics of poly(butylene adipate), poly(butylene isophthalate) and their random copolymers were investigated by means of differential scanning calorimetry. Multiple endotherms, commonly observed on the melting polyesters, were found to be influenced by crystallization temperature and composition. By applying the Hoffman-Weeks method to the isothermally crystallized samples, thc equilibrium melting temperatures of the homopolymers were obtained. From calorimetric results on samples with different degree of crystallinity, the equilibrium melting enthalpy of poly(butylene isophthalate) was calculated and the presence of a crystal-amorphous interphase in copolymers was evidenced. Isothermal melt crystallization kinetics was analyzed according to the Avrami equation. As expected, the introduction of a comonomer was found to decrease the overall crystallization rate of the polymers. Values of Avrami exponent close to three were obtained for all the samples, independently of composition and crystallization temperature, in agreement with a crystallization process originating from predetermined nuclei and characterized by three-dimensional spherulitic growth. In the case of poly(butylene isophthalate), the dependence of the rate of crystallization on T c shows a maximum at an undercooling of approximately 60 C.

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.

Biodegradability of blends of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) with cellulose acetate esters in activated sludge

Blends of the bacterially produced polyester poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) with cellulose acetate esters (CAE) further substituted with propionyl or butyryl groups (degree of substitution: 2.60 propionyl and 0.36 acetyl or 2.59 butyryl and 0.36 acetyl, respectively) were exposed for 4 months to activated sludge to determine their biodegradability. Samples of such blends made by solution-mixing and solvent-casting had complex morphologies in which both individual components as well as a miscible blend phase were present. Additionally, the two opposite surfaces of solvent-cast films showed both physical and chemical differences. After 2 months, samples of pure PHBV had degraded by more than 98% (15 mg/cm2 of surface area), whereas a pure CAE sample had degraded less than 1% (<0.2 mg/cm2). Samples containing 25% CAE lost less than 40% of their initial weights (6 mg/cm2) over the total 4-month period. Samples with 50% CAE lost up to 16% weight (2 mg/cm2), whereas those containing 75% CAE lost only slightly more weight than corresponding sterile control samples (1 mg/cm2). NMR results confirm that weight loss from samples containing 25% CAE resulted only from degradation of PHBV and that the surface of samples became enriched in CAE. Solvent-cast film samples containing equal amounts of PHBV and CAE degraded preferentially on the surface which formed at the polymer-air interface. Scanning electron microscopy and attenuated total reflectance infrared spectroscopy revealed this surface to have a rougher texture and a greater PHBV content.

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.

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.

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.