Maria Pizzoli

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.

Molecular motions of chitosan in the solid state

Abstract The relaxation behavior of chitosan has been investigated by dynamic mechanical and dielectric spectroscopy over a wide temperature and frequency range. Two dispersion regions are found in the spectrum of the dry polysaccharide: a relaxation (γ) at low temperature (− 102° at 3 Hz; ° H =47 kJ/mol) and another relaxation process above room temperature (130° at 3 Hz; ° H ∼ 100 kJ/mol). Absorbed water strongly modifies the relaxation spectrum of chitosan below room temperature, giving rise to a new relaxation (βd) at temperatures higher than the γ peak. With increasing water content, the γ peak is progressively depressed, while the βd relaxation intensifies and moves to lower temperatures. In room-stored samples (∼10% absorbed water) the βd peak is the only observable relaxation in the viscoelastic spectrum of chitosan below room temperature. The γ and βd loss processes are attributed to local motions of the polysaccharide backbone and of complex polymer-water units, respectively. The characteristic parameters of the high-temperature peak indicate that the relaxation originates from short-range rather than cooperative molecular motions.

Viscoelastic and thermal properties of bacterial poly(d-(−)-β-hydroxybutyrate)

Abstract Three poly( d -(-)-β-hydroxybutyrate) (PHB) samples from Rhbizobium spp. have been characterized in order to evaluate the effects of different extraction procedures of the polymer. Only the molecular weight is found to change, being 6 × 10 4 for the sample extracted with HCl (1 m and of the order of 10 6 for the samples extracted with acetone. Thermogravimetric results on PHB with different molecular weights, indicate that the temperature at which weight loss becomes significant is lower than 230°C only for the lowest molecular weight examined (6 × 10 4 ). The calorimetric properties strongly depend on thermal history. The d.s.c. curves of ‘room stored’ samples show only a melting endotherm at 177°C, whose area increases with annealing. Quenching from the melt shows evidence an intense glass transition (ΔCp = 0.43 J/g deg) in the vicinity of 0°C, followed by a ‘cold crystallization’ peak preceding melting. The viscoelastic spectrum shows three relaxations: a water-related low temperature relaxation (−80°C), the glass transition (apparent activation energy ΔH a = 356 KJ/mol) and a broad relaxation in the temperature range between T g and T m due to motions in the crystalline phase.

Light-scattering, X-ray diffraction, elemental analysis and infrared spectro- photometry characterization of chitosan, a chelating polymer

Measurements on chitosan, which is used as a selective chromatographic support in inorganic chromatography, show that its molecular weight is 1.2 x 10(5), the nitrogen content is 7.4%, and its crystalline structure is not lost after adsorption of metal ions, which are co-ordinated with the nitrogen atoms of the -NH(2) groups of the polymer. Chitosan treated with copper sulphate exhibits a new crystal structure and a distinctive infrared spectrum, is quite stable and does not shrink, and is proposed as a chromatographic support for ligand-exchange chromatography.

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.

Composition dependence of the glass transition temperature of polymer-diluent systems: 1. Experimental evidence of a dual behaviour in plasticized PVC

The glass transitions of six PVC-diluent systems have been studied using differential scanning calorimetry (d.s.c.). The diluents were: di-(methyl, ethyl, n-propyl, n-butyl)-phthalate, n-butylacetate and tritolylphosphate. A large number of compositions have been examined over the whole concentration range, from pure polymer to pure diluent. For all systems but PVC-butylacetate, the Tgconcentration dependence shows a ‘cusp’ in the vicinity of 40% diluent content. The width of the glass transition increases in the concentration range of the ‘cusp’ reaching values as high as 50°C. PVC-butylacetate mixtures show two glass transitions, both decreasing with increasing diluent content, in a narrow composition range. For all systems two Tgconcentration dependencies can be identified: the fast decrease of the polymer Tg caused by plasticizer addition and the much slower increase of the diluent Tg due to the presence of the dissolved polymer molecules. Also the specific heat increment at Tg(ΔCp) shows a dual concentration dependence, suggesting that it is the component present ‘in excess’ that dictates the ΔCpcomposition behaviour.

Composition dependence of the glass transition of polymer-diluent mixtures: 2. Two concomitant glass transition processes as a general feature of plasticized polymers

The available theoretical and empirical treatments concerning the glass transition temperature, Tg, of polymer-diluent mixtures do not account for the occurrence of the ‘cusp’ in the Tgcomposition dependence or of the two concomitant glass transitions recently reported by these authors. The only treatment predicting a change of curvature in Tg vs. concentration, due to Braun and Kovacs, does not describe satisfactorily the behaviour of the seven polymer-diluent systems examined. In order to compare the results with the available literature data, a normalization procedure is developed, whose main effect is to evidence that the Tgconcentration dependence of all polymer-diluent systems is composed of two branches. It is concluded that in polymer-diluent mixtures still considered homogeneous at a macroscopic level two different mobilization phenomena occur, related to mobilization of ‘hindered diluent’ and ‘plasticized polymer’, respectively. The possibility of revealing the two phenomena individually depends strongly on the technique being used as well as on the peculiar physical properties of the binary system being examined.

Dynamic mechanical relaxations of poly(vinylidene fluoride)-poly(vinylpyrrolidone) blends

Abstract Dynamic mechanical measurements on blends of poly(vinylidene fluoride) (PVDF) and poly(vinylpyrrolidone) (PVP) over the whole composition range are reported from −150 to 220°C. The results provide evidence of miscibility of PVDF with PVP. Two ranges of compositions are identified. When the PVP content is higher than 40%, crystallization of PVDF is inhibited and single-phase, homogeneous mixtures are obtained. At lower PVP concentrations, three phases coexist: a homogeneous blend of quasi-constant composition, crystalline PVDF and a pure amorphous PVDF phase, the so-called ‘interphase’ evidenced by a relaxation at about −40°C. For the partially crystalline blends, the viscoelastic spectrum is shown to depend strongly on thermal history.

Effect of thermal history on Tg and corresponding Cp changes in PVC of different stereoregularities

Abstract Samples of poly(vinyl chloride) polymerized at temperatures from −60°C to +90°C, and therefore of different degrees of syndiotacticity and crystallinity, have been thermally treated in an attempt to reduce their content of ordered structures. Changes in order have been monitored by measuring Tg and the corresponding specific heat increment Δcp. Partially syndiotactic samples have higher Tg and lower Δcp than samples that are nearly atactic. After thermal treatment the differences decrease but do not vanish, even for samples heat-treated to about 250°C. This seems to indicate that some ordered structures are very stable even at relatively high temperatures. A quantitative estimate of the ordered structure content, based on Δcp data, is proposed.

Further evidence of an unusual Tg-concentration dependence for plasticized polyvinylchloride

SummaryThe glass transition temperature-composition dependence for the systems PVC-dimethylphthalate and PVC-di-n-propylphthalate has been determined in the whole range of concentration. The glass transition temperature of the mixtures decreases with increasing diluent content and in both cases shows a discontinuity at a critical composition (w1≃0.4). At diluent weight fractions lower than 0.4, the theoretical equations by Kelley-Bueche and CouchmanKarasz satisfactorily fit the experimental results. The marked changes in the glass transition parameters (Tg, Δcp, width of the transition) which occur in the intermediate range of concentration (0.4<w1<0.6), although difficult to visualize in physical terms, indicate an enhanced mobility of the relaxing units. Moreover, the properties of the mixtures in the high diluent concentration range seem to be dictated by the properties of the pure diluent.