Maurizio Avella

Poly-d-(−)(3-hydroxybutyrate)/poly(ethylene oxide) blends: phase diagram, thermal and crystallization behaviour

Abstract Differential scanning calorimetry and optical microscopy were used to determine the miscibility behaviour of poly- d (−)(3-hydroxybutyrate) (PHB) and poly(ethylene oxide) (PEO) mixtures. It was found that PHB and PEO are miscible in the melt. Consequently the blend exhibits a single glass transition temperature and a depression of the equilibrium melting temperature of PHB. The study of the isothermal crystallization process shows that at a given crystallization temperature the presence of PEO causes a depression in the growth rate of PHB spherulites. The blend exhibits a phase diagram characterized by the presence, below the apparent melting temperature of PHB and PEO, of interlamellar and/or interfibrillar homogeneous amorphous PHB/PEO mixtures. The Flory-Huggins interaction parameter (χ12), obtained from melting point depression data, is composition dependent, and its value is always negative.

Review Properties of blends and composites based on poly(3-hydroxy)butyrate (PHB) and poly(3-hydroxybutyrate-hydroxyvalerate) (PHBV) copolymers

Poly(3-hydroxy)butyrate (PHB) and poly(3-hydroxybutyrate-hydroxyvalerate) (PHBV) copolymers are microbial polyesters presenting the advantages of biodegradability and biocompatibility over other thermoplastics with useful mechanical properties. However, their costs and performances must be adjusted by blending with suitable polymers. In this article the miscibility, morphology, mechanical behaviour and other prominent characteristics of a representative number of blends and composites of PHB and PHBV are summarized. In particular, blends with a few polyethers, polyesters, polyvinylacrylates and polysaccharides are illustrated. Furthermore, a brief paragraph deals with PHB/vegetal fiber composites. A wide range of properties emerges by blending with polymers having very different molecular structures and characteristics, such as crystallinity, glass transition and melting temperatures. The microstructure of the blends, resulting from thermodynamic and kinetic factors, is regarded as an important factor in controlling the mechanical and the biodegradation behaviours. Moreover, some considerations upon the nature of the “driving force” of the miscibility have been made in order to explain miscibility behaviour differences.

Preparation and characterisation of compatibilised polycaprolactone/starch composites

Polycaprolactone/high amylose starch blends were prepared by the adding of a proper compatibiliser constituted by low molecular weight PCL modified on the terminal groups by using pyromellitic anhydride. Thermal, mechanical and morphological analyses were performed in order to show the better performances of these blends compared to mechanical ones obtained without the use of the compatibiliser. Finally, the biodegradability of the materials, by a compost simulation test, was also tested to assess the influence of the compatibiliser presence on the whole biodegradation process of PCL.

CRYSTALLIZATION BEHAVIOUR OF POLY(ETHYLENE OXIDE) FROM POLY(3-HYDROXYBUTYRATE)/POLY(ETHYLENE OXIDE) BLENDS : PHASE STRUCTURING, MORPHOLOGY AND THERMAL BEHAVIOUR

Abstract The influence of composition and thermal history on the phase structure and crystallization processes of poly( d (−)-3-hydroxybutyrate) (PHB) and poly(ethylene oxide) (PEO) blends at temperatures below the melting temperature of PHB has been investigated by differential scanning calorimetry (d.s.c.) and scanning electron microscopy. PHB and PEO, both crystallizable polymers, are compatible in the melt, where only one homogeneous phase is formed. But complex phase separation can take place when PHB crystallizes isothermally in the presence of the one-phase melt blend at temperatures higher than the melting temperature of PEO. During growth of the PHB spherulites, some PEO molecules are trapped in interlamellar regions, forming a homogeneous solution with uncrystallized PHB. Other PEO molecules are probably rejected into interfibrillar regions, forming almost pure PEO domains. Such domains of PEO crystallized on cooling, as shown by d.s.c. and scanning electron micrographs at temperatures between 45 and 35°C, close to the crystallization temperature of pure PEO. On the contrary, the PEO molecules trapped with uncrystallized PHB in interlamellar regions of PHB spherulites can crystallize only after cooling to lower temperatures, between −20 and −30°C. This behaviour is related to the fact that the amorphous PHB/PEO solution has a composition-dependent glass transition temperature higher than that of pure PEO: so the diffusion of PEO molecules is lowered. This complex phase separation is also influenced by the growth rate of PHB spherulites.

Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) and wheat straw fibre composites: thermal, mechanical properties and biodegradation behaviour

The thermal and mechanical behaviour of a biotechnological polyester (poly(3-hydroxybutyrate-co-hydroxyvalerate) (PHBV) reinforced with wheat straw fibres has been investigated. In order to improve chemico-physical interactions between the components, the reinforcing agent has been previously submitted to a treatment with high temperature steam leading to fibres richer in cellulose and more reactive. The addition of straw fibres has been found to increase the rate of PHBV crystallisation, while it does not affect the crystallinity content. Furthermore, the comparison of the mechanical properties has shown that the composites exhibit higher Young moduli and lower values of both the stress (σB) and strain (∈B) to break than the neat matrix of PHBV. The biodegradability in different environments by means of short and long term tests has been studied. It has been observed that the presence of straw does not affect biodegradation rate evaluated in liquid environment and in long term soil burial tests. In the composting simulation test the rate of biodegradation is reduced for composites with more than 10% of straw content. The morphology of the composites has also been investigated and correlated to the biodegradation process.

Broom fibers as reinforcing materials for polypropylene‐based composites

Broom fibers have been used as reinforcement for the conventional polypro- pylene (iPP) and a maleate modified one (iPPMA). A conventional alkaline treatment and a steam explosion extraction process were applied to obtain the cellulosic material from broom branches. Composites were prepared by melt mixing materials with differ- ent weight percentages of broom fibers. Also ternary blends (iPPMA/iPP/broom fibers 5/45/50 wt) were obtained to examine the possibility of utilizing the maleate polypro- pylene as a compatibilizing agent. The fibers and the composites were thermally, mor- phologically, and mechanically characterized. Water absorption tests, to examine the behavior of these materials in wet conditions, were also performed. Particular attention was addressed to the study of the fiber/matrix interfacial adhesion. The results showed that the iPPMA-based composites, reinforced with alkaline extracted broom fibers, present specific mechanical properties competitive with those of the homologous poly- propylene-based materials reinforced with short glass fibers. The ternary blends gave similar properties to those of the corresponding whole iPPMA-based composites. It is considered that the esteric linkage between the cellulose {OH, and the maleic anhy- dride groups grafted on the polypropylene backbone is greatly responsible for the simi- larity in the properties. In spite of better adhesion observed in the samples reinforced by the steam-exploded fibers, less improvement of the mechanical properties was observed, owing to significant damage of the structure of the fibers during the steam explosion process. A general decrease of mechanical properties is observed in normal polypropyl- ene-based composites. The results are also supported by the water absorption tests: whereby the iPPMA-based composites showed good capability to return their dry prop- erties when kept in an oven after wetting for many days. q 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68: 1077-1089, 1998

European current standardization for plastic packaging recoverable through composting and biodegradation

In this work current European standardization and a novel draft on the usage of biodegradable and compostable plastics in packaging sector are reviewed. The state members of the European Community follow the directive 92/64 EC that harmonizes the national measures concerning the management of packaging and packaging waste. Nevertheless, in this directive only a very brief part is dedicated to compostable and biodegradable materials. Therefore a draft of European standard was elaborated about the requirements for packaging recoverable through composting and biodegradation and it will probably be approved within a few months.

Influence of molecular mass, thermal treatment and nucleating agent on structure and fracture toughness of isotactic polypropylene

Abstract The influence of processing, crystallization conditions and molecular characteristics on the fracture behaviour of isotactic polypropylene obtained by a new catalyst system was investigated. The sample specimens were prepared by using two extreme crystallization conditions — quenching or slow crystallization — in order to obtain crystals and amorphous phases with different structure. Interesting correlations between fracture parameters and some morphological parameters such as long spacing and lamellar thickness of the samples were found. The SEM fractographic analysis provides useful information on the influence of factors such as molecular weight, spherulite size and undercooling. Nucleating agents were used to tailor the dimensions of spherulites.

Poly(3-hydroxybutyrate)/poly(methyleneoxide) blends: thermal, crystallization and mechanical behaviour

Abstract Blends of poly(3-hydroxybutyrate) (PHB)/poly(methylene oxide) (POM) were prepared by melt mixing and subsequent compression moulding. Crystallization, thermal behaviour, morphology and mechanical properties of the blends were studied by using differential scanning calorimetry, optical and scanning electron microscopy, and dynamic-mechanical analysis. The immiscibility of the two polymers in the liquid state was demonstrated. Moreover, two distinct spherulitic phases were evidenced in the solid state and changes of the texture structure with the composition were also observed. Finally, tensile and impact tests were carried out in order to establish the mechanical behaviour of the blends.

Polypropylene reinforced with silicon carbide whiskers

Thermal, crystallization and mechanical behaviour of isotactic polypropylene (iPP) reinforced with advanced silicon carbide whiskers (SiCw) has been investigated. It is well established that the existence of chemical and physical interactions between the matrix and the reinforcement enhances the cohesive strength at the interphase thus improving the mechanical performance of the composite. In order to improve chemico-physical interactions between the components of the inorganic–organic composite system, their affinity has been enhanced in two ways: by coating the whiskers with a thin layer of acrylate-grafted polydivinylbenzene and by using as matrix a chemically modified polypropylene. The mechanical properties of the resulting composite materials have been compared and related to the dispersion grade of the whiskers within the matrices and the morphology of the samples.