Micaela Vannini

Synthesis and radiocarbon evidence of terephthalate polyesters completely prepared from renewable resources

Monomers used for the synthesis of terephthalate polyesters have been prepared starting from renewable resources. In particular, dimethyl terephthalate was synthesised starting from bio-limonene while butanediol was synthesised starting from bio-succinic acid. Using these bio-monomers it was possible to synthesise polyesters with the same chemical structure and molecular weight of commercially available polymers. Moreover, the polymers obtained from bio-based monomers, present the same thermal properties of the polyesters obtained using petrol-derived monomers. A poly(butylene terephthalate) completely obtained from renewable resources was also synthesised. The radiocarbon and isotope mass spectroscopy analysis confirmed that this polyester contains 94 ± 3% of bio-based material.

Fully biobased poly(propylene 2,5-furandicarboxylate) for packaging applications: excellent barrier properties as a function of crystallinity

High molecular weight, amorphous poly(propylene 2,5-furandicarboxylate) has been aged at 135 °C for different times. The crystal phase contributes to achieve exceptionally low oxygen transmission rates and also good impermeability to water vapors, making PPF one of the most interesting fully biobased polyesters for packaging applications.

Sustainable polyesters for powder coating applications from recycled PET, isosorbide and succinic acid

A new method for the synthesis of polyesters that combines the chemical recycling of poly(ethylene terephthalate) (PET) with the use of monomers derived from renewable resources, such as isosorbide and succinic acid, has been developed. A kinetic study has been performed in order to determine the best catalyst for PET depolymerisation with isosorbide and for the subsequent polycondensation of PET oligomers with succinic acid. Using the correct amounts of isosorbide and succinic acid it is possible to obtain polymers which well fit the properties (glass transition temperature and end-group composition) necessary for powder coating applications. The coating produced using this new environmentally friendly approach presents applicative properties similar, and in some cases superior, to those of a commercial coating obtained from non-renewable resources.

A Sustainable Route to a Terephthalic Acid Precursor.

A new synthetic pathway for the production of p-toluic acid has been developed starting from reagents derived from renewable resources. A Diels-Alder reaction between sorbic and acrylic acids is followed by a combined dehydrogenation/ decarboxylation process, providing p-toluic acid in high yields. This route permits to use milder conditions compared to other Diels-Alder approaches reported in the literature, and therefore can contribute to a more sustainable terephthalic acid production.

Advances in the synthesis of bio-based aromatic polyesters: novel copolymers derived from vanillic acid and ε-caprolactone

A new and sustainable pathway for the synthesis of polyesters and copolyesters derived from vanillic acid is suggested. The poor reactivity of the fenolic –OH group of vanillic acid has been overcome by etherification reactions with biobased ethylene carbonate: the full procedure towards poly(ethylene vanillate) (PEV) avoids solvents and purification steps and uses only bio-based reagents. The PEV thus obtained is an example of bio-based PET mimics, characterized by high thermal transitions and a notable level of crystallinity. However, probably due to its low molecular weight, the material is brittle. In order to solve such problems and to exploit the aromatic structure of PEV to enhance the properties of aliphatic polyesters, new copolymers based on PEV and poly-e-caprolactone were prepared. The new materials are characterized by an EV crystalline phase and tunable thermal properties according to the composition.

Electrical properties of resin monomers used in restorative dentistry

OBJECTIVES The application of an electric field has been shown to positively influence the impregnation of the resin monomers currently used in dentin bonding systems during hybrid layer formation. This study presents an experimental characterization of the electrical properties of these monomers with the aim of both correlating them to their chemical structures and seeking an insight into the mechanisms of the monomer migration under an applied electric field. METHODS Some common monomers examined were TEGDMA (triethyleneglycoldimethacrylate), HEMA (2-hydroxyethyl methacrylate), UDMA (urethane dimethacrylate), 2-MP (bis[2-(methacryloyloxy)ethyl] phosphate, TCDM di(hydroxyethyl methacrylate) ester of 5-(2,5-dioxotetrahydrofurfuryl)-3-methyl-3-cyclohexenyl-1,2-dicarboxylic anhydride) and Bis-GMA [2,2-bis(4-2-hydroxy-3-methacryloyloxypropoxyphenyl)propane]. A customized cell produced for the measurement of the electrical properties of monomers was manufactured and electrical conductivity and permittivity of resin monomers were measured. RESULTS The permittivity of the tested monomers is largely affected by electrical frequency. The large values of permittivity and dielectric losses observed as frequency decreased, indicate a dominant effect of ionic polarization, particularly evident in materials showing the highest conductivity. Permittivity and conductivity of the tested monomers showed a similar behavior, i.e. materials with the lowest permittivity also show small values of conductivity and vice versa. SIGNIFICANCE The results of the present study revealed a good correlation between electrical properties and Hoy solubility parameters and, in particular, the higher the polar contribution (polar forces plus hydrogen bonding) the higher the permittivity and conductivity. The most relevant outcome of this study is that the electrophoretic mechanism prevails on the electroendoosmotic effect in determining the monomer migration under the application of electric fields.

Retting Process as a Pretreatment of Natural Fibers for the Development of Polymer Composites

The development of high-performance materials made from natural resources is increasing worldwide. Within this framework, natural fiber reinforced polymeric composites now experience great expansion and applications in many fields, ranging from the automotive to the construction sector. The great challenge in producing composites containing natural fibers and with controlled features is connected to the great variation in properties and characteristics of fibers. The quality of the natural fibers is largely determined by the efficiency of the treatment process and can dramatically influence the properties of the final composites. The overall fiber extraction processes, applied to vegetable fibers, is called retting and consists in the separation of fiber bundles from the cuticularized epidermis and the woody core cells. Today, many efforts are being made to optimize the retting methods in terms of fiber quality production, reduction of environmental issues and production costs. This chapter aims to provide a classification and an overview of the retting procedures that have been developed during years and are applied to extract mainly bast fibers.

Chemical recycling of post-consumer compact discs towards novel polymers for powder coating applications

New processes for the chemical recycling of bisphenol A polycarbonate (PC), directly from post-consumer compact discs, have been developed. The first recycling method is based on the use of molecules that can be derived from renewable resources (isosorbide, ethylene carbonate and succinic acid). A second procedure involves a one-pot reaction of post consumer PC with ethylene carbonate, without complete degradation to low molecular weight products. The final polymers feature properties that make them suitable for powder coating applications.

Bio-Based PA11/Graphene Nanocomposites Prepared by In Situ Polymerization

Bio-based polyamide 11 (PA11)-graphene nanocomposites with different filler concentrations (0.25, 0.5, 0.75, 1.5 and 3 wt%) were prepared by In Situ polymerization starting from a water dispersed suspension of graphene nanoplatelets. The effects of the incorporation of the filler were studied in terms of molecular, morphological, thermal and dynamic mechanical properties of the final materials. During the crystallization process from the melt, the filler induces a notable nucleating effect even if the crystal growth rate tends to decrease. The glass transition temperature tends to shift to higher temperatures indicating a decrement of the molecular mobility. Thermal stability is enhanced confirming a good filler dispersion into the matrix. Mechanical reinforcement, investigated by means of a dynamic mechanical thermal analyzer was also highlighted. It was observed that a graphene concentration of 0.75 wt% induces the highest final performances.

Poly( m -xylylene adipamide)-based Copolyamides: Effect of the Chemical Structure on Oxygen Permeation Properties

Poly(m-xylylene adipamide) (MXD6) is a well-known polyamide, widely used in engineering applications for a favourable set of mechanical properties and in packaging materials manufacturing because of its excellent gas barrier properties. In this work new random copolymers based on MXD6 were prepared by melt polycondensation of different comonomers (diacids and diamines) together with m-xylylene diamine and adipic acid with the aim of studying the effect of various chemical structures on the final barrier properties and trying to improve barrier performances of MXD6 at high humidity level. The resulting copolyamides were characterized in order to investigate the structureproperty relationships. Attention has been focused on the changes in glass transition temperature, density, sub-Tg relaxations. Interesting correlations between structure and oxygen permeation properties have been found.