Paola Marchese

Influence of the activity of transesterification catalysts on the phase behavior of PC-PET blends

Samples of PC/PET blends, prepared by reactive blending in the presence of different catalysts, were analyzed by 1 H NMR and DSC, in order to evidence the effects of the transesterification reactions on the molecular structure and thermal properties. The 1 H NMR analysis evidences the formation of copolymers whose degree of randomness increases with the mixing time. The thermal analysis shows that the melting peak, due to the crystalline phase of PET, tends to disappear with increasing mixing time and, then, with decreasing block length in the PC-PET copolymers. At the same time, the two amorphous phases (PET and PC rich phases), characterized by two glass transitions, tend to originate only one glass transition which is observed when the block length is 15 monomeric units or lower. This copolymer structure is reached rapidly in the presence of catalysts based on titanium and samarium, at intermediate times for catalysts based on europium, cerium, calcium/antimony, erbium and does not occur at all with terbium catalyst.

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.

Effects of annealing on crystallinity and phase behaviour of PET/PC block copolymers

The effects of the annealing on the properties of PET/PC block copolymers, obtained by reactive blending in the presence of different catalysts and for different mixing times, have been studied. The annealing, performed in conditions that promote the crystallization, has been used to better understand the role of block length in determining the phase behaviour. The copolymers characterized by blocks with molecular weight larger than 8000 are able to reorganize towards more ordered domains. This rearrangement maintains the phase separation, as two crystalline phases are present before and after annealing, due to the immiscibility of long blocks. In copolymers characterized by blocks with molecular weight equal to about 2500, that is the higher limit for the miscibility in the amorphous state in PET/PC block copolymers studied in this work, the rearrangement of the chains during annealing causes a phase separation leading to two crystalline phases. Only in the copolymers with molecular weight of blocks lower than 1500, the very short block length hinders the crystallization: therefore, only in this case a phase separation does not take place after annealing.

Preparation of new biobased polyesters containing glycerol and their photodurability for outdoor applications

The synthesis of novel poly(butylene dodecanoate)s containing different percentages of glycerol was successfully carried out. The polyesters are characterized by branched or cross-linked molecular structures, according to the glycerol content. The modification of the linear backbone of the poly(butylene dodecanoate) increases the rigidity and induces significant changes in the polymer behavior toward photodegradation with respect to UV irradiation. Such a result could be very significant for specific outdoor applications of the novel polyesters.

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.

Powder coatings for indoor applications from renewable resources and recycled polymers

Powder coatings have been prepared using a sustainable polyester synthesized by combining the chemical recycling of polymers, recovered from post-consumer waste streams, with the use of bio-based monomers. The coatings obtained using this environmentally friendly approach have been compared with those based on a traditional polyester synthesized using nonrenewable resources. The results demonstrate that the new eco-friendly resin presents application performances that in some cases are superior compared to those of the commercial, petro-derived coating. This behavior, combined with the sustainable character of the new technology, gives important advantages in comparison to the conventional resins and opens new possibilities in market segments where the current powder coating has limited applications.

The effect of aliphatic chain length on thermal properties of poly(alkylene dicarboxylate)s

Abstract Some poly(alkylene dicarboxylate)s, derived from ethanediol or 1,4- butanediol and different diacids, have been synthesized and analyzed by DSC to determine the correlations existing between the thermal properties and the length of the aliphatic chain. The polymers show crystallization and melting temperatures and enthalpies which increase as the polymethylene segments lengthen, due to the formation of more stable crystals. The samples derived from ethanediol are peculiar; they show reorganization processes during the melting and the melting temperatures are notably higher with respect to those of the other polyesters. This behavior is discussed. Isothermal analysis highlights that poly(alkylene dicarboxylate)s are fast crystallizing polymers. The Avrami analysis suggests a crystallization mechanism characterized by heterogeneous nucleation and three dimensional growth; secondary crystallizations is present only in the samples characterized by short -(CH2)- sequences, due to the reorganization of less perfect crystalline forms. A comparative study between the crystallization rates as a function of the undercooling is reported.

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.

Synthesis and characterization of novel water-soluble polyamides with enhanced gas barrier properties

Poly(hexamethylene isophthalamide) (PA6I), an amorphous polymer characterized by high temperature resistance and significant oxygen barrier performances, has been chemically modified by using the 5-sulfoisophthalic acid sodium salt as a comonomer. Then, ionic groups have been randomly distributed along the polymeric chains. The new sulfonated PA6I samples were studied in order to understand structure–property relationships. It results that ionomeric PA6Is present an increment of Tg and, accordingly, a decrement of the oxygen transmission rate at 50% of relative humidity with the increment of the ionic content. Ionic groups, indeed, induce the formation of new interactions among the polymer chains, and then, a complex macromolecular network is realized. Interestingly, a molar amount of ionic groups equal to or higher than 10% makes sulfonated polyamides water-soluble. This characteristic, exploited to prepare new coatings on different polymers, opens a range of new applications for ionomeric PA6I.