Foto del docente

Nadia Lotti

Full Professor

Department of Civil, Chemical, Environmental, and Materials Engineering

Academic discipline: CHIM/07 Principles of Chemistry for Applied Technologies

Research

Keywords: Biodegradation Polyesters Polymer synthesis Crystallization kinetics Polymer characterization Biobased polymers Nanocomposites Barrier properties LCA analysis Nano systems for the controlled drug delivery Chemical modifications of commercial polymers Biopolymers for tissue engineering Novel disulfide-containing polyesters Compostability studies BDS molecular dynamics studies Atomic Force Microscopy

- Eco-friendly polymers for sustainable fodd packaging , green building and coatings

- Synthesis and characterization of novel polymeric materials for biomedical applications.

- Study of polymer crystallization process

- Complex analyses of dynamic phenomena and of polymeric material structure

- Preparation and characterization of "Eco-friendly nanocomposites" for food packaging and biomedical applications.

- Synthesis and characterization of novel S-S containing polyesters.

- Synthesis and characterization of bio-based polyureas

 

Eco-friendly polymers for food packaging, green building and coating applications

This research field is mainly focused on the synthesis and characterization of novel biodegradable polymers and copolymers which offer physicochemical properties suitable for the desired application. An alternative approach consist in the chemical modification of  commercially available polymers to make them attractive for different uses.

Regardless of the synthetic approach adopted, the main goal is to find out structure-properties relationships of main interest for designing a material which completely fits the requested specifications. As an example, green food packaging materials must accomplish basic requirements to be an ideal candidate for food, which includes barrier properties (water vapor, gases, light and aroma), optical properties (transparency), strength, welding and molding properties, disposal requirements, antistatic properties and, above all, strictly follow food safety.

Copolymerization as well as physical and/or reactive blending approach are an effective way of achieving a deliverable combination of properties, which are often absent in single component polymers. Moreover, the final properties of the material can be favorably modified, depending on the kind, relative amount, distribution and architecture of the comonomeric units or, in the case of mixture, by properly varying the homopolymers and blend composition. The choice of the monomers to be used in the polymerization process as well as of the comonomeric unit to be introduced along the polymeric chain of the parent homopolymer will be made on the basis of the requirements that the materials have to satisfy.

The so synthesized polymers are fully and deeply characterized both using the technology available in the DICAM labs and through collaborations with other research groups.

Polymeric materials for biomedical applications

As it is well known, polymers are the most versatile class of materials, thus can be favorably designed to fulfill the needs related to the variety of tissues and diseases involved in the human body. The research group has recently focused its activities on two main aspects of  biomedical engineering:  tissue engineering, controlled drug release and polymers with antibacterial properties.

Tissue engineering The control of molecular structure and tridimensional architecture of synthetic polymeric constructs (scaffolds) - designed to reproduce the typical properties of the damage tissue - is a key element for controlling cell adhesion, proliferation, migration and differentiation. In the field of tissue engineering the possibility to employ scaffolds mimicking native tissue is limited by the scarce availability of biocompatible and biodegradable polymers with proper mechanical properties, especially in terms of stiffness.

Controlled drug release Classical methods of drug delivery exhibit specific problems that scientists are attempting to address. The goal of new drug delivery systems, therefore, is to deliver medications intact to specifically targeted parts of the body and to release them in a controlled way depending on the required treatment regime. The design of the drug carrier is fundamental in order to achieve the correct tissutal and cellular localization of drug molecules and perform an adequate release. In this framework, polymers and copolymers are the most promising tool to obtain materials showing specifically designed properties to be employed as drug carriers.

 

Investigation of polymer crystallization process

It is well known that crystallization is a phase transition that plays an important role in determining the morphology of a polymer for a wide range of technological processes, in which commodities are formed from synthetic plastics. Therefore, studies of the isothermal crystallization of polymers commonly have been used to investigate the specific mechanisms of the crystallization process and from a technical standpoint are relevant to optimizing process conditions. In fact, the morphological structure (size, shape, perfection, orientation of crystallites), which is formed by crystallization from the molten state, influences strongly most of the physical and mechanical properties of polymeric products. Moreover, because the crystal structure and morphology (the crystal habit and organization of crystals into aggregates of a higher order) are responsible for many properties of the final products, knowledge of the crystallization mechanism is crucial for designing materials with the required properties. The crystallization kinetics are investigated by DSC and hot-stage optical microscopy (MO), both available at the laboratories of the Department. MO technique, beside measuring spherulitic growth rate, allows to obtain information on crystal phase morphology, which changes with undercooling degree and therefore with Tc. Both melt isothermal and non-isothermal crystallization kinetics studies are carried out. Melt isothermal crystallization kinetics is investigated by DSC technique and the data analyzed according to the Avrami's treatment, which allows the calculation of kinetic constant of crystallization process. On the contrary, the data obtained from measurements carried out under non-isothermal conditions are analyzed according Tobin and Ozawa equations. The crystallization process is also investigated employing equipments located at other research laboratories, such as: XRD, AFM and DETA. Lastly, crystallization rate is correlated with polymer chemical structure, to establish structure-property relationship, which are fundamental to design a new material with “ad hoc†properties. For copolymers, crystallization parameters are correlated with copolymer composition (random copolymers) and with molecular architecture, i.e. crystallisable block length (block copolymers).

Complex analyses of dynamic processes and of polymeric material structure.

As is well known, molecular motions of amorphous macromolecular chains are deeply affected by sample crystallinty degree because amorphous macromolecular segments have to relax among crystalline regions at temperatures above glass transition temperature. Such constraints significantly influences energy dissipation mechanism. As a consequence, some important physical properties, such as mechanical ones, are affected by crystallinty degree. Aim of such researches is therefore to establish correlation between molecular motions, investigated by means of dielectric spectroscopy, and system order degree, evaluated by X-ray measurements. Such correlations are indeed crucial to optimize the physical properties of a material. Such studies are carried out in collaboration with Reserch Group of prof. Ezquerra (CSIC-Madrid).

 

Preparation and characterization of "Eco-friendly nanocomposites" for food packaging and biomedical applications.

The skills developed by the research group in the field of polymeric composites and nanocomposites arise from the specific needs for high-performance materials, characterized by highly specific properties and by low environmental impact. The applications of these materials are wide in fact, depending on the type of nanofiller employed, they are characterized by high mechanical performance, heat resistance, reduced gas permeability and flammability and by specificic properties, such as conduction, optical, antibacterial and photo-catalytic properties. In all cases, in order to obtain the best possible performance of the final material, the main parameters that are developed and optimized are the physicochemical properties of the inorganic phase, such as the surface area, the morphology, the particle size, the interaction with the polymer chains and their functional groups, but also the degree of dispersion and adhesion at the interface with the matrix, which play a crucial role and can be controlled by acting on the chemical modification of fillers and on the techniques used for their mixing with the matrix. the nanoparticles are dispersed by melt mixing using Brabender or co-rotating twin-screw extruders. Moreover, in the field of nanocomposite materials research has focused on the preparation of materials based on poly (butylene succinate) (PBS), which constitutes one of the most emerging biopolymers. Currently the application of this polyester is limited due to the high production costs and reduced mechanical and gas barrier properties. To solve these issues nanocomposites with nanocellulosic fibers have been prepared. Excellent results in terms of adhesion at the interface and mechanical properties were obtained without chemically altering the fibers and then developing a final material completely "bio".

Synthesis and characterization of bio-based polyureas

In the recent years great interest has been focused on organic carbonates (OCs), resulting an important class of molecules with a wide range of applications. OCs can be employed with success as chemical intermediates, thanks to their non-toxicity and biodegradability, but also as green aprotic solvents, due to their high boiling point and high solvency. Moreover, OCs in presence of ammine can react leading to ureas and polyureas (PU). These materials boast higher chemical, thermal and mechanical stabilities compared to polyurethane counterpart and can be processed in form of fibers and film for suitable applications in medical filed and food preservation. Despite PU have been known since years, recently, on the base of their high performance, new applications are under studies (special coatings, innovative elastomers, production of special composite materials with unique properties). The main drawback of PU is related to their most common process of synthesis that employed the addition of pretty toxic compounds as polyisocyanates with polyamines even if the notorious toxicity of isocyanate. For this reason, the possibility to use OCs for the production of PUs represents a hot topic. An added value is done also by recent development of different bio-based amines; butane diamine and pentane diamine has been obtained from lysine and ornithine, respectively, opening new perspectives for the synthesis of bio-PU. Among the different routes proposed, the reaction of cyclic carbonates -as propylene carbonate or diphenyl carbonate, DPC- with diamines or polyamines. is pretty promising. Nevertheless, these reactions need to be conducted at above 90°C and take hours to achieve high conversions; moreover, catalyst is required to increase the rate and the final yield and, in order to guarantee homogeneous solutions, solvents as tetramethylene sulfone or toluene are often used. With the aim of overcoming these drawbacks, a new synthesis performed in presence of catechol carbonate, a very promising OC molecule, is proposed. The few papers available report its good reactivity in presence of aliphatic alcohols and polyols, as glycerol, to obtain the corresponding symmetric carbonates and glycerol carbonate. For this reason, CC was employed in a new solvent/catalyst free polycondensation process in presence of different potentially biobased diamines, as 1,4-butanediamide, 1,5-pentandiamine and 1,6-hexandiamine, in order to obtain bio-PUs.

“One-pot” process for the preparation of polyurea’s was successfully applied, leading to highly crystalline PUs. This novel synthetic strategy opens new possibilities in the non-isocyanate route toward polyureas production. Moreover, the simple and quantitative recovery of cathecol, produced as product, ca be isolated as pure crystals in amount between 85 to 100%, together with the use of bio-based diamine building blocks, as 1,4-butandiamine,1,5-pentandiamine and 1,6-hexametilendiammine, confers to this process a green basis. The products were completely characterized showing a really high thermal stability that make them suitable for high temperature applications.