We report on the optical characterization of very high-efficiency and high-resolution holographic volume phase transmission gratings. The gratings are recorded in a new photo-polymerizable mixture made by epoxy-resin and multi-acrylate. The epoxy-resin used is known to make tenacious acrylate-based films. The holographic mixture contains two photo-initiators, the synergic effect of which enables a reliable photo-polymerization process in the visible region of the electromagnetic spectrum. The recorded holograms are mechanically stable, show long-term temporal stability and very high values of diffraction efficiency, coupled with good angular selectivity due to a relatively narrow band of wavelengths. We measured the intensity of the transmitted beam and calculated the intensity of the diffracted beam at different wavelengths, deriving the refractive index modulation and the grating pitch by fitting the experimental data with a slightly modified theoretical approach. These kind of mixtures can be used in several fields of application, such as chemical or bio-sensors, high resolution optical sensors, high-density optical data storage, encryption and security.

Thermosetting cold-cured resins are largely used as structural adhesives and/or matrix to manufacture and apply fiber reinforced polymer (FRP) composites employed inretrofitting technique. The slow development of their mechanical, adhesive and physical properties due to a cold-cure process represents a serious inconvenience in the repair procedures of large structures. Furthermore, the durability of these materials is still unclear, especially when they are outdoor exposed to common or harsh environmental conditions. These issues are likely to hamper the enormous potential of structural adhesives in construction field and their composites employed for strengthening and rehabilitation of infrastructures. The development of innovative nanostructured (hybrid) materials based on thermosetting (mainly epoxy) resins to be used as structural adhesives, and possibly as matrices for FRP composites, has been recently explored in the view to overcome some of the well-known drawbacks of traditional structural adhesives and matrices for construction industry. Some of the recent findings in this field will be illustrated.

A study was carried out on the effect of a hybrid linear-hyperbranched poly(butylene adipate) copolymer on the properties of a commercial epoxy resin. First, the synthesis of the hyperbranched systems was optimized. These systems were obtained by reacting linear oligomers with 1,1,1-tris(hydroxymethyl)propane used as branching agent and varying the reaction times from 16 to 44 h. The synthesized samples were characterized through matrix-assisted laser desorption ionization time-of-flight mass spectrometry, differential scanning calorimetry and thermogravimetric analysis. Results showed that for reaction times of 30 h a highly branched system, namely 5HB30, was obtained. This system was chosen as toughening agent for a commercial high-performance epoxy resin. A kinetics analysis of epoxy/5HB30 blends indicated that the hyperbranched system had no accelerator or catalytic effect on the crosslinking reaction in the resin. Furthermore, it was demonstrated that 5HB30 acted as an excellent toughening agent, increasing significantly impact resistance up to 90% with respect to neat epoxy resin. The toughness behaviours of epoxy-based blends were explained by investigating the fracture surface after impact tests through scanning electron microscopy before and after solvent etching. It was observed that the globular-like hyperbranch-rich domains, dispersed throughout the continuous epoxy resin, were able to absorb the impact energy without affecting thermal stability.

the materials and methods used for the preparation of interpenetrated polymer network (IPN) by UV curing processes are reported. In particular, recent developments on the formation and characterization of some sequential IPN based on mixtures of commercially available diglycidyl ether of bisphenol-A (DGEBA) epoxy resins and UV curable epoxy-dimethacrylate resins are discussed. Finally, the photopolymerization kinetic behavior and thermal properties of some UV curable mixtures based on the modified epoxy- dimethacrylate resins for the preparation and characterization of a grafted sequential IPN are described.

The photo-oxidative degradation of a densely cross-linked epoxide/diamine network based on tetraglycidyl -4,4' diaminodiphenylmethane (TGDDM) and 4,4' diaminodiphenyl sulphone (DDS) has been investigated by FTIR spectroscopy, dynamic-mechanical analysis (DMA) and compressive mechanical tests. The FTIR measurements allowed us to monitor the degradation process of the different groups present in the TGDDM/DDS network and to obtain reliable kinetic data. On this basis the most likely photo-degradation mechanisms were proposed. Dynamic-mechanical measurements and mechanical compressive tests were used to gain an insight in the effect of the photo-oxidative degradation on the relaxation processes of the epoxy network and on the mechanical performances

Epoxy adhesives are successfully employed in many...

Epoxy resins find wide applications in many fields and have been extensively studied. In particular, great effort has been devoted to the study of the mechanism of crosslinking reactions analysing the factors affecting the molecular network and the physical properties of the hardened material. A detailed understanding of the "curing process" and of the structure-properties relationship, in fact, is essential to control and optimise the process parameters in order to tailor the performance of the of cured systems. Different analytical techniques have been employed to this aim. Among them, FTIR (Fourier transform infrared) spectroscopy has proved to be very helpful allowing quantitative measurements of the variations of functional groups during the crosslinking reactions. In the present work, a review of the scientific publications dealing with the application of FTIR to study the mechanism and the kinetic of the "curing process" of epoxy resins hardened with amines, is presented. This kind of formulation, in fact, is one of the most frequently used and, therefore, has been extensively studied. The main characteristic absorbance peaks of epoxy-amine systems have been listed and discussed. Finally, the kinetic equations more widely employed to determine the degree of conversion and the kinetic parameters, have been reported.

Novel epoxy terminated monomers based on imine groups were synthesized and their mesogenic properties studied. Aliphatic spacers of different lengths were introduced between the rigid unit and glycidylic group, and their liquid crystalline behavior was examined.They were reacted with primary aromatic amines inside a magnetic field so that the formation of anisotropic networks could be investigated. Thermosets with locked nematic textures were obtained in all cases. The influence of a 7.1 T magnetic field on the macroscopic orientation of these materials was studied and the mechanichal properties of the resulting networks were evaluated by dynamic-mechanical analysis.