Mario Abbate

Thermosetting bismaleimide/reactive rubber blends: Curing kinetics and mechanical behavior

A maleimido-terminated butadiene–acrylonitrile copolymer was employed as an impact modifier for a commercial thermosetting bismaleimide resin. FTIR spectroscopy was used to monitor in real time the kinetics of the curing process in this blend system at different temperatures. The toughening agent was found to produce strong effects on the kinetics and mechanism of the curing process. The fracture toughness parameters Kc and Gc showed a substantial enhancement as the rubber content in the blend was increased. Only a modest reduction of the elastic modulus and of the compressive yield stress was brought about by incorporation of the impact modifier.

A novel reactive liquid rubber with maleimide end groups for the toughening of unsaturated polyester resins

An amino-terminated butadiene–acrylonitrile copolymer was chemically modified into a maleim-ido-terminated rubber and was used as a toughening agent for an unsaturated polyester resin. The reactive rubber was characterized by Fourier transform infrared spectroscopy. The mechanical and fracture properties of the blends containing the unmodified and the modified rubbers were investigated. Furthermore, a morphological analysis was carried out by scanning and transmission electron microscopy. A substantial enhancement of toughness was found when the modified rubber was used in place of the plain copolymer.

PDLC based on unsaturated polyester resins: molecular, morphological and thermo-optical analysis

A thermosetting matrix based on an unsaturated polyester resin was employed to realise a Polymer Dispersed Liquid Crystal (PDLC) system by a UV induced curing process. A molecular, morphological and thermo-optical characterisation of this system is presented. The chemical and structural properties were investigated by transmission FT-IR spectra in the near infrared frequency range and by dynamic-mechanical analysis. The results indicated that, upon curing, the matrix retains its intrinsic properties even for compositions very rich in the LC component (40 wt %). The morphology, investigated by optical and electron microscopy, showed phase separation before and after the curing process. Image analysis demonstrated that the cured materials had morphological features suitable to achieve interesting thermo-optical properties. In particular, the composition containing 40 wt % of LC exhibited the typical behaviour of a thermo-optical switch. Interesting optical bistability effects were also demonstrated for this particular composition.

Thermosetting PDLCs : Cure, morphology and thermo-optical response

Abstract Two thermosetting matrices based, respectively, on an unsaturated polyester resin and a bifunctional epoxy resin were employed to prepare Polymer Dispersed Liquid Crystal (PDLC) systems. A molecular, morphological and thermo-optical characterisation of these systems is presented. The unsaturated polyester based system was found to be phase-separated at all compositions. Image analysis demonstrated morphological features suitable to achieve interesting thermo-optical properties, particularly for the composition containing 40 wt % of LC. The epoxy based system was found to be miscibie before curing at all compositions. A phase separation occurred upon curing for LC contents higher than 40 wt %. In this composition range also this system behaves as an efficient thermo-optical switch.

Liquid crystals dispersed in thermosetting polymer matrices: molecular, morphological, and thermo-optical analysis

A first molecular, morphological and thermo-optical characterisation of a new type of Polymer Dispersed Liquid Crystal (PDLC) is presented. The chemical and structural properties are investigated by transmission FT4R spectra. The photopolymerisation process is analysed with optical monitoring, in order to obtain the best curing conditions. An experimental study on the transmithvity as a function of the temperature shows a seff-transparency effect, which occurs near the phase transition. An interpretation of the experimental results in tenns of a nonlinearity of thermal origin is given, using the theory of nonlinear scattering in heterogeneous media. The temperature switch, obtained in such a condition, suggests the possibility of employing such a material to realise a new type of all-optical temperature sensors and open the horizon to a new class ofthermo-optical devices.

PHOTO‐AGING OF HIGH PERFORMANCE EPOXIES: SPECTROSCOPIC, MECHANICAL AND DYNAMIC‐MECHANICAL INVESTIGATIONS

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 thermal analysis (DMTA) and compressive mechanical tests. The FTIR measurements allowed us to monitor the degradation process of the several groups present in the TGDDM/DDS network and to obtain reliable kinetic data. On this basis the most likely photo‐degradation mechanisms were proposed, and the main pathways through which the degradation reaction proceeds were identified. Dynamic‐mechanical measurements and mechanical 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.

Electro-optical properties of an epoxy-based polymer-dispersed liquid crystal

Electro-optical properties of an epoxy-based polymer dispersed liquid crystal (PDLC) have been investigated. A morphological analysis has been performed by optical microscopy in order to estimate initially the average diameter of the liquid crystal microdroplets dispersed in the polymeric matrix. We present the observation of an electro-optical switching effect from an opaque to a transparent state occurring at a threshold value of the applied field in a PDLC. Optical responses of the composite film under the conditions of an externally applied ac electric field and a film thickness of 50μm, were determined using an Argon laser. The experimental result showed promising switching times with a rise time of 200 μsec and a decay time of 2.2 msec and an exceptionally high contrast ratio up to 410. These result demonstrate the validity of employing this new PDLC in electro-optical devices.