E. Martuscelli

An interpenetrated system based on a tetrafunctional epoxy resin and a thermosetting bismaleimide: Structure–properties correlation

The kinetics and mechanism of the curing process of a thermosetting blend formed by tetraglycidyl-4,4′-diaminodiphenyl methane and N,N′-bismaleimido-4,4′-diphenyl methane (BMI) cured in the presence of 4,4′-diaminodiphenyl sulfone, was investigated in detail by Fourier transform infrared spectroscopy. Information on the molecular structure of the network formed upon curing was derived. Dynamic-mechanical measurements on dry samples indicated an interpenetrated polymer network-like structure. Sorption measurements at 70°C showed a reduction of the water uptake at equilibrium in the presence of substantial amounts of BMI in the system (43.5% body weight). Finally, the dynamic-mechanical analysis of wet samples demonstrated a reduction of the plasticizing efficiency of the absorbed water in the presence of BMI.

Kapok/cotton Fabric–Polypropylene Composites

Kapok/cotton fabric has been used as reinforcement for conventional polypropylene and maleic anhydride grafted polypropylene resins. Treating the reinforcement with acetic anhydride and sodium hydroxide has modified the fabric (fibres). Thermal and mechanical properties of the composites were investigated. Results show that fibre modification gives a significant improvement to the thermal properties of the plant fibres, whereas tests on the mechanical properties of the composites showed poor tensile strength. Mercerisation and weathering were found to impart toughness to the materials, with acetylation showing slightly less rigidity compared to other treatments on either the fibre or composites. The modified polypropylene improved the tensile modulus and had the least toughness of the kapok/cotton reinforced composites. MAiPP reinforced with the plant fibres gave better flexural strength and the same flexural modulus at lower fibre content compared with glass fibre reinforced MAiPP.

Tetrafunctional epoxy resins: Modeling the curing kinetics based on FTIR spectroscopy data

The curing kinetics of two thermosetting systems based on a tetrafunctional epoxy resin was investigated by Fourier transform infrared spectroscopy. Two formulations were studied, in which the hardener was an aromatic diamine and a carboxylic dianhydride, respectively. The quantitative evaluation of the epoxy conversion was based on spectra collected in the near-infrared range (8000–4000 cm−1) as well as in the medium infrared range (4000–400 cm−1). The kinetic parameters evaluated in the above frequency intervals were significantly different. The reasons for such a discrepancy are discussed critically. Several kinetic models, based on the widely employed Kamal approach, were applied to verify their predictive capability. Satisfactory results were obtained for the amine-cured system, particularly with a modified equation taking into account the autocatalytic nature of the process as well as a limiting diffusional effect. Less accurate results were achieved for the anhydride-cured system.

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.

A polymer network of unsaturated polyester and bismaleimide resins: 1. Kinetics, mechanism and molecular structure

Abstract An unsaturated polyester resin has been modified by adding a thermosetting bismaleimide as a second co-reactive monomer. The bismaleimide resin was readily dissolved in the uncured polyester matrix up to a concentration of about 20 wt%. Fourier transform infra-red (FTi.r.) spectroscopy was employed to monitor the cure kinetics of this complex system. The available spectroscopic evidence indicated that both the mechanism and the kinetics of the crosslinking process were strongly affected by the presence of the bismaleimide in the system. The molecular structure of this intercrosslinked network is discussed. The dynamic mechanical behaviour of a typical blend composition was found to be in agreement with the proposed molecular structure.

Cure kinetics and ultimate properties of a tetrafunctional epoxy resin toughened by a perfluoro-ether oligomer

Abstract A commercial grade of a tetrafunctional epoxy resin (TGDDM) has been modified by the addition of a perfluoro-ether oligomer to improve the toughness. The cure characteristics of a typical composition of this mixture have been investigated by in situ FT-NIR spectroscopy. It has been found that the presence of the fluoro-oligomer induces a two-fold reduction of the initial curing rate, which has been discussed in terms of the cure mechanism. For all the investigated compositions, the final conversion of the reactants did not change with respect to that of the unmodified resin. The phase structure of this system has been investigated by dynamic-mechanical analysis and by scanning electron microscopy. Both these techniques showed no evidence of a two-phase morphology. Finally, the fracture parameter Gc has been found to increase significantly for concentrations of the modifier exceeding 10 parts by weight.

Recycling of plastic car components : The case of a multilayer item based on polypropylene

The recycling of a particular internal car component with a multilayer structure such as the dashboard has been extensively investigated. On this item, based on polyolefins, a thermal, spectroscopic, mechanical and morphological analysis has been performed. The recycled material showed a strong worsening in the mechanical and impact properties due to the occurrence of thermo-oxidative and thermo-mechanical degradation phenomena taking place during processing. A limited improvement in the mechanical behaviour has been obtained by adding, during the recycling, a suitable antioxidant and stabiliser additive. A more significant enhancement has been achieved in terms of deformation at break, impact toughness and overall morphology when an ethylene-propylene copolymer and virgin polypropylene were added to the formulation during the recycling process. By this procedure materials with properties suitable to be reused for the same or for similar applications within the car have been obtained.

A novel compatibilizer for the toughening of unsaturated polyester resins

A block-copolymer of the type A–B–A was synthesized from a commercial polybutadiene rubber (PBD) and an unsaturated polyester (UP) prepolymer. The reaction process was monitored via Fourier transform–infrared spectroscopy. The obtained copolymer was used as compatibilizing agent for UP/PBD blends. Fracture measurements performed on the cured materials demonstrated a substantial enhancement of tougheness in the presence of the copolymer. The morphological analysis of the fracture surfaces showed that the presence of the compatibilizing agent produced a strong reduction of the size of the rubber particles, a better interface adhesion and an increase of localized shear yielding in the UP matrix around the rubber particles.

FTIR spectroscopy and physical properties of an epoxy/bismaleimide IPN system

Blends of a tetrafunctional epoxy resin and a thermosetting bismaleimide (BMI) resin cured with 4,4′-diamino diphenyl sulfone were investigated. Information on the conversion ofthe reactive groups upon curing was obtained by Fourier transform infrared spectroscopy. Dynamic-mechanical tests carried out on both dry and wet samples indicated the formation of an IPN-like structure and a considerable reduction of the plasticizing effect of the water absorbed in the presence of BMI. Sorption measurements at 70 °C revealed a reductionof the equilibrium water uptake with respect to the neat epoxy matrix, and a slight increase of the apparent diffusion coefficient. Furthermore, the presence of BMI enhanced such properties as the flexural elastic modulus and the compressive yield stress while reducing slightly the fracture parameters KIc, and GIc (critical stress intensity factor and critical strain energy release rate, respectively), as a consequence of the reduced ability of the IPN network to be plastically deformed under loading.