New processes in the environmental chemistry of nitrite: nitration of phenol upon nitrite photoinduced oxidation

The role of nitrite as an environmental factor has been widely recognized. Nitrite is a relevant source of *OH in the atmosphere, both in the gas phase via photolysis of gaseous HNO2 and in atmospheric hydrometeors by photolysis of NO2-. In aqueous systems, *OH production through nitrite photolysis can be negligible due to the competition for light absorption by dissolved Fe(III), colloidal iron oxides, and nitrate. These photoexcited oxidants interact with NO2- and HNO2 to form *NO2, either directly or via formation of *OH. As a consequence, nitrite and nitrous acid may act as *NO2 rather than *OH sources. The radical *NO2 is involved in the nitration of many aromatic compounds, of which phenol is a model in this work. Kinetic measurements using 2-propanol as *OH scavenger show that the direct production of *OH by aqueous Fe(III) species decreases as pH increases. At slightly acidic and neutral pH values, oxidation of nitrite occurs by direct electron transfer to photoexcited Fe(III)aq species or colloidal iron oxides, in addition to the *OH-mediated oxidation of NO2-. The reported findings suggest a completely new role of nitrite in aquatic environments.     

Structure–property relationships of polyurethane-based materials (PUPA) for applications in biomedicine

Polyurethane poly(amido–amine) (PUPA) is a modified polyurethane whose chains are crosslinked with those of a tertiary aminic polymer [poly(amido–amine) (N₂LL)] by the bifunctional agent hexamethylenediisocyanate (HMDI). PUPA is capable of complexing heparin; a behavior that is related to the presence of poly(amido-amine). The effect of the chemical composition of the starting mixture and/or the reaction time on the morphology and physical properties was studied by using differential scanning calorimetry, dynamic mechanical experiments, x-ray, scanning electron microscopy, and Fourier transform infrared attenuated total reflection analyses. © 1993 John Wiley & Sons, Inc.     

Carbon dioxide as refrigerant for tap water heat pumps: A comparison with the traditional solution

Increased concern about the environmental impact of the refrigeration technology is leading toward design solutions aimed at improving the energy efficiency of the related applications, using eco-friendly refrigerants, i.e. ozone-friendly and with the least possible global warming potential (GWP). In this respect, carbon dioxide (ASHRAE R744) is seen today as one of the most promising refrigerants and is raising great interest in industrial and scientific fields. In the present work, the plant options are investigated, which are related to the design of air/water heat pumps for tap water using CO₂. A comparison is made, in terms of energy efficiency, between a system working with CO₂ and a similar one working with HFC R134a; such a comparison is carried out by means of a simulation model of a refrigerating machine/heat pump, characterized by a detailed representation of the heat exchangers, based on their subdivision into elementary volumes. Results show that carbon dioxide is an interesting substitute for synthetic fluids, if the design of the system is focused to take advantage of its properties.     

Wind energy in the world: Reality and prospects

This report presents an overview of the various aspects of the use of wind energy for the production of electricity with special regard to: available resources; the state-of-the art of the technology; the worldwide wind energy applications; the present situation and foreseeable development of the world wind energy market in the next two decades; the economics of wind-generated electricity. Possible restraints to and benefits from wind plant integration in utility systems are also considered.     

Compatibilisation of polystyrene-polyolefin blends

Summary The impact properties of 1:1 polyolefin-polystyrene blends compatibilised with a series of hydrogenated styrene-butadiene block copolymers of various structures have been studied with a view to establishing a structure-property realationship. The most effective compatibiliser in this context appears to be a low molecular weight triblock (Kraton G1652). Addition of only 5% Kraton G1652 affords a ca. three-fold improvement in the impact strength for a 1:1 PP/PS blend over the uncompatibilised blend and leads to near HIPS impact strength for a 1:1 LDPE/PS blend. This compatibiliser is as effective as a high molecular weight tapered diblock and appears to be substantially more effective than either low molecular weight diblocks or a higher molecular weight triblock.     

Maleated polyisobutylene: A novel toughener for unsaturated polyester resins

A polyisobutene rubber was modified by grafting succinic anhydride onto its end groups and has been used as a toughening agent for an unsaturated polyester resin. Both the functionalization and the successive reaction between the modified rubber and the polyester was investigated by Fourier transform infrared spectroscopy (FTIR). The yield behavior of the cured resins was studied by compression measurements, while the fracture properties were determined at low and high strain rate. A morphological analysis of the investigated blends has been carried out by scanning electron microscopy (SEM). A considerable enhancement of tougheness has been achieved when the modified rubber was used in place of the plain polyisobutene. The effect was found to depend on the grafting degree of the rubber and on the time period during which the two-component mixture was allowed to react prior to the curing process. © 1995 John Wiley & Sons, Inc.