Mohamed Taha

Diels–Alder thermoresponsive networks based on high maleimide-functionalized urethane prepolymers

Thermoreversible polyurethane networks were successfully prepared by Diels–Alder reaction using a highly maleimide-functionalized urethane prepolymer with an epoxy-based furan coupling agent or a furan-functionalized polyurethane. Highly functional maleimide prepolymers with various functionalities were synthesized by the isocyanate-alcohol reaction from glycerol, H12MDI, and protected N-hydroxymethylmaleimide. Thermal behavior and de-crosslinking of the networks were studied via thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and solubility tests. Swelling tests allowed the evaluation of the networks’ density. Thermal properties and crosslinking density were influenced by furan and maleimide functionalities and by the nature of the diene. Denser networks with lower de-crosslinking temperatures were obtained using the epoxy-based furan coupling agent. With the furan-functionalized polyurethanes, looser networks and higher de-crosslinking temperatures were obtained. These higher de-crosslinking temperatures were attributed to the presence of more physical links in the networks.

The concept of conversion distribution in reactive processing

A new concept of conversion distribution applied to the continuous chemical modification and polymerization of polymers in a twin screw extruder was discussed. The kinetics and the residence time distribution function ( RTD ) are two undissociable parameters in reactive extrusion because their combination reflects the degree of homogeneity of the modified polymer at the die die exit of the extruder. A function G defining the distribution of the modification rate allowed us to evaluate the distribution of the extent of the conversion around the mean conversion. This study has underlined the predominant role of the kinetics on the structural homogeneity of the modified product. This new concept was developed, within a framework of reactive processing, from previous works on chemical modification of polymers and polycondensation in corotating twin screw extruder.

Facile elaboration of polymethylmethacrylate / polyurethane interpenetrating networks using Diels-Alder reactions

Thermo-reversible PMMA/PU interpenetrating polymer networks were successfully prepared by Diels-Alder (DA) reaction using a furan-functionalized polymethyl methacrylate, furan-functionalized polyurethane and a maleimide-based coupling agent. First, homo-networks were synthesized and characterized in order to predict the characteristics of the corresponding interpenetrating network. Polyurethane networks were confirmed to be reversible with a temperature of retro-Diels-Alder varying from 135xa0°C to 144xa0°C depending on the cross-linking density. PMMA/PU blends are completely immiscible as shown by the presence of two Tgs corresponding to the two phases in DSC results. Due to the presence of supramolecular interactions, no phase separation was observed in the simultaneously cross-linked PMMA/PU networks. Thermal behavior and de-cross-linking of the IPNs were studied by DSC, solubility tests and rheology. Swelling tests allowed the evaluation of the networks density.

Fly ash stabilization-solidification using polymer-concrete double matrices

Abstract Air Pollution Control residues from Municipal Solid Waste Incineration (APC MSWI) solidification in low density polyethylene (LDPE), polystyrene (PS), poly(vinyl chloride) (PVC) or on polymer blends were realized by co-rotating twin-screw extrusion. Retention properties of different polymers were compared to those of concrete and polymer-concrete double barrier materials. The use of double organic-inorganic barrier resulted in higher retention. Matrix retention performance were as follows: polymer-concrete > PVC > LDPE > two polymer blends > three polymer blends > concrete. The addition of compatibilizers improved retention performance of polymer blends. This study opens new perspectives for the use of plastic waste for fly ash solidification.

Solvent-free preparation, characterization, and properties of SEBS–g–polycarbonate copolymers

The reactions between polycarbonate (PC) and polystyrene-block-poly(ethylene-butylene)-block-polystyrene-grafted-maleic anhydride (SEBS–g–MAH) is a novel, convenient, solvent-free, and easy way to create SEBS–g–PC in order to compatibilize polystyrene and PC blends. This study determines the most efficient catalyst among Tin (II) bis(2-ethylhexanoate) (SnOct2), 1,5,7-Triazabicyclo[4.4.0]dec-5-ene (TBD), Titanium tetrabutoxide (Ti(OBu)4) and Sodium 4-hydroxybenzenesulfonate dihydrate (SHBS) in the molten state at 220u2009°C. From 20 to 30u2009wt% of SEBS-g-MAH (or KFG) chains became insoluble. The size exclusion chromatography analyses showed the formation of a double distribution due to PC chains scission and grafting reactions onto SEBS–g–MAH with the exception of the Ti(BuO)4 use. Fine microstructures with a percolation effect proved the efficiency of both the TBD and the SnOct2. The PC transition temperature decreased in at least 10u2009°C, confirmed that only SnOct2 and TBD were efficient to catalyze the grafting reactions. No evolution was observed with the SHBS and Ti(OBu)4.