The generic aim of the present work is to reduce the time required for glycolytic depolymerization of PET by employing microwave irradiation instead of the conventional heating process. Glycolysis of PET was performed in the presence of glycols of different molecular weight under microwave irradiation. Experimental conditions like PET : glycol ratio, reaction time and concentration of glycerol were optimized to maximize the product yield. In the presence of ethylene glycol, bis-(hydroxyethyl) terephthalate (BHET) could be obtained in excellent yields in significantly lesser time (30 min) as compared to 8-9 h by conventional heating process. The BHET yield could further be increased by a second step glycolysis of the residual oligomers. This increased efficiency of the microwave assisted process has been attributed to the high microwave absorption capacity of glycols which results from their high loss factor. PET could also be glycolysed in the presence of higher glycols, however the reactivity of diols was found to decrease with increase in the molecular weight. The polyols obtained were reacted with aromatic diphenylmethane diisocyanate to prepare polyurethane foams, which were characterized by various techniques for determination of their physical, mechanical and structural properties. The compressive strength of the polyurethane foams was found to be inversely proportional to the molecular weight of the glycolysed polyol used for its preparation.
In this article, the potential of amine‐functionalized poly(styrene) (PS) microspheres as toughening agent for epoxy resin has been explored. PS microspheres were prepared by suspension polymerization, where the monomer concentration and stirring speed was varied to control the microsphere dimensions (52–183 µm). The obtained microspheres were chemically functionalized with an aim to improve its dispersion within the epoxy matrix. The amine groups generated on the microsphere surface offer a potential site of covalent linkage with the epoxy matrix, thereby resulting in increased compatibility and improved properties. Epoxy composites containing varying amounts of microspheres (1–7% w/w) were prepared and their mechanical properties were evaluated under both quasi‐static as well as dynamic conditions. The amination of poly(styrene) (APS) led to improved dispersion of the rigid microspheres in the epoxy matrix, which was evident from higher impact strength and fracture energies (GIC) as compared to its neat analogs. The izod impact strength and GIC increased by 33% and 150%, respectively, on introduction of 3% APS. This was accompanied with an increase in the tensile modulus and strength of the epoxy resin. Further increase in loading led to agglomeration of the microspheres, which in turn resulted in lowering of impact strength and toughness. Excellent agreement was found between the experimentally measured modulae and the predictions made on the basis of Halpin–Tsai and Lewis–Neilson models. Fracture surface morphology was studied to arrive at the principal toughening mechanisms behind the experimental findings. POLYM. COMPOS., 36:174–183, 2015. © 2014 Society of Plastics Engineers
The potential of poly(ethyleneterephthalate) glycolysates toward improving the energy absorption characteristics of cycloaliphatic epoxy resins has been explored. Microwave-assisted glycolytic depolymerization of PET was performed in the presence of polyether diols of different molecular weights. The obtained glycolysates were blended with epoxy, and their mechanical properties were studied under both quasi-static and dynamic conditions. Significant improvements were observed, which were found to depend both on the amount as well as nature of glycolysate. Amine functionalities were introduced at the terminal positions of glycolysates to improve the compatibility between the two phases. The amine derivatives exhibited superior performance and the Mode I fracture toughness (K IC ) of epoxy increased by $18% in optimized compositions, which is indicative of its improved notch sensitivity. Neat epoxy specimens fractured in a brittle fashion, but all the blends exhibited ductile failure, as evidenced by surface morphological investigations. The mechanical properties of epoxy blends prepared with analogous aliphatic polyols, both before and after amine functionalization, were also studied which clearly reveal the beneficial role of aromatic groups toward improving the toughness of the base cycloaliphatic epoxy resin without compromising on the material stiffness.
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