PU Matrix Research Articles

Pyrolysis of PU/CFCs wastes

In the TGA experiments, the activation energy (25–30 kcal mol −1) and preexponential constant (ln A=34.6 h −1) of the pyrolysis of PU/CFCs wastes were obtained. At least three discrete features at 328, 423, and 443 K are observed corresponding to desorption of CFC-141b from external, internal, and crosslink of the PU matrix, respectively. It indicates that pyrolysis of the PU polymer (at elevated temperatures) may not be effected by the presence of CFCs. In a single pass through the heated sodium oxalate bed (573 K) caused a nearly complete mineralization of CFC-141b.

Determination of lanthanides and actinides in uranium materials by high-performance liquid chromatography with inductively coupled plasma mass spectrometric detection

The determination of Nd, U and Pu by isotope dilution analysis is well known as the classical method for the calculation of the burn-up of a nuclear fuel. Numerous isobaric overlaps restrict the direct determination of fission product and actinide isotopes by mass spectrometry and therefore an extensive chemical separation is required. As a first step towards the development of a more advanced method for the determination of fission product isotopes in irradiated uranium fuel, high-performance liquid chromatographic (HPLC) and inductively coupled plasma mass spectrometric (ICP-MS) systems were installed in glove-boxes and all the lanthanides were separated by HPLC and detected on-line by ICP-MS. As high U and Pu concentrations strongly suppress the signals of trace elements in ICP-MS, a separation method to elute U and Pu first was developed. Thus it was possible to determine the isotopic composition of Nd in a high U and Pu matrix. With the same equipment, a method was developed to prevent isobaric overlaps in the mass spectrum by separating U, Am and Pu.

Experiences at Trombay in Monitoring Actinide Intakes by Occupational Workers by Direct External Counting

Direct assessment of lung/liver/skeletal burdens of actinides (Pu/Am/U) for monitoring intakes froms part of the ongoing internal dosimetry programmes for occupational workers at Trombay. The majority of the measurements are performed with a 200 mm diameter phoswich detector operating with pulse-shape discrimination based on ORTEC electronics. Additional detectors (NaI(Tl), a miniature CdTe and a special coaxial HPGe) are also employed whenever needed. All the detection systems are located inside a graded lined 20 cm thick steel chamber. Calibration techniques include both in vivo methods as well as the use of a realistic torso phantom. Utilising these facilities, routine, special/operational, confirmatory and follow-up monitoring programmes have been extensively conducted. A brief description is given of the facilities, procedures employed and methodologies for computation of committed effective dose equivalent (CEDE). Monitoring data have have also been analysed to observe elimination patterns with respect to actinide aerosols deposited in the lung. These have been compared with the metabolic models currently in use. In particular, unusually long retention half-times for natural uranium, class Y behavior of 241 AmO 2 (embedded in Pu matrix), and super class Y behaviour of Pu aerosols in human lungs have been observed. Likely effects of these findings on the estimates of internal doses are considered

The effects of functional azo initiator on PMMA and polyurethane IPN systems. II. The influence of the interface and the matrix structure on the mechanical properties

AbstractThe mechanical properties of materials prepared by a new method for modifying the structure of polyurethane/poly(methyl methacrylate) (PU/PMMA) interpenetrating polymer networks (IPNs) by using a reactive azo initiator were investigated by means of tensile test, tear test, and dynamic mechanical thermal analysis (DMTA) measurement. The structures of these IPNs were similar to the particulate filled elastomers. It was found that the reactive initiator, which could form blocks of PMMA within the PU matrix (rubber), changed both the filler‐matrix interface and the matrix structure. The mechanical properties of these IPNs were dominated by the matrix structure and the interface.

The effects of functional azo initiator on PMMA and polyurethane IPN systems. I. Synthesis, characterization, and thermal effects

AbstractThe use of functional azo initiators and the thermal history of the materials have been shown to exert significant effects on the properties of interpenetrating polymer networks (IPNs). The IPNs prepared with a reactive azo initiator from MDI and 1,2‐PBD (1,2‐polybutadiene diol) with PMMA have been found to exhibit greater ductility, lower rigidity, and lower moduli than IPNs prepared with AIBN. This probably resulted from the attached PMMA blocks modifying the properties of the PU matrix phases. Increasing thermal treatment of IPNs prepared from either the reactive or the normal azo initiators exhibited increased Tg values in both DSC and DMTA scans. These results have been explained by increased association from chemical reactions between the hard segments of the polyurethane and poly(methyl methacrylate) ester groups.