Glycolysis Recycling of Waste Polyurethane Rigid Foam Using Different Catalysts

Dramatically increasing waste polyurethane rigid foam(WPRF)draws the attention of the world.A mixture of ethylene glycol(EG)and diethylene glycol(DEG)is used as glycolysis agents.WPRF was subjected to alcoholysis using different catalysts which are titanium ethylene glycol and potassium hydroxide to obtain recycled polyol,respectively.The effect of a different catalyst on the viscosity and hydroxyl value of recycled polyol is discussed.The regenerated polyurethane(RPU)is performed using the recycled polyol.Infrared spectrum,compressive strength,apparent density,water absorption,scanning electron microscope,and thermogravimetric analysis are carried out to investigate the effect of WPRF degradation using different catalysts.The results show that titanium glycol is more efficient than potassium hydroxide in almost all conditions.The viscosity of the recycled polyol is relatively low,and the hydroxyl value meets the requirements of industrial use.When the titanium glycol titanium addition amount is 0.05%,the prepared RPU has a compressive strength of 0.24 MPa,an apparent density of 41.75 kg/m^(3),and a good foam structure.Besides,the water absorption rate of the RPU under the two catalytic systems is not much different,and the thermal stability is good.The recycled polyol can generally partially replace traditional polyols to prepare polyurethane rigid foams with good comprehensive properties.

High temperature performance of coaxial h-BN/CNT wires above 1,000 ℃:Thermionic electron emission and thermally activated conductivity

The development of wires and cables that can tolerate extremely high temperatures will be very important for probing extreme environments, such as in solar exploration, fire disasters, high-temperature materials processing, aeronautics and astronautics. In this paper, a lightweight high-temperature coaxial h-boron nitride (BN)/carbon nanotube (CNT) wire is synthesized by the chemical vapor deposition (CVD) epitaxial growth of h-BN on CNT yarn. The epitaxially grown h-BN acts as both an insulating material and a jacket that protects against oxidation. It has been shown that the thermionic electron emission (1,200 K) and thermally activated conductivity (1,000 K) are two principal mechanisms for insulation failure of h-BN at high temperatures. The thermionic emission of h-BN can provide the work function of h-BN, which ranges from 4.22 to 4.61 eV in the temperature range of 1,306-1,787 K. The change in the resistivity of h-BN with temperature follows the ohmic conduction model of an insulator, and it can provide the “electron activation energy”(the energy from the Fermi level to the conduction band of h-BN), which ranges from 2.79 to 3.08 eV, corresponding to a band gap for h-BN ranging from 5.6 to 6.2 eV. However, since the leakage current is very small, both phenomena have no obvious influence on the signal transmission at the working temperature. This lightweight coaxial h-BN/CNT wire can tolerate 1,200 ℃ in air and can transmit electrical signals as normal. It is hoped that this lightweight high-temperature wire will open up new possibilities for a wide range of applications in extreme high-temperature conditions.