Working cycle of conventional light-driven molecular rotary motors (LDMRMs), especially Feringa-type motors, usually have four steps, two photoisomerization steps, and two thermal helix inversion (THI) steps. THI steps hinder the ability of the motor to operate at lower temperatures and limit the rotation speed of LDMRMs. A three-stroke LDMRM, 2-(2,7-dimethyl-2,3-dihydro-1H-inden-1-ylidene)-1,2-dihydro-3H-pyrrol-3-one (DDIY), is proposed, which is capable of completing an unidirectional rotation by two photoisomerization steps and one thermal helix inversion step at room temperature. On the basis of trajectory surface-hopping simulation at the semi-empirical OM2/MRCI level, the EP→ZP and ZP→EM nonadiabatic photoisomerization dynamics of DDIY were systematically analyzed. Quantum yields of EP→ZP and ZP→EM photoisomerization of DDIY are ca. 34% and 18%, respectively. Both EP→ZP and ZP→EM photoisomerization processes occur on an ultrafast time scale (ca. 100–300 fs). This three-stroke LDMRM may stimulate further research for the development of new families of more efficient LDMRMs.
Using phytic acid (PA) and piperazine (Pi) as raw materials, piperazine phytate (PA‐Pi) was fabricated by simple ionic reaction. Furthermore, A series of rigid polyurethane foam/piperazine phytate (RPUF/PA‐Pi) composites were prepared by one‐step water‐blown technology. Thermogravimetric (TG) results showed that the addition of PA‐Pi improved the thermal stability of RPUF/PA‐Pi composites at high temperature. At 700°C, RPUF/PA‐Pi20 exhibited the highest carbon residue of 25.8 wt%. Cone calorimetry and smoke density tests suggested that PA‐Pi could reduce the heat and smoke release during combustion process of the composites, thus reducing their fire hazard. Thermogravimetric‐Fourier transform infrared spectroscopy (TG‐FTIR) indicated that PA‐Pi significantly inhibited the release of toxic gases (isocyanate compounds, aromatic compounds, CO and HCN) and flammable gases (hydrocarbons and esters) during the decomposition process of RPUF/PA‐Pi composites, effectively improving fire performance of the composites. Scanning electron microscope (SEM), Raman and Fourier transform infrared spectroscopy (FTIR) were used to characterize the carbon residue of RPUF/PA‐Pi composites. The results showed that PA‐Pi could promote the formation of dense carbon layer of composites and effectively prevented heat and mass transfer in the combustion process.
Rigid polyurethane foam/ammonium polyphosphate/cobalt phytate (RPUF/APP/PA-Co) composites were prepared by one-step water-blown method using ammonium polyphosphate (APP)/cobalt phytate (PA-Co) as a flame retardant system. The char residue of RPUF/APP/PA-Co increased significantly than that of RPUF, indicating that the thermal stability of composites was enhanced. Cone calorimetry and smoke density tests showed that when 40 phr APP and 10 phr PA-Co were added, the total heat release and smoke release of RPUF/APP40/PA-Co10 composite decreased significantly. TG-IR test confirmed that APP/PA-Co could significantly inhibit the release of flammable gases (hydrocarbons, esters) and toxic gases (aromatic compounds, isocyanate, CO, HCN,) of RPUF/APP/PA-Co composites and improve the fire resistance of composites. SEM-EDS, Raman spectra and FTIR were applied to investigate the char residues of composites. The results showed that APP/PA-Co loading was beneficial to the generation of dense char layer with high degree of graphitization and reducing the release of combustible substances and smoke of composites.
A series of FR‐RPUF composites were prepared by a one‐step water foaming process with ammonium polyphosphate (APP) and steel slag (SS) as flame retardants. Thermogravimetric analysis (TG), limiting oxygen index (LOI), UL‐94 vertical combustion test, microscale combustion calorimetry (MCC), TG‐Fourier transform infrared spectrometry (TG‐FTIR), scanning electron microscopy (SEM), Raman spectra and FTIR were used to investigate the thermal stability, flame retardancy, combustion performance, gas phase products, and char residue morphology of FR‐RPUF composites. TG test results showed that the initial decomposition temperature (T‐5wt%) and char residue rate at 700°C of RPUF/APP/SS composites were significantly enhanced by the addition of APP and SS, and the thermal stability of the composites was improved. Flame retardant test results confirmed the significantly increased LOI values of RPUF/APP/SS composites with V‐0 rating. TG‐FTIR also confirmed the obviously decreased release of toxic gases and flammable gases in the combustion of RPUF/APP/SS composites. SEM and Raman spectra of char residues for the composites suggested that APP/SS system improved the compactness and graphitization degree of char layer for RPUF/APP/SS composite. The above researches provide a new strategy for the utilization of SS in fire safety engineering.
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