The reaction of a desulphurized kraft lignin with hexamethylene diamine and dimethyl carbonate has allowed the development of isocyanate-free polyurethane resins.The present research work is based on previous studies ...The reaction of a desulphurized kraft lignin with hexamethylene diamine and dimethyl carbonate has allowed the development of isocyanate-free polyurethane resins.The present research work is based on previous studies made with hydrolyzable and condensed tannins,but takes advantage of the higher number of hydroxyl groups present in lignin and their different aliphatic and aromatic character.The obtained materials were analyzed by Fourier transform infrared(FTIR)spectroscopy,matrix-assisted laser desorption ionization time-of-flight(MALDI-TOF)mass spectrometry and solid-state cross-polarization/magic angle spinning(CP MAS)13C nuclear magnetic resonance(NMR),which have revealed the presence of urethane functions.The interpretation of the results has shown a larger number of species than when tannins were used and has indicated the presence of two types of bonds in the new molecules formed:ionic and covalent bonds.展开更多
Glucose-based non-isocyanate polyurethanes(NIPU)were prepared by reaction of glucose with dimethyl carbonate and hexamethylene diamine.These were used to prepare partially biobased polyurethane foams by reaction with ...Glucose-based non-isocyanate polyurethanes(NIPU)were prepared by reaction of glucose with dimethyl carbonate and hexamethylene diamine.These were used to prepare partially biobased polyurethane foams by reaction with NaHCO3 as a blowing agent and addition of a silane coupling agent having different functions such as coreactant and adjuvant to obtain more uniform and smaller cells.The foams were foamed and hardened by applying heat.The foams presented very limited fire resistance indicating that as for synthetic polyurethane foams the eventual use of a fire retardant appears to be necessary.The 2 hours water absorption was used to indicate if close cells or open cells occur.More characteristic is their stress strain behaviour.While compression does indeed flatten the cell walls nonetheless the cellular structure is maintained and the cell walls have not been destroyed.This indicates a certain level of elasticity in the cell walls of formulations containing NaHCO3.In effect the macro-appearance of this foams,confirms this explanation as the foam is densified and holds together.展开更多
Double cantilever beam tests were used to measure the energy release rates of linear vibrational welded moso bamboo joints.The influence of the length of the preserved cracks,the different combinations of the inner an...Double cantilever beam tests were used to measure the energy release rates of linear vibrational welded moso bamboo joints.The influence of the length of the preserved cracks,the different combinations of the inner and outer bamboo surfaces and the moisture content is studied herein.The experimental compliance method,which is based on linear elastic fracture mechanics and has been shown to be an ideal method,was used to analyze data with the power equation.The results show that the preserved initial crack length does not have a significant effect on the final measured energy release rate,while the moso bamboo combination does affect the properties dramatically.The welded moso bamboo joints with inner-inner surfaces have the highest energy release rate of 122 J/m^2.The average energy release of the outer-outer combination was only 102 J/m^2.The expansion of the cracks also became easier when the moisture content of the welded joints was 18.5%compared to 4.5% and 10.1%.So the moisture resistance of the welded joints should be duly improved.展开更多
文摘The reaction of a desulphurized kraft lignin with hexamethylene diamine and dimethyl carbonate has allowed the development of isocyanate-free polyurethane resins.The present research work is based on previous studies made with hydrolyzable and condensed tannins,but takes advantage of the higher number of hydroxyl groups present in lignin and their different aliphatic and aromatic character.The obtained materials were analyzed by Fourier transform infrared(FTIR)spectroscopy,matrix-assisted laser desorption ionization time-of-flight(MALDI-TOF)mass spectrometry and solid-state cross-polarization/magic angle spinning(CP MAS)13C nuclear magnetic resonance(NMR),which have revealed the presence of urethane functions.The interpretation of the results has shown a larger number of species than when tannins were used and has indicated the presence of two types of bonds in the new molecules formed:ionic and covalent bonds.
文摘Glucose-based non-isocyanate polyurethanes(NIPU)were prepared by reaction of glucose with dimethyl carbonate and hexamethylene diamine.These were used to prepare partially biobased polyurethane foams by reaction with NaHCO3 as a blowing agent and addition of a silane coupling agent having different functions such as coreactant and adjuvant to obtain more uniform and smaller cells.The foams were foamed and hardened by applying heat.The foams presented very limited fire resistance indicating that as for synthetic polyurethane foams the eventual use of a fire retardant appears to be necessary.The 2 hours water absorption was used to indicate if close cells or open cells occur.More characteristic is their stress strain behaviour.While compression does indeed flatten the cell walls nonetheless the cellular structure is maintained and the cell walls have not been destroyed.This indicates a certain level of elasticity in the cell walls of formulations containing NaHCO3.In effect the macro-appearance of this foams,confirms this explanation as the foam is densified and holds together.
文摘Double cantilever beam tests were used to measure the energy release rates of linear vibrational welded moso bamboo joints.The influence of the length of the preserved cracks,the different combinations of the inner and outer bamboo surfaces and the moisture content is studied herein.The experimental compliance method,which is based on linear elastic fracture mechanics and has been shown to be an ideal method,was used to analyze data with the power equation.The results show that the preserved initial crack length does not have a significant effect on the final measured energy release rate,while the moso bamboo combination does affect the properties dramatically.The welded moso bamboo joints with inner-inner surfaces have the highest energy release rate of 122 J/m^2.The average energy release of the outer-outer combination was only 102 J/m^2.The expansion of the cracks also became easier when the moisture content of the welded joints was 18.5%compared to 4.5% and 10.1%.So the moisture resistance of the welded joints should be duly improved.
