A novel intumescent flame retardant coating, consisting of poly（vinylphosphonic acid） （PVPA） as the acid source and branched polyethylenimine （BPEI） as the blowing agent, was constructed on the surface of ramie ...A novel intumescent flame retardant coating, consisting of poly（vinylphosphonic acid） （PVPA） as the acid source and branched polyethylenimine （BPEI） as the blowing agent, was constructed on the surface of ramie fabrics by alternate assembly to remarkably improve the flame retardancy of ramie. The PVPA/BPEI coating on the surface of individual fibers of ramie fabric pyrolyzes to form protective char layer upon heating/burning and improves the flame retardancy of ramie. Thermogravimetric analysis reveals that the PVPA/BPEI-coated ramie fabrics left as much as 25.8 wt% residue at 600 ~C, while the control （uncoated） fabric left less than 1.4 wt% residue. Vertical flame test shows that all PVPA/BPEI-coated fabrics have shorter after-flame time, and the residues well preserved the original weave structure and fiber morphology, whereas, the uncoated fabric left only ashes. Microscale combustion calorimetry shows that the PVPA/BPEI coatings greatly reduce the total heat release by as much as 66% and the heat release capacity by 76%, relative to those of the uncoated fabric.展开更多
Hydrophilic polymer coatings on artificial implants generate excellent tribological properties.The friction properties of polymer coatings are affected by salt ion factors.Herein,the atomic force microscopy(AFM)was us...Hydrophilic polymer coatings on artificial implants generate excellent tribological properties.The friction properties of polymer coatings are affected by salt ion factors.Herein,the atomic force microscopy(AFM)was used to show that the superlubricity was achieved between poly(vinylphosphonic acid)(PVPA)-modified Ti6Al4V and polystyrene(PS)microsphere probe lubricated with monovalent salt solutions(LiCl,NaCl,KCl,and CsCl).Considering that adhesion is an important cause of friction changes,the AFM was further utilized to obtain adhesion between friction pairs in different salt solutions.The results indicated that the larger the cation radius in the lubricant,the smaller the adhesion,and the lower the friction coefficient of the PVPA coating.The electrostatic interaction between the PVPA and one-valence cations in lubricants was analyzed by the molecular dynamics(MD)simulation as it was found to be the main influencing factor of the adhesion.Combined analysis results of friction and adhesion indicated that by adjusting the size of cation radius in lubricant,the adhesion between the tribo-pairs can be changed,and eventually the magnitude of friction can be affected.This study opens up a new avenue for analyzing the friction characteristics of hydrophilic polymer coatings from the perspective of intermolecular forces.展开更多
The stability of the tribological properties of polymer coatings is vital to ensure their long term use.The superlubricity of the poly(vinylphosphonic acid) (PVPA)-modified Ti6A14V/polytetrafluoroethylene (PTFE)interf...The stability of the tribological properties of polymer coatings is vital to ensure their long term use.The superlubricity of the poly(vinylphosphonic acid) (PVPA)-modified Ti6A14V/polytetrafluoroethylene (PTFE)interface can be obtained when lubricated by phosphate-buffered saline (PBS,pH =7.2),but not when lubricated by deionized water and ethanol.Therefore,the mechanisms for the superlubricity of PVPA coatings affected by lubricant were investigated in detail.The stability of the PVPA coatings and their compatibility with the lubricant are critical factors in realizing ideal tribological properties of PVPA coatings.Robust PVPA coatings are stable under a wide range of pH values (6-10) using PBS as the basic solution,and are also characterized by superlubricity.The hydrolysis kinetics of phosphate anhydride is the main reason for the pH responses.In addition,along with stability,PVPA coatings exhibit different friction coefficients in salt solutions which are composed of various ions,which indicates that the compatibility between PVPA coatings and the lubricant can be used to regulate the superlubricity properties.Based on a fundamental understanding of the mechanism of surperlubricity by considering the effects of the lubricant,PVPA coatings with stability and perfect tribological performance are expected to be applied in more aspects.展开更多
基金financially supported by the National Basic Research Program of China(Nos.2010CB631105 and 2011CB612307)
文摘A novel intumescent flame retardant coating, consisting of poly（vinylphosphonic acid） （PVPA） as the acid source and branched polyethylenimine （BPEI） as the blowing agent, was constructed on the surface of ramie fabrics by alternate assembly to remarkably improve the flame retardancy of ramie. The PVPA/BPEI coating on the surface of individual fibers of ramie fabric pyrolyzes to form protective char layer upon heating/burning and improves the flame retardancy of ramie. Thermogravimetric analysis reveals that the PVPA/BPEI-coated ramie fabrics left as much as 25.8 wt% residue at 600 ~C, while the control （uncoated） fabric left less than 1.4 wt% residue. Vertical flame test shows that all PVPA/BPEI-coated fabrics have shorter after-flame time, and the residues well preserved the original weave structure and fiber morphology, whereas, the uncoated fabric left only ashes. Microscale combustion calorimetry shows that the PVPA/BPEI coatings greatly reduce the total heat release by as much as 66% and the heat release capacity by 76%, relative to those of the uncoated fabric.
基金supported by the National Natural Science Foundation of China(51705010)the Beijing Natural Science Foundation(3192003)+2 种基金the General Project of Science and Technology Plan from Beijing Educational Committee(KM201810005013)the Tribology Science Fund of State Key Laboratory of Tribology(STLEKF16A02 and SKLTKF19B08)the training program of Rixin talent and outstanding talent from Beijing University of Technology.
文摘Hydrophilic polymer coatings on artificial implants generate excellent tribological properties.The friction properties of polymer coatings are affected by salt ion factors.Herein,the atomic force microscopy(AFM)was used to show that the superlubricity was achieved between poly(vinylphosphonic acid)(PVPA)-modified Ti6Al4V and polystyrene(PS)microsphere probe lubricated with monovalent salt solutions(LiCl,NaCl,KCl,and CsCl).Considering that adhesion is an important cause of friction changes,the AFM was further utilized to obtain adhesion between friction pairs in different salt solutions.The results indicated that the larger the cation radius in the lubricant,the smaller the adhesion,and the lower the friction coefficient of the PVPA coating.The electrostatic interaction between the PVPA and one-valence cations in lubricants was analyzed by the molecular dynamics(MD)simulation as it was found to be the main influencing factor of the adhesion.Combined analysis results of friction and adhesion indicated that by adjusting the size of cation radius in lubricant,the adhesion between the tribo-pairs can be changed,and eventually the magnitude of friction can be affected.This study opens up a new avenue for analyzing the friction characteristics of hydrophilic polymer coatings from the perspective of intermolecular forces.
基金The authors also appreciate the funding supported by the Beijing Natural Science Foundation，the Tribology Science Fund of State Key Laboratory of Tribology，as well as the National Natural Science Foundation of China
文摘The stability of the tribological properties of polymer coatings is vital to ensure their long term use.The superlubricity of the poly(vinylphosphonic acid) (PVPA)-modified Ti6A14V/polytetrafluoroethylene (PTFE)interface can be obtained when lubricated by phosphate-buffered saline (PBS,pH =7.2),but not when lubricated by deionized water and ethanol.Therefore,the mechanisms for the superlubricity of PVPA coatings affected by lubricant were investigated in detail.The stability of the PVPA coatings and their compatibility with the lubricant are critical factors in realizing ideal tribological properties of PVPA coatings.Robust PVPA coatings are stable under a wide range of pH values (6-10) using PBS as the basic solution,and are also characterized by superlubricity.The hydrolysis kinetics of phosphate anhydride is the main reason for the pH responses.In addition,along with stability,PVPA coatings exhibit different friction coefficients in salt solutions which are composed of various ions,which indicates that the compatibility between PVPA coatings and the lubricant can be used to regulate the superlubricity properties.Based on a fundamental understanding of the mechanism of surperlubricity by considering the effects of the lubricant,PVPA coatings with stability and perfect tribological performance are expected to be applied in more aspects.
