By introducing semicrystalline moieties into hyperbranched molecular smictures three kinds of prepolymers of potential use as UV powder coatings were prepared and characterized.
A type of polymer-coated molybdenum powder used in selective laser sintering technology was prepared by coating polymer on molybdenum particles and frozen grinding techniques, with the maximum particle diameter of 71 ...A type of polymer-coated molybdenum powder used in selective laser sintering technology was prepared by coating polymer on molybdenum particles and frozen grinding techniques, with the maximum particle diameter of 71 μm. The laser sintering experiments of polymer-coated molybdenum powder were conducted by using the self-developed selective laser sintering machine (HLRP-350I). The method of microscopic analysis was used to investigate the dynamic laser sintering process of polymer-coated molybdenum powder. Based on the study, the laser sintering mechanisms of polymer-coated molybdenum powder were presented. It is found that the mechanism is viscous flow when the laser sintering temperature is between 100 ℃ and 160 ℃, which can be described by a two-sphere model; and the mechanism is melting /solidification when the temperature is above 160 ℃.展开更多
The technology of length-alterable line-scanning laser sintering was introduced. Based on the research of laser heating property, powder thermal physics parameters and laser sintering process, a numerical model of the...The technology of length-alterable line-scanning laser sintering was introduced. Based on the research of laser heating property, powder thermal physics parameters and laser sintering process, a numerical model of the temperature field during length-alterable line-scanning and laser sintering of polymer-coated molybdenum powder was presented. Finite element method (FEM) was used to simulate the temperature field during laser sintering process. In order to verify the simulated results, a measuring system was developed to study the laser sintering temperature field. Infrared meter was introduced to measure the surface temperature of sintering powder; the temperature of its inside part was measured by thermocouple. The measured results were compared with the numerical simulation results; the conformity between them is good and the relative error is less than 5%.展开更多
A type of polymer-coated Al2O3/ZrO2/TiC ceramic powder was prepared. The laser sintering mechanism of polymer-coated Al2O3/ZrO2/TiC powder was investigated by studying the dynamic laser sintering process. It is found ...A type of polymer-coated Al2O3/ZrO2/TiC ceramic powder was prepared. The laser sintering mechanism of polymer-coated Al2O3/ZrO2/TiC powder was investigated by studying the dynamic laser sintering process. It is found that the mechanism is viscous flow when the sintering temperature is between 80 ℃ and 120 ℃, and it is melting/solidification when the temperature is above 120 ℃. The process parameters of selective laser sintering were optimized by using ortho-design method. The results show that the optimal parameters include laser power of 14 W, scanning velocity of 1 400 mm/s, preheating temperature of 50 ℃ and powder depth of 0.15 mm. A two-step post-treatment process is adopted to improve the mechanical properties of laser sintered part, which includes polymer debinding and high temperature sintering. After vacuum sintering for 2 h at 1 650 ℃, the bending strength and fracture toughness of Al2O3/ZrO2/TiC ceramic part reach 358 MPa and 6.9 MPa·m1/2, respectively.展开更多
Polymers are widely used materials in aerospace,automotive,construction,medical devices and pharmaceuticals.Polymers are being promoted rapidly due to their ease of manufacturing and improved material properties.Resea...Polymers are widely used materials in aerospace,automotive,construction,medical devices and pharmaceuticals.Polymers are being promoted rapidly due to their ease of manufacturing and improved material properties.Research on polymer processing technology should be paid more attention to due to the increasing demand for polymer applications.Selective laser sintering(SLS)uses a laser to sinter powdered materials(typical polyamide),and it is one of the critical additive manufacturing(AM)techniques of polymer.It irradiates the laser beam on the defined areas by a computer-aided design three-dimensional(3D)model to bind the material together to create a designed 3D solid structure.SLS has many advantages,such as no support structures and excellent mechanical properties resembling injection moulded parts compared with other AM methods.However,the ability of SLS to process polymers is still affected by some defects,such as the porous structure and limited available types of SLS polymers.Therefore,this article reviews the current state-of-the-art SLS of polymers,including the fundamental principles in this technique,the SLS developments of typical polymers,and the essential process parameters in SLS.Furthermore,the applications of SLS are focused,and the conclusions and perspectives are discussed.展开更多
The graphene oxide powder(GOP)obtained from the spray drying process often exhibits poor redispersibility which is considered due to the partial reduction of GO sheets.The reduction of drying temperature can effective...The graphene oxide powder(GOP)obtained from the spray drying process often exhibits poor redispersibility which is considered due to the partial reduction of GO sheets.The reduction of drying temperature can effectively increase the redispersibility of GOP,but result in a decreased drying efficiency.Herein,we found that the redispersibility of GOP is strongly affected by its microstructure,which is determined by the feed concentration.With the increase of feed concentration,the GO nanosheet assembly varies from the disordered stacking to relatively oriented assembly,making the morphology of the GOP transform from balllike(the most crumpled one)to flakelike(the least crumpled one),and the 0.8 mgml 1 is the threshold concentration for the morphology,structure,and redispersibility change.Once the feed concentration reaches 0.8 mg ml 1,the appearance of the nematic phase in droplet ensures the relatively oriented assembly of GO sheets to form the layered structure with a low crumpling degree,which greatly improves the polar parts surface tension of the solid GOP,making the GOP easier to form hydrogen bonding with water during the redispersion process,thus stabilizing dispersion.This work provides useful information for understanding the relationships between the morphology,microstructure,and final redispersibility of GOPs.展开更多
Dynamic rheological characteristics of polypropylene (PP) filled with ultra-fine full-vulcanized powdered rubber (UFPR) composed of styrene-butadiene copolymer were studied through dynamic rheological measurements on ...Dynamic rheological characteristics of polypropylene (PP) filled with ultra-fine full-vulcanized powdered rubber (UFPR) composed of styrene-butadiene copolymer were studied through dynamic rheological measurements on an Advanced Rheometric Expansion System (ARES). A specific viscoelastic phenomenon, i.e. 'the second plateau', appeared at low frequencies, and exhibits a certain dependence on the amount of rubber particles and the dispersion state in the matrix. This phenomenon is attributed to the formation of aggregation structure of rubber particles. The analyses of Cole-Cole diagrams of the dynamic viscoelastic functions suggest that the heterogeneity of the composites is enhanced on increasing both particle content and temperature.展开更多
The high water content of sludge has always posed significant challenges for its treatment.Synthetic flocculants,which are widely used in sewage treatment plants,can cause secondary pollution during their production a...The high water content of sludge has always posed significant challenges for its treatment.Synthetic flocculants,which are widely used in sewage treatment plants,can cause secondary pollution during their production and use.Thus,natural polymer flocculants made of natural materials have received increased research attention recently.Corncore,an agricultural waste,was modified through alkalization with sodium hydroxide(NaOH)and etherification with cetyltrimethylammonium bromide(CTMAB)in this study.The L16(45)orthogonal array was used to study the modification conditions.The moisture content(MC)of treated sludge was reduced by approximately 37%with the addition of modified corncore powder(MCCP),which was synthesized under optimal conditions.In addition,changes in the functional groups of the material before and after modification were determined by FTIR.Thermogravimetric analysis indicated that MCCP was steady at room temperature,moreover,BET analysis showed that MCCP had greater surface area.The microstructures of material before and after modification were examined by scanning electron microscopy,revealing that MCCP had a flakeshaped structure and had an increased area of contact area with sludge particles.MCCP is a dehydrating agent that can enhance sludge dewaterability through charge neutralization and reagglomeration and provide superior economic benefits.展开更多
Due to large volume and high hardness of thermal insulation materials mostly used in high temperature fields, a composite cooling powder and its thixotropic hydrogel for thermal protection are presented. The core of c...Due to large volume and high hardness of thermal insulation materials mostly used in high temperature fields, a composite cooling powder and its thixotropic hydrogel for thermal protection are presented. The core of composite cooling material powder is super absorbent polymer, composing with metal salt, polysaccharide hydrosol and inorganic particles and other modifiers through a series of composite process, which can be easily stored for a long time. When needed, the powder can be mixed with water to obtain a kind of thixotropic hydrogel in a very short time. Experimental results show this thermal protection technology with thixotropic ability has excellent thermal protection performance, meanwhile flexible, adhesive and low cost, which exerts instantaneous cooling, efficient thermal protection and long-lasting flame-retardant protection.展开更多
In this study, production and mechanical properties of polymer composite materials obtained by using Al2O3, SiO2, MgO and TiO2 hard ceramic fillers were studied. Epoxy resin was used as the matrix material, and four d...In this study, production and mechanical properties of polymer composite materials obtained by using Al2O3, SiO2, MgO and TiO2 hard ceramic fillers were studied. Epoxy resin was used as the matrix material, and four different ceramic powders were mechanically mixed into the resin at 3% and 5% as reinforcement. The mechanical properties of the polymer composite materials were then characterized. For this purpose, flexural modulus and flexural strength of composite materials were determined by using three point bending test and impact toughness of the materials were determined by Charpy impact test. In addition, the hardness values of the samples were determined by Shore D hardness test.展开更多
基金This work was supported by the National Natural Science Foundation of China (No. 59673026).
文摘By introducing semicrystalline moieties into hyperbranched molecular smictures three kinds of prepolymers of potential use as UV powder coatings were prepared and characterized.
基金Project(50675210) supported by the National Natural Science Foundation of ChinaProject(03022) supported by the Key Science Research Program of Education Ministry of ChinaProject(200410250) supported by the Youth Science Foundation of Shanxi Province, China
文摘A type of polymer-coated molybdenum powder used in selective laser sintering technology was prepared by coating polymer on molybdenum particles and frozen grinding techniques, with the maximum particle diameter of 71 μm. The laser sintering experiments of polymer-coated molybdenum powder were conducted by using the self-developed selective laser sintering machine (HLRP-350I). The method of microscopic analysis was used to investigate the dynamic laser sintering process of polymer-coated molybdenum powder. Based on the study, the laser sintering mechanisms of polymer-coated molybdenum powder were presented. It is found that the mechanism is viscous flow when the laser sintering temperature is between 100 ℃ and 160 ℃, which can be described by a two-sphere model; and the mechanism is melting /solidification when the temperature is above 160 ℃.
基金Prqject(03022) supported by the Key Science Research Program of Education Ministry of China Project(200410250) supported by Shanxi Youth Science Foundation
文摘The technology of length-alterable line-scanning laser sintering was introduced. Based on the research of laser heating property, powder thermal physics parameters and laser sintering process, a numerical model of the temperature field during length-alterable line-scanning and laser sintering of polymer-coated molybdenum powder was presented. Finite element method (FEM) was used to simulate the temperature field during laser sintering process. In order to verify the simulated results, a measuring system was developed to study the laser sintering temperature field. Infrared meter was introduced to measure the surface temperature of sintering powder; the temperature of its inside part was measured by thermocouple. The measured results were compared with the numerical simulation results; the conformity between them is good and the relative error is less than 5%.
基金Project(03022) supported by the Key Science Research Program of Education Ministry of China
文摘A type of polymer-coated Al2O3/ZrO2/TiC ceramic powder was prepared. The laser sintering mechanism of polymer-coated Al2O3/ZrO2/TiC powder was investigated by studying the dynamic laser sintering process. It is found that the mechanism is viscous flow when the sintering temperature is between 80 ℃ and 120 ℃, and it is melting/solidification when the temperature is above 120 ℃. The process parameters of selective laser sintering were optimized by using ortho-design method. The results show that the optimal parameters include laser power of 14 W, scanning velocity of 1 400 mm/s, preheating temperature of 50 ℃ and powder depth of 0.15 mm. A two-step post-treatment process is adopted to improve the mechanical properties of laser sintered part, which includes polymer debinding and high temperature sintering. After vacuum sintering for 2 h at 1 650 ℃, the bending strength and fracture toughness of Al2O3/ZrO2/TiC ceramic part reach 358 MPa and 6.9 MPa·m1/2, respectively.
基金the support from the Shanghai Science and Technology Committee Innovation Grant(Grant No.19ZR1404600)Fudan University-CIOMP Joint Fund(FC2020-006)。
文摘Polymers are widely used materials in aerospace,automotive,construction,medical devices and pharmaceuticals.Polymers are being promoted rapidly due to their ease of manufacturing and improved material properties.Research on polymer processing technology should be paid more attention to due to the increasing demand for polymer applications.Selective laser sintering(SLS)uses a laser to sinter powdered materials(typical polyamide),and it is one of the critical additive manufacturing(AM)techniques of polymer.It irradiates the laser beam on the defined areas by a computer-aided design three-dimensional(3D)model to bind the material together to create a designed 3D solid structure.SLS has many advantages,such as no support structures and excellent mechanical properties resembling injection moulded parts compared with other AM methods.However,the ability of SLS to process polymers is still affected by some defects,such as the porous structure and limited available types of SLS polymers.Therefore,this article reviews the current state-of-the-art SLS of polymers,including the fundamental principles in this technique,the SLS developments of typical polymers,and the essential process parameters in SLS.Furthermore,the applications of SLS are focused,and the conclusions and perspectives are discussed.
基金the National Key R&D Program of China(2019YFD1101200,2019YFD1101204)Natural Science Foundation of China(51772150)the Project Funded by the Priority Academic Program Development of Jiangsu Higher Education Institutions(PAPD)Jiangsu Provincial Key Research and Development Program(BE2018008-1).
文摘The graphene oxide powder(GOP)obtained from the spray drying process often exhibits poor redispersibility which is considered due to the partial reduction of GO sheets.The reduction of drying temperature can effectively increase the redispersibility of GOP,but result in a decreased drying efficiency.Herein,we found that the redispersibility of GOP is strongly affected by its microstructure,which is determined by the feed concentration.With the increase of feed concentration,the GO nanosheet assembly varies from the disordered stacking to relatively oriented assembly,making the morphology of the GOP transform from balllike(the most crumpled one)to flakelike(the least crumpled one),and the 0.8 mgml 1 is the threshold concentration for the morphology,structure,and redispersibility change.Once the feed concentration reaches 0.8 mg ml 1,the appearance of the nematic phase in droplet ensures the relatively oriented assembly of GO sheets to form the layered structure with a low crumpling degree,which greatly improves the polar parts surface tension of the solid GOP,making the GOP easier to form hydrogen bonding with water during the redispersion process,thus stabilizing dispersion.This work provides useful information for understanding the relationships between the morphology,microstructure,and final redispersibility of GOPs.
基金This work was supported by the National Science Fund for Distinguished Young Scholars of China (No.50125312) andSpecial Funds for Major State Basic Research Projects (No.G1999064800).
文摘Dynamic rheological characteristics of polypropylene (PP) filled with ultra-fine full-vulcanized powdered rubber (UFPR) composed of styrene-butadiene copolymer were studied through dynamic rheological measurements on an Advanced Rheometric Expansion System (ARES). A specific viscoelastic phenomenon, i.e. 'the second plateau', appeared at low frequencies, and exhibits a certain dependence on the amount of rubber particles and the dispersion state in the matrix. This phenomenon is attributed to the formation of aggregation structure of rubber particles. The analyses of Cole-Cole diagrams of the dynamic viscoelastic functions suggest that the heterogeneity of the composites is enhanced on increasing both particle content and temperature.
基金the National Natural Science Foundation of China(No.21666016)the National Key R&D Program of China(2018YFC1900200)and the Key Laboratory and the Analysis and Testing Foundation of Kunming University of Science and Technology(2017M20162207011,2019P20183107007).
文摘The high water content of sludge has always posed significant challenges for its treatment.Synthetic flocculants,which are widely used in sewage treatment plants,can cause secondary pollution during their production and use.Thus,natural polymer flocculants made of natural materials have received increased research attention recently.Corncore,an agricultural waste,was modified through alkalization with sodium hydroxide(NaOH)and etherification with cetyltrimethylammonium bromide(CTMAB)in this study.The L16(45)orthogonal array was used to study the modification conditions.The moisture content(MC)of treated sludge was reduced by approximately 37%with the addition of modified corncore powder(MCCP),which was synthesized under optimal conditions.In addition,changes in the functional groups of the material before and after modification were determined by FTIR.Thermogravimetric analysis indicated that MCCP was steady at room temperature,moreover,BET analysis showed that MCCP had greater surface area.The microstructures of material before and after modification were examined by scanning electron microscopy,revealing that MCCP had a flakeshaped structure and had an increased area of contact area with sludge particles.MCCP is a dehydrating agent that can enhance sludge dewaterability through charge neutralization and reagglomeration and provide superior economic benefits.
文摘Due to large volume and high hardness of thermal insulation materials mostly used in high temperature fields, a composite cooling powder and its thixotropic hydrogel for thermal protection are presented. The core of composite cooling material powder is super absorbent polymer, composing with metal salt, polysaccharide hydrosol and inorganic particles and other modifiers through a series of composite process, which can be easily stored for a long time. When needed, the powder can be mixed with water to obtain a kind of thixotropic hydrogel in a very short time. Experimental results show this thermal protection technology with thixotropic ability has excellent thermal protection performance, meanwhile flexible, adhesive and low cost, which exerts instantaneous cooling, efficient thermal protection and long-lasting flame-retardant protection.
文摘In this study, production and mechanical properties of polymer composite materials obtained by using Al2O3, SiO2, MgO and TiO2 hard ceramic fillers were studied. Epoxy resin was used as the matrix material, and four different ceramic powders were mechanically mixed into the resin at 3% and 5% as reinforcement. The mechanical properties of the polymer composite materials were then characterized. For this purpose, flexural modulus and flexural strength of composite materials were determined by using three point bending test and impact toughness of the materials were determined by Charpy impact test. In addition, the hardness values of the samples were determined by Shore D hardness test.
