Ethylene-vinyl acetate copolymer(EVA)as a kind of effective polymeric pour point depressant has been extensively used in the pipeline transportation of crude oil to inhibit wax deposition and improve the low temperatu...Ethylene-vinyl acetate copolymer(EVA)as a kind of effective polymeric pour point depressant has been extensively used in the pipeline transportation of crude oil to inhibit wax deposition and improve the low temperature fluidity of crude oil.In this work,molecular dynamics simulations were performed to investigate the effect of EVA on wax-hydrate coexistence system to evaluate the application potentiality of EVA to the flow assurance of deep-sea oilegasewater multiphase flow system.Our simulation results reveal that wax molecules gradually stretched and stacked from random coiling to a directional and ordered crystalline state during the process of wax solidification.The strong affinity of polar vinyl acetate side chains of EVA to neighboring water molecules made the EVA molecule prefer being in a curly state,which disrupted the ordered crystallization of surrounding wax molecules and delayed the solidification rate of wax cluster.In addition,it is found that EVA cocrystallized with wax molecules to form eutectic when the wax was fully solidified.The simulation results of hydrate nucleation and growth show that the EVA molecule displayed a two-sided effect on gas adsorption of wax crystals,which was the key factor that affected the nucleation and growth of hydrates in the methane-water system.The nonpolar hydrocarbon backbone of EVA increased the diffusion rate of methane and water,allowing more methane to diffuse to the surface of wax crystals,reducing the methane concentration in aqueous solutions and inhibiting the hydrate formation.On the other hand,the nonpolar vinyl acetate chains had a repulsive effect on methane,which reduced the adsorption area of methane on the eutectic surface and decreased the adsorption threshold value of the wax crystal.The excluded methane molecules would continue dissociating in the aqueous phase and participating in the nucleation and growth process of hydrates.Therefore,the probability of hydrate formation would be increased.It was worth noting that the inhibition performance of EVA on hydrate formation mainly played a significant role in the system with small wax crystal,while its hydrate promotion effect played a dominant role in the system with lager wax crystal.In summary,EVA could significantly inhibit both of the wax and hydrate deposition for the waxgas-water multiphase system with low wax content.When the wax content in the system was high,the role of EVA was mainly played in the alleviation of wax crystallization rather than the gas hydrates.The results of the present work can contribute to a better understanding of EVA on wax deposition and hydrate formation,and provide theoretical support of the potential industrial applications of EVA.展开更多
The goal is to develop a hybrid IPN network of polyvinyl acetate (PVAc) and ethylene-vinyl acetate (VAE). In this research work, the vinyl acetate (VAc)/ VAE hybrid emulsion and polyvinyl acetate emulsion (PVAc) were ...The goal is to develop a hybrid IPN network of polyvinyl acetate (PVAc) and ethylene-vinyl acetate (VAE). In this research work, the vinyl acetate (VAc)/ VAE hybrid emulsion and polyvinyl acetate emulsion (PVAc) were effectively synthesized. Emulsions with various characteristics have been developed by adjusting the weight ratios between the vinyl acetate monomer and the VAE component. The impacts on the mechanical, thermal, and physical properties of the films were investigated using tests for pencil hardness, tensile shear strength, pH, contact angle measurement, differential scanning calorimetry (DSC), and viscosity. When 5.0 weight percent VAE was added, the tensile shear strength in dry conditions decreased by 18.75% after a 24-hour bonding period, the heat resistance decreased by 26.29% (as per WATT 91) and the tensile shear strength decreased by approximately 36.52% in wet conditions (per EN 204). The pristine sample’s results were also confirmed by the contact angle test. The interpenetrating network (IPN) formation in hybrid PVAc emulsion as primary bonds does not directly attach to PVAc and VAE chains. The addition of VAE reduced the mechanical properties (at dry conditions) and heat resistance as per WATT 91. Contact angle analysis demonstrated that PVAc adhesives containing VAE had increased water resistance when compared to conventional PVA stabilised PVAc homopolymer-based adhesives. When compared to virgin PVAc Homo, the water resistance of the PVAc emulsion polymerization was enhanced by the addition of VAE.展开更多
Sepiolite （S9, B10, B20, B40） and boehmite have been added to an intumecent flame retardant （IFR） system to produce the halogen-free and fire-resistant ethylene-vinyl acetate copolymer （EVM） rubber. The rubber c...Sepiolite （S9, B10, B20, B40） and boehmite have been added to an intumecent flame retardant （IFR） system to produce the halogen-free and fire-resistant ethylene-vinyl acetate copolymer （EVM） rubber. The rubber contains ammonium polyphosphate （APP） as acid source, double pentaerythritol （D-PER） as carbon source and melamine （MN） as gas source. The effects of nano-filler sepiolite and boehmite on the fire-resistant property of EVM rubber based on IFR system were investigated. The test results show that the system with nano-filler of sepiolite B10 has the best fire-resistant property. The process of smoke emission and thermal decomposition, the element composition of char surface and the micro morphology of intumecent char layer of the EVM IFR system with nano-filler were also studied by NBS chamber, thermogravimetric （TG） analysis, X- ray photoelectron spectroscopy （XPS） and scanning electron microscope （SEM）.展开更多
The effect of the different geometrical dimensionality of two dimensional graphene nanosheets （2D GNSs） and one dimensional carbon nanotubes （1D CNTs） on the non-isothermal crystallization of an ethylene-vinyl ace...The effect of the different geometrical dimensionality of two dimensional graphene nanosheets （2D GNSs） and one dimensional carbon nanotubes （1D CNTs） on the non-isothermal crystallization of an ethylene-vinyl acetate （EVA） copolymer at high loading （5 wt%） was studied. Transmission electron microscopy indicated a homogeneous dispersion of GNSs and CNTs in EVA obtained by a solution dispersion process. Fourier-transform infrared spectroscopy and differential scanning calorimetry measurements showed that 1D CNTs and 2D GNSs acted as effective nucleating agents, with a noticeably increased onset crystallization temperature of EVA. A high weight fraction of nano-fillers slowed the overall crystallization rate of composites. At the same crystallization temperatute, the crystallization behavior of GNS/EVA composites was slowed compared to that of the CNT/EVA ones owing to larger nucleus barrier and activation energy of diffusion. Dynamic mechanical relaxation and rheology behavior of CNT/EVA and GNS/EVA composites demonstrated that the planar structure of the GNSs had an intensively negative effect on EVA chain mobility due to interactions between nano- fillers and polymer chains, as well as spatial restriction.展开更多
基金financial support received from National Natural Science Foundation of China(22178378 and 22127812)"Tianchi Talent"Recruitment Program,Xinjiang Tianshan Innovation Team(2022TSYCTD0002)Xinjiang Uygur Region"One Case,One Policy"Strategic Talent Introduction Project(XQZX20240054)are gratefully acknowledged.
文摘Ethylene-vinyl acetate copolymer(EVA)as a kind of effective polymeric pour point depressant has been extensively used in the pipeline transportation of crude oil to inhibit wax deposition and improve the low temperature fluidity of crude oil.In this work,molecular dynamics simulations were performed to investigate the effect of EVA on wax-hydrate coexistence system to evaluate the application potentiality of EVA to the flow assurance of deep-sea oilegasewater multiphase flow system.Our simulation results reveal that wax molecules gradually stretched and stacked from random coiling to a directional and ordered crystalline state during the process of wax solidification.The strong affinity of polar vinyl acetate side chains of EVA to neighboring water molecules made the EVA molecule prefer being in a curly state,which disrupted the ordered crystallization of surrounding wax molecules and delayed the solidification rate of wax cluster.In addition,it is found that EVA cocrystallized with wax molecules to form eutectic when the wax was fully solidified.The simulation results of hydrate nucleation and growth show that the EVA molecule displayed a two-sided effect on gas adsorption of wax crystals,which was the key factor that affected the nucleation and growth of hydrates in the methane-water system.The nonpolar hydrocarbon backbone of EVA increased the diffusion rate of methane and water,allowing more methane to diffuse to the surface of wax crystals,reducing the methane concentration in aqueous solutions and inhibiting the hydrate formation.On the other hand,the nonpolar vinyl acetate chains had a repulsive effect on methane,which reduced the adsorption area of methane on the eutectic surface and decreased the adsorption threshold value of the wax crystal.The excluded methane molecules would continue dissociating in the aqueous phase and participating in the nucleation and growth process of hydrates.Therefore,the probability of hydrate formation would be increased.It was worth noting that the inhibition performance of EVA on hydrate formation mainly played a significant role in the system with small wax crystal,while its hydrate promotion effect played a dominant role in the system with lager wax crystal.In summary,EVA could significantly inhibit both of the wax and hydrate deposition for the waxgas-water multiphase system with low wax content.When the wax content in the system was high,the role of EVA was mainly played in the alleviation of wax crystallization rather than the gas hydrates.The results of the present work can contribute to a better understanding of EVA on wax deposition and hydrate formation,and provide theoretical support of the potential industrial applications of EVA.
文摘The goal is to develop a hybrid IPN network of polyvinyl acetate (PVAc) and ethylene-vinyl acetate (VAE). In this research work, the vinyl acetate (VAc)/ VAE hybrid emulsion and polyvinyl acetate emulsion (PVAc) were effectively synthesized. Emulsions with various characteristics have been developed by adjusting the weight ratios between the vinyl acetate monomer and the VAE component. The impacts on the mechanical, thermal, and physical properties of the films were investigated using tests for pencil hardness, tensile shear strength, pH, contact angle measurement, differential scanning calorimetry (DSC), and viscosity. When 5.0 weight percent VAE was added, the tensile shear strength in dry conditions decreased by 18.75% after a 24-hour bonding period, the heat resistance decreased by 26.29% (as per WATT 91) and the tensile shear strength decreased by approximately 36.52% in wet conditions (per EN 204). The pristine sample’s results were also confirmed by the contact angle test. The interpenetrating network (IPN) formation in hybrid PVAc emulsion as primary bonds does not directly attach to PVAc and VAE chains. The addition of VAE reduced the mechanical properties (at dry conditions) and heat resistance as per WATT 91. Contact angle analysis demonstrated that PVAc adhesives containing VAE had increased water resistance when compared to conventional PVA stabilised PVAc homopolymer-based adhesives. When compared to virgin PVAc Homo, the water resistance of the PVAc emulsion polymerization was enhanced by the addition of VAE.
基金Sponsored by Project in National Key Technology R&D Program(2006BAE03B05-2)
文摘Sepiolite （S9, B10, B20, B40） and boehmite have been added to an intumecent flame retardant （IFR） system to produce the halogen-free and fire-resistant ethylene-vinyl acetate copolymer （EVM） rubber. The rubber contains ammonium polyphosphate （APP） as acid source, double pentaerythritol （D-PER） as carbon source and melamine （MN） as gas source. The effects of nano-filler sepiolite and boehmite on the fire-resistant property of EVM rubber based on IFR system were investigated. The test results show that the system with nano-filler of sepiolite B10 has the best fire-resistant property. The process of smoke emission and thermal decomposition, the element composition of char surface and the micro morphology of intumecent char layer of the EVM IFR system with nano-filler were also studied by NBS chamber, thermogravimetric （TG） analysis, X- ray photoelectron spectroscopy （XPS） and scanning electron microscope （SEM）.
基金supported by the National Science Fund for Distinguished Young Scholars(No.50925311)the National Natural Science Foundation of China(Nos.20976112,51033004)
文摘The effect of the different geometrical dimensionality of two dimensional graphene nanosheets （2D GNSs） and one dimensional carbon nanotubes （1D CNTs） on the non-isothermal crystallization of an ethylene-vinyl acetate （EVA） copolymer at high loading （5 wt%） was studied. Transmission electron microscopy indicated a homogeneous dispersion of GNSs and CNTs in EVA obtained by a solution dispersion process. Fourier-transform infrared spectroscopy and differential scanning calorimetry measurements showed that 1D CNTs and 2D GNSs acted as effective nucleating agents, with a noticeably increased onset crystallization temperature of EVA. A high weight fraction of nano-fillers slowed the overall crystallization rate of composites. At the same crystallization temperatute, the crystallization behavior of GNS/EVA composites was slowed compared to that of the CNT/EVA ones owing to larger nucleus barrier and activation energy of diffusion. Dynamic mechanical relaxation and rheology behavior of CNT/EVA and GNS/EVA composites demonstrated that the planar structure of the GNSs had an intensively negative effect on EVA chain mobility due to interactions between nano- fillers and polymer chains, as well as spatial restriction.
