聚丙烯酸接枝型聚偏氟乙烯多孔膜的pH值感应开关特性

A series of pH-responsive gating membranes, with a wide range of grafting yields, were prepared by grafting poly (acrylic acid) (PAAC) onto porous polyvinylidene fluoride (PVDF) membrane substrates with a plasma-induced pore-filling polymerization method. The effect of grafting yields on gating characteristics of pH-responsive gating membranes was investigated systematically. The results showed that the grafting yield heavily affected water flux, pH-responsiveness coefficient and pH-responsive gating factor of membrane pore size. When the grafting yield was smaller than 1.01%, both flux responsiveness coefficient and pH-responsive gating factor of pore size increased with increasing grafting yield. When the grafting yield was in the range from 1.01% to 6.44%, both flux responsiveness coefficient and pH-responsive gating factor of pore size decreased with increasing grafting yield; however, when the grafting yield was higher than 6.44%, both flux responsiveness coefficient and pH-responsive gating factor of membrane pore size approached to 1, i.e. , little gating characteristics existed. In order to obtain a satisfactory pH-responsive gating property of the membrane, the grafting yield must be kept in a proper range.     

pH and temperature responsive porous membranes via an in situ bulk copolymerization approach

In the present study, an in situ approach to pH and temperature responsive membranes is developed. The membrane matrix is formed through bulk polymerization and crosslinking of liquid monomer 2-hydroxyethyl methacrylate (HEMA) while the membrane pores are formed by the templating of inorganic particles. The functional monomers methacrylic acid (MAA) and N-isopropylacrylamide (NIPAAm) are incorporated into membrane casting solution in order to confer membranes with pH and temperature responsive properties. The poly(HEMA/MAA) membranes exhibit a reversible pH-dependent water flux, while the poly(HEMA/NIPAAm) membranes exhibit a reversible temperature-dependent water flux. The flux of the poly(HEMA/MAA) membrane increased by 70% when pH was decreased from 10.0 to 2.0, while the flux poly(HEMA/NIPAAm) membrane increased by 150% when temperature was increased from 20 to 45 °C. The protein adsorption and antifouling performance of the poly(HEMA/MAA) and poly(HEMA/NIPAAm) membranes also exhibit pH and temperature responsive properties.     

Improving the hydrophilicity of polyethersulfone membrane by the combination of grafting technology and reverse thermally induced phase separation method

In this work, surface grafting modification technology was combined with reverse thermally induced phase separation (RTIPS) method in order to improve the structure and permanent hydrophilicity of polyethersulfone (PES) membranes. Acrylic solution with different concentrations was grafted on the surface of PES membranes while grafting temperature and grafting time were also varied. The modified PES membranes were characterized in all aspects. Attenuated total reflectance Fourier transform-infrared confirmed successful modification of the PES membrane by grafting acrylic acid. Scanning electron microscopy revealed that homogeneous porous top surface as well as spongy-like cross-section structure appeared in the membrane by RTIPS procedure. Moreover, porosity was affected by changes of acrylic acid concentration, grafting temperature, and grafting time. Atomic force microscopy showed that grafting acrylic acid gave a reduction in roughness of PES membrane. Combined with the decreased values of contact angle, the hydrophilicity and antifouling performance of the PES membrane were improved. The pure water flux and BSA rejection rate of the grafted PES membranes were remarkably improved for pure PES membrane and attained a maximum, which was 1,646.24 L/(m²h) and 94.5%, respectively. The long-term test demonstrated that grafting membranes exhibited outstanding elevated water flux recovery ratio (>85%).     

Effect of acid and pH value on the photografting initiated by aliphatic ketones in aqueous solutions

The photografting of methacrylic acid (MAA) onto high‐density polyethylene (HDPE) initiated by aliphatic ketones (acetone, butanone, and cyclohexanone) in aqueous solutions with different pH values adjusted by adding different amount of mineral acids was reported. Acids significantly enhanced the photografting yield, and the extent of grafting generally increased with decreasing pH value. The effect of pH value on the grafting reactions varied with the acid used. The grafting of MAA onto HDPE surface was confirmed with FTIR and SEM characterizations. The water absorbency of the grafted p‐MAA varied with the extent of grafting. When the extent of grafting was less than 2000–3000 μg/cm², grafted p‐MAA absorbed about 25–30% water, whereas at higher extent of grafting, it absorbed about 50% water. The mechanism of the acid enhancement of the photografting of MAA initiated by aliphatic ketones in aqueous solutions is believed to be attributed to the change of the solubility of monomer in the solution and the conformation of grafted chains, both are favorable for accelerating grafting reactions. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Grafting of vinyl monomers onto wood fibers initiated by peroxidation

Summary The oxidation of chemithermomechanical (aspen) pulp with ruthenium tetroxide followed by peroxidation with hydrogen peroxide was performed to study the graft copolymerization of methacrylic acid, epoxypropyl acrylate and epoxypropyl methacrylate. For epoxy monomers, lower pH (i.e. < 5) is more favorable due to the participation of the epoxy group in the grafting reaction in acidic medium. Moreover, the grafting of epoxy monomers appeared more efficient than methacrylic acid.     

Studies on grafting of methacrylic acid on to poly(vinyl chloride) films

The characterization of poly(vinyl chloride-g-methacrylic acid) (PVC-g-MAA) films, prepared by the simultaneous-irradiation technique, was undertaken through swelling measurements, attenuated total reflection infrared spectroscopy (ATRIR), scanning electron microscopy (SEM), electron spectroscopy for chemical analysis (ESCA) and thermogravimetric analysis (TGA). The per cent swelling of grafted PVC in various media increased with the increase in the graft level. A higher per cent swelling was observed in 0-5m NaOH aqueous solution relative to that in distilled water. It is concluded from the ATRIR and ESCA studies that the concentration ratio of oxygen to chlorine atoms on the surface of grafted PVC increased compared with unmodified PVC, indicating grafting of methacrylic acid on to the surface. It was also found that the thermal properties of PVC improved after grafting with methacrylic acid.     

Fouling control in a submerged membrane‐bioreactor by the membrane surface modification

To improve the antifouling characteristics, polypropylene microporous membranes (PPHFMMs) were surface‐modified by the sequential photoinduced graft polymerization of acrylic acid and acrylamide. The grafting density and the grafting chain length, which played important roles in the antifouling characteristics, were controlled in the first and the second step, respectively. The ATR/FTIR results clearly indicated the successful modification on the membrane surface. The static water contact angle of the modified membrane reduced obviously with the increase of the grafting chain length. The contact angle of the acrylic acid modified membranes was lower than that of the acrylamide modified membrane with similar grafting chain length. The grafting chain length increased with the increase of UV irradiation time and monomer concentration. The grafting chain length of poly(acrylic acid) (PAAc) was lower than that of the polyacrylamide (PAAm) under the same polymerization conditions. Pure water flux for the modified membranes increased with the increase of grafting chain length, and had maximums. The antifouling characteristics of the modified membranes in a submerged membrane‐bioreactor (SMBR) were evaluated. The modified membranes showed better filtration performances in the SMBR than the unmodified membrane, and the acrylic acid grafted membrane presented better antifouling characteristics than acrylamide modified membranes. The results demonstrated that the surface carboxyl‐containing membranes were better than the surface amido‐containing membranes. The results of Pearson correlations demonstrated that the PAAc modified membranes with longer grafting chain length had higher flux recoveries, while the PAAm modified membranes with longer grafting chain length had lower flux recoveries. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Surface modification of polypropylene microporous membrane by grafting acrylic acid using physisorbed initiators method

Surface modification of microporous polypropylene (PP) membrane was performed by graft polymerization of acrylic acid using physisorbed initiators method. The factors effecting on the grafting degree such as monomer concentration, reaction temperature and initiator density were determined. The morphological and microstructure changes of the membrane were characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM), and Fourier transform infrared spectroscopy (FTIR). The pure water contact angle, protein adsorbed amount, water flux, and antifouling property of the grafted membrane were investigated. The results indicated that the pore size and porosity of the grafted membrane were reduced and the static contact angle of pure water on the grafted membrane decreased from 108° to 40° with the increase of grafting degree. The amount of protein adsorbed on the grafted membrane decreased about 30% compared to the virgin polypropylene membrane when the grafting degree was 18.71%. Though the water flux reduced, the flux recovery of the grafted membrane increased 82.66% with the grafting degree 16.0%. The hydrophilic and antifouling property of the grafted membrane also were improved. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Pentavalent vanadium ion–cellulose thiocarbonate redox-system induced grafting of methyl methacrylate and other vinyl monomers onto cotton fabric

Cellulose thiocarbonate was prepared by reacting cotton cellulose fabric with carbon disulphide in the presence of sodium hydroxide. The treated fabric formed, with pentavalent vanadium ion, an effective redox system capable of initiating grafting of methyl methacrylate (MMA) and other monomers no+o the cotton fabric. The dependence of grafting on vanadium concentration, pH of the polymerization medium, temperature and duration of grafting, nature and concentration of monomer, and solvent/water ratio was studied. The results indicated that increasing the pentavalent vanadium (V^v) concentration up to 60 mmol/L was accompanied by enhancement in the rate of grafting; the latter was not affected by further increase in V^v concentration. Maximum grafting yield was achieved at pH 2; grafting fell greatly at higher pH. The rate of grafting followed the order: 70° > 60° > 50°C. The graft yield increased significantly by increasing the MMA concentration from 0.5 to 5%. Of the solvents studied, n-propanol and isopropanol enhanced the grafting rate provided that a solvent/water ratio of 5 : 95 was used; a higher solvent ratio decreased the magnitude of grafting. Other solvents, namely, methanol, ethanol, n-butanol, and acetone, in any proportion, decreased the rate of grafting. With the monomer used, the graft yield followed the order: methyl methacrylate > methyl acrylate > methacrylic acid > ethyl methacrylate > acrylic acid. Also reported was a tentative mechanism for vinyl-graft copolymerization onto cotton fabric using cellulose thiocarbonate-V^v. © 1993 John Wiley & Sons, Inc.     

Preparation and characterization of layered membranes constructed by sequential redox‐initiated grafting onto polyacrylonitrile ultrafiltration membranes

Layered membranes were prepared by sequential grafting—by means of redox initiators—of water‐soluble monomers, with oppositely charged ionic groups, onto ultrafiltration (UF) polyacrylonitrile (PAN) membranes at room temperature. Grafting of a single layer of 2‐hydroxyethylmethacrylate (HEMA) onto a PAN membrane gave a highly grafted membrane with a relatively high water flux. Bilayered membranes with various properties containing poly‐2‐(dimethylamino)ethyl methacrylate (p‐2DMAEMA) as the bottom layer and polymethacrylic acid or polystyrenesulfonic acid (p‐SSA) as the upper layer were prepared and compared—by means of infrared spectroscopy and electron microscopy—with single‐layered membranes of grafted polyhydroxyethylmethacrylate. Layered membranes exhibited a significant decline in water flux in comparison with the initial UF membranes. The flux could, however, be manipulated by controlling the concentration of monomers, the time of grafting, and the number of layers. When four layers of p‐2DMAEMA and p‐SSA were sequentially grafted onto a PAN membrane, pure water fluxes were stable over a wide range of pH values and did not change over long storage times. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 509–520, 2005     

Surface modification of polyamide TFC membranes via redox‐initiated graft polymerization of acrylic acid

In this work, the redox‐initiated graft polymerization of acrylic acid (AA) onto the surface of polyamide thin film composite membranes has been carried out to enhance membrane separation and antifouling properties. The membrane surface characteristics were determined through the attenuated total reflection Fourier transform infrared spectra, scanning electron microscopy, atomic force microscopy, and water contact angles. The membrane separation performance was evaluated through membrane flux and rejection of some organic compounds such as reactive red dye (RR261), humic acid, and bovine serum albumin in aqueous feed solutions. The experimental results indicated that the membrane surfaces became more hydrophilic and smoother after grafting of AA. The modified membranes have a better separation performance with a significant enhancement of flux at a great retention. The fouling resistance of the modified membranes is also clearly improved with the higher maintained flux ratio and the lower irreversible fouling factor compared to the unmodified one. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45110.     

Effects of synthesis conditions on radiation-induced graft copolymerization of methacrylic acid on to poly(vinyl chloride) films

Poly(vinyl chloride) (PVC) films were grafted with methacrylic acid (MAA) using a simultaneous-irradiation technique. The effect of solvent ratio (methanol-water) on grafting was studied and maximum grafting was found for an equivolume mixture of methanol and water. The graft level increased with increase of the plasticizer (dioctylphthalate) content in PVC. Grafting was found to be higher at low dose rate and increased linearly up to 0.25 Mrad for all dose rates and then levelled off. Grafting also increased continuously with increasing monomer concentrations up to 5.4mol/litre, but a linear increase in grafting was observed only up to 2.5 mol/litre. The dependences of rate of grafting on dose rate and monomer concentration were found to be 0.62 and 1.20 respectively.     

Aliphatic ketones/water/alcohol as a new photoinitiating system for the photografting of methacrylic acid onto high-density polyethylene

The photografting of methacrylic acid (MAA) onto high-density polyethylene (HDPE) initiated by aliphatic ketones, butanone, pentanone, heptanone, etc. has been reported. When these ketones were used alone or just with ethanol, grafting did not occur. However, grafting took place when a proper butanone/water/ethanol mixed solvent was used. When the volume ratio of butanone was fixed, the grafting of MAA onto HDPE became easier with an increase in the volume ratio of water. The grafting of MAA onto HDPE became easier and faster with a decrease in the volume ratio of butanone. The grafting rate increased with the increase of monomer concentration. The nature of the alcohol also affected the self-initiation by aliphatic ketone; ethanol was found to be better than methanol. Possibly, hydrogen bond formed between aliphatic ketone and water increases the energy and lifetime of the excited state of the ketone, permitting it to act as a grafting and polymerisation initiator. FTIR characterization of the grafted samples proves the successful grafting of MAA onto HDPE. The water absorbency of the grafted samples increased almost linearly with the extent of grafting both in air and in water. The PE films grafted in the butanone/water/ethanol solvent adsorbed approximately 30-40 mass% water per p-MAA.     

单组分自乳化水性环氧树脂的合成及其涂膜性能研究

用有机硅、甲基丙烯酸及其酯类单体接枝改性环氧树脂,合成了具有自乳化性能的水性环氧树脂乳液。用激光粒度分析仪测定乳液的粒径及其分布,用傅里叶红外、热重分析仪对聚合产物作了结构表征和热分析。考察了温度、引发剂用量对接枝率及接枝率对乳液成膜性能的影响;甲基丙烯酸、有机硅及单体总量对乳液稳定性、成膜物耐水性和耐盐水性的影响。结果表明:当配方选用引发剂、有机硅用量分别为单体总质量的5.5%、2.5%,m(单体总量)∶m(环氧树脂)=1∶2,丙烯酸及其酯类单体的玻璃化温度Tg为30℃,体系酸值为35 mgKOH/g,接枝温度为110℃时,制得的水性环氧树脂乳液具有良好的稳定性、耐水性及耐盐水性。     

NMR study of adsorbed water on acrylic acid-grafted and methacrylic acid-grafted cellulose

The water-adsorbing properties of cellulose samples which had been graft copolymerized with hydrophilic vinyl monomers using ceric salt as an initiator were investigated by means of the width of the high-resolution NMR absorption spectrum, water retention, and moisture regain of the samples. In the change of the width at half-value of the spectrum with per cent grafting, a maximum value followed by a minimum value was observed on samples both grafted with acrylic acid and methacrylic acid. Thus, the effect of grafting on the water-adsorbing properties appeared not to be simple. Though no special change in the water retention by grafting was observed, the per cent grafting dependence on the moisture regain in high relative humidity showed a peculiar and definite relation. The per cent grafting giving maximum moisture regain was about 8% and 18% for acrylic acid and methacrylic acid, respectively, and this agreed very well with the minimum widths at half-value. The change in the glass transition temperature of the sample—water system caused by grafting is also described.     

Influence of polydopamine deposition conditions on pure water flux and foulant adhesion resistance of reverse osmosis, ultrafiltration, and microfiltration membranes

The influence of polydopamine (PDOPA) deposition and poly(ethylene glycol) (PEG) grafting on pure water flux and bovine serum albumin (BSA) adhesion of two polysulfone ultrafiltration (UF) membranes, a poly(vinylidene fluoride) microfiltration (MF) membrane, and a polyamide reverse osmosis (RO) membrane is reported. When modified with PDOPA, all membranes exhibited a systematic reduction in protein adhesion. For example, 90 min of PDOPA deposition led to at least 96% reduction in BSA adhesion to these membranes at neutral pH. BSA adhesion was further reduced by subsequent PEG grafting to PDOPA (PDOPA-g-PEG). The membranes’ pure water flux values (i.e., with no foulants present) were influenced to different extents by PDOPA and PDOPA-g-PEG modifications. In the porous membranes (i.e., the UF and MF membranes), the pure water flux reduction due to these modifications correlated with membrane pore size, with the smallest flux reductions observed in the MF membrane (e.g., <1% flux reduction for all PDOPA modification times considered), which have the largest pores, and the largest flux reductions occurring in UF membranes (e.g., a 40% flux reduction after 90 min of PDOPA deposition), which have pore sizes on the order of the PDOPA deposition thickness. The RO membranes, which are essentially non-porous, exhibited a flux reduction of 25% after 90 min of PDOPA deposition.     

Synthesis, characterization and swelling behaviour of poly(methacrylic acid) brushes synthesized using atom transfer radical polymerization

Poly(methacrylic acid) brushes have been prepared utilizing the “grafting from” technique and a living radical synthesis route using a two stage process. Firstly a poly(1-ethoxyethyl methacrylate) brush was synthesized by atom transfer radical polymerization and then thermally decomposed to poly(methacrylic acid). The swelling behaviour of the weak polyacid brush was investigated as a function of pH and salt concentration in aqueous solutions using atomic force microscopy. Force pulling measurements were used to establish the molecular weight and the grafted chain density. The swelling transition was found to be at pH 9; which is significantly different to the pK_a (5.5) of untethered poly(methacrylic acid). We attribute this large shift in pK_a to the high grafting density of these brushes. This can be explained as a result of the Coulombic repulsion of neighbouring charges. High salt concentrations (0.3 M Na⁺) also collapse the brush layer. Conversely low salt concentrations cause an increase in the thickness of the brush, a behaviour expected for osmotic brushes.     

Characterization of the activity of β-galactosidase immobilized on Teflon membranes preactivated with different monomers by γ-irradiation

The activity of β-galactosidase, immobilized by grafting technique on Teflon membranes preactivated with four different monomers, has been characterized from the biochemical and biophysical points of view. The monomers used were acrylic acid or acrylamide, or methacrylic acid and 2-hydroxyethyl methacrylate. When 2-hydroxyethyl methacrylate was used in the second grafting, the first three monomers have been used in the first modification step. The behavior of the free and immobilized enzyme has been analyzed as a function of temperature and pH. For each catalytic membrane, we have found general equations relating the absolute enzyme activity to pH and temperature. From these expressions, the experimental conditions giving the best yield of each catalytic membrane have been calculated. The kinetic parameters for the four membranes have also been determined. The advantages of using these membranes in nonisothermal bioreactors are also indicated. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68: 613–623, 1998     

酶-膜法提取纯化荔枝核中氨基酸

采用酶-膜法提取纯化荔枝核中氨基酸。使用X JT9503中性蛋白酶酶解辅助提取荔枝核中氨基酸,实验确定酶解的优化条件为:酶用量600 U/g、酶解温度50℃、pH=6.5、酶解时间90 m in,氨基酸得率为1.16%。采用水提法和酸解提取法氨基酸得率分别仅为0.41%和0.92%。实验表明,酶解提取法要优于水提法和酸解提取法。使用截留相对分子质量50 000的陶瓷超滤膜纯化酶解提取液,实验表明,膜通量随操作压力和料液温度升高而增加。在操作压力0.22 MPa,料液温度30℃的条件下,膜的平均通量为75.63 L/(m2.h),氨基酸的截留率仅为10.3%,蛋白质的截留率为98.1%,多糖的截留率为85.2%,氨基酸能够与蛋白质、多糖等大分子实现有效分离。     

pH Sensitive polypropylene porous membrane prepared by grafting acrylic acid in supercritical carbon dioxide

pH sensitive membrane was prepared by grafting acrylic acid (AA) on the porous polypropylene (PP) membrane using supercritical (SC) CO₂ as a solvent. The monomer (AA) and the initiator (benzyl peroxide, BPO) were impregnated into the PP substrate with the aid of SC CO₂, and were grafted onto the microporous PP substrate. The grafted membranes were characterized by Fourier transform infrared spectroscopy (FTIR), field emission scanning electron microscopy (FE-SEM), and the water permeability of the virgin and grafted membranes were determined at different pH values. It was demonstrated that the grafting degree (Dg) could be easily controlled by varying operating conditions, such as the monomer concentration, pressure, and temperature during the soaking process. The water permeation of the virgin membrane is nearly independent of pH. However, the water permeation of grafted membranes decreases dramatically with pH as the pH varies from 3 to 6 because the conformation of the PAA changes significantly with the pH of the contacting solution.