首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 31 毫秒
1.
Functionalized poly(ethylene terephthalate) (PET) fibers were synthesized by grafting of maleic acidmethacrylamide (MAA-MAAm) monomer mixtures by using benzoylperoxide as initiator onto PET fibers in an aqueous medium. The functionalized fibers were characterized by Fourier transform infrared spectroscopy, thermogravimetric analysis, differential scanning calorimeter, and scanning electron microscopy. The effects of reaction conditions, such as monomer mixture ratio, monomer mixture and initiator concentration, polymerization time, and temperature on grafting were investigated. In alone grafting of MAA, grafting was not observed. However, the use of MAAm as a comonomer increased the amount of MAA inserted to the PET fiber up to 40.7 %. An increase in the temperature between 75 and 95 °C and also, increase in monomer mixture concentration between 0.50 and 1.00 M increased the grafting rate and saturation graft yield. The graft yield has shown an increase up to an initiator concentration of 1.0×10−2 M and decreased afterwards. The grafting increased the dyeability with disperse, acidic and basic dyes, and water absorption capacity but decreased the thermal stability of the fibers.  相似文献   

2.
Graft copolymerization of acrylamide onto commercial acrylic fibers was carried out using benzoyl peroxide as a free-radical initiator in aqueous medium within the 75–95 °C temperature range. In this study, the effects of initiator and monomer concentration, the amount of fiber, polymerization time, and temperature on the graft yield were investigated. The optimum concentration for initiator was found to be 2.0×10−3 mol/l and the optimum temperature of 85 °C. The activation energy of the reaction was calculated to as 35.81 kJ/mol at the temperature interval of 75–95 °C. The structures and morphologies characterization of grafted fibers was investigated by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and thermogravimetric analysis (TGA). The thermogravimetric analysis data showed that the thermal stability of the acrylic fibers increased with graft yield. The scanning electron photographs showed that the homogeneous appearance of the fiber surface changed and a shell-like heterogeneous structure occurred at the surface with an increasing degree of grafting. The moisture content, water absorption, dyeability, and antimicrobial activity of grafted acrylic fibers were also reported. The results showed that grafting of polyAAm improved the moisture contain, water absorption, dyeability, and antimicrobial activity of fiber.  相似文献   

3.
Three grazing experiments were carried out in late spring (early lactation), summer (mid‐lactation) and autumn (late lactation) to compare the effects of perennial ryegrass cultivar or grass species, sown in binary or multispecies mixtures, on milk yield and nitrogen excretion of dairy cows. Replicated groups of multiparous Holstein Friesian × Jersey cows were offered either a control or high‐sugar perennial ryegrass (Lolium perenne) or tall fescue (Festuca arundinacea) base grass in a binary mixture with white clover (Trifolium repens) or in a multispecies mixture with additional legumes, bromegrass (Bromus willdenowii) and forbs. During each 9‐day experiment, botanical composition, milk production and faecal and urine composition were measured. Milk solid (MS) yield for the control ryegrass, high‐sugar ryegrass and tall fescue grass types averaged, respectively, 1.53, 1.64 and 1.70 kg MS cow?1 day?1 for a binary mixture sward, compared with 1.65, 1.54 and 1.53 kg MS cow?1 day?1 for a multispecies sward. Legume content influenced milk production more than the number of species present in a mixture. There was lower urine N concentration from a multispecies sward compared with a binary mixture. Urine N concentration of cows grazing the control ryegrass, high‐sugar ryegrass and tall fescue grass types averaged, respectively, 4.6, 5.3 and 6.8 g N L?1 for a binary mixture, compared with 4.1, 3.9 and 3.9 g N L?1 for a multispecies mixture. Feeding dairy cows on multispecies swards containing forbs presents an opportunity to reduce N losses without compromising milk yield.  相似文献   

4.
The inherent properties of rayon fibre have been changed with additional properties through graft copolymerization of acrylamide, AAm, by chemical method using ceric ammonium nitrate/nitric acid, (CAN/HNO3), as a redox initiator and γ-radiation induced mutual method. Reaction conditions such as monomer and initiator concentration, liquor ratio, temperature and time of reaction, amount of radiation dose have been optimized with respect to percentage of grafting. Maximum percentage of grafting (Pg), (40 %) using CAN/HNO3 was obtained at [CAN]=31.92×10?3 moles/l, [HNO3]=79.36×10?2 moles/l, [AAm]=14.07×102 moles/l in 20 ml of H2O at 45 °C within 120 min while in case of radiation induced method, maximum Pg (30 %) was obtained at higher monomer concentration (28.14×10?2 moles/l) and time (180 min) in 10 ml of H2O at room temperature with total dose exposure of 11.178 kGy. The graft copolymers were characterized by FTIR, thermogravimetric and scanning electron micrographic analysis. Swelling behaviour in water, methanol, ethanol, acetone and DMF and dyeing and flame retarding properties of rayon fibre and grafted rayon fibre were investigated. Percent dye uptake (71.8 %) was found to be higher than that observed for the pristine fibre (57.4 %) and the grafted fibre after post phosphorylation reaction showed excellent flame retarding properties.  相似文献   

5.
Silk fibrillation, one major weakness of silk fibers, can lead to undesirable fabric appearance. In this research, an effective method for reducing the fibrillation of silk fibers through the graft copolymerization with methyl methacrylate (MMA) has been developed. The major copolymerization factors such as the initiator concentration, MMA monomer concentration, reaction time and temperature were investigated. An AATCC Crockmeter was used to rub the fabric to simulate the abrasion in production to generate the fibrillation. The microscope observation and the evaluation of fibrillation index (FI) were applied to assess the degree of fibrillation of silk fibers. The optimum graft copolymerization factors were obtained. Instrumental analyses, such as FTIR, TG and SEM, proved that the silk fabric had been successfully grafted with MMA monomers. The fibrillation of the grafted silk fibers was considerably reduced since the coated PMMA can protect the silk fiber. In addition, the physical properties such as the crease recovery, breaking strength, and the breaking length of the grafted silk fabrics were also improved.  相似文献   

6.
N,N-diallyl-N,N-dimethylammonium chloride (DADMAC) and vinyl ether of monoethanolamine copolymer (VEMEA) was synthesized by radical polymerization in aqueous media using ammonium persulfate as initiator. Copolymers synthesis was carried out by varying monomer composition at low conversion level. The viscosity of high molecular weight products was measured in aqueous 1 M NaCl solution and it was increased with increasing DADMAC amounts in the copolymer due to increasing positive charge. The structure of the product was identified by FTIR, 1H, 13C-NMR spectroscopies and conductometric titration methods. We calculated monomer reactivity ratios with help of Finemann-Ross, Kelen-Tudos, and inverted Finemann-Ross methods. It was found that DADMAC is more reactive than VEMEA, therefore the amount of DADMAC in the copolymers always dominated regardless of the initial monomer ratio in solution and it was shown that the monomers are connected randomly in the polymer chain. The effect of various parameters such as monomer [M], initiator [I] concentrations, ratio of comonomers, etc. on polymerization was investigated systematically. So, the polymerization rate (Rp) equation was found to be Rp=k[M]2.6[I]0.6 where molar fractions of DADMAC and VEMEA was 90:10 and the temperature was 65 °C. Degree of polymerization was examined by using various monomers and initiator concentrations via the dilatometeric method. It was found that the polymerization rate increased directly with total monomer concentration and initiator content.  相似文献   

7.
Radical melt graft copolymerizations of poly (lactic acid) (PLA) with amide monomers using benzoyl peroxide as an initiator during reactive extrusion is studied. The effects of two monomer types at various concentrations, reaction temperatures and initiator concentrations on the grafting yield are investigated. The results showed that percentage of grafting was significantly enhanced by increasing benzoyl peroxide concentrations up to 12 mpm and then decreased by an increase in the initiator concentration. Furthermore, increasing each monomer concentration up to 450 mpm, improved the grafting yield significantly. Further increase brings about a marked fall in the grafting yield. Fourier Transform Infrared Spectroscopy (FTIR), back titration and nitrogen analyses confirmed that monomers of acrylamide and methacrylamide were successfully grafted onto PLA. The Gel Permeation Chromatography (GPC) data showed that the molecular weight of the grafted PLA samples under optimum conditions does not show any dramatic drop of PLA molecular weight by thermal degradation or hydrolysis of polyester chains, while the polydispersity index is poorly affected by the chemical modification of PLA. Also, the monomer structures affected the grafting yield as well as polymer chain combination. In addition under the same conditions, the grafting yield of acrylamide was more than that of methacrylamide. Thermal properties, molecular weight, density, moisture regain and tensile properties of the samples were also measured.  相似文献   

8.
Poly(n-butyl methacrylate)/poly(methyl methacrylate) polymer networks were synthesized by two-step emulsion polymerization with sodium dodecylsulfonate and polyoxyethylene nonylphenolether as the emulsifier, distilled water as the continuous medium, and potassium persulfate as the initiator. The kinetics of two-step emulsion polymerization was studied. Effects of emulsifier concentration, initiator concentration, and polymerization temperature on monomer conversion and polymerization rate were investigated in detail. Experimental data indicate that both the steady state polymerization rate and monomer conversion increase with the augment of emulsifier concentration, initiator concentration, or reaction temperature.  相似文献   

9.
Poly(trimethylene terephthalate-co-trimethylene 2,6-naphthalate)s (P(TT-co-TN)s) with various copolymer composition were synthesized, and their chain structure, thermal property and crystalline structure were investigated by using1H-NMR spectroscopy, differential scanning calorimetry (DSC) and wide-angle X-ray diffraction (WAXD), respectively. It was found from sequence analysis that all the P(TT-co-TN) copolymers synthesized have a statistical random distribution of TT and TN units. It was also observed from DSC thermograms that the glass transition temperature increases linearly with increasing the TN comonomer content, whereas the melting temperature of copolymer decreases with increasing the corresponding comonomer content in respective PTT- and PTN-based copolymer, showing pseudo-eutectic melting behavior. All the samples melt-crystallized isothermally except for P(TT-co-66 mol % TN) exhibit multiple melting endotherms and clear X-ray diffraction patterns. The multiple melting behavior originates from the dual lamellar population and/or the melting-recrystallization-remelting. The X-ray diffraction patterns are largely divided into two classes depending on the copolymer composition, i.e., PTT and PTNβ-form diffraction patterns, without exhibiting cocrystallization.  相似文献   

10.
The thermal behavior, morphology, ester-interchange reaction of Poly(trimethylene terephthalate) (PTT)/Poly(ethylene terephthalate) (PET) melt blends were investigated over the whole composition range(xPTT/(1-x)PET) using a twinscrew Brabender. The melt blends were analyzed by differential scanning calorimetry (DSC), nuclear magnetic resonance spectroscopy (13C-NMR), and scanning electron microscopy (SEM). Single glass transition temperature (T g ) and cold crystallization temperature (T cc ) were observed in all melt blends. Melt blends were found to be due to the ester-interchange reaction in PTT/PET blend. Also the randomness of copolymer increases because transesterification between PTT and PET increases with increasing blending time. This reaction increases homogeneity of the blends and decreases the degree of crystallinity of the melt blends. In PTT-rich blends, mechanical properties decrease with increase of PET content compared with that of pure PTT. And, in PET-rich blends, tensile modulus decreases with increase of PTT content, but tensile strength and elongation is similar to that of pure PET.  相似文献   

11.
A research programme was undertaken over two consecutive years with the purpose of studying the effect of herb–clover swards on lamb production performance year‐round. The focus of this study was on two consecutive late spring and early summer periods (2011, 2012). In each year, three sward treatments were compared on grazed paddocks with 40 lambs ha?1: (i) grass–clover mixture (perennial ryegrass [Lolium perenne L.] and white clover [Trifolium repens]); (ii) plantain–clover mixture (plantain [Plantago lanceolata], white clover and red clover [Trifolium pratense]); and (iii) chicory–plantain–clover mixture (plantain, chicory [Cichorium intybus L.] and white and red clovers). Lambs were weighed at 2‐week intervals, and carcass weights and GR tissue depth measurements were obtained at slaughter. In both years, lambs on treatments (ii) and (iii) had greater (P < 0·05) final live weight, liveweight gain, carcass weight, dressing‐out percentage and GR tissue depth measurements, and lower feed conversion ratio compared to lambs on treatment (i). Lamb production was similar in treatments (ii) and (iii) (P > 0·05) in each year. Therefore, during the late spring and early summer period, herb–clover mixture swards were found to be a superior option to perennial ryegrass–white clover for finishing lambs.  相似文献   

12.
This study is focused on investigating the feasibility of using silver(I) ions loaded poly(acrylonitrile)-grafted silk fibers as antibacterial dressing material. The optimum grafting conditions for ceric ammonium nitrate induced graft-copolymerization of acrylonitrile onto silk fibers were found to include initiator concentration of 35 mM, catalyst HNO3 concentration of 0.40 M and initiation time of 10 min. The poly(acrylonitrile)-grafted silk fibers were loaded with silver(I) ions by equilibration method. The resulting fibers were investigated for their biocidal action against E. coli, by using zone inhibition and colonies counting method.  相似文献   

13.
In the present work, graft copolymers of acrylamide onto guar gum were synthesized by free radical polymerization using potassium bromate/thiourea redox initiating system. The guar gum and guar gum-g-polyacrylamide were characterized by infrared spectroscopy and thermogravimetric analysis. It was found that the guar gum-g-polyacrylamid was thermally more stable than pure guar gum. The grafting ratio, grafting efficiency, add-on, and conversion increased with the concentration of bromate and acrylamide, whereas they decreased with increasing the concentration of guar gum. The grafting ratio and grafting efficiency showed maximum value at the concentration of thiourea and hydrogen ions of 3.2×10-3 mol dm-3 and 4.0×10-3 mol dm-3, respectively, but decreased with further increasing the thiourea and hydrogen ions concentrations. The increase in temperature from 30 to 45 °C resulted in increasing the grafting ratio while decreasing the conversion. The optimum reaction time for the graft copolymerization was found to be 2 h. Compared to the parent guar gum, the graft copolymer showed higher water swelling capacity and metal ion sorption, as well as better flocculant behaviors.  相似文献   

14.
为了更好地评估与预测三元混合物的毒性相互作用,以3种氨基甲酸酯类农药残杀威、灭多威、速灭威为研究对象,应用均分等效面设计(EESD)法配制三元混合物,应用直接均分射线设计法(EquRay)配制两两混合的二元混合物,测定混合物对乙酰胆碱酯酶(AChE)的抑制效应,基于三角形的3次插值方法构建三元混合物在20%、50%、80%效应的等效面,以浓度加和(CA)与独立作用(IA)为参考模型分析混合物的毒性相互作用。结果表明,Weibull函数能良好地拟合3种氨基甲酸酯类农药及其混合物对AChE的浓度-效应数据(R2>0.99,RMSE<0.03)。基于等效面分析,残杀威、灭多威、速灭威的三元及二元混合物毒性符合CA模型,呈现加和作用,而IA轻微高估了混合物的毒性。共毒系数法也证实这3种氨基甲酸酯类农药呈现加和作用。回归分析发现三元混合物毒性(pECx)与速灭威的浓度分数具有良好的负相关关系。均分等效面设计法与等效面分析法可用于有效评估三元混合物的联合毒性。   相似文献   

15.
Graft copolymerization of granular allyl starch with carboxyl-containing vinyl monomers using H2O2/Fe2+ initiator in aqueous dispersion was investigated for enhancing grafting efficiency of the copolymerization. The graft copolymerization was evaluated in terms of grafting efficiency, grafting ratio, and conversion of monomer to polymer. Influences of both allyl etherification of starch and structures of vinyl monomers used on the copolymerization were revealed. Variables such as molar ratio of Fe2+ to H2O2, initiator concentration, monomer concentration, polymerization temperature, and time of the graft copolymerization were also studied. It was found that allyl etherification of starch enhanced the grafting efficiency and grafting ratio evidently. Acrylic acid exhibited the greatest grafting efficiency and ratio for the copolymerization after starch was allyl-etherified. The copolymerization should be carried out under the protection of nitrogen gas at 30–35 °C for 3 h by using H2O2/Fe(NH4)2(SO4)2 as initiator. Preferred molar ratio of H2O2/Fe(NH4)2(SO4)2/anhydroglucose was in a range of 20/1/1000 to 60/3/2000.  相似文献   

16.
Bombyx mori (B. mori) silk was modified with the nano-TiO2 and chitosan dispersion system by the crosslinking reactions of citric acid (CA) and maleic anhydride (MA). The average size of the nano-TiO2 particles in the aqueous dispersion system was 36.7 nm. The scanning electron microscopy (SEM) micrographs showed that the nano-TiO2 particles were spherical and homogeneously dispersed in the dispersion system, and the surface ofB. mori silk fiber treated with the nano-TiO2 and chitosan dispersion system was rougher than that of the untreated one. X-ray diffraction (XRD) and Fourier transform infrared (FT-IR) Spectrometry indicated that the crystallinity of theB. mori silk fiber increased after treatment. It was also found that the nano-TiO2 and chitosan contributed to significantly enhance the mechanical properties including breaking strength, breaking elongation, initial modulus, rupture work, and elastic recovery property of theB. mori silk fiber. The wrinkle-resistant performance of the treatedB. mori silk fabrics was also greatly improved.  相似文献   

17.
有机硅氧烷接枝改性天然胶乳的制备及结构表征   总被引：2，自引：1，他引：1  
采用接枝共聚制备有机硅氧烷接枝改性天然胶乳,着重考察偶联剂种类和用量、引发剂用量、胶乳浓度、反应温度、反应时间和有机硅氧烷种类及用量等对有机硅在接枝共聚反应中的转化率和接枝率的影响,并采用正交设计试验,探索有机硅氧烷改性天然胶乳的适宜工艺条件。结果表明∶VD4接枝改性天然胶乳的转化率和接枝率均比D2的要高;与其他偶联剂相比,A-171的接枝率也较高;随着有机硅单体用量的增加、反应时间延长、反应温度升高,有机硅单体的转化率和接枝率都升高。有机硅氧烷改性天然胶乳的适宜工艺条件∶胶乳浓度为50%,反应温度为55℃,反应时间为4h,偶联剂A-171用量为1.2%（占橡胶的质量百分率,下同）,有机硅用量为15%,引发剂用量为1.0%。IR分析结果表明∶有机硅氧烷与天然橡胶分子链存在接枝共聚。  相似文献   

18.
Non-fouling surfaces that resist non-specific adsorption of proteins, bacteria, and higher organisms are of particular interest in diverse applications ranging from marine coatings to diagnostic devices and biomedical implants. Poly(ethylene glycol) (PEG) is the most frequently used polymer to impart surfaces with such non-fouling properties. Nevertheless, limitations in PEG stability have stimulated research on alternative polymers that are potentially more stable than PEG. Among them, we previously investigated poly(2-methyl-2-oxazoline) (PMOXA), a peptidomimetic polymer, and found that PMOXA shows excellent anti-fouling properties. Here, we compare the stability of films self-assembled from graft copolymers exposing a dense brush layer of PEG and PMOXA side chains, respectively, in physiological and oxidative media. Before media exposure both film types prevented the adsorption of full serum proteins to below the detection limit of optical waveguide in situ measurements. Before and after media exposure for up to 2 weeks, the total film thickness, chemical composition, and total adsorbed mass of the films were quantified using variable angle spectroscopic ellipsometry (VASE), X-ray photoelectron spectroscopy (XPS), and optical waveguide lightmode spectroscopy (OWLS), respectively. We found (i) that PMOXA graft copolymer films were significantly more stable than PEG graft copolymer films and kept their protein-repellent properties under all investigated conditions and (ii) that film degradation was due to side chain degradation rather than due to copolymer desorption.  相似文献   

19.
Resistance to thiabendazole, sometimes of varying degrees, has occurred in a number of fungal species causing diseases of potato tubers, including skin spot caused by Polyscytalum pustulans. The effect of applying a range of concentrations of thiabendazole, imazalil or a formulated mixture of thiabendazole and imazalil on the development of isolates of P. pustulans partially or fully resistant to thiabendazole and on the control of skin spot over a number of successive generations of seed potato multiplication was examined in a series of experiments over 3 years. Seed tubers were inoculated with a sensitive, partially resistant or fully resistant isolate in the first year of an experiment and combinations of fungicide and a range of concentrations were applied to the seed tubers annually before planting over two or three successive generations. Immersing seed tubers inoculated with the partially resistant isolate in a relatively high concentration of thiabendazole, 0.7 g a.i. l-1, did not result in the development of fully resistant isolates. Moreover, the effect of all fungicides in controlling eye contamination and skin spot did not differ between partially and fully resistant isolates. For seed tubers inoculated with the sensitive isolate, applying thiabendazole resulted in the occurrence of resistant isolates on first-generation daughter tubers, but the effect of fungicide concentration on the frequency of resistant isolates, partially or fully resistant, was inconsistent. In one experiment, the highest frequency of resistance was found at the greatest concentration, 0.4 g a.i. l-1, but, in the second experiment, the frequency was unaffected by the concentration of thiabendazole. On second-generation daughter tubers derived from thiabendazole-treated seed tubers, virtually all isolates were resistant and the frequency of partially and fully resistant isolates was similar to that in the first generation. Applying a mixture of thiabendazole and imazalil to seed tubers inoculated with a sensitive isolate resulted in the development of some resistant isolates in the first year but the frequency did not generally increase with successive applications of the mixture. A mixture of thiabendazole and imazalil, and imazalil alone gave similar control of eye contamination when applied at equivalent concentrations. However, increasing the concentration of imazalil from 0.1 to 0.7 g imazalil l-1 did result in an increasing impairment of plant growth, but the deposits achieved within that range of concentrations were greater than that recommended by the manufacturer. These results demonstrate that control of P. pustulans by thiabendazole, imazalil and a mixture of thiabendazole and imazalil applied at a range of concentrations was similar for isolates partially or fully resistant to thiabendazole.  相似文献   

20.
Present study is focused on the preparation of two layers composite wound dressing for drug release. The outer layer is made of hydrogel which contains of drug and the core layer is made of fabric. The two layers structure of composite dressing is formed by grafting of polyacrylamide-co-acrylic acid hydrogel on cotton fabric using ammonium per sulphate (APS) as chemical initiator and polyethylene glycol (PEG) as crosslinker. The major factors affecting graft copolymerization of hydrogel on cotton fabric are optimized by varying concentration of monomers & initiator, reaction temperature and addition time of crosslinker. Maximum grafting of hydrogel is obtained at 5 % (w/v) APS and 15 % acrylamide/acrylic acid (1:1 w/w ratio) concentration. The FTIR spectra of composite dressing shows characteristics peak of acrylic acid and acrylamide. The composite wound dressing material is loaded with model drug bovine serum albumin (BSA) and drug release behaviour is studied at different pH. The dressing shows drug release in different pH with maximum release of drug in acidic medium.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号