Radiation synthesis of kappa-carrageenan/acrylamide graft copolymers as superabsorbents and their possible applications

Kappa-carrageenan (κC) was modified via graft copolymerization of acrylamide (AAm) using γ-irradiation and followed by alkaline hydrolysis to achieve a novel superabsorbent hydrogel. The effect of grafting variables and alkaline hydrolysis conditions such as κC/AAm compositions and irradiation doses, NaOH concentration, hydrolysis time and temperature were systematically optimized to achieve a hydrogel with swelling capacity as high as possible. Swelling properties and FT-IR of untreated κC-g-PAAm and hydrolyzed κC-g-PAAm (H-κC-g-PAAm) were determined. The swelling capacity of hydrolyzed κC-g-PAAm was about 10 times in distilled water and three times in NaCl solution higher than that for κC-g-PAAm. The swelling of superabsorbing hydrogels was examined in buffer solutions. The swelling capacity of hydrogels was also measured in various salt solutions (LiCl, NaCl, KCl, CaCl₂, and FeCl₃). Results indicated that the swelling ratios decreased with an increase in the ion radius, valence and ionic strength of the salt solutions. Due to their high swelling ability in salt solutions, the hydrogels may be referred to as ‘anti-salt superabsorbent’ polymers. Thus, the salinity of water treated with H-κC-g-PAAm hydrogels was determined. It was found that the H-κC-g-PAAm hydrogels have a capability to absorb and retain the fresh water from the saline solution. The results obtained suggested the possible used of such prepared superabsorbent in agricultural purposes as a material for sodic soil remediation.     

Preparation of cellulose graft copolymers having polypeptide side chains and their blood compatibility

Blood compatibility of cellulose graft copolymers with poly(γ-benzyl-L -glutamate) and poly(N⁵-2-hydroxyethyl-L -glutamine) (Cell-g-PBLG and Cell-g-PHEG) was examined in vivo blood tests. For this purpose, Cell-g-PBLG graft copolymers with PBLG contents ranging from 7 to 60 mol % were prepared by polymerizing N-carboxy-γ-benzyl-L-glutamate(γ-BLG NCA) using aminoethyl cellulose (AE-Cell) with degree of substitution of 0.05 as macroinitiator. Graft copolymerization was carried out under a variety of conditions at 20°C in dimethyl-sulfoxide. Monomer conversion higher than 60% were obtained for all the polymerization runs. The solubility tests revealed that all of the AE-Cell and the polypeptides formed were grafted. The Cell-g-PHEG graft copolymers were prepared by treating Cell-g-PBLG graft copolymers with 2-amino-1-ethanol. Characterization of these graft copolymers were carried out by IR spectroscopy, DSC, and water content measurement. Tests for blood compatibility, in vivo, were made by a method of peripheral vein indwelling suture which was developed by one of the authors. The coating of graft copolymers on the polyester suture was made by casting either from formic acid solution of LiCl/dimethylacetamide solutions using water as the regenerating medium, and the polymer-coated sutures were implanted into a jugular and femoral vein of a dog. The results showed that the graft copolymers examined have excellent antithrombogenic properties.     

Steam-exploded wheat straw fibers as reinforcing material for polypropylene-based composites. Characterization and properties

Composites of wheat straw fibers with polypropylene (iPP) and maleic anhydride modified polypropylene (iPPMA) were prepared. Before being mixed with polypropylene matrices, the wheat straw fibers were subjected to a steam explosion process that induces morphological and structural changes in lignocellulosic materials. Such changes are able to enhance the interactions with the thermoplastic matrix. Compared with iPP, the modified matrix (iPPMA) has shown higher mechanical performances (tensile and impact behavior) and a remarkable decrease of water absorption, that is one of the main drawbacks of natural fiber composites. Finally, the presence of covalent bonds between maleic anhydride and steam-exploded (STEX) fibers, by means of an esterification reaction, produced during the melt-mixing process, can explain the resulting good interfacial adhesion found in iPPMA-based composities.     

微波法接枝改性天然胶乳的制备与表征

采用微波辐射的方法对天然浓缩胶乳进行接枝改性,单体选用甲基丙烯酸甲酯,考察了微波温度、时间、引发剂和单体用量对接枝率、接枝效率的影响,用傅里叶变换红外光谱仪、核磁共振波谱仪来表征接枝产物。结果表明,微波法接枝改性天然胶乳的方法是可行的;适宜的反应条件为:采用过硫酸钾和亚硫酸钠作为引发剂,其用量为0.4%(占橡胶质量的百分数),微波温度为80℃,反应时间为1～2h,单体与胶乳质量比为1∶1。     

Physical properties of model graft copolymers and their use as blend compatibilizers

The present investigation pertains to the structure–property relationships of highly structured graft copolymers. The specific model graft copolymers are based on an elastomeric backbone, i.e., poly(ethyl acrylate), and monodisperse thermoplastic grafts, i.e., polystyrene. The synthesis of these graft copolymers is based on the free-radical polymerization of ethyl acrylate and an anionically polymerized polystyrene macromonomer. It is clearly demonstrated that grafts significantly enhance tensile properties. The level of improvement is directly related to the graft level, i.e., number of grafts/chain, and graft molecular weight. In addition, blending these graft copolymers into their respective homopolymer mixture results in a mechanical performance strikingly dependent on the molecular characteristics of the graft copolymer. For example, tensile strength is maximized at a level between one and two grafts per chain. This result parallels observations noted in blend compatibilization using diblock and triblock copolymers. It is also demonstrated that using mutually grafted copolymers produces an interesting variety of compatibilized ternary (or higher) component blends. © 1994 John Wiley & Sons, Inc.     

Performance and synergistic effect of phenolic and thio antioxidants in ABS graft copolymers

The synergistic effect of phenolic and thio antioxidants on the stabilization of acrylonitrile-butadiene-styrene (ABS) graft copolymers has been studied. Three commercial antioxidants Irganox245, Irganox1076 and dilauryl thiodipropionate (DLTP) were selected. Formulations based on hindered phenols and secondary antioxidant DLTP were prepared. Stabilization was monitored in terms of changes in the functional groups (oxidation products), tensile properties and yellowness index. Differential scanning calorimetry (DSC) and thermogravimetry (TG) were also used to assess the stability. The results indicated that the combination of Irganox245 and DLTP showed much better stabilization effect than the individual components due to the strong synergistic effect. Only weak synergism could be observed in the formulation that contained Irganox1076 and DLTP. Irganox1076 and Irgnox1076/DLTP exhibited similar behaviors between antioxidants with the highest and lowest efficiencies.     

Preparation of chitosan-g-polylactide graft copolymers via self-catalysis of phthaloylchitosan and their complexation with DNA

The graft copolymer of chitosan-g-polylactide (CS-g-PLA) was synthesized successfully through ring-opening polymerization of lactide onto phthaloyl-protected chitosan by a self-catalysis strategy. After graft copolymerization, the phthaloyl groups were deprotected to regenerate free amino groups in the CS-g-PLA. FT-IR and NMR were used to characterize the graft copolymers both before and after the deprotection. We observed that degradation of the grafted PLA chains occurred in the alkaline deprotection process, and this process was optimized. Moreover, the CS-g-PLA containing the amino-polysaccharide backbone was formed into a polyelectrolyte complex with DNA. The resultant CS-g-PLA/DNA complexes were determined to be about 60 nm, with a positive charge above an N/P of 4/1.     

Biofibers as reinforcing fillers in thermoplastic composites

Four biofiber materials were compared against wood flour for their ability to act as reinforcing fillers in melt-blended composites with polypropylene as the matrix polymer. The four materials were a waste wood composite (mixture of plywood, particleboard, and fiberboard), kenaf core, a waste jute–polyester composite panel, and waste newspaper. The composites were prepared either by extrusion or by blending in a high intensity thermokinetic mixer (K-mixer), and mechanical properties were determined on injection molded specimens. Although some property differences were observed compared to wood flour/polypropylene composites, it appeared that any of the four materials might substitute for wood flour if local supply and cost circumstances offered advantages. However, waste newspaper clearly provided the best balance of mechanical properties relative to the other three test materials or wood flour. Relative to wood flour, waste newspaper filler increased unnotched impact by over 30 percent and flexure and tensile strengths by about 25 percent.     

纤维复合材料及其应用

介绍了纤维复合材料的分类、特点及其在现代国民经济中广泛的应用领域。     

Synthesis and applications of reactive carbohydrates. III. Preparation and methylolation of polyacrylamide-carboxymethyl cellulose graft copolymers

Carboxymethyl cellulose (CMC) was treated with HCl at 80°C for different time periods (15 – 60 min). The hydrolyzed CMC samples as well as the original sample were graft copolymerized with acrylamide using K₂S₂O₈ as initiator. It was disclosed that the increasing duration of acid hydrolysis is accompanied by a progressive increment in the copper number of CMC, meanwhile its carboxyl content decreases. Acid hydrolysis enhances significantly the susceptibility of the CMC toward grafting. The latter reduces the copper number of the hydrolyzed CMC samples most probably via conversion of the aldehydic to carboxylic groups under the action of K₂S₂O₈ during grafting. Grafting also reduces the carboxyl content of the original CMC sample while increasing those of the hydrolyzed CMC samples. Methylolation of the polyacrylamide-CMC graft copolymers results in reactive finishes. When the latter were applied to cotton fabric according to the conventional pad-dry-cure method followed by a thorough washing, the fabric retained ca. 86% of the finish derived from the copolymer of CMC and 92% of finishes derived from the copolymers of hydrolyzed CMC.     

微波辐射下淀粉-丙烯酰胺接枝共聚物的合成

以硝酸铈铵作为引发剂、丙烯酰胺为单体,用微波辐射法合成了淀粉接枝丙烯酰胺共聚物。探讨了反应时间、引发剂浓度、单体和淀粉质量比和反应温度等因素对接枝反应的影响。正交实验确定的最优工艺条件为:反应时间20 m in,引发剂浓度4 mmol/L,丙烯酰胺和淀粉质量比2.5∶1,反应温度55℃,最高接枝率和接枝效率分别达到211.6%和74.3%。     

Design and characterization study of LaFeO3 and CaTiO3 composites at microwave frequencies and their applications as dielectric resonator antennas

Technological development leads to the demand for innovation and the discovery of new materials properties. In telecommunications, DRAs (antennas with a dielectric block as radiant element) are a viable option for high frequency applications, where low profile and low losses are desirable, and essential requirements in several cases. A study of the properties of composites of lanthanum ortoferrite LFO (LaFeO₃) and calcium titanate CTO (CaTiO₃) as cylindrical dielectric resonator antennas is presented for the first time. In order to carry out the analysis, the material was produced through the solid state route, and resonators of LFO-CTO solid solutions were manufactured for seven different values of CTO weight fraction (0; 0.15; 0.20; 0.36; 0,56, 0,60 and 1). X-ray diffractometry, dielectric characterization, measurement of antenna parameters and subsequent comparison of measured values with theoretical and simulated values were performed. The antennas in this work showed good gain, good impedance matching, consistent values of return loss, high temperature stability and resonance frequency; all operating at the S band and beginning of the C band of the microwave spectrum.     

Modification of waste silicas by silanes and titanates and their use as reinforcing fillers in elastomer composites

Results on the use of waste silica, a by-product in the production of aluminum fluoride, as an elastomer filler are presented. Modification of the purified silica surface with silane and titanate coupling agents has been carried out. The effect of the type and amount of modifying agent on the physico-mechanical properties in vulcanizates of butadiene-styrene rubber and in polyurethane elastomers has been tested. The mechanical properties of butadiene-styrene rubber vulcanizates filled with waste silica show that the most favorable modifying effect is shown by mercaptosilanes A-189 and A-1893, polysulfide Si-69, and titanate KRTTS, as indicated by increased strength parameters. However, testing of the mechanical properties in polyurethane elastomers filled with waste silica has demonstrated that silica modification with aminosilanes A-1100 and A-1120 yield polyurethane compositions of optimum strength parameters.     

Preparation for graft copolymers of sawdust/vinyl monomers and their application for removal of dye

A kind of cationic exchanging resin of carboxyl sawdust (CSD) was fabricated through the hydrolysis of graft copolymers of sawdust with acrylonitrile (SAN) and sawdust with acrylamide (SAA) that were made by initiator Fe²⁺/H₂O₂. A study of the graft copolymerization was conducted for initiator usage, vinyl monomer usage, and reaction temperature. The hydrolysis under basic/acid conditions was also studied for the yield and acid value of CSD followed to adsorb Basic Pink dye (BPD). Our results show the following: (1) graft copolymers (SAN and SAA) with a high rate of graft copolymerization are readily prepared by suitable usages of initiator and vinyl monomer under a certain temperature; (2) adsorption capacity of CSD is relative to pH of BPD solution and reaches the most adsorption capacity at pH ≈ 6; (3) adsorption capacity of CSD increases along with the augment of its acid value; and (4) the adsorption capacity of the CSD toward BPD increases along with augment of initial concentration of the adsorbate and reaches about 500 mg/g. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 2390–2396, 2002     

Pretreatments of natural fibers and their application as reinforcing material in polymer composites—A review

In recent years, natural fibers reinforced composites have received much attention because of their lightweight, nonabrasive, combustible, nontoxic, low cost and biodegradable properties. Among the various natural fibers; flax, bamboo, sisal, hemp, ramie, jute, and wood fibers are of particular interest. A lot of research work has been performed all over the world on the use of natural fibers as a reinforcing material for the preparation of various types of composites. However, lack of good interfacial adhesion, low melting point, and poor resistance towards moisture make the use of natural fiber reinforced composites less attractive. Pretreatments of the natural fiber can clean the fiber surface, chemically modify the surface, stop the moisture absorption process, and increase the surface roughness. Among the various pretreatment techniques, graft copolymerization and plasma treatment are the best methods for surface modification of natural fibers. Graft copolymers of natural fibers with vinyl monomers provide better adhesion between matrix and fiber. In the present article, the use of pretreated natural fibers in polymer matrix‐based composites has been reviewed. Effect of surface modification of natural fibers on the properties of fibers and fiber reinforced polymer composites has also been discussed. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers     

Sunflower seed cake as reinforcing filler in thermoplastic composites

Dimensional stability, mechanical properties, and melting and crystallization behavior of polypropylene composites filled with sunflower seed cake (SSC) were investigated. Injection molded composites were prepared from the SSC flour and polypropylene with and without maleic anhydride‐grafted polypropylene (MAPP) at 30, 40, 50, and 60 wt % contents of the SSC flour. Twenty‐eight days thickness swelling and water absorption values of the specimens increased by 43 and 56% as the filler content increased from 30 to 60 wt %, respectively. The flexural modulus of the polypropylene composites increased from 3157 to 4363 MPa as the SSC flour increased from 30 to 60 wt %. The maximum flexural strength 38.4 MPa was observed for 40 wt % SSC flour filled specimens. However, further increment in the SCC flour decreased the flexural strength to 31.4 MPa. The tensile strength of the specimens decreased from 22.5 to 14 MPa while the tensile modulus increased from 3023 to 3677 MPa as the SSC flour increased from 30 to 60 wt %. The dimensional stability and mechanical properties of the composites were significantly improved by the incorporation of the coupling agent (MAPP). The effect of the MAPP addition was more pronounced for the strength than for the modulus. The melting temperature and degree of crystallinity of the neat polypropylene decreased with increasing content of the SSC flour. The degree of crystallinity of filled composites considerably increased with the incorporation of the MAPP. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Preparation and properties of fibres based on graft polyamide copolymers

Conclusions 1. Of the proposed methods of synthesizing graft polyamide copolymers, the use of peroxidized polycaproamide, activated by a metal of variable valence, and also radiation initiation of the graft polymerization reaction have found practical application.2. New fibres with improved hygienic, consumer, and special properties have been prepared, based on GPC.3. Effective methods of synthesizing GPC, in combination with the availability of technological equipment, have stimulated further development of the chemistry and technology of fibres from graft polyamide copolymers, which is interesting in the practical respect.Deceased.Translated from Khimicheskie Volokna, No. 4, pp. 9–14, July–August, 1984.     

Modification of polysilanes: Preparation of comb-like graft copolymers

Poly(methylphenylsilylene) has been functionalized by protodearylation with trifluoromethanesulfonic acid. Comb-like graft copolymers have been prepared by polymerizing tetrahydrofuran. 2-methyl-2-oxazoline, and isobutylvinyl ether from a partially triflated poly(methylphenylsilylene) backbone. Model studies using trimethylsilyl trifluoromethanesulfonate to initiate the cationic polymerization of these organic monomers indicated that a promoter was required to achieve more efficient initiation.     

Comparison between dew‐retted and enzyme‐retted flax fibers as reinforcing material for composites

Two kinds of retted Canadian linseed flax fibers, dew‐retted (F1) and enzyme‐retted flax fibers (F2) were characterized in detail for their applications in composites, such as retting degree, thermal stability, tensile strength, and interfacial behavior in polypropylene (PP) matrix. It's clear from Scanning Electron Micrograph that the aspect ratio of F2 was much higher than that of F1 in the light of their separated elementary fibers in most cases. Instead, the elementary fibers of F1 remained tightly bundled into technical fiber wrapping with more non‐cellulose portions. This reflected its lower retting degree and resulted in its lower thermal stability. Single fiber tensile test and single fiber pull‐out test were used to evaluate the fiber tensile properties and fiber/PP interfacial shear strength, respectively. Better retting degree and fewer damages on F2 endowed F2 better tensile property. Consequently, higher aspect ratio, retting degree, and tensile strength proved F2 to be a kind of better reinforcing material than F1 for composites. POLYM. ENG. SCI., 2012. 2011 published by Society of Plastics Engineers