Synthesis,characterization, and polychelatogenic properties of poly(acrylic acid-co-acrylamide)

The radical copolymerization of acrylic acid with acrylamide was carried out at different monomer ratios in solution (DMF) at 60°C. The corresponding homopolymers were also synthesized to compare their metal ion binding abilities. All the copolymers were characterized by elemental analysis. The metal ion binding properties of these water-soluble polymers with Cu(II), Co(II), Ni(II), Cd(II), Zn(II), Pb(II), Hg(II), Fe(III), and Cr(III) ions were investigated in aqueous solution using the Liquid-Phase Polymer-Based Retention (LPR) technique. Poly(acrylic acid-co-acrylamide) showed a higher retention compared to the homopolymers for all the metal ions except of Hg(II), which was not retained. Besides, the retention of Cd(II) is higher than that an addition of the retention of both homopolymers. It may be attributed to a synergic effect. Maximum capacity for Cu(II) at pH 5.0 was determined to be 1 mmol g⁻¹ (63.5 mg g⁻¹). © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35 : 2461–2467, 1997     

Modified chitosan 4. Superabsorbent hydrogels from poly(acrylic acid-co-acrylamide) grafted chitosan with salt- and pH-responsiveness properties

Graft copolymerization of mixtures of acrylic acid (AA) and acrylamide (AAm) onto chitosan was carried out by using potassium persulfate (KPS) as a free radical initiator in the presence of methylenebisacrylamide (MBA) as a crosslinker. The effect of reaction variables, such as MBA concentration and AA/AAm ratio on the water absorbency capacity have been investigated. The polymer structures were confirmed by FTIR spectroscopy. Water absorbencies were compared for the hydrogels before and after alkaline hydrolysis. In the non-hydrolyzed hydrogel, enhanced water absorbency was obtained with increasing AA in monomer feed. However, after saponification, the sample with high AAm ratio exhibited more water absorbency. These behaviors were discussed according to structural parameters. The swelling kinetics of the superabsorbing hydrogels was studied as well. The hydrogels exhibited ampholytic and reversible pH-responsiveness characteristics. The swelling variations were explained according to swelling theory based on the hydrogel chemical structure. The hydrogels exhibited salt-sensitivity and cation exchange properties. The pH-reversibility and on-off switching properties of the hydrogels make the intelligent polymers as good candidates for considering as potential carriers for bioactive agents, e.g. drugs.     

Effects of melamine polyphosphate and halloysite nanotubes on the flammability and thermal behavior of polyamide 6

Melamine polyphosphate (MPP) and halloysite nanotubes (HNT) were introduced to polyamide 6 (PA6) by melt blending in order to improve the fire resistance. PA6 composite containing 12% flame retardants with good spinnability was obtained. The flammability of PA6 composite was characterized by limiting oxygen index (LOI), UL‐94 vertical burning and cone calorimeter (CONE) tests. The results indicated that the LOI value could reach 24.0 vol.% and UL‐94 rating could achieve V2 level at the presence of 12% flame retardants. CONE data demonstrated that peak heat release rate was significantly reduced from 554 kW/m² of neat PA6 to 368 kW/m² of the sample containing flame retardants. Thermal analysis indicated that the thermal stability and char formation were improved by the presence of flame retardants. The morphology of residue char was characterized by scanning electron microscopy; and it suggested that a network‐structured protective char layer had been formed. The possible synergism between MPP/HNT and their flame retardant mechanism was also analyzed and discussed. Copyright © 2014 John Wiley & Sons, Ltd.     

Morphology and properties of low-density (branched) polyethylene

The different types of morphology that can be developed in a large number of low-density (branched) polyethylene whole polymers, as well as in a series of fractions, have been studied for two different extreme crystallization modes. Concomitantly, thermodynamic properties of the same samples have also been determined. After isothermal crystallization at elevated temperatures, spherulitic structures are found in all the whole polymer samples. On the other hand, after rapid crystallization a variety of different types of supermolecular structures are observed which are shown to depend systematically on the concentration of side-chain branches and the relative proportion of high molecular weight species in the sample. This temperature dependence of the morphological forms is opposite to that previously reported for linear polyethylene. The studies with the fractions show that the individual species are not the cause of this behavior; rather, the total composition is the important factor. The thermodynamic properties are also quite different from those of linear polyethylene in showing virtually no molecular weight dependence and being governed primarily by the concentration of short-chain branches. The degrees of crystallinity as determined from density and enthalpy of fusion measurements do not vary much with the two extreme crystallization conditions employed, are not sensitive to the morphology, and differ from one another, even when well-developed spherulites are formed. A major influence of the branching concentration on these properties is clearly indicated.     

Highly efficient removal of uranium(VI) from aqueous solutions by poly(acrylic acid-co-acrylamide) hydrogels

In this study, poly(acrylic acid-co-acrylamide) (PAAAM) hydrogels were used to remove uranium (VI) ions in wastewater and characterized by FTIR, SEM, EDX. The effects of pH value, coexistence of ionic strength, contact time, initial U (VI) ion concentration and adsorption temperature were also studied. Adsorption data fitted well with pseudo-second-order, intra-particle diffusion model and Langmuir isotherm mode, the maximum adsorption capacity of U(VI) was 713.24 mg g^?1. Thermodynamic analysis shows that the adsorption of U(VI) is spontaneous endothermic. PAAAM hydrogel has excellent regeneration performance, after five time adsorption–desorption cycles, the adsorbent still maintained 99.24% adsorption capacity.     

Study on rheological properties and relaxational behavior of poly(dianilinephosphazene)/low-density polyethylene blends

Rheological properties and relaxational behavior of blends of low-density polyethylene (LDPE) and poly(dianilinephosphazene) (PDAP) have been investigated to check miscibility and molecular relaxations in the crystalline and amorphous phases. In the studied shear rate range, all PDAP/LDPE blends exhibited a shear thinning behavior. The experimental data were fitted using the logarithmic rule and serial model to investigate the miscibility of blends. It was found that LDPE and PDAP can achieve a certain degree of miscibility in the molten state. The dynamic mechanical α-, β- and γ-relaxation behavior obtained from dynamic mechanical thermal analysis imply that the two components in the amorphous phase were miscible. The wide-angle X-ray diffraction result showed that these two components interact with each other.     

The influence of melamine phosphate modified MoS2 on the thermal and flammability of poly(butylene succinate) composites

This work reported a facile fabrication method to modify molybdenum disulfide (MoS₂) nanosheets with common flame retardant melamine phosphate (MAP) and then were incorporated into poly(butylene succinate) by melt blending method with the purpose of improving the thermal and flame retardancy properties. MAP modified MoS₂ nanosheets dispersed well in poly(butylene succinate) composites with intercalated structure. The incorporation of MAP modified MoS₂ nanosheets led to an increase of thermal degradation temperature and char formation as well as reduction of the peak heat release rate. Copyright © 2016 John Wiley & Sons, Ltd.     

Adhesive effect of linear low-density polyethylene gels on polyethylene moldings

Adhesive effect of linear low density polyethylene (LLDPE) gels in organic solvents such as decalin, tetralin, and o-dichlorobenzene on high density polyethylene (HDPE) moldings has been investigated by shearing tests, and DSC measurements. For all of the gels the temperature at which the heated gel starts to exhibit the adhesive effect was about 70 °C, which is similar to the result of LDPE gel. In particular, when heated at 110 °C, LLDPE gel in tetralin showed such a strong bond strength that polyethylene plates of 3 mm in thickness and 20 mm in width gave rise to necking. It was found that LLDPE gel behaved as though it added LDPE gel to HDPE gel namely LDPE-like components in LLDPE resin exerted the adhesive effect at lower heating temperature, HDPE-like components exerted the strong adhesive effect at higher heating temperature.     

Characterizing blends of linear low-density and low-density polyethylene by DSC

Summary A two-step isothermal annealing (TSIA) procedure is described that enables the endothermic peaks of low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE) and their blends, to be satisfactorily resolved during analysis by differential scanning calorimetry. A modified form of multistep isothermal annealing, the TSIA procedure produces a highly characteristic profile of the blend components by facilitating the segregation of the phases based on branch density. It is proposed that the TSIA procedure may have significant merit in the identification and quantification of the components in an unknown blend as well as increasing the sensitivity in analytical procedures aimed at blend component quantification.     

Thermal, mechanical and electrical properties of copper powder filled low-density and linear low-density polyethylene composites

Low-density polyethylene (LDPE) and linear low-density polyethylene (LLDPE) with different copper contents were prepared by melt mixing. The copper powder particle distributions were found to be relatively uniform at both low and high copper contents. There was cluster formation of copper particles at higher Cu contents, as well as the formation of percolation paths of copper in the PE matrices. The DSC results show that Cu content has little influence on the melting temperatures of LDPE and LLDPE in these composites. From melting enthalpy results it seems as if copper particles act as nucleating agents, giving rise to increased crystallinities of the polyethylene. The thermal stability of the LDPE filled with Cu powder is better than that for the unfilled polymer. The LLDPE composites show better stability only at lower Cu contents. Generally, the composites show poorer mechanical properties (except Young's modulus) compared to the unfilled polymers. The thermal and electrical conductivities of the composites were higher than that of the pure polyethylene matrix for both the LDPE and LLDPE. From these results the percolation concentration was determined as 18.7 vol.% copper for both polymers.     

Adhesion of linear low-density polyethylene and oligomers

A pressure vessel design is put forward taking the form of a two-layer bottle, the inner sealing layer of which is made of linear low density polyethylene by rotational molding and the external power layer of which is made by winding an oligomer impregnated roving or moldable filament on the inner layer. It is shown that, to achieve the highest adhesion strength, it is necessary to preliminarily prepare the surface of the polyethylene sample by obtaining a particular microstructure and to use epoxy or polyester oligomers with a viscosity low enough to provide complete filling of the polyethylene sample surface texture.     

Flame‐retardant poly (ethylene terephthalate) enabled by a novel melamine polyphosphate nanowire

A novel strategy was developed for the preparation of melamine polyphosphate (MPP) nanowires to achieve a superior flame‐retardant poly (ethylene terephthalate) (PET). Thanks to the well‐designed nanostructure, the prepared MPP nanowires exhibited great thermal stability and flame retardance. Herein with incorporation of only 1‐wt% MPP nanowires (PET/FR1.0 nanocomposite), the limiting oxygen index (LOI) value was dramatically increased to 29.4% from 20.5%, showing self‐extinguishing behavior. Moreover, PET/FR1.0 nanocomposite passed V‐0 UL‐94 rating in the vertical combustion test. However, PET containing 5‐wt% commercial MPP powder (PET/FR_C5.0) only showed a LOI of 27.9% and ignited the absorbent cotton with flammable melt‐droplets. Cone results also presented that introducing 1‐wt% MPP nanowires brought about a crucial decrease in fire hazard of PET, for instance, 11.1% and 7.7% maximum reduction in heat release rate and total heat release, respectively. Thermogravimetric analysis/infrared spectrometry (TG‐FTIR) result indicated that the main pyrolysis volatiles generated from PET degradation including benzoic acid, aromatic compounds, and carbon dioxide were apparently suppressed after introducing MPP nanowires into PET matrixes, suggesting the outstanding obstructing effect of graphited char residue formed in the combustion. This enhanced flame retardancy rooting in addition of MPP nanowires can be attributed to the combined dilution effect in gaseous phase and catalytic carbonization effect in condensed phase.     

Transport properties of annealed,drawn low-density polyethylene (LDPE)

The specific concentration c_a of methylene chloride, the zero-concentration diffusion coefficient D₀, and the concentration coefficient γ_D of the diffusivity in drawn and annealed LDPE were measured. The influence of the drawing rate, of annealing with the ends of the sample free and fixed and the effects of time of standing at room temperature after annealing were investigated. The observed transport properties are in good agreement with the microfibrillar model of fibrous structure, its relaxation during annealing, and the slow crystallization of relaxed tie-molecules upon standing at room temperature.     

Thermal degradation mechanisms of aluminium phosphinate, melamine polyphosphate and zinc borate in poly(methyl methacrylate)

The aim of this study was to investigate the thermal degradability, and in particular, the thermal degradation mechanism of organophosphorus flame-retardant poly(methyl methacrylate) (PMMA). For this purpose thermogravimetry and direct pyrolysis mass spectrometry analyses were used. Release of diethylphosphinic acid, melamine, and several products involving Al-O-P and N-P linkages were detected from the organophosphorus additive containing aluminium diethylphosphinate, melamine polyphosphate and zinc borate. When incorporated in PMMA, reactions of diethylphosphinic acid, melamine and/or their derivatives with the ester group affected the decomposition pathways by generation of (C₂H₅)₂POOCH₃ and HNCO at relatively high temperatures.     

New composite membranes based on crosslinked poly(acrylic acid) and porous polyethylene films

A process for the preparation of new composite membranes via free-radical copolymerization of acrylic acid with a macromolecular crosslinker (allyloxyethylcellulose) on the surface of porous polyethylene films was proposed. To reveal the effect of the porous matrix on the properties of the composites, homogeneous hydrogel membranes based on crosslinked poly(acrylic acid) were studied. The swelling ratio and transport characteristics of the membranes during separation of ethanol-water mixture by pervaporation were determined depending on the ethanol concentration. It was found that all membranes at low ethanol concentrations (0–30 vol %) exhibited high swelling ratios, which drastically decreased in the range 30–40 vol % as a result of gel collapse. The composite membranes had a higher selectivity for water over a broad range of ethanol concentrations than homogeneous membranes, but a lower flux. It was found that the strength and elasticity of porous matrices was retained in the composite membranes, which became mechanically more isotropic owing to the presence of the crosslinked component.     

Effect of urea on poly(methacrylic acid) and poly(acrylic acid) aqueous solutions

The effects of urea on aqueous solutions of both poly(methacrylic acid (PMA) and poly(acrylic acid) (PAA) have been investigated by using potentiometry, viscometry and study of the fluorescence of Auramine O, a cationic dye. The viscosity behaviour of unionized PMA obtained from direct dissolution of solid powder shows that the unneutralized macromolecules can be associated in water. The stability of such “aggregates” seems weak as indicated by their disappearance as soon as the charge density is very low. For PMA salt solution percolated through a cation (H⁺) exchange resin column, no association is observed. The pH-dependent conformational behaviour of PMA which, contrary to PAA, presents compact conformations in water at low charge density is discussed in terms of solvophobic/solvophilic interactions. It is shown that, even for urea concentration up to 8 M, the compact conformations of PMA are not completely destroyed. The formation of H⁺/urea complex is taken into account.     

Rapid and precise release from nano-tracted poly(N-isopropylacrylamide) hydrogels containing linear poly(acrylic acid)

We investigated the rapid and precise molecular release from hydrogels in response to dual stimuli. To achieve precise on/off drug release using thermoresponsive poly(N-isopropylacrylamide) hydrogels, we prepared nano-structured semi-IPNs, which consisted of thermosensitive PNIPAAm networks penetrated by pH-responsive poly(acrylic acid) (PAAc) linear chains and perforated to create nano-tracts as a molecular pathway. The present nano-tracted semi-IPNs show a rapid deswelling response to both temperature and pH. Model drug releases were investigated when simultaneous changes in temperature and pH were applied. We observed that the cationic drug was rapidly released and then abruptly discontinued from the nano-tracted semi-IPNs in response to the dual stimuli, and clear release and stopping cycles were repeatedly observed on successive steps. Moreover, the release rates and amount of drug released were controllable by the deswelling speed of the gels and the PAAc content inside the gels. This novel release system using the nano-tracted semi-IPNs may be useful for the high performance, pulsed release of molecules.     

Characterization and properties of polyethylene blends II. Linear low-density with conventional low-density polyethylene

Melting and crystallization phenomena in blends of a linear low-density polyethylene (LLDPE) (ethylene butene-1 copolymer) with a conventional low-density (branched) polyethylene (LDPE) are explored with emphasis on composition by differential scanning calorimetry (DSC) and light scattering (LS). Two endotherms are evident in the DSC studies of the blends, which suggests the formation of separate crystals. Light-scattering studies indicate that the blend system is predominantly volume filled by the LLDPE component whereby the LDPE component crystallizes as a secondary process within the domain of the LLDPE spherulites. In contrast to those of the LLDPE/HDPE blends, the mechanical and optical relaxation behavior of the LLDPE/LDPE blends are dominated by the LLDPE component in the vicinities of γ and β regions, whereas the trend reverses at high temperature α regions. This observation is accounted for on the basis of the relative restrictions imposed by the deformation of spherulites (which are primarily made up of the LLDPE component) at different time scales.     

Structure and sorption properties of the polyion complex between poly(acrylic acid) and poly(4-vinylpyridine)

A polyion complex was formed from poly(acrylic acid) (PAA) and poly(4-vinylpyridine) (PVP). Its structure and composition were examined by means of infrared spectroscopy (IR), x-ray photoelectron spectroscopy (XPS), and elemental analysis. The polyion complex was obtained by dissolving PAA and PVP together in methanol. The composition of the polyion complex was independent of stirring speed, mixing sequence, and standing time after mixing. However, the composition depended on the concentrations and the ratio of the components in the reaction mixture. Excess of PAA in the product was observed when concentrated solutions (2.0 × 10^?1M) were used for the preparation or when an excess of PAA was added to PVP. The sorption of water vapor by an equimolar PAA/PVP complex at 293 and 303 K was higher than that by the pure components, especially in the low- and middle-pressure regions. In the high-pressure region, however, the uptake was not affected by the complex formation. While hydrogen bond interactions in general decrease sorption, Coulombic interactions between polymer chains increased the sorption capacity.