Water Swelling Measurements Research Articles

Optimizing modified natural rubber in starch-based hydrogels: A cost-effective approach for high-performance sustainable slow-release fertilizer coatings

Effective compatibility between natural rubber (NR) and cassava starch (CSt) is crucial for enhancing the water swelling and retention properties of CSt/NR-based hydrogels. In this study, NR was modified by grafting glycidyl methacrylate (NR-g-GMA, NRG) at 3, 6, and 9 parts per hundred rubber (phr) for blending with CSt. Subsequently, CSt was grafted with acrylamide (AM), crosslinked with N,N′ − methylene-bis-acrylamide (MBA), and interpenetrated with NRG to produce CSt-g-PAM/NRG hydrogels. The resulting CSt-g-PAM/NRGx (x = phr of GMA) hydrogels were characterized using FTIR, XRD, TGA, tensile testing, and water swelling measurements. Results revealed that CSt-g-PAM/NRG3 exhibited the highest equilibrium water swelling at 3300 %, surpassing CSt-g-PAM/NR (1430 %) and demonstrated the highest mechanical strength (0.92 MPa), desirable biodegradability (69 % at 30 days), and good water retention. These properties are attributed to the superior compatibility and stronger interactions between NRG and the CSt-g-PAM networks. Additionally, the WUHNRG3 (urea coated with CSt-g-PAM/NRG3 and wax layers) fertilizer demonstrated good biosafety, an acceptable slow-release rate (50.26 % at 30 days), and effectively promoted the growth of chili plants at a reasonable cost. This study demonstrates that modifying NR with optimal GMA content provides an effective CSt-g-PAM/NRG coating membrane, suitable for sustainable slow-release fertilizers and green agricultural practices.

Realizing Eco-Friendly Water-Resistant Sodium-Alginate-Based Films Blended with a Polyphenolic Aqueous Extract from Grape Pomace Waste for Potential Food Packaging Applications.

Water-resistant and environmentally friendly sodium-alginate-based films have been investigated to develop functional materials to extend the food's shelf-life. A water-stable alginate-based film was prepared, employing both the internal and external gelation approach in the presence of CaCl2. To apply this film to food packaging and thus preserve food quality, the aim of this work is to perform a chemical and physical characterization of the proposed materials, evidencing the main features and stability under different work conditions. Water contact angle measurements showed a value of 65°, suggesting an important reduced hydrophilic character of the obtained alginate films due to the novel CaCl2-induced compacted polymer network. The film's stability was thus checked through swelling measurements in water after varying pH, temperature, and ionic strength. The film was stable at high temperatures and not pH-responsive. Only highly concentrated salt-based solutions negatively affected the proposed packaging, causing a large swelling. Furthermore, a water-based polyphenolic extract from grape (Vitis vinifera L.) pomace waste was embedded inside the films in different amounts in order to confer additional properties. The extract's polyphenolic content (evaluated from HPLC/MS-MS measurements) endowed the films' UV-light screening and enhanced antioxidant properties. These important findings suggest the additional potential role of these films in protecting food from light deterioration. The stability of these hybrid films was also checked by observation, as the polyphenols' presence did not largely alter the alginate network that occurred yet was water-resistant under the described work conditions.

Self-assembled pH-responsive films prepared from mussel anchoring threads.

The byssus is a series of collagen-rich fibers securing mussels to surfaces. The complex but elegant heterogeneous assembly of the various proteins in the threads is responsible for their remarkable mechanical properties combining strength and extensibility. Along with the well-known biocompatibility and biodegradability attributed to collagen-based materials, these mechanical properties are highly desirable to produce biomaterials for soft tissue engineering and drug delivery applications. In order to replicate the byssus natural features and properties, we prepared a soluble byssus protein hydrolyzate (BPH) that can generate water-insoluble self-standing films. Atomic force and scanning electron microscopy revealed the presence of self-assembled collagen-like fibrils at the surface of the films. Infrared spectroscopy analysis of the film formation showed that insolubility is caused by the self-assembly of polypeptides from the hydrolyzate into antiparallel β-sheets, aggregated β-strands and collagen triple-helix structures. The mechanical properties and water swelling measurements on the films can be reversibly pH-modulated by modifying the electrostatic interactions between the ∼30 mol% of charged amino acids. Optimal mechanical properties and minimum swelling are obtained at the isoelectric point (pH 4.5). Higher or lower pH treatment reversibly decreases their stiffness and strength and increases their swelling ratio. Altogether, our results show that byssus proteins are an interesting sustainable feedstock for preparing new solid-state pH-tuneable biomaterials.

Investigation of mechanical and thermodynamic properties of pH-sensitive poly(N,N -dimethylaminoethyl methacrylate) hydrogels prepared with different crosslinking agents

pH-sensitive poly(N,N-dimethylaminoethyl methacrylate) hydrogels were synthesized by free-radical crosslinking polymerization using two different crosslinking agents; tetraethylene glycol dimethacrylate (TEGMA) and N,N′-methylenebis(acrylamide) (BAAm). The influence of the polymerization factors such as the type of the crosslinking agent and the gel preparation concentration on the swelling behavior, the gel strength, the effective crosslinking density and the average chain length between the crosslink points for the resulting hydrogels was investigated. The results of the equilibrium swelling measurements in water showed that the linear swelling ratio of the resulting hydrogels increases with increasing gel preparation concentration. The swelling ratio of PDMAEMA hydrogels crosslinked with BAAm is larger than those for hydrogels crosslinked with TEGMA over the entire range of the polymer network concentration. The hydrogels exhibit very sharp pH-sensitive phase transition in a very narrow range of pH between 7.7 and 8.0. From the mechanical measurements, it was also found that the linear swelling ratio of resulting hydrogels depends on the crosslinking density and also the type of the crosslinker used in the preparation. The resulting hydrogels are thought to be good candidates for pH-sensitive drug delivery systems. POLYM. ENG. SCI. 2013. © 2012 Society of Plastics Engineers

Modification of polyamide reverse osmosis membranes seeking for better resistance to oxidizing agents

One of the major limitations in the use of commercial aromatic polyamide thin film composite (TFC) reverse osmosis (RO) membranes is to maintain high performance over a long period of operation, due to the sensitivity of polyamide (PA) skin layer to oxidizing agents, such as chlorine, even at very low concentrations in feed water. This article reports surface modification of a commercial TFC RO membrane (BW30-Dow Filmtec) by covering it with a thin film of poly(vinyl alcohol) (PVA) crosslinked with glutaraldehyde (GA) to improve its resistance to chlorine. Crosslinking reaction was carried out at 25 and <TEX>$40^{\circ}C$</TEX> by using PVA 1.0 wt.% solutions at different GA/PVA mass ratio, namely 0.0022, 0.0043 and 0.013. Water swelling measurements indicated a maximum crosslinking density for PVA films prepared at <TEX>$40^{\circ}C$</TEX> and GA/PVA 0.0043. ATR-FTIR and TGA analysis confirmed the reaction between GA and PVA. SEM images of the original and modified membranes were used to evaluate the surface coating. Chlorine resistance of original and modified membranes was evaluated by exposing it to an oxidant solution (NaClO 300 mg/L, NaCl 2,000 mg/L, pH 9.5) and measuring water permeability and salt rejection during more than 100 h period. The surface modification effectively was demonstrated by increasing the chlorine resistance of PA commercial membrane from 1,000 ppm.h to more than 15.000 ppm.h.

γ‐Radiation‐induced graft copolymerization of acrylic acid onto poly(ethylene terephthalate) films: A study by thermal analysis

AbstractThe grafting of acrylic acid onto poly(ethylene terephthalate) films with γ radiation was carried out. The effects of different parameters, such as the monomer concentration, inhibitor concentration, and irradiation dose, on the grafting yield were investigated. The grafting yield depended on these parameters, and its maximum value was obtained at a 1.5% inhibitor concentration and a 40% monomer concentration. The obtained grafting films were characterized with water swelling measurements, differential scanning calorimetry, and thermogravimetric analysis. The results of differential scanning calorimetry showed decreases in the heat capacity step and the glass‐transition temperature with increasing grafting yield. The ability of poly(ethylene terephthalate) to crystallize and the size of the crystalline domains were affected by the grafting. The grafted poly(ethylene terephthalate) that was obtained was tested as an ion exchanger for copper, nickel, cobalt, and lead. The capacity of the grafted films for ion recovery was dependent on the grafting yield. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 198–203, 2006

Grafting of silica during the processing of silica‐filled SBR: Comparison between length and content of the silane

AbstractThe treatment of nanoscopic silica grafted in the blend during the processing of silica‐filled styrene butadiene rubber was performed with silane, introduced at different concentrations, or at a constant concentration with a given length of alkyl chain. From swelling measurements in water and in solvent, the maximum silane content that can be grafted has been calculated as a function of the length of the silane alkyl chains as well as their efficiency to cover the silica surface. The found values are close to the values found in the literature for grafting in solution. Moreover, a direct correspondence between the length of the silane alkyl chains and their concentration has been deduced. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 143–152, 2006

Alginic acid–silica hydrogel coatings for the protection of osmotic distillation membranes against wet-out by surface-active agents

The formulation of organic–inorganic polymer composites can be used to enhance selected properties, such as susceptibility to microbial attack, thermal stability, mechanical strength and water sorption capability. Accordingly, a series of alginic acid–silica hydrogel films was prepared for testing as protective coating materials for PTFE osmotic distillation membranes. Unprotected hydrophobic membranes are subject to wet-out when contacted by surface-active agents, such as oils and detergents. Films containing 5, 10, 15 and 20 wt.% silica, with and without the addition of glycerol for plasticisation, moisturisation and silica dispersion, were characterised using scanning electron microscopy, X-ray diffraction, differential scanning calorimetry, mechanical strength measurements, and water-swelling measurements. Composites prepared with glycerol addition had better thermal stability, mechanical strength and water sorption capability than those prepared without glycerol addition. Uncoated membranes and membranes coated with composites prepared with glycerol addition were tested for OD performance and resistance to surface-active agents using pure water, orange oil (limonene)–water mixtures, and sodium dodecylbenzene sulfonate detergent solutions. Uncoated membranes showed immediate hydrophobicity loss in the presence of orange oil and detergent. For coated membranes, no wet-out occurred over the 15 h duration of three consecutive 5 h OD trials using orange oil–water mixtures. In the case of detergent solutions, the coating afforded protection to the membrane for 4–5 h. In a separate trial, no wet-out occurred when the coated side of the membrane was placed in contact with 1.2 wt.% orange oil for 72 h.

Physically Cross-Linked Alkylacrylamide Hydrogels: Phase Behavior and Microstructure

The volume phase transition and the microstructure of physically cross-linked hydrogels composed of either N,N-dimethylacrylamide (DMA) or N-isopropylacrylamide (NIPA) and 2-(N-ethylfluorooctanesulfonamido)ethyl acrylate, FOSA, were studied using differential scanning calorimetry (DSC), water swelling measurements (WS), and small-angle X-ray scattering (SAXS). DSC and WS measurements showed that FOSA/NIPA gels exhibited a volume phase transition (VPT) but that the FOSA/DMA gels did not. The temperature of the VPT (TVPT) for the FOSA/NIPA gels was lower than that for the covalent NIPA gel, and TVPT decreased and the transition broadened with increasing FOSA concentration. A peak in the SAXS structure factor indicated that the hydrophobic interactions promoted nanophase separation in both gelsin the dry and hydrated states.

Swelling kinetics of poly(N‐vinylimidazole‐co‐sodium styrenesulfonate) hydrogels

AbstractHydrogels of N‐vinylimidazole and sodium styrenesulfonate were synthesized by radical crosslinking copolymerization. Transient swelling measurements in water, at room temperature, reveal an unusual behavior. For some gel compositions, the swelling time dependency is about a δ function: dry hydrogel pellets swell up readily to reach a high degree of swelling and, spontaneously, they deswell to collapse. Such peculiarity was interpreted in terms of several competing events in the swelling mechanism: water diffusion toward the gel, chain disentanglement, sodium–proton interchange through the gel–external bath boundary, approaching of chains to allow interaction of sulfonate groups with neighboring protonated imidazole moieties and diffusion of water outside the gel. The results of cyclic swelling–deswelling following abrupt changes of composition in the external bath, from water to sodium hydroxide solution, support that mechanism. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 191–200, 2002

Gamma radiation induced graft copolymerization of acrylamide onto poly(vinyl chloride) films

Grafting of acrylamide (AAm) onto poly(vinyl chloride) (PVC) films using gamma radiation has been carried out. The effects of different parameters on the graft yield have been investigated. These parameters include radiation dose, monomer concentration, solvent composition, types of inhibitors and acidity of the medium. In addition, the effects of the multifunctional monomers N,N′-methylene allyl amide (MAAm) and 2,4,6-triallyloxy-1,3,5 triazine (TARA) on the graft yield have been investigated. It has been found that methanol/water mixture in the ratio (1:1) is the proper diluent mixture for enhancing the graft copolymerization process. The presence of sulphuric acid in the reaction medium adversely affects the graft yield more than acetic acid. The presence of MAAm in the reaction medium markedly increases the graft yield, while TARA has practically no effect on the grafting process. Grafted films have been characterized and evidence of grafting has been obtained using thermal and spectroscopic analysis together with swelling measurements in water. © 1998 SCI.

Gamma radiation induced graft copolymerization of acrylamide onto poly(vinyl chloride) films

Grafting of acrylamide (AAm) onto poly(vinyl chloride) (PVC) films using gamma radiation has been carried out. The effects of different parameters on the graft yield have been investigated. These parameters include radiation dose, monomer concentration, solvent composition, types of inhibitors and acidity of the medium. In addition, the effects of the multifunctional monomers N,N′-methylene allyl amide (MAAm) and 2,4,6-triallyloxy-1,3,5 triazine (TARA) on the graft yield have been investigated. It has been found that methanol/water mixture in the ratio (1:1) is the proper diluent mixture for enhancing the graft copolymerization process. The presence of sulphuric acid in the reaction medium adversely affects the graft yield more than acetic acid. The presence of MAAm in the reaction medium markedly increases the graft yield, while TARA has practically no effect on the grafting process. Grafted films have been characterized and evidence of grafting has been obtained using thermal and spectroscopic analysis together with swelling measurements in water. © 1998 SCI.

Photopolymerization of poly(tetramethylene ether) glycol diacrylates and properties of the obtained networks

Abstract A series of poly(tetramethylene ether) glycol α,ω-diacrylates have been prepared from the corresponding hydroxy-terminated oligomers. The acrylation reaction, performed with acrylic acid in the presence of p -toluenesulfonic acid as a catalyst, allowed us to obtain oligomers with M n in the range 250–2000 and an acrylic functionality close to 2. The M n of the acrylated product was always lower than that of the starting oligomer, suggesting the occurrence of degradation reactions. These were attributed to an acidic hydrolytic attack on the oligomer chain. The oligomers were subjected to an ultra-violet light promoted curing process as thin films on glass substrates under N 2 atmosphere. Complete acrylic double-bond conversion was obtained in all cases, with the exception of the oligomer with the lowest molecular weight. The thermal and mechanical properties of the networks were investigated by means of differential scanning calorimetry, thermomechanical analysis and dynamic mechanical thermal analysis (d.m.t.a.). Amorphous and rubbery materials were obtained with the exception of those from the oligomers of the highest molecular weight, which showed partial crystallinity. By means of thermal analysis and d.m.t.a., T g values were measured and correlated to the molecular weights of the oligomers used. In particular, the T g values, as a function of the crosslinking density, agreed with those calculated by the Nielsen equation. Moreover, equilibrium swelling measurements in water were performed. The results obtained are discussed on the basis of Flory's theory and interpreted in terms of the solubility parameters and the crosslinking densities of the networks.

Cytarabine release from α,β-poly( N-hydroxyethyl)- dl-aspartamide matrices cross-linked through γ-radiation

α,β-poly( N-hydroxyethyl)- dl-aspartamide solutions were cross-linked through γ-radiation and the systems obtained were tested as matrices for drug sustained release, using cytarabine as model drug. We performed the characterization of the cross-linked polymer, both drug-loaded and unloaded, through water swelling measurements, scanning electron microscopy and X-ray analysis. Finally, we investigated the in vitro release behaviour of cytarabine.

Synthesis and characterization of new amphiphilic polyurethane compositions

New segmented polyurethanes containing in the chain extender molecule (dihydroxyethyl- n-hexadecylamine, DHHA) both a hydrophobic long alkyl group and a tertiary ammonium group (whose polarity was further increased by quaternization reaction), are described. In order to evaluate the influence of the chain extender content on the polymer properties, also polymers containing DHHA and 1,4 butanediol at different molar ratios have been prepared. The obtained polymers were characterized by i.r., NMR, DSC, viscometry and water swelling measurements.