Gel Fraction Value Research Articles

Bioinspired H-bond cross-linking of nanostructured gelatine by inorganic goethite α-FeOOH

This paper reports the effect of goethite nanowire filler on hydrogen (H) linking in gelatine. Nanostructured gelatine that would otherwise be soluble becomes insoluble in water at room temperature if goethite nanowire filler is added. The experimental results reveal a significant increase in the gel fraction of the composite with 6 vol% α-iron (III) oxide-hydroxide (α-FeOOH) additive, reaching over 73% after being kept in water, compared with that of pristine gelatine, with a mere 13% gel fraction. In the presented composite, the solubility of gelatine can also be controlled by visible light, as absorption in the narrow-band-gap α-iron (III) oxide-hydroxide results in local heating of nanowires. The illuminated 6 vol% α-iron (III) oxide-hydroxide/gelatine composite shows a gel fraction of 13.4%, while the control sample kept in the dark exhibits a high gel fraction value of 73.8%. The observed remotely switchable disintegration of gelatine by visible light presents a feature that can be used in designing temporary tissue engineering and drug delivery substrates.

Alternative Polysaccharide Wound Dressing from Heat-Moisture Starch/Basil Seed (O. Basilicum L.) Mucilage with Incorporated Glycolic Acid Antimicrobial Agent

In order to improve the behavior in water and the mechanical properties of heat-moisture treated starch, natural basil seed mucilage with high hydrophilicity and crystallinity was incorporated for wound dressing application. In addition, succinic acid cross-linking was used to enhance the durability of the material in water and glycolic acid was utilized as an antimicrobial agent. The effectiveness of the cross-linking process could be observed from the significant increase in dimensional stability from higher gel fraction value and increment of mechanical properties. Furthermore, the incorporation of glycolic acid into the wound dressing films demonstrated antibacterial efficacy, resulting in 100% bacterial reduction against S. aureus and E. coli strains. These films exhibited low cytotoxicity toward human epidermal keratinocytes (HaCaT) cells, indicating their potential for biomedical applications. Moreover, functional group analysis, crystallinity, morphology, thermal properties, gel fraction, water vapor transmission rate, free swell absorption, and mechanical properties were also examined.

COMPARISON OF BRACKET WATER DESALINATION TESTS IN THE FORM OF POWDER, GRANULES AND GREEN ALGAE HYDROGEL

This research was motivated by the problem of lack of clean water around the coast of Rainbow Beach in Karawang because the water quality is poor and still brackish. Untreated brackish water poses a risk to human health if drunk for a long time and can trigger skin diseases if used for bathing. The well water taken is located in the Pelangi Coastal Area, Pedes Karawang. This research aims to test the ability of brackish water desalination using powder, granules, and three variations of green algae hydrogel. This research uses a quasi-experimental method by comparing it with zeolite as a standard for brackish water desalination. The research results show that the resulting hydrogel preparation has a solid, brittle shape, a dark green color, and a distinctive odor of green algae. The best viscosity value is in the H4 formula. All green algae hydrogel formulas have good pH values, while the best swelling ratio value is in the H2 formula, and the best gel fraction value is in the H4 formula. From the results of the research that has been carried out, it can be concluded that the hydrogel, granule, and green algae powder preparations can desalinate brackish water based on the results of pH, temperature, salinity, sodium ion, and magnesium ion tests compared with zeolite, where the 6 g hydrogel preparation shows the best desalination capability of brackish water at the three well sample points

Superabsorbent Hydrogel from Cassava Waste Pulp – Acrylamide – Acrylic Acid to Increase Water Holding Capacity in Sandy Soils

In this investigation, a superabsorbent hydrogel was produced from cassava waste pulp (CWP) and acrylic acid (AA) – acrylamide (AAm) in a ratio of 2:1.5:1 (CWP:AA:AAm) by grafting and crosslinking methods. The grafting procedure is initiated with ammonium persulfate (APS) at a concentration of 1%. In this study, cross-linked structures were produced using several concentrations of methylene bisacrylamide (MBA) (0%, 0.5%, 1%, and 1.5%). The impact of MBA concentration on the properties of the superabsorbent hydrogel was observed. The parameters investigated in this study included the equilibrium degree of swelling (EDS), grafting degree, gel fraction, and swelling kinetics (comprising the swelling exponent, swelling constant, and diffusion coefficient). Following this, the hydrogels were sprinkled into sandy soil with the purpose of examining the effects of hydrogel incorporation on the soil’s water holding capacity. The sample with a concentration of 0.5% MBA yielded the highest EDS at 9178% (g/g), as determined by the results. The gel fraction value obtained for the sample was 81.04% (g/g) and the crosslink density of this sample was measured to be 2.78 × 1023 m-3, while the maximal water holding capacity was found to be 54.16%.

Preparation and Characterization of PVA/Na-CMC Hydrogel from OPEFB Cross-Linked by Maleic Anhydride

PVA/Na-CMC hydrogels were prepared from polyvinyl alcohol (PVA) and Na-CMC isolated from OPEFB. Maleic anhydrous (MA) was introduced as a crosslinking agent during the formation of the hydrogel process. The characterization of the PVA/Na-CMC hydrogels was carried out using Fourier Transform Infrared (FTIR), Scanning Electron Microscope (SEM), and physical characterization methods, including swelling ratio and gel fraction analysis. The addition of MA was observed to increase the number of crosslinks. The optimum PVA/Na-CMC hydrogel composition was achieved at a PVA: Na-CMC ratio of 5:3 (P5C3M), with a pore size of approximately 3.643 ± 0,913 μm, a swelling ratio of 3104%, and a gel fraction value of 72.72%.

Study of the carbamate/aldehyde reaction, a new pathway towards NIPU materials

An innovative alternative to the synthesis of non-isocyanate polyurethanes (NIPUs) thermoset materials was thoroughly investigated. This pathway, involving the reaction between primary carbamate functions and aldehyde functions, was studied using model reactions between ethyl carbamate and different aldehydes that lead to the highlights of the key parameters as well as the first reported proposed mechanism for this reaction. In a second time, polycarbamates synthesized from two different polyols were synthesized via transcarbamoylation before participating in a polycondensation reaction with different monoaldehydes. First a linear NIPU oligomer was synthesized using a dicarbamate derived from ethylene glycol and benzaldehyde. This product was analysed by NMR spectroscopy and MALDI-TOF mass spectrometry. This oligomer exhibited low molar masses attributed to many secondary termination reactions, mainly due to the presence of acetic anhydride used as solvent in the reaction. Cross-linked NIPU materials were then synthesized without solvent, from the reaction between a tricarbamate derived from trimethylol propane and vanillin, a biobased monoaldehyde, for the first time. The process parameters for the synthesis of these materials were optimized to obtain biobased NIPU thermosetting networks with gel fraction (GF) in dimethylsulfoxide (DMSO) up to 82%, with Tg values ranging between 39 °C and 65 °C depending on the GF value. This study brings a much needed highlight on the little-known carbamate/aldehyde reaction and demonstrates its potential for the synthesis of novel biobased NIPU thermosetting coatings using a simple monoaldehyde such as vanillin.

The Effect of Variation of Raw Material Ratio on Hydrogel Based on K-Carrageean - Acrylamide as a Carrier of Ammonium Nitrate Fertilizer

Hydrogels based on natural polymers such as carrageenan are currently being developed to improve efficiency in agriculture. By enriching hydrogels with fertilizers, they will be released slowly into the soil. Enrichment of fertilizers on carrageenan-based hydrogels was carried out and analyzed with the response of swelling ability, gel fraction value of grafting degree, to the hydrogel's ability to release the fertilizer trapped in it. Carrageenan is used because its use as a natural polymer has not been widely explored, especially in the non-food sector. The results showed that the average swelling value of carrageenan-based hydrogel to ammonium nitrate solution ranged from 750.00% - 1,633.33%. The gel fraction values obtained ranged from 74.06% to 87.51%, and the degree of grafting ranged from 85.33% to 93.59%. These values indicate a relatively high degree of tissue density and grafting of acrylamide monomer on carrageenan, which means that the carrageenan:AAm based hydrogel has strong mechanical properties. The ability to release ammonium nitrate samples from the hydrogel carrageenan-based has a value ranging from 8.86% to 44.92% in five days of observation. Interpretation of the test results, the best ratio of carrageenan:AAm is 1:1, due to its relatively low release value but still has good swelling and mechanical properties.Keywords: Hydrogel; Carrageenan; Acrilamyde; Fertilizer release

Formation and properties of cross-linked polymer films based on biocompatible polymers

Cross-linked polymer films based on polyvinyl alcohol and polyacrylamide have been prepared via radical cross-linking initiated by peroxide containing reactive copolymers. The influence of temperature, nature and concentration of cross-linking agents onto gel-fraction value and properties of polymer films has been studied. Obtained cross-linked polymer films are characterized by improved physico-mechanical properties that depend on the content of peroxide containing copolymer and on the presence of additional cross-linking agent.

Free Volume Effect via Various Chemical Structured Monomers on Adhesion Property and Relative Permittivity in Acrylic Pressure Sensitive Adhesives.

Acrylic pressure-sensitive adhesives (PSAs) are used as fixatives between layers of a display. PSAs’ function is an important factor that determines the performance of the display. Of the various display types available, the touch screen panel (TSP) of smart devices is firmly related to the relative permittivity of the elementals. Therefore, adjusting the relative permittivity of the PSA is indispensable for driving the TSP. Accordingly, selected acrylic pre-polymers were polymerized and the pre-polymer was blended and cross-linked with monomers with different chemical structure to adjust the relative permittivity. The monomers were hexametyldisiloxane (HMDS), N-vinylcaprolactam (NVC), tert-butyl acrylate (TBA), and isooctadecyl acrylate (ISTA). The gel fraction and transmittance as a function of the monomers show a similar result to the pure acrylic PSA. However, the gel fraction value decreased to about 90% and the transmittance decreased to about 85%, due to the immiscibility between nonpolar HMDS and acrylic PSA. On the other hand, the adhesion properties were improved when NVC was added because of the polarity of the nitrogen group. In addition, the relative permittivity of the PSA decreased regardless of the monomer chosen. There was, however, a difference in the optimal content of each monomer, and NVC decreased from 4 phr content to about 3.4 in reducing relative permittivity. Through the above results, it was confirmed that NVC having a nitrogen group is most advantageous in lowering adhesion properties and relative permittivity, and necessitates further research based on the findings.

Freeze-thawed humic acid/polyvinyl alcohol supramolecular hydrogels

Novel supramolecular hydrogels were prepared on the basis of polyvinyl alcohol loaded with different amounts of humic acid nanoparticles via a freezing-thawing method. The results showed the humic acid nanoparticles act as functional sites to aggregate the polyvinyl alcohol chains and result in the formation of three-dimensional supramolecular networks. It was shown that the humic acid nanoparticles can interact with the polyvinyl alcohol chains and interconnect the polymeric chains as functional crosslinkers. The results showed up to 3.4 % increase in the gel fraction value of polyvinyl alcohol hydrogel by incorporating humic acid nanoparticles. In addition, 2.5 and 5.7 °C increases in the glass transition temperature and the melting point of polyvinyl alcohol hydrogel were observed by incorporating 9 wt.% of humic acid, respectively. By incorporating the mentioned level of humic acid, up to 87 and 26 % increases were observed in the storage modulus at glassy state and crystallinity of polyvinyl alcohol hydrogel.

The Effectiveness of UV-LED Photopolymerisation over Conventional UV-Mercury for Polyurethane Acrylate Coating

This paper presents the effect of UV-LED and UV-mercury as the light source toward curing behaviour of urethane acrylate coating. The UV-curable coating was prepared based on aliphatic urethane acrylate oligomer, 2-ethylhexyl acrylate (2-EHA), methyl methacrylate (MMA), trimethylolpropane triacrylate (TMPTA), and commercial photoinitiator. The effect of irradiation time on curing behaviour was investigated using Fourier Transform Infra-Red (FTIR) and the percentage of C=C conversion was calculated. From the ATR-FTIR spectra, the C=C absorption peak at 810 cm-1 and 1635 cm-1 was found to be decreased after UV irradiation, indicated the proceeding of the polymerisation reaction. In term of C=C conversion, UV-LED irradiation showed better results with 97-99% than UV-mercury irradiation which is 86-96%. It was also observed that the tackiness of the coating reduced via UV-LED irradiation, suggesting higher conversion of monomers. Gel fraction of the coating also measured and higher gel fraction values, > 98% in this study was associated with higher cross-linking density. The results of this study depicted that UV-LED is a viable alternative to replace UV-mercury-based lamp in the coating industry.

Hydrogels based on oxidized starches from different botanical sources for release of fertilizers

Herein, hydrogels based on starch from corn, sweet cassava and bitter cassava were prepared by a straightforward approach. The hydrogels were obtained by an oxidation process using the redox system KMnO4/NaHSO3 which leads to the formation of carbonyl and carboxyl groups with minimum polymer hydrolysis. The resulting oxidized samples as well as the native starches were extensively characterized by scanning electron microscopy, thermogravimetric analysis and wide angle X-ray scattering, among others. High gel fraction values and low degree of crystallinity were obtained in all the cases, which values vary slightly depending on the botanical source. High swelling capacity was observed for all the samples, which behave as hydrogels. The influence of the ionic strength and pH in the swelling capacity of the oxidized starches was also studied. The samples exhibit an anti-polyelectrolyte behavior and the water uptake increases at basic pH as the carboxylic groups become ionized. The hydrogels were also loaded with urea, potassium nitrate and ammonium sulfate as model fertilizers and their potential for controlled release was investigated.

Synthesis and characterization of eco-friendly carboxymethyl cellulose based carbon foam using electron beam irradiation

Abstract Carbon foams were prepared by carbonization process without additional stabilization process after manufacturing carboxymethyl cellulose (CMC) composites using a facile electron beam irradiation (EBI) method. A gel fractionation technique was used to study cross-linking degree of infusible structure in the produced CMC composite materials. We observed an increase in cross-linking with increasing CA concentration and EBI doses between 20 kGy and 80 kGy. The CMC composite prepared using 4 wt% CA and 80 kGy EBI represents the highest gel fraction value of ∼98%, showing the highest carbon yields and compressive strength due to the increase of cross-linked parts in carbon foam obtained from these CMC composites, which lowers break defects after carbonization. In addition, available surface area was estimated via Brunauer-Emmett-Teller analysis of the carbon foam samples. The carbon foam produced from the CMC composite treated with 4 wt% CA via 80 kGy resulted in highest specific surface area of 372.06 m2/g and adsorption pore size of 2.20 nm indicating greater interaction between gas and the carbon atoms.

Wood Sawdust/Natural Rubber Ecocomposites Cross-Linked by Electron Beam Irradiation.

The obtaining and characterization of some polymeric eco-composites based on wood sawdust and natural rubber is presented. The natural rubber was cross-linked using the electron beam irradiation. The irradiation doses were of 75, 150, 300 and 600 kGy and the concentrations of wood sawdust were of 10 and 20 phr, respectively. As a result of wood sawdust adding, the physical and mechanical properties such as hardness, modulus at 100% elongation and tensile strength, showed significant improvements. The presence of wood sawdust fibers has a reinforcing effect on natural rubber, similar or better than of mineral fillers. An increase in the irradiation dose leads to the increasing of cross-link density, which is reflected in the improvement of hardness, modulus at 100% elongation and tensile strength of blends. The cross-linking rates, appreciated using the Flory-Rehner equation, have increased with the amount of wood sawdust in blends and with the irradiation dose. Even if the gel fraction values have varied irregularly with the amount of wood sawdust and irradiation dose it was over 90% for all blends, except for the samples without wood sawdust irradiated with 75 kGy. The water uptake increased with increasing of fiber content and decreased with the irradiation dose.

Polymeric composites based on natural rubber and hemp fibers

The purpose of this work is to present the results of preparing a polymeric composite with enhanced properties based on natural rubber and hemp. Amounts of 10 and 20 phr hemp were used to obtain the composites. The samples have been processed by sulfur vulcanization and characterized by several methods. The mechanical characteristics, gel fraction, cross-link density, rubber-fiber interactions and water uptake have been investigated depending on the hemp content. Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) techniques were also employed for characterization. The values of hardness, tensile strength and tearing strength have increased with the fiber content increasing due to the interaction between the fibers and natural rubber. Also, good adhesion between hemp fibers and rubber matrix was observed in SEM micrographs. The gel fraction value was over 95 % for all composites and increased with the increasing of hemp content. The cross-link density was determined on the basis of equilibrium solvent-swelling measurements applying the modified Flory–Rehner equation. It was observed that cross-linking density of composites increased slightly with the increase of amount of hemp but still was lower than that of the natural rubber without hemp. The extent of interaction between rubber and fiber was determined using the Kraus equation. Results of water absorption tests showed that water uptake increased with the increase of fiber content and temperature. The physical and chemical investigations have shown the reinforcing effect of hemp on sulfur vulcanized natural rubber, as well.

Role of electron beam irradiation on superabsorbent behaviors of carboxymethyl cellulose

Superabsorbent materials derived from synthetic polymers can cause various environmental problems. In this study, eco-friendly superabsorbent materials were prepared from a mixture of carboxymethyl cellulose (CMC) as a raw material and different concentrations of citric acid (CA) as a crosslinking agent through electron beam irradiation (EBI). The results showed that the CMC/2 wt% CA and CMC/4 wt% CA samples obtained using 20-kGy EBI showed the highest gel fraction value of over 95 % and the highest swelling degree of around 7,000 %. In addition, the water retention of the swollen CMC/2 wt% CA gel decreased steadily to around 63 % of the initial absorbed water during a period of 7 h, and then remained at around 60 %.

Effects of benzoyl peroxide on some properties of composites based on hemp and natural rubber

The obtaining and characterization of polymer composites based on natural rubber and hemp, in which the elastomer crosslinking has been achieved with benzoyl peroxide, are presented. The mechanical characteristics, gel fraction, crosslink density, water uptake swelling parameters and FTIR of the composites based on natural rubber and hemp fiber vulcanized by dibenzoyl peroxide have been investigated as a function of the hemp content. The hardness, modulus at 100 % elongation, tearing strength, tensile strength and elongation at break have been improving with the increasing of fiber content in composites materials due to the better interaction of fiber in natural rubber composites. These results indicate that hemp has a reinforcing effect on natural rubber. Gel fraction value is over 95 % for all blends and varies irregularly depending on the amount of hemp in the composites. The crosslinking density (ν) of samples increases as the amount of hemp in blends increases, because hemp act as a filler in natural rubber blends and leads to reinforcement of the blends. The water uptake and swelling parameters also increases with the increasing of the amount of fiber content, because of the hemp hydrophilic characteristics.

Mineral kaolinite clay for preparation of nanocomposite hydrogels

AbstractIn this work, nanocomposite hydrogels on the basis of polyvinyl alcohol and mineral kaolinite clay were prepared via freezing–thawing cyclic method without using any chemical crosslinkers as well as any intercalants for modification of kaolinite. The nanocomposite hydrogels were characterized by XRD, TEM, SEM, and FTIR methods. The effect of kaolinite content on the gel fraction values of nanocomposite hydrogels was investigated. Thermal and mechanical properties of prepared nanocomposite hydrogels were also studied using the DSC, DMTA, and hardness tests. Finally, the swelling and dehydration kinetics of nanocomposite hydrogels were studied at different temperatures. The morphology of prepared nanocomposite hydrogels was determined as intercalated morphology on the basis of XRD and TEM techniques. The role of kaolinite in the creation of supramolecular crosslinked network of polyvinyl alcohol was exhibited by FTIR and gel fraction tests. The thermal and mechanical experiments showed the reinforcing effect of kaolinite in the polyvinyl alcohol matrix. Swelling and dehydration tests showed that an increase of kaolinite content causes a decrease in the swelling ratio as well as in the dehydration rate of nanocomposite hydrogels. On the other hand, direct dependences of the swelling ratio and dehydration rate to the temperature were observed for all nanocomposite hydrogels. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Dehydration kinetics of polyvinyl alcohol nanocomposite hydrogels containing Na-montmorillonite nanoclay

A series of freeze-thawed, polyvinyl alcohol nanocomposite hydrogels were prepared using various loading levels (0–15 wt%) of hydrophilic natural Na-montmorillonite nanoclay. The morphology of nanocomposite hydrogels, their dehydration kinetics at different temperatures and the effect of Na-montmorillonite on the gelation process were investigated. The results showed a partially exfoliated morphology for the prepared nanocomposite hydrogels. Also by increasing the amount of nanoclay incorporated into the specimens, the gel fraction values of nanocomposite hydrogels were increased. According to the dehydration tests, the dehydration rates of nanocomposite hydrogels exhibited an inverse dependency on the nanoclay loading level and a direct dependency on the dehydration temperature. Finally, it was concluded that the dehydration mechanism of all specimens prepared is non-Fickian at 20 °C, while it is Fickian at 37 °C and 55 °C.

Investigation of radiation‐crosslinked foam of LDPE/EVA blends

Low-density polyethylene/ethylene–vinyl acetate copolymer (LDPE/EVA) blend was irradiated by γ-ray and then expanded by heat as a foamed material. The EVA content in the LDPE/EVA blend was benefited to form a gel. The gel fraction values of LDPE/EVA blend with 30% EVA content were higher than those of other blends in a same given dose; its gel fraction value was 1.7 times as those values of the LDPE without EVA. The gel fractions of the LDPE/EVA blend were increased with radiation dose in oxygen, in air, and in nitrogen, and the formation of gel was limited by oxygen. The oxidation products of the foam of the LDPE/EVA blend were observed in nitrogen, in oxygen by Fourier transform IR spectra. The LDPE/EVA blend system has no protection effect from oxidation in comparison with the LDPE system without EVA, which has less oxidation product than those without EVA in a same given gel fraction. The gel fraction of the LDPE/EVA blend around 25–35%, radiation dose 25±5 kGy, irradiated by γ-ray in air or in nitrogen, with higher expansion ratio (19), smaller cell diameter (0.175 mm), lower apparent density (0.042 g/cm3), higher tensile strength (0.40 MPa), and longer elongation at break (290–360%) foam of the LDPE/EVA blend were selected. These were optimum condition for application in this system. The relations among gel fraction of the LDPE/EVA blend, expansion ratio, apparent density, average cell diameter, and mechanical properties of the foam were discussed. © 1996 John Wiley & Sons, Inc.