• Macromolecular Research
• /
• v.16 no.1
• /
• pp.45-50
• /
• 2008

This study examined the swelling behavior and in vitro release of a model drug, tetracycline-HCl, from alginate and alginate-polyaspartate (Alg-PASP) composite gel beads. The alginate and Alg-PASP composite beads were prepared using an ionic crosslinking method with aqueous $Ca^{2+}$. Their microporous morphology was observed by scanning electron microscopy. The swelling ratio of the beads in different media varied according to their composition, cross-linking density ($Ca^{2+}$ concentration), and pH of the aqueous medium. The in vitro release experiment of the tetracycline-HCl encapsulated beads in different media suggests that the release of the drug is governed mainly by the swelling properties of the polymer network. The presence of PASP was found to significantly influence the swelling properties and drug release profile.

• Elastomers and Composites
• /
• v.53 no.2
• /
• pp.48-51
• /
• 2018

10, 20, 30, and 40% of polyvinyl chloride (PVC) were added to nitrile butadiene rubber (NBR) to modify the latter. The NBR/PVC composites containing pure NBR were synthesized to investigate properties, such as crosslinking density, hardness, tensile strength, abrasion resistance, heat resistance, solvent resistance, and filler dispersion. The experimental result revealed a decrease in crosslinking density and heat resistance with increase in the PVC content. In contrast, addition of PVC to NBR resulted in enhancement of hardness, tensile strength, solvent resistance, and filler dispersion.

• Polymer(Korea)
• /
• v.31 no.5
• /
• pp.410-416
• /
• 2007

Monodisperse polymer particles were prepared via one- step seeded polymerization using PMMA as seed particles, and HDDA, triEGDMA or EGDMA as crosslinking monomer. For the study, the effects of 1) the ratio of the absorbed monomer to the seed polymer particles (swelling ratio), 2) the characteristics of crosslinking monomer, 3) electroless Ni plating, and 4) electroless Au Plating on the variation of mechanical properties of polymer particles, such as recovery rate, K-values, breaking strength and breaking displacement were investigated by using MCT (micro compression test). It was observed that swelling ratio of polymer particles influenced only on breaking strength of polymer Particles, while electroless plating did on recovery rate, K-values ($K_{10}\;and\;K_{20}$) and breaking strength of electroless plated polymer particles. However, breaking displacement and K-values ($K_{30}{\sim}K_{50}$) were more or less insensitive to electroless plating.

• Applied Chemistry for Engineering
• /
• v.10 no.3
• /
• pp.419-426
• /
• 1999

In this study, the reaction rate constant, activation energy, total crosslinking density, elastic constant, cure properties ($t_5,\;t_{90}$), modulus, and abrasion resistance of rubber compounds were investigated as a function of cure temperatures, cure systems and reinforcing filler loadings. Reaction rate constants showed strong dependence on thc carbon black loading, cure temperature and cure system, and increased sharply with increasing the reaction temperatures. The lowest activation energy was obtained in the efficient cure (EC) system which corresponds to the high level of sulfur to accelerator ratio, and the activation energy was decreased with decreasing the carbon black loadings. The change of carbon black loadings directly affects the modulus and abrasion resistance, but the change of cure system showed various effects on the rubber compounds. Increased carbon black loadings showed the high modulus, improved abrasion resistance and short scorch time but decrease in crosslinking density and elastic constant. Higher crosslinking density and elastic constant were shown in the EC cure system regardless of carbon black loadings, but scorch timc ($t_5$) was not affected by the change of the ratio of sulfur to accelerator. Rapid optimum cure time ($t_{90}$) were showen in the EC cure system. Also, the equivalent cure curve coefficient of rubber compound was 0.96 for conventional cure (CC) system, and 0.94 for semi-efficient cure (SEC) and EC system regardless carbon black loadings. As regarding the abrasion resistance, wear volume showed the logarithmic increase for the loaded weight.

• Elastomers and Composites
• /
• v.35 no.2
• /
• pp.106-114
• /
• 2000

The foam of ethylene vinyl acetate (EVA)/styrene-vinyl isoprene-styrene triblock copolymer(SVIS) blend was prepared to improve the shock-absorption and compression set characteristics at room temperature. The effects of blowing agent and blend ratio of EVA/SVIS on expansion ratio, cell structure and mechanical properties of the foam were investigated. As the SVIS content increased, the viscosity of blends was increased but the crosslinking rate was slow down, the expansion ratio was decreased. and the specific gravity was increased. At room temperature, the resilience was not affected by increasing the amount of blowing agent. The value of tan ${\delta}$ was increased by increasing the amount of SVIS. As a result, the value of compression set was decreased. This is due to the increased values of specific gravity and crosslinking density of the EVA/SVIS foam.

• Polymer(Korea)
• /
• v.27 no.3
• /
• pp.195-200
• /
• 2003

Alginate is a natural ionic polymer including numerous anionic groups and can be actuated by the ionic group under the electric field. The crosslinked alginate films were fabricated with CaCl$_2$. The thermal, mechanical and electroresponse properties of the films were investigated by thermogravimetric analysis, tensile and bending tests. The initial degradation and tensile strength increased according to the degree of crosslinking. Also, the swelling ratio of the films increased with decreasing degree of crosslinking and increasing pH due to free volume and electrostatic repulsion. The films actuated by an electric stimulus exhibited gentle and flexible action like a pendulum. In the electric field, the electric stimuli such as the applied voltage, ionic strength and kind of electrolyte solution had an effect on the electroresponse of the films. Alginate films with 5 wt% crosslinking agent showed the highest bending angle and reversible bending behavior. When the ionic strength of NaCl and KCl electrolyte solution was 0.1 M, the films showed the highest electroresponse. The bending behavior of the films increased with the applied voltage.

• Elastomers and Composites
• /
• v.47 no.1
• /
• pp.75-81
• /
• 2012

Acrylic rubber was synthesized using ethyl acrylate. butyl acrylate, methoxyethyl acrylate as main monomers and glycidyl methacrylate as cure site monomer by emulsion polymerization. Rubber compound was made by adding 2,2-bis[4-(4-aminophenoxy)phenyl]propane as crosslinking agent. Increase of ethyl acrylate content in the main monomer ratio resulted in enhancement of heat resistance due to decrease of glass transition temperature in acrylic rubber. And also oil resistance was increased with increasing content of ethyl acrylate because ethyl acrylate has the highest ester concentration in the three main monomers. With content of 2,2-bis[4-(4-aminophenoxy)phenyl]propane, both tensile strength and elongation were increased until 2 phr, but in higher content than that, they decreased owing to reduction of viscosity and elongation by increase of crosslinking density.

• Polymer(Korea)
• /
• v.37 no.1
• /
• pp.15-21
• /
• 2013

Encapsulation of a paraffin wax core as a phase change material with polystyrene shell and the its thermal characteristics caused by the encapsulation were studied. For the nanoencapsulation, the miniemulsion polymerization method was selected. The factors affecting the thermal properties of prepared nanocapsule particles of phase change material were analysed in aspect of the structure of crosslinking agents, amounts of surfactant, ratio of paraffin wax to monomer, and hydrophilicity of initiators. It was assumed that Oswald ripening plays the most important role in the changes of particle size, particle morphology, and thermal capacity of nanocapsule core. It was elucidated that the thermal capacity was also dependent on the hydrophilicity and crosslinking density of polystyrene shell components.

• Geomechanics and Engineering
• /
• v.33 no.1
• /
• pp.29-40
• /
• 2023

Xanthan gum and starch compound biopolymer (XS), an environmentally friendly soil-binding material produced from natural resources, has been suggested as a slope protection material to enhance soil strength and erosion resistance. Insufficient wet strength and the consequent durability concerns remain, despite XS biopolymer-soil treatment showing high strength and erosion resistance in the dried state, even with a small dosage of soil mass. These concerns need to be solved to improve the field applicability and post-stability of this treatment. This study explored the utilization of an alkaline-based cation crosslinking method using calcium hydroxide and sodium hydroxide to induce non-thermal gelation, resulting in the enhancement of the wet strength and durability of biopolymer-treated soil. Laboratory experiments were conducted to assess the unconfined compressive strength and cyclic wetting-drying durability performance of the treated soil using a selected recipe based on a preliminary gel formation test. The results demonstrated that the uniformity of the gel structure and gelling time varied depending on the ratio of crosslinkers to biopolymer; consequently, the strength of the soil was affected. Subsequently, site soil treated with the recipe, which showed the best performance in indoor assessment, was implemented on the field slope at the bridge abutment via compaction and pressurized spraying methods to assess feasibility in field implementation. Moreover, the variation in surface soil hardness was monitored periodically for one year. Both slopes implemented by the two construction methods showed sufficient stability against detachment and scouring, with a higher soil hardness index than the natural slope for a year.

• Bulletin of the Korean Chemical Society
• /
• v.20 no.3
• /
• pp.333-336
• /
• 1999

The polyaniline films with various insoluble parts are fabricated. The oxidation state (1-y) of these polyaniline is 0.53 and 0.54, respectively. To control the interchain and intrachain interaction of the polymer, the polyaniline films are stretched with appropriate ratio. The insoluble part of polyaniline synthesized at room temperature (low molecular weight) is 12%-76% and that of polyaniline synthesized at 0 'IC (intermediate molecular weight) is 65%-89%. The low molecular weight polyaniline films with various drawing ratios have amorphous structure. In the intermediate weight polyaniline films, the crystallinity of films increases with drawing ratio as well as insoluble part. The difference of the insoluble part affects electrical conductivity which is increased dramatically with draw ratio. In particular, the higher insoluble part caused greater increase in electrical conductivity.