Equilibrium Swelling Technique Research Articles

PH Sensitive Drug Delivery Behavior of Palmyra Palm Kernel Hydrogel of Chemotherapeutic Agent.

This study examined the gel behavior of naturally-occurring palmyra palm kernel (PPK). Due to the presence of polysaccharide in PPK hydrogels, they exhibit excellent swelling behavior in response to pH. Chemotherapeutic drug 5-fluorouracil (5-FU) was encapsulated in these gels using an equilibrium swelling technique. It was found that 5-FU had an encapsulation efficiency of up to 62%. To demonstrate the drug stability in the gels, the PPK hydrogels were characterized using fourier transform infrared spectroscopy, differential scanning calorimetry, and X-ray diffraction. The results showed that the PPK hydrogel matrix contained molecularly dispersed 5-FU drug. The PPK hydrogel exhibited a denser structure and a rough surface, according to images obtained by scanning electron microscopy. In vitro release tests were carried out at pH 1.2 (gastric fluid) and 7.4 (intestinal fluid). The efficacy of the encapsulation and the release patterns were influenced by the network topology of the PPK hydrogel. The release patterns showed that 5-FU was released gradually over a time internal of more than 12 h. The findings suggest that naturally-occurring PPK hydrogels loaded with chemotherapeutic drugs could be employed to treat colon cancer.

Ablation and thermal insulation properties of silicone rubber-polyarylacetylene-carbonwoven laminates for solid rocket motor

ABSTRACT Silicone rubber-polyarylacetylene-carbon woven laminates (SRWL) with two-dimensional structure were prepared using needled technique. The ablation and insulation mechanism of SRWL were investigated by oxyacetylene flame system, equilibrium swelling technique, thermogravimetry (TG), scanning electron microscopy (SEM) and X-ray diffraction (XRD). Results showed that the molecular weight between the crosslinks of the interlaminar complex is reduced with the increasing of the content of polyarylacetylene (PA). SRWL with PA has superior anti-ablation properties and high residue compared with that of without PA. With the increasing of PA content, the linear ablation rate of SRWL first decreases and then increases. When the content of PA is 10 phr, the linear ablation rate is 0.0276 mm s−1 and the back-face temperature peak is 71 °C. SRWL filled with 10 phr concentration of PA show comparably improved ablation properties and PA hinders the thermal transmission because of forming of compactly integrated self-protection refractory layer, ceramic compounds such as SiC, Si and some endothermic behaviour.

Pharmacokinetic evaluation of microgels for targeted and sustained delivery of acid labile active pharmaceutical agent in animal model

The study was aimed to evaluate the feasibility of chemically crosslinked pH responsive copolymeric microgels of 2-hydroxyethyl methacrylate and itaconic acid (p (HEMA-co-IA)) for targeted and sustained delivery of acid labile active pharmaceutical agents. Esomeprazole (model drug) was loaded by equilibrium swelling technique into microgels, obtained by suspension polymerization. The resultant microgels were spherical with average size of 6.43 ± 1.2 μm and percent esomeprazole loading was 65 ± 1.3%. In vitro dissolution studies confirmed the potential use of p (HEMA-co-IA) microgels to protect the drug from acidic pH of the stomach and to deliver the drug in response to intestinal pH over extended period of time. A single dose non-compartmental pharmacokinetic evaluation was performed in healthy rabbits in order to investigate the in vivo performance. The results showed delayed and extended release of the drug from the microgels, with decreased Cmax, prolonged tmax, increased AUC0-t and prolonged MRT in comparison to oral drug solution. The differences were statistically significant. The study concluded that p (HEMA-co-IA) microgels have potential for preferential drug delivery into higher pH environment over prolonged period of time.

Probing small network differences in sulfur‐cured rubber compounds by combining nuclear magnetic resonance and swelling methods

ABSTRACTWe studied the network structure of elastomers based on polyisoprene, polybutadiene, and their blends in the narrow range of formulations compatible with actual use in the automotive tyre industry. Cross‐link density (CLD) was quantified comparatively by low‐field 1H multiple quantum time domain nuclear magnetic resonance (MQ TD‐NMR) and by equilibrium swelling technique. The robustness and agreement of the two methods was demonstrated in measuring minute alterations of unfilled vulcanizates beyond the optimum cure time. Comparison with samples where polysulfidic bonds were selectively cleaved also demonstrates that the length of the sulfur chain constituting the cross‐link does not significantly affect residual dipolar coupling. Kraus, Lorenz, and Parks correction for filler restriction on swelling is validated by MQ TD‐NMR, which also allows extracting information on cross‐link distribution not provided by swelling measurement. Cross‐link distributions in the blends were demonstrated to be significantly different from the weighted average of the pure samples, while average proton–proton residual dipolar coupling values correspond. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42700.

Modular mobility investigation of polymer binder bitumen

This paper is aimed to obtain polymer binder bitumen for the road applications with improved properties. Objectives included studying the degradation of crumb rubber during devulcanization in melted petroleum bitumen for its modification and resulted structural properties of bitumen. Using equilibrium swelling technique reduced density of the polymer chains was observed and analysis of sol-gel fractions showed a significant decrease in gel fraction. Under selected method of devulcanization 64% of the backbone rubber remained. With The H1 NMR relaxation method the reduction of bitumen molecular mobility was observed due to thickening of its light fractions. The effectiveness of devulcanization was optimized using a new agent in a powder form and vacuum application. The developed binder has an improved spectrum of physical and technical properties such as softening point temperature, hardness, elasticity, frost resistance, low temperature characteristics.

Characterization of network parameters for UHMWPE by plane strain compression

Ultra-high molecular weight polyethylene (PE) is used as a bearing material for total joint replacement prostheses since it is a tough, wear-resistant semicrystalline polymer. Despite its high resistance to wear, PE components have shown measureable wear in vivo, which can cause wear-particle induced osteolysis. Crosslinking of PE using ionizing radiation has been shown to increase wear resistance since both chemical crosslinks and physical entanglements provide high resistance to wear. Molecular characterization of crosslinked PEs is usually conducted using equilibrium swelling or by quantifying gel content. In this study, we compared crosslink densities and molecular weight between crosslinks derived from equilibrium swelling to those obtained by applying the Gaussian and Eight-Chain model to describe plane strain compression of the PE melt. The latter approach has the advantage of accounting for contributions of entanglements to the overall crosslink density, which solvent-based techniques largely neglect. As expected, the crosslink density calculated from model fitting increased monotonically with increase in radiation dose in a 0–200kGy dose range, with a corresponding monotonic decrease in molecular weight between crosslinks, but provided higher values of crosslink density and correspondingly lower values of molecular weight between crosslinks compared to the equilibrium swelling technique.

Effect of precured degrees on morphology, thermal, and mechanical properties of BR/SBR/NR foams

The ternary composites of 1,4‐cis polybutadiene rubbers (BR), styrene–butadiene rubber (SBR), and natural rubber (NR) foams containing chemical blowing agents Oxybis (benzene sulfonyl) hydrazide (OBSH) were prepared by two‐stage compression molding technique with various precured degrees. Foam force rheometer indicated that the cure rate was match with foaming rate at precured degree of 30%, which the time of the maximum foaming rate was earlier only 14 s than that of the maximum cure rate. SEM presented that the number of cell was denser at precured degree of 30% than those with other precured degrees. The average cell size declined, cell wall thickness became thicker, and cell distribution became narrower just as precured degree was increasing. The results of crosslinking density was measured by equilibrium swelling technique in good agreement with that of magnetism resonance crosslinking density spectrometer measurement, which crosslinking density was increased as precured degrees increased. Differential scanning calorimeter showed that each curve exhibits two steps in heat capacity for BR/SBR/NR foams. With further increase of precured degrees, the two groups of Tgs were all shift to the higher temperature, and the area of the melting peak decreased gradually between −20°C and −40°C. TGA results demonstrated that BR/SBR/NR foams with various precured degrees obtained better thermal stability than those of non‐precured foams. The high density of polymeric foams exhibits the high mechanical properties such as tensile strength, tear strength, and elongation at break. The inflection points of density, cell density, and hardness were all appeared at precured degree of 30%. POLYM. COMPOS., 34:849–859, 2013. © 2013 Society of Plastics Engineers

Effect of Rubber–Filler Interaction on Transport of Aromatic Liquids through High Density Polyethylene/Ethylene Propylene Diene Terpolymer Rubber Blends

The sorption and transport of four aromatic hydrocarbons through dynamically vulcanized high density polyethylene/ethylene propylene diene terpolymer rubber blends filled with carbon black and that filled with silica at the same loading have been investigated in the temperature range of 28–58 °C by an equilibrium swelling technique . Blends loaded with high abrasion furnace (HAF) black and those with silica of same loading have been used. The silica-incorporated blends sorbed a higher amount of aromatic solvents compared with the HAF filled blends. This has been explained in terms of the differences in the interaction between the filler particles and the blend components. The swelling coefficient, diffusion coefficient, and molar mass between cross-links have been computed to complement the experimental observations.

Investigation of interfacial adhesion in nylon-6 fibre/NBR composites through restricted equilibrium swelling technique

Short nylon-6 fibre reinforced acrylonitrile butadiene rubber (NBR) composites were prepared and the interfacial adhesion was evaluated by the restricted solvent swelling technique. The solvents used were N,N-dimethyl formamide (DMF), dimethyl sulphoxide (DMSO) and acetonitrile. As the fibre content increased, the solvent uptake decreased, which has been attributed to the increased hindrance to solvent penetration due to better fibre–rubber interaction. It was observed that the ratio of change in volume fraction of rubber before and after swelling to the volume fraction of rubber before swelling (V 0 – V r/V 0) was lower for a bonding agent added composite, compared to the unbonded one. Anisotropic swelling studies were carried out to analyze the extent of fibre alignment and fibre–matrix interaction. It was seen that in strongly bonded composites, the swelling mainly took place in the thickness direction. The rubber–fibre interaction has also been examined by the Lorenz–Parks and Kraus equations.

Interaction of silica and carbon black fillers with natural rubber/poly(ethylene‐co‐vinyl acetate) matrix by swelling studies

AbstractThe interaction of a black filler and a white filler, which are extensively used in the rubber industry, with natural rubber/poly (ethylene‐co‐vinyl acetate) (NR/EVA) blends vulcanized by DCP has been examined by equilibrium swelling technique. Blends loaded with intermediate super abrasion furnace black (ISAF) and those with silica (SiO2), of same loading, have been used. The silica incorporated blends sorbed a higher amount of aromatic solvents, compared with the ISAF filled blends, when NR was the continuous phase. However, the silica filled systems showed lower sorption characteristics when EVA became the continuous phase. This has been explained in terms of the differences in the interaction between the filler particles and the blend components. The swelling coefficient, diffusion coefficient, and molar mass between crosslinks have been computed to complement the experimental observations. POLYM. COMPOS., 28:705–712, 2007. © 2007 Society of Plastics Engineers

Investigation on interfacial adhesion of short sisal/coir hybrid fibre reinforced natural rubber composites by restricted equilibrium swelling technique

Interfacial adhesion of sisal/coir hybrid fibre reinforced natural rubber (NR) composites has been characterized by restricted equilibrium swelling technique with special reference to the effects of fibre loading, orientation and bonding agent. The swelling parameters of NR composites with and without bonding agent were evaluated with three aromatic solvents, namely; benzene, toluene and xylene, by a sorption gravimetric method. As fibre content and penetrant size increase, the solvent uptake has been found to decrease due to the increased hindrance and good fibre–rubber interaction. The bonding agent added mixes showed enhanced restriction to swelling and it is seen that the ratio of change in volume fraction of rubber before and after swelling to the volume fraction of rubber before swelling (V 0 – V r/V 0) is lower for bonding agent added composites, when compared to an unbonded one. The anisotropic swelling studies were carried out to analyse the extent of fibre alignment and fibre–matrix interaction. In strongly bonded composites, the swelling has been mainly observed to take place in the thickness direction, as attested by optical photographs. The rubber–fibre interaction has also been examined by Lorenz–Parks and Kraus equations.

Interfacial adhesion in sisal fiber/SBR composites: an investigation by the restricted equilibrium swelling technique

Short sisal fiber-reinforced styrene butadiene rubber (SBR) composites were prepared and characterized by the restricted solvent swelling technique. The solvent swelling characteristics of SBR composites containing untreated and bonding agent-added mixes were investigated in a series of aromatic solvents, such as benzene, toluene, and xylene. The diffusion experiments were conducted by the sorption gravimetric method. The adhesion between the rubber and short sisal fibers was evaluated from the restricted equilibrium swelling measurements. The anisotropy of swelling of the composite was confirmed by this study. The effect of fiber orientation in controlling the anisotropy of restricted swelling was also demonstrated. As the fiber content increased, the solvent uptake decreased, due to the increased hindrance and good fiber-rubber interactions. Bonding agent-added mixes showed enhanced restriction to swelling, due to the strong interfacial adhesion. The bonding system containing hexa-resorcinol in the mix produces an in-situ resin, which binds the fiber and the rubber matrix firmly. In addition, as the penetrant size increases from benzene to xylene, the uptake decreases. The swelling index values of the composites support this observation. Due to the improved adhesion between the short sisal fiber and SBR, the ratio of the volume fraction of rubber in the dry composite sample to the swollen sample (V T) decreases. The extent of fiber orientation of the composites was also analysed from the restricted swelling method. SEM studies of the composite revealed the orientation of short fibers. The sorption data support the Fickian diffusion trend, which is typical in the case of cross-linked rubbers.

The mechanism of triallylcyanurate as a coagent in EPDM peroxide vulcanization

AbstractThe reaction mechanism of ethylene‐propylene‐diene (EPDM) peroxide vulcanization, in the presence of triallylcyanurate (TAC), as a coagent, was studied by IR spectroscopy and equilibrium swelling technique. Coagent TAC is added in EPDM polymer to prevent the scission of polymer chains during the curing process. Because of this incompatibility with polymer, TAC was supposed to reside in small domains. To establish the existence of coagent bridges, the cleavage of ether linkages in the vulcanizates was made. After that treatment, IR measurements proved incorporation of coagent in polymer network. Measurements of allyl absorbances and the s‐triazine ring indicated that crosslink efficiency is enhanced and homopolymerization and cyclization take place in the presence of the coagent. In addition, the swelling results and IR measurements confirmed that the properties of the polymer, such as molecular mass and molecular mass distribution, will determine which of these reactions will predominate during the vulcanization process.

Functionalization of Poly(Organophosphazenes). IX. Light-Induced Grafting Reactions of Maleates onto Aryloxy-Substituted Poly(Organophosphazenes)

In this paper the light-induced grafting reaction of dimethyl maleate, diethyl maleate, dibutyl maleate and diethyl fumarate, onto aryloxysubstituted phosphazene polymers, to form polyphosphazene copolymers containing grafted succinate groups, is investigated by means of IR spectroscopy and the equilibrium swelling technique of polyphosphazene films. The importance of several different experimental factors that can influence the final succinate grafting yields is discussed, i.e. the type and concentration of the polyphosphazenes and of the unsaturated products, reaction time, the absence or presence of molecular oxygen or of the 1-vinyl-2-pyrrolidone monomer, and the concentration of the benzoin ethyl ether photoinitiator. Furthermore, it is shown that the overall efficiency of the lightinduced grafting process is lower than that previously measured for the reaction initiated thermally using peroxide species, and that the photochemical grafting reaction always occurs with no degradation of the phosphazene macromolecules. The possibility of exploiting these new phosphazene substrates in blend technology has been considered.