Reena Singhal

Effect of dynamic crosslinking on impact strength and other mechanical properties of polypropylene/ethylene-propylene-diene rubber blends

The deformation and fracture behavior of several dynamic vulcanizate blends of isotactic polypropylene with ethylene-propylene-diene rubber (EPDM) was examined and compared with those of uncrosslinked blends of PP/EPDM. These blends were prepared by melt mixing in an internal mixer at 190°C in a composition range of 10–40 wt % EPDM rubber. The variation in yield stress, the strength of fibrils of the craze, and the number density of the EPDM rubber domains (morphology fixation) that are dominant factors for enhancing interfacial adhesion and toughness in dynamic vulcanizate blends were evaluated. The ductility and toughness of these materials were explained in light of the composition between crack formation and the degree of plastic deformation through crazing and shear yielding. The physicomechanical properties including the hardness, yield stress, Youngs modulus, percentage elongation, impact strength, flexural strength, and flexural modulus of dynamic vulcanized blends were found to be consistent and displayed higher values compared with uncrosslinked blends. The nucleation effect of the crosslinked particles and the decrease of crystallinity of the EPDM rubber were also considered to contribute to the improvement in the impact strength.

Effect of dynamic crosslinking on tensile yield behavior of polypropylene/ethylene-propylene-diene rubber blends

Tensile yield behavior of the blends of polypropylene (PP) with ethylene-propylene-diene rubber (EPDM) is studied in blend composition range 0-40 wt % EPDM rubber. These blends were prepared in a laboratory internal mixer by simultaneous blending and dynamic vulcanization. Vulcanization was performed with dimethylol phenolic resin. For comparison, unvulcanized PP/EPDM blends were also prepared. In comparison to the unvulcanized blends, dynamically vulcanized blends showed higher yield stress and modulus. The increase of interfacial adhesion caused by production of three-dimensional network is considered to be the most important factor in the improvement. It permits the interaction of the stress concentrate zone developed at the rubber particles and causes shear yielding of the PP matrix. Systematic changes with varying blend composition were found in stress-strain behavior in the yield region, viz., in yield stress, yield strain, width of yield peak, and work of yield. Analysis of yield stress data on the basis of the various expressions of first power and two-thirds power laws of blend compositions dependence and the porosity model led to consistent results from all expression about the variation of stress concentration effect in both unvulcanized and vulcanized blend systems. Shapes and sizes of dispersed rubber phase (EPDM) domains at various blend compositions were studied by scanning electron microscopy.

Synthesis of Poly (Acrylamide-co-Acrylic Acid) based Superabsorbent Hydrogels: Study of Network Parameters and Swelling Behaviour

This article investigates the synthesis of superabsorbent hydrogels (SAHs) based on acrylamide and acrylic acid by solution polymerization in the presence of N,N′-methylenebisacrylamide (NMBA) as a cross-linker and potassium per sulphate as initiator. In this work the acrylamide content was varied in a large range of 30–70% (mole of total monomer) in feed, in order to study its effect on swelling behavior. The results indicate that when acrylamide content present in the hydrogels was increased from 17.23–35.85% (mole of the total monomer); then equilibrium water absorbency also increased from 276–573 (g water/g sample). But when acrylamide content was further increased from 35.85–50.24%, then equilibrium water absorbency abruptly decreased. The equilibrium water absorbency of various copolymeric hydrogels was also investigated in different concentration of saline solutions. The effect of SAHs on growth of seeds of lentil was also studied. The hydrogels were also characterized by fourier-transform infrared spectroscopy (FT-IR), nuclear magnetic resonance (NMR), scanning electron microscopy (SEM); and network parameters such as average molecular weight between cross-links (Mc) and cross-link density (q) were determined to explain the swelling behavior.

A Review: Tailor-made Hydrogel Structures (Classifications and Synthesis Parameters)

ABSTRACT Hydrogels are being prepared for use in a wide variety of applications ranging from medicines, tissue engineering, superabsorbents, controlled release of drugs & fertilizers, and oil absorbers etc. This review highlights hydrogel structure and their different classifications under various heads. It also discusses various routes to obtain tailormade hydrogels by polymerizing a combination of two or more monomers with proper type of crosslinks in order to obtain desired properties in the resulting hydrogel. Novel hydrogel configurations like microgels and nanogels, slide ring gels, double network hydrogels and nanocomposite gels have also been reviewed. GRAPHICAL ABSTRACT

Synthesis of poly(acrylamide-co-acrylic acid)-based super-absorbent hydrogels by gamma radiation : study of swelling behaviour and network parameters

A series of poly(acrylamide-co-acrylic acid) (poly(AAm-co-AAc))-based super-absorbent hydrogels (SAHs) was prepared by gamma radiation at the dose rate of 15 kGy. The amount of AAm was varied in the range of 30–70% (mol of total monomer) in feed. The co-polymers were characterized by Fourier transform infrared spectroscopy, scanning electron microscopy, nuclear magnetic resonance and network parameters, such as average molar mass between cross-links and cross-link density, were determined to explain the swelling behaviour. The experimental results indicated that an increase in the AAm content present in the hydrogels varied from 38.87% to 64.02%, equilibrium water absorbency decreased from 872 to 402 g H2O/g sample. The equilibrium water absorbency of various SAHs was investigated in different concentration of saline solutions. The effect of synthesized co-polymer on growth of seeds of ladyfinger is reported.

CURING AND RHEOLOGICAL BEHAVIOR OF VINYL ESTER RESINS PREPARED IN THE PRESENCE OF TERTIARY AMINES

Vinyl ester resins V1, V2 & V3 of acid value (∼6 mg KOH g−1 solid) were synthesized using bisphenol-A epoxy and acrylic acid in the presence of triethyl-, tripropyl- and tributyl-, amines in 210, 270 and 340 minutes, respectively. The synthesized resins were characterized by FTIR spectroscopy and a new peak at 2360 cm−1 was observed which is due to attachment of amines to resin structure by hydrogen bond. The curing behavior of synthesized resin containing 40% styrene (w/w) and 2% benzoyl peroxide was studied using DSC technique and found to be affected by presence of amines. Activation energy and frequency factor for the curing reaction increases from 14 Kcal mol−1 to 23 Kcal mol−1. Rheological behavior of resins containing 40% styrene was studied using a Haake Rotovisco RV20 viscometer, and viscosity was found to increase with shear rate up to 200 sec−1. The average values of activation energy at constant shear stress (6-15 Pa) were 12.94, 13.20, 13.70 Kcal mol−1 for V1, V2 and V3, respectively. The act...

Methyl Orange adsorption by reuse of a waste adsorbent poly(AAc/AM/SH)-MB superabsorbent hydrogel: matrix effects, adsorption thermodynamic and kinetics studies

AbstractThe traditional method for the treatment of used adsorbents is usually recovery for recycling or direct discarding them. In the present study, a more potential and economical method is described to reutilize a waste adsorbent. Poly(AAc/AM/SH) SAHs have proved to be a good adsorbent for cationic MB dye, and after adsorption, the SAHs were recovered for recycling. In this work, the waste MB dye loaded poly(AAc/AM/SH) SAHs were not recovered but directly applied to adsorb an anionic MO dye from another waste solution. The poly(AAc/AM/SH) SAHs after the MB dye adsorption were stable and suitable for MO dye adsorption for altered surface structures within a wide pH range. The various factors affecting the MO dye adsorption, including pH, contact time, ionic strength, initial concentration of the MO dye, and temperature, were systematically investigated. The equilibrium adsorption data fitted very well to the Langmuir adsorption isotherm and the maximum MO dye adsorption capacity reached to a high of 13...

Regenerable hydrogels based on poly(acrylic acid-sodium acrylate-acrylamide) modified by sodium humate for high removal of Pb2+ and Fe2+ ions: metal adsorption kinetics and thermodynamic studies

ABSTRACTA novel superabsorbent hydrogel based on poly(acrylic acid-sodium acrylate-acrylamide)/sodium humate poly(AAc-SA-AM)/SH was applied as adsorbent to adsorb metal ions (Pb2+, Fe2+) from the aqueous solutions. The factors affecting adsorption capacity of the poly(AAc-SA-AM)/SH hydrogel such as contact time, pH, temperature, SH content (wt.%), initial concentration of the metal ion, and ionic strength were systematically investigated. Results from the experimental data revealed that an appropriate addition of SH (2.44 wt.%) not only increases the metal ion adsorption of poly(AAc-SA-AM) hydrogel but also improves its regeneration ability. The results showed that the adsorption equilibrium data fitted the Langmuir isotherm better than the Freundlich isotherm. The maximum binding capacity for Pb2+ ion was 198 and 164 mg/g/l for Fe2+ ion for per g of poly(AAc-SA-AM)/SH (SH4) hydrogel (high as compared to many other adsorbents). The changes in thermodynamic parameters were also calculated, and the negative...

Synthesis and characterization of poly(AAm-co-BMA-co-AAc) hydrogels: effect of acrylamide content on swelling behaviour

Poly(acrylamide-co-butyl methacrylate-co-acrylic acid) hydrogels were prepared in various concentrations of a dioxane/water mixture as polymerization media using different percentages of cross-linker and by varying the amount of acrylamide over 4-fold in order to study the effect of acrylamide content on swelling behaviour of hydrogels. It was found that hydrogels prepared in 50% aqueous dioxane solution exhibited the highest swelling. The results also indicated that with increasing acrylamide content, swelling increased initially. And when acrylamide content further increased to 66% (based on total monomer), the swelling decreased gradually. Detailed swelling kinetics, such as swelling ratio, transport exponent n and diffusion coefficient D, were studied and the effect of pH on equilibrium swelling was also studied. The hydrogels were also characterized by network parameters, such as molecular weight between cross-links (M c) and cross-link density (q), that were determined to explain the swelling behaviour. The hydrogels were also characterized by Fourier transform infrared spectroscopy, elemental analysis, differential scanning calorimetry and scanning electron microscopy.

A Study on Interaction and Solubility of Acetaminophen with Poly(AM-co-HEA-co-AA) Hydrogels by DSC: Effect on Drug Diffusion Behavior

In the present study, acetaminophen solubility and its interaction with poly(AM-co-HEA-co-AA) hydrogels containing acetaminophen (AMP) from 15% to 35% was determined by DSC thermogram; and confirmed by SEM and FTIR analysis. Results obtained by DSC indicated that acetaminophen dissolved up to 16.33% loading, while acetaminophen above the concentration 16.33% existed in crystalline form in matrices, and was responsible for the melting corresponding to the melting of acetaminophen crystals. The heat required to melt the crystalline portion of acetaminophen was theoretically calculated by using an equation, and its validity was confirmed through melting enthalpies observed experimentally. The effect of increasing amount crystalline acetaminophen on the matrix swelling, and simultaneous controlled release of acetaminophen was investigated. The drug diffusion kinetic was analyzed by fitting early-time, late-time and etters diffusion models to the drug release data observed experimentally. By increasing drug loading, values of all drug diffusional coefficients (i.e., early-time, late-time and etters) were decreased, and rank of diffusion coefficients for each hydrogel matrix was followed in the order of etters> late-time >early-time. From model fitting, it was observed that with increasing AMP content in hydrogels matrix, the applicability of early time and late time model were improved; and for 35% AMP containing hydrogel, early time was applicable for first 60% drug diffusion; late-time model was applicable for latter 50% drug diffusion; indicating that diffusion characteristics can be altered by increasing crystalline acetaminophen depending on the% acetaminophen loading in hydrogel. Etters model was best applicable to all type of hydrogel matrices, and followed over entire range of drug diffusion process.