A. K. Nagpal

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.

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.

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.

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.

Reactive Blends of Epoxy Resin (DGEBA) Cross-Linked by Anionically Polymerized Polycaprolactam: Adhesive Property and Chemical Resistance

Different ratios of epoxy resin (i.e., diglycidyl ether of bisphenol-A [DGEBA] and caprolactam) have been used to synthesize DGEBA/polycaprolactam reactive blends by carrying out anionic polymerization of caprolactam at 140°C. Anionic polymerization conducted by a strong base such as sodium hydride was used as a catalyst along with a cocatalyst such as N-acetyl caprolactam. The experiments were carried out to study the effect of composition on the adhesive property (i.e., lap shear strength and chemical resistance of the reactive blends). It was observed that the lap shear strength of the reactive blends increased with increasing DGEBA content from 50 to 70 wt% and increased drastically above 70 wt% DGEBA content with all metals (i.e., copper, aluminum, stainless steel, and mild steel). The lap shear strengths of all these reactive blends were observed to be maximum on mild steel. The study of chemical resistance indicates that the films of reactive blends Ep75Ca25 and Ep80Ca20 with 75 and 80 wt% DGEBA content showed better resistance to acids, alkalies, and solvents than the reactive blends Ep50Ca50 and Ep70Ca30 with 50 and 70 wt% DGEBA content. Among the solvents, methyl ethyl ketone, toluene, and methanol were found to be more attacking as compared to acetone, xylene, and ethanol.

A study on copolymeric hydrogels based on acrylamide-methacrylate and its modified vinyl-amine-containing derivative

—Acrylamide-co-methyl methylacrylate (AAm-co-MMA) copolymeric hydrogels of different ratios were prepared by using chemical and physical crosslinks. The physically crosslinked hydrogels were prepared by solution polymerization using benzoyl peroxide as an initiator, while the chemically crosslinked hydrogels were prepared by using N, N -methylene bisacrylamide (N, N′-MBA) as crosslinking agent. This copolymeric hydrogel was further modified by Hofmann degradation to improve its swelling behaviour. 1H-nuclear magnetic resonance (1H-NMR), Fourier transform infra-red spectroscopy (FT-IR), differential scanning calorimetry (DSC) and elemental analysis have been used to characterize the copolymeric gel. Elemental analysis has been used to evaluate the copolymer composition. The influence of environmental conditions such as temperature and pH value on the swelling behaviour of these copolymeric gels was investigated. Results showed that the hydrogels exhibited different equilibrium swelling ratios at different pH and temperature of swelling medium. The temperature and pH sensitivities of these gels also depended on the AAm content in the copolymeric hydrogels. These hydrogels exhibited 2135% swelling at 60°C, which was reversible and very good dimensional stability was mentioned. This was due to hydrolysis of amide groups could be hydrolyzed to form negatively charged carboxylate ion in hydrogels in response to an external pH and temperature variation.

A Study on Effect of Acrylic Acid Content on Swelling Behavior of Poly(AAm‐co‐BMA‐co‐AAc) Hydrogels

Poly(acrylamide-co-Nbutylmethacrylate-co-acrylic acid) [poly(AAm‐co‐NBMA‐co‐AAc)] hydrogels were prepared by varying the of acrylic acid content four‐fold in hydrogel. The effect of acrylic acid content on swelling behavior of the resulting poly(AAm‐co‐NBMA‐co‐AAc) hydrogels was studied, and it was found that the equilibrium swelling ratio increased from 54.47 to 127.03 with increasing the acrylic acid content from 20% to 66% in the feed. Detailed swelling kinetics such as swelling ratio, transport exponent ‘n’, diffusion coefficient ‘D’ were determined and the effect of pH on equilibrium swelling was studied. The hydrogels were also characterized by FTIR, DSC, SEM analysis, and network parameters such as molecular weight between crosslink (Mc) and crosslink density (q) were determined, explaining the swelling behavior.

Synthesis of poly(acrylamide-co-methyl methacrylate) chemically cross-linked hydrogels and their application in controlled release of model drugs

Poly(acrylamide-co-methyl methacrylate) (poly(AAm-co-MMA)) hydrogels with chemical cross-links have been prepared using two monomers (acrylamide and methyl methacrylate) and cross-linker (N,N′-methylene bis acrylamide) (NN′-MBA) in different stoichiometric ratios. The effects of monomer ratio and cross-linking agent concentration on the swelling behaviour of poly(AAm-co-MMA)hydrogels were investigated. Swelling parameters such as equilibrium degree of swelling and swelling ratio, and network parameters such as molecular mass between cross-links (M c) and cross-link density (q) were determined. Depending on the monomer concentration, the M c values of hydrogels were varied from 1452.00 to 10 602.16 g/mol and q values of hydrogels were varied from 6.09 × 102 to 0.75 × 102. Depending on the cross-linking agent concentration the M c values of hydrogels were varied from 1463.57 to 2143.94 g/mol and q values of hydrogels were varied from 5.63 × 102 to 3.99 × 102. The ability of this co-polymeric hydrogel for use in controlled release of model drugs such as benzoic acid (BA), salicylic acid (SA) and p-nitroaniline (P-NA) was also studied.

Effect of dynamic crosslinking on crystallization and thermal degradation of polypropylene in polypropylene (PP)/ethylene–propylene DIENE (EPDM) rubber blends

Blends of isotactic polypropylene and ethylene propylene diene (EPDM) rubber were dynamically vulcanized using the dimethylol phenolic resin/stannous chloride crosslinking system. The EPDM blends are thermally more stable than polypropylene (PP). Dynamic curing rendered the vulcanizate thermally more stable than unvulcanized blends. The variations in degree of crosslinking and degree of crystallinity are the main factors for observed increase in thermal stability of vulcanized blends. Degree of crosslinking increases the interfacial adhesion between the PP and EPDM phases. Dimethylol phenolic resin used as a compatibilizer also enhanced the thermal stability of the PP/EPDM blends. Crystallization of PP in the blends of PP/EPDM was also studied through modulated differential scanning calorimetry. Other detailed analyses of endotherm peaks obtained after first and second melts in terms of heat of enthalpy, degree of undercooling, and degree of crystallinity were also evaluated. Kinetic parameters were also determined.

Synthesis and Characterization of Solventless Polyester Varnish Based on Di Cyclo Penta Diene (DCPD)

Solventless polyester varnish was synthesized by polyesterification reaction of fumaric acid (FA), propylene glycol (PG) and dicyclo penta diene (DCPD) using triphenyl phenol (TPP) as accelerator. The resulting material was characterized by FT-IR and NMR spectroscopy. The electrical properties of varnish were also measured; volume resistivity was found 5.22 × 1017 Ohm-cm at room temperature, which fulfills main requirement of electrical insulating material. Solventless polyester varnish was crosslinked with styrene, vinyl toluene, and blend of both monomers, respectively in different ratios. Tensile strength of different type of the cured varnish with vinyl monomers was also determined, which was very high for vinyl toluene cured varnish. Thermal stability of the cured samples was determined by Thermogravimetric analyzer (TGA).