Bishnu P. Panda

Mechanism of Toughening in Rubber Toughened Polyolefin—A Review

The recent advances and theories in the studies of the toughening mechanism have been reviewed to explain the effect of rubber particles in different rubber modified Polyolefin materials. To elucidate toughening effect, major theories e.g., critical particle distance, particle size, micro deformation by stress field of rubber, shear yielding and crazing phenomena has been reviewed. Based on these theories, variety of blends of rubber modified Polyolefin materials has been compared but no one of these provided adequate information to be considered as total theory of toughening. To achieve the objective of toughening, it is important to maintain critical particle size, uniform particle distribution and good interfacial adhesion by inclusion of suitable compatibilizer in the matrix. Particular attention has been paid to study the type of morphology and bimodal distribution of rubber particles to elucidated toughening effect. Rubber particle cavitation, which comes from micro-voids and rubber phase interface are then further discussed. GRAPHICAL ABSTRACT

Mechanical Behavior and Fracture Toughness Evaluation of Multiphase Polymer Nanocomposites Using Impact and -Integral via Locus Method

Fracture behaviors of fibrillar silicate clay (MMT) filled thermoplastic polyolefin (TPO) containing polypropylene (PP) blended with ethylene-propylene-diene monomer (EPDM) were systematically investigated using impact test method and -integral by locus method. Drastic increase in impact strength is observed for all developed compositions and generally shows higher value for the selected phases containing dispersed nanoclay in PP matrix. A fracture mechanics approach has been adopted by mode I test, and the effects of specimen geometry have been investigated. Increase in interlaminar fracture energy value, , and -integral value, , is marked as the crack propagated through the composite; that is, a rising “-curve” is observed. Toughness measurements revealed that the fracture toughness increased with increasing clay content reaching maximum at 3 wt% of clay than pure PP. Moreover, enhancement of fracture toughness was more remarkable than that of stiffness. The fracture surfaces taken from different specimens were observed for exploring the fracture mechanisms using transmission electron microscopy (TEM) revealed a strong particle-matrix adhesion.

Mechanical and damage tolerance behavior of short sisal fiber reinforced recycled polypropylene biocomposites

Sisal fiber (SF) reinforced recycled polypropylene biocomposites were prepared by melt blending technique. Biocomposites prepared with the incorporation of 40 wt% untreated sisal fiber loading showed a marginal improvement in mechanical properties as compared with matrix recycled polypropylene. SF surface was mercerized and maleic anhydride grafted polypropylene was used as a coupling agent for better fiber matrix interfacial bonding. Mercerized sisal fiber reinforced biocomposites prepared with compatibilizer (maleic anhydride grafted polypropylene) shows significant improvement in tensile and flexural strength. Damage tolerance of recycled polypropylene matrix and its biocomposites were evaluated in monotonic and cyclic tensile test. Untreated sisal fiber reinforced biocomposites prepared with maleic anhydride grafted polypropylene shows improvement in damage tolerance compared with untreated sisal fiber biocomposites. Impact fractured morphology of biocomposites revealed better interfacial bonding between fiber, maleic anhydride grafted polypropylene, and recycled polypropylene matrix.

Effects of geometry and temperature on mode I interlaminar fracture of filled polypropylene-elastomer nanocomposite

In this study, organically modified Na-MMT clay was used for the preparation of blend nanocomposites containing different ratios of polypropylene (PP) and ethylene propylene diene monomer (EPDM) elastomer in a twin screw extruder. Maleic-grafted PP (MAPP) was used as compatibilizer for making PP hydrophilic. Surface modification of Na-MMT was made by using amino propyl trimethoxy silane (APS) and trimethyl amine as coupling agent with surface grafting catalyst, respectively. A fracture mechanics approach has been adopted by mode I test and the effects of specimen geometry have been investigated. Increase in interlaminar fracture energy value, Gc, was observed as the crack propagated through the composite, i.e. a rising ‘R-curve’ for both blend and nanocomposites. Deep fracture studies were carried out at different temperatures (−60 °C to 60 °C) using Izod impact and SENT tests. Fracture energy, fracture stress and brittle ductile transition were determined from crack initiation and propagation process, which showed significant improvement in impact and fracture energy at positive temperature. The wide-angle X-ray diffraction (XRD) patterns showed increased d-spacing of clay layers, indicating enhanced compatibility between PP and clay with the addition of maleated polypropylene (MAPP). Morphology/impact property relationships and an explanation of the toughening mechanisms were made by comparing the impact properties with scanning electron micrographs (SEMs) of fracture surfaces. The transmission electron microscopy (TEM) photomicrographs illustrated the intercalated and partially exfoliated structures of the hybrids with clay, MAPP and elastomer.

Thermokinetics behavior of epoxy adhesive reinforced with low viscous aliphatic reactive diluent and nano-fillers

The current study reports the effect of low viscous aliphatic reactive diluent (RD), MWCNT and VGCF on the curing kinetics of amine cured epoxy adhesive system employing non-isothermal differential scanning calorimetric (DSC) technique. Non-isothermal DSC thermograms of epoxy adhesive were studied at various heating rates: 5, 10 and 15 °C/min. The decrease in the exothermic peak height with the introduction of MWCNTs and VGCFs was taken as proof of the acceleration effect of nano-fillers on the epoxy-amine curing reaction. Also, increased Tonset, TP and ΔHcurs values were observed for epoxy/RD adhesive system at all heating rates. The value of activation energy (Ea) was determined using Kissinger and Flynn-Wall-Ozawa methods. Experimental results showed that the addition of 10 wt% RD increased the Ea from 60 to 63 kJ/mol on account of the reduced viscosity, allowing better contact of resin with the curing agent. Furthermore, MWCNTs have an accelerating effect on the cure kinetics that does not change the autocatalytic cure reaction mechanism of epoxy resin. It was also found that the addition of MWCNT and VGCF decreases the overall degree of conversion, as evident with lower ΔHcure and Ea of the cured adhesive when compared with epoxy/RD system. The dependency of Ea on degree of conversion ranging from α =0.1 to 0.9was also investigated. The two normalized functions y(α) and z(α) were also considered in order to study the complex curing mechanism. The kinetic parameters m, n and lnA were obtained by using two parameter autocatalytic Sestak-Berggren model. The curves revealed good agreement between experimentally determined and theoretically obtained MWCNT/VGCF reinforced epoxy adhesive systems.

Damage tolerance behaviour of cloisite 15A incorporated recycled polypropylene nanocomposites and bionanocomposites

ABSTRACT In the present investigation, recycled polypropylene (rPP) used as a matrix was modified by incorporating nanofillers through melt blending technique to prepare a masterbatch of nanocomposites. Untreated sisal fibre and mercerised sisal fibres were further incorporated into the nanocomposites for the preparation of bionanocomposites. Bionanocomposites containing 40 wt% of UT fibre and 5 wt% of MA-g-PP revealed an increase in the tensile strength and modulus to the tune of 27% and 370%, respectively, compared to rPP. The flexural strength and modulus also increased to the tune of 129% and 269%, respectively, compared to rPP. Further, the surface treatment of the fibre slightly increased the mechanical properties and stiffness of bionanocomposites. Interfacial strength between fibre and matrix was also evaluated by using Turcsanyi and Sato–Furukawa models. Damage tolerance of rPP nanocomposites and its bionanocomposites was evaluated using single-edge-notch specimens. The notch length ‘a’ to width ‘W’ ratios, a/W, were chosen as 0.3, 0.45 and 0.6. The nanocomposites showed better damage tolerance as compared to the rPP matrix. The corrugated structure with increased fractured surface area was observed in scanning electron microscopy. Better dispersion of clay in the nanocomposites was observed in transmission electron microscopy.

A Review on Waterborne Thermosetting Polyurethane Coatings Based on Castor Oil: Synthesis, Characterization, and Application

ABSTRACT Waterborne polyurethane coatings made from castor oil as polyol resource, replacing oil from fossil fuels are attracting lot of recognition during recent decades. In this review, castor oil and its modifications to synthesize various biobased waterborne polyurethane and their nanocomposite systems have been addressed. Various synthesis procedures for waterborne polyurethane dispersions and their applications as a coating material have been described. This review will be helpful to the green research community for selection of monomer and further development of biobased waterborne polyurethane utilizing advanced technology. GRAPHICAL ABSTRACT

Recent Developments on Epoxy-Based Thermally Conductive Adhesives (TCA): A Review

ABSTRACT The development of new polymer-based conductive adhesives with specific performances and improved conductivity are increasingly critical for thermally interface material (TIM). Epoxy resins have been widely used as a common interface material for conductive adhesives due to its well-known ability to accept wide range of fillers possibly derived from carbon, metallic or ceramic sources. These conductive fillers with high inherent thermal conductivity, together with a possibility to characterize and manipulate the system, leads to the production of thermally conductive adhesives with higher knowledge content for a number of electronics applications. GRAPHICAL ABSTRACT

The castor oil based water borne polyurethane dispersion; effect of -NCO/OH content: synthesis, characterization and properties

Abstract In this work, a novel bio-renewable castor oil (CO) based aqueous polyurethane (PU) anionic prepolymer dispersion was prepared successfully using isophorone diisocyanate (IPDI) and dimethylol propionic acid (DMPA) as internal emulsifier maintaining NCO/OH molar ratios of 1:3 and 1:5, respectively. The intermolecular H-bonding change, type and intensity of the obtained films with change in molar ratio were investigated by analyzing with Fourier transform-infrared (FT-IR). The morphology of the films was recorded with scanning electron microscopy (SEM) and transmittance electron microscopy (TEM). The coating properties for the film were also studied and discussed. The structure-property relationship with different molar ratios of prepolymer revealed an increasing pattern showing increase in the hard segment content increases the physico-mechanical properties of the CO based PU prepolymer. The FT-IR deconvolution results are in agreement with the film properties. The excellent abrasion resistance properties of CO based films agree well with the surface morphology and FT-IR results. The outcome of the study also suggests use of CO as a better alternative to replace petroleum based polyol for feature perspective.

Mechanical and morphological investigation of virgin polyethylene and silver nanoparticle-loaded nanocomposites film: comprehensive analysis of kinetic models for non-isothermal crystallization

This research was accomplished to examine the mechanical, morphological and crystallization kinetics study of polyethylene/silver nanoparticles (Ag-NPs) nanocomposite films. In this research, low-density polyethylene (LDPE) nanocomposite films were prepared containing Ag-NPs using maleic-anhydride-grafted low-density polyethylene (LDPE-g-MAH) as a compatibilizer by the melt mixing process. From mechanical property evaluation, it is revealed that the LDPE/LDPE-g-MAH/Ag-NPs nanocomposite films showed decreased tensile strength as compared with virgin LDPE matrix. Thermal characteristics of the prepared virgin LDPE and its nanocomposite films were studied by differential scanning calorimetry (DSC). Comprehensive analysis of different kinetic models such as the Avrami and Mo model on non-isothermal crystallization kinetics was performed in order to correlate the rate of crystallization and its various kinetic parameters. Further, the macrokinetic equation as proposed by Malkin has been applied to describe the kinetics of crystallization in the light of the Avrami equation. Concerning virgin LDPE and Ag-NP-reinforced LDPE, the former shows primary crystallization, whereas the later exhibits both primary and secondary crystallization with varying Avrami exponents. Kinetic parameters are recognized, and confirm the influence of Ag-NPs on crystallization kinetics. X-ray diffraction spectroscopy and transmission electron microscopic analysis of the nanocomposite films were conducted to verify the dispersion of inorganic filler particles in the resulting hybrids.