Karingamanna Jayanarayanan

Impact, tear, and dielectric properties of cotton/polypropylene commingled composites

Natural fibers can be used as reinforcements in thermoplastic non-structural applications. Commingling them with matrix fibers lowers the melt flow distance of molten matrix during the processing. In this study, polypropylene (PP) and textile cotton fibers were commingled and fabricated to composite laminates. Process variables like temperature, pressure, and holding time affect the mechanical properties like impact strength and tear resistance. Fiber content and winding pattern or fiber orientation were also important for the optimization of the mechanical properties. The modification of the interface by chemical treatments of the matrix or reinforcement with reagents like potassium permanganate, benzoyl peroxide, and maleic anhydride modified PP enhances some mechanical properties like tear strength of cotton fiber-reinforced PP commingled composite systems. Fiber content, treatments, and moisture also varies dielectric constant and volume resistivity.

Morphology and Mechanical Properties of Normal Blends and In-Situ Microfibrillar Composites from Low-Density Polyethylene and Poly(ethylene terephthalate)

In this work, normal blends, microfibrillar blends and composites were prepared from low density polyethylene (LDPE) and poly(ethylene terephthalate) (PET) in 85/15 and 75/25 w/w% ratio in the presence and absence of a compatibilizer polyethylene grafted with maleic anhydride (PE-g-MA). The microfibrillar composites (MFCs) were prepared using extrusion – drawing – isotropization technique. The morphology development of the microfibrillar blends and composites was studied using scanning electron microscopy (SEM). The presence of 5 wt% PE-g-MA compatibilizer affected the continuity of the fibrils differently in 75/25 and 85/15 w/w% microfibrillar blends. In the case of normal blends the addition of compatibiliser reduced the size of the dispersed PET phase. The presence of PET microfibrils improved the tensile properties of the microfibrillar composites. The normal blends exhibited a relatively ductile failure during tensile loading in comparison with the microfibrillar composites. The microfibrillar nature of the dispersed phase was found to improve the stiffness of the composite rather than their impact strength.

Dynamic Mechanical Analysis of in situ Microfibrillar Composites Based on PP and PET

Microfibrillar composites (MFCs) based on polypropylene and poly (ethylene terephthalate) were prepared by a three step process namely blending (extrusion), fibrilization (drawing) and isotropization, using different draw ratios (viz. 2, 5, 8 and 10). The drawn (stretched) blend was injection moulded at a temperature between the melting points of the two polymers, leading to isotropization. During this step PET microfibrils got randomly distributed in an isotropic PP matrix to complete the formation of microfibrillar in situ composites. The dynamic mechanical properties such as storage modulus (E′), loss modulus (E″) and mechanical loss factor (tan δ) of PP, neat blend and in situ composites were investigated. The E′ values were found to increase up to a stretch ratio of 8. The glass transition temperature (Tg) of PP in the MFC was found to shift to higher values with an increase in stretch ratio. The presence of microfibrils showed a positive effect on the modulus at temperatures above Tg of PP, especially for the samples drawn at stretch ratio 5 and 8. The tan δ and E″ modulus spectra indicated a strong influence of the microfibrils on the magnitude of α and β relaxations of PP. The effect of test frequency on storage modulus, loss modulus and tan δ was studied.

Effect of blend ratio on the mechanical and sorption behaviour of polymer-polymer microfibrillar composites from low-density polyethylene and polyethylene terephthalate

The morphology of the neat blends, microfibrillar blends and the corresponding microfibrillar composites based on low-density polyethylene and polyethylene terephthalate was analyzed. As the polyethylene terephthalate concentration increased, an increase in the diameter of polyethylene terephthalate spheres/fibrils was observed. The fibrils with relatively uniform diameter distribution were obtained in the range of 15–25 wt% polyethylene terephthalate concentration. The tensile properties of the blends and microfibrillar composites increased with polyethylene terephthalate concentration up to an optimum level. The neat blends exhibited inferior tensile properties in comparison with the microfibrillar composites. As the polyethylene terephthalate concentration increased, the solvent uptake reduced. The diffusivity and permeability of the microfibrillar composites were lower than the corresponding blends. The solvent uptake was found to be lowest for the composite with 25 wt% polyethylene terephthalate concentration. The polyethylene terephthalate microfibrils in the microfibrillar composites offered a tortuous path for the diffusion of the solvent.

Hybrid nanocomposites based on poly aryl ether ketone, boron carbide and multi walled carbon nanotubes: Evaluation of tensile, dynamic mechanical and thermal degradation properties

Abstract In this study an attempt has been made to incorporate a radiation resistant filler like boron carbide (B4C) nanopowder along with multi walled carbon nanotubes (MWCNT) in a high performance polymer namely poly aryl ether ketone (PAEK) for potential applications in the nuclear industry. The dispersion of nanofillers in PAEK was established by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Infra red (IR) spectroscopy indicated the interaction between functionalized MWCNT (F-MWCNT) and PAEK. The optimum combination of B4C and F-MWCNT was obtained from the tensile property analysis. It was found from the dynamic mechanical analysis that the storage modulus of the composite at elevated temperature was enhanced by B4C inclusions. Mechanical damping factor spectra showed the shift of PAEK glass transition temperature to higher values due to the presence of B4C and F-MWCNT. Thermogravimetric analysis (TGA) presented the resistance offered by B4C to the degradation of PAEK especially at elevated temperatures.

Microstructure Development, Wear Characteristics and Kinetics of Thermal Decomposition of Hybrid Nanocomposites Based on Poly Aryl Ether Ketone, Boron Carbide and Multi Walled Carbon Nanotubes

In the present study a high performance polymer poly aryl ether ketone (PAEK) is reinforced with micro and nano boron carbide (B4C) and functionalized multi walled carbon nanotubes (F-MWCNT) to investigate the individual and hybrid effect of the fillers. Optical microscopy and transmission electron microscopy suggested the dispersion of micro and nano fillers respectively in PAEK matrix. The inclusion of B4C nano fillers increased the hardness of the composites which aided the wear resistance of the composites. The morphological features of the worn surface of the samples are analyzed using scanning electron microscopy. It is found from the izod impact test analysis that the impact strength of the composite enhanced by the F-MWCNT inclusion. The thermal properties of PAEK in the composites are studied using differential scanning calorimetry and it revealed dominant effect of F-MWCNT influencing the thermal transitions than the B4C particles. The kinetics of thermal degradation of various composites is analyzed using Coats–Redfern method. The positive influence of B4C in the matrix indicates that the thermal degradation is delayed due to the higher activation energy it possesses. The overall results shows that the hybrid nanocomposite exhibits better properties compared to individual micro and nano composites.

Experimental and micromechanical modeling of fracture toughness: MWCNT-reinforced polypropylene/glass fiber hybrid composites

In this study, polypropylene-based nano and hybrid composites are prepared with 20 wt% glass fiber and multiwalled carbon nanotubes (MWCNTs) ranging up to 5 wt%. The multiaxial stress fields developed during external loading of composites cause crack propagation by various fracture mechanisms. Among the nanocomposites, it is observed that the critical stress intensity factor (KI) is highest for the one prepared at 3 wt% loading of MWCNTs. The synergistic effect of multiscale fillers in hybrid composite with MWCNT content of 3 wt% results in superior fracture toughness properties as evidenced by 16.6% increase in KI with respect to neat PP. Analytical expressions that take into account the fracture mechanisms like particle debonding and matrix yielding are employed to estimate the composite crack resistance and then compared with experimentally obtained fracture toughness properties. The fracture toughness properties are found to be dependent on composition of fillers, matrix yield strain, and debonding strain of the composites.

Dynamic Mechanical Thermal Analysis of Polymer Nanocomposites

Abstract The objective of this chapter is to establish the use of dynamic mechanical thermal analysis in characterizing polymer nanocomposites. Dynamic mechanical analysis is a powerful tool employed to comprehend thermal transitions of viscoelastic materials by characterizing the evolution of their macromolecular relaxation as a function of temperature and loading frequency. The presence of nanofillers perturbs the relaxation of the polymer chains affecting the stiffness, rigidity, and energy absorbing capability of polymeric materials. The modifications in the viscoelastic behavior of the polymers with the inclusion of nanofillers can be effectively studied from the storage/loss moduli and damping factor spectra obtained from this analysis. In this chapter, the potential of dynamic mechanical thermal analysis is assessed by focusing on the ability of the technique to offer information not only on the viscoelastic performance of filled thermoplastic, thermosets, and elastomeric materials, but also on the miscibility and interface strengthening of polymer blends with nanoinclusions. The various theoretical equations used for modeling dynamic mechanical properties of polymer nanocomposites are discussed in detail.

Conducting Polyurethane Composites

Abstract Conducting polyurethane-based nanocomposites have been identified as one of the promising class of materials which find considerable attractive applications in various fields, such as construction, packaging, automotive, aerospace, military, medical, and electrical and electronics. In this chapter various aspects of conducting polyurethane nanocomposites are addressed, starting with their fabrication and ending with their applications. This chapter discusses various conducting polyurethane nanocomposites reinforced with various conducting fillers, such as carbon black, carbon nanotube, and graphene and also discusses a large variety of applications of composites which include shape memory, actuator sensors, and electromagnetic interference shielding fields.

Conducting Polyurethane Blends: Recent Advances and Perspectives

Abstract Polyurethane (PU) is a very important material with versatile properties. Melt blending of polyurethane with an intrinsic conducting polymer can improve the polyurethane properties such as electrical conductivity, corrosion protection, and electromagnetic shielding. The properties of blends are dependent upon the compatibility of the blend constituents. The main aim of this chapter is to explain the various properties and application of conducting polyurethane blends which are produced by mixing conducting polymers such as polyaniline, polypyrrole, or polythiophene with polyurethane. The rapid development of the new generation of electronic devices such as power sources, displays, and sensors requires intensive research on conducting polymer blends to improve the conductivity of insulating polymers and hence a wider application in fields such as electronics, electrical, automotive, aerospace, and the military.Polyurethane (PU) is a very important material with versatile properties. Melt blending of polyurethane with an intrinsic conducting polymer can improve the polyurethane properties such as electrical conductivity, corrosion protection, and electromagnetic shielding. The properties of blends are dependent upon the compatibility of the blend constituents. The main aim of this chapter is to explain the various properties and application of conducting polyurethane blends which are produced by mixing conducting polymers such as polyaniline, polypyrrole, or polythiophene with polyurethane. The rapid development of the new generation of electronic devices such as power sources, displays, and sensors requires intensive research on conducting polymer blends to improve the conductivity of insulating polymers and hence a wider application in fields such as electronics, electrical, automotive, aerospace, and the military.