Kestur Gundappa Satyanarayana

Nanocomposites: synthesis, structure, properties and new application opportunities

Nanocomposites, a high performance material exhibit unusual property combinations and unique design possibilities. With an estimated annual growth rate of about 25% and fastest demand to be in engineering plastics and elastomers, their potential is so striking that they are useful in several areas ranging from packaging to biomedical applications. In this unified overview the three types of matrix nanocomposites are presented underlining the need for these materials, their processing methods and some recent results on structure, properties and potential applications, perspectives including need for such materials in future space mission and other interesting applications together with market and safety aspects. Possible uses of natural materials such as clay based minerals, chrysotile and lignocellulosic fibers are highlighted. Being environmentally friendly, applications of nanocomposites offer new technology and business opportunities for several sectors of the aerospace, automotive, electronics and biotechnology industries.

Selection of high strength natural fibers

By means of dimensional selection of natural lignocellulosic fibers, based on precise diameter measurements, it was recently possible to obtain fibers with relatively higher tensile strength. The present article overviews works on the statistical evaluation, through the Weibull analysis, of the ultimate tensile stress of eight lignocellulosic fibers: sisal, ramie, curaua, jute, bamboo, coir, piassava and buriti. It is shown that, for all of these fibers, the tensile strength holds an inverse relationship with the fiber diameter. Statistically this relationship conforms to a hyperbolic type of analytical equation, which discloses the possibility of unusually high strength fibers to be selected in association with very small diameters. A structural analysis using scanning electron microscopy offered an explanation to the strengthening mechanisms responsible for the superior performance of these dimensionally selected fibers.

Preparation and characterization of biodegradable composites based on Brazilian cassava starch, corn starch and green coconut fibers

Increasing search for new materials with high premium on eco-friendliness, new trend is emerging in materials development such as composites, which are well established for a wide variety of applications. With growing interest and importance of renewable bioresources has led to more stress on the use of locally available materials. This paper presents preliminary results on the preparation and characterization of composites based on Brazilian coconut fibers and starches of cassava and corn. The raw materials were characterized for their morphology, chemical composition, and thermal properties and X-ray diffraction studies. Coir fibers were also tested for their tensile properties showing increasing strength and Youngs modulus with decreasing diameter, while the % elongation remaining constant. Lignin content of coir was found to be 35%. Structure and properties of composites containing 0, 5 10, 15% fibers in both the matrices and prepared by compression molding would be compared. For the 2 types of starch, there was an increase in the tensile strength by the increasing proportion of fiber. The effect of moisture in the composite stress affects the strength and percentage elongation. The water absorption was higher in the composites made from cassava starch.

Effect of Processing Conditions on Tensile Properties of Green Composites of Castor Oil Cake Starch-Plant Fibers

The authors have characterized castor oil cake (COS) and ‘crude’ glycerin (CG) and carried out preliminary studies to assess their composites containing plant fibers prepared under manual conditions. Based on the results obtained in the study, efforts were made to prepare similar ‘green’ composites under controlled conditions. This paper presents preparation and characterization of composites using COS and CG as matrix with banana and sugarcane bagasse fibers under controlled temperature and pressure. While stress-strain curves of the matrix material were found to be typical of thermoplastics, those of composites showed a smaller plastic region. Youngs modulus, yield strength, ultimate tensile strength and strain at break obtained were found to be different from those reported earlier that were obtained by manual method. The values of these properties for matrix were found to be lower than those reported earlier for similar matrix. However, the values for the above properties in the composites (prepared with this matrix) were found to be higher than those obtained under manual conditions. These results are explained by the fractographic studies, which revealed good fiber/ matrix adhesion.

Effect of domestic compatabilizer on the performance of polypropylene-sawdust composites

Greater concern for environmental safety and fuel economy has increased interest in the use of renewable resources for development of new materials. Wood–plastic composites, made of recycled plastic and wood wastes, are very attractive in this respect, making this one of the most dynamic areas of new developments in the plastics industry in the past decade. This paper presents the preparation and characterization of polypropylene-sawdust composites by compression molding using maleated polypropylene (MAPP) produced in Brazil by reactive extrusion, with different amounts of two types of peroxides. The MAPP was characterized for thermal properties, melt flow index, and chemical structure, while the composites containing both uncoated and MAPP-coated sawdust were characterized for mechanical properties to understand the effect of coating as well as to compare these properties with those of composites prepared with commercial MAPP. The MAPP was efficient as a compatabilizer for polypropylene/sawdust composites. Better impact and tensile properties were observed in composites prepared with medium and high melt flow index compatibilizer concentrations, respectively.

Preparation and Characterization of Nano Silica from Equisetum arvenses

With the progress of nanotechnology and increase in demand, several silica processing industries have started producing silica nanoparticles. As a result, the search for new sources capable of producing this material has been attracting the interest of many researchers. With this background, a study was carried out to obtain silica nano particles from the Equisetum arvenses, a plant that possesses one of the highest amounts of silicon. This paper presents the preparation of nano silica particles with different combinations of acid washing and calcination at varying temperatures between 773 K and 873 K. The nanoparticles produced were characterized for nitrogen adsorption, morphology using transmission electron microscope and structural analysis by X-ray fluorescence and diffraction. It was found that nanoparticles produced by two cycles of acid washing and calcination at 773 K gave the best results, producing a material with white color, the highest specific surface area of about 330 m²/g with diameter of about 8 nm, and 93.5% of amorphous silica. The nanoparticles obtained can be potential industrial raw material for many applications.

Effect of processing parameters on the properties of polypropylene–sawdust composites:

Considering the boom in the market for wood plastic composite (WPC) products due to their relatively high specific strength properties, low maintenance costs, and wide range of applications, many authors have studied the performance of these composites prepared by reactive extrusion with different compatibilizers and peroxide types. This paper presents the density, chemical composition, and morphology of sawdust and the preparation and characterization of WPC with polypropylene by compression molding using different amounts of sawdust with and without coating with compatibilizer. Good-quality WPCs were obtained, as evident from almost identical experimental and theoretical density values of these composites. The WPCs prepared without compatibilizer coating exhibited low tensile properties. Irrespective of coating by different compatibilizers, the maximum tensile strength of all the WPCs decreased with increasing amount of sawdust. The WPCs prepared with uncoated sawdust fibers absorbed much more water than those prepared with compatibilizer-coated fibers, the latter showing increasing water intake with increasing amount of sawdust. These results are discussed in terms of melt-flow index, density differences, and adhesion between the sawdust and polypropylene.

Charpy impact resistance of alkali treated curaua reinforced polyester composites

Natural fibers obtained from cellulose-based plants are being used as reinforcement of polymer composite owing to both environmental and technical advantages. One important technical characteristic of most lignocellulosic fibers is the bend flexibility, which allows them to resist impact forces. As a consequence, there is an increasing application of these lignocellulosic fibers in automobile parts that, during a crash event, should absorb the impact energy without splitting into sharp pieces. The present work investigates the toughness behavior of polyester composites reinforced with up to 30% in volume of alkali treated continuous and aligned curaua fibers by means of Charpy impact tests. It was found that the incorporation of treated curaua fibers increased the composite absorbed impact energy but not as much as in composites reinforced with non-treated fibers. Macroscopic observation, and scanning electron microscopy analysis of fracture surface, revealed that the main mechanism for the increase in the Charpy notch toughness is the interfacial rupture between the curaua fiber and the polyester matrix.

Evaluation of polypropylene/saw dust composites prepared with maleated polypropylene (mapp) produced by reactive extrusion

Considering the importance of the environment and fuel economy, the Brazilian automotive industry has focused on the development of lightweight materials based on renewable resources. Replacement of PPtalc composite by PP- saw dust composite is a promising possibility. This paper presents the preparation of maleated polypropylene (MAPP) through reactive extrusion using different amounts of peroxides and maleic anhydride as well its characterization. Using 20% of saw dust coated with different amounts of prepared MAPP, several composites were prepared including one with commercial MAPP. Injection molded samples of all these composites along with that without the compatibilizer were characterized for mechanical properties. These studies indicated fulfilling the proposed objectives: (i) finding the optimal reactive extrusion conditions to prepare MAPP samples; (ii) preparation of PP/saw dust composites with and without MAPP coating; (iii) to arrive at optimized composite to get the best performance through their characterization for various properties of all the produced composites.

Effect of the type of fiber (coconut, eucalyptus, or pine) and compatibilizer on the properties of extruded composites of recycled high density polyethylene

Because of the growing interest in recycling agro-industrial materials to address both environmental concerns and add value to products, this paper reports experiments to develop composites using recycled high density polyethylene and three lignocellulosic fiber powders. The composites were processed with and without compatibilizer by extrusion and characterized. The melt flow index, mechanical properties, and water absorption of composites with compatibilizer varied with the type of fibers, with composites having eucalyptus fiber showing the best results for flexural and compressive strength and water absorption. However, no significant gain in flexural and compressive strengths was observed in composites containing coconut fibers and those without compatibilizer. Screw-holding strength and hardness values were highest in composites containing coconut fibers. The mechanical properties can be explained based on morphology and fractographic studies of composites. Linear thermal coefficient values of all the composites were lower than those of the matrix due to the presence of fillers.