Samrat Mukhopadhyay

Physical Modification of Natural Fibers and Thermoplastic Films for Composites - A Review

The article throws light on the physical methods to modify natural fibers to be used in composites. Physical methods in natural fiber processing are used to separate natural fiber bundles into individual filaments and to modify the surface structure of the fibers so as to improve the use of natural fibers in composites. Steam explosion and thermomechanical processes fall in the first category while plasma, dielectric barrier techniques and corona fall in the second. The physical treatments have also been used to modify the thermoplastic polymeric films like polyethylene and polypropylene in a bid to impart reactivity. Reviewing such developments, the areas for further research are suggested.

Mechanical properties of natural fibre-reinforced composites

Natural fibres were initially used in composite materials to predominately improve bulk and reduce cost rather than improving mechanical properties. But the environmental problems associated with the production and use of synthetic fibres have changed the scenario. In the previous decade, natural fibres have been extensively used as reinforcement materials for both synthetic and bio-degradable matrices. Natural fibre reinforcements have mostly improved flexural and impact properties, but tensile strength improvement has been marginal and has been an area of investigation. Many attempts have been made towards improving mechanical properties, with efforts directed at improving the interface, newer methods of production of composites, new modelling techniques etc. In this detailed review, an attempt is made to critically analyse the various research efforts directed towards improving the mechanical properties of natural fibre reinforced composites.

Some Studies on Mudar Fibers

In this work, Mudar fibers (Calotropis procera) have been characterized for their physical, chemical, and tensile properties. Mudar fibers have good length, strength, uniformity, fineness, and excellent moisture absorption. The study highlights the difficulties in spinning 100% Mudar yarn. Subsequently, a 75/25 Mudar/cotton blend is successfully spun in a cotton spinning system and the results are analyzed. Smooth Mudar fibers develop convolutions when treated with 5% NaOH, which can render spinning possible with fibers treated in such a way. The yarns have enough potential in natural fiber-reinforced composites and other industrial textiles application.

Variability of Tensile Properties of Fibers from Pseudostem of Banana Plant

This paper reports the variability of mechanical properties of banana fibers with respect to diameter, testing speed and gauge length. We report interesting findings on banana fibers. Tenacity of the fibers significantly improved for the fibers with lower linear density. An increase in speed resulted in improvement of fiber properties to a certain degree. Higher gauge lengths resulted in poor properties due to an increase in flaws in the structure. The banana fibers showed very high variability in linear density and mechanical properties.

A review on the use of fibers in reinforced cementitious concrete

Various fibers have been used to reinforce concrete to enhance properties of cement. This review critically analyses the use of different natural and synthetic fibers, the treatments done on some of them to be used in concrete, their strength and weaknesses to be used for such applications. In natural fibers, bamboo coir and jute which have been extensively used have been discussed. Also, the effect of alkali present in cement mixture on the degradation of natural fibers has been detailed. Critical observations such as change in crack pattern, effect of nature of fibers, and the environment in which they are reinforced have been discussed. Effect of use of different sealing materials for the hydrophobic fibers on the ultimate property of the reinforced concrete has been reviewed for various fibers. A comprehensive review of the synthetic fibers predominantly used in such reinforcements—PP, PE, and nylon—has been given along with a critical comparative study of recent developments in the field. The fiber–matrix interface studies have been discussed and further research areas have been suggested.

Drawing of polypropylene filaments on a gradient heater

Abstract High modulus and high tenacity polypropylene filament has been prepared by drawing as-spun filament on a heater having a gradient of temperature. The fiber properties are significantly affected by gradient heater settings, that is, nature and extent of gradient and end temperatures. Very high draw ratios are obtained through gradient drawing, resulting in high crystal perfection and crystallinity, along with very low void fraction. The gradient-drawn filaments showed superior mechanical as well as thermal properties when compared to filaments drawn over a constant temperature heater. Fibers having initial modulus of 17.5 GPa and tenacity of 750 MPa have been prepared in the process. Very low shrinkage of 7% at 150°C indicates excellent thermal stability of the gradient-drawn filaments.

Spider Silk - Providing New Insights in the Field of High Performance Materials

Despite being spun at ambient temperatures and pressures the excellent tensile and elongational properties of spider silk makes it very useful. A recent insight into the wonderful spinning process of the spider throws new light on the research on fibers. This article tries to overview the research in the last decade stressing on the interesting spinning and drawing techniques of the spider and some of its tensile and thermal properties, which makes the fiber unique. The recent characterizing techniques used to investigate spider silk have been discussed in depth and the future areas of research outlined.

Coir Fiber for Heat Insulation

Natural fibers are environment-friendly materials for their biodegradability and renewable characteristics. This paper details a comparative study of one of the natural fibers—coir and a mineral fiber asbestos-reinforced composite with respect to their behavioral aspects. In this experimental investigation, four sheets were cast with different fiber percentage and length (based on the total weight of cement fly ash and water) maintaining similar ingredients ratio. Load bearing capacity, water absorption, impermeability, acid resistance, and density tests were performed on the asbestos sheets and on the coir–cement sheet. An attempt has been made to develop a low cast technology of coir fiber-reinforced corrugated sheets as a substitute for hazardous asbestos. This method can be used in rural areas with the use of simple equipment.

Production and Properties of High-Modulus—High-Tenacity Polypropylene Filaments

Polypropylene (PP) filaments have become one of the most important industrial filaments. Fibers from advanced Ziegler-Natta and metallocene catalyst-based polypropylene have made inroads in technical textiles. High-modulus—high-tenacity PP filaments have found various uses in industrial applications on the basis of their superior properties and inert nature. The feed parameters as well as the processing variables - all have an important impact on the ultimate properties of PP filament, as has been observed by various researchers. This article critically reviews the production of high-modulus—high-tenacity PP filament along with proposed changes in microstructure leading to the superior mechanical properties. The contribution of crystallite and amorphous orientations, amorphous modulus, crystallinity, taut-tie molecules, and flaws in the shaping of mechanical properties of such filaments have been discussed. The chasm between practical and theoretical values in modulus and tenacity values are still large and a great deal of challenge involved in achieving high draw ratios. In most of the cases, high draw ratios have been achieved with single or multiple steps but with low strain rates and low processing speeds. Majority of the processes are batch processes and limits productivity.

Effect of pressure on structure and properties of lyocell fabric-based all-cellulose composite laminates

Abstract In this work, all-cellulose composite (ACC) laminates were manufactured from lyocell fabric using a simple hand lay-up and compression molding-based surface-selective dissolution technique. In dissolution step, temperature and dissolution time were fixed and pressure varied. Subsequently, the dissolved cellulose was regenerated via solvent exchange and then dried by hot-pressing. The microstructures of ACC laminates were analyzed by scanning electron microscope micrographs and measuring void content. Optimum microstructure and mechanical properties were obtained with a pressure of 1 MPa, but slightly deteriorated with further increase in pressure. The highest tensile strength and modulus achieved were 44.24 ± 2.2 MPa and 1.78 ± 0.14 GPa, respectively, for ACC-3. Best flexural strength and modulus obtained were 48.95 ± 2.87 MPa and 0.96 ± 0.21 GPa, respectively, for the same sample. The T-peel strength of ACC-3 also was very high, 2.78 ± 0.34 MPa. Application of pressure during drying had a great role on controlling shrinkage and internal voids in ACC laminates.