Suhara Panthapulakkal

Studies on the Water Absorption Properties of Short Hemp—Glass Fiber Hybrid Polypropylene Composites

Hemp fiber is one of the inexpensive and readily available bast natural fibers and hemp-fiber reinforced polymer composite products have gained considerable attraction for automotive interior products. Though extensive research has been made on the performance evaluation of these composite materials, not much data is available on the moisture absorption of the composites, which restricts their use in exterior applications. This study aims to investigate the moisture absorption of short hemp fiber and hemp-glass hybrid reinforced thermoplastic composites to study their suitability in outdoor applications. The water absorption properties and its effect on the tensile properties of hemp and hemp/glass fiber hybrid polypropylene (PP) composites prepared by an injection molding process were investigated. Effect of hybridization on the water uptake and the kinetics of moisture absorption of the hemp fiber composites were evaluated by immersing the hybrid composite samples in distilled water at different temperatures, of 40, 60 and 80°C. The composites showed a Fickian mode of diffusion; however, a deviation was observed at higher temperature and may be attributed to the microcraks developed at the interface and dissolution of the lower molecular weight substances from the natural fibers. Equilibrium moisture content (Mm) showed that water up take of 40 wt% hemp fiber reinforced PP composites was highest and incorporation of glass fiber decreased the water uptake significantly (40%). Equilibrium moisture content was found to be independent of temperature, while diffusion coefficient (D) was increased with temperature. Effect of water absorption on the tensile properties of the composites showed that there is a significant reduction in strength and stiffness. It was observed that hybridization with glass fibers did not have any significant effect on the strength properties of the aged samples. The tensile properties of the re-dried aged samples showed an increased retention of strength properties after drying; however a complete recovery of the properties has not been achieved. This indicated that water absorption is not a physical process and permanent damage occurred to the composite after aging.

Enhancement of Processability of Rice Husk Filled High-density Polyethylene Composite Profiles

The effect of coupling agent and processing aid on the performance properties of rice husk filled high-density polyethylene (HDPE) composites was studied. Composite profiles of HDPE filled with 65% rice husk were extruded using a single screw extruder with die dimensions of 3 8 mm. Processability and performance properties of the composites were highly dependent on the concentration of the coupling agent and processing aid in the composite formulation. Attempt was made to optimize the composite formulation with respect to both coupling agent and processing aid to attain optimum mechanical and water absorption properties with an optimum extrusion rate. Incorporation of a terpolymer (ethylene-acrylic ester-maleic anhydride) based coupling agent enhanced the properties of the composites with a significant reduction in the extrusion rate. Addition of processing aid enhanced the extrusion rate and showed a negative impact on the performance properties. Composites with a coupling agent to processing aid ratio of 0.73: 0.59 by weight showed an optimum combination of performance properties and extrusion rate.

Preparation and Characterization of Cellulose Nanofibril Films from Wood Fibre and Their Thermoplastic Polycarbonate Composites

The aim of this study was to develop cellulose-nanofibril-film-reinforced polycarbonate composites by compression molding. Nano fibres were prepared from wood pulp fibres by mechanical defibrillation, and diameter distribution of the fibres produced was in the range of 1–100 nm. Nanofibre films were prepared from the nanofibre suspensions and were characterized in terms of strength properties, crystallinity, and thermal properties. Strength and modulus of the nano fibre films prepared were 240 MPa and 11 GPa, respectively. Thermal properties of the sheets demonstrated the suitability of processing fibre sheets at high temperature. Tensile properties of the films subjected to composite-processing conditions demonstrated the thermal stability of the fibre films during the compression molding process. Nanocomposites of different fibre loads were prepared by press-molding nano fibre sheets with different thickness in between polycarbonate sheet at 205°C under pressure. The tensile modulus and strength of the polycarbonate increased with the incorporation of the fibres. The strength of the thermoplastic increased 24% with 10% of the fibres and is increased up to 30% with 18% of the fibres. Tensile modulus of the polycarbonate demonstrated significant enhancement (about 100%).

Investigation of Structural Changes of Alkaline-extracted Wood Using X-ray Microtomography and X-ray Diffraction: A Comparison of Microwave versus Conventional Method of Extraction

Abstract The effect of extraction of wood components on wood anatomy and cellulose crystallinity was studied using X-ray computed microtomography (micro CT) and X-ray crystallography. Micro CT of the xylem vessels of birch wood samples was used for the quantitative determination of the wood porosity after conventional and microwave extraction. The method was also used as an indirect means for the determination of temperature generated inside the fibers. Original porosity of birch wood was 18.5 ± 1.5%, and porosity increased with both extractions. The increase in wood porosity after 10 minutes of microwave extraction was double that of wood after conventional method of extraction at 90°C for two hours (42% vs. 26%), indicating a sudden rupture of the wood structure due to the volumetric heating effect produced by the microwave heating. Comparison of porosities of the conventionally extracted samples at different temperatures for the same duration indicated that the temperature generated inside the fibers during 10 minutes of microwave extraction is around 120°C. Crystallinity of cellulose did not change after both extractions, suggesting that the extraction did not affect the strength of the fibers.

The effect of sodium hydroxide surface treatment on the tensile strength and elastic modulus of cellulose nanofiber

The use of cellulose nanofibers in the reinforcement of polymers has applications in bio-based building materials. However, one problem observed when using cellulose nanofibers within composites is the difficulty of ensuring their adequate dispersion. The phenomenon of agglomeration is attributed to the high density of polarized hydroxyl groups at the surface of cellulose nanofibers. Initial observations indicate that cellulose nanofiber agglomeration, in a cement matrix at volume fractions larger than 0.1%, are theorized to have contributed to the brittle failure mode of the paste. In order to expand the use of cellulose nanofibers in bio-based building materials, it is necessary to reduce their agglomeration and improve their dispersion within a polymer through surface modifications in an effort to improve their reinforcing capability in composite materials. As such, a mild alkali treatment with sodium hydroxide (NaOH), also known as mercerization, was chosen for use in this study due to its longstanding establishment as a common, low cost, and simple process. Alkali treatment was found to improve the values of tensile strength and modulus, compared to the untreated strips, by 20% and 24%, respectively. These results could be attributed to the rearrangement of fibrils along the direction of tensile deformation, as a result of the dissolution of lignin and hemicelluloses fractions.

Natural fiber and hybrid fiber thermoplastic composites: Advancements in lightweighting applications

Natural fiber composites and hybrid fiber composites with natural fibers and a small portion of synthetic fibers are gaining momentum in various industry sectors such as automotive, aerospace, construction, sporting goods, and marine applications. The popularity of these composites has resulted mainly from their lightweight, design friendliness, and the awareness towards the sustainable product design. Though hybrid composites with natural fiber and glass fiber combinations have opened up new applications, the authors see the future trend as the composites based on natural fiber and carbon fiber composites, as these composites are very efficient in lightweighting compared to their glass counterparts. The use of unused and inexpensive agricultural residues in making composites can have economic, social, and technological benefits. Further, use of lightweight composites in automotives improves fuel efficiency and has a positive impact on the environment because of emission reduction. Hybrid composites using waste residues and/or recycled carbon fiber could be the next-generation cost-effective material for the lightweighting application.