Facile fabrication of arecanut palm sheath based robust hydrophobic cellulose nanopapers via self-assembly of ZnO nanoflakes and its shelf-life prediction for sustainable packaging applications

Cellulose nanofibers have been extracted from arecanut palm sheath fibers via mild oxalic acid hydrolysis coupled with steam explosion technique. Cellulose nanofibers with diameter of 20.23 nm were obtained from arecanut palm sheath fibers. A series of robust hydrophobic cellulose nanopapers were fabricated by combining the synergistic effect of surface roughness induced by the successful deposition of zinc oxide (ZnO) nanoflakes and stearic acid modification via a simple and cost-effective method. In this work, agro-waste arecanut palm sheath was employed as a novel source for the extraction of cellulose nanofibers. 2 wt% of ZnO nanoflakes and 1 M concentration of stearic acid were used to fabricate mechanically robust hydrophobic cellulose nanopapers with a water contact angle (WCA) of 134°. During the deposition of zinc oxide nanoflakes on the CNP for inducing surface roughness, a hydrogen bonding interaction is formed between the hydroxyl groups of cellulose nanofibers and the zinc oxide nanoflakes. When this surface roughened CNP was dipped in stearic acid solution. The hydroxyl groups in zinc oxide nanoflakes undergoes esterification reaction with carboxyl groups in stearic acid solution forming an insoluble stearate layer and thus inducing hydrophobicity on CNP. The fabricated hydrophobic cellulose nanopaper displayed a tensile strength of 22.4 MPa and better UV blocking ability which is highly desirable for the sustainable packaging material in the current scenario. Furthermore, the service life of the pristine and modified cellulose nanopapers was predicted using the Arrhenius equation based on the tensile properties obtained during the accelerated ageing studies. The outcome of this study would be broadening the potential applications of hydrophobic and mechanically robust cellulose nanopapers in sustainable packaging applications.

Experimental and Simulation Studies on Nonwoven Polypropylene-Nitrile Rubber Blend: Recycling of Medical Face Masks to an Engineering Product

The battle against the COVID-19 pandemic counters the waste management system, as billions of single-use face masks are used per day all over the world. Proper disposal of used face masks without jeopardizing the health and the environment is a challenge. Herein, a novel method for recycling of medical face masks has been studied. This method incorporates the nonwoven polypropylene (PP) fiber, which is taken off from the mask after disinfecting it, with acrylonitrile butadiene rubber (NBR) using maleic anhydride as the compatibilizer, which results in a PP-NBR blend with a high percentage economy. The PP-NBR blends show enhanced thermomechanical properties among which, 70 wt % PP content shows superior properties compared to other composites with 40, 50, and 60 wt % of PP. The fully Atomistic simulation of PP-NBR blend with compatibilizer shows an improved tensile and barrier properties, which is in good agreement with the experimental studies. The molecular dynamics simulation confirms that the compatibility between non-polar PP and polar NBR phases are vitally important for increasing the interfacial adhesion and impeding the phase separation.

Fire-safe and environmentally friendly nanocomposites based on layered double hydroxides and ethylene propylene diene elastomer

The capability of layered double hydroxide has been explored as a potential flame retardant filler and the effect of the mechanical properties, dynamic mechanical properties, and thermal stability of the composites was also studied.

UNMODIFIED LDH AS REINFORCING FILLER FOR XNBR AND THE DEVELOPMENT OF FLAME-RETARDANT ELASTOMER COMPOSITES

Layered double hydroxides (LDHs), inorganic clay materials with mixed metals present in the structure along with some interlayer cations, have immense potential for use as a filler in rubbers. We report the preparation and properties of a set of novel nanocomposites consisting of a LDH dispersed in carboxylic–acrylonitrile–butadiene rubber (XNBR). We succeed in obtaining significantly improved physical properties by altering the chemical structure of a LDH with Zn and Al ions (Zn-Al LDH). In particular, we discover a significant reinforcing effect. This occurs despite the size difference between the LDH and traditional reinforcing fillers such as precipitated silica and carbon black. Both the elastic modulus and tensile strength increase. This increase is a function of the LDH concentration and, reaches a maximum value when the LDH concentration is at 100 phr. Experimental evidence suggests that this reinforcing effect is due to direct ion-to-ion interaction between the filler and the matrix. In addition, we report that the presence of the nanofiller positively affects the flame retardence and thermal decomposition of the nanocomposites. We attribute this effect to the presence of a layer formed by the nanofiller.

Influence of Matrix Polarity on the Properties of Ethylene Vinyl Acetate-Carbon Nanofiller Nanocomposites

A series of ethylene vinyl acetate (EVA) nanocomposites using four kinds of EVA with 40, 50, 60, and 70 wt% vinyl acetate (VA) contents and three different carbon-based nanofillers-expanded graphite (EG), multi-walled carbon nanotube (MWCNT), and carbon nanofiber (CNF) have been prepared via solution blending. The influence of the matrix polarity and the nature of nanofillers on the morphology and properties of EVA nanocomposites have been investigated. It is observed that the sample with lowest vinyl acetate content exhibits highest mechanical properties. However, the enhancement in mechanical properties with the incorporation of various nanofillers is the highest for EVA with high VA content. This trend has been followed in both dynamic mechanical properties and thermal conductivity of the nanocomposites. EVA copolymer undergoes a transition from partial to complete amorphousness between 40 and 50 wt% VA content, and this changes the dispersion of the nanofillers. The high VA-containing polymers show more affinity toward fillers due to the large free volume available and allow easy dispersion of nanofillers in the amorphous rubbery phase, as confirmed from the morphological studies. The thermal stability of the nanocomposites is also influenced by the type of nanofiller.

Influence of functionalization of multi-walled carbon nanotubes on the properties of ethylene vinyl acetate nanocomposites

Commercially available multiwalled carbon nanotubes (MWNT) were chemically modified by amine, acid and silane and their ethylene vinyl acetate (EVA) based nanocomposites were prepared. Unmodified and modified nanotubes were characterized by thermogravimetry, X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy and transmission electron microscopy. Early degradation of modified nanotubes from the thermogravimetry study proved the presence of functional groups on nanotube surface. Increase in D-band to G-band ratio and a shift in radial breathing mode peaks from the Raman spectra indicated the generation of surface defects due to functionalization and variation in van der Waals force of attraction between nanotube aggregates on modification. The unmodified nanotubes improved the tensile strength by 30% with 4 weight% of filler. Amine modification imparted further increase in strength due to the presence of functional groups on the nanotube surface and the subsequent better dispersion of the nanotubes in the polymer matrix. The silane treatment imparted maximum improvement in various properties of the nanocomposites. The nanotubes provided better thermal degradation stability and also higher thermal conductivity to virgin EVA. The results were well supported by the morphological as well as swelling study of the various samples.

High Strength - Low Hardness Thermoplastic Elastomers from Ethylene-Butene Copolymers and Low Density Polyethylene

A thermoplastic elastomer (TPE) is a rubbery material with final properties and functional performance similar to those of a conventional vulcanized rubber at ambient temperature, yet it can be processed as a thermoplastic at elevated temperature. The main objective of the present investigation was to prepare novel olefinic thermoplastic elastomers based on blends of a thermoplastic i.e. low density polyethylene (PE) and new ethylene-butene copolymers (PEB), which would have higher strength and lower hardness compared to the existing TPEs. The 70:30 PEB: PE blend exhibited the best properties. Ethylene vinyl acetate was found to work as compatibilizer at lower loadings in these blends. The resultant blends were of low hardness (60–80 Shore A) and high strength (26–33 MPa). The interaction parameter and the morphology of the blends were the key parameters, which governed the final properties of blends.

Bioaccumulation and toxicity of zinc in the green alga, Cladophora glomerata

The bioaccumulation and toxicity of zinc in Cladophora glomerata from two populations in the River Roding, Essex, UK, were examined in experimental laboratory flowing-water channels. Plants were subjected to zinc concentrations ranging from 0 to 4.0 mg litre(-1) at current velocities of 20-33 cm s(-1) for up to 3 h. Zinc in algal tissue was then quantified and toxicity was assessed by the ability of the alga to grow in a recovery medium after the experimental treatment. There was little difference in zinc bioaccumulation between Cladophora from the site showing mild organic pollution and that from the site subjected to considerable inputs from urban and motorway runoff. Uptake of zinc increased with increasing concentration in the test solution and was linear and proportional up to 0.4 mg litre(-1). Three stages of uptake were identified with the most dramatic accumulation occurring in the first 10 min. Experimental concentration factors ranged from 1.9-5.2 x 10(3), which were in agreement with those previously obtained in the field. Cellular damage was evident in Cladophora subjected to 0.4 mg litre(-1) zinc, and this increased with increasing zinc concentration, thus leading to the conclusion that, at times, the levels of zinc found in the river could be potentially damaging.

Recovery by riffle macroinvertebrates in a river after a major accidental spillage of chlorpyrifos

The impact of a major spillage of the insecticide 'Dursban' on the riffle macroinvertebrates along 19 km of the River Roding, Essex, is described. Five affected riffles and an upstream control were kick-sampled at approximately 10-week intervals for two years following the spill, and the results are compared with species composition and relative abundance data collected from the same sites during the previous six years. Initial concentrations of the active ingredient, chlorpyrifos, in river water (up to 2.5 mg litre(-1)) exceeded the level lethal to all the aquatic arthropods present by at least 10-fold, and this group of macroinvertebrates was eliminated. Molluscs and annelids, which are relatively tolerant of chlorpyrifos, survived. Since these groups already dominated the lowermost urban reaches, the impact of the spill was greatest further upstream, where reaches with a better water quality previously supported a more diverse and abundant arthropod fauna. Chlorpyrifos residues in water declined below 1 microg litre(-1) within 11 weeks, but sediment within 5 km of the spillage site remained highly contaminated for considerably longer. Of ten arthropod taxa previously common to all sites, chironomid larvae were first to recolonise affected reaches, 13 weeks after the spill. The isopod Asellus aquaticus, was also quick to recover. Although other arthropods had recolonised most sites within 79 weeks, the coleopteran Oulimnius tuberculatus and the epheremeropteran Caenis moesta had failed to return to the lowermost reaches after 108 weeks. Downstream drift was probably the principal factor influencing the pattern of arthropod recolonisation, with the location and aquatic fauna of tributary streams entering the affected reaches being particularly important.