Biocomposites reinforced with natural fibers: 2000–2010

Novel cattail fiber composites: converting waste biomass into reinforcement for composites

Vacuum-assisted resin transfer molding (VARTM), used in manufacturing medium to large-sized composites for transportation industries, requires non-woven mats. While non-woven glass mats used in these applications are optimized for resin impregnation and properties, such optimized mats for natural fibers are not available. In the current research, cattail fibers were extracted from plants (18-30% yield) using alkali retting and non-woven cattail fiber mat was manufactured. The extracted fibers exhibited a normal distribution in diameter (d avg. = 32.1 µm); the modulus and strength varied inversely with diameter, and their average values were 19.1 GPa and 172.3 MPa, respectively. The cattail fiber composites were manufactured using non-woven mats, Stypol polyester resin, VARTM pressure (101 kPa) and compression molding pressures (260 and 560 kPa) and tested. Out-of-plane permeability changed with the fiber volume fraction (V f) of the mats, which was influenced by areal density, thickness, and fiber packing in the mat. The cattail fibers reinforced the Stypol resin significantly. The modulus and the strength increased with consolidation pressures due to the increase in V f, with maximum values of 7.4 GPa and 48 MPa, respectively, demonstrating the utility of cattail fibers from waste biomass as reinforcements.

Critical Review of Natural Fiber Reinforced Hybrid Composites: Processing, Properties, Applications and Cost

Increasing scientific interest has occurred concerning the utilization of natural fiber-enhanced hybrid composites that incorporate one or more types of natural enhancement. Annual natural fiber production is estimated to be 1,783,965 × 103 tons/year. Extensive studies have been conducted in the domains of natural/synthetic as well as natural/natural hybrid composites. As synthetic fibers have better rigidity and strength than natural fibers, natural/synthetic hybrid composites have superior qualities via hybridization compared to natural composites in fibers. In general, natural fiber compounds have lower characteristics, limiting the use of natural composites reinforced by fiber. Significant effort was spent in enhancing the mechanical characteristics of this group of materials to increase their strengths and applications, especially via the hybridization process, by manipulating the characteristics of fiber-reinforced composite materials. Current studies concentrate on enhancing the understanding of natural fiber-matrix adhesion, enhancing processing methods, and natural fiber compatibility. The optimal and resilient conceptions have also been addressed due to the inherently more significant variabilities. Moreover, much research has tackled natural fiber reinforced hybrid composite costs. In addition, this review article aims to offer a review of the variables that lead to the mechanical and structural failure of natural fiber reinforced polymer composites, as well as an overview of the details and costings of the composites.

Analysis of the Frequency of Acoustic Emission Events in Terms of the Assessment of the Reduction of Mechanical Parameters of Cellulose-Cement Composites

The article proposes the application of the acoustic emission method as a technique for the evaluation of mechanical parameters of cellulose–cement composites. The analysis focused on frequency values in a time series analysis of elements subject to three-point flexural stress. In the course of a statistic analysis, it has been demonstrated that a significant reduction of the recorded frequency values is associated with a considerable reduction in strength. This allowed the authors to determine the range of frequencies related to the depreciation in the strength of an element. The tests were carried out on elements cut from a full-size cellulose–cement board. Samples exposed to potential operational factors (environmental and exceptional) were analysed. It was shown that the frequencies recorded before reaching the maximum load during bending of samples exposed to environmental factors (water and low temperature) were significantly different (were much lower) from the sounds emitted by elements subjected to exceptional factors (fire and high temperature). Considering the fact that the analysed frequencies of acoustic emission events occur before the maximum stresses in the material are reached and the elements are destroyed, this provides the basis for the use of the acoustic emission method to assess the condition of cellulose–cement composites in terms of lowering mechanical parameters by observing the frequency of events generated by the material during load action. It was found that generating by material frequencies above 300 kHz during bending does not result in a significant decrease in mechanical parameters. The emission of signals with frequencies ranging from 200 to 300 kHz indicate that there was a decline in strength exceeding 25% but less than 50%. The registration of signals with frequencies below 200 kHz indicates that the reduction in mechanical parameters was greater than 50%.

Characteristics of Unidirectional Green Wood Fiber/Polylactic Acid Composite Parts Printed with Various Layer Thicknesses by Fused Filament Fabrication

In this study, the effect of layer thickness on the physicomechanical properties of the wood fiber-polylactic acid composite (WPC) part obtained by fused filament fabrication (FFF) was investigated. The results showed that most of the characteristics of the FFF-printed WPC part significantly depended on the printing layer thickness. As the layer thickness increased, the density of the printed WPC part decreased significantly, while the dimensional stability of the water-immersed WPC part decreased. In addition, specific tensile properties increased and the other specific mechanical properties (flexural, compressive, and shear properties) decreased with increasing layer thickness. Furthermore, scanning electronic microscopy micrographs illustrated that the number of voids and defects was more often observed on the surface of the WPC part printed with higher layer thickness. Therefore, these results indicated that the different layer thicknesses in FFF manufacturing have a substantial impact on the dimensional stability and specific mechanical properties of the FFF-printed WPC part.

Development and Characterization of a 3D Printed Cocoa Bean Shell Filled Recycled Polypropylene for Sustainable Composites

Natural filler-based composites are an environmentally friendly and potentially sustainable alternative to synthetic or plastic counterparts. Recycling polymers and using agro-industrial wastes are measures that help to achieve a circular economy. Thus, this work presents the development and characterization of a 3D printing filament based on recycled polypropylene and cocoa bean shells, which has not been explored yet. The obtained composites were thermally and physically characterized. In addition, the warping effect, mechanical, and morphological analyses were performed on 3D printed specimens. Thermal analysis exhibited decreased thermal stability when cacao bean shell (CBS) particles were added due to their lignocellulosic content. A reduction in both melting enthalpy and crystallinity percentage was identified. This is caused by the increase in the amorphous structures present in the hemicellulose and lignin of the CBS. Mechanical tests showed high dependence of the mechanical properties on the 3D printing raster angle. Tensile strength increased when a raster angle of 0° was used, compared to specimens printed at 90°, due to the load direction. Tensile strength and fracture strain were improved with CBS addition in specimens printed at 90°, and better bonding between adjacent layers was achieved. Electron microscope images identified particle fracture, filler-matrix debonding, and matrix breakage as the central failure mechanisms. These failure mechanisms are attributed to the poor interfacial bonding between the CBS particles and the matrix, which reduced the tensile properties of specimens printed at 0°. On the other hand, the printing process showed that cocoa bean shell particles reduced by 67% the characteristic warping effect of recycled polypropylene during 3D printing, which is advantageous for 3D printing applications of the rPP. Thereby, potential sustainable natural filler composite filaments for 3D printing applications with low density and low cost can be developed, adding value to agro-industrial and plastic wastes.

Effect of the Micronization of Pulp Fibers on the Properties of Green Composites

Green composites, composed of bio-based matrices and natural fibers, are a sustainable alternative for composites based on conventional thermoplastics and glass fibers. In this work, micronized bleached Eucalyptus kraft pulp (BEKP) fibers were used as reinforcement in biopolymeric matrices, namely poly(lactic acid) (PLA) and poly(hydroxybutyrate) (PHB). The influence of the load and aspect ratio of the mechanically treated microfibers on the morphology, water uptake, melt flowability, and mechanical and thermal properties of the green composites were investigated. Increasing fiber loads raised the tensile and flexural moduli as well as the tensile strength of the composites, while decreasing their elongation at the break and melt flow rate. The reduced aspect ratio of the micronized fibers (in the range from 11.0 to 28.9) improved their embedment in the matrices, particularly for PHB, leading to superior mechanical performance and lower water uptake when compared with the composites with non-micronized pulp fibers. The overall results show that micronization is a simple and sustainable alternative for conventional chemical treatments in the manufacturing of entirely bio-based composites.

Experimental Determination of Coefficients for the Renner Model of the Thermodynamic Equation of State of the Poly(butylene succinate) and Wheat Bran Biocomposites

This paper presents the assumptions of a thermodynamic equation of state for polymers according to the Renner model. The experiments involved extruding a biocomposite based on poly(butylene succinate) that was filled with ground wheat bran with its size not exceeding 200 μm. The biocomposite was produced in pellet form with three different contents by weight of wheat bran, i.e., 10%, 30% and 50%. All specimens were examined for their thermodynamic p-v-T characteristics. Taking advantage of the SimFit module of Cadmould 3D-F, experimental results were used to determine the coefficients of thermodynamic equation of state for the tested biocomposite according to the Renner model. The coefficients were then used to calculate transition temperature and to create diagrams illustrating the relationship between pressure, temperature and specific volume for the tested biocomposite. The obtained results can serve as a basis for assessing the suitability of the biocomposite for injection molding, selecting technological parameters of this process, as well as for analyzing shrinkage and defects of injection-molded parts.

Fibre-Cement Panel Ventilated Façade Smart Control System

This paper outlines a design for a fibre-cement panel ventilated façade smart control system based on the acoustic emission method. The paper also provides methodology and test results, as well as statistical analysis of the three-point bending results with AE signal acquisition as a basis for the development of the system in question. The test items were samples cut from a full-size fibre-cement panel for interior and exterior use, according to the standard guidelines. The recorded acoustic emission signals were classified statistically into four classes, which were assigned to the processes occurring in the material structure as a result of the applied load. The system development was based on the differences between the characteristics of the individual signal classes and their number for each test case, as well as on the different distribution of successive classes over time. Given the results of the tests and the resulting conclusions indicating the applicability of the acoustic emission method (based on signal classification using the k-means algorithm for the assessment of variations in the mechanical parameters of cement-fibre composites), a methodology for such assessment was therefore developed. The approach proposed is a reasonable method for assessing the variation in mechanical parameters of fibre-cement panels on the basis of the parameters determined by the non-destructive method indicated.

Sunflower Stalks versus Corn Cobs as Raw Materials for Sustainable Concrete

Concrete, the most common material in the building industry, involves the use of mineral aggregates that represent an exhaustible resource, despite their large availability. For a series of applications, these mineral aggregates can be replaced by vegetal ones, which represent an easy renewable natural resource. In this study, two types of vegetal raw materials, namely sunflower stalks and corn cobs, were used in developing 10 compositions of ecological microconcrete, with different percentages involved: 20%, 35%, 50%, 65% and 80%; they were analyzed from the perspectives of density, compressive strength, splitting tensile strength, resistance to repeated freeze-thaw cycles, modulus of elasticity and thermal conductivity. The results revealed that the microconcretes with sunflower stalks registered slightly higher densities and better results regarding the compressive strength, splitting tensile strength, modulus of elasticity, and freeze-thaw resistance than those with corn cobs. Lightweight concrete is obtained when more than 50% replacement rates of the mineral aggregates are used.

The Use of Computed Tomography in the Study of Microstructure of Molded Pieces Made of Poly(3-hydroxybutyric-co-3-hydroxyvaleric acid) (PHBV) Biocomposites with Natural Fiber

In order to determine the structure homogeneity of biocomposites filled with fibers, as well as the evaluation of fibers’ arrangement and their orientation on the sample cross-section at varied injection rates, a study was conducted using computed tomography (CT). The main advantage of this test is the fact that in order to assess the microstructure on cross-sections, the samples do not have to be processed mechanically, which allows for presenting the actual image of the microstructure. The paper presents the issues of such tests for the biocomposite of poly (3-hydroxybutyric-co-3-hydroxyvaleric acid) (PHBV)-hemp fibers. It should be emphasized that CT scanning of PHBV-hemp fiber biocomposites is quite difficult to perform due to the similar density of the fibers and the polymer matrix. Due to the high difficulty of distinguishing fibers against the background of the polymer matrix during CT examination, a biocomposite containing 15% hemp fibers was analyzed. The samples for testing were manufactured using the injection molding process at variable injection rates, i.e., 10, 35 and 70 cm³/s. The images obtained by computed tomography show the distribution of hemp fibers and their clusters in the PHBV matrix and the degree of porosity on the sample cross-section. There were significant microstructural differences for the samples injected at the highest injection rates, including, among others, the occurrence of a smaller number of fibers and pores on the surface layer of the molded piece. The phenomenon observed was verified by testing chosen mechanical properties, shrinkage and water absorption of the samples. Some properties improved with an increasing injection rate, while others deteriorated and vice versa. An analysis of biocomposites’ microstructures using computed tomography provides a wide range of possibilities for future research, including an assessment of the structure of the molded parts. These tests may allow one, for example, to detect the cause of molded piece properties decreasing in a specific area as a result of a high degree of fiber disorientation, as well as the defects resulting from high porosity of the material. Such analyses can be particularly useful for producers that deal with the injection molding of pieces molded with specific properties.

Composites of a Polypropylene Random Copolymer and Date Stone Flour: Crystalline Details and Mechanical Response

Several composites were prepared based on a polypropylene random copolymer (PPR) and different amounts of date stone flour (DSF). This cellulosic fiber was silanized beforehand in order to reduce its hydrophilicity and improve the interfacial adhesion with the polymer. Other composites were also obtained, including a sorbitol derivative as an effective nucleant. Films made from these composites were prepared using two different thermal treatments, involving slow crystallization and rapid cooling from the melt. Scanning electron microscopy was used to evaluate the morphological features and the DSF particle dispersion within the PPR matrix. X-ray diffraction experiments and differential scanning calorimetry tests were employed to assess the crystalline characteristics and for the phase transitions, paying especial attention to the effects of the DSF and nucleating agent on PPR crystallization. An important nucleation ability was found for DSF, and evidently for the sorbitol derivative. The peak crystallization temperature upon cooling was considerably increased by the incorporation of either the nucleant or DSF. Additionally, a much higher proportion of orthorhombic crystals developed in relation to the monoclinic ones. Moreover, the mechanical responses were estimated from the microhardness experiments and significant improvements were found with increasing DSF contents. All of these findings indicate that the use of silanized DSF is a fairly good approach for the preparation of polymeric eco-composites, taking advantage of the widespread availability of this lignocellulosic material, which is otherwise wasted.

Effect of Evening Primrose (Oenothera biennis) Oil Cake on the Properties of Polyurethane/Polyisocyanurate Bio-Composites

Rigid polyurethane/polyisocyanurate (RPU/PIR) foam formulations were modified by evening primrose (Oenothera biennis) oil cake as a bio-filler in the amount of 5 to 50 wt.%. The obtained foams were tested in terms of processing parameters, cellular structure (SEM analysis), physico-mechanical properties (apparent density, compressive strength, brittleness, accelerated aging tests), thermal insulation properties (thermal conductivity coefficient, closed cells content, absorbability and water absorption), flammability, smoke emission, and thermal properties. The obtained results showed that the amount of bio-filler had a significant influence on the morphology of the modified foams. Thorough mixing of the polyurethane premix allowed better homogenization of the bio-filler in the polyurethane matrix, resulting in a regular cellular structure. This resulted in an improvement in the physico-mechanical and thermal insulation properties as well as a reduction in the flammability of the obtained materials. This research provided important information on the management of the waste product from the edible oil industry and the production process of fire-safe RPU/PIR foams with improved performance properties. Due to these beneficial effects, it was found that the use of evening primrose oil cake as a bio-filler for RPU/PIR foams opens a new way of waste management to obtain new “green” materials.

Critical Factors for Optimum Biodegradation of Bast Fiber’s Gums in Bacterial Retting

Bast fiber plants require a post-harvest process to yield useable natural cellulosic fibers, denoted as retting or degumming. It encompasses the degradation of the cell wall’s non-cellulosic gummy substances (NCGs), facilitating fibers separations, setting the fiber’s quality, and determining downstream usages. Due to the inconvenience of traditional retting practices, bacterial inoculum and enzyme applications for retting gained attention. Therefore, concurrent changes of agroclimatic and socioeconomic conditions, the conventional water retting confront multiple difficulties, bast industries become vulnerable, and bacterial agents mediated augmented bio-retting processes trying to adapt to sustainability. However, this process’s success demands a delicate balance among substrates and retting-related biotic and abiotic factors. These critical factors were coupled to degrade bast fibers NCGs in bacterial retting while holistically disregarded in basic research. In this study, a set of factors were defined that critically regulates the process and requires to be comprehended to achieve optimum retting without failure. This review presents the bacterial strain characteristics, enzyme potentials, specific bast plant cell wall’s structure, compositions, solvents, and interactions relating to the maximum NCGs removal. Among plants, associated factors pectin is the primary biding material that determines the process’s dynamics, while its degree of esterification has a proficient effect through bacterial enzymatic degradation. The accomplished bast plant cell wall’s structure, macerating solvents pH, and temperature greatly influence the bacterial retting process. This article also highlights the remediation process of water retting pollution in a biocompatible manner concerning the bast fiber industry’s endurance.

Incorporation of Biochar to Improve Mechanical, Thermal and Electrical Properties of Polymer Composites

The strive for utilization of green fillers in polymer composite has increased focus on application of natural biomass-based fillers. Biochar has garnered a lot of attention as a filler material and has the potential to replace conventionally used inorganic mineral fillers. Biochar is a carbon rich product obtained from thermochemical conversion of biomass in nitrogen environment. In this review, current studies dealing with incorporation of biochar in polymer matrices as a reinforcement and conductive filler were addressed. Each study mentioned here is nuanced, while addressing the same goal of utilization of biochar as a filler. In this review paper, an in-depth analysis of biochar and its structure is presented. The paper explored the various methods employed in fabrication of the biocomposites. A thorough review on the effect of addition of biochar on the overall composite properties showed immense promise in improving the overall composite properties. An analysis of the possible knowledge gaps was also done, and improvements were suggested. Through this study we tried to present the status of application of biochar as a filler material and its potential future applications.

Heat Transfer in Straw-Based Thermal Insulating Materials

An analytic-empirical model was developed to describe the heat transfer process in raw straw bulks based on laboratory experiments for calculating the thermal performance of straw-based walls and thermal insulations. During the tests, two different types of straw were investigated. The first was barley, which we used to compose our model and identify the influencing model parameters, and the second was wheat straw, which was used only for validation. Both straws were tested in their raw, natural bulks without any modification except drying. We tested the thermal conductivity of the materials in a bulk density range between 80 and 180 kg/m³ as well as the stem density, material density, cellulose content, and porosity. The proposed model considers the raw straw stems as natural composites that contain different solids and gas phases that are connected in parallel to each other. We identified and separated the following thermal conductivity factors: solid conduction, gas conduction in stem bulks with conduction factors for pore gas, void gas, and gaps among stems, as well as radiation. These factors are affected by the type of straw and their bulk density. Therefore, we introduced empirical flatness and reverse flatness factors to our model, describing the relationship between heat conduction in stems and voids to bulk density using the geometric parameters of undisturbed and compressed stems. After the validation, our model achieved good agreement with the measured thermal conductivities. As an additional outcome of our research, the optimal bulk densities of two different straw types were found to be similar at 120 kg/m³.

Evaluation of the Mechanical and Biocidal Properties of Lapacho from Tabebuia Plant as a Biocomposite Material

The aim of this article is to discuss in detail the physicochemical properties of polylactide (PLA) reinforced by cortex fibers, which may cause bacterial mortality and increased biodegradation rates. PLA biocomposites containing cortex Lapacho fibers from Tabebuia (1-10 wt%) were prepared by extrusion and injection moulding processes. The effects of Lapacho on the mechanical and biocidal properties of the biocomposites were studied using tensile and impact tests, dynamic mechanical analysis (DMA), differential scanning calorimetry (DSC), thermogravimetry (TG), and the method of evaluating the antibacterial activity of antibacterial treated according to the standard ISO 22196:2011. It also presented the effects of Lapacho on the structural properties and biodegradation rates of biocomposites. This research study provides very important results complementing the current state of knowledge about the biocidal properties of Lapacho from Tabebuia plants and about cortex-reinforced biocomposites.

Comprehensive characterization of raw and alkali (NaOH) treated natural fibers from Symphirema involucratum stem

The present study investigated the effect of alkali treatment on the enhancement of Physico-chemical, tensile, thermal and surface properties of Symphirema involucratum stem fiber (SISF). The investigation of chemical constituents of optimally alkalized SISF revealed that ideal increment of cellulose content (68.69 wt%) and desired modification of other chemical components was accomplished through 60 min immersion period. An increase in the crystallinity index to 33.33% and small crystallite size to 3.21 nm was noted by X-ray diffraction analysis. Moreover, the treated fiber was found suitable for light-weight applications since physical analysis acknowledges that the density of the fiber augmented to 1424 kg/m³after surface treatment that reduces total weight percentage. The enhancements in tensile strength (471.2 ± 19.8 MPa), tensile modulus (5.82 ± 0.77 GPa) and thermal stability (371 °C) were noted that ensures the treated fiber has good mechanical and thermal properties required for composite preparation. These findings validated that the optimally surface-modified SISF is a suitable material for lightweight composite structures, for the time being.

Potential Application of Peppermint (Mentha piperita L.), German Chamomile (Matricaria chamomilla L.) and Yarrow (Achillea millefolium L.) as Active Fillers in Natural Rubber Biocomposites

In this study, peppermint (Mentha piperita L.), German chamomile (Matricaria chamomilla L.) and yarrow (Achillea millefolium L.) were applied as natural fibrous fillers to create biocomposites containing substances of plant origin. The purpose of the work was to investigate the activity and effectiveness of selected plants as a material for the modification of natural rubber composites. This research was the first approach to examine the usefulness of peppermint, German chamomile and yarrow in the field of polymer technology. Dried and ground plant particles were subjected to Fourier transmission infrared spectroscopy (FTIR) and UV–Vis spectroscopy, thermogravimetric analysis (TGA), goniometric measurements (contact angle) and scanning electron microscopy (SEM). The characterization of natural rubber composites filled with bio-additives was performed including rheometric measurements, FTIR, TGA, cross-linking density, mechanical properties and colour change after simulated aging processes. Composites filled with natural fillers showed improved barrier properties and mechanical strength. Moreover, an increase in the cross-linking density of the materials before and after the simulated aging processes, compared to the reference sample, was observed.

Effect of Mercerization/Alkali Surface Treatment of Natural Fibres and Their Utilization in Polymer Composites: Mechanical and Morphological Studies

Environmental pollution, such as air, water, and soil pollution, has become the most serious issue. Soil pollution is a major concern as it generally affects the lands and makes them non-fertile. The main cause of soil pollution is agro-waste. It may be possible to mitigate the agro-waste pollution by re-utilizing this agro-waste, namely natural fibres (NFs), by blending into polymer-based material to reinforce the polymer composite. However, there are pros and cons to this approach. Consequently, the polymer composite materials fabricated using NFs are inferior to those polymer composites that are reinforced by, e.g., carbon or glass fibres from the mechanical properties’ perspectives. The limitations of utilizing natural fibres in polymer matrix are their high moisture absorption, resulting in high swelling rate and degradation, inferior resistance to fire and chemical, and inferior mechanical properties. In particular, the NF polymer composites exhibit inferior interfacial adhesion between the fibre and the matrix, which, if improved, ultimately overcome all the listed limitations and improve the mechanical properties of the developed composites. To improve the interfacial adhesion leading to the enhancement of the mechanical properties, optimum chemical treatment such as Alkalization/Mercerization of the fibres have been explored. This article discusses the Mercerization/Alkali surface treatment method for NFs and its effects on the fibres regarding the Mercerization/Alkali surface treatment method for NFs and its effect on the fibres regarding their utilization in the polymer composites, the morphological features, and mechanical properties of composites.

Extraction and determination of the Pimelea toxin simplexin in complex plant-polymer biocomposites using ultrahigh-performance liquid chromatography coupled with quadrupole Orbitrap mass spectrometry

In the present paper, we describe how a robust and fundamental methodology was developed for extraction and determination of a principal natural toxin compound, simplexin, from a series of bulk biocomposites. These complex matrices were fabricated by direct encapsulating either ground plant particles or an ethanolic crude extract of the Australian toxic pasture plant Pimelea trichostachya in the biodegradable polymer poly(3-hydroxybutyrate-co-3-hydroxyvalerate). Proton nuclear magnetic resonance spectroscopy was initially employed to examine the chemical compositions of these complicated systems. Then, a more sensitive strategy was developed and validated by combining solid-phase extraction and ultrahigh-performance liquid chromatography hyphenated with a quadrupole Orbitrap mass spectrometer for the quantification of simplexin embedded in different biocomposites. Satisfactory linearity (R² > 0.99) and recovery ranges (86.8-116%) with precision (relative standard deviations) of between 0.2 and 13% (n = 3) were achieved from seven biocomposites. The established protocol was further shown to be accurate and reliable in confirming the homogeneous distribution of the simplexin in different biocomposite formulations. A limited mass transfer of simplexin (< 3.5%) from one of the biocomposites into a simulated but sterilized in vitro rumen environment after a 10-day incubation was also revealed by utilizing the method. This quantitative analysis of targeted natural product within plant material-integrated polymeric platforms has potential application when controlled release is required in the bovine rumen and other biological systems. Graphical abstract.

Bionic Design and 3D Printing of Continuous Carbon Fiber-Reinforced Polylactic Acid Composite with Barbicel Structure of Eagle-Owl Feather

Inspired by eagle-owl feather with characteristics of light weight and high strength, the bionic continuous carbon fiber-reinforced polylactic acid composite with barbicel structure was successfully 3D printed. Under the action of external load, angles between barbicels and rachis structure of eagle-owl feather decreased, which consumed a part of energy and built structure base of bionic feather structure model with a certain arrangement angle of continuous carbon fiber. Variation of bionic structure model design parameters significantly affected the mechanical properties of the 3D printing bionic composites. The relatively low continuous carbon fiber content on tensile force direction restricted enhancement of tensile strength of bionic composite. However, attributed to different angle arrangement of continuous carbon fiber, the propagation of cracks in bionic composite was hindered, exhibiting high impact resistance. The effective and feasible bionic feather design and 3D printing of continuous carbon fiber-reinforced polylactic acid composite extended the corresponding application in the areas with high impact loads.

Effects of water absorption on the mechanical properties of hybrid natural fibre/phenol formaldehyde composites

This investigation is carried out to understand the effects of water absorption on the mechanical properties of hybrid phenol formaldehyde (PF) composite fabricated with Areca Fine Fibres (AFFs) and Calotropis Gigantea Fibre (CGF). Hybrid CGF/AFF/PF composites were manufactured using the hand layup technique at varying weight percentages of fibre reinforcement (25, 35 and 45%). Hybrid composite having 35 wt.% showed better mechanical properties (tensile strength ca. 59 MPa, flexural strength ca. 73 MPa and impact strength 1.43 kJ/m²) under wet and dry conditions as compared to the other hybrid composites. In general, the inclusion of the fibres enhanced the mechanical properties of neat PF. Increase in the fibre content increased the water absorption, however, after 120 h of immersion, all the composites attained an equilibrium state.

Geopolymers and Fiber-Reinforced Concrete Composites in Civil Engineering

This paper discusses the influence of fiber reinforcement on the properties of geopolymer concrete composites, based on fly ash, ground granulated blast furnace slag and metakaolin. Traditional concrete composites are brittle in nature due to low tensile strength. The inclusion of fibrous material alters brittle behavior of concrete along with a significant improvement in mechanical properties i.e., toughness, strain and flexural strength. Ordinary Portland cement (OPC) is mainly used as a binding agent in concrete composites. However, current environmental awareness promotes the use of alternative binders i.e., geopolymers, to replace OPC because in OPC production, significant quantity of CO₂ is released that creates environmental pollution. Geopolymer concrete composites have been characterized using a wide range of analytical tools including scanning electron microscopy (SEM) and elemental detection X-ray spectroscopy (EDX). Insight into the physicochemical behavior of geopolymers, their constituents and reinforcement with natural polymeric fibers for the making of concrete composites has been gained. Focus has been given to the use of sisal, jute, basalt and glass fibers.

Opuntia spp. Fibre Characterisation to Obtain Sustainable Materials in the Composites Field

Some studies have evaluated the use of Opuntia as reinforcement for polymeric matrices, obtaining good results in energy absorption tests and increasing the tensile elastic modulus. However, no studies focusing on the previous characterisation of the fibres and their treatment to improve compatibility with polymeric matrices have been found. This work analyses the chemical composition of Opuntia maxima (OM) and Opuntia dillenii (OD) cladodes and fibre, studying how different treatments influence it. AOAC 2000 methods were used to determine non-structural components and the Van Soest method was used to estimate structural components. Surface characteristics of the samples were also evaluated by Fourier Transform Infrared Spectroscopy (FTIR). Opuntia fibre presented higher cellulose (50–66%) and lignin (6–14%) content and lower hemicellulose (8–13%) content than Opuntia cladodes (9–14% cellulose, 20–50% hemicellulose, 1–4% lignin). Despite the variability of lignocellulosic materials, OD cladodes treated with water and acetic acid achieved an increase in the structural components. Alkaline fibre treatment removed pectin and hemicellulose from the fibre surface, slightly increasing the cellulose content. Future research should evaluate whether the treated Opuntia fibre can improve the mechanical properties of reinforced polymer.

Lignin-Based High-Performance Fibers by Textile Spinning Techniques

As a major component of lignocellulosic biomass, lignin is one of the largest natural resources of biopolymers and, thus, an abundant and renewable raw material for products, such as high-performance fibers for industrial applications. Direct conversion of lignin has long been investigated, but the fiber spinning process for lignin is difficult and the obtained fibers exhibit unsatisfactory mechanical performance mainly due to the amorphous chemical structure, low molecular weight of lignin, and broad molecular weight distribution. Therefore, different textile spinning techniques, modifications of lignin, and incorporation of lignin into polymers have been and are being developed to increase lignin's spinnability and compatibility with existing materials to yield fibers with better mechanical performance. This review presents the latest advances in the textile fabrication techniques, modified lignin-based high-performance fibers, and their potential in the enhancement of the mechanical performance.

Damping Behavior of Thermoplastic Organic Sheets with Continuous Natural Fiber-Reinforcement

In the field of lightweight construction, the use of natural fibers as reinforcement in composites has been increasingly discussed. Additionally, the damping properties of natural fibers are known from fiber materials such as fiber insulation boards. In the scope of the work presented here, the focus is on identifying the potential of natural fibers for lightweight structures with high vibration damping capacity. For this purpose, test specimens made of flax fiber-reinforced and glass fiber-reinforced thermoplastic composites were manufactured and characterized. Contrary to expectations, the flax fiber-reinforced composite exhibited an almost isotropic damping characteristic. A comparison of the damping and stiffness properties determined by measurement confirms the high potential of natural fiber-reinforced materials for lightweight structures with high damping.

A review on Borassus flabellifer lignocellulose fiber reinforced polymer composites

Natural fiber composites play an important role for developing high performance engineering materials due to its facile availability, recyclability and eco-friendly nature. Borassus flabellifer products are significant and economical for urban and rural areas, and its fruit, leaf stalk and leaves are used in domestic purposes and some of them are disposed as waste. This waste part of Borassus flabellifer serves as a potential resource for natural fibers and utilized as raw material for reinforced polymer composites. The aim of this article narrates a comprehensive overview of Borassus fibers and its composites. Alkali treatment techniques, different fabrication methods, preparation of different matrices reinforced with bio-fibers and chemical, mechanical, thermal, morphological properties of Borassus fibers and its composites have been studied. Overall, this review article highlights, investigates and identifies gaps of the earlier research work, and provides the resourceful data for future work in various streams with Borassus fiber as reinforcement.

Influence of the Alkali Treatment of Flax and Hemp Fibers on the Properties of PHBV Based Biocomposites

This study assessed the impact of alkali treatment of hemp and flax fibers on mechanical properties (determined by means of the uniaxial tensile test, impact tensile strength test and hardness test), processing properties (the course of the extrusion and injection process) and usable properties (shrinkage of molded pieces, degree of water absorption) of biocomposites on the base of poly (3-hydroxybutyric-co-3-hydroxyvaleric acid) (PHBV) biopolymer. For this purpose, 1 mm of length flax and hemp fibers was surface-modified by means of aqueous solution of NaOH (sodium hydroxide) with concentrations of 2%, 5% and 10%. The composites were made using the extrusion technology. The test specimens were produced by injection molding technology. In total, eight types of biocomposites with modified and non-modified fibers were produced, and each biocomposite contained the same filler content (15 wt.%). Their properties were compared in some cases with pure PHBV polymer. In the case of biocomposites filled with hemp fibers, it was noted that an increase of the alkalizing solution concentration improved most of the tested properties of the obtained biocomposites. On the other hand, in the case of flax fibers, there was a significant decrease in most of the mechanical properties tested for the composite containing fibers etched by 10% NaOH solution. The obtained results were verified by examining fibers and the destroyed specimens with a scanning electron microscope (SEM) and an optical microscope, which confirmed, especially, the significant geometry changes of the flax fibers etched by 10% NaOH solution. This procedure also resulted in a significant change of processing properties—a composite of this fiber type required about 20 °C lower temperature during the extrusion and injection molding process in order to obtain the right product. These results lead to the important conclusion that for each filler of the plant-origin and polymer matrix, the fiber alkalization method should be selected individually in order to improve the specific properties of biocomposites.

Influence of Calcium Silicate and Hydrophobic Agent Coatings on Thermal, Water Barrier, Mechanical and Biodegradation Properties of Cellulose

Thin films of cellulose and cellulose–CaSiO₃ composites were prepared using 1-ethyl-3-methylimidazolium acetate (EMIMAc) as the dissolution medium and the composites were regenerated from an anti-solvent. The surface hydrophilicity of the resultant cellulose composites was lowered by coating them with three different hydrophobizing agents, specifically, trichloro(octadecyl)silane (TOS), ethyl 2-cyanoacrylate (E2CA) and octadecylphosphonic acid (ODPA), using a simple dip-coating technique. The prepared materials were subjected to flame retardancy, water barrier, thermal, mechanical and biodegradation properties analyses. The addition of CaSiO₃ into the cellulose increased the degradation temperature and flame retardant properties of the cellulose. The water barrier property of cellulose–CaSiO₃ composites under long term water exposure completely depends on the nature of the hydrophobic agents used for the surface modification process. All of the cellulose composites behaved mechanically as a pure elastic material with a glassy state from room temperature to 250 °C, and from 20% to 70% relative humidity (RH). The presence of the CaSiO₃ filler had no effect on the elastic modulus, but it seemed to increase after the TOS surface treatment. Biodegradability of the cellulose was evaluated by enzyme treatments and the influence of CaSiO₃ and hydrophobic agents was also derived.

Potential Uses of Musaceae Wastes: Case of Application in the Development of Bio-Based Composites

The Musaceae family has significant potential as a source of lignocellulosic fibres and starch from the plant's bunches and pseudostems. These materials, which have traditionally been considered waste, can be used to produce fully bio-based composites to replace petroleum-derived synthetic plastics in some sectors such as packaging, the automotive industry, and implants. The fibres extracted from Musaceae have mechanical, thermal, and physicochemical properties that allow them to compete with other natural fibres such as sisal, henequen, fique, and jute, among others, which are currently used in the preparation of bio-based composites. Despite the potential use of Musaceae residues, there are currently not many records related to bio-based composites' developments using starches, flours, and lignocellulosic fibres from banana and plantain pseudostems. In this sense, the present study focusses on the description of the Musaceae components and the review of experimental reports where both lignocellulosic fibre from banana pseudostem and flour and starch are used with different biodegradable and non-biodegradable matrices, specifying the types of surface modification, the processing techniques used, and the applications achieved.

Degradation Behavior, Biocompatibility, Electrochemical Performance, and Circularity Potential of Transient Batteries

Transient technology seeks the development of materials, devices, or systems that undergo controlled degradation processes after a stable operation period, leaving behind harmless residues. To enable externally powered fully transient devices operating for longer periods compared to passive devices, transient batteries are needed. Albeit transient batteries are initially intended for biomedical applications, they represent an effective solution to circumvent the current contaminant leakage into the environment. Transient technology enables a more efficient recycling as it enhances material retrieval rates, limiting both human and environmental exposures to the hazardous pollutants present in conventional batteries. Little efforts are focused to catalog and understand the degradation characteristics of transient batteries. As the energy field is a property-driven science, not only electrochemical performance but also their degradation behavior plays a pivotal role in defining the specific end-use applications. The state-of-the-art transient batteries are critically reviewed with special emphasis on the degradation mechanisms, transiency time, and biocompatibility of the released degradation products. The potential of transient batteries to change the current paradigm that considers batteries as harmful waste is highlighted. Overall, transient batteries are ready for takeoff and hold a promising future to be a frontrunner in the uptake of circular economy concepts.

Recycled Cellulose Fiber Reinforced Plaster

This paper aims to develop recycled fiber reinforced cement plaster mortar with a good workability of fresh mixture, and insulation, mechanical and adhesive properties of the final hardened product for indoor application. The effect of the incorporation of different portions of three types of cellulose fibers from waste paper recycling into cement mortar (cement/sand ratio of 1:3) on its properties of workability, as well as other physical and mechanical parameters, was studied. The waste paper fiber (WPF) samples were characterized by their different cellulose contents, degree of polymerization, and residues from paper-making. The cement to waste paper fiber mass ratios (C/WPF) ranged from 500:1 to 3:1, and significantly influenced the consistency, bulk density, thermal conductivity, water absorption behavior, and compressive and flexural strength of the fiber-cement mortars. The workability tests of the fiber-cement mortars containing less than 2% WPF achieved optimal properties corresponding to plastic mortars (140–200 mm). The development of dry bulk density and thermal conductivity values of 28-day hardened fiber-cement mortars was favorable with a declining C/WPF ratio, while increasing the fiber content in cement mortars led to a worsening of the water absorption behavior and a lower mechanical performance of the mortars. These key findings were related to a higher porosity and weaker adhesion of fibers and cement particles at the matrix-fiber interface. The adhesion ability of fiber-cement plastering mortar based on WPF samples with the highest cellulose content as a fine filler and two types of mixed hydraulic binder (cement with finely ground granulated blast furnace slag and natural limestone) on commonly used substrates, such as brick and aerated concrete blocks, was also investigated. The adhesive strength testing of these hardened fiber-cement plaster mortars on both substrates revealed lime-cement mortar to be more suitable for fine plaster. The different behavior of fiber-cement containing finely ground slag manifested in a greater depth of the plaster layer failure, crack formation, and in greater damage to the cohesion between the substrate and mortar for the observed time.

Recent Advances in Elongational Flow Dominated Polymer Processing Technologies

The continuous development of plasticizing conveying methods and devices has been carried out to meet the needs of the polymer processing industry. As compared to the conventional shear-flow-dominated plasticizing and conveying techniques, a new method for processing polymers based on elongational flow was proposed. This new method and the related devices such as vane extruders, eccentric rotor extruders and so on, exhibited multiple advantages including shorter processing time, higher mixing effectiveness, improved product performance and better adaptability to various material systems. The development of new techniques in the field of polymer material processing has opened up a broad space for the development of new plastic products, improved product performance and reduced processing costs. In this review, recent advances concerning the processing techniques based on elongational flow are summarized, and the broad applications in polymer processing as well as some future opportunities and challenges in this vibrant area are elucidated in detail.

On the Use of Paper Sludge as Filler in Biocomposites for Injection Moulding

The potential use of paper sludge (PS) as filler in the production of bio-composites based on poly lactic acid (PLA) and polybutylene adipate terephthalate (PBAT) was investigated. PS/PLA/PBAT composites, with addition of acetyl tributyl citrate (ATBC) as biobased plasticizer, were produced with PS loadings up to 30 wt.% by twin-screw extrusion followed by injection moulding. The composites were characterized by rheological measurements, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and mechanical tests (tensile and impact resistance) to study the effect of PS on the processability, thermal stability, crystallinity and mechanical performance of polymeric matrix. The optimized composites at higher PS content were successfully processed to produce pots for horticulture and, in view of this application, preliminary phytotoxicity tests were conducted using the germination test on Lepidium sativum L. seeds. Results revealed that developed composites up to 30 wt.% PS had good processability by extrusion and injection moulding showing that PS is a potential substitute of calcium carbonate as filler in the production of bio-composites, and the absence of phytotoxic effects showed the possibility of their use in the production of pots/items for applications in floriculture and/or horticulture.

Extraction, Treatment and Applications of Natural Fibers for Bio-Composites – A Critical Review

Nowadays, sustainable and eco-friendly products are gaining more attention in various engineering industries owing to their considerable strength-to-weight ratio, abundant availability, and recyclability. The properties of biofibers depend on the cultivation method, environmental conditions, and extraction method. Biofibers are hauled out by dew retting, water retting, and mechanical decortication methods. The properties of natural fiber–reinforced composites can be enhanced by proper physical and chemical treatments. The aim of this study is to propose a complete evaluation of the different extraction methods applied on natural fibers. Various physical and chemical treatment methods were used to ascertain the properties of optimized natural fiber-reinforced composites for various industrial applications. The key findings derived from various existing data and the chemical treatment results of the biofiber-reinforced composite are specifically highlighted with critical assessment. The properties and use of natural fiber-reinforced composites in the various fields of applications have made them candidates of choice over synthetic petroleum–based fibers.

Combination of Corn Pith Fiber and Biobased Flame Retardant: A Novel Method toward Flame Retardancy, Thermal Stability, and Mechanical Properties of Polylactide

Some crop by-products are considered to be promising materials for the development of novel biobased products for industrial applications. The flammability of these alternatives to conventional materials is a constraint to expanded applications. Polylactide (PLA) composites containing a combination of oxidized corn pith fiber (OCC) and a biobased flame retardant (PA-THAM) have been prepared via an in situ modification method. SEM/EDS, FTIR and TGA were performed to establish that PA-THAM was coated onto the surface of OCC. The mechanical properties, thermal stability and fire behavior of PLA-based biocomposites were investigated. The incorporation of 5 phr PA-THAM imparted biocomposite good interfacial adhesion and increased decomposition temperature at 10% mass loss by 50 °C. The flame retardant properties were also improved, as reflected by an increased LOI value, a UL-94 V-2 rating, reduction of PHRR, and increased formation of char residue. Therefore, the introduction of 5 phr PA-THAM can maintain a good balance between flame retardancy and mechanical properties of this PLA/OCC system.

Insight into the Surface Properties of Wood Fiber-Polymer Composites

The surface properties of wood fiber (WF) filled polymer composites depend on the filler loading and are closely related to the distribution and orientation in the polymer matrix. In this study, wood fibers (WF) were incorporated into thermoplastic composites based on non-recycled polypropylene (PP) and recycled (R-PP) composites by melt compounding and injection moulding. ATR-FTIR (attenuated total reflection Fourier transform infrared spectroscopy) measurements clearly showed the propagation of WF functional groups at the surface layer of WF-PP/WF-R-PP composites preferentially with WF loading up to 30%. Optical microscopy and nanoindentation method confirmed the alignment of thinner skin layer of WF-PP/WF-R-PP composites with increasing WF addition. The thickness of the skin layer was mainly influenced by the WF loading. The effect of the addition of WF on modulus and hardness, at least at 30 and 40 wt.%, varies for PP and R-PP matrix. On the other hand, surface zeta potential measurements show increased hydrophilicity with increasing amounts of WF. Moreover, WF in PP/R-PP matrix is also responsible for the antioxidant properties of these composites as measured by DPPH (2,2′-diphenyl-1-picrylhydrazyl) assay.

Kenaf Fiber/Pet Yarn Reinforced Epoxy Hybrid Polymer Composites: Morphological, Tensile, and Flammability Properties

The application of natural fibers is rapidly growing in many sectors, such as construction, automobile, and furniture. Kenaf fiber (KF) is a natural fiber that is in demand owing to its eco-friendly and renewable nature. Nowadays, there are various new applications for kenaf, such as in absorbents and building materials. It also has commercial applications, such as in the automotive industry. Magnesium hydroxide (Mg(OH)₂) is used as a fire retardant as it is low in cost and has good flame retardancy, while polyester yarn (PET) has high tensile strength. The aim of this study was to determine the horizontal burning rate, tensile strength, and surface morphology of kenaf fiber/PET yarn reinforced epoxy fire retardant composites. The composites were prepared by hybridized epoxy and Mg(OH)₂ PET with different amounts of KF content (0%, 20%, 35%, and 50%) using the cold press method. The specimen with 35% KF (epoxy/PET/KF-35) displayed better flammability properties and had the lowest average burning rate of 14.55 mm/min, while epoxy/PET/KF-50 with 50% KF had the highest tensile strength of all the samples. This was due to fewer defects being detected on the surface morphology of epoxy/PET/KF-35 compared to the other samples, which influenced the mechanical properties of the composites.

Potential for Natural Fiber Reinforcement in PLA Polymer Filaments for Fused Deposition Modeling (FDM) Additive Manufacturing: A Review

In this review, the potential of natural fiber and kenaf fiber (KF) reinforced PLA composite filament for fused deposition modeling (FDM) 3D-printing technology is highlighted. Additive manufacturing is a material-processing method in which the addition of materials layer by layer creates a three-dimensional object. Unfortunately, it still cannot compete with conventional manufacturing processes, and instead serves as an economically effective tool for small-batch or high-variety product production. Being preformed of composite filaments makes it easiest to print using an FDM 3D printer without or with minimum alteration to the hardware parts. On the other hand, natural fiber-reinforced polymer composite filaments have gained great attention in the market. However, uneven printing, clogging, and the inhomogeneous distribution of the fiber-matrix remain the main challenges. At the same time, kenaf fibers are one of the most popular reinforcements in polymer composites. Although they have a good record on strength reinforcement, with low cost and light weight, kenaf fiber reinforcement PLA filament is still seldom seen in previous studies. Therefore, this review serves to promote kenaf fiber in PLA composite filaments for FDM 3D printing. To promote the use of natural fiber-reinforced polymer composite in AM, eight challenges must be solved and carried out. Moreover, some concerns arise to achieve long-term sustainability and market acceptability of KF/PLA composite filaments.

The Challenges and Future Perspective of Woven Kenaf Reinforcement in Thermoset Polymer Composites in Malaysia: A Review

In this review, the challenges faced by woven kenaf thermoset polymer composites in Malaysia were addressed with respect to three major aspects: woven kenaf reinforcement quality, Malaysian citizen awareness of woven kenaf thermoset composite products, and government supports. Kenaf plantations were introduced in Malaysia in the last two decades, but have generally not produced much kenaf composite product that has been widely accepted by the public. However, woven kenaf fiber enhances the thermoset composites to a similar degree or better than other natural fibers, especially with respect to impact resistance. Woven kenaf composites have been applied in automotive structural studies in Malaysia, yet they are still far from commercialization. Hence, this review discusses the kenaf fiber woven in Malaysia, thermoset and bio-based thermoset polymers, thermoset composite processing methods and, most importantly, the challenges faced in Malaysia. This review sets guidelines, provides an overview, and shares knowledge as to the potential challenges currently faced by woven kenaf reinforcements in thermoset polymer composites, allowing researchers to shift their interests and plans for conducting future studies on woven kenaf thermoset polymer composites.

Physical and Mechanical Properties of Natural Leaf Fiber-Reinforced Epoxy Polyester Composites

In recent times, demand for light weight and high strength materials fabricated from natural fibres has increased tremendously. The use of natural fibres has rapidly increased due to their high availability, low density, and renewable capability over synthetic fibre. Natural leaf fibres are easy to extract from the plant (retting process is easy), which offers high stiffness, less energy consumption, less health risk, environment friendly, and better insulation property than the synthetic fibre-based composite. Natural leaf fibre composites have low machining wear with low cost and excellent performance in engineering applications, and hence established as superior reinforcing materials compared to other plant fibres. In this review, the physical and mechanical properties of different natural leaf fibre-based composites are addressed. The influences of fibre loading and fibre length on mechanical properties are discussed for different matrices-based composite materials. The surface modifications of natural fibre also play a crucial role in improving physical and mechanical properties regarding composite materials due to improved fibre/matrix adhesion. Additionally, the present review also deals with the effect of silane-treated leaf fibre-reinforced thermoset composite, which play an important role in enhancing the mechanical and physical properties of the composites.