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Fibers collected from the husk of areca nut trees were chopped to a length of 30 mm and were either used as such or subjected to alkaline treatment by immersion in a 5% sodium hydroxide (NaOH) solution. The untreated and treated fibers were investigated using thermogravimetric analysis (TGA) before the fabrication of composites using an epoxy matrix. Different amounts of fibers were introduced in the matrix, fabricating the composite by compression molding. The composites were subjected to tensile, flexural, and Charpy impact and Shore D hardness testing, which all demonstrated the considerable advantage obtained with the growing quantity of fibers, especially when employing treated fibers, except in the case of hardness, where limited advantages were encountered. Wear tests were carried out on treated fiber composites and the surface morphology of the worn-out samples was studied, which also demonstrated the improvement in fiber-matrix bonding obtained with the growing amount of fibers. The main limitation of the fibers was their low elongation even after treatment. The fibers hardly reached 4%, which might represent a quite normal value for this kind of fibers, possibly due to with tendency to fibrillation. This would somehow compare these composites with others with similar amounts and lengths of natural fibers.

This research explores natural fiber composites (NFCs) as alternatives to traditional materials such as fiberglass. By examining fibers like abaca, bamboo, banana, coir, flax, hemp, jute, kenaf, pineapple leaf (PALF), sisal, and others, we emphasize their lower weight, cost-effectiveness, competitive mechanical properties, commendable specific strength, and potential for biodegradability. NFCs offer practical and eco-friendly substitutes for conventional composite fibers in industries like construction, automotive, and packaging. The article provides a brief overview of NFCs, covering their chemical, physical, and mechanical characteristics, and highlights diverse applications. The comparative analysis underscores the potential of natural fibers as sustainable choices in various industries.

Green composite materials are a means of reducing reliance on synthetic and especially single-use plastics (SUP) and raising public awareness of the need for urgent action to protect the planet. Natural (lignocellulosic) fibres are increasingly utilized as the reinforcement in polymer matrix composites, in search for increased renewability and sustainability. This work concerns the effect of washing ramie (Boehmeria nivea) fibres using sodium lauryl sulphate (SLS) surfactant. The SLS-treated ramie fibres were examined for their morphological, physical, thermal, structural, and mechanical properties by powder X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, thermogravimetric analysis (TGA), scanning electron microscopy (SEM), and tensile testing. SLS treated ramie fibres density and crystallinity index values were 1.23 g/cc and 84.5%, respectively, with a very high cellulose content of 81.3%, because hemicellulose and loose particles were dissolved. SEM images depicted the relevant changes, with no significant damage on treated fibre surfaces. With some assistance from the treatment, fibres initiated their degradation only above 250 °C, culminating at 327 °C, which appears suitable for the manufacturing of composites with the most common matrices.

In this study the recent developments in raw materials, manufacturing processes, and applications of natural fiber composites (NFCs) were reviewed. Natural fibers can represent a substitute for man-made fibers (including glass, aramid, and carbon) in a variety of biocomposite applications. Physical and chemical properties of the natural fibers are given and compared with the synthetic fibers. Advantages and disadvantages of NFCs in comparison with synthetic fibers such as glass and carbon fibers have been proposed. Criteria are described for the selection and processing of natural fibers for polymer composites used in different sectors such as automotive and building industries. The nanocellulose production methods, unique properties, and its recent industrial application in various sectors are given. This short review on NFCs considers their chemical, physical, and mechanical characteristics, as well as their various applications.

Mycelium from fungi can serve as the matrix or as a self-grown binder in a biocomposite. The reinforcing component may consist of various combinations of agro-based waste in short fiber or powder form. The complexity of their development is linked not only to the selection of the substrate, but also to the growth conditions of the mycelial material and its consolidation in a final form by the temperature increase that takes place. These materials have initially been proposed as a replacement for polystyrene foams, and the characterization is concentrated on compression performance and acoustic and thermal insulation properties. The present review concentrates on substrates that originated from the large productive system based on hemp (shives or hurds, waste fibers, and mats). Attention is paid to the performance obtained and to the amount of waste that is possibly employed to serve as the substrate.

This work presents an investigation on the quality of parts manufactured using fused deposition modeling (FDM), which is influenced by a large number of different elements. Some of which are based on the materials used in the production of the part, though others are rather pertinent to the process parameters. The manufacturing process and filament formulation has also a significant impact on the cost of the final product, as well as its physical, mechanical, and thermal properties. As the result, judicious combination of parameters can effectively act toward fine-tuning FDM toward three-dimensional printing (3DP) of pieces with quality fit-for-application. In this sense, the use of design of experiments (DOEs) is often needed for the purpose. Printing process parameters, including layer height, wall thickness, temperature, printing velocity, and tool path, have been discussed, in the understanding that 3DP time increases with decreasing layer thickness, and in turn increases production time and overall cost. A specific account is given on recent developments increasingly and more thoroughly focused on recognizing the impact of the process parameters and raw materials on the final product.

This research focuses on hybrid woven fibre metal laminates (HWFMLs), specifically on the innovative hybridization of natural woven fibres (NWFs) with aluminium diamond microexpandable mesh (Al-DMEM) in thin laminates. More specifically, it investigates the effect on the mechanical and water absorption properties of incorporating basalt (B), jute (J), banana (Bn) fibres, and Al-DMEM as reinforcing materials in a traditional epoxy resin. Several stacking sequences were compared and discussed. The basalt-banana-aluminium-banana-basalt (BBnABnB) (five layers) laminate exhibited remarkable compressive strength (25.7 MPa), interlaminar shear strength (25.2 MPa), Izod impact strength (2.98 J), tensile strength (42.8 MPa), and tensile modulus (3.1 GPa). Other laminates, despite their limited tensile strain, still offered advantages in other loading modes. In particular, basalt-jute-aluminium-jute-basalt (BJAJB) (five layers) laminate showed notable performance with a compressive strength of 16.70 MPa and interlaminar shear strength of 20.85 MPa. In comparison, the basalt-aluminium-basalt (BAB) (three layers) demonstrated compressive strength equal to 6.87 MPa and interlaminar shear strength (ILSS) equal to 9.07 MPa.

New fibers extracted from plant barks are a recent subject of investigation as possible fillers for polymer composites. In this work, Grewia Monticola Sond (GMS) fibers have been characterized from a morphological, chemical, and thermal point of view. This involved using a number of techniques, including Fourier infrared spectroscopy (FTIR), X-ray diffraction (×RD), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), atomic force microscopy (AFM), and 13C nuclear magnetic resonance (NMR). Results indicated that GMS fibers have relatively high cellulose (55%), with 33.5% crystallinity index and a crystallite size of 4.89 nm, and lower hemicellulose (14%) and lignin (15%) contents. The fibers showed cellulose degradation onset at around 324°C, while kinetic activation energy (74.18 kJ/mol) is quite low. The roughness of the fibers was in the range expected for similar natural fibers, and they may be considered silky according to their kurtosis values. As for possible application in composites, they would definitely withstand process temperatures with thermoplastics. However, their not very high crystallinity and low crystallite size might suggest a limited strength, to be verified in future after optimizing GMS fiber extraction from bark.

The stem bark of Acacia caesia, or Senegalia caesia, richly available in the Western Ghats of Tamilnadu and Kerala, India, does potentially offer a ligno-cellulosic fiber, which was characterized in this work, studying its chemical composition, morphology, and thermal degradation. The as-received fibers, which were extracted as technical fibers with diameters ranging between 100 and 150 µm, had a density of 1200 kg/m3. Their composition included 37% cellulose, 20% hemicellulose and 18% lignin, not very dissimilar, among other fibers, from alfa esparto and particularly coir. Their thermal degradation onset was at 308°C, which suggested a potential in composite application with traditional oil-based matrices and possibly also in the long run on bio-based ones. However, their high roughness and easy splitting of the fibers suggested that possible use as the filler for composites would require fiber treatment, namely, to remove undesired loose parts, hence regularizing their geometry. This would also serve to reduce the likeliness of longitudinal splitting, which is a widely recognized occurrence during stripping of bark fibers.

The tensile strength of fibers extracted by retting from Acacia Caesia bark was measured and their fracture morphology was examined, with the idea to propose their potential use as the reinforcement in polymer composites. Four categories of fibers were investigated, namely untreated and treated with a concentration of 5, 10 and 15% sodium hydroxide (NaOH) for 24 hours at ambient temperature. The increase of alkali concentration resulted in a gradual reduction of hemicellulose, wax, and moisture, which on the other side increased the fiber density. Single fiber tensile tests were performed according to ASTM D3822 standard. The fracture surfaces of the fibers were observed using an optical microscope and scanning electron microscope (SEM). The tensile tests revealed that the 10% NaOH treatment sample showed the highest performance, namely an average tensile strength of 16.2 (±5.63) N with an ultimate elongation of 4.6 (± 1.0)%. SEM evidenced the different possible morphologies of Acacia Caesia bark fiber fractures, including sliding and tearing, splitting and torsion of fibrils.

The present work centers on aluminum-based metal matrix composites (AMCs), synthesized via stir casting and then processed by electrical discharge machining (EDM) in the case of Al7075 as a matrix and 6 wt.% boron carbide (B4C) as reinforcement. A design of experiment (DoE) approach, powered by hybrid optimization techniques (such as the entropy weight method (EWM), grey relational analysis (GRA) incorporated Taguchi method) was used to investigate the relationship between current (I), pulse ON time (Ton), pulse OFF time (Toff), and electrode gap (Gap) as input parameters and the material removal rate (MRR), tool wear rate (TWR), and surface roughness (SR) as response parameters. The results showed that an I = 140 A, Ton = 120 ms, Toff = 50 ms, and Gap = 0.4 mm combination gives the best response parameters of MRR = 0.5628 mm3/min, TWR = 0.0048 mm3/min, and SR = 4.4034 μs.

The optimization of heat transfer in heat exchanging equipment is paramount for the efficient management of energy resources in both industrial and residential settings. In pursuit of this goal, this empirical study embarked on enhancing the heat transfer performance of a double pipe heat exchanger (DPHX) by introducing silver (Ag)-graphene oxide (GO) hybrid nanofluids into the annulus of the heat exchanger. To achieve this, three distinct molar concentrations of Ag ornamented GO hybrid nanoparticles were synthesized by blending GO nanoparticles with silver nitrate at molarities of 0.03 M, 0.06 M, and 0.09 M. These Ag-GO hybrid nanoparticles were then dispersed in the base fluid, resulting in the formation of three distinct hybrid nanofluids, each with a consistent weight percentage of 0.05 wt%. Thorough characterization and evaluation of thermophysical properties were performed on the resulting hybrid nanomaterials and nanofluids, respectively. Remarkably, the most significant enhancement in heat transfer coefficient, Nusselt number, and thermal performance index (62.9%, 33.55%, and 1.29, respectively) was observed with the 0.09 M Ag-GO hybrid nanofluid, operating at a Reynolds number of 1,451 and a flow rate of 47 g/s. These findings highlight the substantial improvement in thermophysical properties of the base fluid and the intensification of heat transfer in the DPHX with increasing Ag molarity over GO. In summary, this study emphasizes the vital importance of optimizing the molarity of the material, which also plays a significant role in nanoparticle synthesis to achieve the optimal amplification of heat transfer.

This study explores the effect of alkali treatment at ambient (25 °C) and elevated temperatures (100 °C) on the physicochemical, structural, morphological, and thermal properties of Calamus tenuis cane fibers (CTCFs) for the first time. Our purpose is to investigate their potential use as reinforcement in polymer composites, since cane fibers are generally known for their accurate and consistent geometrical orientation. Treatment with 8% (w/v) sodium hydroxide (NaOH) is carried out at ambient temperature and at 100 °C for 4 h. Chemical analysis and Fourier transform IR spectroscopy (FTIR) indicate some removal of non-cellulosic elements from CTCFs during alkali treatment, resulting in increased surface roughness, as confirmed by using SEM micrographs. This removal of non-cellulosic elements leads to an enhancement in the density of the treated CTCFs. Untreated and treated fibers are analyzed for maximum degradation temperature, thermal stability, and kinetic activation energy (Ea) using thermogravimetric analysis (TGA). In particular, Ea was considerably diminished with treatment and temperature. X-ray diffraction (XRD) results show an improved crystallinity index (37.38% to 44.02%) and crystallite size (2.73 nm to 2.98 nm) for fibers treated with 8% NaOH at ambient temperature. In conclusion, a general benefit was achieved by treating CTCFs, though the influence of increasing temperature treatment appears controversial.

Residual stress significantly affects the mechanical properties, physical properties, and durability of materials. It is meaningful to evaluate the residual stress using non-destructive methods. However, existing techniques are expensive and have low accuracy and narrow applicability. In this paper, both infrared and terahertz techniques were used to quantitatively evaluate the residual stress of high-density polyethylene (HDPE) under tensile loading. For the terahertz technique, a new theory based on stress-optics law and Poisson’s effect is proposed. For the infrared technique, line-scan thermographic (LST) was used to extract the thermal diffusivity of HDPE. The residual stress caused by plastic deformation is quantitatively related to thermal diffusivity. Conclusively, THz-TDS shows an obvious improvement in residual stress detectability.

In recent years, there has been growing interest in utilizing bark fibers as reinforcements for polymer composites. This study focused on the characterization of epoxy composites reinforced with Acacia caesia bark (ACB) fibers, considering their mechanical, morphological, and thermal properties. Various amounts of ACB fibers with three different lengths (10, 20, and 30 mm) were incorporated into the composites, ranging from 10 to 35 wt.% in 5% increments. This resulted in 18 sample categories, which were compared to neat epoxy samples. The findings demonstrated that the introduction of ACB fibers, even at the highest fiber content, led to improved mechanical performance. However, a transition in fiber length from 20 to 30 mm exhibited conflicting effects on the composite, likely due to the tendency of bark fibers to bend and split into fibrils during loading. Regarding thermal degradation, the advantages over neat epoxy were evident, particularly for 20 mm fibers, suggesting enhanced interfacial bonding between the matrix and the reinforcement. The epoxy adequately protected the bark fibers, enabling the composite to withstand degradation at temperatures comparable to pure resin, with minimal structural damage below 320 °C.

Tensile properties of banana fibers extracted from the peel of the fruit of the Cavendish sub-group were studied. A total of 43 fibers were manually extracted from the peel of green bananas, measuring five diameters from each fiber. The fibers were examined under the optical microscope up to a 50× magnification and their cross-sectional area (CSA) was observed. Tensile tests were conducted on the extracted banana fibers and Young’s modulus was calculated using apparent area from microscopy observations, then calculating a fiber area correction factor (FACF) to reduce the relevant error. Geometry and extent of the lumen were also measured.

A thermoplastic starch (TPS) was produced, starting with potato starch, glycerol and acetic acid, to shape it in films of thickness around 100 microns. To TPS iron waste filing particles, in the amount of 12% the weight of starch, were introduced in different modalities: as received, reduced in size by the use of a mortar, after treatment with hydrochloric acid, and after treatment and removal of hydrochloric acid. Morphological studies were carried out by optical and scanning electron microscopy and illustrated that the dispersion of iron filings was not optimal, though some improvement was observed by a reduced dimension of the particles. Tensile tests indicated the considerable improvement of stiffness offered by the insertion of iron particles to TPS, although the ultimate strain was reduced to less than 10%. Thermal characterization using thermogravimetry allowed revealing the three typical peaks for potato starch degradation, with only a slight decrease due to iron introduction. EDS allowed evaluating the presence of impurities in the iron filings and evidenced that the presence of iron was more effective on the surface than in the rest of the film. As a final consideration, An improvement in electrical conductivity by over an order of magnitude was obtained by the TPS+Fe+HCl film with respect to pure TPS.

The term “sea waste” generally refers to any solid, liquid, or gaseous material or substance that is discarded, disposed of, or abandoned in the ocean, sea, or any other body of salty water, such as a lagoon, etc. This includes waste generated by human activities on land that makes its way into the ocean, as well as waste generated by ships and other vessels at sea. Examples of sea waste include plastic debris, chemicals and toxic substances, oil spills, sewage, and other forms of pollution. These pollutants can harm marine ecosystems, endanger marine life, and impact human health and wellbeing. Efforts are being made by governments, organizations, researchers, and individuals to reduce the amount of sea waste generated, and to clean up existing waste in the ocean. Less attention is usually paid to waste materials of natural origin as they are considered (sometimes wrongly) to be less critical; an example is the tons of organic and inorganic material of natural origin that wash up on the beaches daily and must be landfilled or incinerated. The present paper intends to provide an updated review of research experiences and engineering solutions that are able to offer a second life to natural (biological) sea waste by incorporating it into the creation of new, more sustainable materials, and especially composites.

The specific interest for the use of bark in materials, instead than for energy recovery, is owed to circular economy considerations, since bark fibers are normally byproducts or even waste from other sectors, and therefore their use would globally reduce the amount of refuse by replacing other materials in the production of composites. For the purpose of promoting their application in polymer composites, mainly under a geometry of short random fibers, bark fibers are extracted and treated, normally chemically by alkali. Following this, investigations are increasingly carried out on their chemical composition. More specifically, this includes measuring cellulose, hemicellulose, and lignin content and their modification with treatment on their thermal properties and degradation profile, and on the mechanical performance of the fibers and of the tentatively obtained composites. This work aims at reviewing the current state of studies, trying to elicit which bark fibers might be most promising among the potentially enormous number of these, clarifying which of these have received some attention in literature and trying to elicit the reason for this specific interest. These can be more thoroughly characterized for the purpose of further use, also in competition with other fibers not from bark, but from bast, leaves, etc., and pertaining to developed production systems (cotton, hemp, flax, jute, etc.). The latter are already widely employed in the production of composites, a possibility scantly explored so far for bark fibers. However, some initial works on bark fiber composites and both thermoplastic and thermosetting are indicated and the importance of some parameters (aspect ratio, chemical treatment) is discussed.

Apart from the widely discussed pineapple leaf fibers, normally referred to as PALF, fibers from other parts of the plant also exist, particularly those in the fruit crown, which are known as pineapple crown leaf fibers (PCLF). In this work, PCLF were characterized using thermogravimetric analysis (TGA), Fourier transform IR spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), and atomic force microscopy (AFM). The results indicated that the properties of PCLF do not greatly differ from those observed for PALF. In particular, a cellulose content of over 67% was observed, with approximately 76% crystallinity. The main degradation phenomena of the fibers took place between 230 and 380 °C, peaking at 324 °C, which is in line with observations in other fibers which have similar cellulose and crystalline contents. There was 13.4% residue at 680 °C. Bare mechanical retting of PCLF, although not allowing a full and thorough degumming, which would only be achieved through more aggressive chemical treatment, enabled aspect ratios of over 103 to be obtained. This indicates some potential for their application as short fibers in composites. In this respect, the considerable roughness of PCLF when compared to other leaf-extracted fibers, and in particular when compared to PALF, could suggest an ability to obtain a sufficiently sound fiber–matrix interface.

This paper aims at investigating the influence of the addition of milled glass fibers upon quasi-static indentation (QSI) properties of glass/epoxy composite laminates. The QSI behavior was experimentally studied by evaluating indentation force, residual dent depth, energy absorbed and size of the damaged area for different indentation depths. Following the QSI tests, the filler-loaded glass/epoxy samples were subjected to three-point bending tests in order to measure residual flexural strength, and the results were compared with the baseline glass/epoxy samples. Both tests were performed with online acoustic emission monitoring in order to observe damage progression and characterize different fracture mechanisms associated with loading. The results show that the filler-loaded laminates exhibit a substantial improvement in the peak force and contact stiffness, with a reduced permanent damage both in terms of depth and of area, in comparison with the baseline ones. It is found that the filler presence offers greater stiffness and higher energy dissipation through toughening mechanisms such as filler debonding/pullout and filler bridging/interlocking.

The wear performance of jute/coir unsaturated polyester composites, filled with eggshell powder (ESP) and nanoclay (NC), were examined, concentrating on two measured parameters, coefficient of friction (COF) and wear rate (WR). To assess the possibilities of this material, a Taguchi study, based on grey relational analysis (GRA), was carried out, based on three testing parameters of the wear performance, load (10, 20, and 30 N), speed (100, 150, and 200 rpm), and sliding distance (30, 40, and 50 m). The material showed promising characteristics especially at high load, low speed, and high sliding distance. When comparing the respective influence of the three different parameters, the speed proved to be the most critical, this suggested the possible application of the biocomposite only for very low values of it. On the other hand, it was also elucidated that the presence and interfacial adhesion of the two fillers considerably hindered the formation of ploughing during wear test, despite the fact that degradation might be continuous and critical as far as loading progresses.

The contribution of natural lignocellulosic fibers to the reduction in wear damage in polymer resins is of interest, especially when two of these fibers can combine their respective effects. Wear properties of hybrid kenaf/banana epoxy composites have been investigated using three different total amount of fibers, 20, 30 and 40 wt.%, at loading forces up to 30 N and to sliding distances of up to 75 m. This demonstrated that the introduction of the highest level of fibers proved the most suitable for consistency of results and containment of wear with increasing load, as was also found from the morphological evaluation of wear degradation using scanning electron microscopy (SEM). Subsequently, tensile, flexural and impact properties of as-received and post-water-saturation hybrid composites were examined. The tests revealed a limited reduction in tensile and flexural strength, not exceeding 10% of the initial values, which were very high compared to similar materials, almost reaching 140 MPa for tensile strength and exceeding 170 MPa for flexural strength. In contrast, a higher standard deviation of values was found for impact strength, although the decrease in average values was only slightly above 10%. The results suggest the availability of these hybrids for wear-resisting applications in high-moisture environments, and the even more limited water absorption conferred by banana fibers added to kenaf ones.

A poly(urethane-acrylate) polymer (PUA) was synthesized, and a sufficiently high molecular weight starting from urethane-acrylate oligomer (UAO) was obtained. PUA was then loaded with two types of powdered ligno-cellulosic waste, namely from licorice root and palm leaf, in amounts of 1, 5 and 10%, and the obtained composites were chemically and mechanically characterized. FTIR analysis of final PUA synthesized used for the composite production confirmed the new bonds formed during the polymerization process. The degradation temperatures of the two types of waste used were in line with what observed in most common natural fibers with an onset at 270 °C for licorice waste, and at 290 °C for palm leaf one. The former was more abundant in cellulose (44% vs. 12% lignin), whilst the latter was richer in lignin (30% vs. 26% cellulose). In the composites, only a limited reduction of degradation temperature was observed for palm leaf waste addition and some dispersion issues are observed for licorice root, leading to fluctuating results. Tensile performance of the composites indicates some reduction with respect to the pure polymer in terms of tensile strength, though stabilizing between data with 5 and 10% filler. In contrast, Shore A hardness of both composites slightly increases with higher filler content, while in stiffness-driven applications licorice-based composites showed potential due to an increase up to 50% compared to neat PUA. In general terms, the fracture surfaces tend to become rougher with filler introduction, which indicates the need for optimizing interfacial adhesion.

Organisms and their features represent a complex system of solutions that can efficiently inspire the development of original and cutting-edge design applications: the related discipline is known as biomimetics. From the smallest to the largest, every species has developed and adapted different working principles based on their relative dimensional realm. In nature, size changes determine remarkable effects in organismal structures, functions, and evolutionary innovations. Similarly, size and scaling rules need to be considered in the biomimetic transfer of solutions to different dimensions, from nature to artefacts. The observation of principles that occur at very small scales, such as for nano- and microstructures, can often be seen and transferred to a macroscopic scale. However, this transfer is not always possible; numerous biological structures lose their functionality when applied to different scale dimensions. Hence, the evaluation of the effects and changes in scaling biological working principles to the final design dimension is crucial for the success of any biomimetic transfer process. This review intends to provide biologists and designers with an overview regarding scale-related principles in organismal design and their application to technical projects regarding mechanics, optics, electricity, and acoustics.

As possible substitutes for non-biodegradable synthetic fibre, ligno-cellulosic fibres have attracted much interest for their eco-friendliness; a large number of them are already used for the production of green polymer composites. The search for further green candidates brings into focus other fibres not previously considered, yet part of other production systems, therefore available as by-products or refuse. The purpose of this study is to explore the potential of alkali treatment with 5% sodium hydroxide (NaOH) to enhance the properties of bark-extracted Acacia Caesia Bark (ACB) fibres. The microscopic structure of the treated fibres was elucidated using scanning electron microscopy (SEM). Moreover, the fibres were characterised in terms of chemical composition and density and subjected to single-fibre tensile tests (SFTT). Following their physico-chemical characterisation, fibre samples underwent thermal characterisation by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC), and their crystallinity was assessed using X-ray diffraction (XRD). This level of alkali treatment only marginally modified the structure of the fibres and offered some improvement in their tensile strength. This suggested that they compare well with other bark fibres and that their thermal profile showed some increase of degradation onset temperature with respect to untreated ACB fibres. Their crystallinity would allow their application in the form of fibres with an average length of approximately 150 mm, even in thermoplastic biocomposites.

Objectives This work concerned the study of auxetic materials are cellular structures with negative Poisson’s ratio, therefore bending, instead of stretching, when pulled, therefore offering support. Methods/Analysis Nature is able to develop irregular cellular structures, making them denser only when needed and sparser in other areas and this experience has been applied to the development of structure with auxetic geometries other than the classical bow-shaped one. Findings The study of these inherent characteristics of nature allowed the development of three innovative auxetic patterns, not existing in literature, modifying their structure to optimize their function, starting from the study of elementary geometrical shapes to arrive to auxetic unitary cells formed by concave polygons, united to other geometrical elements so to obtain auxetic structures both of multicellular type and of node-link type. Novelty/Improvement The knowledge acquired about novel auxetic structures has been applied to the development of an innovative neckbrace for orthopaedic purposes, which is comfortable, in that it is flexible, resistant, anatomical and transpiring.

The introduction of natural fibers as a filler in a natural rubber (NR) matrix can be of relevance for their eco-friendly and sustainable nature as the substitute for carbon-based fillers. In this work, short Phormium tenax fibers were introduced in random orientation into a NR matrix in different lengths (6, 10, and 14 mm) and various amounts (10, 20, and 30%, taking 100 as the NR weight). The composite was fabricated using a two-roll mill according to American Society for Testing and Materials (ASTM) D3184-11 standard. Several properties were determined, namely tensile and tear characteristics, hardness, and abrasion resistance. The results suggest that the shortest fiber length used, 6 mm, offered the best combination between loss of mechanical (tensile and tear) properties and hardness and the most acceptable resistance to abrasion, with the properties increasing with the amount of fibers present in NR. As a consequence, it is indicated that a higher amount of fibers could be possibly introduced, especially to achieve harder composites, though this would require a more controlled mixing process not excessively reducing tensile elongation at break.

In the present study, a model is presented to optimize the fabrication parameters of natural fiber reinforced polyester matrix composites with dual fillers. In particular, jute fiber mat was chosen as reinforcement and eggshell powder (ESP) and montmorillonite nanoclay (NC) were selected as fillers. The weight per square meter (GSM) of the fiber, the weight percentage of ESP and NC have been chosen as independent variables and the influence of these variables on tensile, flexural and impact strength of the composite has been inspected. The permutations of the different combinations of factors are intended to accomplish higher interfacial strength with the lowest possible number of tested specimens. The experiments were designed by the Taguchi strategy and a novel multi-objective optimization technique named COPRAS (COmplex PRoportional ASsessment of alternatives) was used to determine the optimal parameter combinations. Affirmation tests were performed with the optimal parameter settings and the mechanical properties were evaluated and compared. Experimental results show that fiber GSM and eggshell powder content are significant variables that improve mechanical strength, while the nanoclay appears less important.

The present work is focused on improving mode I and mode II delamination resistance of glass/epoxy composite laminates (50 wt.% of glass fibers) with milled glass fibers, added in various amounts (2.5, 5, 7.5 and 10% of the epoxy weight). Including fillers in the interlayer enhances the delamination resistance by providing a bridging effect, therefore demanding additional energy to initiate the crack in the interlaminar domain, which results in turn in enhanced fracture toughness. The maximal increase of mode I and mode II fracture toughness and of flexural strength was obtained by the addition of 5% milled glass fiber. The mechanism observed suggests that crack propagation is stabilized even leading to its arrest/deflection, as a considerable amount of milled glass fiber filler was oriented transverse to the crack path. In contrast, at higher filler loading, tendency towards stress concentration grows due to local agglomeration and improper dispersion of excess fillers in inter/intralaminar resin channel, causing poor adhesion to the matrix, which leads to reduction in fracture toughness, strength and strain to failure. Fractured surfaces analyzed using scanning electron microscopy (SEM) revealed a number of mechanisms, such as crack deflection, individual debonding and filler/matrix interlocking, all contributing in various ways to improve fracture toughness.

Dry fibers coming from garden waste, originating from Opuntia ficus indica, were introduced in amounts of either 8 or 16 wt % into a self-produced thermoplastic starch (TPS) based on potato starch and glycerol. Thermal (differential scanning calorimetry, DSC), mechanical (tensile tests), and morphological characterization with scanning electron microscopy (SEM) and performing energy-dispersive X-ray spectrometry (microanalysis) were carried out. The results indicated that the uneven distribution and variable geometry of fibers introduced led to a reduction of tensile stress and strain with respect to pure TPS. However, the positive effects of prolonged mixing and increased thickness were highlighted, which suggest the fabrication of the composite could be improved in the future by controlling the manufacturing procedure.

Natural fibers, including mineral and plant fibers, are increasingly used for polymer composite materials due to their low environmental impact. In this paper, thermographic non-destructive inspection techniques were used to evaluate and characterize basalt, jute/hemp and bagasse fibers composite panels. Different defects were analyzed in terms of impact damage, delaminations and resin abnormalities. Of particular interest, homogeneous particleboards of sugarcane bagasse, a new plant fiber material, were studied. Pulsed phase thermography and principal component thermography were used as the post-processing methods. In addition, ultrasonic C-scan and continuous wave terahertz imaging were also carried out on the mineral fiber laminates for comparative purposes. Finally, an analytical comparison of different methods was given.

In this work, the apparent shear strength at the interface between a bamboo fiber and the surrounding poly(lactic acid) (PLA) matrix is quantified. A method for processing pull-out test samples within a controlled embedded length is proposed and the details of the test procedure are presented, along with a critical discussion of the results. Two series of samples are considered: untreated and mercerized bamboo fibers from the same batch, embedded in the same polyester matrix. Electron and optical microscopy are used to observe the fiber–matrix interface before and after the test, and to identify the failure mode of each sample, especially as regards the occurrence of fibrillation in the fiber bundles. The values of apparent interfacial shear strength are calculated only for regular fibers successfully pulled out from the matrix, and reported with their statistical variations. Mercerization, whose efficiency was proven by Fourier transform infrared (FTIR) spectroscopy, did not appear though to improve the quality of the interface (τapp = 7.0 ± 3.1 MPa for untreated fibers and τapp = 5.3 ± 2.4 MPa for treated fibers).