Evaluation of highly filled epoxy composites modified with walnut shell waste filler

New biobased chitosan-modified peach kernel shell composites and examining their behavior in different environmental conditions

Bisphenol A-type epoxy (ER) is a versatile synthetic polymer preferred for composite materials but non-biodegradability raises challenges for composites recycling in particular. The present study first investigated the potential usability of peach kernel shells (PKSh) waste as fillers in ER to decrease the cost of composite materials and increase their bio-based content. Different chemical modifications were performed to increase the poor compatibility between the hydrophilic lignocellulosic filler and the hydrophobic polymer matrix. The modified PKShs were obtained by alkali treatment (NaOH-PKSh), coating with biopolymer chitosan (CTS-PKSh), and cross-linking of CTS with glutaraldehyde (GA@CTS-PKSh). The aging of composites is a highly topical subject given the increasing use of composites in structural applications in many industries. The composites' thermal stability and dynamic-mechanical properties in different aging environments (water, seawater, and hydrothermal) were examined. The order of the aging conditions in terms of their effects on the composite properties was: hydrothermal > water > seawater. The ER/GA@CTS-PKSh composite was the most resistant to all environmental conditions. The tensile strength of epoxy matrix (ER) increased max. by 7.78 %, 21.11 %, 42.22 %, and 45.46 % in the case of raw, NaOH-PKSh, CTS-PKSh, and GA@CTS-PKSh fillers, respectively. Composites showed higher absorption in both UV and visible regions.

Synthesis and Characterization of Polyaniline Emeraldine Salt (PANI-ES) Colloids Using Potato Starch as a Stabilizer to Enhance the Physicochemical Properties and Processability

Conductive polymers, such as polyaniline (PANI), have interesting applications, ranging from flexible electronics, energy storage devices, sensors, antistatic or anticorrosion coatings, etc. However, the full exploitation of conductive polymers still poses a challenge due to their low processability. The use of compatible stabilizers to obtain dispersible and stable colloids is among the possible solutions to overcome such drawbacks. In this work, potato starch was used as a steric stabilizer for the preparation of colloidal polyaniline (emeraldine salt, ES)/starch composites by exploiting the oxidative polymerization of aniline in aqueous solutions with various starch-to-aniline ratios. The polyaniline/starch bio-composites were subjected to structural, spectroscopic, thermal, morphological, and electrochemical analyses. The samples were then tested for their dispersibility/solubility in a range of organic solvents. The results demonstrated the formation of PANI/starch biocomposites with a smaller average size than starch particles, showing improved aqueous dispersion and enhanced solubility in organic solvents. With respect to previously reported PANI-EB (emeraldine base)/starch composites, the novel colloids displayed a lower overall crystallinity, but the conductive nature of PANI-ES enhanced its electrochemical properties, resulting in richer redox chemistry, particularly evident in its oxidation behavior, as observed through cyclic voltammetry. Finally, as proof of the improved processability, the colloids were successfully integrated into a thin polyether sulfone (PES) membrane.

Innovative Materials Based on Epoxy Resin for Use as Seat Elements in Bulk Transport

The subject of this research is the development of epoxy composites with a defined service life for the purpose of seat elements in rail vehicles, which will be more environmentally friendly. The produced materials based on epoxy resin filled with PLA or PLA and quercetin were subjected to solar aging tests for 800 h to investigate the impact of the additives used on the aging behavior of the epoxy matrix. Firstly, the TGA analysis showed that the use of the proposed additives allowed for the maintenance of the thermal stability of the epoxy resin. Moreover, based on an optical microscopy test, it was noticed that the introduction of PLA and PLA with quercetin did not contribute to an increase in matrix defects. The one-directional tensile tests carried out before and after solar aging showed that the presence of polylactide in epoxy composites causes a slight growth of the stiffness and strength. Based on contact angle and color change measurements, it was found that quercetin was oxidized, thus ensuring protection for the epoxy matrix. This phenomenon was confirmed by FTIR study, where the carbonyl index (CI) value for the R-PLA-Q composite was lower than for the reference sample. The obtained composite structures may be a good alternative to traditionally used systems as seat elements in rail vehicles, which are not only characterized by high aging resistance but are also more eco-friendly.

Influence of a Biofiller, Polylactide, on the General Characteristics of Epoxy-Based Materials

The aim of this work was to obtain epoxy-based composite structures with good mechanical performance, high aging resistance, and an improved degradability profile. For this purpose, powdered polylactide in the amount of 5, 10, 20, 30, and 40 phr was introduced into the epoxy resin, and the composites were fabricated by a simple method, which is similar to that used on an industrial scale in the fabrication of these products. The first analysis concerned the study of the effect of PLA addition to epoxy resin-based composites on their mechanical properties. One-directional tensile tests of samples were performed for three directions (0, 90, and 45 degrees referring to the plate edges). Another aspect of this research was the assessment of the resistance of these composites to long-term exposure to solar radiation and elevated temperature. Based on the obtained results, it was observed that the samples containing 20 or 40 phr of polylactide were characterized by the lowest resistance to the solar aging process. It was therefore concluded that the optimal amount of polylactide in the epoxy resin composite should not be greater than 10 phr to maintain its mechanical behavior and high aging resistance. In the available literature, there are many examples in which scientists have proposed the use of various biofillers (e.g., lignin, starch, rice husk, coconut shell powder) in epoxy composites; however, the impact of polylactide on the general characteristics of the epoxy resin has not been described so far. Therefore, this work perfectly fills the gaps in the literature and may contribute to a more widespread use of additives of natural origin, which may constitute an excellent alternative to commonly used non-renewable compounds.

Effect of the Addition of Naringenin Derived from Citrus on the Properties of Epoxy Resin Compositions

This research concerns the modification of commercially available epoxy resin with flame retardants in order to obtain aging-resistant and antimicrobial polymeric materials with a plant stabilizer dedicated to use in rail transport. Polymer compositions based on epoxy resin, fiberglass fabric, and naringenin were prepared. Naringenin was added as a natural stabilizer at 2, 4, and 8 phr. The materials were subjected to solar aging lasting 800 h. The hardness of the samples, surface energy, and carbonyl indexes were determined, and the color change in the composition after aging was analyzed. In addition, microscopic observations, analyses of mechanical properties, and microbiological tests were performed. The hardness determination showed that the samples retained their functional properties after solar aging. The increase in the polar component of the surface energy of all materials indicated the beginning of the degradation process of the composites. The tensile one-directional tests were carried out for plane samples taken in three directions (0, 90, and 45 degrees referred to a plate edge) before and after the aging process. The addition of naringenin did not affect the functional and surface properties of the epoxy resin-based materials. Polyphenol stabilized polymer composites, as evidenced by the results of carbonyl indexes. Moreover, the obtained samples showed good antimicrobial properties for E. coli and C. albicans in the field of testing the viability of microbial cells in contact with the tested surfaces.

The impact of thermomechanical and chemical treatment of waste Brewers' spent grain and soil biodegradation of sustainable Mater-Bi-Based biocomposites

Due to the massive plastic pollution, development of sustainable and biodegradable polymer materials is crucial to reduce environmental burdens and support climate neutrality. Application of lignocellulosic wastes as fillers for polymer composites was broadly reported, but analysis of biodegradation behavior of resulting biocomposites was rarely examined. Herein, sustainable Mater-Bi-based biocomposites filled with thermomechanically- and chemically-modified brewers' spent grain (BSG) were prepared and subjected to 12-week soil burial test simulating their biodegradation in natural environment. BSG stabilizing effect on polymer matrix affected by the content of melanoidins and antioxidant phytochemicals, along with the impact of diisocyanate applied to strengthen the interfacial adhesion. Biocomposites showed 25-35 wt% mass loss over 12 weeks resulting from swelling of BSG filler and sample microcracking, which increased surface roughness by 247-448 %. The degree of decomposition was partially reduced by BSG modifications pointing to the stabilizing effect of melanoidins and phytochemicals, and enhanced interfacial adhesion. Soil burial-induced structural changes enhanced biocomposites' thermal stability determined by thermogravimetric analysis shifting decomposition onset by 14.4-32.0 °C due to the biodegradation of lower molecular weight starch macromolecules confirmed by differential scanning calorimetry. For unfilled Mater-Bi, it caused an average 32 % reduction in complex viscosity and storage modulus captured by oscillatory rheological measurements. Nonetheless, the inverse effect was noted for biocomposites where modulus increased even by one order of magnitude due to the swelling of BSG particles and amorphous phase decomposition. Presented results indicate that BSG promotes soil degradation of Mater-Bi and its rate can be engineered by biofiller treatment elaboration.

Quasi-Static Flexural Behavior of Epoxy-Matrix-Reinforced Crump Rubber Composites

Waste tires have emerged as a severe environmental threat worldwide as they create a number of disposal and landfill burden issues. In the present study, environmental pollutant crump rubber derived from waste discarded tires was reinforced with epoxy resin and prepared by means of an open-mold casting method to assess its mechanical properties. The impact of crump rubber content (0, 10, 20 and 30 vol.%) on the mechanical behavior of the composites was assessed using three-point bending tests at a constant strain rate of 0.1 and 0.01 mm/s. The stress–strain profiles of the 0.01 mm/s specimens revealed higher strains to failure compared with the 0.1 mm/s tested specimens and all the specimens showed brittle failure. Irrespective of the strain rates, tests revealed a marginal increase in the strength values of the composites and a significant increase in the modulus of all the composites compared with neat epoxy specimens. The results suggest that crump rubber can be effectively used in utilitarian composites requiring good flexural modulus and strength properties. Crump rubber epoxy composites with 30 vol.% of crump rubber showed higher modulus and strength compared with neat epoxy and other composites owing to the toughening phase induced by the crump rubber particles. The failure and fracture features of the specimens were analyzed using scanning electron microscopy.

Natural Fillers as Potential Modifying Agents for Epoxy Composition: A Review

Epoxy resins as important organic matrices, thanks to their chemical structure and the possibility of modification, have unique properties, which contribute to the fact that these materials have been used in many composite industries for many years. Epoxy resins are repeatedly used in exacting applications due to their exquisite mechanical properties, thermal stability, scratch resistance, and chemical resistance. Moreover, epoxy materials also have really strong resistance to solvents, chemical attacks, and climatic aging. The presented features confirm the fact that there is a constant interest of scientists in the modification of resins and understanding its mechanisms, as well as in the development of these materials to obtain systems with the required properties. Most of the recent studies in the literature are focused on green fillers such as post-agricultural waste powder (cashew nuts powder, coconut shell powder, rice husks, date seed), grass fiber (bamboo fibers), bast/leaf fiber (hemp fibers, banana bark fibers, pineapple leaf), and other natural fibers (waste tea fibers, palm ash) as reinforcement for epoxy resins rather than traditional non-biodegradable fillers due to their sustainability, low cost, wide availability, and the use of waste, which is environmentally friendly. Furthermore, the advantages of natural fillers over traditional fillers are acceptable specific strength and modulus, lightweight, and good biodegradability, which is very desirable nowadays. Therefore, the development and progress of "green products" based on epoxy resin and natural fillers as reinforcements have been increasing. Many uses of natural plant-derived fillers include many plant wastes, such as banana bark, coconut shell, and waste peanut shell, can be found in the literature. Partially biodegradable polymers obtained by using natural fillers and epoxy polymers can successfully reduce the undesirable epoxy and synthetic fiber waste. Additionally, partially biopolymers based on epoxy resins, which will be presented in the paper, are more useful than commercial polymers due to the low cost and improved good thermomechanical properties.

Analysis, Development, and Scaling-Up of Poly(lactic acid) (PLA) Biocomposites with Hazelnuts Shell Powder (HSP)

In this work, two different typologies of hazelnuts shell powders (HSPs) having different granulometric distributions were melt-compounded into poly(lactic acid) (PLA) matrix. Different HSPs concentration (from 20 up to 40 wt.%) were investigated with the aim to obtain final biocomposites with a high filler quantity, acceptable mechanical properties, and good melt fluidity in order to be processable. For the best composition, the scale-up in a semi-industrial extruder was then explored. Good results were achieved for the scaled-up composites; in fact, thanks to the extruder venting system, the residual moisture is efficiently removed, guaranteeing to the final composites improved mechanical and melt fluidity properties, when compared to the lab-scaled composites. Analytical models were also adopted to predict the trend of mechanical properties (in particular, tensile strength), also considering the effect of HSPs sizes and the role of the interfacial adhesion between the fillers and the matrix.

Studies of Resistance of PP/Natural Filler Polymer Composites to Decomposition Caused by Fungi

The article discusses the grain morphology of the natural filler from hazelnut and walnut shell flour. It was observed that the geometry of both meals is similar to each other and resembles uneven balls in shape. The heterogeneity and well-developed outer surface of the flour grains allow for filling the voids with the polymer matrix. The analysis of the surface of the SEM images allowed to observe the presence of natural filler flour grains in the entire volume of the produced polymer composites, uneven distribution and small agglomerates, as well as the presence of voids, distributed in the matrix and in the matrix/filler interface. As a result of the visual evaluation of the activity of microorganisms (mycelium) on the surface of the produced polymer composite materials PP/hazelnut and walnut shell flour with a different % share, different fraction, it was found that the best fungistatic effect was shown by the samples marked with the symbol hazelnut at the fraction 315-443 µm. The least fungistatic material was found to be the samples with walnut shell meal filler at the fraction 315-443 µm (F2 and F4), on which the microorganisms achieved significant growth (more than 50% of the test area). The highest value of contact angle was obtained for samples with hazelnut filler fraction 315-443 (C2 and C4), which also confirms its best fungistatic effect.

Recycling of spent coffee grounds for useful extracts and green composites

Large amounts of spent coffee grounds (SCGs) are often discarded and there is a need to find alternative disposal methods due to environmental concerns. This project aims to develop sustainable materials by re-purposing spent coffee grounds (SCGs). Oil extraction was performed using different organic solvents and yielded approximately 10% coffee oil. Coffee oil contains potentially useful chemical compounds such as fatty acids and caffeine. They also exhibited antioxidant properties. Extracted SCGs (ESCGs) were blended with epoxy resin to form composites. ESCG composites displayed a general decrease in mechanical properties relative to epoxy. However, improvements were observed when comparing ESCG composites and SCG composites. The greatest improvement belongs to epoxy composite filled with acetone-ESCGs, where the tensile strength, flexural modulus and flexural strength increased to 23.4 MPa, 3.02 GPa and 42.9 MPa respectively. This study presents a way to exploit waste materials which contributes to the goal of sustainability.

Spent coffee grounds are mostly discarded as waste. Here we recycle them for chemical compounds and as composite material fillers. Our study evaluated the chemical composition of coffee oil extracts and mechanical properties of composites formed.

Manufacturing and Characterization of Green Composites with Partially Biobased Epoxy Resin and Flaxseed Flour Wastes

In the present work, green-composites from a partially biobased epoxy resin (BioEP) reinforced with lignocellulosic particles, obtained from flax industry by-products or wastes, have been manufactured by casting. In this study, the flaxseed has been crushed by two different mechanical milling processes to achieve different particle sizes, namely coarse size (CFF), and fine size (FFF) particle flaxseed flour, with a particle size ranging between 100–220 µm and 40–140 µm respectively. Subsequently, different loadings of each particle size (10, 20, 30, and 40 wt%) were mixed with the BioEP resin and poured into a mold and subjected to a curing cycle to obtain solid samples for mechanical, thermal, water absorption, and morphological characterization. The main aim of this research was to study the effect of the particle size and its content on the overall properties of composites with BioEP. The results show that the best mechanical properties were obtained for composites with a low reinforcement content (10 wt%) and with the finest particle size (FFF) due to a better dispersion into the matrix, and a better polymer-particle interaction too. This also resulted in a lower water absorption capacity due to the presence of fewer voids in the developed composites. Therefore, this study shows the feasibility of using flax wastes from the seeds as a filler in highly environmentally friendly composites with a wood-like appearance with potential use in furniture or automotive sectors.

Preparation, Thermal, and Mechanical Characterization of UV-Cured Polymer Biocomposites with Lignin

The preparation and the thermal and mechanical characteristics of lignin-containing polymer biocomposites were studied. Bisphenol A glycerolate (1 glycerol/phenol) diacrylate (BPA.GDA) was used as the main monomer, and butyl acrylate (BA), 2-ethylhexyl acrylate (EHA) or styrene (St) was used as the reactive diluent. Unmodified lignin (L) or lignin modified with methacryloyl chloride (L-M) was applied as an ecofriendly component. The influences of the lignin, its modification, and of the type of reactive diluent on the properties of the composites were investigated. In the biocomposites with unmodified lignin, the lignin mainly acted as a filler, and it seemed that interactions occurred between the hydroxyl groups of the lignin and the carbonyl groups of the acrylates. When methacrylated lignin was applied, it seemed to take part in the creation of a polymer network. When styrene was added as a reactive diluent, the biocomposites had a more homogeneous structure, and their thermal resistance was higher than those with acrylate monomers. The use of lignin and its methacrylic derivative as a component in polymer composites promotes sustainability in the plastics industry and can have a positive influence on environmental problems related to waste generation.

A Comprehensive Review on the Chemical Constituents and Functional Uses of Walnut (Juglans spp.) Husk

The walnut (Juglans spp.) is an appreciated nut that belongs to the Juglandaceae family. The fruit includes four main parts: the kernel, the skin, the shell, and the green husk. It is widely cultivated due to its edible kernel. In walnut production centers, high amounts of the husk as an agro-forest waste product are produced and discarded away. Recently, it has been demonstrated that the walnut green husk could be valued as a source of different natural bioactive compounds with excellent antioxidant and antimicrobial properties. Regarding this respect, in this contribution, the current scientific knowledge on the antioxidant and antiradical activities, various identified and isolated individual chemical constituents, as well as the functional applications of the walnut husk with more emphasis on the Persian walnut (Juglans regia L.) are reviewed.

Thermal Stability, Fire and Smoke Behaviour of Epoxy Composites Modified with Plant Waste Fillers

The influence of plant fillers on the flammability and smoke emission of natural composites was investigated. Epoxy composites with 15, 25, and 35 wt % of walnut and hazelnut shell, as well as sunflower husk, were prepared and examined. The ground organic components were characterized by grain size distribution, thermogravimetric analysis (TGA) and microstructure observations (SEM). The composite materials were subjected to dynamic mechanical analysis (DMA) and structural evaluation with scanning electron microscopy. Cone calorimeter tests and TGA determined the influence of plant waste filler addition on thermal stability and flammability. Moreover, the semi-volatile and volatile compounds that evolved during the thermal decomposition of selected samples were identified using a steady state tube furnace and a gas chromatograph with a mass spectrometer. The intensity of the degradation reduced as a function of increasing filler content, while the yield of residue corresponded to the amount of lignin that is contained in the tested plants. Moreover, the incorporation of agricultural waste materials resulted in the formation of a char layer, which inhibits the burning process. The yield of char depended on the amount and type of the filler. The composites containing ground hazelnut shell formed swollen char that was shaped in multicellular layers, similar to intumescent fire retardants.

Enhanced Interfacial Adhesion of Polylactide/Poly(ε-caprolactone)/Walnut Shell Flour Composites by Reactive Extrusion with Maleinized Linseed Oil

Novel green composites were prepared by melt compounding a binary blend of polylactide (PLA) and poly(ε-caprolactone) (PCL) at 4/1 (wt/wt) with particles of walnut shell flour (WSF) in the 10–40 wt % range, which were obtained as a waste from the agro-food industry. Maleinized linseed oil (MLO) was added at 5 parts per hundred resin (phr) of composite to counteract the intrinsically low compatibility between the biopolymer blend matrix and the lignocellulosic fillers. Although the incorporation of WSF tended to reduce the mechanical strength and thermal stability of PLA/PCL, the MLO-containing composites filled with up to 20 wt % WSF showed superior ductility and a more balanced thermomechanical response. The morphological analysis revealed that the performance improvement attained was related to a plasticization phenomenon of the biopolymer blend and, more interestingly, to an enhancement of the interfacial adhesion of the green composites achieved by extrusion with the multi-functionalized vegetable oil.