Thermal and Flammability Characteristics of Blended Jatropha Bio-Epoxy as Matrix in Carbon Fiber–Reinforced Polymer

Preparations and Thermal Properties of PDMS-AlN-Al2O3 Composites through the Incorporation of Poly(Catechol-Amine)-Modified Boron Nitride Nanotubes

As one of the emerging nanomaterials, boron nitride nanotubes (BNNTs) provide promising opportunities for diverse applications due to their unique properties, such as high thermal conductivity, immense inertness, and high-temperature durability, while the instability of BNNTs due to their high surface induces agglomerates susceptible to the loss of their advantages. Therefore, the proper functionalization of BNNTs is crucial to highlight their fundamental characteristics. Herein, a simplistic low-cost approach of BNNT surface modification through catechol-polyamine (CAPA) interfacial polymerization is postulated to improve its dispersibility on the polymeric matrix. The modified BNNT was assimilated as a filler additive with AlN/Al2O3 filling materials in a PDMS polymeric matrix to prepare a thermal interface material (TIM). The resulting composite exhibits a heightened isotropic thermal conductivity of 8.10 W/mK, which is a ~47.27% increase compared to pristine composite 5.50 W/mK, and this can be ascribed to the improved BNNT dispersion forming interconnected phonon pathways and the thermal interface resistance reduction due to its augmented compatibility with the polymeric matrix. Moreover, the fabricated composite manifests a fire resistance improvement of ~10% in LOI relative to the neat composite sample, which can be correlated to the thermal stability shift in the TGA and DTA data. An enhancement in thermal permanence is stipulated due to a melting point (Tm) shift of ∼38.5 °C upon the integration of BNNT-CAPA. This improvement can be associated with the good distribution and adhesion of BNNT-CAPA in the polymeric matrix, integrated with its inherent thermal stability, good charring capability, and free radical scavenging effect due to the presence of CAPA on its surface. This study offers new insights into BNNT utilization and its corresponding incorporation into the polymeric matrix, which provides a prospective direction in the preparation of multifunctional materials for electric devices.

Novel Bio-Based Materials: From Castor Oil to Epoxy Resins for Engineering Applications

The paper presents the synthesis and thermal behavior of novel epoxy resins prepared from epoxidized castor oil in the presence of or without trimethylolpropane triglycidyl ether (TMP) crosslinked with 3-hexahydro-4-methylphtalic anhydride (MHHPA) and their comparison with a petroleum-based epoxy resin (MHHPA and TMP). Epoxidized castor oil (ECO) was obtained via in situ epoxidation of castor oil with peroxyacetic acid. The chemical structures of castor oil (CO), ECO, and epoxy matrix were confirmed using FT-IR and 1H-NMR spectroscopy. The morphological and thermal behavior of the resulting products have been investigated. Compared to petroleum-based resins, castor oil-based ones have a lower Tg. Anyway, the introduction of TMP increases the Tg of the resins containing ECO. The morphological behavior is not significantly influenced by using ECO or by adding TMP in the synthesis of resins. The dielectric properties of epoxy resins have been analyzed as a function of frequency (1 kHz-1 MHz) and temperature (-50 to 200 °C). The water absorption test showed that as Tg increased, the percent mass of water ingress decreased.

Upcycling of the Used Cigarette Butt Filters through Pyrolysis Process: Detailed Kinetic Mechanism with Bio-Char Characterization

Thermo-chemical conversion via the pyrolysis of cigarette butt (CB) filters was successfully valorized and upcycled in the pre-carbonization and carbonization stages. The pre-carbonization stage (devolatilization) of the precursor material (cellulose acetate filter, r-CAcF) was analyzed by micro-scale experiments under non-isothermal conditions using TG-DTG-DTA and DSC techniques. The results of a detailed kinetic study showed that the decomposition of r-CAcF takes place via complex mechanisms, including consecutive reaction steps and two single-step reactions. Consecutive stages include the α-transition referred to as a cellulose polymorphic transformation (cellulose I → II) through crystallization mechanism changes, where a more thermodynamically ordered system was obtained. It was found that the transformation rate of cellulose I → II ('cellulose regeneration') is strongly affected by the presence of alkali metals and the deacetylation process. Two single-step reactions showed significant overlapping behavior, which involves a nucleation-controlled scission mechanism (producing levoglucosan, gaseous products, and abundant radicals) and hydrolytic decomposition of cellulose by catalytic cleavage of glycosidic bonds with the presence of an acidic catalyst. A macro-scale experiment showed that the operating temperature and heating rate had the most notable effects on the total surface area of the manufactured carbon. A substantial degree of mesoporosity with a median pore radius of 3.1695 nm was identified. The presence of macroporosity on the carbon surface and acidic surface functional groups was observed.

Thermal Response of Biocarbon-Filled Hemp Fiber-Reinforced Bioepoxy Composites

We investigated the thermal conductivity of materials based on pyrolysis temperature, filler loading, filler size, and type of biomass feedstock. Hemp stalk and switchgrass were pyrolyzed at 450, 550, and 650 °C and crushed into 50, 75, and 100 μm particle sizes. Biocarbon fillers (10, 15, and 20 wt %) were added to the bioepoxy polymer matrix. The study showed increased filler loading and particle size increased thermal conductivity-the biocomposite samples with 20 wt % filler loading of 100 μm particle size of the biocarbon obtained at 650 °C showed the maximum thermal conductivity in both hemp biocarbon-filled composites (0.59 W·m^-1·K^-1) and switchgrass-filled composites (0.58 W·m^-1·K^-1) with the highest flame time. Biocarbon in biofiber-reinforced polymer composites can improve thermal conductivity and extend the flame time. These findings significantly contribute to developing hemp-based bioepoxy composite materials for thermal applications in various fields. These include insulating materials for buildings and thermal management systems, energy-efficient applications, and help in material selection and product design with a positive environmental impact.

Evaluation of Natural and Modified Castor Oil Incorporation on the Melt Processing and Physico-Chemical Properties of Polylactic Acid

Bio-based plasticizers derived from renewable resources represent a sustainable replacement for petrochemical-based plasticizers. Vegetable oils are widely available, non-toxic and biodegradable, resistant to evaporation, mostly colorless and stable to light and heat, and are a suitable alternative for phthalate plasticizers. Plasticized poly(lactic acid) (PLA) materials containing 5 wt%, 10 wt%, 15 wt% and 20 wt% natural castor oil (R) were prepared by melt blending to improve the ductility of PLA. Three castor oil adducts with maleic anhydride (MA), methyl nadic anhydride (methyl-5-norbornene-2,3-dicarboxylic anhydride) (NA) and hexahydro-4-methylphthalic anhydride (HA), previously synthesized, were incorporated in a concentration of 15 wt% each in PLA and compared with PLA plasticized with natural R. The physico-chemical properties of PLA/R blends were investigated by means of processability, chemical structure, surface wettability, mechanical, rheological and thermal characteristics. The addition of natural and modified R significantly improved the melt processing by decreasing the melt viscosity by ~95%, increased the surface hydrophobicity, enhanced the flexibility by ~14 times in the case of PLA/20R blend and ~11 times in the case of PLA/15R-MA blend as compared with neat PLA. The TG/DTG results showed that the natural R used up to 20 wt% could significantly improve the thermal stability of PLA, similar to the maleic anhydride-modified R. Based on the obtained results, up to 20 wt% natural R and 15 wt% MA-, HA- or NA-modified R might be used as environmentally friendly plasticizers that can improve the overall properties of PLA, depending on the intended food packaging applications.

Choosing the Right Lignin to Fully Replace Bisphenol A in Epoxy Resin Formulation

Thirteen unmodified lignin samples from different biomass sources and isolation processes were characterized and used to entirely replace bisphenol A (BPA) in the formulation of solubilized epoxy resins using a developed novel method. The objective was to measure the reactivity of different lignins toward bio-based epichlorohydrin (ECH). The epoxy contents of various bio-based epoxidized lignins were measured by titration and 1 H NMR spectroscopy methods. A partial least square regression (PLS-R) model with 92 % fitting accuracy and 90 % prediction ability was developed to find correlations between lignin properties and their epoxy contents. The results showed that lignins with higher phenolic hydroxy content and lower molecular weights were more suitable for replacing 100 % of toxic BPA in the formulation of epoxy resins. Additionally, two epoxidized lignin samples (highest epoxy contents) cured by using a bio-based hardener (Cardolite GX-3090) were found to show comparable thermomechanical performances and thermal stabilities to a petroleum-based (DGEBA) epoxy system.

Hydrothermal Carbon as Reactive Fillers to Produce Sustainable Biocomposites with Aromatic Bio-Based Epoxy Resins

Thiswork is focused on the development of sustainable biocomposites based on epoxy bioresin reinforced with a natural porous material (hydrochar, HC) that is the product of spruce bark wastes subjected to hydrothermal decomposition. To identify the influence of hydrochar as a reinforcing material on the designed composites, seven formulations were prepared and tested. An aromatic epoxy monomer derived from wood biomass was used to generate the polymeric matrix, and the formulations were prepared varying the filler concentration from 0 to 30 wt %. The reactivity of these formulations, together with the structural, thermal, and mechanical properties of bio-based resin and biocomposites, are investigated. Surprisingly, the reactivity study performed by differential scanning calorimetry (DSC) revealed that HC has a strong impact on polymerization, leading to an important increase in reaction enthalpy and to a decrease of temperature range. The Fourier Transform Infrared Spectroscopy (FT-IR) investigations confirmed the chemical bonding between the resin and the HC, while the dynamic mechanical analysis (DMA) showed increased values of crosslink density and of storage moduli in the biocomposites products compared to the neat bioresin. Thermogravimetric analysis (TGA) points out that the addition of hydrochar led to an improvement of the thermal stability of the biocomposites compared with the neat resorcinol diglycidyl ether (RDGE)-based resin (T_5% = 337 °C) by ≈2–7 °C. Significantly, the biocomposites with 15–20 wt % hydrochar showed a higher stiffness value compared to neat epoxy resin, 92SD vs. 82SD, respectively.

Polyhydroxybutyrate Bioresins with High Thermal Stability by Cross-linking with Resorcinol Diglycidyl Ether

The development of sustainable materials by employing natural and nontoxic resources has been attracting much attention over the previous years. In this work, we discuss for the first time the chemical combination between resorcinol diglycidyl ether (RDGE), an aromatic biobased thermosetting monomer, and polyhydroxybutyrate (PHB), a bioderived and biodegradable thermoplastic polyester. By this combination, we aimed to associate the high thermal stability of RDGE with a toughening effect by the aliphatic chains of PHB. The investigations on the mechanism of the cross-linking reaction and on the structural connectivity between the two components were realized by Fourier transform infrared (FTIR) and NMR spectroscopies. We found that the epoxide polymerization catalyzed by tertiary amines triggers the formation of crotonyl species by polyhydroxybutyrate cleavage. Two-dimensional NMR experiments show that polyhydroxybutyrate fragments covalently bind as side chains to the rigid aromatic network of the epoxide frame. The cross-linking between the two systems entails the formation of new ester and ether bonds. The obtained structures show a network homogeneity confirmed by a single T_g, from 85 to 47 °C, as a function of the formulation, and tan δ values from 87 to 53 °C. The combination of the two comonomers showed a positive effect. The PHB increased the toughness of RDGE-based thermosets, improving the material elasticity by increasing the chain length between the cross-links. An important result of this study is the high thermal stability of RDGE/PHB bioresins, with the T_5% varying between 330 and 310 °C as a function of the PHB ratio.

An effective utilization of MXene and its effect on electromagnetic interference shielding: flexible, free-standing and thermally conductive composite from MXene–PAT–poly(p-aminophenol)–polyaniline co-polymer

MXene and conductive polymers are attractive candidates for electromagnetic interference shielding (EMI) applications. The MXene–PAT-conductive polymer (CP) composites were fabricated by a cost-effective spray coating technique and characterized using X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), X-ray diffraction (XRD) and Raman spectroscopy. A new approach has been developed for the synthesis of exfoliated MXene. The MXene–PAT–poly(p-aminophenol)–polyaniline co-polymer composite exhibited good electric conductivity (EC) of 7.813 S cm⁻¹. The composites revealed an excellent thermal properties, which were 0.687 W (m K)⁻¹ thermal conductivity, 2.247 J (g K)⁻¹ heat capacity, 0.282 mm² s⁻¹ thermal diffusivity and 1.330 W s^1/2 m⁻² K⁻¹ thermal effusivity. The composites showed 99.99% shielding efficiency and the MXene–PAT–PANI–PpAP composite (MXPATPA) had EMI shielding effectiveness of 45.18 dB at 8.2 GHz. The reduced form of MXene (r-Ti₃C₂T_x) increased the shielding effectiveness (SE) by 7.26% and the absorption (SE_A) was greatly enhanced by the ant farm like structure. The composites possess excellent thermal and EMI SE characteristics, thus can be applied in areas, such as mobile phones, military utensils, heat-emitting electronic devices, automobiles and radars.

MXene and conductive polymers are attractive candidates for electromagnetic interference shielding (EMI) applications.