Dynamic Mechanical Analysis Results Research Articles

Investigation of Thermal, Mechanical and Shape Memory Properties of 3D-Printed Functionally Graded Nanocomposite Materials.

In this study, a 3D-printed photocurable resin was developed by incorporating graphene nanoplatelets functionalised with melamine to investigate the thermal, mechanical, fracture and shape memory behaviours. The objective of this work was to produce a printed functionally graded nanocomposite material that has a smart temperature-responsive structure; presents good thermal stability, strength and fracture toughness; and can demonstrate shape-changing motions, such as sequential transformations, over time. The functionalised graphene nanoplatelets were examined via thermogravimetric analysis, Fourier transform infrared spectroscopy, Raman spectroscopy and ultraviolet-visible spectroscopy. Thermogravimetric analysis showed that the degradation temperature of the nanocomposite containing 0.1 wt% of functionalised graphene nanoplatelets at the weight loss of 5% was 304 °C, greater than that of the neat one by 29%. Dynamic mechanical analysis results showed property enhancements of the storage modulus and glass transition temperature. Fracture toughness, tensile strength and impact resistance were improved by 18%, 35% and 78%, respectively. The shape memory tests were performed to obtain the temperature-time recovery behaviour of the 3D-printed structures. The addition of functionalised graphene nanoplatelets demonstrated an enhancement in the shape recovery ratios. Generally, the five subsequent cycles were notably stable with a high recovery ratio of 97-100% for the flat shape and circular shape of the M-GNP specimens. On the other hand, these values were between 91% and 94% for the corresponding neat specimens.

Phase morphology, rheological behavior and mechanical properties of supertough biobased poly(lactic acid) reactive ternary blends

Poly(lactic acid) (PLA) is one of the most promising bio-based polyester with great potential to replace for the petroleum-based polymers, which can significantly reduce greenhouse gas emissions. However, the inherent brittleness of PLA seriously restricts its broad applications. Herein, PLA/poly(ε-caprolactone) (PCL)/ethylene methyl acrylate-glycidyl methacrylate (EMA-GMA) ternary blends with different phase structures were prepared through reactive blending. The reactions between the epoxy groups of EMA-GMA and the carboxyl and hydroxyl end groups of PLA and PCL and were evidenced from the Fourier transform infrared spectroscopy, dynamic mechanical analysis and rheological results. The atomic force microscopy (AFM) images clearly revealed the formation of stack structure of the PCL and EMA-GMA minor phases in PLA/PCL/EMA-GMA (80/15/5) blend, and core-shell particle structures in PLA/PCL/EMA-GMA (80/10/10) and (80/5/15) blends. In terms of elongation at break and impact toughness, PLA/PCL/EMA-GMA (80/5/15) blend presents the best properties among all the compositions. Moreover, it also behaved excellent stiffness-toughness balance. The toughening mechanism can be ascribed to the formation of core-shell structure and the existence of interfacial adhesion in the ternary blends. This work can provide guide for the preparation and design of PLA-based partially renewable supertough materials that can compete with conventional petro-derived plastics.

Synthesis and characterization of low dielectric constant polybenzoxazines with different fluorine contents

AbstractThe rapid development of integrated circuits puts forward higher requirements for low dielectric constant polymers. In this study, two fluorinated benzoxazine monomers, bis‐(3,4‐dihydro‐3‐(4‐fluoro‐3‐(trifluoromethyl)phenyl)‐2H‐1,3‐benzoxazine)isopropane (BA‐ftfa) and bis‐(3,4‐dihydro‐3‐(4‐fluoro‐3‐(trifluoromethyl)phenyl)‐2H‐1,3‐benzoxazine)isoperfluoropropane (BAF‐ftfa), were successfully synthesized. Differential scanning calorimeter (DSC) was used to monitor the thermal curing behaviors of the monomers and their mixtures. Five groups of polybenzoxazine samples with different fluorine content (25% ~ 35%) were obtained by copolymerizing the two monomers with different mass ratios. The effects of fluorine content on dielectric properties were investigated and the results show that PBAF‐ftfa with the highest fluorine content has the lowest dielectric constant of 2.53 at 1 MHz. Furthermore, the results of thermogravimetric analysis (TGA) and dynamic mechanical analysis (DMA) show that all polymers possess excellent thermal stability and exhibit high glass transition temperatures over than 180°C.

Design, fabrication and characterization of dynamic covalent polymer networks containing reversible Diels-Alder adducts derived from vegetable oil and furfural

The exploration of novel bio-based functional polymers has high application value and confirms to sustainable development strategies following the increasing shortage of fossil resources. In this research, several different recyclable bio-based dynamic covalent polymer networks (DCPNs) containing dynamic Diels-Alder bonds from vegetable oil and furan were designed and fabricated via a simple preparation process. The reprocessability, shape memory, molecular structures, thermal properties and mechanical properties of the DCPNs were all investigated. 1H nuclear magnetic resonance (1H-NMR) and Fourier transform infrared spectroscopy (FTIR) analysises demonstrated the target reactive products were all successfully synthesized. Variable-temperature FTIR and differential scanning calorimetry revealed the changing rule of dynamic Diels-Alder bond molecular structures with temperature. The DCPNs possess controllable tensile properties including superior ductility and certain rigidity via adjusting fatty chain component, which is in accordance with the result of dynamic mechanical analysis. Thermal gravimetric analysis demonstrated the DCPNs had excellent thermostability, and the main peak decomposition temperatures were all above 460 °C. The nature of the dynamic Diels-Alder bonds could make shattered DCPNs be reprocessed multiple times under relatively mild conditions. The DCPNs displayed certain shape memory properties, and the shape fixation and recovery ratio at the last two cycles were kept above 95.53% and 84.58%, respectively. This work will help with the development on this kind of bio-based polymers containing dynamic Diels-Alder covalent bonds.

Nanoscale dynamic mechanical analysis on interfaces of biological composites

Biological composites incorporate structural arrays of rigid-elastic reinforcements made of minerals or crystalline biopolymers, which are connected by thin, compliant, and viscoelastic macromolecular matrix material. The near-interface regions of these biological composites grant them energy dissipation capabilities against dynamic mechanical loadings, which promote various biomechanical functions such as impact adsorption, fracture toughness, and mechanical signal filtering. Here, we employ theoretical modeling and finite-element simulations to analyze the mechanical response of the near-interface in biological composites to nanoscale dynamic mechanical analysis (DMA). We identified the dominating load-bearing mechanisms of the near-interface region and employed these insights to introduce simple semi-empirical formulations for approaching the mechanical properties (storage and loss moduli) of the biological composite from the nanoscale DMA results. Our analysis paves the way for the nanomechanical characterization of biological composites in diverse natural materials systems, which can also be employed for bioinspired and biomedical configurations.

Seismic Response of Earth-Rock Dams with Innovative Antiseepage Walls on the Effect of Microscopic Fluid-Solid Coupling

In dykes and dam projects, the microscopic fluid-solid coupling effect from the interaction between soil skeleton and pore water during an earthquake is crucial to consider, as it can lead to dam safety problems. To control seepage in medium- and small-sized dams, polymer antiseepage walls have emerged as effective measures. In recent years, this method has been increasingly utilized in projects worldwide as it is essential for preventing potential dam safety issues. To address concerns related to seismic safety, this study conducts theoretical analysis, model tests, and numerical simulations to investigate the seismic response of earth-rock dams with polymer antiseepage walls, with a specific focus on the microscopic fluid-solid coupling effect. The dynamic viscoelastic constitutive model used in this study incorporates Biot’s theory of dynamic consolidation and the results of dynamic mechanical analysis (DMA) of polymer materials. To validate the model, a centrifuge test is performed, and it is then utilized to study the seismic response of earth-rock dams with polymer antiseepage walls. Furthermore, the influence of factors such as fluid-solid coupling, water level, polymer material density, and wall thickness on the seismic response of dams with antiseepage walls is analyzed. Finally, the seismic safety of the earth-rock dam with the polymer antiseepage wall is thoroughly examined. The results emphasize the need to consider the fluid-solid coupling effect, as factors like water level and design parameters of the antiseepage wall significantly impact the seismic response of earth-rock dams with polymer antiseepage walls.

Soft acrylate monomer-based optically clear adhesive for foldable electronics: Mechanical characterization and fractography analysis under large strain

Touchscreen panels and foldable smartphones rely heavily on optically clear adhesives (OCAs) to function effectively. Therefore, these applications have created a demand for OCAs that are flexible, bendable, or stretchable with high transparency. Developing highly viscoelastic, and optically clear adhesives is crucial for flexible electronics to become commercially viable. This study focuses on synthesizing UV-curable soft acrylate-based OCAs using 2-ethylhexyl acrylate (EHA) and 2-hydroxyethyl acrylate (HEA) as functional monomers without any solvent or crosslinker. To make the OCAs stronger under various mechanical loading types, liquid OCAs with primary and final curing under pressure were used to endure high shear stress and strain. Based on the dynamic mechanical analysis results, the shear stresses of samples at room temperature and 65 °C increased from 9.41 ± 0.6 and 2.91 ± 0.31 (90 wt% EHA, cohesive failure) to 97.5 ± 8.54, and 57.81 ± 1.52 kPa (70 wt% EHA, not failed), respectively. Besides, it should be noted that the OCA hyper-viscoelasticity properties were studied in all of the mechanical experiments, and 500 % large strain was applied to match the actual strain loading in the foldable screens. In this condition, the OCA layer's large deformation behavior and other mechanical properties are more relevant for real-world applications. The fabricated OCAs in this study exhibit competitiveness comparable to commercial OCAs, such as TMS and V0, in terms of performance and quality. Moreover, the potential utilization of 70 wt% EHA (49.7 kPa) in various applications, including stretchable displays, wearable electronic devices, and foldable smartphones, is demonstrated through 3-point tests (100 cycles), wrist bending tests (100–120 cycles), and fatigue tests for up to 10,000 cycles.

Accelerated aging behavior and degradation mechanism of nitrile rubber in thermal air and hydraulic oil environments

AbstractThe aging behavior and degradation mechanism of nitrile rubber (NBR) under free and compression states were investigated in simulated air and hydraulic oil environments at various elevated temperatures. The variations in the crosslinking density, volatile components and the chemical structure of NBR during aging were studied using equilibrium swelling testing and dynamic mechanical analysis (DMA), pyrolysis‐gas chromatography–mass spectrometry and attenuated total reflection‐Fourier transform infrared spectroscopy. The migration of additives in different media and the crosslinking density of NBR aged in different conditions were compared. The tensile strength, DMA, and thermogravimetric analysis results were consistent with the changes in the crosslinking density of NBR and the migration of additives. Four effects of the simulated hydraulic system on the thermal aging of NBR were examined. Both the compression stress and the oil medium slowed the aging of NBR. The results can provide new insights into the use of NBR products in lubricating oil environments and NBR lifespan prediction in hydraulic working conditions.

Synthesis and properties of silicone‐epoxy polymer with long silicone chain

AbstractSilicone‐epoxy polymers (SEP) with different n(SiH)/n(CC) ratios were synthesized through the hydrosilylation reaction of diallyl bisphenol A epoxy resin (DADGEBA) and hydrogen‐containing silicone oil (HS) with long silicone chain. The structure of SEP was characterized by Fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance spectroscopy (1H NMR), and gel permeation chromatography (GPC), and the compatibility of the curing system was studied by dynamic mechanical analysis (DMA) and scanning electron microscope (SEM). DMA and SEM results showed that after curing with epoxy curing agent, the compatibility of the curing system was excellent. The mechanical, bonding, and thermal properties of the cured product were also measured. The cured product exhibited superior thermal stability and mechanical properties. High toughness of SEP was provided by the long silicone chain, and high mechanical strength was provided by the cross‐linking networks. The maximum tensile strength was 15.64 MPa, the maximum elongation at break was 62%, and the maximum tensile lap‐shear strength was 8.89 MPa. The silicone‐epoxy polymers can be widely used in electronic packaging in the future.

Evaluation of Coconut Fibre Reinforced Low Density Polyethelene Composites

Physical, mechanical and dynamic properties of composites produced from coconut fibres using pure water sachet (LDPE) as matrix were evaluated in this study in order to assess its suitability for use as particleboards. The LDPE (waste water sachets) and coconut coir/fibre were collected, shredded and milled into pellets. Five compositions with coconut fibre loading 5, 10, 15, 20, and 25%, and corresponding LDPE of 95, 90, 85, 80 and 75%. A sixth sample with 100% LDPE was also produced as control. The LDPE samples were heated at 170°C for 30 minutes, and each melted solution was loaded with the corresponding coconut fibres and the mixture stirred and poured into a pre-designed metallic mould, pressed and cured in air for 24 hours. The results show that water absorption, swelling thickness and flaking concentration increased with, while the density decreased. The bending strength decreased with fibre loading, while the tensile strength, compressive strength and modulus of elasticity increased with increasing loading to a point before decreasing sharply. The results of dynamic mechanical analysis for the storage and loss modulus shows that as the temperature of the samples was increased these properties reduced except for the damping factor which increased. On the whole, the results showed that the sample with 15% coconut fibres loading and 85% LDPE exhibits more desirable properties compared with the others. These results imply that the composites produced from coconut fibres with LDPE as a matrix can be used as particleboards as well as in areas other areas of applications in the automobile industries. This will improve on savings in foreign exchange and mitigate environmental degradation as result of indiscriminate disposal of portable water sachets and coconut fibres.

The effects of surface modified date‐palm fiber fillers upon the thermo‐physical performances of high density polyethylene‐polyvinyl chloride blend with maleic anhydride as a grafting agent

AbstractTo demonstrate the upcycling of thermoplastic waste with good thermo‐physical properties, high density polyethylene (HDPE; 80 phr) and polyvinyl chloride (PVC; 20 phr) are mixed as the matrix using maleic anhydride (MAH) reinforced with unmodified and modified date palm fibers (DPFs; 30 phr). The effects of in situ grafting of MAH onto the DPFs‐HDPE‐PVC composites upon the resultant thermo‐physical characteristics are investigated and analyzed via Fourier transform infrared spectroscopy and scanning electron microscopy. Thus, the effective compatibilizing of both the HDPE‐PVC component and the grafted HDPE‐PVC blend with the modified DPFs are confirmed. In addition, the results of dynamical mechanical analysis and differential scanning calorimetry indicate that the glass transition temperature (Tg) of the composite is enhanced by the incorporation of modified DPFs. The thermal, mechanical, and water uptake properties of the composites are also improved. Rheological analysis at low frequency reveals that the introduction of hydrolyzed DPFs results in a higher complex viscosity (1.94 × 106 Pa s) and storage modulus (119,844 MPa) for the obtained composite (designated G‐Hydro). Overall, the G‐Hydro composite exhibits the best performance, making it ideal for a variety of construction and building purposes.

Fabrication of new proton conducting membrane for fuel cell applications based on porous polyimide Matrimid® and hydrophobic protic ionic liquid

AbstractA new proton conducting membrane has been developed by impregnation of porous polyimide Matrimid® (PI) with hydrophobic protic ionic liquid triethylammonium bis(trifluoromethylsulfonyl)imide (TEA‐TFSI). According to the results of dynamic mechanical analysis (DMA), PI/TEA‐TFSI membrane has satisfactory viscoelastic properties in the temperature range 25–100°C. However, the sharp drop in storage modulus (E') occurs at higher temperatures that is probably caused by the plasticizing effect of ionic liquid. To improve the mechanical properties of PI matrix, it was impregnated with the solution of polyetheramine Jeffamine® D‐400 in the TEA‐TFSI. This approach allowed to obtain a partially cross‐linked PI which is more resistant to deformation at elevated temperatures. Thus, DMA study revealed a storage modulus around 400 MPa for PI/Jeffamine/TEA‐TFSI membrane up to 150°C, like neat porous Matrimid®. Thermogravimetric analysis results indicate high thermal stability of PI/Jeffamine/TEA‐TFSI composite with thermal degradation point of 343°C. The ionic conductivity of the composite membrane is 4·10−3 S/cm at room temperature and reaches the level of 10−2 S/cm above 100°C. Overall, the results of this study indicate that partially cross‐linked porous PI impregnated with hydrophobic protic ionic liquid is a promising polymer electrolyte membrane for fuel cells operating at elevated temperatures in water‐free conditions.

Doping C60(OH) to Regulate the Crosslink Network and Energy Band Structures of Epoxy Resin and Allow for Electronic Directional Drive in C60(OH)/EP

The interfacial effect of nanoparticles can effectively regulate electron migration in epoxy composites. In this article, hydroxylated C60 [C60(OH)] was prepared and added to epoxy resin (EP). The inhibition of electron motion in epoxy composites was realized, and the dielectric strength of the epoxy composites was improved. The results of dynamic mechanical analysis (DMA) showed that C60(OH) regulated the structure of the crosslinked EP network and increased the crosslink density by 16.5%. The results of a density functional theory (DFT) simulation showed that the doping of C60(OH) formed a potential energy barrier at the C60(OH)-EP interface, which was conducive to the directional migration and capture of electrons driven to C60(OH). Electrostatic force microscopy (EFM) and pulsed electroacoustic (PEA) experiments showed that C60(OH) had a strong ability to capture charge, and the charge migration rate of C60(OH)/EP was 43% lower than that of pure EP in the presence of 10 kV/mm when the EP was doped with 0.1wt% C60(OH). The breakdown strength and volume resistivity increased by 17.87% and 222%, respectively. Thus, this article provides a new method to improve the dielectric strength of epoxy composites.

Amino Acids as Bio-Based Curing Agents for Epoxy Resin: Correlation of Network Structure and Mechanical Properties.

Bio-based alternatives for petroleum-based thermosets are crucial for implementing sustainable practices in fiber-reinforced polymer composites. Therefore, the mechanical properties of diglycidyl ether of bisphenol a (DGEBA) cured with either l-arginine, l-citrulline, γ-aminobutyric acid, l-glutamine, l-tryptophan, or l-tyrosine were investigated to determine the potential of amino acids as bio-based curing agents for epoxy resins. Depending on the curing agent, the glass transition temperature, Young’s modulus, tensile strength, and critical stress intensity factor range from 98.1 ∘C to 188.3 ∘C, 2.6 GPa to 3.5 GPa, 39.4 MPa to 46.4 MPa, and 0.48 MPam0.5 to 1.34 MPam0.5, respectively. This shows that amino acids as curing agents for epoxy resins result in thermosets with a wide range of thermo-mechanical properties and that the choice of curing agent has significant influence on the thermoset’s properties. After collecting the results of dynamic mechanical analysis (DMA), tensile, flexural, compression, and compact tension tests, the functionality f, cross-link density νC, glass transition temperature Tg, Young’s modulus ET, compression yield strength σCy, critical stress intensity factor in mode I KIC, fracture energy GIC, and diameter of the plastic zone dp are correlated with one another to analyze their inter-dependencies. Here, the cross-link density correlates strongly positively with Tg, ET, and σCy, and strongly negatively with KIC, GIC, and dp. This shows that the cross-link density of DGEBA cured with amino acids has a crucial influence on their thermo-mechanical properties and that the thermosets considered may either be stiff and strong or tough, but hardly both at the same time.

Shape memory behavior of polyacrylate-based amorphous nanocomposite hydrogel under uniaxial tension: Modeling and experimental

In the present work, a comprehensive constitutive equation was developed to predict the shape memory behavior of amorphous nanocomposite hydrogel systems. The effects of interfaces of nanoparticles and micro-vessels of water with polymeric matrix and their thermal and physicomechanical properties on the model prediction were considered. An amorphous polyacrylate-based hydrogel with the glass transition temperature as a switching temperature was selected. Nanocomposite hydrogels containing 0.2 and 1.2 wt% of multiwall carbon nanotubes were prepared. The accuracy of the proposed model was evaluated with experimental data for all the selected systems. The dynamic mechanical analysis results of the shape memory behavior showed the presence of nanoparticles increased the shape fixing ratio and the rate of shape recovery of polyacrylamide nanocomposite hydrogels. The model prediction of shape recovery ratio in all systems was 100%. A comparison of the model prediction with the shape memory experimental data revealed a good agreement.

Influence of chlorotrifluoroethylene on crystal structure and polymer dynamics of poly(vinylidenefluoride-co-chlorotrifluoroethylene) antibacterial copolymers

<abstract> <p>The effect of chlorotrifluoroethylene (CTFE) on dynamic relaxations of poly(vinylidenefluoride-co-chlorotrifluoroethylene) films (P(VDF-CTFE)) containing 0, 10, 15 and 20% of CTFE was investigated via broadband dielectric spectroscopy (DRS) and dynamic mechanical analysis (DMA). The interpretation was accompanied by the crystal structure obtained from Fourier transform infrared spectroscopy, wide-angle X-ray diffraction, small-angle X-ray scattering and differential scanning calorimetry. Increment of CTFE contents caused reducing the degree of crystallinity but did not impact the long period, lamellar thickness, and amorphous layer thickness. Four dynamic processes were clearly observed in DRS spectra for the neat poly(vinylidene fluoride) and P(VDF-CTFE) which were attributed to the local motion of amorphous chains (<italic>β</italic>), the segmental relaxation of amorphous chains (<italic>α</italic><sub>1</sub>), the local conformational rearrangement of the TGTGʹ conformation (<italic>α</italic><sub>2</sub>) and the process associated with Maxwell–Wagner–Sillars interfacial polarization (α<sub>MWS</sub>). The extra relaxation was observed for P(VDF-CTFE), which was more likely associated to the molecular motion of CTFE chain segments (<italic>α</italic><sub>c</sub>), correspondent with DMA results. These PVDF and P(VDF-CTFE) conducted as self-antibacterial materials.</p> </abstract>

Fabrication of proton exchange membrane for non-humidified fuel cells based on polyimide Matrimid® and hydrophobic protic ionic liquid

New proton exchange membrane based on polyimide Matrimid® (PI) and hydrophobic protic ionic liquid, 1-methylimidazolium bis(trifluoromethylsulfonyl)imide (MIM-TFSI), has been prepared by casting from methylene chloride/dimethylformamide solution. Infrared analysis revealed physicochemical interactions between 1-methylimidazolium cations and imide groups of PI. The results of mechanical testing indicate significantly reduced tensile strength of PI/MIM-TFSI composite membrane compared to neat polymer. Moreover, the dynamical mechanical analysis results revealed sharp drop in storage modulus (E´) of the polymer film above 60 °C. To improve the elastic properties of the membrane, PI was successively cross-linked with polyetheramine Jeffamine® D-2000 (10 mol. %) in methylene chloride/dimethylformamide solution, as well as in solid film at 100 °C. This approach allowed to prepare PI/Jeffamine/MIM-TFSI (70 wt. %) composite film which has an acceptable E' value of 210 MPa at 140 °C. According to thermal gravimetric analysis data, PI/Jeffamine/MIM-TFSI composite has a thermal degradation point (i.e. 5 % weight loss) of 286 °C. The ionic conductivity of PI/Jeffamine/MIM-TFSI composite membrane is around 10–4 S/cm at room temperature and reaches the minimal level of 10–3 S/cm, required for fuel cell applications, above 100 °C. Overall, the results of this study indicate that the cross-linking of polyimide Matrimid with flexible polyetheramine Jeffamine is an efficient approach for preparing dense composite membrane with high content of the protic ionic liquid. Such polymer-electrolyte membrane has the reasonable combination of good stiffness, thermal stability, and ionic conductivity and therefore is a promising candidate for use in fuel cells operating at elevated temperatures in water-free conditions.

Selected Simple Natural Antimicrobial Terpenoids as Additives to Control Biodegradation of Polyhydroxy Butyrate.

In this experimental research, different types of essential oils (EOs) were blended with polyhydroxybutyrate (PHB) to study the influence of these additives on PHB degradation. The blends were developed by incorporating three terpenoids at two concentrations (1 and 3%). The mineralization rate obtained from CO2 released from each sample was the factor that defined biodegradation. Furthermore, scanning electron microscope (SEM), differential scanning calorimetry (DSC), and dynamic mechanical analysis (DMA) were used in this research. The biodegradation percentages of PHB blended with 3% of eucalyptol, limonene, and thymol after 226 days were reached 66.4%, 73.3%, and 76.9%, respectively, while the rate for pure PHB was 100% after 198 days, and SEM images proved these results. Mechanical analysis of the samples showed that eucalyptol had the highest resistance level, even before the burial test. The other additives showed excellent mechanical properties although they had less mechanical strength than pure PHB after extrusion. The samples' mechanical properties improved due to their crystallinity and decreased glass transition temperature (Tg). DSC results showed that blending terpenoids caused a reduction in Tg, which is evident in the DMA results, and a negligible reduction in melting point (Tm).

Effect of clay minerals on the flame retardancy of polylactic acid/ammonium polyphosphate system

The overview of the literature reveals the lack of comprehensive study on the effect of clay minerals in flame-retarded polylactic acid (PLA) composites. This research focuses on sepiolite (SEP) and montmorillonite (MMT) clay minerals and their impact on ammonium polyphosphate (APP)-based intumescent flame-retardant (IFR) system in PLA. The effects of the clay mineral types, their surface modification (O-SEP and O-MMT, respectively) and their concentration in PLA/APP composites on the flame-retardant properties were comprehensively evaluated through thermal and flammability tests. Overall, the sepiolite-containing samples showed the greatest decrease in pHRR and THR values at the 3 m/m% loading level. The sepiolites showed stronger interfacial interactions with the PLA matrix than the montmorillonites, and the organomodification proved to improve the compatibility of both types of clay minerals according to the dynamic mechanical analysis (DMA) results. Yet, the organomodification had a contradictory effect on the flame-retardant properties. In the case of sepiolites, it proved to be beneficial as the O-SEP added composite achieved a 60% decrease in the pHRR value and reduced the THR value to 60%. For montmorillonites, the improved compatibility by the organomodification with the PLA matrix seemed to hinder its flame-retardant effectiveness, as the critical point to its flame-retardant mechanism is the rapid migration and accumulation of the clay minerals towards the surface of the polymer.

Flexural, impact and dynamic mechanical analysis of hybrid composites: Olive tree leaves powder/ pineapple leaf fibre/epoxy matrix

The objective of this work is to determine the suitability of olive tree leaves powder (OTL) as reinforcement along with pineapple leaf fibre (PALF) in the epoxy composites. The parent and hybrid composites were fabricated using the hot press technique with the overall fibre loading at 40 wt% and OTL: PALF in the ratio of 50:50, 30:70 and 70:30, respectively. The fabricated composites were characterized using dynamic mechanical analysis (DMA), flexural and impact tests. As the proportion of PALF was increased in the hybrid composites, impact strength improved significantly. However, hybrid composites were not effective in withstanding the bending load where their bending strength and flexural modulus were lower than the parent composites. Hybrid composites outperformed parent composites with superior storage modulus, lower loss modulus and lower damping factor as per the DMA results.