Compatibilization of Polyamide 6/Cyclic Olefinic Copolymer Blends for the Development of Multifunctional Thermoplastic Composites with Self-Healing Capability.

This study investigated the self-healing properties of PA6/COC blends, in particular, the impact of three compatibilizers on the rheological, microstructural, and thermomechanical properties. Dynamic rheological analysis revealed that ethylene glycidyl methacrylate (E-GMA) played a crucial role in reducing interfacial tension and promoting PA6 chain entanglement with COC domains. Mechanical tests showed that poly(ethylene)-graft-maleic anhydride (PE-g-MAH) and polyolefin elastomer-graft-maleic anhydride (POE-g-MAH) compatibilizers enhanced elongation at break, while E-GMA had a milder effect. A thermal healing process at 140 °C for 1 h was carried out on specimens broken in fracture toughness tests, performed under quasi-static and impact conditions, and healing efficiency (HE) was evaluated as the ratio of critical stress intensity factors of healed and virgin samples. All the compatibilizers increased HE, especially E-GMA, achieving 28.5% and 68% in quasi-static and impact conditions, respectively. SEM images of specimens tested in quasi-static conditions showed that all the compatibilizers induced PA6 plasticization and crack corrugation, thus hindering COC flow in the crack zone. Conversely, under impact conditions, E-GMA led to the formation of brittle fractures with planar surfaces, promoting COC flow and thus higher HE values. This study demonstrated that compatibilizers, loading mode, and fracture surface morphologies strongly influenced self-healing performance.

Effect of Different Cellulose Fillers on the Properties of Xanthan-Based Composites for Soil Conditioning Applications.

The aim of this study was to investigate the effect of different types of natural cellulose-based fillers on the properties of Xanthan gum (XG) in order to develop novel bio-based soil conditioners (SCs) that could be used in forestry and agricultural applications. Rheological measurements highlighted that SCs with cellulose fillers characterized by a high aspect ratio and low oxide ash content exhibited an average increase of 21% in yield stress compared to neat Xanthan gum. The presence of cellulose fillers in the composites resulted in a slower water release than that of neat XG, limiting the volumetric shrinkage during the drying process. Furthermore, an analysis of the water absorption and water retention capacity of soils treated with the different SCs was carried out, demonstrating that the addition of 1.8 wt.% of SC with optimized composition to the soil led to an increase in water absorption capacity from 34% up to 69%. From the soil water retention curves, it was observed that the addition of SCs significantly increased the amount of water effectively available for plants in the area between field capacity and permanent wilting point (100-1000 kPa). From practical experiments on grass growth, it was observed that these SCs improved the water regulation of the soil, thus increasing the probability of plant survival under drought conditions.

Ladder-like Poly(methacryloxypropyl) silsesquioxane-Al2O3-polybutadiene Flexible Nanocomposites with High Thermal Conductivity.

Ladder-like poly(methacryloxypropyl)-silsesquioxanes (LPMASQ) are photocurable Si-based gels characterized by a double-stranded structure that ensures superior thermal stability and mechanical properties than common organic polymers. In this work, these attractive features were exploited to produce, in combination with alumina nanoparticles (NPs), both unmodified and functionalized with methacryloxypropyl-trimethoxysilane (MPTMS), LPMASQ/Al2O3 composites displaying remarkable thermal conductivity. Additionally, we combined LPMASQ with polybutadiene (PB) to produce hybrid nanocomposites with the addition of functionalized Al2O3 NPs. The materials underwent thermal stability, structural, and morphological evaluations via thermogravimetric analysis (TGA), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDXS), Fourier transform infrared spectroscopy (FTIR), and solid-state nuclear magnetic resonance (NMR). Both blending PB with LPMASQ and surface functionalization of nanoparticles proved to be effective strategies for incorporating a higher ceramic filler amount in the matrices, resulting in significant increases in thermal conductivity. Specifically, a 113.6% increase in comparison to the bare matrix was achieved at relatively low filler content (11.2 vol%) in the presence of 40 wt% LPMASQ. Results highlight the potential of ladder-like silsesquioxanes in the field of thermally conductive polymers and their applications in heat dissipation for flexible electronic devices.

On the Selective Enzymatic Recycling of Poly(pentamethylene 2,5-furanoate)/Poly(lactic acid) Blends and Multiblock Copolymers.

Among novel renewable furanoate-based polyesters, poly(pentamethylene 2,5-furandicarboxylate) (PPeF) shows outstanding gas barrier properties and high flexibility. PPeF blending/copolymerization with another well-known bio-based polymer, poly(lactic acid) (PLA), leads to considerably better mechanical and gas barrier properties of the latter, making it suitable for flexible food packaging applications. In this work, enzymatic depolymerization of PLA/PPeF blends with different compositions (1, 3, 5, 20, 30, and 50 wt % PPeF) and a PLA-PPeF block copolymer (50 wt % PPeF) by cutinase 1 from Thermobifida cellulositilytica (Thc_Cut1) was investigated as a possible recycling strategy. Based on quantification of weight loss and high-performance liquid chromatography (HPLC) analysis of released molecules, faster hydrolysis was seen for PLA/PPeF blends with increasing PPeF content when compared to neat PLA, while the block copolymer (P(LA50PeF50)) was significantly less susceptible to hydrolysis. Surface morphology analysis (via scanning electron microscopy), Fourier transform infrared spectroscopy, and NMR analysis confirmed preferential hydrolysis of the PPeF component. Through crystallization, 2,5-furandicarboxylic acid was selectively recovered from the depolymerized films and used for the resynthesis of the PPeF homopolymer, demonstrating the potential of enzymes for novel recycling concepts. The possibility of selective recovery of 2,5-furandicarboxylic acid from the completely depolymerized films with a 75% yield could bring further evidence of the high value of these materials, both in the form of blends and copolymers, for a sustainable whole packaging life cycle, where PPeF is potentially enzymatically recycled and PLA is mechanically recycled.

Toughening Effect of 2,5-Furandicaboxylate Polyesters on Polylactide-Based Renewable Fibers.

This work presents the successful preparation and characterization of polylactide/poly(propylene 2,5-furandicarboxylate) (PLA/PPF) and polylactide/poly(butylene 2,5-furandicarboxylate) (PLA/PBF) blends in form of bulk and fiber samples and investigates the influence of poly(alkylene furanoate) (PAF) concentration (0 to 20 wt%) and compatibilization on the physical, thermal, and mechanical properties. Both blend types, although immiscible, are successfully compatibilized by Joncryl (J), which improves the interfacial adhesion and reduces the size of PPF and PBF domains. Mechanical tests on bulk samples show that only PBF is able to effectively toughen PLA, as PLA/PBF blends with 5-10 wt% PBF showed a distinct yield point, remarkable necking propagation, and increased strain at break (up to 55%), while PPF did not show significant plasticizing effects. The toughening ability of PBF is attributed to its lower glass transition temperature and greater toughness than PPF. For fiber samples, increasing the PPF and PBF amount improves the elastic modulus and mechanical strength, particularly for PBF-containing fibers collected at higher take-up speeds. Remarkably, in fiber samples, plasticizing effects are observed for both PPF and PBF, with significantly higher strain at break values compared to neat PLA (up to 455%), likely due to a further microstructural homogenization, enhanced compatibility, and load transfer between PLA and PAF phases following the fiber spinning process. SEM analysis confirms the deformation of PPF domains, which is probably due to a "plastic-rubber" transition during tensile testing. The orientation and possible crystallization of PPF and PBF domains contribute to increased tensile strength and elastic modulus. This work showcases the potential of PPF and PBF in tailoring the thermo-mechanical properties of PLA in both bulk and fiber forms, expanding their applications in the packaging and textile industry.

Characterization of Cyclic Olefin Copolymers for Insulin Reservoir in an Artificial Pancreas.

Type-1 diabetes is one of the most prevalent metabolic disorders worldwide. It results in a significant lack of insulin production by the pancreas and the ensuing hyperglycemia, which needs to be regulated through a tailored administration of insulin throughout the day. Recent studies have shown great advancements in developing an implantable artificial pancreas. However, some improvements are still required, including the optimal biomaterials and technologies to produce the implantable insulin reservoir. Here, we discuss the employment of two types of cyclic olefin copolymers (Topas 5013L-10 and Topas 8007S-04) for an insulin reservoir fabrication. After a preliminary thermomechanical analysis, Topas 8007S-04 was selected as the best material to fabricate a 3D-printed insulin reservoir due to its higher strength and lower glass transition temperature (Tg). Fiber deposition modeling was used to manufacture a reservoir-like structure, which was employed to assess the ability of the material to prevent insulin aggregation. Although the surface texture presents a localized roughness, the ultraviolet analysis did not detect any significant insulin aggregation over a timeframe of 14 days. These interesting results make Topas 8007S-04 cyclic olefin copolymer a potential candidate biomaterial for fabricating structural components in an implantable artificial pancreas.

Development of a Xanthan Gum Based Superabsorbent and Water Retaining Composites for Agricultural and Forestry Applications.

In this work, bio-based hydrogel composites of xanthan gum and cellulose fibers were developed to be used both as soil conditioners and topsoil covers, to promote plant growth and forest protection. The rheological, morphological, and water absorption properties of produced hydrogels were comprehensively investigated, together with the analysis of the effect of hydrogel addition to the soil. Specifically, the moisture absorption capability of these hydrogels was above 1000%, even after multiple dewatering/rehydration cycles. Moreover, the soil treated with 1.8 wt% of these materials increased the water absorption capacity by approximately 60% and reduced the water evaporation rate, due to the formation of a physical network between the soil, xanthan gum and cellulose fibers. Practical experiments on the growth of herbaceous and tomato plants were also performed, showing that the addition of less than 2 wt% of hydrogels into the soil resulted in higher growth rate values than untreated soil. Furthermore, it has been demonstrated that the use of the produced topsoil covers helped promote plant growth. The exceptional water-regulating properties of the investigated materials could allow for the development of a simple, inexpensive and scalable technology to be extensively applied in forestry and/or agricultural applications, to improve plant resilience and face the challenges related to climate change.

Evaluation of the Physical and Shape Memory Properties of Fully Biodegradable Poly(lactic acid) (PLA)/Poly(butylene adipate terephthalate) (PBAT) Blends.

Biodegradable polymers have recently become popular; in particular, blends of poly(lactic acid) (PLA) and poly(butylene adipate terephthalate) (PBAT) have recently attracted significant attention due to their potential application in the packaging field. However, there is little information about the thermomechanical properties of these blends and especially the effect induced by the addition of PBAT on the shape memory properties of PLA. This work, therefore, aims at producing and investigating the microstructural, thermomechanical and shape memory properties of PLA/PBAT blends prepared by melt compounding. More specifically, PLA and PBAT were melt-blended in a wide range of relative concentrations (from 85/15 to 25/75 wt%). A microstructural investigation was carried out, evidencing the immiscibility and the low interfacial adhesion between the PLA and PBAT phases. The immiscibility was also confirmed by differential scanning calorimetry (DSC). A thermogravimetric analysis (TGA) revealed that the addition of PBAT slightly improved the thermal stability of PLA. The stiffness and strength of the blends decreased with the PBAT amount, while the elongation at break remained comparable to that of neat PLA up to a PBAT content of 45 wt%, while a significant increment in ductility was observed only for higher PBAT concentrations. The shape memory performance of PLA was impaired by the addition of PBAT, probably due to the low interfacial adhesion observed in the blends. These results constitute a basis for future research on these innovative biodegradable polymer blends, and their physical properties might be further enhanced by adding suitable compatibilizers.

A Green Treatment Mitigates the Limitations of Coffee Silver Skin as a Filler for PLA/PBSA Compatibilized Biocomposites.

The development of fully renewable and biodegradable composites for short-term applications was pursued by combining a compatibilized poly(lactic acid) (PLA)/poly(butylene succinate-co-adipate) (PBSA) (60:40 wt:wt) blend with coffee silver skin (CSS), an industrial byproduct from coffee processing. An epoxy-based reactive agent (Joncryl ADR-4468) was added as a compatibilizer. CSS was incorporated at 5, 10, and 20 wt% in the blend both in the as-received state and after a simple thermal treatment in boiling water, which was performed to mitigate the negative impact of this filler on the rheological and mechanical properties of the blend. The CSS treatment effectively increased the filler degradation temperature of 30-40 °C, enabling stable melt processing of the composites. It also improved filler-matrix adhesion, resulting in enhanced impact properties (up to +172% increase in impact energy compared to the untreated filler). Therefore, treated CSS demonstrated potential as an effective green reinforcement for PLA/PBSA blends for rigid packaging applications. Future works will focus on studying suitable surface modification of CSS to further increase the interfacial interaction and the tensile quasi-static properties, to fully exploit the capabilities of this renewable material toward the development of eco-friendly composites.

Development of Novel Polypropylene Syntactic Foams Containing Paraffin Microcapsules for Thermal Energy Storage Applications.

polypropylene (PP) syntactic foams (SFs) containing hollow glass microspheres (HGMs) possess low density and elevated mechanical properties, which can be tuned according to the specific application. A possible way to improve their multifunctionality could be the incorporation of organic Phase Change Materials (PCMs), widely used for thermal energy storage (TES) applications. In the present work, a PCM constituted by encapsulated paraffin, having a melting temperature of 57 °C, was embedded in a compatibilized polypropylene SF by melt compounding and hot pressing at different relative amounts. The rheological, morphological, thermal, and mechanical properties of the prepared materials were systematically investigated. Rheological properties in the molten state were strongly affected by the introduction of both PCMs and HGMs. As expected, the introduction of HGMs reduced both the foam density and thermal conductivity, while the enthalpy of fusion (representing the TES capability) was proportional to the PCM concentration. The mechanical properties of these foams were improved by the incorporation of HGMs, while they were reduced by addition of PCMs. Therefore, the combination of PCMs and HGMs in a PP matrix generated multifunctional materials with tunable thermo-mechanical properties, with a wide range of applications in the automotive, oil, textile, electronics, and aerospace fields.

Thermotropic Optical Response of Silicone-Paraffin Flexible Blends.

Organic phase change materials, e.g., paraffins, are attracting increasing attention in thermal energy storage (TES) and thermal management applications. However, they also manifest interesting optical properties such as thermotropism, as they can switch from optically opaque to transparent reversibly and promptly at the melting temperature. This work aims at exploiting this feature to produce flexible silicone-based blends with thermotropic properties for applications in glazed windows or thermal sensors. Blends are produced by adding paraffin (Tm = 44 °C, up to 10 phr) to a silicone bicomponent mixture, and, for the first time, cetyltrimethylammonium bromide (CTAB) is also added to promote paraffin dispersion and avoid its exudation. CTAB is proven effective in preventing paraffin exudation both in the solid and in the liquid state when added in a fraction above 3 phr with respect to paraffin. Rheological results show that paraffin decreases the complex viscosity, but neither paraffin nor CTAB modifies the curing behavior of silicone, which indicates uniform processability across the investigated compositions. On the other hand, paraffin causes a decrease in the stress and strain at break at 60 °C, and this effect is amplified by CTAB, which acts as a defect and stress concentrator. Conversely, at room temperature, solid paraffin only slightly impairs the mechanical properties, while CTAB increases both the elastic modulus and tensile strength, as also highlighted with ANOVA. Finally, optical transmittance results suggest that the maximum transmittance difference below and above the melting temperature (65-70 percentage points) is reached for paraffin amounts of 3 to 5 phr and a CTAB amount of max. 0.15 phr.

Thermo-Mechanical Behavior of Novel EPDM Foams Containing a Phase Change Material for Thermal Energy Storage Applications.

In this paper Ethylene Propylene Diene Monomer rubber (EPDM) foams were filled with different amounts of paraffin, a common phase change material (PCM) having a melting temperature at about 70 °C, to develop novel rubber foams with thermal energy storage (TES) capabilities. Samples were prepared by melt compounding and hot pressing, and the effects of three foaming methods were investigated. In particular, two series of samples were produced through conventional foaming techniques, involving physical (Micropearl® F82, MP, Lehvoss Italia s.r.l. Saronno, Italia) and chemical (Hostatron® P0168, H, Clariant GmbH, Ahrensburg, Germany) blowing agents, while the salt leaching method was adopted to produce another series of foams. Scanning electron microscopy (SEM) and density measurements showed that MP led to the formation of a closed-cell porosity, while a mixed closed-cell/open-cell morphology was detected for the H foamed samples. On the other hand, foams produced through salt leaching were mainly characterized by an open-cell porosity. The qualitative analysis of paraffin leakage revealed that at 90 °C only the foams produced through salt leaching suffered from significant PCM leakage. Consequently, the thermo-mechanical properties were investigated only in samples produced with H and MP. Differential Scanning Calorimetry (DSC) analysis revealed that EPDM/paraffin foams were endowed by good TES properties, especially at higher PCM contents (up to 145 J/g with a paraffin amount of 60 wt%). Tensile and compressive tests demonstrated the addition of the PCM increased the stiffness at 25 °C, while the opposite effect was observed above the melting temperature of paraffin. These results suggest that the EPDM foams produced with H and MP show an interesting potential for thermal management of electronic devices.

Compatibilization of Polylactide/Poly(ethylene 2,5-furanoate) (PLA/PEF) Blends for Sustainable and Bioderived Packaging.

Despite the advantages of polylactide (PLA), its inadequate UV-shielding and gas-barrier properties undermine its wide application as a flexible packaging film for perishable items. These issues are addressed in this work by investigating the properties of melt-mixed, fully bioderived blends of polylactide (PLA) and poly(ethylene furanoate) (PEF), as a function of the PEF weight fraction (1-30 wt %) and the amount of the commercial compatibilizer/chain extender Joncryl ADR 4468 (J, 0.25-1 phr). J mitigates the immiscibility of the two polymer phases by decreasing and homogenizing the PEF domain size; for the blend containing 10 wt % of PEF, the PEF domain size drops from 0.67 ± 0.46 µm of the uncompatibilized blend to 0.26 ± 0.14 with 1 phr of J. Moreover, the increase in the complex viscosity of PLA and PLA/PEF blends with the J content evidences the effectiveness of J as a chain extender. This dual positive contribution of J is reflected in the mechanical properties of PLA/PEF blends. Whereas the uncompatibilized blend with 10 wt % of PEF shows lower mechanical performance than neat PLA, all the compatibilized blends show higher tensile strength and strain at break, while retaining their high elastic moduli. The effects of PEF on the UV- and oxygen-barrier properties of PLA are also remarkable. Adding only 1 wt % of PEF makes the blend an excellent barrier for UV rays, with the transmittance at 320 nm dropping from 52.8% of neat PLA to 0.4% of the sample with 1 wt % PEF, while keeping good transparency in the visible region. PEF is also responsible for a sensible decrease in the oxygen transmission rate, which decreases from 189 cc/m2·day for neat PLA to 144 cc/m2·day with only 1 wt % of PEF. This work emphasizes the synergistic effects of PEF and J in enhancing the thermal, mechanical, UV-shielding, and gas-barrier properties of PLA, which results in bioderived blends that are very promising for packaging applications.

Improving the Wet-Spinning and Drawing Processes of Poly(lactide)/Poly(ethylene furanoate) and Polylactide/Poly(dodecamethylene furanoate) Fiber Blends.

This work aims to produce poly(lactic acid) (PLA)/poly(alkylene furanoate)s (PAF)s fiber blends for textile applications and evaluates their microstructural, chemical, thermal, and mechanical properties. The work focuses on two PAFs with very different alkyl chain lengths, i.e., poly(ethylene 2,5-furandicarboxylate) (PEF) and poly(dodecamethylene 2,5-furandicarboxylate) (PDoF), which were blended in solution at various concentrations (in the range 2.5-10 wt %) with PLA, wet spun, and subsequently drawn. Light optical micrographs highlight that PLA/PEF blends present large and concentrate PEF domains, whereas PLA/PDoF blends show small and homogeneously distributed PDoF domains. The blends appear to be immiscible, which is confirmed also by scanning electron microscopy (SEM), Fourier-Transform Infrared (FT-IR) spectroscopy, and differential scanning calorimetry (DSC). Thermogravimetric analysis (TGA) highlights that the addition of the PAFs improves the thermal stability of the fibers. The drawing process, which was carried out at 80 °C with a heat setting step at 95 °C and at three draw ratios, improves the mechanical properties of the fibers upon the addition of the PAFs. The results obtained in this study are promising and may serve as a basis for future investigations on these novel bio-based fiber blends, which can contribute to increase the environmental sustainability of industrial textiles.

Improving the Thermomechanical Properties of Poly(lactic acid) via Reduced Graphene Oxide and Bioderived Poly(decamethylene 2,5-furandicarboxylate).

Polylactide (PLA) is the most widely used biopolymer, but its poor ductility and scarce gas barrier properties limit its applications in the packaging field. In this work, for the first time, the properties of PLA solvent-cast films are improved by the addition of a second biopolymer, i.e., poly(decamethylene 2,5-furandicarboxylate) (PDeF), added in a weight fraction of 10 wt%, and a carbon-based nanofiller, i.e., reduced graphene oxide (rGO), added in concentrations of 0.25-2 phr. PLA and PDeF are immiscible, as evidenced by scanning electron microscopy (SEM) and Fourier-transform infrared (FTIR) spectroscopy, with PDeF spheroidal domains showing poor adhesion to PLA. The addition of 0.25 phr of rGO, which preferentially segregates in the PDeF domains, makes them smaller and considerably rougher and improves the interfacial interaction. Differential scanning calorimetry (DSC) confirms the immiscibility of the two polymer phases and highlights that rGO enhances the crystallinity of both polymer phases (especially of PDeF). Thermogravimetric analysis (TGA) highlights the positive impact of rGO and PDeF on the thermal degradation resistance of PLA. Quasi-static tensile tests evidence that adding 10 wt% of PDeF and a small fraction of rGO (0.25 phr) to PLA considerably enhances the strain at break, which raises from 5.3% of neat PLA to 10.0% by adding 10 wt% of PDeF, up to 75.8% by adding also 0.25 phr of rGO, thereby highlighting the compatibilizing role of rGO on this blend. On the other hand, a further increase in rGO concentration decreases the strain at break due to agglomeration but enhances the mechanical stiffness and strength up to an rGO concentration of 1 phr. Overall, these results highlight the positive and synergistic contribution of PDeF and rGO in enhancing the thermomechanical properties of PLA, and the resulting nanocomposites are promising for packaging applications.

Special Issue "Investigation of Polymer Nanocomposites' Performance".

Through this editorial, we aim to present the main aspects related to the scientific contributions that can be found in the Special Issue dedicated to the topic "Investigation of Polymer Nanocomposites' Performance" [...].

Statistical Modeling and Optimization of the Drawing Process of Bioderived Polylactide/Poly(dodecylene furanoate) Wet-Spun Fibers.

Drawing is a well-established method to improve the mechanical properties of wet-spun fibers, as it orients the polymer chains, increases the chain density, and homogenizes the microstructure. This work aims to investigate how drawing variables, such as the draw ratio, drawing speed, and temperature affect the elastic modulus (E) and the strain at break (εB) of biobased wet-spun fibers constituted by neat polylactic acid (PLA) and a PLA/poly(dodecamethylene 2,5-furandicarboxylate) (PDoF) (80/20 wt/wt) blend. Drawing experiments were conducted with a design of experiment (DOE) approach following a 24 full factorial design. The results of the quasi-static tensile tests on the drawn fibers, analyzed by the analysis of variance (ANOVA) and modeled through the response surface methodology (RSM), highlight that the presence of PDoF significantly lowers E, which instead is maximized if the temperature and draw ratio are both low. On the other hand, εB is enhanced when the drawing is performed at a high temperature. Finally, a genetic algorithm was implemented to find the optimal combination of drawing parameters that maximize both E and εB. The resulting Pareto curve highlights that the temperature influences the mechanical results only for neat PLA fibers, as the stiffness increases by drawing at lower temperatures, while optimal Pareto points for PLA/PDoF fibers are mainly determined by the draw ratio and the draw rate.

Evaluating the Multifunctional Performance of Structural Composites for Thermal Energy Storage.

The simultaneous need for high specific mechanical properties and thermal energy storage (TES) function, present in several applications (e.g., electric vehicles), can be effectively addressed by multifunctional polymer-matrix composites containing a reinforcing agent and a phase change material (PCM). The PCMs generally decrease the mechanical properties of the host structural composites, but a multifunctional composite can still be beneficial in terms of mass saving, compared to two monofunctional units performing the structural and heat management functions individually. To quantify any possible advantages, this paper proposes an approach that determines the conditions for an effective mass saving at the system level and ranks the investigated structural TES composites with a parameter called multifunctional efficiency. It is found that the potential mass saving is higher when the volume fraction of the reinforcement is kept constant also when the PCM fraction increases or when the single phases (reinforcement, PCM) are themselves multifunctional.

Mechanical Behaviour of Multifunctional Epoxy/Hollow Glass Microspheres/Paraffin Microcapsules Syntactic Foams for Thermal Management.

Epoxy/hollow glass microsphere (HGM) syntactic foams (SFs) are peculiar materials developed to combine low density, low thermal conductivity, and elevated mechanical properties. In this work, multifunctional SFs endowed with both structural and thermal management properties were produced for the first time, by combining an epoxy matrix with HGM and a microencapsulated phase change material (PCM) having a melting temperature of 43 °C. Systems with a total filler content (HGM + PCM) up to 40 vol% were prepared and characterized from the mechanical point of view with a broad experimental campaign comprising quasi-static, impact, and fracture toughness tests. The experimental results were statistically treated and fitted with a linear model, to produce ternary phase diagrams to provide a comprehensive interpretation of the mechanical behaviour of the prepared foams. In quasi-static tests, HGM introduction helps to retain the specific tensile elastic modulus and to increase the specific compressive modulus. The brittle nature of HGMs decreases the Charpy impact properties of the SFs, while the PCM insertion improve their toughness. This result is confirmed in KIC and GIC tests, where the composition with 20 vol% of PCM shows an increase of 80% and 370% in KIC and GIC in to neat epoxy, respectively. The most promising compositions are those combining PCM and HGMs with a total particle volume fraction up to 40 vol%, thanks to their optimal combination of thermal management capability, lightness, thermal insulation, and mechanical properties. The ability to fine-tune the properties of the SFs, together with the acquired thermal energy storage (TES) capability, confirm the great potential of these multifunctional materials in automotive, electronics, and aerospace industries.

Thermal Mending of Electroactive Carbon/Epoxy Laminates Using a Porous Poly(ε-caprolactone) Electrospun Mesh.

For the first time, a porous mesh of poly(ε-caprolactone) (PCL) was electrospun directly onto carbon fiber (CF) plies and used to develop novel structural epoxy (EP) composites with electro-activated self-healing properties. Three samples, i.e., the neat EP/CF composite and two laminates containing a limited amount of PCL (i.e., 5 wt.% and 10 wt.%), were prepared and characterized from a microstructural and thermo-mechanical point of view. The introduction of the PCL mesh led to a reduction in the flexural stress at break (by 17%), of the interlaminar shear strength (by 15%), and of the interlaminar shear strength (by 39%). The interlaminar fracture toughness of the prepared laminates was evaluated under mode I, and broken samples were thermally mended at 80 °C (i.e., above the melting temperature of PCL) by resistive heating generated by a current flow within the samples through Joule's effect. It was demonstrated that, thanks to the presence of the electrospun PCL mesh, the laminate with a PCL of 10 wt.% showed healing efficiency values up to 31%.