In the last years, continuous-fiber-reinforced thermoplastic composites (CFRTCs) received an increasing interest for their potential advantages over composites with thermosetting resin mainly in ...terms of i) shorter manufacturing cycles ii) higher impact resistance and toughness and iii) recyclability at the end of first life. The main strategies for recycling CFRTCs are here reviewed on the basis of the information available in the scientific literature. The main recycling options currently available for CFRTCs can be broadly divided into mechanical, thermal and chemical methodologies. Moreover, the concept of all-polymer composites, i.e. composites in which both matrix and reinforcing components are made with thermoplastic polymers, is discussed in view of their relevance in recycling technology.
Short-fiber-reinforced thermoplastic composites (SFRTCs) and particle-filled thermoplastic composites (PFTCs) are widely used in various industrial sectors, from automotive to electronic appliances, ...from building constructions to domestic equipment. Their environmental impact could be significantly reduced through both open and closed loop recycling, which allows a reduction of the usage of new resources and limit the energy consumption and CO2 release associated to their production. The main challenges and opportunities in the recycling of SFRTCs and PFTCs are currently represented by i) reprocessing (also called mechanical recycling), use of recycled matrices ii) use of recycled fibers, iii) use of waste composites, iv) chemical recycling. Opportunities and current limitations in the recycling strategies and technologies for SFRTCs and PFTCs are here reviewed.
This review summarizes the recent (from year 2000) advancements in the interphase tailoring of fiber-reinforced polymer composites. The scientific and technological achievements are classified on the ...basis of the selected strategies distinguishing between (i) interphase tailoring via sizing/coating on fibers, (ii) creation of hierarchical fibers by nanostructures, (iii) fiber surface modifications by polymer deposition and (iv) potential effects of matrix modifications on the interphase formation. Special attention was paid to report on efforts dedicated to the creation of (multi)functional interphase in polymer composites. This review is round up by listing current trends in the characterization and modelling of the interphase. In the final outlook, future opportunities and challenges in the engineering of fiber/matrix interphase are summarized.
This work is focused on the preparation and characterization of novel multifunctional structural composites with thermal energy storage (TES) capability. Structural laminates were obtained by ...combining an epoxy resin, a paraffinic phase change material (PCM) stabilized with carbon nanotubes (CNTs), and reinforcing carbon fibers. The stabilized paraffin kept its ability to melt and crystallize in the laminates, and the melting enthalpy of the composites was proportional to the paraffin weight fraction with a maximum value of 47.4 J/cm3. This thermal response was preserved even after fifty consecutive heating-cooling cycles. Moreover, the thermal conductivity of the laminates through thickness direction resulted to increase proportionally to the content of CNT-stabilized PCM. The capability of the developed TES laminates to contribute to the thermal energy management was also proven by monitoring their cooling rates through thermal imaging. The flexural modulus was only slightly affected by the presence of the PCM, while a decrease of flexural strength, strain at break and interlaminar shear strength was detected. Optical microscopy highlighted that this could be attributed to the preferential location of the PCM in the interlaminar region. The obtained results demonstrated the feasibility of the concept of multifunctional structural TES composites.
End-of-life options of tyres. A review Valentini, Francesco; Pegoretti, Alessandro
Advanced industrial and engineering polymer research,
October 2022, 2022-10-00, 2022-10-01, Volume:
5, Issue:
4
Journal Article
Peer reviewed
Open access
The increasing motorisation rate worldwide is responsible for the demand of huge quantities of tyres that, after their useful service life, become waste and should be properly managed. Due to the ...relative low cost of tyres and the complexity related to recycling, worldwide around 41% of the total amount of end-of-life tyres is discarded into landfills or stockpiles without any recovery of the material or of the energy. Moreover, the chemical composition of tyres makes them extremely resistant to degradation phenomena with a potential long-term permanence in the environment. The high energy amount required for the production of tyres and the related environmental impact should encourage the recycling of tyres and also promote the adoption of maintenance activities, such as retreading, that allow a considerable increase in the useful service life of tyres with consequent reduction in GHG emissions. In this article the relevant literature describing the current status of end-of-life options worldwide, the European legislation regarding tyre waste, their possible uses and the related environmental aspects are presented.
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.
Composite acrylonitrile-butadiene-styrene (ABS)/carbon nanotubes (CNT) filaments at 1, 2, 4, 6 and 8 wt %, suitable for fused deposition modelling (FDM) were obtained by using a completely ...solvent-free process based on direct melt compounding and extrusion. The optimal CNT content in the filaments for FDM was found to be 6 wt %; for this composite, a detailed investigation of the thermal, mechanical and electrical properties was performed. Presence of CNT in ABS filaments and 3D-printed parts resulted in a significant enhancement of the tensile modulus and strength, accompanied by a reduction of the elongation at break. As documented by dynamic mechanical thermal analysis, the stiffening effect of CNTs in ABS is particularly pronounced at high temperatures. Besides, the presence of CNT in 3D-printed parts accounts for better creep and thermal dimensional stabilities of 3D-printed parts, accompanied by a reduction of the coefficient of thermal expansion). 3D-printed nanocomposite samples with 6 wt % of CNT exhibited a good electrical conductivity, even if lower than pristine composite filaments.
Graphene oxide (GO) can increase the fiber/matrix interfacial shear strength (ISS) in glass fibers (GF) reinforced epoxy composites. To validate our argument, GO was synthesized and deposited over GF ...through electrophoretic deposition. Tuned voltage lead to different thickness of deposited GO steadily increasing with the electric field up to 10 V/cm. Coated fibers were aligned in a mold and an epoxy matrix was used to create a single-fiber microcomposite. Fragmentation test showed significantly higher ISS values for coated over bare fibers with increments up to a factor of about 2 and proportional to the amount of GO deposited on the GF. Tribological tests were performed at nanoscale by atomic force microscopy to measure the delamination strength between GO and GF. This latter resulted to be much higher than the ISS thus proving the efficiency of the new GO fiber coating method here proposed for producing advanced graphene based composites. The failure of the composite at the GO/matrix rather than at the GO/GF interface was also confirmed by scanning electron microscopy observation of the fracture surfaces of microcomposites.
A paraffin wax was shape stabilized with 10 wt % of carbon nanotubes (CNTs) and dispersed in various concentrations in an epoxy resin to develop a novel blend with thermal energy storage ...capabilities. Thermogravimetric analysis showed that CNTs improve the thermal stability of paraffin, while differential scanning calorimetry showed that the paraffin kept its ability to melt and crystallize, with enthalpy values almost proportional to the paraffin fraction. In contrast, a noticeable loss of enthalpy was observed for epoxy/wax blends without CNTs, which was mainly attributed to the partial exudation of paraffin out of the epoxy matrix during the curing phase. Dynamic mechanical thermal analysis contributed to elucidate the effects of the melting of the paraffin phase on the viscoelastic properties of the epoxy blends. Flexural elastic modulus and strength of the blends decreased with the wax/CNT content according to a rule of mixtures, while flexural strain at break values deviate positively from it. These results show the potentialities of the investigated epoxy blends for the development of multifunctional structural composites.
PDF
