Green Material Development Through Mechanical Recycling of Waste Polyurethane Foam and Thermoplastic Polyurethane

SummaryThis paper identifies the extent to which circular economy (CE) practices are relevant for the implementation of the Sustainable Development Goals (SDGs). The results of a literature review and a matching exercise to determine the relationship between CE practices and SDG targets show that CE practices, potentially, can contribute directly to achieving a significant number of SDG targets. The strongest relationships exist between CE practices and the targets of SDG 6 (Clean Water and Sanitation), SDG 7 (Affordable and Clean Energy), SDG 8 (Decent Work and Economic Growth), SDG 12 (Responsible Consumption and Production), and SDG 15 (Life on Land). The paper also explores synergies that can be created through CE practices among several of the SDG targets. Furthermore, it identifies several potential trade‐offs between targets for decent work, safe working environments, human health and current CE practices relating to recycling of municipal waste, e‐waste and wastewater, and provides suggestions how these can be overcome. The paper concludes that CE practices can be applied as a “toolbox” and specific implementation approaches for achieving a sizeable number of SDG targets. Further empirical research is necessary to determine which specific types of partnerships and means of implementation are required to apply CE practices in the SDG context.

SummaryAs a highly resistant polymer family, polyurethanes (PU) are responsible for increasing environmental issues. Then, PU biodegradation is a challenging way to develop sustainable waste management processes based on biological recycling. Since the metabolic diversity of fungi is a major asset for polymer degradation, nearly thirty strains were isolated from sampling on six different PU wastes‐containing environments. A screening of the fungi on four thermoplastic PU (TPU) with different macromolecular architectures led to the selection of three strains able to use two polyester PU as sole carbon source: Alternaria sp., Penicillium section Lanata‐Divaricata and Aspergillus section flavi. Weight loss, FT‐IR, Scanning Electron Microscopy and Size Exclusion Chromatography analyses revealed that these three fungi degrade slightly and similarly a fatty acid dimer‐based TPU while variability of degradation was noticed on a polycaprolactone‐based TPU. On this last TPU, robust analysis of the degraded polymers showed that the Penicillium strain was the best degrading microorganism. Membrane enzymes seemed to be involved in this degradation. It is the first time that a strain of Penicillium of the section Lanata‐Divaricata displaying PU biodegradation ability is isolated. These newly discovered fungi are promising for the development of polyester PU waste management process.

Purpose This study attempts to assess how the textile and apparel (T&A) industry in Bangladesh is influenced by circular economy (CE) practices in terms of achieving the sustainable development goals (SDGs), with a focus on the moderating influence of competitive intensity (CI) and the mediating effect of I4.0 technologies. It bridges the knowledge gap about how CI and I4.0 technologies may drive CE practices to promote sustainability in the T&A industry. Design/methodology/approach In this study,partial least square-structural equation modeling (PLS-SEM) was used to examine survey data gathered from Bangladeshi T&A industry professionals, including manufacturing and management experts. Six hypotheses pertaining to direct, mediated and moderated impact were assessed using SmartPLS version 4 software. Findings The results show that attaining the targeted SDGs is significantly aided by CE practices that are pertinent to the T&A industry, such as reduction, repair, remanufacturing, and recycling. Five relevant I4.0 technologies like autonomous robots, cloud computing, cybersecurity, Internet of things and system integration can play a major mediating role in this interaction. Nevertheless, neither the association between CE practices and the SDGs nor the relationship between I4.0 and the SDGs was substantially moderated by CI. Originality/value To support the influence of CE practices on the T&A industry’s SDGs attainment, several outstanding research works have been executed. More precisely, very few research has been performed for Bangladeshi T&A industry. This study makes an effort to quantify the various effects of CE and I4.0 on SDGs that have been validated by CI for the first time.

This study examines the enhancement of thermal conductivity in flexible polymer composites (FPC) by blending engineering grade polyester based thermoplastic polyurethane (TPU) with multi-walled carbon nanotubes (MWCNT) and graphene nanoplatelets (GNP) nanofillers in varying proportions. TPU, recognized for its sustainability and recyclability, is increasingly preferred in advanced material applications. The global thermoplastic polyurethane (TPU) market is projected to expand at a compound annual growth rate (CAGR) of 6.5% during the period from 2021 to 2028, reflecting its increasing demand across multiple industries. The conductive composites developed in the present study were characterized using scanning electron microscopy (SEM), thermo-gravimetric analysis (TGA), differential scanning calorimeter (DSC), steady-state temperature measurement, and mechanical fracture tests to evaluate their morphological, mechanical, and thermal properties. The thermal conductivity (k) results for the TPU/MWCNT/GNP composite film with 93/3.5/3.5 by wt.% showed a significant rise of 390.5%. The highest thermal conductivity value of 0.981 W/mK was achieved for the composite film with 7 wt.% of combined MWCNT and GNP. The SEM analysis revealed a uniform dispersion of nanofillers within the composite matrix. Furthermore, the thermal stability of the composite improved by 4.2°C to 38.9°C, and the thermal decomposition increased by 9.36%. The thermal degradation was reduced by 12.02% for the TPU matrix containing 7 wt.% of combined MWCNT and GNP nanofillers. These findings highlight the potential of TPU composites for sustainable and efficient thermal management applications, aligning with global megatrends in material innovation.

Electrospinning is a cost-effective and versatile method for producing submicron fibers. Although this method is relatively simple, at the theoretical level the interactions between process parameters and their influence on the fiber morphology are not yet fully understood. In this paper, the aim was finding optimal electrospinning parameters in order to obtain the smallest fiber diameter by using Taguchi's methodology. The nanofibers produced by electrospinning a solution of Thermoplastic Polyurethane (TPU) in Dimethylformamide (DMF). Polymer concentration and process parameters were considered as the effective factors. Taguchi's L9 orthogonal design (4 parameters, 3 levels) was applied to the experiential design. Optimal electrospinning conditions were determined using the signal-to-noise (S/N) ratio with Minitab 17 software. The morphology of the nanofibers was studied by a Scanning Electron Microscope (SEM). Thereafter, a tensile tester machine was used to assess mechanical properties of nanofibrous scaffolds. The analysis of DoE experiments showed that TPU concentration was the most significant parameter. An optimum combination to reach smallest diameters was yielded at 12 wt% polymer concentration, 16 kV of the supply voltage, 0.1 ml/h feed rate and 15 cm tip-to-distance. An empirical model was extracted and verified using confirmation test. The average diameter of nanofibers at the optimum conditions was in the range of 242.10 to 257.92 nm at a confidence level 95% which was in close agreement with the predicted value by the Taguchi technique. Also, the mechanical properties increased with decreasing fibers diameter. This study demonstrated Taguchi method was successfully applied to the optimization of electrospinning conditions for TPU nanofibers and the presented scaffold can mimic the structure of Extracellular Matrix (ECM).

A correlation between thermal, optical and morphological properties of self-sustained filmsformed from blends of poly(3-hexylthiophene) (P3HT) and thermoplastic polyurethane(TPU), with 1, 10 and 20 wt% of P3HT in TPU, is established. Images of scanningelectron microscopy (SEM) show the formation of domains of P3HT into the TPUmatrix, characterizing the blend material as heterogeneous. The heat capacity(Cp) dependence on P3HT contents was investigated in a large temperature interval. In theregion of the TPU glass transition, the difference between the experimental and predictedΔCp values is more pronounced for the 1 wt% case, which strongly suggests that in this casethere is a higher influence of the P3HT chains on the TPU matrix. The SEM images for the1 wt% blended film present the formation of the smallest P3HT domains in the TPUmatrix. The relatively high reduction of the PL intensity of the pure electronic transitionpeak in the 1 wt% blended film, in comparison to the other blended films and also to a pureP3HT film, favours the assumption that the smallest P3HT domains are at the originof a more structural disordered character. This fact is in agreement with theresults obtained by Raman spectroscopy and also by photoluminescence resolvedby polarization in stretched self-sustained films, showing an ample correlationbetween morphological, thermal and optical properties of these blended materials. Inaddition, the thermoplastic properties of the polyurethane configure very goodconditions for tensile drawing of P3HT and other conjugated polymer molecules.

A melt blending process was employed to prepare nanocomposites based on thermoplastic polyurethane (TPU) and multiwalled carbon nanotubes (MWNT). The content of MWNT filled in TPU was increased till 40 phr (parts per hundreds of rubber). The morphological, structural and mechanical properties of the resulting TPU nanocomposites were systematically investigated using scanning electron microscope (SEM), transmission electron microscope (TEM), differential scanning calorimetry (DSC), X-ray diffraction (XRD), dynamic mechanical thermal analysis (DMTA) and tensile testing. The results indicated that the unmodified MWNT were dispersed finely and uniformly in the TPU matrix beyond expectation, and the microphase separation structures of the TPU nanocomposites were slightly affected by the presence of MWNT. The mechanical properties of the TPU nanocomposites containing various amounts of MWNT at both room temperature and 120 °C were studied, which demonstrated that the modulus of TPU were greatly increased and the high temperature tensile strength of TPU was also prominently improved when MWNT content is higher. Moreover, the TPU nanocomposites exhibited improved thermal and electrical conductivities that might mean the TPU/MWNT nanocomposites have potential application as multifunctional materials.

A new method to reclaim thermoset polyurethane (PU) foam by thermo-mechanical degradation using a batch Drais mixer was investigated, and the performance of reclaimed PU in blends with polyamide-12 (PA-12) or thermoplastic polyurethane (TPU) was studied. The reclamation method used disrupts the crosslinked structure of PU, decreasing its degree of crosslinking, which was confirmed through the determination of gel content, and by DSC, TGA and FTIR analyses. Under severe reclaiming conditions, the reclaimed PU was found to retain about half of its initial gel content. The blends of original PU and reclaimed PU (PU-r) with PA-12 and with TPU were prepared using a twin-screw extruder and were characterized with respect to their mechanical properties. For the PA-12/PU 75/25 blend, the addition of PU was observed to toughen the PA-12 matrix whereas for TPU/PU blends, the rubber-like behavior of TPU was not significantly affected by the presence of PU. The remarkable mechanical behavior of the blends attests to the high compatibility of PU-r with both PA-12 and TPU. This may be due to the physical interactions between the blend components, leading to high interfacial adhesion. The reclamation of PU-r before its melt processing with PA-12 or TPU was found to improve the processability during the injection molding of the PA-12/PU-r and TPU/PU-r blends.

This study aims to explore the effects of Thermoplastic Polyurethane (TPU) content on the weld line properties of Polypropylene (PP) and Acrylonitrile Butadiene Styrene (ABS) blends. In PP/TPU blends, increasing the TPU content results in a significant decrease in the PP/TPU composite’s ultimate tensile strength (UTS) and elongation values. Blends with 10 wt%, 15 wt%, and 20 wt% TPU and pure PP outperform blends with 10 wt%, 15 wt%, and 20 wt% TPU and recycled PP in terms of UTS value. The blend with 10 wt% TPU and pure PP achieves the highest UTS value of 21.85 MPa. However, the blend’s elongation decreases due to the poor bonding in the weld line area. According to Taguchi’s analysis, the TPU factor has a more significant overall influence on the mechanical properties of PP/TPU blends than the recycled PP factor. Scanning electron microscope (SEM) results show that the TPU area has a dimple shape on the fracture surface due to its significantly higher elongation value. The 15 wt% TPU sample achieves the highest UTS value of 35.7 MPa in ABS/TPU blends, which is considerably higher than other cases, indicating good compatibility between ABS and TPU. The sample containing 20 wt% TPU has the lowest UTS value of 21.2 MPa. Furthermore, the elongation-changing pattern corresponds to the UTS value. Interestingly, SEM results present that the fracture surface of this blend is flatter than the PP/TPU blend due to a higher compatibility rate. The 30 wt% TPU sample has a higher rate of dimple area than the 10 wt% TPU sample. Moreover, ABS/TPU blends gain a higher UTS value than PP/TPU blends. Increasing the TPU ratio mainly reduces the elastic modulus of both ABS/TPU blends and PP/TPU blends. This study reveals the advantages and disadvantages of mixing TPU with PP or ABS to ensure that it meets the requirements of the intended applications.

Few thermoplastic polyurethane (TPU) blending materials are reported to tune shape‐memory capability, self‐healing ability, and recyclability as well as mechanical property due to the different requirement of phase morphologies. This work focuses on how reversible epoxy domains affect the structures and properties of TPUs that contain disulfide bonds in main chains. The blended epoxy oligomers with dangling furan groups are miscible with the TPU. Self‐healing efficiency can be improved by such miscible epoxy oligomers that are also beneficial for shape recovery but harmful for shape fixation. In the presence of bis(4‐maleimidophenyl)methane (BMI), crosslinked epoxy domains phase separate from the TPU matrix to form microscale domains after the Diels–Alder (DA) reaction between furan groups and maleimide groups in BMI. Elastic modulus and tensile strength of TPU are greatly improved in comparison with pristine TPU and TPU/epoxy blends without BMI. The phase‐separated domains deteriorate the self‐healing, and the presence of phase‐separated microdomains facilitates the shape fixation but deteriorates the shape recovery. This work is not only useful to further understand the relation between structures of polymer blends with intelligent features, but also offers a useful approach to adjust the properties and capabilities of TPU in a cost‐effective manner.

Thermoplastic Polyurethane (TPU) is a highly versatile material with superior physical properties but high cost. Melt blending of TPU with Polyolefins (PO) can lower the cost and improve mechanical and chemical properties. Since TPU and PO are completely immiscible polymers, property enhancement cannot be attained. Effect of incorporation of Polypropylene Copolymer (PPCP) as compatibilizer on the miscibility of the blends and effect of calcium carbonate as filler to enhance the mechanical properties were studied. Blends were produced by melt mixing using a single screw extruder. Miscibility studies were done using Scanning Electron Microscope (SEM) and thermal characteristics were determined using Differential Scanning Calorimeter (DSC). Mechanical properties like tensile strength, impact strength, flexural strength and hardness were also studied using Universal Testing Machine (UTM). The results show that the blend having 20% loading of polyurethane (PU) with suitable compatibilizers and calcium carbonate gives excellent performance in all aspects.

Short carbon fibers (CF) with different surface sized (epoxy (EP) and polyurethane (PU)) were used as reinforcing agent in thermoplastic polyurethane (TPU) based composites. Composites containing 5, 10, 15, and 20 weight % sized and desized CFs were prepared by using melt-mixing method. The surface characteristics of CFs were examined by energy dispersive X-ray spectroscopy (EDX) and Fourier transform infrared spectroscopy (FTIR). Tensile testing, shore hardness test, dynamic mechanical analysis (DMA) and melt flow index (MFI) test were performed for determining final composite properties. The dispersion of CFs in TPU matrix was examined by scanning electron microscopy (SEM). Tensile strength, Youngs’ modulus and Shore hardness of TPU were enhanced by the addition of sized CFs. About two-fold improvement for tensile strength and ten-fold improvement for Youngs’ modulus were observed with the incorporation of 20 wt% EP-CF and PU-CF in TPU. The storage modulus of PU-CF containing composites was higher than those of TPU and other composites. No remarkable change was observed in MFI value of TPU after CF loadings. Processing conditions in this work was suitable for composite production. Sized CFs exhibited better dispersion with regard to desized CF due to the stronger adhesion of TPU matrix to fiber surface.

The pre-experiment of the present study revealed that polyurethane (PU) synthesized using poly (hexamethylene carbonate) glycol (PHC) has high melt viscosity and is difficult to process. Therefore, poly (trimethylene carbonate) glycol (PTC) was employed to synthesize a PU product with low melt viscosity. First, four types of thermoplastic polyurethane (TPU) were formed through one-step solvent-free synthesis. TPU is presented in the format “TPU-X-Y,” with X representing the polyol (PTC or PHC, around 1000 molecular weight) and Y the chain extender (1,3-propane diol [PDO] or 1,4-butane diol [BDO]) used. The TPU was synthesized using a fixed molar ratio of (isocyanate):(polyol):(chain extender) = 2:1:1 and compared. The results indicated that chain entanglement often occurred among the long carbon chains of PHC. The synthesized TPU employed a property of PTC, namely converting polarity into reverse polarity in high temperatures, to resolve the high melt viscosity of TPU of the PHC series, which causes processing difficulties. The synthesized TPU-PTC-PDO exhibited favorable molecular arrangements. Given its polarity, TPU-PTC-PDO has outstanding tensile properties (strength at break: 41.10 ± 10.78 MPa; 100% modulus = 6.73 ± 0.12 MPa), making processing at lower temperatures (180 or 190 °C) feasible. With the inclusion of PTC, the synthesized polycarbonate TPU exhibits the advantages of polycarbonate and is suitable for a wide range of applications.

This study contributes to the fundamental knowledge of circular economy practices by identifying key trends related to future challenges and opportunities for Sustainable Development Goal (SDG) 12 (Responsible Consumption and Production) and assessing regional position gaps and global attributes. Most countries are experiencing progress in implementing circular economy practices for SDG12 considering that a circular economy is essential for product reuse and development. However, these efforts have been neglected, and inadequate political and economic systems impede concept implementation. This study aims to present a circular economy practice model and investigate potential opportunities and challenges for SDG12. A hybrid systematic data-driven analysis is applied. The findings highlight the importance of circular design and innovation, resource efficiency and management, and energy and environmental sustainability in advancing the circular economy transition and addressing the SDG12 challenges and opportunities in practices in both the overall situation and among regions.

PurposeUncovering the relationship between Industry 4.0 (I4.0) technologies and circular economy (CE) practices is critical not only for implementing CE but also for leveraging I4.0 to achieve sustainable development goals. However, the potential connection between them – especially how different I4.0 technologies may influence various CE practices – remains inadequately researched. The purpose of this study was to quantitatively explore the impacts of various I4.0 technologies on CE practices.Design/methodology/approachA mixed method consisting of a systematic literature review, content analysis, and social network analysis was adopted. First, 266 articles were selected and mined for contents of I4.0 technologies and CE practices; 27 I4.0 technologies and 21 CE practices were identified. Second, 62 articles were found that prove the positive influence of I4.0 technologies on CE practices, and 124 relationships were identified. Third, based on evidence supporting the link between I4.0 technologies and CE practices, a two-mode network and two one-mode networks were constructed, and their network density and degree centrality indicators were analyzed.FindingsI4.0 technologies have a low application scope and degree for promoting CE. The adoption of a single I4.0 technology has limited effect on CE practices, and wider benefits can be realized through integrating I4.0 technologies. The Internet of Things (IoT), additive manufacturing, big data and analytics, and artificial intelligence (AI) are among the top technologies promoting CE implementation and reduction and recycling were identified as the main mechanism. The integration of these technologies is the most popular and effective. Twelve CE practices were identified to be the most widely implemented and supported by I4.0 technologies.Research limitations/implicationsFirst, only journal articles, reviews, and online publications written in English were selected, excluding articles published in other languages. Therefore, the results obtained only represent a specific group of scholars, which may be fragmented to a certain extent. Second, because the extraction of the impact of I4.0 on CE mainly relies on a manual literature review, this paper only provides the statistics of the number of publications involving relationships, while lacking the weight measurement of relationships.Originality/valueA comprehensive, quantitative, and visual analysis method was employed to unveil the current implementation levels of I4.0 technologies and CE practices. Further, it was explored how different I4.0 technologies can affect various CE aspects, how different I4.0 technologies are integrated to promote CE realization, and how various CE practices are implemented simultaneously by I4.0 technologies.