Energy harvesting has been identified as a key enabling technology for the Internet of Things as ... more Energy harvesting has been identified as a key enabling technology for the Internet of Things as it allows a battery-less functioning of electronic devices. While the use of ambient sources of energy is commonly seen as sustainable due to their renewable nature, raw material consumption and recyclability need to be assessed to ensure true sustainability. This is especially relevant in electronics, due to their high complexity stemming from the variety of components and materials in their composition. This work presents the case study of the application of the 12 Principles of Green Engineering to an energy-harvesting platform in the early technology development phase. Specifically, the technological areas of design for disassembly, materials for substitution, fabrication efficiency, and manufacturing processes that enable the use of recycled materials have been evaluated. This has allowed us to identify hazardous raw materials and recommend their substitution. Further recommendations include the adoption of mechanical fixtures to fasten lump components. Additional strategies have been identified but their application has been found out of reach of the technology developers, such as the increase in the manufacturing batch size or the inclusion of solvent recycling, which can only be implemented at larger manufacturing scales. Further strategies, such as the use of recycled Si wafers or dry adhesives as fixtures, represent future solutions for the reduction in the environmental impact which require further R&D efforts from different disciplines. This highlights the need for holistic and multidisciplinary research efforts to fully achieve the circular design.
Insulating polymeric foams have an important role to play in increasing energy efficiency and the... more Insulating polymeric foams have an important role to play in increasing energy efficiency and therefore contributing to combating climate change. Their development in recent years has been driven towards the reduction of thermal conductivity and achievement of the required mechanical properties as main targets towards sustainability. This perception of sustainability has overseen the choice of raw materials, which are often toxic, or has placed research efforts on optimizing one constituent while the other necessary reactants remain hazardous. The transition to the circular economy requires a holistic understanding of sustainability and a shift in design methodology and the resulting research focus. This paper identifies research needs and possible strategies for polymeric foam development compatible with Circular Product Design and Green Engineering, based on an extensive literature review. Identified research needs include material characterization of a broader spectrum of polymer...
In the context of replacing polyurethane foam in DH pre-insulated pipes due to the toxicity of th... more In the context of replacing polyurethane foam in DH pre-insulated pipes due to the toxicity of the diisocyanates, and facilitating recycling by eliminating the need to separate material layers of the sandwich structure, the foaming of PB-1 with CO2 is being studied. The assessment of the plasticization effect induced by CO2 in the polymer melt and determination of the melting point depression is required for the establishment and optimization of the foaming processing window. In this paper, a method for the determination of the melting point through image analysis is presented, validated and used for the study of PB-1 – CO2 solutions. The obtained results through image analysis agree with those obtained with differential scanning calorimetry, validating the method. The CO2 - induced melting point depression of PB-1 was determined as ΔT = 140C.
Polymeric foams are a key element of many multifunctional sandwich structures. The most commonly ... more Polymeric foams are a key element of many multifunctional sandwich structures. The most commonly used polymeric foam, polyurethane, presents environmental drawbacks, related to poor recyclability and the use of toxic diisocyanates for their manufacturing. The separation of layers in sandwich structures is a further unresolved hurdle toward the recyclability of these elements. There is a need for broad
The piping network is the essence of DHC. Its insulation is fundamental for its correct and effic... more The piping network is the essence of DHC. Its insulation is fundamental for its correct and efficient functioning. State of the art DHC networks are insulated with polyurethane (PU) foam, which presents outstanding mechanical and insulating properties. However, the high toxicity of the diisocyanates (European Chemical Agency, 2008) required for its production and the recently approved European Restriction on their Use (European Commission, 2020) highlight the need for sustainable alternatives. Polyethylene terephthalate (PET) foam has been previously identified as a promising candidate for DHC given its mechanical properties (Ramnäs, 2008) and high insulation capacity retention, due to slow gas diffusion (Mangs, 2005). However, its behavior upon ageing remains unexplored. Without this knowledge, the material cannot be reliably introduced in the market. The objective of this work is to experimentally investigate PET foam's ageing behavior, with a focus on the effects of thermal cycling, thermally induced crystallinity and hygrothermal degradation on its mechanical properties. Different ageing trials were conducted in an environmental chamber. The effects on the mechanical properties and crystalline structure were evaluated. No degradation was found in the scenarios covered by this study. Service temperature over 100 • C is found possible thanks to thermally induced crystallization. c
Fatigue & Fracture of Engineering Materials & Structures, 2020
District heating (DH) pre-insulated pipes are a sandwich assembly composed by a steel heat servic... more District heating (DH) pre-insulated pipes are a sandwich assembly composed by a steel heat service pipe, polyurethane (PU) foam and polyethylene casing. The foam acts as bond between the steel pipe and casing. The application has high constraints for the foam, as it is subjected to cyclic multiaxial stresses, high cyclic temperatures and long expected service life. In this study, we evaluate if and how cyclic loads affect the shear strength, shear modulus, toughness and failure behaviour of the PU foam in DH pipes sandwich assembly compared with unaged reference samples. We have found that the simultaneous application of mechanical and thermal loads weakens the strength and increases the stiffness of the foam and that this change is not caused by degradation of the molecular structure. Crack initiation and propagation along the pipe samples follow a very consistent pattern between samples, with cracks initiating in Mode II and propagating in Mode I. The consistent axial displacement of approximately 2 cm from each other suggests the formation of strain localizations. K E Y W O R D S cyclic loading, district heating, fatigue, foam, polyurethane, sandwich structure 1 | INTRODUCTION District heating (DH) pre-insulated pipes sandwich assembly composed of a steel heat service pipe, insulating material (polyurethane [PU] foam) and polyethylene (PE) casing, which are bonded by the insulating material. 1 The pipe networks are directly buried underground. The DH system's start-up and shut downs, as well as fluctuations on heat demand and ambient temperature, subject the piping network to thermal and mechanical cycling due to the thermal expansion. The axial expansion of the pipes is partially counteracted by frictional forces acting between the ground and the casing, with the shear stresses transferred through the PU foam bond. Therefore, the use of pre-insulated pipes has implied the simplification of the laying methods, employing cold laying instead of expansion facilities like compensators or U-bends, being more cost effective. 2 The PU foam layer needs to withstand the shear stresses without failure for the network lifetime to preserve its load bearing function. Knowledge on the ageing mechanisms of the PU foam is of great importance in order to ensure the pipe assembly performs as specified during its service life, as well as to asses if this service life could be extended. The EN253:2019 standard 1 assumes that the failure of the PU bond and hence the service life is driven by
Measures to increase the share of renewables in heat generation, combined with increased energy e... more Measures to increase the share of renewables in heat generation, combined with increased energy efficiency provide a direct emissions reduction on the heating sector. Energy efficiency measures, as well as the role-out of sustainable heating technologies such as district heating networks have one key actor: insulation. However, state of the art insulating materials such as polyurethane or polystyrene have severe environmental drawbacks incompatible with today’s transition to the circular economy, and are the Achilles’ heel of the sector in terms of sustainability. Biobased and biodegradable polylactic acid (PLA) foam could be a promising replacement for fossil-based polymeric insulating foams. This study provides data on the mechanical behaviour of expanded PLA foam under different temperatures, which will help to assess its potential use as insulation where the foam is subject to heat.
The polyurethane foam in district heating pre-insulated pipes has a critical role to play both as... more The polyurethane foam in district heating pre-insulated pipes has a critical role to play both as thermal insulation and as load bearing element, as it serves as bond between the medium pipe and the casing. Hence, knowledge on how the foam behaves under multiaxial stresses is of great importance for the design as well as for aging predictions of the network. It is known that cell shape anisotropy in polymeric foams leads to anisotropy in its mechanical properties. In this study, we evaluate and quantify the microstructural anisotropy of PU foam from pre-insulated pipes as well as its mechanical behaviour under compression in the three orthogonal directions. We cover rigid and flexible PU foam, batch and continuous manufacturing, and different pipe diameters. The results were compared with those predicted by available rectangular and Kelvin cell shape models. We have found that PU from pre-insulated pipes is orthotropic and present stronger anisotropy than that typically found in PU ...
In the context of replacing polyurethane foam in DH pre-insulated pipes due to the toxicity of th... more In the context of replacing polyurethane foam in DH pre-insulated pipes due to the toxicity of the diisocyanates, and facilitating recycling by eliminating the need to separate material layers of the sandwich structure, the foaming of PB-1 with CO2 is being studied. The assessment of the plasticization effect induced by CO2 in the polymer melt and determination of the melting point depression is required for the establishment and optimization of the foaming processing window. In this paper, a method for the determination of the melting point through image analysis is presented, validated and used for the study of PB-1 – CO2 solutions. The obtained results through image analysis agree with those obtained with differential scanning calorimetry, validating the method. The CO2 - induced melting point depression of PB-1 was determined as ΔT = 140C.
The recently approved restriction on diisocyanates highlights the health and safety issues concer... more The recently approved restriction on diisocyanates highlights the health and safety issues concerning polyurethane manufacturing and the relevance of developing sustainable insulating polymeric foams. This is particularly challenging for applications where the foam is subjected to high temperatures (>80 °C) and bear loads, such as insulating and bonding material for district heating pipes. As part of a PhD project concerning pre-insulated district heating pipes for the circular economy, polybutylene (PB-1) has been identified as a promising candidate for the application, due to its low thermal conductivity, high-temperature mechanical properties, retention, excellent environmental stress cracking resistance (ESCR) and outstanding creep resistance. It is a recyclable thermoplastic and of non-toxic nature, pre-requisites for circular product development. On the contrary to other polyolefins, PB-1 is reported to strain-harden and has high melt strength, required properties for foami...
The piping network is the essence of DHC. Its insulation is fundamental for its correct and effic... more The piping network is the essence of DHC. Its insulation is fundamental for its correct and efficient functioning. State of the art DHC networks are insulated with polyurethane (PU) foam, which presents outstanding mechanical and insulating properties. However, the high toxicity of the diisocyanates (European Chemical Agency, 2008) required for its production and the recently approved European Restriction on their Use (European Commission, 2020) highlight the need for sustainable alternatives. Polyethylene terephthalate (PET) foam has been previously identified as a promising candidate for DHC given its mechanical properties (Ramnäs, 2008) and high insulation capacity retention, due to slow gas diffusion (Mangs, 2005). However, its behavior upon ageing remains unexplored. Without this knowledge, the material cannot be reliably introduced in the market. The objective of this work is to experimentally investigate PET foam's ageing behavior, with a focus on the effects of thermal cycling, thermally induced crystallinity and hygrothermal degradation on its mechanical properties. Different ageing trials were conducted in an environmental chamber. The effects on the mechanical properties and crystalline structure were evaluated. No degradation was found in the scenarios covered by this study. Service temperature over 100 • C is found possible thanks to thermally induced crystallization. c
Polymeric foams are a key element of many multifunctional sandwich structures. The most commonly ... more Polymeric foams are a key element of many multifunctional sandwich structures. The most commonly used polymeric foam, polyurethane, presents environmental drawbacks, related to poor recyclability and the use of toxic diisocyanates for their manufacturing. The separation of layers in sandwich structures is a further unresolved hurdle toward the recyclability of these elements. There is a need for broad
Fatigue and Fracture of Engineering Materials and Structures , 2020
District heating (DH) pre-insulated pipes are a sandwich assembly composed by a steel heat servic... more District heating (DH) pre-insulated pipes are a sandwich assembly composed by a steel heat service pipe, polyurethane (PU) foam and polyethylene casing. The foam acts as bond between the steel pipe and casing. The application has high constraints for the foam, as it is subjected to cyclic multiaxial stresses, high cyclic temperatures and long expected service life. In this study, we evaluate if and how cyclic loads affect the shear strength, shear modulus, toughness and failure behaviour of the PU foam in DH pipes sandwich assembly compared with unaged reference samples. We have found that the simultaneous application of mechanical and thermal loads weakens the strength and increases the stiffness of the foam and that this change is not caused by degradation of the molecular structure. Crack initiation and propagation along the pipe samples follow a very consistent pattern between samples, with cracks initiating in Mode II and propagating in Mode I. The consistent axial displacement of approximately 2 cm from each other suggests the formation of strain localizations. K E Y W O R D S cyclic loading, district heating, fatigue, foam, polyurethane, sandwich structure 1 | INTRODUCTION District heating (DH) pre-insulated pipes sandwich assembly composed of a steel heat service pipe, insulating material (polyurethane [PU] foam) and polyethylene (PE) casing, which are bonded by the insulating material. 1 The pipe networks are directly buried underground. The DH system's start-up and shut downs, as well as fluctuations on heat demand and ambient temperature, subject the piping network to thermal and mechanical cycling due to the thermal expansion. The axial expansion of the pipes is partially counteracted by frictional forces acting between the ground and the casing, with the shear stresses transferred through the PU foam bond. Therefore, the use of pre-insulated pipes has implied the simplification of the laying methods, employing cold laying instead of expansion facilities like compensators or U-bends, being more cost effective. 2 The PU foam layer needs to withstand the shear stresses without failure for the network lifetime to preserve its load bearing function. Knowledge on the ageing mechanisms of the PU foam is of great importance in order to ensure the pipe assembly performs as specified during its service life, as well as to asses if this service life could be extended. The EN253:2019 standard 1 assumes that the failure of the PU bond and hence the service life is driven by
Measures to increase the share of renewables in heat generation, combined with increased energy e... more Measures to increase the share of renewables in heat generation, combined with increased energy efficiency provide a direct emissions reduction on the heating sector. Energy efficiency measures, as well as the role-out of sustainable heating technologies such as district heating networks have one key actor: insulation. However, state of the art insulating materials such as polyurethane or polystyrene have severe environmental drawbacks incompatible with today's transition to the circular economy, and are the Achilles' heel of the sector in terms of sustainability. Biobased and biodegradable polylactic acid (PLA) foam could be a promising replacement for fossil-based polymeric insulating foams. This study provides data on the mechanical behaviour of expanded PLA foam under different temperatures, which will help to assess its potential use as insulation where the foam is subject to heat.
The polyurethane foam in district heating pre-insulated pipes has a critical role to play both as... more The polyurethane foam in district heating pre-insulated pipes has a critical role to play both as thermal insulation and as load bearing element, as it serves as bond between the medium pipe and the casing. Hence, knowledge on how the foam behaves under multiaxial stresses is of great importance for the design as well as for aging predictions of the network. It is known that cell shape anisotropy in polymeric foams leads to anisotropy in its mechanical properties. In this study, we evaluate and quantify the microstructural anisotropy of PU foam from pre-insulated pipes as well as its mechanical behaviour under compression in the three orthogonal directions. We cover rigid and flexible PU foam, batch and continuous manufacturing, and different pipe diameters. The results were compared with those predicted by available rectangular and Kelvin cell shape models. We have found that PU from pre-insulated pipes is orthotropic and present stronger anisotropy than that typically found in PU slabs. The traditional bonded pipes under consideration behaved in a similar way. However, when comparing the two flexible pipes in this study, despite no significant differences in cell shape anisotropy were found, a significantly different behaviour for the E modulus ratio was observed. This shows that while the manufacturing process exerts the main influence on cell shape anisotropy, to explain the difference in stiffness behaviour other factors need to be taken into consideration, such as cell size and cell size variability.
District heating pre-insulated pipes are a sandwich structure of material layers. Polyurethane
fo... more District heating pre-insulated pipes are a sandwich structure of material layers. Polyurethane foam bonds the medium pipe with the casing, providing an insulating function as well as a load bearing function. The high toxicity of the di-isocyanates required for its manufacturing triggers the need for a replacement. In this work, alternatives have been researched and developed considering the requirements of the circular economy. Two technology readiness levels (TRL) were covered. The higher TRL involved the evaluation of commercially available polymeric foam alternatives. Polyethene terephthalate foam was selected, and its ageing behaviour concerning degradation sources inherent to the application was studied in detail to confirm the fulfilment of the required service life. No degradation of the mechanical properties was found after exposure to thermal cycles or hygrothermal conditions at temperatures below its glass transition, which would correspond to the scenario of groundwater ingress. The previously determined highest service temperature of 80ºC was found conservative, as annealing at 100ºC increases its strength, allowing this service temperature. All results suggest it is a suitable candidate for the insulation of steel medium pipes. The fast embrittlement upon exposure to hot moisture, as would occur due to permeation of the heat carrier through a plastic pipe, prevents its recommendation for this case. The lower TRL research involved the re-evaluation of the complete sandwich assembly, from a cradle-to-cradle perspective. The foamability of polybutene-1 was explored, with the ultimate target of allowing the manufacturing of the sandwich element out of a single material, as to facilitate its recycling. Favourable grades for foaming were identified, confirming its foamability. The relationships between process parameters and the foam’s microstructure were evaluated. Foams in the required size for mechanical and insulating properties characterization were successfully produced. Mechanical properties of PU from state-of-the-art flexible plastic medium pipes fall in the prediction bands obtained from the produced PB-1 foams. This provides confidence on the suitability for the application.
Energy harvesting has been identified as a key enabling technology for the Internet of Things as ... more Energy harvesting has been identified as a key enabling technology for the Internet of Things as it allows a battery-less functioning of electronic devices. While the use of ambient sources of energy is commonly seen as sustainable due to their renewable nature, raw material consumption and recyclability need to be assessed to ensure true sustainability. This is especially relevant in electronics, due to their high complexity stemming from the variety of components and materials in their composition. This work presents the case study of the application of the 12 Principles of Green Engineering to an energy-harvesting platform in the early technology development phase. Specifically, the technological areas of design for disassembly, materials for substitution, fabrication efficiency, and manufacturing processes that enable the use of recycled materials have been evaluated. This has allowed us to identify hazardous raw materials and recommend their substitution. Further recommendations include the adoption of mechanical fixtures to fasten lump components. Additional strategies have been identified but their application has been found out of reach of the technology developers, such as the increase in the manufacturing batch size or the inclusion of solvent recycling, which can only be implemented at larger manufacturing scales. Further strategies, such as the use of recycled Si wafers or dry adhesives as fixtures, represent future solutions for the reduction in the environmental impact which require further R&D efforts from different disciplines. This highlights the need for holistic and multidisciplinary research efforts to fully achieve the circular design.
Insulating polymeric foams have an important role to play in increasing energy efficiency and the... more Insulating polymeric foams have an important role to play in increasing energy efficiency and therefore contributing to combating climate change. Their development in recent years has been driven towards the reduction of thermal conductivity and achievement of the required mechanical properties as main targets towards sustainability. This perception of sustainability has overseen the choice of raw materials, which are often toxic, or has placed research efforts on optimizing one constituent while the other necessary reactants remain hazardous. The transition to the circular economy requires a holistic understanding of sustainability and a shift in design methodology and the resulting research focus. This paper identifies research needs and possible strategies for polymeric foam development compatible with Circular Product Design and Green Engineering, based on an extensive literature review. Identified research needs include material characterization of a broader spectrum of polymer...
In the context of replacing polyurethane foam in DH pre-insulated pipes due to the toxicity of th... more In the context of replacing polyurethane foam in DH pre-insulated pipes due to the toxicity of the diisocyanates, and facilitating recycling by eliminating the need to separate material layers of the sandwich structure, the foaming of PB-1 with CO2 is being studied. The assessment of the plasticization effect induced by CO2 in the polymer melt and determination of the melting point depression is required for the establishment and optimization of the foaming processing window. In this paper, a method for the determination of the melting point through image analysis is presented, validated and used for the study of PB-1 – CO2 solutions. The obtained results through image analysis agree with those obtained with differential scanning calorimetry, validating the method. The CO2 - induced melting point depression of PB-1 was determined as ΔT = 140C.
Polymeric foams are a key element of many multifunctional sandwich structures. The most commonly ... more Polymeric foams are a key element of many multifunctional sandwich structures. The most commonly used polymeric foam, polyurethane, presents environmental drawbacks, related to poor recyclability and the use of toxic diisocyanates for their manufacturing. The separation of layers in sandwich structures is a further unresolved hurdle toward the recyclability of these elements. There is a need for broad
The piping network is the essence of DHC. Its insulation is fundamental for its correct and effic... more The piping network is the essence of DHC. Its insulation is fundamental for its correct and efficient functioning. State of the art DHC networks are insulated with polyurethane (PU) foam, which presents outstanding mechanical and insulating properties. However, the high toxicity of the diisocyanates (European Chemical Agency, 2008) required for its production and the recently approved European Restriction on their Use (European Commission, 2020) highlight the need for sustainable alternatives. Polyethylene terephthalate (PET) foam has been previously identified as a promising candidate for DHC given its mechanical properties (Ramnäs, 2008) and high insulation capacity retention, due to slow gas diffusion (Mangs, 2005). However, its behavior upon ageing remains unexplored. Without this knowledge, the material cannot be reliably introduced in the market. The objective of this work is to experimentally investigate PET foam's ageing behavior, with a focus on the effects of thermal cycling, thermally induced crystallinity and hygrothermal degradation on its mechanical properties. Different ageing trials were conducted in an environmental chamber. The effects on the mechanical properties and crystalline structure were evaluated. No degradation was found in the scenarios covered by this study. Service temperature over 100 • C is found possible thanks to thermally induced crystallization. c
Fatigue & Fracture of Engineering Materials & Structures, 2020
District heating (DH) pre-insulated pipes are a sandwich assembly composed by a steel heat servic... more District heating (DH) pre-insulated pipes are a sandwich assembly composed by a steel heat service pipe, polyurethane (PU) foam and polyethylene casing. The foam acts as bond between the steel pipe and casing. The application has high constraints for the foam, as it is subjected to cyclic multiaxial stresses, high cyclic temperatures and long expected service life. In this study, we evaluate if and how cyclic loads affect the shear strength, shear modulus, toughness and failure behaviour of the PU foam in DH pipes sandwich assembly compared with unaged reference samples. We have found that the simultaneous application of mechanical and thermal loads weakens the strength and increases the stiffness of the foam and that this change is not caused by degradation of the molecular structure. Crack initiation and propagation along the pipe samples follow a very consistent pattern between samples, with cracks initiating in Mode II and propagating in Mode I. The consistent axial displacement of approximately 2 cm from each other suggests the formation of strain localizations. K E Y W O R D S cyclic loading, district heating, fatigue, foam, polyurethane, sandwich structure 1 | INTRODUCTION District heating (DH) pre-insulated pipes sandwich assembly composed of a steel heat service pipe, insulating material (polyurethane [PU] foam) and polyethylene (PE) casing, which are bonded by the insulating material. 1 The pipe networks are directly buried underground. The DH system's start-up and shut downs, as well as fluctuations on heat demand and ambient temperature, subject the piping network to thermal and mechanical cycling due to the thermal expansion. The axial expansion of the pipes is partially counteracted by frictional forces acting between the ground and the casing, with the shear stresses transferred through the PU foam bond. Therefore, the use of pre-insulated pipes has implied the simplification of the laying methods, employing cold laying instead of expansion facilities like compensators or U-bends, being more cost effective. 2 The PU foam layer needs to withstand the shear stresses without failure for the network lifetime to preserve its load bearing function. Knowledge on the ageing mechanisms of the PU foam is of great importance in order to ensure the pipe assembly performs as specified during its service life, as well as to asses if this service life could be extended. The EN253:2019 standard 1 assumes that the failure of the PU bond and hence the service life is driven by
Measures to increase the share of renewables in heat generation, combined with increased energy e... more Measures to increase the share of renewables in heat generation, combined with increased energy efficiency provide a direct emissions reduction on the heating sector. Energy efficiency measures, as well as the role-out of sustainable heating technologies such as district heating networks have one key actor: insulation. However, state of the art insulating materials such as polyurethane or polystyrene have severe environmental drawbacks incompatible with today’s transition to the circular economy, and are the Achilles’ heel of the sector in terms of sustainability. Biobased and biodegradable polylactic acid (PLA) foam could be a promising replacement for fossil-based polymeric insulating foams. This study provides data on the mechanical behaviour of expanded PLA foam under different temperatures, which will help to assess its potential use as insulation where the foam is subject to heat.
The polyurethane foam in district heating pre-insulated pipes has a critical role to play both as... more The polyurethane foam in district heating pre-insulated pipes has a critical role to play both as thermal insulation and as load bearing element, as it serves as bond between the medium pipe and the casing. Hence, knowledge on how the foam behaves under multiaxial stresses is of great importance for the design as well as for aging predictions of the network. It is known that cell shape anisotropy in polymeric foams leads to anisotropy in its mechanical properties. In this study, we evaluate and quantify the microstructural anisotropy of PU foam from pre-insulated pipes as well as its mechanical behaviour under compression in the three orthogonal directions. We cover rigid and flexible PU foam, batch and continuous manufacturing, and different pipe diameters. The results were compared with those predicted by available rectangular and Kelvin cell shape models. We have found that PU from pre-insulated pipes is orthotropic and present stronger anisotropy than that typically found in PU ...
In the context of replacing polyurethane foam in DH pre-insulated pipes due to the toxicity of th... more In the context of replacing polyurethane foam in DH pre-insulated pipes due to the toxicity of the diisocyanates, and facilitating recycling by eliminating the need to separate material layers of the sandwich structure, the foaming of PB-1 with CO2 is being studied. The assessment of the plasticization effect induced by CO2 in the polymer melt and determination of the melting point depression is required for the establishment and optimization of the foaming processing window. In this paper, a method for the determination of the melting point through image analysis is presented, validated and used for the study of PB-1 – CO2 solutions. The obtained results through image analysis agree with those obtained with differential scanning calorimetry, validating the method. The CO2 - induced melting point depression of PB-1 was determined as ΔT = 140C.
The recently approved restriction on diisocyanates highlights the health and safety issues concer... more The recently approved restriction on diisocyanates highlights the health and safety issues concerning polyurethane manufacturing and the relevance of developing sustainable insulating polymeric foams. This is particularly challenging for applications where the foam is subjected to high temperatures (>80 °C) and bear loads, such as insulating and bonding material for district heating pipes. As part of a PhD project concerning pre-insulated district heating pipes for the circular economy, polybutylene (PB-1) has been identified as a promising candidate for the application, due to its low thermal conductivity, high-temperature mechanical properties, retention, excellent environmental stress cracking resistance (ESCR) and outstanding creep resistance. It is a recyclable thermoplastic and of non-toxic nature, pre-requisites for circular product development. On the contrary to other polyolefins, PB-1 is reported to strain-harden and has high melt strength, required properties for foami...
The piping network is the essence of DHC. Its insulation is fundamental for its correct and effic... more The piping network is the essence of DHC. Its insulation is fundamental for its correct and efficient functioning. State of the art DHC networks are insulated with polyurethane (PU) foam, which presents outstanding mechanical and insulating properties. However, the high toxicity of the diisocyanates (European Chemical Agency, 2008) required for its production and the recently approved European Restriction on their Use (European Commission, 2020) highlight the need for sustainable alternatives. Polyethylene terephthalate (PET) foam has been previously identified as a promising candidate for DHC given its mechanical properties (Ramnäs, 2008) and high insulation capacity retention, due to slow gas diffusion (Mangs, 2005). However, its behavior upon ageing remains unexplored. Without this knowledge, the material cannot be reliably introduced in the market. The objective of this work is to experimentally investigate PET foam's ageing behavior, with a focus on the effects of thermal cycling, thermally induced crystallinity and hygrothermal degradation on its mechanical properties. Different ageing trials were conducted in an environmental chamber. The effects on the mechanical properties and crystalline structure were evaluated. No degradation was found in the scenarios covered by this study. Service temperature over 100 • C is found possible thanks to thermally induced crystallization. c
Polymeric foams are a key element of many multifunctional sandwich structures. The most commonly ... more Polymeric foams are a key element of many multifunctional sandwich structures. The most commonly used polymeric foam, polyurethane, presents environmental drawbacks, related to poor recyclability and the use of toxic diisocyanates for their manufacturing. The separation of layers in sandwich structures is a further unresolved hurdle toward the recyclability of these elements. There is a need for broad
Fatigue and Fracture of Engineering Materials and Structures , 2020
District heating (DH) pre-insulated pipes are a sandwich assembly composed by a steel heat servic... more District heating (DH) pre-insulated pipes are a sandwich assembly composed by a steel heat service pipe, polyurethane (PU) foam and polyethylene casing. The foam acts as bond between the steel pipe and casing. The application has high constraints for the foam, as it is subjected to cyclic multiaxial stresses, high cyclic temperatures and long expected service life. In this study, we evaluate if and how cyclic loads affect the shear strength, shear modulus, toughness and failure behaviour of the PU foam in DH pipes sandwich assembly compared with unaged reference samples. We have found that the simultaneous application of mechanical and thermal loads weakens the strength and increases the stiffness of the foam and that this change is not caused by degradation of the molecular structure. Crack initiation and propagation along the pipe samples follow a very consistent pattern between samples, with cracks initiating in Mode II and propagating in Mode I. The consistent axial displacement of approximately 2 cm from each other suggests the formation of strain localizations. K E Y W O R D S cyclic loading, district heating, fatigue, foam, polyurethane, sandwich structure 1 | INTRODUCTION District heating (DH) pre-insulated pipes sandwich assembly composed of a steel heat service pipe, insulating material (polyurethane [PU] foam) and polyethylene (PE) casing, which are bonded by the insulating material. 1 The pipe networks are directly buried underground. The DH system's start-up and shut downs, as well as fluctuations on heat demand and ambient temperature, subject the piping network to thermal and mechanical cycling due to the thermal expansion. The axial expansion of the pipes is partially counteracted by frictional forces acting between the ground and the casing, with the shear stresses transferred through the PU foam bond. Therefore, the use of pre-insulated pipes has implied the simplification of the laying methods, employing cold laying instead of expansion facilities like compensators or U-bends, being more cost effective. 2 The PU foam layer needs to withstand the shear stresses without failure for the network lifetime to preserve its load bearing function. Knowledge on the ageing mechanisms of the PU foam is of great importance in order to ensure the pipe assembly performs as specified during its service life, as well as to asses if this service life could be extended. The EN253:2019 standard 1 assumes that the failure of the PU bond and hence the service life is driven by
Measures to increase the share of renewables in heat generation, combined with increased energy e... more Measures to increase the share of renewables in heat generation, combined with increased energy efficiency provide a direct emissions reduction on the heating sector. Energy efficiency measures, as well as the role-out of sustainable heating technologies such as district heating networks have one key actor: insulation. However, state of the art insulating materials such as polyurethane or polystyrene have severe environmental drawbacks incompatible with today's transition to the circular economy, and are the Achilles' heel of the sector in terms of sustainability. Biobased and biodegradable polylactic acid (PLA) foam could be a promising replacement for fossil-based polymeric insulating foams. This study provides data on the mechanical behaviour of expanded PLA foam under different temperatures, which will help to assess its potential use as insulation where the foam is subject to heat.
The polyurethane foam in district heating pre-insulated pipes has a critical role to play both as... more The polyurethane foam in district heating pre-insulated pipes has a critical role to play both as thermal insulation and as load bearing element, as it serves as bond between the medium pipe and the casing. Hence, knowledge on how the foam behaves under multiaxial stresses is of great importance for the design as well as for aging predictions of the network. It is known that cell shape anisotropy in polymeric foams leads to anisotropy in its mechanical properties. In this study, we evaluate and quantify the microstructural anisotropy of PU foam from pre-insulated pipes as well as its mechanical behaviour under compression in the three orthogonal directions. We cover rigid and flexible PU foam, batch and continuous manufacturing, and different pipe diameters. The results were compared with those predicted by available rectangular and Kelvin cell shape models. We have found that PU from pre-insulated pipes is orthotropic and present stronger anisotropy than that typically found in PU slabs. The traditional bonded pipes under consideration behaved in a similar way. However, when comparing the two flexible pipes in this study, despite no significant differences in cell shape anisotropy were found, a significantly different behaviour for the E modulus ratio was observed. This shows that while the manufacturing process exerts the main influence on cell shape anisotropy, to explain the difference in stiffness behaviour other factors need to be taken into consideration, such as cell size and cell size variability.
District heating pre-insulated pipes are a sandwich structure of material layers. Polyurethane
fo... more District heating pre-insulated pipes are a sandwich structure of material layers. Polyurethane foam bonds the medium pipe with the casing, providing an insulating function as well as a load bearing function. The high toxicity of the di-isocyanates required for its manufacturing triggers the need for a replacement. In this work, alternatives have been researched and developed considering the requirements of the circular economy. Two technology readiness levels (TRL) were covered. The higher TRL involved the evaluation of commercially available polymeric foam alternatives. Polyethene terephthalate foam was selected, and its ageing behaviour concerning degradation sources inherent to the application was studied in detail to confirm the fulfilment of the required service life. No degradation of the mechanical properties was found after exposure to thermal cycles or hygrothermal conditions at temperatures below its glass transition, which would correspond to the scenario of groundwater ingress. The previously determined highest service temperature of 80ºC was found conservative, as annealing at 100ºC increases its strength, allowing this service temperature. All results suggest it is a suitable candidate for the insulation of steel medium pipes. The fast embrittlement upon exposure to hot moisture, as would occur due to permeation of the heat carrier through a plastic pipe, prevents its recommendation for this case. The lower TRL research involved the re-evaluation of the complete sandwich assembly, from a cradle-to-cradle perspective. The foamability of polybutene-1 was explored, with the ultimate target of allowing the manufacturing of the sandwich element out of a single material, as to facilitate its recycling. Favourable grades for foaming were identified, confirming its foamability. The relationships between process parameters and the foam’s microstructure were evaluated. Foams in the required size for mechanical and insulating properties characterization were successfully produced. Mechanical properties of PU from state-of-the-art flexible plastic medium pipes fall in the prediction bands obtained from the produced PB-1 foams. This provides confidence on the suitability for the application.
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plasticization effect induced by CO2 in the polymer melt and determination of the melting point depression is required for the establishment and optimization of the foaming processing window.
In this paper, a method for the determination of the melting point through image analysis is presented, validated and used for the study of PB-1 – CO2 solutions. The obtained results through image analysis agree with those obtained with differential scanning calorimetry, validating the
method. The CO2 - induced melting point depression of PB-1 was determined as ΔT = 140C.
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foam bonds the medium pipe with the casing, providing an insulating function as well as a load
bearing function. The high toxicity of the di-isocyanates required for its manufacturing triggers
the need for a replacement. In this work, alternatives have been researched and developed
considering the requirements of the circular economy. Two technology readiness levels (TRL)
were covered. The higher TRL involved the evaluation of commercially available polymeric foam
alternatives. Polyethene terephthalate foam was selected, and its ageing behaviour concerning
degradation sources inherent to the application was studied in detail to confirm the fulfilment of
the required service life. No degradation of the mechanical properties was found after exposure
to thermal cycles or hygrothermal conditions at temperatures below its glass transition, which
would correspond to the scenario of groundwater ingress. The previously determined highest
service temperature of 80ºC was found conservative, as annealing at 100ºC increases its strength,
allowing this service temperature. All results suggest it is a suitable candidate for the insulation
of steel medium pipes. The fast embrittlement upon exposure to hot moisture, as would occur
due to permeation of the heat carrier through a plastic pipe, prevents its recommendation for
this case.
The lower TRL research involved the re-evaluation of the complete sandwich assembly, from a
cradle-to-cradle perspective. The foamability of polybutene-1 was explored, with the ultimate
target of allowing the manufacturing of the sandwich element out of a single material, as to
facilitate its recycling. Favourable grades for foaming were identified, confirming its foamability. The
relationships between process parameters and the foam’s microstructure were evaluated. Foams
in the required size for mechanical and insulating properties characterization were successfully
produced. Mechanical properties of PU from state-of-the-art flexible plastic medium pipes fall in
the prediction bands obtained from the produced PB-1 foams. This provides confidence on the
suitability for the application.
plasticization effect induced by CO2 in the polymer melt and determination of the melting point depression is required for the establishment and optimization of the foaming processing window.
In this paper, a method for the determination of the melting point through image analysis is presented, validated and used for the study of PB-1 – CO2 solutions. The obtained results through image analysis agree with those obtained with differential scanning calorimetry, validating the
method. The CO2 - induced melting point depression of PB-1 was determined as ΔT = 140C.
foam bonds the medium pipe with the casing, providing an insulating function as well as a load
bearing function. The high toxicity of the di-isocyanates required for its manufacturing triggers
the need for a replacement. In this work, alternatives have been researched and developed
considering the requirements of the circular economy. Two technology readiness levels (TRL)
were covered. The higher TRL involved the evaluation of commercially available polymeric foam
alternatives. Polyethene terephthalate foam was selected, and its ageing behaviour concerning
degradation sources inherent to the application was studied in detail to confirm the fulfilment of
the required service life. No degradation of the mechanical properties was found after exposure
to thermal cycles or hygrothermal conditions at temperatures below its glass transition, which
would correspond to the scenario of groundwater ingress. The previously determined highest
service temperature of 80ºC was found conservative, as annealing at 100ºC increases its strength,
allowing this service temperature. All results suggest it is a suitable candidate for the insulation
of steel medium pipes. The fast embrittlement upon exposure to hot moisture, as would occur
due to permeation of the heat carrier through a plastic pipe, prevents its recommendation for
this case.
The lower TRL research involved the re-evaluation of the complete sandwich assembly, from a
cradle-to-cradle perspective. The foamability of polybutene-1 was explored, with the ultimate
target of allowing the manufacturing of the sandwich element out of a single material, as to
facilitate its recycling. Favourable grades for foaming were identified, confirming its foamability. The
relationships between process parameters and the foam’s microstructure were evaluated. Foams
in the required size for mechanical and insulating properties characterization were successfully
produced. Mechanical properties of PU from state-of-the-art flexible plastic medium pipes fall in
the prediction bands obtained from the produced PB-1 foams. This provides confidence on the
suitability for the application.