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For some closed cell foam insulation products, the thermal conductivity increases at low temperatures, contrary to single thermal resistance values provided by manufacturers. This phenomenon has been demonstrated in various polyurethane and polyisocyanurate insulations. The reduction in thermal performance has been attributed to the diffusion of air and blowing agent through the foam and to the condensation of blowing agent. Aging processes such as freeze-thaw cycling, moisture accumulation, and polymer degradation further increase thermal conductivity. The initial cell structure plays a role in dictating the thermal performance. To further understand the loss of thermal performance in closed cell foams, microstructure and chemical characterization was performed in this study. The aging behavior of foam insulations was analyzed by imaging foams with SEM and by measuring foam. Changes in the polymer physical attributes were identified and compared to increases in thermal conductivity. This project also used gas chromatography and quantified changes in pentane concentration in polyisocyanurate foams that have undergone aging

In this study, functionally graded foam made of Inconel 625 superalloy was successfully produced using the template replication method, with open-cell polyurethane foams as a precursor. The products have a similar pore morphology as the templates and adjacent layers were successfully sintered together by particle bonding. Sound absorption experiments on graded metallic foams reveal that the sound absorption at particular frequency ranges can be improved by various permutations of foam layers. For graded foam of two distinct pore sizes, a mathematical equation was proposed to predict the location of the intersection point of the sound absorption curves, thereby aiding in graded foam design. An increase in sound absorption coefficients by resonance-like effects can be introduced before the intersection points by placing the foam layer of smaller pore size nearer to the sound source. The sound absorption performances can be further customized when the thickness proportion of the pore sizes is changed and when the number of distinct pore sizes used is increased. The sound absorption performance at lower frequencies is generally boosted by resonance-like effects when the layer of foam with the largest pore size is placed furthest from the sound source. Given the same composition of foam with a fixed thickness proportion of pore sizes, one can introduce resonance-like effects to improve the sound absorption performance compared to other permutations while possibly satisfying weight requirements in practical applications. This study provides valuable insights and mathematical guidelines in the design and manufacturing of functionally graded metallic foam for specific applications.

In recent years, shape memory polyurethanes have gained substantial attention and are targeted for a range of smart and functional materials. In this work, the development of nanocrystalline celluloses (CNCs) enabled polycaprolactone-based shape memory polyurethane biocomposite using an in situ one-pot reactions is reported. The incorporation of up to 10 wt. % CNCs resulted in a remarkable enhancement in the tensile strength at yield (from 0.2 MPa to 7.2 MPa), tensile strength at break (167% improvement), and modulus of elasticity (from 3.5 to 139.3 MPa) while maintaining the elongation at break. This was attributed to the simultaneous action of CNCs as a nucleating agent for crystallization and highly compatibilized reinforcing agent of the network. Moreover, the in situ incorporation of CNCs enhanced the shape memory capability of polyurethanes, which enables its employment in functional material applications, such as the biomedical sector. The intimate interfacial adhesion between the CNCs and the polymer matrix, which promoted shape fixating and recovery, was confirmed by fractured surface morphology studies. Rheology characterizations provided strong evidence that the addition of CNCs increased the shape fixity attributed to the stiffness of CNCs below the glass transition temperature (Tg) compared to the neat PU in conjuncture with the higher Tg of CNCs. Overall, the developed polymer nanocomposites are appealing materials for biomedical applications.

Acknowledgements: This work has been supported by EPSRC, via an industrial CASE award (for YC) with AWE (EP/R511870/1). © British Crown Copyright 2020/AWE., Tensile stress–strain testing and creep testing have been carried out on a polyurethane rubber, at three temperatures, with and without either particulate or short fibre alumina reinforcement. A previous paper reported concerning composites with particulate reinforcement and the present work is focused on the effect of the fibres. The samples were made via a blending and extrusion process that produced a certain degree of fibre alignment (along the direction of loading). Prior milling procedures were used to produce fibres with two different ranges of aspect ratio (with averages about 10 and 16). When expressed as true stress–strain relationships, all materials exhibit approximately linear responses. The dependence of stiffness on the volume fraction and aspect ratio of the reinforcement was found to conform well to the Eshelby model predictions. Moreover, the creep behaviour of all of the materials can be captured well by a Miller–Norton formulation, using the average matrix stress predicted by the Eshelby model. A striking conclusion is that it is both predicted and observed that short fibres are much more effective in reducing the creep rate than is the case with particles.

In this work, softeners obtained from various companies were applied to the polyamide6.6/polyurethane fabrics which are used in sportswear industry using impregnation and exhaustion methods; water vapor permeability were determined for humidity control, air permeability and capillarity tests of these fabrics were studied. In addition, the wool hydrolysate obtained from the waste wool was also applied to these fabrics by using exhaustion method and the fabric properties were compared. In order to investigate the washing resistance of the process, experiments were performed with 1% and 3% potassium aluminum sulfate KAl(SO₄)2 and aluminum sulfate Al2(SO4) under the same conditions. The chemical and morphological surface properties of the fabrics were examined by using X-ray photoelectron spectroscopy (XPS). It was observed that the capillarity, water vapor and air permeability, and handle values of fabrics treated with wool hydrolysate were better and more resistant to consecutive washings than the fabrics treated with commercial recipes. Furthermore, this process did not have a side effect on the color difference and whiteness values of the fabrics treated with wool hydrolysate. Thus, an example of sustainable, economical and environmental study was done.

Flexible polyurethane foam (FPUF) is the most used polyurethane, but the highly flammable characteristic limits its widespread usage. In this work, ZIF-8@Ti3C2Txwas synthesized to reduce the heat and toxic gases of FPUF. Flame-retardant FPUF was characterized by cone calorimeter (Cone), thermogravimetric analysis/fourier-transform infrared spectroscopy (TG-FTIR), tensileand compression tests. Compared with pure FPUF, these results showed that the peak of heat release rate (PHRR), total heat release (THR), CO and HCN of FPUF6 decreased by 46%, 69%, 27% and 43.5%, respectively. Moreover, the tensile and compression strength of FPUF6 demonstrated a 52% and 130% increment, respectively. The superior dual metal catalytical charring-forming effect and physical barrier effect of ZIF-8@Ti3C2Tx were achieved. In summary, a simple and reliable strategy for preparing flame-retardant FPUF with reinforced mechanical and fire safety properties was provided.

In households, considerable costs are related to energy losses, which are a consequence of maintaining comfortable living temperatures. Improved isolation and utilization of energy harvesting devices is the key to reducing energy losses and the related costs. Polymeric solar absorbers are cost-effective solar energy harvesters that can significantly reduce the energy cost for individual households. One of the concerns related to polymers is their flammability. To mitigate the flammability risk, the present work explores the development of solar absorber paints with flame-retardant properties. Bridged 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) derivatives (NED and PHED) in concertation ranges of 10–15 wt% were used in a polyurethane-based matrix to demonstrate the effect of additives on the fire retardancy of the material. Additionally, the rheological and thermal properties of the composite materials were evaluated and described. Furthermore, aluminium and PPS (polyethylene sulphide) substrates were coated with solar absorber paint based on a 15% FR (fire retardant) additive formulation, for which the thermal stability at 150 °C for 655 h was evaluated. It was discovered that PHED is more compatible with the polyurethane matrix than NED, and as expected, a greater amount of FR additives resulted in improved flame retardancy. The long-term stability of absorber paint coatings on Al and PPS was also successfully confirmed by confirming stable solar absorptance and thermal emittance. In future prospects, we believe that the flame retardancy of polyurethane-based coatings could be further improved, and the utilization of covalently bonded FRs should also be considered.

This work aims to study the effects of the size of water hyacinth fiber (WHF) on the properties of a rigid sound absorption material from recycled palm oil-based polyurethane foam (PUF) Polyurethane Foam Compositecomposite. By fixing the NCO index of 100 with the WHF content of 1%wt, the sizes of WHF were varied from 80, 40, and 20 mesh to study the properties of PUF. The compression strength, optical microscopy, and sound absorption coefficient (SAC) of the PUF composite were tested. Reducing the mesh size of WHF from 80 to 20, the compression strength of PUF increased from 0.33 to 0.47 N/mm2. PUF with a WHF mesh size of 80 and a SAC value of 0.92 was suitable for sound absorption. Therefore, the PUF derived from both water hyacinth and used palm oil could be used as a promising alternative green material for sound absorption application.

In this paper, a new polymer composite was prepared using polypropylene and Fe2O3 microparticles. Effect of weight fraction and microparticle size on the tensile strength and Young's modulus were studied experimentally. Also, SEM image of fracture surfaces was investigated. The experimental design of experiments was performed using a response surface methodology. Tensile test specimens consist of 5–20% Fe2O3 microparticles of five different sizes from 33 μm to 125 μm. The results showed that by increasing the weight fraction of the reinforcement, Young's modulus was improved compared to the pure sample, and elongation percentage was decreased. Also, as the size of the microparticles increased, the effect of the particles on the mechanical properties of the PP/Fe2O3 composite was reduced. For specimens containing 20wt.% of Fe2O3 and particle size higher than 91 μm due to the agglomeration of microparticles, the tensile strength reduced by 16%. However, if 20 wt.% of Fe2O3 microparticles with a particle size less than 33 μm were added, the use of these microparticles would increase Young's modulus by 300% and the tensile strength by 60%. Finally, it has been shown that dramatic improvements in the mechanical properties can be achieved by the incorporation of a suitable amount of Fe2O3 microparticles in polypropylene.

The research carries out the simulation of the growth of the polyurethane foam inside a mold, in order to optimize the resources. The aim finds the accurate option within a production process both in the incorporation of a new product as in improving an existing one. Using the Moldex3D program, the project obtains a mathematical model to calculate parameters such as the viscosity of the material, pressure, volume, temperature, curing, foaming, heat capacity, thermal conductivity and mechanical properties of the material. The density obtained for the material analyzed experimentally is 59.09 kg·m−3 with a uniform watering at the base with a 10 degrees mold inclination with 1740 g of material and air outlets that help to obtain better conditions of mold, seeking to reduce the time used by 25% and reduce manufacturing costs.

SiC porous ceramics (SPCs) are key functional medium materials, which are widely applied as porous burners. However, SPCs produced via the polyurethane sponge replica technique usually exhibit a randomly distributed cellular structure, leading to vulnerability and a low combustion efficiency for the porous burners. In this study, SPCs were structurally designed via novel 3D printed resin template technique; this endowed the SPCs with synergistically optimized strength and combustion characteristics. SPCs containing tetrakaidecahedron, octahedron and cubic cells were successfully prepared via SiC slurry coating and sintering in air. The cell parameters determined the strength and combustion properties of the SPCs. The SPCs containing cubic cells exhibited the largest strength and strain, because more struts were present parallel to the loading direction; this is more advantageous for stress bearing compared to those vertical to the loading direction. The tetrakaidecahedron cell facilitated the formation of a disturbance effect within the SPCs to a higher extent than the cubic and octahedron cells, thereby enhancing the heat exchange performance between the fluid and porous framework. Hence, the SPC with tetrakaidecahedron cells exhibited the best combustion properties, which resulted in the highest surface temperature and lowest pollution emission.

Fatigue and rutting phenomena are major distresses in asphalt pavements. Asphalt mixture properties are highly dependent upon the asphalt binder and the mastic behavior. The purpose of this study was to investigate the behavior of the asphalt binder and the mastic, modified by the synthesized polyurethane, at high and intermediate temperatures. The filler/asphalt binder ratio (by weight) was 1.0. The dynamic shear rheometer (DSR) was used to measure fatigue (G∗sin δ) and rutting (G∗/sin δ) parameters. In this study, the multiple stress creep and recovery (MSCR) test was also utilized to calculate the rutting potential of the asphalt binder and the mastic. Parameters of the non-recoverable compliance (Jnr) and the percentage recovery (%) were evaluated at high temperatures. The obtained results indicated that the synthesized polyurethane improved the rutting and fatigue properties. There was a significant correlation between the asphalt binder and the mastic in terms of the complex modulus (R2 = 0.9958), rutting (R2 = 0.9944), and the non-recoverable compliance (R2 = 0.9707). For the fatigue parameter (R2 = 0.9852), the complex modulus (R2 = 0.9855), and the phase angle (R2 = 0.8262), significant relationships were observed between the asphalt binder and mastic samples at intermediate temperatures. Overall, the chemical reaction between the filler and the asphalt binder could be effective in different behaviors of the mastic and asphalt binder. There was a 112%–164% increase in the G∗sin δ parameter for mastics, compared to that of the asphalt binder. The complex modulus was 6 times higher by adding the filler content.

This paper presents an experimental investigation about the effect of elevated temperature on the mechanical properties of two polyurethane (PUR) foams, with densities of 40 kg/m3 and 93 kg/m3. The experimental campaign included shear and compressive tests over a temperature range of 20°C–200°C, performed to assess the degradation of the mechanical properties of the PUR foams with temperature. To validate the diagonal tension shear test method adopted in this investigation, a numerical study was also performed, namely to assess the (shear) stress state developed within the foam. The results obtained validated the adopted test procedures, showing that the compressive and shear responses are strongly affected by elevated temperature, due to the softening of the polymeric material when it undergoes the glass transition process. For the temperature range considered in this study, both strength and modulus in shear and compression present an approximately linear reduction with temperature.

Exploration of the effect of crosslinking point structures on elastomer properties is significant in the formulation design and performance optimization of elastomers. In the work, we used an equal molar random copolyether of hydroxyl terminated 3,3-bis(azidomethyl)oxetane and tetrahydrofuran (PBT) as a prepolymer, and two PBT elastomers with different crosslinking point structures were prepared by reacting PBT with polyfunctional isocyanate compound N100 and TMP/HDI. FTIR spectrum analysis and swelling tests indicated that N100 crosslinked elastomer S0 and TMP/HDI crosslinked elastomer S4 had an identical chemical crosslinking network. For elastomer S0, hydrogen-bonded urea carbonyl and hydrogen-bonded carbamate carbonyl existed simultaneously, whereas only hydrogen-bonded carbamate carbonyl existed for elastomer S4. Low-field nuclear magnetic resonance measurements analysis indicated that hydrogen-bonding association was among elastomer crosslinking points. Dynamic mechanical analysis showed that the stronger urea carbonyl hydrogen bonding among crosslinks provided elastomer S0 with a lower glass transition temperature (− 37 °C) and a lower modulus loss factor. Elastomer S4 with weaker carbamate carbonyl hydrogen bonding among crosslinking points yielded a higher glass transition temperature (− 30 °C) and higher modulus loss factors. Elastomer S0 presented a higher tensile modulus, and elastomer S4 presented a higher tensile strength and elongation-at-break. These findings provided an experimental and theoretical basis for adjusting mechanical properties of end-crosslinked elastomer by constructing different crosslinking point structure.

The sustainability of production systems in wood processing, wood industry, and wooden waste disposal is an important issue for European industry and society. Proper development of products based on renewable wood resources gives an opportunity to provide materials with long-term environmental, social, and economic sustainability. This study aims to establish a new way of forestry and agricultural waste materials utilization by synthesis of bio-based polyols and manufacturing of polyurethane wood composites (PU-WC). The first part of this paper describes the liquefaction of wood shavings at a temperature of 150 °C for 6 h in three different solvents—glycerol, poly (ethylene glycol) and their mixture in a 1:1 ratio. The second part deals with the synthesis of polyurethane (PU) resins containing 90% of biopolyol. Eight sets of materials with different NCO:OH ratios were obtained in a one-step method using a hydraulic press. These materials were characterized, and the material with the most promising properties was selected for polyurethane wood composites production. Composites with 40%, 50%, 60%, and 70% of wood shavings were obtained. The addition of filler caused an increase in flexural strength, Young`s modulus, hardness, and impact strength. Scanning electron microscopy (SEM) showed good adhesion between the polymer and the filler. The optimum filler content is between 50 and 60% by weight of the composite. The presented study provides a significant step toward a greener alternative for materials produced mainly from non-renewable resources.

Modified reduced graphene oxide (rtgo) was prepared by using γ - isocyanate propyl triethoxysilane (IPTS) as modifier. Graphene / polyurethane nanocomposites were prepared by in-situ polymerization. Graphene / polyurethane composites were characterized by scanning electron microscopy, TGA, DIN abrasion and electronic universal testing machine. The effects of different reaction formulations and graphene addition on the wear resistance and mechanical properties of the composites were studied. The results show that the wear resistance and tear resistance of the composite can be greatly improved after the functional graphene is compounded with polyurethane.

A kind of organic/inorganic composite material composed of waterborne polyurethane and sepiolite was prepared in this work. Sepiolite was organically modified by three kinds of silane coupling agents, and then compounded with waterborne polyurethane through layer-by-layer method in order to prepare composite materials. X-ray diffraction (XRD) and Fourier transform infrared (FTIR) show the crystal and chemistry structure of sepiolite samples, and confirmed the preparation of organic sepiolite. Scanning electron microscope (SEM) and energy dispersive X-ray spectroscopy (EDS) showed the surface microstructure and elemental content of sepiolite and organic sepiolite, and was consistent with the XRD results. Transmission electron microscope (TEM) examination of waterborne polyurethane composites surfaces showed that sepiolite particles were regularly dispersed in the waterborne polyurethane matrix. Thermal resistance of waterborne polyurethane composites was determined by thermogravimetry analyzer (TG) and derivative thermogravimetry analyzer (DTG), differential scanning calorimetry (DSC), gas chromatography (GC), and mass chromatography (MS). Mechanical behavior was examined by tensile strength tester, showed higher break strength than that of the control waterborne polyurethane. Therefore, organically modified sepiolite was considered to be a kind of wonderful inorganic material that could be used to improve the thermal stability and mechanical property of polymer.

The development of polymer-based composites with self-healing and recyclable capability has attracted the attention of several researchers for resource recycling and environment protection. In this work, Halloysite nanotubes (HNTs) reinforced polyurethane materials (PU) with self-healing and recyclable ability were constructed by in situ polymerization method. The mechanical, thermal amd morphological properties of PU and related composites were studied. The morphology of samples fracture surface ensured the homogeneous dispersion of HNTs in the polymer matrix. Moreover, thermal stability was improved with the incorporation of the HNTs. The tensile test showed strength increased with HNTs content increased. The tensile strength of composites increases from 23.38 to 34.92 MPa at 2 wt% HNTs. Therefore, the designed strategy provides a simple approach for preparing high mechanical properties, reprocessing and self-healing ability polyurethane composites.

Polymer is a kind of high molecular elastic material. The polymer cement mortar composite material formed by mixing it with cement mortar has the advantages of light weight, high strength, and good durability compared with traditional mortar materials. The effect of polyurethane polymer content on mechanical properties and microstructure of polyvinyl alcohol (PVA) fiber cement mortar was studied by compressive test, flexural test, and SEM analysis. The test results show that as the content of polyurethane increases, the compressive strength gradually decreases, and the flexural strength gradually increases. The addition of polyurethane helps to optimize the microstructure of PVA mortar, improve the compactness of the material, and enhance the bending resistance of the mortar. The mechanical properties of materials obtained from the experiment can provide references for engineering applications.

Carbon nanomaterials were used to enhance desired properties of polymeric matrices. Combining varied carbon nanofillers with dissimilar dimensions can lead to synergy through effective dispersion. In this work, mechanical, thermal, acoustic, and dielectric properties of polyurethane (PU) hybrid nanocomposites were investigated. PU containing multi-walled carbon nanotubes (MWCNT) and graphene nanoplatelets (GNPs) were used to evaluate the effects of single and hybrid nanofillers on the final properties of nanocomposites. The results showed a synergistic effect between nanofillers, in which the hybrid nanocomposites exhibit better performance, relative to the single inclusion of the nanofillers. These hybrid nanofillers improved dispersion quality in the polymer matrix due to the formation of a GNPs/CNTs 3D architecture, in which tensile strength, thermal conductivity, acoustic transmission loss, and dielectric constant of PU were enhanced by about 43%, 5%, 51%, and 13% at 0.25 wt% loadings, respectively. The overall properties of the hybrid nanocomposite revealed the superiority over the single nanofiller system in multifunctionality, evaluated by a performance index.

Polyurethane mixtures are regarded as novel polymer pavement materials that can overcome the shortcomings of poor mechanical properties and loose particles of open-graded friction course (OGFC). Ow...

Melamine was grafted to a polyurethane (PU) frame and utilized for cross-linking PU via amino groups. The degree of crosslinking and the solution viscosity increased notably after grafting melamine due to the formation of crosslinks. The thermal transition of the soft segment was not significantly affected, but the glass transition was observed at a slightly higher temperature in case of the grafted melamine. Melamine-mediated crosslinking increased not only the breaking tensile stress but also the shape recovery performance of PU. In addition, crosslinked PU was more flexible at low temperature than unmodified PU. Overall, melamine-mediated crosslinking improved the tensile resistance to stress, the recovery tendency to the initial shape, and the flexibility with minor changes in the thermal transition, tensile strain, and shape retention at a low temperature.

Airless tires are the best innovation for military tactical vehicles in carrying out the Army's main tasks for military tactical even peace support operations and war military operations. However, in its development there are still imperfections in the results, its fabrications in the adhesion between polyurethane and natural rubber. Therefore, the researchers aimed to develop the adhesion between polyurethane and natural rubber. In this research, a quantitative experimental method was used, namely by varying the hardness of natural rubber and polyurethane to determine the right hardness for airless tires for maximum adhesion. The problem that occurs is that the adhesive glue with the tire tread is problematic, resulting in a tire tread condition without air being released. In carrying out the research, a function test was carried out with a planned weight of 4,500 Kg. Based on the results of the tests that carried out, the correct result was obtained, namely the elongation at break of the most appropriate type of polyurethane L100, which was 9.287 MPa. In order to achieve the goal, namely the appropriate level of elasticity between polyurethane and natural rubber so as to be able to glue the spokes and tire treads, in the end the wheel rotation will rotate according to the desired elasticity.

This work aims to evaluate the mechanical and flammability behavior of the green laminate polymeric composite of polyurethane (PU) derived from vegetable oils with reinforcement of cotton fiber (CF) unidirectional fabrics and added alumina trihydrate (ATH). Specimens of PU and PU doped with different ATH contents (10%, 20%, and 30%) were manufactured by casting process and the CF/PU composites and CFs/PU composites with ATH by the vacuum bag process, with three different stacking sequences (fibers oriented on 0°, ± 45°, and 90°). Vertical and horizontal tests of flammability were performed, and the CFs/PU composite showed a higher burning rate than the pure polymer, the difference was a 50% higher speed. However, the addition of ATH to the composite showed an enhancement of its flammability, the smallest burning rate was exhibited. The PU/CFs laminate (0°) exhibited a tensile stiffness and strength twice that presented by the pure PU. Through the SEM (scanning electron microscopy) investigation, when, ATH was added to the composite, there was a decrease in the fiber-matrix interface quality, presence of voids, and larger occurrences of pull out, which explains, besides a smaller volumetric fraction of reinforcement exhibited, decrease in tensile strength.

A reactive hot-melt resin (polyurethane) was used to manufacture Guadua composites with a certain flexibility, high processing speed, good initial rigidity, and high temperature performance. These composites can support a moderate tensile stress, allow for large strains at low stresses, and have a low density and a working temperature range of -40 °C and 110 °C. During the flexural test, bamboo composites with reactive polyurethane matrix do not break or fail during the test. A polyurethane-based reactive hot-melt resin was characterized by tensile tests, Shore hardness tests, differential scanning calorimetry, and thermogravimetry. Besides, a composite material was made with Guadua fiber and polyester matrix, which had a greater strength in the test of tension and flexion, although it had a lower percentage of elongation than the composite material with reactive polyurethane. Guadua fiber can increase the strength by 266% of polyurethane matrix and 228% of polyester matrix.

To achieve adaptation to the heat dissipation effect of electronic devices in the 5G era and improvement of the anisotropic thermal conductivity of the insulating polymer, three-dimensional (3D) PU@BNNS-OH network structure was constructed via layer-by-layer assembly with polyurethane (PU) foam as the robust skeleton of three-dimensional structure, and hydroxylated boron nitride nanosheet (BNNS-OH) as thermal conductive filler. Then PU@BNNS-OH was composited with polyvinyl alcohol (PVA) via microwave-assisted curing method to get the final thermal conductivity composites (PVA/PU@BNNS-OH). The result showed that the interconnected thermal conductivity network was significantly effective in improving the anisotropic thermal conductivity of the composite with high-temperature endurance and moderate mechanical property. When the BNNS-OH coating is 10 wt%, the optimal thermal conductivity of the composite is 4.68 W· $${\mathrm{m}}^{-1}$$ · $${\mathrm{K}}^{-1}$$ and the thermal conductivity enhancement efficiency is 45.50, which is significantly higher than others reported in the literature. Both the finite element analysis and thermal infrared analysis indicated that the thermal conductivity of the composites was significantly improved and paved the way for its potential application. The present microwave-assisted synthesis strategy is fast and energy-saving and can be widely used for synthesizing different insulated polymer-based thermal interface materials.

Polyurethane polymer grouting material has been effectively applied and promoted in the repair of road damages in nonfrozen areas. However, this material undergoes an exothermic reaction in the curing stage, which can cause a thermal disturbance in the frozen soil subgrade. To minimize the influence of the thermal disturbance of the polyurethane polymer grouting material in the repair of the frozen soil subgrade, an experiment was conducted to reduce the heat of the curing reaction under the influence of different proportions of a foaming agent, high-boiling point solvent, catalyst, and prepolymer. According to these test results, a proportioning scheme for the low exothermic polymer grouting material was formulated. The results indicated that the curing reaction temperature threshold of the polyurethane polymer grouting material was negatively related to the proportion of physical foaming agent (HCFC-141b) and high-boiling point solvent and positively related to the proportion of water weight. In the three stages of rapid temperature rise, slow temperature rise, and constant temperature, the rate of the temperature rise of the low exothermic polymer grouting material was lower than that of the common polymer, and the curing temperature threshold was 30.34% lower at a value of 101°C. At a density of 80 kg/m3, the compressive strength and tensile strength of the low heat release polymer grouting material were lower than those of the common polymer grouting material, thereby ensuring the excellent performance of polyurethane foam and providing a theoretical reference for the rapid repair of frozen soil roadbed diseases.

Thermal ageing at elevated temperatures is the standard method to determine the service life of pre-insulated district heating pipes nowadays. However, DH pipes are also subjected to axial movements which can affect the adhesion strength between the polyurethane foam and the service pipe. This contact surface is usually exposed to the highest temperatures. In this project, DH pipes were aged at elevated temperatures and at the same time cyclic axial loads were applied. Two DH pipes were only exposed to thermal ageing at 130 and 140 °C, while two other similar pipes were also exposed to cyclic axial loads. The adhesion strength was evaluated as the function of ageing time using the RISE plug method. Any changes in the chemical structure of the PUR samples were also observed using Fourier transform infrared spectroscopy. Comparing the results in this investigation, we found that the degradation of the mechanically loaded pipes was significantly faster than the degradation observed in non-loaded pipes at the same ageing temperatures. The FTIR study revealed that cyclic mechanical loads accelerated the chemical degradation of the PUR foam during thermal ageing. This study shows how important it is to consider all influencing factors in accelerated ageing. The methods presented here should be considered as an alternative to thermal ageing at high temperatures because the combination of mechanical and thermal loads reproduces better the real operating conditions. It is even of bigger interest when energy from different sources will be connected to the fourth generation of DH networks, which can cause more temperature fluctuations.

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 (Ramnas, 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.