TPU Composites Research Articles

Synthesis of CoMn‐LDH@MXene Hybrid Materials as Flame Retardant to Effectively Improve the Fire Safety of Thermoplastic Polyurethane

AbstractIn recent years, MXene 2D materials have shown good performance in enhancing the flame retardant properties of composite materials, but it is still tricky to improve the compatibility with the polymer matrix. This work explores a simple method for the synthesis of MXene based nanohybrids (CoMn‐LDH@MXene) by hydrothermal synthesis using MXene and layered double hydroxides (CoMn‐LDH) to construct a flame retardant system with excellent performance. The results show that the MXene nanosheets are less built up and more dispersed in the TPU collective due to the inclusion of LDH, giving the TPU composites excellent flame retardant and smoke suppressant properties. Compared to TPU without flame retardant, TPU composites with 2 wt% CoMn‐LDH@MXene reduced PHRR by 33.7 % and THR by 28.7 %. The TPU/2wt %CoMn‐LDH@MXene composites also showed better flame and smoke suppression performance, PSPR, TSP, PCO and PCO2 were reduced by 44.4 %, 22.7 %, 37.7 % and 27.2 % respectively, the production of Hydrocarbons and HCN were also reduced. Barrier effect of transition metal oxide catalysed carbon layer formation, combustion blocking effect of hybrid material nanosheets, cooling effect of water vapour from thermal decomposition of LDH and the gas phase dilution effect are the main reasons for the increased fire safety of TPU composites.

Designing of layered double hydroxide, metal oxides, and borate‐reinforced thermoplastic polyurethanes composites

AbstractThermoplastic polyurethanes (TPUs) are widely used in automotive, medical, and marine applications due to their excellent properties such as high tensile strength, flexibility, and durability. However, the presence of isocyanate groups in TPUs increases their flammability and produces toxic gases during combustion, limiting their application. Here, the study aims to modify TPUs to improve their flame‐retardant behavior. Various fillers such as metal oxides, Layer double hydroxides (LDH), and borates were synthesized and added into the TPU matrix by using extrusion and compression molding. At a 10% loading of Zinc‐Magnesium oxides, a limiting oxygen index (LOI) of 25% was achieved, along with no dripping and complete burning cessation within 20 s. Magnesium aluminium LDH exhibited maximum flame retardancy at a 5% loading, with an LOI of 25%, burning cessation within 23 s without dripping, and a V1 rating. Overall, this research aims to develop TPU composites with improved fire safety properties by incorporating various additives. The synthesized additives showed potential for enhancing the mechanical, thermal, and flame‐retardant properties of TPU.

Effects of Fabrication Process of Conductive TPU Composites on Dual-Function Gas Sensor and Energy Devices

Effects of Fabrication Process of Conductive TPU Composites on Dual-Function Gas Sensor and Energy Devices

Realizing balanced flame retardancy and electromagnetic interference shielding in hierarchical elastomer nanocomposites

The combination of electromagnetic interference (EMI) shielding performance and flame-retardant property is essential for applications in the field of electronics and electrics. To date, there have been few successful cases in achieving such portfolios, due to the different mechanisms and even mutual exclusivity of these two attributes. Herein, an ammonium polyphosphate@chitosan@carbon nanotube (APP@CS@MWCNT) core-multishell hybrid was synthesized by microencapsulation technology. Then, the hybrid was introduced into TPU matrix to fabricate TPU composites, acting as surface layer. Meanwhile, MXene film was used as intermediate layer to construct hierarchical TPU composites. The obtained results showed that after introduction of 1 wt% APP@CS@MWCNT hybrid, the peak of heat release rate (PHRR) and the peak of smoke produce rate (PSPR) of TPU composites decreased by 67.4% and 35.6%, respectively, compared with those of pure TPU. Owing to multiple reflection losses, interface polarization losses, and charge carrier movement-induced thermal dissipation, TPU/15AC@4M−SW exhibited the highest EMI shielding performance, and obtained shielding effectiveness values of 35.7 dB and 38.9 dB in X band and K band, respectively.

Effect of multidimensional filler hybridization on the mechanical properties of thermoplastic polyurethane composites prepared by selective laser sintering

AbstractThis paper aims to improve the tensile strength and thermal stability performance of selective laser sintered thermoplastic polyurethane elastomer/spherical alumina/graphene oxide/silicon nitride whisker (TPU/Al2O3/GO/Si3N4ws) composites by investigating the synergistic enhancement of fillers with different dimensions, and solving the problem of excessive porosity, material delamination, and low tensile strength during sintering of semi‐crystalline polymer TPU problems. The results show that the synergistic effect of multidimensional fillers leads to the tensile strength of TPU composites up to 12.1 MPa at 8.9 wt% Al2O3, 0.1 wt% GO and 1.0 wt% Si3N4ws hybrid fillers, which is 38.9% higher than that of pure TPU. In addition, the elongation at break of TPU/Al2O3/GO/Si3N4ws composites was maintained at 254%, which still has good toughness. The effect of fillers on the selective laser sintering (SLS) process, thermal stability, melting, and crystallization behaviors of the composites was also investigated in this work. In general, the multidimensional filler compounding synergistically constructing a three‐dimensional network structure has some improvement on the thermomechanical behavior of TPU composites with a fixed mass component addition.

Achieving superior fire safety for TPU 3D‐printed workpiece with EP/PBz/PDMS coating

AbstractTo reduce the possibility of the TPU 3D‐printed workpiece causing a fire, a flame‐retardant coating containing phosphorus, nitrogen, silicon, and benzene rings was fabricated on the TPU workpiece surface. When the MSDS content in the coating is 30 phr, the coated TPU composites LOL reached 29.5%, achieved V‐0 rating at the UL‐94 test and its peak heat release rate was reduced by 71.3% in the cone calorimeter test. When the MSDS content was increased to 20 phr, a continuous char layer was observed. Moreover, the EP/PBz/PDMS coating improved the thermal stability and tensile strength of TPU 3D‐printed workpiece. When the coating burns, it forms a dense charcoal layer, which isolates oxygen. The substrate wrapped by the charcoal layer undergoes a carbonization reaction when heated, preventing the substrate from burning further, resulting in improved flame retardancy, smoke suppression and dripping resistance of TPU.

Highly enhanced thermal conductivity of TPU composites with segregated network constructed by the in-situ reduction of copper

Cu@TPU composite particles with a structure of TPU core and Cu particles shell were fabricated by in-suite reduction of Cu on the surface of TPU granules. The Cu@TPU composites were then prepared by the hot compression of the as-prepared core-shell particles. The Cu@TPU composite granules were characterized by X-ray photoelectron spectroscopy, X-ray diffraction, thermogravimetric analysis and scanning electron microscopy, which verified that the outer layer of core-shell structure was Cu particles and the connection between Cu and TPU was chemical bonding. The cross-section of Cu@TPU composites showed typical pattern of segregated structure and the surface of those was covered by a layer of Cu particles. With the stacking effect of the special location of Cu and the chemical connection between Cu and TPU, the Cu@TPU composites exhibited a high thermal conductivity of 3.2146 W/m K at 23 vol% filler loading, which was 2.6 times to that of Cu/TPU composites fabricated through simple blending. The TC data of the composites were correlated with Foygel’s model. In addition, the dielectric properties and electrical conductivity of the composites were measured.

Temperature-Dependent modelling of tension, in-Plane shear, and bending behaviour in non-isothermal thermo-Stamping process simulation of unidirectional UHMWPE fibre reinforced thermoplastic TPU composites

This study proposes a macroscopic finite element modelling and simulation approach considering the temperature dependency of both in-plane membrane and out-of-plane bending behaviours. This approach enables the investigation of the effect of the deformation mechanisms on the quality of the formed thermoplastic composite parts during the thermo-forming process. The temperature-dependent constitutive model of the in-plane tensional behaviour is considered linear, whereas the in-plane shear stiffness is modelled based on the nonlinear hypoelastic constitutive equation. The out-of-plane bending behaviour is considered by decoupling the membrane and bending method. A numerical simulation strategy is developed by implementing the ABAQUS software via a VUMAT subroutine. Moreover, a modified method is introduced for the qualitative and quantitative assessment of the wrinkling intensity generated in the forming process. The validated strategy is used to investigate the influences of the various temperature conditions of the forming process and the underlying mechanisms to optimise the thermo-stamping process.

Boosting fire safety and mechanical performance of thermoplastic polyurethane by the face-to-face two-dimensional phosphorene/MXene architecture

• A black phosphorus-MXene@polydopamine nanohybrid was synthesized. • The TPU/BP-MXene@PDA nanocomposite simultaneously showed reinforcing and toughening effects towards TPU. • The TPU/BP-MXene@PDA nanocomposite could be achieved excellent thermal stability, mechanical properties and flame retardancy. • A synergistic flame-retardant mechanism between black phosphorus and MXene in the TPU were discussed and clarified. Black phosphorus (BP), as one of the most promising fillers for flame retarding polymer, has been seriously limited in practical application, due to the agglomeration and poor structural stability challenges. Here, the BP was modified by MXene and polydopamine (PDA) via ultrasonication and dopamine modification strategy to improve the structural stability and dispersibility in the matrix. Then, the obtained (BP-MXene@PDA) nanohybrid was employed to promote the mechanical performance, thermal stability, and flame retardancy of thermoplastic polyurethane elastomer (TPU). The resultant TPU composite containing 2 wt.% of BP1-MXene2@PDA showed a 19.2% improvement in the tensile strength and a 13.8% increase in the elongation at break compared to those of the pure TPU. The thermogravimetric analysis suggested that BP-MXene@PDA clearly enhances the thermal stability of TPU composites. Furthermore, the introduction of the BP-MXene@PDA nanohybrids could considerably improve the flame retardancy of TPU composite, i.e., 64.2% and 27.3% decrease in peak heat release rate and total heat release, respectively. The flame-retardant mechanisms of TPU/BP-MXene@PDA in the gas phase and condensed phase were investigated systematically. This work provides a novel strategy to simultaneously enhance the fire safety and mechanical properties of TPU, thus expanding its industrial applications.

The preparation of phosphorus and nitrogen-containing structure towards the enhancement of flame retardancy for thermoplastic polyurethane elastomer

Thermoplastic polyurethane elastomer (TPU) is an easily flammable materials with serious droplets and smoke toxicity, which critically restrict its practical application. In order to improve the flame retardancy of TPU, the present work designed a halogen free flame retardant (AL-APP) containing phosphorus and nitrogen elements via the modification of ammonium polyphosphate (APP) with sodium alendronate (Al). It was found that the limiting oxygen index of TPU/AL-APP5 composites increased from 20.7 % to 26.5 % and got past the V-0 rating without any droplets in the UL-94 vertical measurement. Meanwhile, the peak heat release rate (PHRR) and total heat release (THR) of TPU/AL-APP5 system reduced from 1021 to 255 kW/m2 and 87.5–61.2 MJ/m2 in cone calorimeter (CC) measurement when comparing to that of purchased TPU. According the thermogravimetric-infrared and Raman spectroscopy results, the production of the inert gas and formation of continuous carbon layer of AL-APP mutually improved the fire safety of TPU composites. Furthermore, the elongation at break of TPU/AL-APP5 was significantly increased by 19.9 % than that of neat TPU, showing a better softness and elasticity than neat TPU. According the above results, it was concluded that this work advancing in the high flame-retarding efficient and good mechanical property for TPU composites via a simple method.

Contribution of surface silanization process on mechanical characteristics of TPU‐based composites involving feldspar and quartz minerals

AbstractIn this study, quartz and feldspar powders were surface treated using a silane coupling agent to achieve a more compatible mineral surface with the polymer matrix. Details of surface characteristics of minerals were examined by energy‐dissipative X‐ray spectroscopy, contact angle measurements, and infrared spectroscopy. Thermoplastic polyurethane‐TPU was compounded with minerals using the melt‐blending technique. Mechanical, thermo‐mechanical, melt‐flow, and morphological characterizations of TPU and relevant composites were performed by utilizing tensile and Shore hardness tests, dynamic mechanical analysis (DMA), melt flow index (MFI) measurements, and scanning electron microscopy (SEM), respectively. Water repellency of TPU and composites were also evaluated experimentally. Effects of surface treatments were discussed by comparing the results of composites filled with pristine and modified minerals. Results revealed that enrichment of quartz and feldspar surfaces confer mechanical and thermo‐mechanical performance of composites. Mineral inclusions caused no drastic changes to the MFI parameter of TPU. The silane layer on the mineral surface displayed a barrier effect to water uptake of composites. Homogeneous dispersion and improved interfacial adhesion of mineral particles to the TPU phase were confirmed with help of SEM observations. Quartz exhibited slightly higher performance thanks to its silica‐rich composition. The findings of this research exhibited the considerable influence of the silane layer on the mineral surface on the mechanical performance of TPU‐based composites.

Multi-dimensional fillers synergistically enhanced thermal conductivity of TPU composites in selective laser sintering technology

With the rapid development of the electronic field, the requirements for thermal management materials are increasing to satisfy the heat dissipation of electronic devices. Due to the shortcomings of low precision and difficulty in forming thermal conductive composites with complex structures in traditional technologies, it is necessary to explore a new forming process. Selective laser sintering (SLS) is an important 3D printing technology, which can manufacture diverse parts with complex shapes and be used in various fields. In this study, TPU/AlN/h-BN/MWCNTs composites were successfully developed by selecting three different dimensions of thermally conductive fillers and combining them with the SLS process. The research shows that the thermal conductivity of TPU composites can reach up to 1.13 W/mK with 20 wt% AlN, 15 wt% h-BN, and 1 wt% MWCNTs hybrid fillers, which is 491 % higher than that of pure TPU, ascribed to the synergistic effect of multi-dimensional fillers. In addition, the tensile strength and elongation at break of TPU/AlN/h-BN/MWCNTs composites maintain 16.5 MPa and 294 %, which still has excellent mechanical properties. This work also investigated the influence of fillers on the SLS process, thermal stability, melting, and crystallization behavior of composites. It reveals an effective, feasible strategy for TPU composites with excellent thermal conductive and complex shapes.

Thermoplastic polyurethane composites based on aluminum hypophosphite/modified iron tailings system with outstanding fire performance

AbstractIron tailings (IT) is the remaining industrial solid waste after beneficiation. The accumulation of billion tons of tailings not only occupies valuable land resources but also causes serious environmental pollution and human harm. This work aims to explore the potential application of IT in flame retardant field. The modified iron tailings (MIT) were combined with aluminum hypophosphite (AHP) to prepare a series of TPU/AHP/MIT composites by melt blending method. Thermogravimetric (TGA) test indicated that MIT and AHP significantly improved the thermal stability of the composites. The char residue of TPU/AHP22.5/MIT2.5 was enhanced to 29.60 wt% compared with 27.51 wt% of TPU/AHP25. Cone calorimetry test (CCT) confirmed that PHRR and THR of TPU/AHP15/MIT10 were decreased by 88.4% and 55.2% compared with those of pure TPU. Adding 2.5 wt% MIT could reduce the gas production of the TPU/AHP system by 32.82%. Scanning electron microscopy (SEM) and Raman spectroscopy tests confirmed that AHP/MIT system could increase the thickness and graphitization degree of char residue for the TPU composites, and thus increase the thermal stability and fire resistance of the composites. Lastly, the possible fire retarding mechanism of TPU/AHP/MIT composites was illustrated. This work provided a novel strategy for utilization of IT.

Improved the dielectric properties of thermoplastic polyurethane elastomer filled with MXene nanosheets and BaTiO3 nanofibers

To achieve high deformation under a low electric field intensity is still a big challenge for the dielectric elastomers (DE) potentially used in artificial electronic skin and artificial muscles. Herein, poly-dopamine (PDA) modified 1D barium titanate (BT@PDA) nanofibers and 2D MXene nanosheets with high aspect ratio and large dipole moment were fabricated, and introduced into TPU elastomers. Results showed that the interfacial polarization and micro-capacitor structure formed by MXene sheets lead to the high dielectric constant, and high dielectric loss of MXene/TPU composites with low modulus. The interfacial polarization caused by BT@PDA nanofibers resulting in high dielectric constant and low dielectric loss of BT@PDA/TPU composites with high modulus. Combing the advantages of the two fillers, the MXene/BT@PDA/TPU composites showed high dielectric constant, low dielectric loss, low modulus. The electrical sensitivity factor of 0.5 wt% MXene/5 wt% BT@PDA/TPU composite (11.38) was much higher than the sum of that of 0.5 wt% MXene/TPU (1.73) and 5 wt% BT@PDA/TPU (4.35) composites at a low filler content, showing the 0.5 wt% MXene/5 wt% BT@PDA/TPU dielectric composite had a large deformation under a low electric field. This work can provide an effect strategy to design DE nanocomposites with good deformation performance.

Covalent synthesis of 3-chloropropyltrimethoxysilane onto para-aramid nanofibers for TPU composites: Flame retardancy, toxicity reduction, and mechanical property

In this paper, 3-chloropropyltrimethoxysilane was covalently bonded to the surface of para-aramid nanofibers named ANF-Si for flame retardant TPU. It was found ANF-Si could be more uniformly dispersed in the TPU compared to ANF, because the flame retardant properties of TPU could be enhanced by ANF-Si due to the presence of propyltrimethoxysilane. The pHRR and THR value of the TPU/ANF-Si0.250 sample with 0.250 wt% ANF-Si decreased by 60.5% and 37.2% compared with pure TPU, respectively. In addition, the values of pHRR and THR for the TPU/ANF-Si0.250 sample decreased by 5.6% and 71.0% compared with that of TPU/ANF0.250. Moreover, the release of CO and CO2 was also significantly reduced compared to TPU. The values of total CO release and total CO2 release of TPU/ANF-Si0.250 were reduced by 6.0% and 38.8% compared with pure TPU. Therefore, ANF-Si was able to shape the thermal decomposition process of TPU, changed the structure of the char layer, promoted carbonization and produced less flammable gases to achieve good flame retardancy of TPU. From the Raman spectra, the graphitization of the char layer of ANF-Si was enhanced, which was very beneficial to improve the flame retardant properties. In addition, ANF-Si improved the mechanical properties of TPU/ANF-Si. This work demonstrated the feasibility of using ANF modified with 3-chloropropyltrimethoxysilane as a flame retardant for TPU and provided a new modification strategy for improving the blend of ANF and TPU.

Graphite-like Carbon Nitride/Polyphosphoramide Nanohybrids for Enhancement on Thermal Stability and Flame Retardancy of Thermoplastic Polyurethane Elastomers

Many efforts have been made to enhance the fire safety of thermoplastic polyurethane elastomers (TPUs) by reducing the heat release rate and smoke emission. Suppressing the emission of smoke and reducing toxic gases generated in the case of TPU burning play a key role to enable TPU meet the eco-friendly and safety requirements. In this work, poly diaminodiphenyl phosphonic methane (PDMPD) with higher thermal stability and catalytic char formation capacity was synthesized; graphitic carbon nitride/PDMPD (CPDMPD) hybrids were fabricated, and their effect on the thermal behavior and flame retardancy of TPU composites was studied. The peak heat release rate (PHRR), the total heat release, the CO yield, and the smoke release of TPU show an obvious reduction on account of addition of CPDMPD hybrids according to the cone tests. TPU/CPDMPD4 is endowed with a reduction of 49.0% of the PHRR. In this work, molecular designing and physical function are integrated to prepare versatile additives of polymers with optimized thermal stability and flame retardancy.

Highly Enhanced Thermal Conductivity of Tpu Composites with Segregated Network Constructed by the In-Situ Reduction of Copper

Highly Enhanced Thermal Conductivity of Tpu Composites with Segregated Network Constructed by the In-Situ Reduction of Copper

Effect of the Segmental Structure of Thermoplastic Polyurethane (Hardness) on the Interfacial Adhesion of Textile-Grade Carbon Fiber Composites

In polymer composites, the fiber–matrix interface is primarily influenced by the surface treatment of the fibers and polymer morphology. Previous studies have investigated the effect of surface treatment of carbon fiber on the mechanical properties of the resulting composites. However, very few studies have explored the chemical structural modification of polymer effect on the fiber–matrix adhesion. In this work, the interfaces of soft thermoplastic polyurethane (S-TPU) and hard-segmented TPU (H-TPU) were investigated through surface, thermal, and mechanical characterization. A textile-grade carbon fiber (TCF) with 1% concentration of epoxy sizing (an emerging material for nonaerospace applications with 450 K filament tows) was used as a reinforcement to investigate the structure–property relationship at the interface. Atomic force microscopy results showed 39% higher surface roughness for S-TPU than for H-TPU. X-ray photoelectron spectroscopy results revealed a 550% increase in C═O content, which can provide multiple hydrogen bonding networks in H-TPU, and these C═O bonds can produce a strong chemical bond at the fiber–matrix interface. Dynamic mechanical analysis and differential scanning calorimetry results confirmed the presence of hydrogen bonding that enhances the cross-linked density by 232% in H-TPU compared to S-TPU. The improved mechanical properties of H-TPU composites, such as flexural, impact and tensile by 30, 50, and 130% compared to S-TPU composites, prove that the crystallinity and hydrogen bonding significantly increase the load bearing capacity due to the strong interface. The mechanical properties of TCF–TPU composites validate the formation of chemical bonds through a nucleophilic addition reaction at the interface and improve the bond strength of the composites. Thus, tailoring the polyurethane structure broadens the performance of segmented TPU in conjunction with TCF reinforcement, which has implications for cost-effective, high-strength composites.

Synergistic function of N‐P‐Cu containing supermolecular assembly networks in intumescent flame retardant thermoplastic polyurethane

AbstractThe design of high‐performance compounded flame retardants based on multielement can be of great significance for reducing the flammability of polymer materials. In this article, a new type of N‐P‐Cu containing supermolecular assembly network (MPCSN) flame retardant was prepared and subsequently added into thermoplastic polyurethane elastomer (TPU)/silicon microencapsulated ammonium polyphosphate (SiAPP) composites. The obtained results indicated that a series of TPU/SiAPP/MPCSN composites exhibited strong adhesions with the TPU matrix. Additionally, the thermal and flame retardant performances of TPU composites were markedly improved after the introduction of different proportions of SiAPP to MPCSN. For example, the peak of heat release rate, the total heat release, the peak of smoke production rate, the total smoke release of the TPU composite containing 7.5 wt% SiAPP and 2.5 wt% MPCSN (TPU/SiAPP3/MPCSN1) remarkably decreased by 68.7%, 52.9%, 52.4%, and 49.4%, respectively, besides the highest LOI value (27.5 vol%) and UL‐94 V‐0 rating, compared with those of pure TPU. The improved flame retardance of the TPU/SiAPP3/MPCSN1 composite was due to the explanations: On one hand, a compact intumescent char effectively protected the TPU matrix from heat and oxygen and retarded the gaseous products permeation into the combustion zone; on the other hand, evolved phosphorus‐containing free radicals captured the H• and HO• generated from the TPU material. The synergistic effect of SiAPP and MPCSN resulted in strong flame suppression, accompanied by 10.8% and 37.8% reductions in FIGRA and Av‐EHC, respectively. This article offers a facile approach to fabricate highly effective flame‐retardant TPU composites.

Superior fire safety performances of chelates copper(II) salicylaldehyde complexes with intumescent flame retardant TPU

To improve the flame retardant of thermoplastic polyurethane elastomer (TPU) is a very important issue in fire hazard fields. In this article, the structure of copper (II) chelate salicylaldehyde (CuSA) was characterized by X‐ray diffraction (XRD), Fourier transform infrared (FTIR), and scanning electron microscopy (SEM). The influence of CuSA on the fire safety performances of TPU/APP composites was intensively investigated using cone calorimeter test (CCT), smoke density test (SDT), micro‐scale combustion calorimetry (MCC), thermogravimetric‐Fourier transform infrared spectrum (TG‐FTIR), and other testing methods. The CCT test results showed that the peak heat release rate (pHRR) value of CuSA2 sample was 128.1 kW/m2, which was much lower than that of TPU‐APP sample with the pHRR value of 161.9 kW/m2. The SDT test results showed that the luminous flux of CuSA4 is much higher than that of TPU‐APP sample. Therefore, an appropriate amount of CuSA had obvious improvement of fire safety performances in TPU composites. This work provides a new idea for the design and manufacture of fire safety materials.