Thermoplastic Polyurethane Composites Research Articles

A novel triazine-based covalent organic framework: Enhancement fire resistance and mechanical performances of thermoplastic polyurethanes

In this study, we decided to synthesize a flame-retardant triazine-based covalent organic framework (FT-COF) via solvothermal reaction, to improve the fire safety and mechanical properties of thermoplastic polyurethane (TPU). By adding 3.0 wt% of FT-COF, the tensile strength and elongation of TPU increased by 69% and 12%, respectively. After incorporating of FT-COF nanoparticles, the thermal stability of TPU was significantly improved that resulted in the increasing of char residue up to 158% for TPU/FT-COF 3%. With addition of 3.0 wt% FT-COF, the peak heat release rate, total heat release of TPU composite were dramatically decreased by 51.6% and 47.3%, respectively. Besides, the TPU/FT-COF 3% indicated distinct reductions in the total smoke release (41.1%) and the peak of carbon monoxide production rate (43.53%). This study offers a new plan to outstandingly reducing the flammability of TPU, thus developing its industrial usage.

A REVIEW: RELATION ON NATURAL FIBER LOADING TO THE TENSILE PROPERTIES OF TPU COMPOSITES

The natural fiber is considered recyclable and may have some potential for some application. Nowadays, this type of fiber has to gain popularity as a filler in polymer composites. Besides, it is readily available and environmentally friendly. It is also inexpensive because they are non-toxic and biodegradable waste. This paper presents the various natural fiber from fruit skin, fruit peel, agricultural residue, waste, and others as fillers in thermoplastic polyurethane (TPU). The author also reflects the key issue related to the effect of filler loading on the tensile properties of TPU composites. In general, the tensile strength of the natural fiber-filled polymer composites increases with fiber loading. The tensile properties are mainly influenced by the interfacial adhesion between the polymer and the fibers. Other than that, each type of fiber also plays a vital role in its properties and polymer adhesion. This review only focuses on the latest studies in the range of seven years from 2013 to 2019 [1].
 Keywords: Thermoplastic polyurethane, natural fiber, fiber loading, tensile properties, composites

Surface modified boron nitride towards enhanced thermal and mechanical performance of thermoplastic polyurethane composite

Owing to the unpredictable advancement in electronic devices, the demand for highly thermally conductive and electrically insulating material is increasing day by day. Besides, surface treatment of chemically inert hexagonal boron nitride (h-BN) sheets found challenging and a distressing contention towards its acceptable thermal transportation. Herein, h-BN sheets are functionalized with divergent amines (its three isomers) to obtain their astonishing properties like high disperse ability and development of interfacial conduction in polymer composite. This comparative study elucidates the significance of the covalent interaction of amines (-NH2) with h-BN lattice as well as strong hydrogen bonding with thermoplastic polyurethane (TPU) matrix. It is demonstrated that both ortho-phenylenediamine o-PDA-BN and para-phenylenediamine p-PDA-BN filled TPU composites exhibit higher through-plane thermal conductivity (┴TC) of 2.06 and 1.96 W m−1 K−1 respectively by substantially establishing a higher thermal transportation path at high filler loading of 45 wt %. Whereas, meta-phenylenediamine m-PDA-BN composites reveal somewhat low ┴TC of 1.27 W m−1 K−1 at the same filler loading. Interestingly, all fabricated composites consisting of functionalized BN (f-BN) and TPU show unprecedented thermal and mechanical properties at such a high filler loading which demonstrates their great potential for packaging application in microelectronics.

Soft flexible conductive CNT nanocomposites for ECG monitoring

With the continuing development and interest in wearable electronics and smart textiles, the need for a flexible conductive electrode for use in portable and wearable electrocardiogram (ECG) for long term monitoring rises. Here, we assess the efficacy and performance of various conductive composite polymers in collecting electrical signals from the heart. Thermoplastic polyurethane (TPU), ethylene-vinyl acetate (EVA), and styrene-butadiene-styrene (SBS) were blended with 1%, 2%, 5%, and 10% carbon nanotube (CNT) content using ultrasonication and compression molding techniques. The elastic modulus of the composites increased dramatically at 5% CNT and higher due to the high tensile modulus of the CNTs. The conductivity of each material also increased due to the formation of the conductive network past the percolation threshold. At 10% CNT, SBS, TPU, and EVA had conductivities of 257.9, 51.5, and 2.41 S m−1 respectively. TPU and SBS composites had better strain response due to their linearity between resistance and strain. On the acquisition of electrical signals from the heart, only 5% and 10% SBS-CNT composites were able to detect the ECG waves from the heart. The performance of the material met and even exceeded that of the commercial electrodes with slightly less high frequency noise.

Copper metal‐organic framework toward flame‐retardant enhancement of thermoplastic polyurethane elastomer composites based on ammonium polyphosphate

In this article, copper metal‐organic framework (MOF‐Cu) was synthesized and used as synergism with ammonium polyphosphate (APP) to prepare flame‐retardant thermoplastic polyurethane (TPU) composites. The synergistic flame‐retardant effects between MOF‐Cu and APP in TPU composites were studied by cone calorimeter (CCT), limiting oxygen index tests (LOI), vertical burning tests (UL‐94), smoke density test, etc. The results showed that MOF‐Cu had some flame‐retardant effects on TPU, and APP had good flame retardancy in TPU/APP composites. And, the flame retardancy of TPU/APP was further enhanced when MOF‐Cu was used as synergism with APP. It has been found that the peak heat release rate (pHRR) and total heat release (THR) values of TPU/Cu0.0625 sample were reduced by 26.0% and 1.3% compared with pure TPU, respectively. And the pHRR and THR values of TPU/APP sample were reduced by 70.3% and 15.8% compared with pure TPU. In the case of TPU/APP/Cu0.0625 sample, the pHRR and THR values were furtherly reduced by 19.2% and 63.4% compared with TPU/APP, because of the minor amount of MOF‐Cu. It has been found MOF‐Cu cannot suppress the smoke release and reduce the total smoke release (TSR) value. However, 0.125 wt% MOF‐Cu can make the TSR value of TPU/APP/Cu0.125 sample reduce to 227.8 m2/m2, which was 23.4% lower than that of TPU/APP. The good synergistic flame‐retardant effect between MOF‐Cu and APP was obtained by the catalyzing carbonization process to form the char residue layer with high graphitization and expansion degree.

Highly Thermally Conductive 3D Printed Graphene Filled Polymer Composites for Scalable Thermal Management Applications.

Efficient thermal transportation in a preferred direction is highly favorable for thermal management issues. The combination of 3D printing and two-dimensional (2D) materials such as graphene, BN, and so on enables infinite possibilities for hierarchically aligned structure programming. In this work, we report the formation of the asymmetrically aligned structure of graphene filled thermoplastic polyurethane (TPU) composites during 3D printing process. The as-printed vertically aligned structure demonstrates a through-plane thermal conductivity (TC) up to 12 W m-1 K-1 at 45 wt % graphene content, which is ∼8 times of that of a horizontally printed structure and surpasses many of the traditional particle reinforced polymer composites. The superior TC is mainly attributed to the anisotropic structure design that benefited from the preferable degree of orientation of graphene and the multiscale dense structure realized by finely controlling the printing parameters. Finite element method (FEM) confirms the essential impact of anisotropic TC design for highly thermal conductive composites. This study provides an effective way to develop 3D printed graphene-based polymer composites for scalable thermal-related applications such as battery thermal management, electric packaging, and so on.

Effects of flame retardants integrated with citrate and ammonium polyphosphate on thermal stability and flame retardancy of thermoplastic polyurethane elastomer

Three citrates, which incorporate cobalt citrate (CoC), copper citrate (CuC), and yttrium citrate (YC), were combined with ammonium polyphosphate (APP) as a flame retardant to improve the flame retardancy and thermal stability of thermoplastic polyurethane (TPU). The cone calorimeter test (CCT) results demonstrated that the PHRR (peak heat release rate) values of TPU‐2, TPU‐3, and TPU‐4 were decreased from 271.4 kW/m2 for TPU‐1 to 188.0, 256.9, and 219.0 kW/m2, respectively. Besides, compared with TPU‐1, the release of CO and CO2 of TPU composites that containing citrate were decreased. The limiting oxygen index (LOI) value for TPU‐1 (containing 8.0 wt% APP) was 26.5% while that of TPU‐4 was increased to 27.5% and reached to V‐0 rating on the vertical burning test. Thermogravimetric analysis (TG) indicated that containing both APP and citrate accelerated the degradation of TPU composites but increased the char residue. In detail, the char residue of TPU‐0 was 6.3 wt% at 685°C, while that of TPU‐3 was reached to 45.2 wt% at N2 atmosphere. Laser Raman spectroscopy (LRS) showed that the degree of graphitization of TPU composites had been increased after adding the citrates. X‐ray photoelectron spectrometer (XPS) and gas chromatography/mass spectrometry (GC‐MS) illustrated that citrate and APP exerted barriers effect in the condensed phase. This work provided a new way of flame retardant that integrated with citrate and APP for TPU composites.

An urethane-based phosphonate ester for improving flame retardancy and smoke suppression of thermoplastic polyurethane

The flame-retardant thermoplastic polyurethane (TPU) with remarkable smoke suppression, anti-dripping and mechanical properties has been still a big conundrum in the field of fire safety science. In this article, an urethane-based phosphonate ester (UPE) flame retardant additive was successfully synthesized and incorporated into TPU. The fire safety, mechanical performance and flame-retardant mechanisms of TPU/UPE composites were lucubrated. With the incorporation of only 10 wt% UPE, TPU/10 wt% UPE composites passed UL-94 V-0 rating without dripping and the limited oxygen index (LOI) value reached 28.8%. Cone calorimetry tests indicated that the peak value of heat release and smoke production of TPU/10 wt% UPE composites were significantly diminished with the reduction of 70.6 and 54.1% in comparison with that of pure TPU. The analysis of flame-retarded mechanism for TPU/UPE indicated that UPE efficiently exerted free radical capture effect in gaseous phase, and stimulated the decomposition and charring of TPU composites in advance and the formation of high-quality char layer exerted isolation role in condensed phase. Therefore, the fire safety of TPU composites was enhanced by the incorporation of UPE. Meanwhile, the mechanical performance of TPU/UPE composite was well remained due to the good compatibility between UPE and TPU matrix. This work supplied a promising way for fabricating fire-safety TPU composites with preferable comprehensive properties.

Flexible thermoplastic polyurethane-carbon nanotube composites for electromagnetic interference shielding and thermal management

• Flexible TPU composites were prepared by NIPS assisted solution mixing method. • Long length MWCNT composites offer a remarkable EMI SE value of 42.5 dB. • Short length MWCNT based composites exhibit excellent thermal management. • Short length MWCNT based composites possess good electromechanical performance. Lightweight, flexible, and thermally conductive electromagnetic interference (EMI) shielding materials have garnered front facet research interest because of urgent demand to address the EM wave pollution. Herein, inspired from the effectiveness of interconnected networks of different types of carbon nanotubes (CNTs), an endeavored to design three types of CNTs based thermoplastic polyurethane (TPU) composites through a facile solution blending with non-solvent induced phase separation (NIPS) strategy. The effect of different length of CNTs on the EMI shielding, electrical and thermal conductivity performance of TPU nanocomposites have been studied explicitly. The composite with long length CNT (10 wt%) offered a remarkable EMI shielding efficiency of 42.5 dB, the electrical conductivity of 1.9 × 10 −3 S/cm, whereas composite with short length CNTs showed a thermal conductivity of 0.51 W/mK and the corresponding thermal conductivity enhancement efficiency exceeded 145% relative to pure TPU. Incorporation of long length CNTs helped to form unique interconnected conductive networks within the TPU matrix that boost more the electron or charge transferability inside the composites, improvement in mechanical properties, EMI shielding, and electrical properties than that of short length CNTs. In contrast, short length CNTs display significant electromechanical performance and heat transferability than that of long length CNTs. The composites showed a high response in electrical conductivity and minor change in EMI shielding efficiency with repeated bending cycles. This work provides a corelated remark of different types of CNT based TPU composites for superior EMI SE and thermal management applications for next generation wearable and stretchable electronics.

Surface modification of bamboo fibers by diammonium phosphate and their applications in flame retardant thermoplastic polyurethane

AbstractBamboo fibers (BF) were used as charring agent in thermoplastic polyurethane (TPU), together with ammonium polyphosphate (APP) to prepare intumescent flame retardant composites. In order to improve the dispersibility and flame retardant efficiency, BF was grafted with diammonium phosphate (DAP), named as modified bamboo fibers (M‐BF). By the presence of 8 wt% APP and 2 wt% M‐BF, the sample could achieve the maximal limiting oxygen index (LOI) value of 30.5% and V‐0 rating in UL‐94 test. The peak heat release rate for TPU/8APP/2 M‐BF is 190 kW/m2, which is 86.0% lower than that of neat TPU. Besides, TPU/8APP/2 M‐BF sample presented a tensile strength of 23.0 MPa, which was slightly lower than neat TPU sample. The thermogravimetric analysis for TPU composites and the morphology observation of the char demonstrated that APP and M‐BF took effects on condensed phase through promoting the formation of intumescent char structure and free radical trapping. Meanwhile, it could release inert gases in gas phase. Therefore, M‐BF exhibited great potential in applying as renewable charring agent for alleviating the depletion of petroleum resources.

High dielectric constant, flexible and easy-processable calcium copper titanate/thermoplastic polyurethane (CCTO/TPU) composites through simple casting method

In the past few years, there has been a significant demand for the development of high dielectric constant polymer composites for flexible electronic applications. However, the development of these flexible and stretchable dielectrics through simple and economical processing methods still remains challenging. In the present work, we have addressed this problem by developing high dielectric constant, flexible, calcium copper titanate (CCTO)/ thermoplastic polyurethane (TPU) composites through a simple and cost-effective casting method. At room temperature, 40 vol% CCTO/TPU composite exhibited a dielectric constant of 56 (1 kHz) along with an elongation at break of 202%, making it a promising dielectric material for flexible electronics. To our knowledge this is the best among the reported works in ceramic/ polyurethane composites, exhibiting a remarkable combination of high dielectric constant, excellent elongation at break and good mechanical strength. A prototype embedded capacitor was fabricated on copper cladded printed circuit board (PCB) by spin coating and a specific capacitance of 1.05 nF/cm2 was achieved at 1 kHz.

Improvement of the electromechanical properties of thermoplastic polyurethane composite by ionic liquid modified multiwall carbon nanotubes

Abstract Carbon nanotubes (CNTs) were non-covalently modified by two categories of ionic liquids (ILs), including 1-vinyl-3-ethylimidazole bromide (VEIMBr) and 1-vinyl-3-hexylimidazole bromide (VHIMBr) in the ratio of 1:1 and 1:4, respectively. The surface interaction between CNTs and ILs was well-characterized by FTIR, Raman spectra, XPS, etc. Thermoplastic polyurethane (TPU) containing different amounts of CNTs/ILs was fabricated by melting blending method. TPU-CNTs/ILs composites exhibited simultaneously enhanced electromechanical properties with improved dielectric constant and lowered elastic modulus. The electromechanical sensitivity of sample TPU-3CNT/12VHIMBr increased by approximately 45 times in comparison with that of pure TPU at 200 Hz. Besides, improved dispersion of CNTs/ILs in the TPU matrix was also exhibited.

Smoke suppressant in flame retarded thermoplastic polyurethane composites: Synergistic effect and mechanism study

Considerable smoke and toxic volatiles generation has compromised the application of thermoplastic polyurethane (TPU) and caused a great threat to human life. Here, nano-MgFe layered double hydroxide (MgFe-LDH) with uniform particle size was synthesized to reduce smoke density and toxic gases of TPU composites using ammonium polyphosphate (APP) as a flame retardant agent. The results show that the combination of 16 wt.% APP and 4 wt.% MgFe-LDH greatly decreased the smoke density (D20min and Ds, max), smoke production rate (SPR) and heat release rate (HRR) of TPU composites. Furthermore, the MgFe-LDH synergist demonstrated high efficiency in decreasing total volatiled products and toxic volatiles evolved, such as the CO, HCN and isocyanates. The reason was mainly attributed to the chemical reaction between MgFe-LDH and APP, which can promote the compactness of char layers with fine microstructure formed in the decomposition process of MgFe-LDH/APP/TPU composites. The protective char layers could act as barriers between combustion zone and matrix to protect the unburned substrate and promote smoke suppression effect.

A comparative study between vapor phase polymerized PPy and PEDOT - Thermoplastic polyurethane composites for ammonia sensing

In this study, in situ vapor phase polymerization (VPP) of (1) 3,4-ethylenedioxythiophene (EDOT) and (2) pyrrole (Py) on an oxidant-impregnated thermoplastic polyurethane (TPU) substrate was conducted to produce a (1) PEDOT-TPU hybrid film and (2) PPy-TPU hybrid film. Scanning electron microscopy, atomic force microscopy, and energy dispersive x-ray spectroscopy confirmed the formation of uniform, rough surfaces of PPy and PEDOT on the TPU matrix. Both PPy-TPU and PEDOT-TPU films showed excellent thermal stability across the temperature range of 300 °C–400 °C and enhanced mechanical properties, depicted by very high stress and strain values. The performance of these hybrid films to detect ammonia (NH3) gas was investigated and then optimized under the effects of varying temperature, ammonia concentration, and monomer type used. The PEDOT-TPU and PPy-TPU showed remarkable sensitivity to NH3 gas, with coefficients of variation of 0.9858 and 0.9653, respectively. Particularly, the PEDOT-TPU sensor showed higher responsiveness to NH3 at higher operating temperatures owing to its higher surface roughness and thermal stability. These flexible, stretchable, smart conducting polymer composite materials fabricated using VPP are therefore potential candidates for monitoring toxic and non-toxic gases.

Dynamic mechanical and EWF study of reactive organo-montmorillonite and carbon black filled polyurethane nanocomposites

ABSTRACT In this work we have focussed to examine the effect of carbon black (CB) (3 wt%) and reactive organo-modified montmorillonite R-OMMT (1–3 wt%) on rheological, tensile, thermal, and fracture properties of thermoplastic polyurethane (TPU). XRD curves shows that completely exfoliated structures were obtained using 1 wt% and 2 wt% R-OMMT as a compatibilizer in CB reinforced TPU composites, whereas 3 wt% R-OMMT shows intercalated structures which may be due to agglomeration of clay nanoparticles beyond 2 wt%. Using 2 wt% R-OMMT, essential and nonessential work required for fracture was found to increase by 16.8% and 74%, respectively.

Preparation of boron nitride nanosheets via polyethyleneimine assisted sand milling: towards thermal conductivity and insulation applications.

Hexagonal boron nitride (h-BN) is often used as a filler in polymer composites due to its good thermal conductivity and insulation properties. However, the compatibility between h-BN and the matrix limits its application areas. To overcome this issue, a combination of mechanical liquid phase exfoliation and chemical interfacial modification was adopted in this work. Polyethyleneimine (PEI) was used as the exfoliation reagent to prepare PEI-functionalized h-BN nanosheets, denoted as PEI@BNNS. Thermoplastic polyurethane (TPU) composites with different contents of h-BN and PEI@BNNS which were recorded as h-BN/TPU and PEI@BNNS/TPU were successfully prepared through a hot-pressing process, respectively. The results show that PEI@BNNS/TPU composites have better in-plane thermal conductivity while maintaining insulation, and with the content of 5 wt% PEI@BNNS, the in-plane thermal conductivity of the PEI@BNNS/TPU composite is up to 0.61 W m−1 K−1, which is three times that of pure TPU (0.22 W m−1 K−1).

Waste to resource: preparation of an efficient adsorbent and its sustainable utilization in flame retardant polyurethane composites.

In order to realize the comprehensive utilization of industrial solid waste and the treatment of water eutrophication, the flower-like magnesium hydroxide (MH) was synthesized from phosphorus tailings by sulfuric acid hydrolysis and a hydrothermal method and then was modified with a metal organic framework (MOF) to remove the phosphates enriched in water through adsorption. Both MH and MOF-modified MH (MH@MOF) presented good removal performance of phosphates. The phosphate-adsorbed composites (MH–P and MH@MOF–P) were sustainably used as effective flame retardants for thermoplastic polyurethane (TPU) at low loadings by a solution blending method. The cone calorimetry test results showed that MH@MOF–P can significantly reduce the heat release rate (HRR), smoke production rate (SPR), total smoke release (TSR), CO release rate and CO2 release rate of TPU composites, compared with those of neat TPU. The novel strategy proposed in this work is of great significance for resource recycling, environmental governance and improving fire safety of polymer materials.

Quantifying dielectric and microwave absorption properties of barium titanate and strontium ferrite filled polymer composites

In the present study, dielectric and microwave absorbing properties of barium titanate (BaTiO3) and strontium ferrite (SrFe12O19) filled thermoplastic polyurethane composites were investigated. The variations of the dielectric parameters of the BaTiO3 filled composite samples with filler concentration were also modeled and simulated by the power-law model to predict dielectric coefficients of the samples for higher filler concentrations. Comparing the prediction of the Power-law model and experimental measured dielectric values indicate that the Power-law model predicts dielectric parameters of the composite with acceptable accuracy. Microwave absorption analyses of the composite samples showed that SrFe12O19 is more effective than BaTiO3 on the enhancement of microwave absorption capability of TPU. The hybrid composite samples that contained both SrFe12O19 and BaTiO3 were also prepared, and their microwave absorption performance was evaluated. It was observed that much lower RL values than that of the composite samples, which were filled SrFe12O19 or BaTiO3 could be obtained by the hybrid composites. However, absorption bandwidth of them was narrower than counterparts that contained the same amount of SrFe12O19.

Experimental investigation of flame retardancy and mechanical properties of APP/EG/TPU multilayer composites prepared by microlayer coextrusion technology

AbstractIn this paper, ammonium polyphosphate(APP)/expandable graphite(EG)/thermoplastic polyurethane (TPU) composites were prepared by microlayer coextrusion technology, APP and EG fillers had good synergistic flame retardancy and excellent dispersion in TPU matrix, which greatly improved the flame retardancy and mechanical properties of multilayer composites. The dispersion of APP and EG in TPU was characterized by using SEM, the flame retardancy of composites was characterized by using UL94 and LOI, the thermal stability of composites was characterized by using TGA and DTG, and tensile test was used to characterized the mechanical properties of composites. SEM showed that the microlayer coextrusion technology significantly improved the dispersion of APP and EG in TPU. As showed by the experimental results, the vertical combustion level of ordinary blended composites reached V‐2 after adding only one kind of filler either APP or EG, and the vertical combustion level of ordinary blended composites reached V‐0 with APP and EG applied together, while the vertical combustion level of microlayer coextruded composites all reached V‐0 when the total addition of APP and EG was 15%. In particular, the LOI value of microlayer coextruded composites was 30.9%, while the LOI value of ordinary blended composites only was 27.9% when APP: EG = 1: 1. At this time, the flame retardancy level of APP/EG/TPU composites was the best. In addition, the thermal stability and mechanical properties of microlayer coextruded composites were far superior to ordinary blended composites. In conclusion, the synergistic flame retardancy of APP and EG fillers and the dispersion of APP and EG fillers in TPU matrix played a significant role in enhancing flame retardancy and mechanical properties.

Mechanical and EMI shielding properties of solid and microcellular TPU/nanographite composite membranes

Tough, flexible, and conductive polymer composites show numerous advantages over conventional metal-based materials for EMI shielding applications, for example, in enclosures and packages of electronic devices, due to their low density, high flexibility, excellent corrosion resistance, and easy processing. Herein, thermoplastic polyurethane (TPU) was compounded with flake-shaped nanographite to prepare flexible polymer composite membranes with enhanced mechanical and EMI shielding properties. To regulate TPU/graphite composite's properties, microcellular foaming with carbon dioxide was used to prepare microcellular TPU/graphite composite membranes. Nanographite can significantly promote cell nucleation and hence lead to a refined cellular structure. With 20 wt% nanographite, cell density can be increased by two orders of magnitude. By adding the optimal amount of nanographite, the tensile strength and modulus can be increased up to 28% and 39%, compared to TPU. Although microcellular foaming compromises the tensile properties of the composites, it can significantly enhance their elasticity with more than a 20% decrease in hysteresis loss in comparison to solid ones. Moreover, it is also found that TPU composites with high graphite contents significantly enhanced EMI shielding properties, and microcellular foaming leads to relatively worse EMI shielding performance. Both solid and foamed TPU/graphite composites show promising prospects in EMI shielding applications.