Thermoplastic Polyurethane Chains Research Articles

Exploring thermodynamic and structural properties of carbon nanotube/thermoplastic polyurethane nanocomposites from atomistic molecular dynamics simulations.

Carbon nanotubes (CNTs) and thermoplastic polyurethane (TPU) nanocomposites have emerged as promising materials for various applications in the field of nanotechnology. An understanding of the thermodynamic and structural properties is of fundamental significance in designing and fabricating CNT/TPU nanocomposites with desired properties. To this end, this work has employed atomistic molecular dynamics (MD) simulations to study the thermal properties and interfacial characteristics of TPU composites filled with pristine or functionalized single-walled carbon nanotubes (SWNTs). Simulations reveal that the introduction of SWNTs suppresses TPU chain dynamics and favors the hydrogen bond formation induced by the wrapping of TPU chains around SWNTs, leading to an increase of glass transition temperature (Tg) and a reduction of volumetric coefficient of thermal expansion (CTE) in the rubbery state. Compared to pristine and hydrogenated SWNTs, SWNTs featuring polar groups, such as carboxyl (-COOH), oxhydryl (-OH) and amine (-NH2) groups, show improved affinity for TPU molecules, suppressing polymer mobility. Analysis of SWNT/TPU binding energy and solubility parameter suggests that electrostatic interactions are responsible for such a functionalized SWNT/TPU interface enhancement. Furthermore, the amine groups exhibit the highest potential for forming hydrogen bonds with the urethane carbonyl (-C[double bond, length as m-dash]O) of TPU chains, resulting in lowest polymer mobility and highest Tg. In general, this research work could provide some guidance for material design of polymer nanocomposites and future simulations relevant to TPUs.

Erucamide/thermoplastic polyurethane blend with low coefficient of friction, high elasticity and good mechanical properties for intelligent wearable devices

AbstractIn this study, erucamide as a non‐toxic and tasteless lubricant was melt blended with thermoplastic polyurethane (TPU) to reduce the coefficient of friction (COF) of TPU and thus to improve the wearing comfort of intelligent wearable devices. The results show that when the content of erucamide reaches percolation, erucamide can migrate to the TPU surface, forming a layer of lubrication film, and thus significantly reduces the COF of TPU. In addition, erucamide with amide groups can form hydrogen bonds with carbamate groups from TPU chains and thus can disrupt the hydrogen bonds between two amide groups of TPU chains. With the introduction of erucamide, the chain mobility of TPU increases, the partial phase mixing of soft phase and hard phase of TPU occurs, and the interchain interaction between TPU chains decreases. Under the appropriate content of erucamide (0.5 wt%), both the elasticity and processability of TPU are also significantly improved, whereas the high tensile strength, tear strength and elongation at break of the TPU blend is still obtained, facilitating its practical application in intelligent wearable devices. © 2022 Society of Industrial Chemistry.

Vitamin C aqueous solution assisted in-situ reduction of graphene oxide in flexible thermoplastic polyurethane

Graphene oxide (GO) is usually used as a precursor of reduced GO (rGO) in polymer matrices for improving their properties. However, reduction degree of GO in conventional melt mixing is usually limited. In this work, thermoplastic polyurethane (TPU)/rGO nanocomposite is prepared via water-assisted mixing extrusion with vitamin C (VC) aqueous solution injection. In situ chemical reduction (ISCR) by the VC and in situ thermal reduction (ISTR) by the thermal energy from both extruder barrel heating and screw shear are simultaneously enhanced for the GO, which are indicated by disappearances of O–H peak at the FTIR spectrum and O–C=O peak at the XPS spectrum of the rGO powder extracted from the prepared nanocomposite. Thus high reduction degree of the GO is obtained (with C/O atom ratio of 9.83 for the extracted rGO powder). This is attributed to the following two aspects: (1) TPU chains plasticized by water can better intercalate into GO galleries, thus enhancing the stripping of oxygen-containing groups from GO surface and the ISTR of the GO; (2) the screw shear action helps to disperse the VC of the injected VC aqueous solution in the TPU melt and increase the contact between the VC and GO, therefore enhancing the ISCR of the GO. The prepared TPU/GO nanocomposite exhibits enhanced dielectric permittivity.

Development of turkey feather fiber-filled thermoplastic polyurethane composites: Thermal, mechanical, water-uptake, and morphological characterizations

This present study centers sensitively on the determination of the effect of natural turkey feather fibers (TFFs) loading on fundamental features (thermal, mechanical, water-uptake, and micro-structural) of thermoplastic polyurethane (TPU). The composites with different TFFs contents (3, 6, 9, and 12 wt.%) were fabricated by the melt blending method using the twin screw extruder and micro-injection molder. The samples were characterized by means of differential scanning calorimeter (DSC), universal mechanical (tensile and hardness) tester, water-uptake, and scanning electron microscope (SEM) techniques. The thermal analysis depicted that the melting temperatures of the soft and hard segments as well as the crystallinity degree of TPU increased consistently with the increase of TFFs loading level thanks to the formation of better close-packed TPU chains in the matrices. As for the mechanical test results, when compared neat TPU, the tensile strengths were reinforced by 26.8% and 19.7%, and the modulus increased by 6.6% and 45.1% for the composite samples including 3% and 6% of TFFs, respectively. However, drastic diminishment were observed at further contents. Additionally, TFFs loadings brought about gradual increase in the water-uptake capacities of the composites due to the increasing of the number of voids and omnipresent flaws in TPU matrices. The taken SEM images also revealed that, at low contents, there existed the enrichment of interfacial adhesion between TFFs and TPU matrix, whereas the morphological appearance of the composites get worse at high contents accompanied by the formation of micro-structural defects.

A comparison of thermoplastic polyurethane incorporated with graphene oxide and thermally reduced graphene oxide: Reduction is not always necessary

ABSTRACTDespite wide applications of reduced graphene‐oxide (GO)‐reinforced polymer‐based composites, the necessity of the reduction procedure toward GO is still controversial. In this article, thermoplastic polyurethane (TPU) composites incorporated with GO and thermally reduced graphene oxide (TGO) were fabricated. GO and TGO exhibited different effects on crystallization behaviors, and mechanical and thermal properties of the TPU matrix. With 2.0 wt % filler loading, TPU composite reinforced by GO (TPU‐GO‐2 wt %) exhibited better thermal stability than that reinforced by TGO (TPU‐TGO‐2 wt %). The interfacial interaction between the nanofillers and the TPU matrix as well as their influence on the mobility of TPU chains were investigated, which proved that GO is superior to TGO in improving interface adhesion and maintaining crystallization of the TPU matrix. Compared with TPU‐TGO‐2 wt %, improved mechanical properties of TPU‐GO‐2 wt % were also evidenced owing to more oxygen‐containing groups. This work demonstrates that the reduction of GO is not always necessary in fabricating polymer composites. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47745.

Thermoplastic polyurethane-carbon black nanocomposite coating: Fabrication and solid particle erosion resistance

Carbon black (CB)/thermoplastic polyurethane (TPU) nanocomposites with a range of nanoparticle loadings were prepared successfully by using a joint co-coagulation technique and hot pressing. The presence of hydrogen bonding interactions between the CB particles and TPU chains was identified from the results of Fourier transform infrared (FT-IR) spectroscopy and differential scanning calorimetry (DSC). Uniform dispersion of CB particles throughout the TPU matrix improved the overall mechanical properties of the TPU nanocomposites, as compared with the neat TPU. The thermal conductivity and thermal stability of the CB/TPU nanocomposites were also found to be enhanced with increasing the CB loading. All samples exhibited a rapid increase of erosion rate with the impact velocity between 20 and 30 m/s. The largest and smallest erosion rates (ER) were observed at 30° and 90° impact angle, respectively, for all CB/TPU nanocomposites. This shows a typical ductile erosion behavior in this material. In addition, the ER (TPU-2CB > TPU-12CB > TPU > TPU-6CB) under all test conditions showed an opposite trend to the tensile strength. These results indicate that the CB/TPU nanocomposites are suitable for protective coatings.

Morphology, rheological and crystallization behavior in thermoplastic polyurethane toughed poly(l-lactide) with stereocomplex crystallites

Melt-blending poly(l-lactide) (PLLA) with elastomers has been well demonstrated to improve toughness of PLLA. Here, we show a poly(d-lactide) (PDLA) grafted thermoplastic polyurethane (TPU) (TPU-g-PDLA) toughed PLLA with simultaneous formation of few amount stereocomplex crystallites (SCs) which exhibited higher efficient toughening than that of PLLA with TPU. The TPU-g-PDLA was prepared by the in-situ melt-reaction of TPU and PDLA with 4, 4’-diphenylmethane diisocyanate (MDI). A comparative study on morphology, rheological and crystallization behavior was also carried in PLLA/TPU, PLLA/TPU-g-PDLA and PLLA/TPU/PDLA samples. The PLLA/TPU-g-PDLA samples show the highest crystallization rate, complex viscosity, impact strength and tensile strength among PLLA/TPU, PLLA/TPU-g-PDLA and PLLA/TPU/PDLA samples, indicating that the higher interfacial interaction between TPU-g-PDLA and PLLA. Furthermore, TPU chains in TPU-g-PDLA were thought to break the intermolecular interaction of PLLA and rapid its crystallization and increase crystallinity.

Laser-induced blackening on surfaces of thermoplastic polyurethane/BiOCl composites

Using Bismuth Oxychloride (BiOCl) as a laser-sensitive component, and thermoplastic polyurethane (TPU) as the matrix, the TPU/BiOCl composite capable of laser marking can easily be produced by melt blending of TPU with various proportions of BiOCl. The TPU/BiOCl composite samples showed high contrast black markings on the surface after laser treatment, depending on the BiOCl loading and laser fluence in terms of visual and microscopic analysis. The laser-induced blackening on material surfaces was examined by XPS, XRD, and Raman spectroscopy. The results revealed that the laser-induced blackening on the composite surface entails laser absorption of the BiOCl particles and local heating of the surrounding TPU chains. This led to the generation of amorphous black carbonised materials and the reduction of BiOCl into black bismuth metal. The carbonisation of TPU chains and the photo-thermal conversion of BiOCl particles synergistically contributed to the formation of the black-coloured marking on composite surfaces.

Largely improved electromechanical properties of thermoplastic polyurethane dielectric elastomers by the synergistic effect of polyethylene glycol and partially reduced graphene oxide

In this study, moderate content of polyethylene glycol (PEG) with ionic conductivity and low content of graphene oxide (GO) were simultaneously introduced into thermoplastic polyurethane (TPU) followed by in-situ chemical reduction of GO (rGO) to prepare TPU/PEG/rGO dielectric elastomer (DE) composites with largely improved electromechanical performance. The results showed that PEG remarkably disrupted the hydrogen bonds between TPU chains in TPU/PEG/rGO composites and formed new hydrogen bonds with TPU. In addition, PEG molecules can also form hydrogen bonds with rGO, leading to the coating of PEG on GO and thus the separation of rGO from TPU. Interestingly, PEG and rGO showed significant synergistic effect on the dielectric constant (ε′) of the composites, resulting in the large increase in ε′ at 103 Hz from 7 for pristine TPU to 71 for TPU/PEG/rGO composite. This was attributed to the increase in dipole polarizability of TPU chains caused by the disruption of hydrogen bonds and the increase in interfacial polarizability caused by the favorable electron transfer from partially reduced GO coated by PEG to TPU. The elastic modulus (Y) of the TPU/PEG/rGO composites largely decreased because of the plasticizing effect of PEG and the separation of GO from TPU. Owing to the simultaneous increase in ε′ and decrease in Y, the composite showed 49 times increase in electromechanical sensitivity (β) and 6.5 times increase in actuated strain at a certain electric field over that of pristine TPU.

Fumed silica/polyurethane nanocomposites: effect of silica concentration and its surface modification on rheology and mechanical properties

The effects of nanosilica type and its content on microstructure, mechanical properties, and rheology of thermoplastic polyurethane (TPU) nanocomposites were investigated. Three different types of silica which included: unmodified (Si-Un) and commercially modified with octylsilane (Si-OS) and polydimethylsiloxane (Si-PDMS) with 5, 10, and 15 wt% of all fillers, were prepared by solution casting method. Scanning electron microscopy (SEM) showed that surface treatment of nanosilica with OS and PDMS reduced the aggregation of particles and improved their dispersion at microlevel. The effect of adding nanoparticles on microdomain morphology of TPU was studied by transmission electron microscopy (TEM), infrared spectroscopy (FTIR), and differential scanning calorimetry (DSC). The results demonstrated a relatively good interaction between the hard and soft segments in the presence of treated nanosilica that hindered the crystallization of hard segments in TPU. Thermogravimetric analysis (TGA) and tensile test showed that nanocomposites with treated nanosilica have better thermal stability and mechanical properties. The dynamic rheological studies indicated that nanocomposites containing Si-OS and Si-PDMS (with better dispersion and higher interface between the soft and hard domains in TPU) have improved viscoelastic properties in comparison with nanocomposites with untreated silica. In this study, dynamic frequency sweep data were correlated by a generalized Maxwell model and found that elastic constants of TPU chains were improved in the presence of modified silica nanoparticles.

Improved actuated strain of dielectric elastomer through disruption of hydrogen bonds of thermoplastic polyurethane by adding diaminonaphthalene

We used a novel and simple approach to increase the actuated strain at low electric field of thermoplastic polyurethane (TPU) through the disruption of the hydrogen bonds of TPU by adding diaminonaphthalene (DAN) into the matrix. DAN as proton donors disrupted the original N–H/C=O hydrogen bonds between the TPU chains, improving the polarizability of the chains, thus increasing the dielectric constant of TPU. Meanwhile, DAN greatly decreased the elastic modulus of TPU by disrupting the hydrogen bonds of TPU. The simultaneous increase in dielectric constant and decrease in elastic modulus resulted in a 330% increase in electromechanical sensitivity at 103 Hz and a 500% increase in actuated strain at the low electric field of 20 V μm−1, facilitating the application of dielectric elastomers (DEs) in the biological and medical fields, where a low electric field is required. In addition, our DAN/TPU DE exhibited good mechanical strength.

Largely improved actuation strain at low electric field of dielectric elastomer by combining disrupting hydrogen bonds with ionic conductivity

Dielectric elastomer actuators (DEAs) can lead to surprisingly large deformations by applying an electric field. The biggest challenge for DEAs is to get a large actuated strain at a low electric field. Herein, a novel approach was used to largely improve the actuated strain at a low electric field of a thermoplastic polyurethane (TPU) dielectric elastomer (DE) by introducing polyethylene glycol (PEG) oligomer into the matrix. The dielectric constant (er) of TPU was obviously increased by adding PEG due to the combined effect of the increase in the interfacial polarization ability of TPU/PEG blends by the ionic conductivity of PEG and the increase in dipole polarization ability of TPU chain segments by the disruption of hydrogen bonds of TPU chains. Meanwhile, the elastic modulus (Y) of TPU was obviously decreased due to the plasticizing effect of PEG on TPU. The simultaneous increase in er and decrease in Y resulted in a 7500% increase in actuated strain at a low electric field (3 V μm−1) by adding PEG. The actuated strain (5.22% at 3 V μm−1) is considerably higher than that of other DEs at the same electric field reported in the literatures. Our work provides a simple and effective method to largely improve the actuated strain at a low electric field of a DE, facilitating the application of DE in biological and medical fields.

Electronic, electric and electrochemical properties of bioactive nanomembranes made of polythiophene:thermoplastic polyurethane

The electronic, electric and electrochemical response of nanomembranes prepared by using spin-coating mixtures of a semiconducting polythiophene derivative (P3TMA) and thermoplastic polyurethane (TPU) has been exhaustively examined by UV-vis spectroscopy, conductive AFM, current/voltage measurements and cyclic voltammetry. TPU:P3TMA nanomembranes were reported to be good substrates for applications related to tissue engineering, acting as a cellular matrix for cell adhesion and proliferation. Both TPU:P3TMA and P3TMA nanomembranes show semiconductor behavior with very similar band gap energy (2.35 and 2.32 eV, respectively), which has been attributed to the influence of the fabrication process on the π-conjugation length and packing interactions of P3TMA chains. This behavior is in opposition to the observations in THF solution, which indicates that the band gap energy of P3TMA is clearly lower than that of the mixture, independently of the concentration. The current and conductivity values determined for the nanomembranes, which range from 0.43 to 1.85 pA and from 2.23 × 10−5 to 5.19 × 10−6 S cm−1, respectively, evidence inhomogeneity in the P3TMA-rich domains. This has been associated with the irregular distribution of the doped chains and the presence of insulating TPU chains. The voltammetric response of TPU:P3TMA and P3TMA nanomembranes is similar in terms of ability to store charge and electrochemical stability. Overall results indicate that TPU:P3TMA nanomembranes are potential candidates for the fabrication of bioactive substrates able to promote cell regeneration through electrical or electrochemical stimulation.

Molecular-level modeling and experimental investigation into the high performance nature and low hysteresis of thermoplastic polyurethane/multi-walled carbon nanotube nanocomposites

Multi-walled carbon nanotube (MWCNT) reinforced thermoplastic polyurethane (TPU) nanocomposites were prepared using solution casting techniques and exhibited better thermal stability and improved mechanical performance. Scanning electron microscopy indicated a homogeneous dispersion of the carbon nanotubes (CNT) within the polymeric matrix at low filler loadings and a cluster formation at higher loadings. Stress–strain of the MWCNT-TPU nanocomposites showed optimum performance and lowest hysteresis for the 0.5% MWCNT nanocomposites due to the confinement of the TPU chains between the large number of the nanofiller particles. Molecular modeling showed that low MWCNTs content caused the moduli to increase due to the drastic drop in the number of configurational states accessible to the chains, which resulted in a significant decrease in the entropy of the chains and a corresponding increase in the elastic moduli. Higher MWCNTs loadings caused a restriction in the TPU movement as indicated by its mean-square displacements. The enthalpy of mixing the TPU with MWCNTs was estimated and confirmed the repulsive interactions between the nanoparticles (MWCNT) and the polymeric chains, which created an additional excluded volume that the TPU segments were not allowed to occupy and thus forcing the conformational characteristics of the polymeric chains to deviate away from those of the bulk chains.

Effect of organoclay with various organic modifiers on the morphological, mechanical, and gas barrier properties of thermoplastic polyurethane/organoclay nanocomposites

Thermoplastic polyurethane (TPU)/organoclay nanocomposites are prepared through a melt extrusion process. The TPU is combined with four differently modified organoclays, namely, I.28E, I.30P, I.34TCN, and I.44P. Wide-angle X-ray diffraction and transmission electron microscopy results show that the addition of I.34TCN and I.30P to TPU/organoclay nanocomposites results in the nearly exfoliated structures of the nanocomposites. Addition of I.28E leads to partially intercalated nanocomposites, whereas I.44P cannot disperse effectively in the nanocomposites. Organoclay can enhance the mechanical and gas barrier properties of TPU. The enhancement follows the order TPU/I.34TCN ≥ TPU/I.30P > TPU/I.28E > TPU/I.44P, which is consistent with the degree of dispersion and exfoliation of silicate layers. In addition, Fourier transform infrared absorption spectra show that more hydrogen bonding sites are introduced between the clay modifiers and TPU chains in the TPU/I.34TCN and TPU/I.30P nanocomposites; this has a positive impact on the dispersion of the organoclay and, consequently, the mechanical and gas barrier properties of the nanocomposites.

A new process for crosslinking thermoplastic polyurethanes using rubber industry techniques

AbstractNew polyurethane materials were obtained after chemical modification of a commercial thermoplastic polyurethane (TPU) using diisocyanates and diols or diamines. The reaction can be easily processed by the well‐known calendering technique often used by the rubber industry. It leads to a remarkable improvement of the thermomechanical properties of the material, due to the formation of chemical crosslinks between the TPU chains (“vulcanization”). As this new processing consists only of an intimate mixing of the starting TPU with solid reagents, followed by molding and curing stages, it allows the use of any and possibly highly reactive solid monomer (especially damines), which could not otherwise be considered except with constraining techniques like RIM; in the same way, the incorporation of organic or inorganic fillers also becomes possible.

Miscibility in thermoplastic polyurethane elastomer/poly(styrene-co-acrylonitrile) blends

Blends of a thermoplastic polyurethane (TPU) with poly(styrene-co-acrylonitrile) (SAN) were investigated by differential scanning calorimetry (DSC) and dielectric spectroscopy. Blends were prepared by kneading. A shift of the glass transition temperatures ( T g ) and specific heat increments ( ΔC p ) at the T g have shown that SAN dissolves more in the TPU-rich phase than TPU in the SAN-rich phase. From dielectric measurements it could be concluded that the relaxation processes in the TPU/SAN blends occur at the same temperatures as the relaxation processes in pure components, which suggests that the motions of TPU chains are decoupled from the motions of SAN chains. The addition of TPU to SAN copolymer causes a plasticizing effect at very low concentrations.

Moulding a mould and a mould liner skin of composite material for moulding an article of composite material: (British Aerospace plc, UK) GB 2 243 107 A (23 October 1991)

Graphene oxide (GO) is usually used as a precursor of reduced GO (rGO) in polymer matrices for improving their properties. However, reduction degree of GO in conventional melt mixing is usually limited. In this work, thermoplastic polyurethane (TPU)/rGO nanocomposite is prepared via water-assisted mixing extrusion with vitamin C (VC) aqueous solution injection. In situ chemical reduction (ISCR) by the VC and in situ thermal reduction (ISTR) by the thermal energy from both extruder barrel heating and screw shear are simultaneously enhanced for the GO, which are indicated by disappearances of O–H peak at the FTIR spectrum and O–C=O peak at the XPS spectrum of the rGO powder extracted from the prepared nanocomposite. Thus high reduction degree of the GO is obtained (with C/O atom ratio of 9.83 for the extracted rGO powder). This is attributed to the following two aspects: (1) TPU chains plasticized by water can better intercalate into GO galleries, thus enhancing the stripping of oxygen-containing groups from GO surface and the ISTR of the GO; (2) the screw shear action helps to disperse the VC of the injected VC aqueous solution in the TPU melt and increase the contact between the VC and GO, therefore enhancing the ISCR of the GO. The prepared TPU/GO nanocomposite exhibits enhanced dielectric permittivity.