Series Of Thermoplastic Polyurethanes Research Articles

3D-Printed Thermoplastic Polyurethane Electrodes for Customizable, Flexible Lithium-Ion Batteries with an Ultra-Long Lifetime.

3D printing technology has demonstrated great potential in fabricating flexible and customizable high-performance batteries, which are highly desired in the forthcoming intelligent and ubiquitous energy era. However, a significant performance gap, especially in cycling stability, still exists between the 3D-printed and conventional electrodes, seriously limiting the practical applications of 3D-printed batteries. Here, for the first time, a series of thermoplastic polyurethane (TPU)-based 3D-printed electrodes is developed via fused deposition modeling for flexible and customizable high-performance lithium-ion batteries. The TPU-based electrode filaments in kilogram order are prepared via a facile extrusion method. As a result, the electrodes are well-printed with high dimensional accuracy, flexibility, and mechanical stability. Notably, 3D-printed TPU-LFP electrodes exhibit a capacity retention of 100% after 300 cycles at 1C, which is among the best cycling performance of all the reported 3D-printed electrodes. Such excellent performance is associated with the superb stress cushioning properties of the TPU-based electrodes that can accommodate the volume change during the cycling and thus significantly prevent the collapse of 3D-printed electrode structures. The findings not only provide a new avenue to achieve customizable and flexible batteries but also guide a promising way to erase the performance gap between 3D-printed and conventional lithium-ion batteries.

Depolymerised lignin oil: A promising building block towards thermoplasticity in polyurethanes

The use of lignin as building block in the preparation of lignin-based thermoplastics has been a great challenge for the scientific community. Indeed, both the heterogeneous branched structure and the high hydroxyl functionality of lignin favours crosslinking reactions leading to the formation of thermosetting chemical structures. Some attempts have been made to circumvent these limitations, although the approaches required labour-intensive and time-consuming modifications of lignin and used only a relatively low amount in the materials. To tackle this problem, the present work employs lignin hydrogenolysis oil (LHO) which contains a low hydroxyl functionality oligomeric fraction suitable for the synthesis of thermoplastic polyurethanes (TPUs) via a two-step polymerization process. A series of TPUs were synthesized to investigate the impact of lignin content as well as soft segment molar mass on the chemical and thermo-mechanical properties of the materials. The study demonstrates that the use of high lignin content (38–46 wt. %) and high molar mass of the polyol (polypropylene glycol, PPG, Mn=4 kg mol−1) enhanced the mechanical properties of the obtained TPUs compared to counterpart polymers synthesized with lower molar mass of PPG. Additionally, LHO-based TPUs were applied as hot-melt adhesives for wood and their bonding strengths were evaluated by single lap shear tests. The lap shear adhesiveness was found to increase with increasing LHO concentration and decreasing molar mass of PPG. The developed methodology could lead to the preparation of robust thermoplastic lignin-based polyurethanes with a wide range of desired properties.

Multi-stimuli responsive shape memory behavior of dual-switch TPU/CB/CNC hybrid nanocomposites as triggered by heat, water, ethanol, and pH

Herein, a series of thermoplastic polyurethane (TPU)/carbomer (CB)/nano-celluloses (CNCs) multi-responsive shape-memory nanocomposite films were tailored using CNCs as a crosslinker. The impact of CNCs content on the mechanical properties of the TPU/CB/CNC nanocomposite films has been comprehensively studied by which the best CNCs loading was reported at 5 wt%. The chemistry and microstructure of the nanocomposite film have been precisely elucidated by FT-IR spectroscopy, 1H NMR spectrum, XRD, and DSC to verify the reaction of –CO-NH– in TPU with –COOH in CB—forming quaternary ammonium ionic and hydrogen bonds. The shape-memory properties of the TPU/CB/CNC nanocomposite film were also investigated in different conditions such as water, ethanol, acid, alkali, and heat. Moreover, the shape recovery behavior of the nanocomposite film was examined by changing pH, which affects the quaternary ammonium ionic and hydrogen bonds as switch units. Although the shape of the thin nanocomposite film has successfully recovered in the alkaline environment, the internal structure was damaged. After transfer to the acidic environment, the destroyed internal structure of the strip was revived, and its strength improved to carry a foolproof load. Eventually, the as-made nanocomposite film has a multi-responsive capability against water, ethanol, pH, and heat, representing its potential in slow-release drug and flexible robotic as well as electronic applications.

Elastic Nanofibrous Membranes for Medical and Personal Protection Applications: Manufacturing, Anti-COVID-19, and Anti-Colistin Resistant Bacteria Evaluation.

Herein, in the present work two series of thermoplastic polyurethane (TPU) nanofibers were manufactured using the electrospinning techniques with ZnO and CuO nanoparticles for a potential use as an elastic functional layer in antimicrobial applications. Percentages of 0%, 2 wt%, and 4 wt% of the nanoparticles were used. The morphological characterization of the electrospun TPU and TPU/NPs composites nanofibers were observed by using scanning electron microscopy to show the average fiber diameter and it was in the range of 90–150 nm with a significant impact of the nanoparticle type. Mechanical characterization showed that TPU nanofiber membranes exhibit excellent mechanical properties with ultra-high elastic properties. Elongation at break reached up to 92.5%. The assessment of the developed nanofiber membranes for medical and personal protection applications was done against various colistin resistant bacterial strains and the results showed an increment activity by increasing the metal oxide concentration up to 83% reduction rate by using TPU/ZnO 4% nanofibers against K. pneumoniae strain 10. The bacterial growth was completely eradicated after 8 and 16 h incubation with TPU/ZnO and TPU/CuO nanofibers, respectively. The nanofibers SEM study reveals the adsorption of the bacterial cells on the metal oxides nanofibers surface which led to cell lysis and releasing of their content. Finally, in vitro study against Spike S-protein from SARS-CoV-2 was also evaluated to investigate the potent effectiveness of the proposed nanofibers in the virus deactivation. The results showed that the metal oxide concentration is an effective factor in the antiviral activity due to the observed pattern of increasing the antibacterial and antiviral activity by increasing the metal oxide concentration; however, TPU/ZnO nanofibers showed a potent antiviral activity in relation to TPU/CuO.

Analysis of the Foaming Window for Thermoplastic Polyurethane with Different Hard Segment Contents

A series of thermoplastic polyurethanes (TPUs) with different amounts of hard segments (HS) (40, 50 and 60 wt.%) are synthesized by a pre-polymer method. These synthesized TPUs are characterized by Shore hardness, gel permeation chromatography (GPC), differential scanning calorimetry (DSC), wide angle X-ray diffraction (WAXD), dynamic mechanical thermal analysis (DMTA), and rheology. Then, these materials are foamed by a one-step gas dissolution foaming process and the processing window that allows producing homogeneous foams is analyzed. The effect of foaming temperature from 140 to 180 °C on the cellular structure and on density is evaluated, fixing a saturation pressure of 20 MPa and a saturation time of 1 h. Among the TPUs studied, only that with 50 wt.% HS allows obtaining a stable foam, whose better features are reached after foaming at 170 °C. Finally, the foaming of TPU with 50 wt.% HS is optimized by varying the saturation pressure from 10 to 25 MPa at 170 °C. The optimum saturation and foaming conditions are 25 MPa and 170 °C for 1 h, which gives foams with the lowest relative density of 0.74, the smallest average cell size of 4 μm, and the higher cell nucleation density of 8.0 × 109 nuclei/cm3. As a final conclusion of this investigation, the TPU with 50 wt.% HS is the only one that can be foamed under the saturation and foaming conditions used in this study. TPU foams containing 50 wt.% HS with a cell size below 15 microns and porosity of 1.4–18.6% can be obtained using foaming temperatures from 140 to 180 °C, saturation pressure of 20 MPa, and saturation time of 1 h. Varying the saturation pressure from 10 to 25 MPa and fixing the foaming temperature of 170 °C and saturation pressure of 1 h results in TPU foams with a cell size of below 37 microns and porosity of 1.7–21.2%.

Green and controlled synthesis of short diol oligomers from polyhydroxyalkanoate to develop fully biobased thermoplastics

Polyhydroxyalkanoates (PHAs) are a biodegradable and biobased family of bacterial polyesters with different architectures. Among them, the poly-3-hydroxybutyrate (PHB) is one of the most conventional and easily obtained by biotechnologies from different bioresources. However, this thermoplastic polyester known since more than 50 years presents until now only very limited applications due to a certain number of drawbacks such as poor mechanical properties, high degree of crystallinity, and low thermal stability. One major way to valorize this bacterial polyester could be to develop controlled building blocks for the synthesis of new generation of biobased polymers. In this way, short linear PHB diols oligomers (oligoPHB-diol) with controlled low molar masses have been successfully obtained from a new synthetic pathway using reactive solvents in a green way. Different transesterification reaction parameters were investigated to control the PHB molar mass decrease, such as the catalyst and reactive solvent contents, the temperature and the reactive solvent type. Obtained oligomers were then analyzed in detail and further incorporated into fully biobased thermoplastics. In this work, thermoplastic polyurethanes (TPU) were elaborated as an example of second-generation biobased thermoplastics. To obtain TPUs with high biobased content, a dimer fatty acid-based diisocyanate, the dimeryl diisocyanate, and another biobased diol, the isosorbide, were used. Two series of TPUs were prepared with (i) varying the isosorbide/oligoPHB-diol ratio, and (ii) different oligoPHB-diol molar mass. Materials were fully evaluated for their structural, thermal and mechanical properties, as well as their crystalline behavior. A large range of properties were obtained for these innovative thermoplastics which could open a large range of applications with a green and sustainable approach.

Effect of molecular weight on the properties of polyethylene glycol polyurethane-co-polydimethylsiloxane polyurethane

ABSTRACT A series of thermoplastic polyurethanes (TPUs) composed of polyethylene glycol polyurethane (PEG-PU) and polydimethylsiloxane polyurethane (PDMS-PU) were prepared to examine the effects of the PEG molecular weight (MW) on the surface and physical properties. The adaptive PEG-PU-co-PDMS-PU structures resembled the architectures of a diblock copolymer, which used the MW-fractionated PEG. The sufficient MW dependence was observed within the range 200 < MW < 400, indicating that the increased urethane groups of PEG-PU block limit the surface and physical properties of these samples. The difference in properties according to the degree of the urethane groups was evaluated using a universal test machine (UTM) as well as by measuring the contact angle and water vapor transmission rate (WVTR).

Solvent-Free One-Shot Synthesis of Thermoplastic Polyurethane Based on Bio-Poly(1,3-propylene succinate) Glycol with Temperature-Sensitive Shape Memory Behavior.

In this work, a new family of fully biobased thermoplastic polyurethanes (TPUs) with thermo-induced shape memory is developed. First, a series of TPUs were successfully synthesized by the one-shot solvent-free bulk polymerization of bio-poly(1,3-propylene succinate) glycol (PPS) with various molecular weights (Mn = 1000, 2000, 3000, and 4000), 1,4-butanediol (BDO), and 4,4′-methylene diphenyl diisocyanate (MDI). These polyurethanes (PUs) are denoted as PPS-x-TPUs (x = 1000, 2000, 3000, and 4000), where x represents the Mn of PPS in the polymers. To determine the effect of the molecular weight of the soft segment of PU, all PPS–TPUs were formed with the same hard segment content (32.5 wt %). The soft segment with high molecular weight in PPS-4000-TPU caused a high degree of soft segment entanglement and formed many secondary bonds. PPS-4000-TPU exhibited better mechanical (tensile strength: 64.13 MPa and hardness: 90A) and thermomechanical properties (maximum loading: 2.95 MPa and maximum strain: 144%) than PPS-1000-TPU. At an appropriate shape memory programming temperature, all synthesized PPS-x-TPUs exhibited excellent shape memory behaviors with a fixed shape rate of >99% and a shape recovery rate of >86% in the first round and 95% in the following rounds. Therefore, these bio-TPUs with shape memory have potential for use in smart fabrics.

TPU/PLA blend foams: Enhanced foamability, structural stability, and implications for shape memory foams

ABSTRACTA series of thermoplastic polyurethane (TPU)/poly(lactic acid) (PLA) blends are studied in terms of morphological, thermal, and rheological properties by scanning electron microscopy, differential scanning calorimetry, and rheometry. Using supercritical CO2 batch foaming, the foamability of the blends is systematically investigated. It is found that the 80/20 (wt %/wt %) TPU/PLA blend (TPU80%) shows vastly enhanced foamability over a wide range of foaming conditions to produce foams with a myriad of cellular morphology. The foamability enhancement results from the improved cell nucleation and growth, and the changes in the polymer microstructure. Compared to elastic TPU foams, the TPU80% retain their shapes 3.4 times better. Mechanism for the enhanced stability is proposed and verified using Kohlrausch–Williams–Watts model. The materials developed in the study and the mechanistic understanding of the shape fixation process may facilitate the advancement of elastomeric foams in conventional use as well as in novel shape memory applications. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47416.

Thermoplastic PCL-b-PEG-b-PCL and HDI Polyurethanes for Extrusion-Based 3D-Printing of Tough Hydrogels.

Novel tough hydrogel materials are required for 3D-printing applications. Here, a series of thermoplastic polyurethanes (TPUs) based on poly(ɛ-caprolactone)-b-poly(ethylene glycol)-b-poly(ɛ-caprolactone) (PCL-b-PEG-b-PCL) triblock copolymers and hexamethylene diisocyanate (HDI) were developed with PEG contents varying between 30 and 70 mol%. These showed excellent mechanical properties not only when dry, but also when hydrated: TPUs prepared from PCL-b-PEG-b-PCL with PEG of Mn 6 kg/mol (PCL7-PEG6-PCL7) took up 122 wt.% upon hydration and had an E-modulus of 52 ± 10 MPa, a tensile strength of 17 ± 2 MPa, and a strain at break of 1553 ± 155% in the hydrated state. They had a fracture energy of 17976 ± 3011 N/mm2 and a high tearing energy of 72 kJ/m2. TPUs prepared using PEG with Mn of 10 kg/mol (PCL5-PEG10-PCL5) took up 534% water and were more flexible. When wet, they had an E-modulus of 7 ± 2 MPa, a tensile strength of 4 ± 1 MPa, and a strain at break of 147 ± 41%. These hydrogels had a fracture energy of 513 ± 267 N/mm2 and a tearing energy of 16 kJ/m2. The latter TPU was first extruded into filaments and then processed into designed porous hydrogel structures by 3D-printing. These hydrogels can be used in 3D printing of tissue engineering scaffolds with high fracture toughness.

Effect of soft/hard segments in poly (tetramethylene glycol)-Polyurethane for water barrier film

A series of thermoplastic polyurethanes (TPUs) with the same molecular weight but different soft/hard ratios were synthesized by in-situ condensation polymerization using poly (tetramethylene glycol) (PTMG) as the polyol and methylene diphenyl diisocyanate (MDI) as the isocyanate. The weight fractions of the hard segments were varied from 0.0 to 0.4. The structures of the TPU series were analyzed by Fourier transform infrared spectroscopy and gel permeation chromatography. The changes in the thermal and optical properties due to the hard segment crystallinity were also measured by differential scanning calorimetry and UV–vis spectroscopy. Increasing the hard content promoted phase separation and served as absorption blocks in the TPU. The water vapor permeability of the TPU films with different soft/hard ratios ranged from 223.63 to 116.26 g/m2 day.

Clarifying the Origin of Multiple Melting of Segmented Thermoplastic Polyurethanes by Fast Scanning Calorimetry

Segmented thermoplastic polyurethanes (TPU) often show multiple endothermic signals during melting in conventional differential scanning calorimetry (DSC). Repeated reorganization during heating and separate crystal melting and phase mixing have been proposed as the origin of this phenomenon. We used fast scanning calorimetry on a series of TPUs with polyether soft segments and hard segments consisting of 4,4′-methylenediphenyl diisocyanate and 1,4-butanediol to differentiate between the two possibilities. Fast heating scans (>500 °C s–1) of isothermally crystallized samples exhibited only a single melting peak, while complementary experiments on quenched, fully amorphous samples showed a single glass transition step indicating a homogeneous mixed phase. These results prove that the multiple melting peaks observed in DSC are related to reorganization during heating, i.e., repeated melting and recrystallization. Phase separation during cooling of such TPUs is induced by crystallization. A comparison with c...

Dynamic thermo-mechanical and impact properties of helical auxetic yarns

Abstract This paper presents an experimental investigation of the dynamic thermo-mechanical and impact properties of helical auxetic yarns (HAYs). A series of thermoplastic polyurethane (TPU) core fibres fabricated using an extrusion process have been wrapped with either ultra-high-molecular-weight polyethylene (UHMWPE) wrap or stainless steel wire wrap to form helical auxetic yarns. Dynamic mechanical analysis (DMA) measurements indicated that the core/wrap diameter ratio and the initial wrap angle influenced significantly the dynamic thermo-mechanical behaviour of HAYs. The impact test results have shown that the fibre property, impact velocity and the initial wrap angle had great effect on the impact response of a HAY. Importantly, in this work it is shown that an optimal wrap angle can be found to give the best combination of stiffness, energy absorption and auxetic performance of HAYs.

Morphology and Mechanical Properties of Thermoplastic Polyurethanes Containing Polyisobutylene/Poly(tetramethylene oxide) Mixed Segments

We investigated the thermal properties, microphase separated structure and mechanical properties of a series of thermoplastic polyurethanes (TPUs) containing both polyisobutylene (PIB) and poly(tetramethylene oxide) (PTMO) diols in the soft segment (SS). A series of TPUs were prepared with the same weight fraction of the SS but different ratio between PIB and PTMO diols. Molecular weight of the PTMO diol and chemical structure of the hard segment (HS) also varied. Dynamic mechanical analysis (DMA) measurements did not reveal strong microphase separation between PIB and PTMO in the SS. While it has been assumed that incorporating PTMO diol into the SS can enhance the phase mixing between the hard segment (HS) and SS, our results indicated that, in most cases, the degree of microphase separation of TPUs based on mixed diols is slightly higher than that of TPUs based on only PIB diol.

Thermoplastic polyurethanes with isosorbide chain extender

ABSTRACTIsosorbide, a renewable diol derived from starch, was used alone or in combination with butane diol (BD) as the chain extender in two series of thermoplastic polyurethanes (TPU) with 50 and 70% polytetramethylene ether glycol (PTMEG) soft segment concentration (SSC), respectively. In the synthesized TPUs, the hard segment composition was systematically varied in both series following BD/isosorbide molar ratios of 100 : 0; 75 : 25; 50 : 50; 25 : 75, and 0 : 100 to examine in detail the effect of chain extenders on properties of segmented polyurethane elastomers with different morphologies. We found that polyurethanes with 50% SSC were hard elastomers with Shore D hardness of around 50, which is consistent with assumed co‐continuous morphology. Polymers with 70% SSC displayed lower Shore A hardness of 74–79 (Shore D around 25) as a result of globular hard domains dispersed in the soft matrix. Insertion of isosorbide increased rigidity, melting point and glass transition temperature of hard segments and tensile strength of elastomers with 50% SSC. These effects were weaker or non‐existent in 70% SSC series due to the short hard segments and low content of isosorbide. We also found that the thermal stability was lowered by increasing isosorbide content in both series. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42830.

Thermoplastic polyurethanes with controlled morphology based on methylenediphenyldiisocyanate/isosorbide/butanediol hard segments

Isosorbide, a cyclic, rigid and renewable diol, was used as a chain extender in two series of thermoplastic polyurethanes (PUs). Isosorbide was used alone or in combination with butanediol to examine the effects on the morphology of PU. Two series of materials were prepared – one with dispersed hard domains in a matrix of polytetramethylene ether glycol soft segments of molecular weight 1400 g mol−1 (at 70 wt% soft segment concentration, SSC) and the other with co-continuous soft and hard phases at 50 wt% SSC. We investigated the detailed morphology of these materials with optical and atomic force microscopy, as well as ultra-small-angle X-ray scattering. The atomic force microscopy measurements confirmed the different morphologies in PUs with 50 wt% SSC and with 70 wt% SSC. Small-angle X-ray scattering data showed that in PU with 70 wt% SSC, the hard domain size varied between 2.4 and 2.9 nm, and decreased with increasing isosorbide content. In PU with 70 wt% SSC, we found that the correlation length and average repeat distances became smaller with increasing isosorbide content. We estimated the thickness of the diffuse phase boundary for PU with 70 wt% SSC to be ca 0.5 nm, decreasing slightly with increasing isosorbide content. © 2015 Society of Chemical Industry

Mechanical, Thermal and Morphology Properties of Thermoplastic Polyurethane Copolymers Incorporating α,ω-Dihydroxy-[poly(propyleneoxide)-poly (dimethylsiloxane)-poly(propyleneoxide)] of Varying Poly(propyleneoxide) Molecular Weight

Novel segmented thermoplastic polyurethane (TPU) copolymers were synthesized using two-step solventless bulk polymerization. 4,4’-methylenediphenyl diisocyanate (MDI) and 1,4-Butanediol (BDO) were used to form hard segment of TPU and α,ω-dihydroxy-[poly(propyleneoxide)-poly (dimethylsiloxane)-poly(propyleneoxide)] (α,ω-dihydroxy-(PPO-PDMS-PPO)) was used to form soft segment of TPU, where the molar ratio of the –N=C=O/OH was 1.02 and the hard segment weight percentage was 30%. A series of TPUs were characterized by fourier transform infrared spectroscopy (FT-IR). The investigation of triblock oligomer’s PPO molecular weight impact on the derived TPU’s mechanical properties, thermal performance, surface water repellency and morphology performance was carried by Instron material tester, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), water contact angles (WCA), scanning electron microscope and energy dispersive X-ray spectroscopy (SEM-EDX) and wide angle X-ray diffraction (WAXD), respectively. FT-IR confirmed α,ω-dihydroxy-(PPO-PDMS-PPO) well cooperating into urethane structure and analyzed hydrogen bonding between N-H group with hard segment C=O group and N-H group with soft segment C-O-C group. DSC and WAXD results showed α,ω-dihydroxy-(PPO-PDMS-PPO) segments crystallization. SEM-EDX results showed that the presence of a spherulitic morphology, which arose from the crystallization of the PPO segments. The thermal properties measured by TGA and DSC were slightly affected by molecular weight of PPO and microphase separation. The weight loss of TPUs started between 294°C and 300°C, and Tg was in the range of -70°C to -107°C. TPU copolymers’ surface hydrophobicity property was excellent with WCA range of 95° to 112°. TPU-3 with 1000 molecular weight PPO has the optimized mechanical properties with tensile strength 16.4 MPa and the modulus at 100% elongation 6.2 MPa and elongation 398%.

Simultaneous Reinforcing and Toughening of Polyurethane via Grafting on the Surface of Microfibrillated Cellulose

In the present work, a series of thermoplastic polyurethane (TPU)/microfibrillated cellulose (MFC) nanocomposites were successfully synthesized via in situ polymerization. TPU was covalently grafted onto the MFC by particular association with the hard segments, as evidenced by Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and thermogravimetric analysis. The adequate dispersion and network structure of MFC in the TPU matrix and the strong interfacial interaction through covalent grafting and hydrogen bonding between MFC and TPU resulted in significantly improved mechanical properties and thermostability of the prepared nanocomposites. The tensile strength and elongation-at-break of the nanocomposite containing only 1 wt % MFC were increased by 4.5-fold and 1.8-fold compared with that of neat TPU, respectively. It was also very interesting to find that the glass transition temperature (Tg) of TPU was decreased significantly with the introduction of MFC, indicating potential for low-temperature resistance applications. Most importantly, compared with TPU nanocomposites reinforced with other nanofillers, the TPU/MFC nanocomposites prepared in this work exhibited excellent transparency and higher reinforcing efficiency.

Electrospinning Thermoplastic Polyurethane-Contained Collagen Nanofibers for Tissue-Engineering Applications

Electrospinning is a new method used in tissue engineering. It can spin fibers in nanoscale by electrostatic force. A series of thermoplastic polyurethane (TPU)/collagen blend nanofibrous membranes was prepared with different weight ratios and concentrations via electrospinning. The two biopolymers used 1,1,1,3,3,3,-hexafluoro-2-propanol (HFP) as solvent. The electrospun TPU-contained collagen nanofibers were characterized using scanning electron microscopy (SEM), XPS spectroscopy, atomic force microscopy, apparent density and porosity measurement, contact-angle measurement, mechanical tensile testing and viability of pig iliac endothelial cells (PIECs) on blended nanofiber mats. Our data indicate that fiber diameter was influenced by both polymer concentration and blend weight ratio of collagen to TPU. The average diameter of nanofibers gradually decreases with increasing collagen content in the blend. XPS analysis indicates that collagen is found to be present at the surface of blended nanofiber. The results of porosity and contact-angle measurement suggest that with the collagen content in the blend system, the porosity and hydrophilicity of the nanofiber mats is greatly improved. We have also characterized the molecular interactions in TPU/collagen complex by Fourier transform infrared spectroscopy (FT-IR). The result could demonstrate that there were no intermolecular bonds between the molecules of TPU and collagen. The ultimate tensile stress and strain were carried out and the data confirmed the FT-IR results. The TPU/collagen blend nanofibrous mats were further investigated as promising scaffold for PIEC culture. The cell proliferation and SEM morphology observations showed that the cells could not only favorably grow well on the surface of blend nanofibrous mats, but also able to migrate inside the scaffold within 24 h of culture. These results suggest that the blend nanofibers of TPU/collagen are designed to mimic the native extracellular matrix for tissue engineering and develop functional biomaterials.

Effect of Hard Segments on Morphology and Properties of Thermoplastic Polyurethanes

A series of thermoplastic polyurethanes was synthesized with varying hard segment composition or content and the effect of the hard segments on morphology and properties was studied by differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), thermal mechanical analysis (TMA), Fourier transform infrared analysis (FTIR) and tensile testing. The diisocyanates included 4,4' -diphenylmethane diisocyanate (MDI) and 4,4' -dicyclohexylmethane diisocyanates (H,2MDI). The chain extenders 1,4-butanediol, 1,5-pentanediol and 1,3-butanediol were used. The soft segment material was poly(oxytetramethylene) glycol of molecular weight 2000. It was found that the interchain attractive forces between hard segments affect physical properties and morphologies. The degree of phase mixing, hardness and strength increased with increasing hard segment content and with decreasing degree of hard segment crystallinity (packing arrangements) at the same hard segment content.