Mechanical Properties Of Polyurethane Research Articles

Effect of inorganic fillers on mechanical properties of polyurethanes

Effect of inorganic fillers on mechanical properties of polyurethanes

Effect of Starch Loading on the Thermo-Mechanical and Morphological Properties of Polyurethane Composites.

The advancements in material science and technology have made polyurethane (PU) one of the most important renewable polymers. Enhancing the physio-chemical and mechanical properties of PU has become the theme of this and many other studies. One of these enhancements was carried out by adding starch to PU to form new renewable materials called polyurethane-starch composites (PUS). In this study, PUS composites are prepared by adding starch at 0.5, 1.0, 1.5, and 2.0 wt.% to a PU matrix. The mechanical, thermal, and morphological properties of PU and PUS composites were investigated. Scanning electron microscope (SEM) images of PU and PUS fractured surfaces show cracks and agglomeration in PUS at 1.5 wt.% starch. The thermo-mechanical properties of the PUS composites were improved as starch content increased to 1.5 wt.% and declined by more starch loading. Despite this reduction, the mechanical properties were still better than that of neat PU. The mechanical strength increased as starch content increased to 1.5 wt.%. The tensile, flexural, and impact strengths of the PUS composites were found to be 9.62 MPa, 126.04 MPa, and 12.87 × 10−3 J/mm2, respectively, at 1.5 wt.% starch. Thermal studies showed that the thermal stability and crystallization temperature of the PUS composites increased compared to that of PU. The loss modulus curves showed that neat PU crystallizes at 124 °C and at 127 °C for PUS-0.5 wt.% and rises with increasing loading from 0.5 to 2 wt.%.

Effect of microstructure closed-pore content on the mechanical properties of flexible polyurethane foam

Poroelastic models are constructed based on a set of physical parameters known as the Biot’s parameters (for isotropic materials these are comprised of 5 non-acoustical parameters and 4 mechanical parameters). These macroscopic properties are inter-correlated and dependent on the microstructure of the foam. Therefore, to optimize vibroacoustic behavior, the correlation between foam microstructure and macroscopic properties is needed. In this study, the effect of closed windows content (known as reticulation rate), cell size, and relative density on the mechanical properties of polyurethane (PU) foam are numerically studied using an isotropic, tetrakaidecahedral unit cell. Then, an existing analytical model that correlates unit cell microstructure properties (thickness and length of struts) of fully reticulated foams to their mechanical properties is extended numerically. The membrane thickness is considered to be thinner at the center and larger at the edge of the window. The ratio of membrane thickness to strut thickness is either considered to be fixed or variable. Results show that the Young’s modulus and Poisson’s ratio of unit cells with smaller cells size, when relative density is fixed, are more affected by closed window content.

Low-Initial-Modulus Biodegradable Polyurethane Elastomers for Soft Tissue Regeneration.

The mechanical match between synthetic scaffold and host tissue remains challenging in tissue regeneration. The elastic soft tissues exhibit low initial moduli with a J-shaped tensile curve. Suitable synthetic polymer scaffolds require low initial modulus and elasticity. To achieve these requirements, random copolymers poly(δ-valerolactone-co-ε-caprolactone) (PVCL) and hydrophilic poly(ethylene glycol) (PEG) were combined into a triblock copolymer, PVCL-PEG-PVCL, which was used as a soft segment to synthesize a family of biodegradable elastomeric polyurethanes (PU) with low initial moduli. The triblock copolymers were varied in chemical components, molecular weights, and hydrophilicities. The mechanical properties of polyurethanes in dry and wet states can be tuned by altering the molecular weights and hydrophilicities of the soft segments. Increasing the length of either PVCL or PEG in the soft segments reduced initial moduli of the polyurethane films and scaffolds in dry and wet states. The polymer films are found to have good cell compatibility and to support fibroblast growth in vitro. Selected polyurethanes were processed into porous scaffolds by a thermally induced phase-separation technique. The scaffold from PU-PEG1K-PVCL6K had an initial modulus of 0.60 ± 0.14 MPa, which is comparable with the initial modulus of human myocardium (0.02-0.50 MPa). In vivo mouse subcutaneous implantation of the porous scaffolds showed minimal chronic inflammatory response and intensive cell infiltration, which indicated good tissue compatibility of the scaffolds. Biodegradable polyurethane elastomers with low initial modulus and good biocompatibility and processability would be an attractive alternative scaffold material for soft tissue regeneration, especially for heart muscle.

Characterization of Polyurethane Coated Aerospace Aluminium Alloy (7075) By DSC, XRD and Adhesion Test

The research is envisaging characterizing the Polyurethane (PU) coating on AA 7075 so as to predict the aircraft coating life. Differential Scanning Calorimetry (DSC) and X-ray Diffractometry have been employed to investigate the differences in thermal behavior and crystalline structure of the polyurethane (GB BOND 141). DSC can be used to examine the material from a subambient starting temperature to the glass transition event and finally through the crystalline melting region. X-ray diffraction (XRD) provides important structural information about the polyurethane in the structure of semi-crystalline polymer substance consisting of two phases, viz., amorphous and crystalline as well as their fine texture which has a strong effect on physical and mechanical properties of polyurethane. After analyzing the characteristics, the extent of coating loss is examining visually in order to evaluate the adhesion property before carrying out the peel-off test.

Superior Performance of Polyurethane Based on Natural Melanin Nanoparticles.

Melanin, a kind of well-known multifunctional biomacromolecules that are widely distributed in natural sources. In this work, polyurethane (PU)/melanin nanocomposites with enhanced tensile strength and toughness were successfully fabricated via in situ polymerization. It was found that the tensile strength (σ), elongation-at-break (εmax), and toughness (W) were improved from 5.6 MPa, 770%, and 33 MJ/m3 for PU to 51.5 MPa, 1880%, and 413 MJ/m3 for PU/melanin (2 wt %) nanocomposite, respectively. Micromorphology indicated that individualized melanin nanoparticles were specifically linked to the hard domains of PU chains and fine dispersed in matrix. FTIR, DSC, and AFM results suggested melanin induced an improvement in degree of phase separation, which resulted in remarkable enhancements in mechanical properties of PU. However, with further increasing content of melanin, a relatively large-scale phase separation was formed and led to a decrease in mechanical properties of PU. In addition, interactions between melanin and hard segments of PU were increased, leading to a higher TgHS. Moreover, the dynamic mechanical properties and rheological behavior of PU/melanin nanocomposites were further investigated.

Thermal and mechanical properties of polyurethanes modified with L-ascorbic acid

In this study we report the thermal and mechanical properties of polyurethanes modified with ascorbic acid (AA). Ascorbic acid was used as a modifier at concentration of 1 or 2 mass%. The antioxidative properties of AA may improve the biocompatibility of the obtained materials, which were designed for biomedical applications. In this paper we describe characterization of obtained unmodified and ascorbic acid modified polyurethanes with the use of following methods: dynamic mechanical analysis, thermogravimetric analysis and mechanical tests including tensile strength, elongation at break, abrasive resistance, and hardness. Results of performed studies suggests that synthesized polyurethane materials may be suitable candidates for biomedical applications such as tissue scaffolds or implants, where required tensile strength is in the range of 1–14 MPa and elongation at break is approximately in the range of 100–380 %.

Synthesis of thermally and mechanically improved polyurethane-urea elastomers by using novel diamines as chain extenders

AbstractThis article reports the synthesis of novel diamines as chain extenders for the improvement of thermal and mechanical properties of polyurethane (PU). Three novel diamine, 1,2-di(p-aminophenoxy)ethane (BAE), 1,2-di(p-aminophenoxy)propane (BAP) and 2,2-bis(p-(p-aminophenoxy)phenyl)propane (BAPP) were synthesized as chain extenders. Formation of diamines and their reaction with PU prepolymer was analyzed by using Fourier transform infrared attenuated total reflectance (FTIR-ATR) spectroscopy. The conversion of the free isocyanate group (NCO) into a urethane-urea group was confirmed through the disappearance of the isocyanate peak at 2244 cm-1. The thermogravimetric analysis (TGA) reveals the thermal stabilization effect of urethane-urea hard segments of the polyurethane system. From the SAXS investigations, the hard segment inter-domain spacing (d) was calculated, which was 24 nm for the reference sample, and 25, 26, and 28.5 nm for the synthesized PU systems. Mechanical test shows an increase in the Young’s modulus and yield strength with BAE and BAP diamines, while BAPP diamine based systems reveal lower modulus values as compared to the reference sample.

High cis-1,4 Hydroxyl-Terminated Polybutadiene-Based Polyurethanes with Extremely Low Glass Transition Temperature and Excellent Mechanical Properties

A series of polyurethanes have been prepared from hydroxyl-terminated polybutadiene (HTPB) with high cis-1,4 content and commercial free-radical-polymerized HTPB (FHTPB). The mechanical properties of cured polyurethane (PU) samples have been studied by tensile testing and dynamic mechanical analysis (DMA), and their thermal properties have been tested by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The NCO/OH ratio, chain extension coefficient (r), and microstructure of HTPB and FHTPB have a large influence on the mechanical properties of PUs. Meanwhile, the cyclic tensile testing indicated that the HTPB-based PUs had an outstanding elasticity. Both DSC and DMA analyses showed that the HTPB-based PUs had a glass transition temperature much lower than that of the FHTPB-based PUs. The hydrophobicity of the surface of PUs was verified by measuring their water contact angles.

Effect of Varying Mixing Ratios and Pre-Heat Temperature on the Mechanical Properties of Polyurethane (PU) Foam

The continuous growth of the usage of Polyurethane foams requires that designers and manufacturers investigate the appropriate factors that affect their production and full usage in order to exploit their full potential. This research reports the effects of the mixing ratio of the main constituents (polyol and diisocyanate) which form the polyurethane foams and different pre-heat temperatures of the separate chemicals before mixing. The work has documented that there is a significant reduction of foaming time of 452seconds at 20oC to 54seconds at 100oC when the main constituents are pre-heated before mixing. Both tensile and compressive strengths are improved with increasing the ratio of diisocyanate to polyol. The density of the foam also increases when the concentration of polyol is increased.

Thermal Aging Effect on Mechanical Properties of Polyurethane

This study concerns the effect of thermal aging on mechanical properties of polyurethane. Polyurethane samples were exposed at 85° and 120°C under inert atmosphere. Mechanical tests were carried out on these samples the aging period. Tensile tests were performed to see the effect of aging on elastic modulus (E), stress (σr), and strain (ϵr) at break. It was shown that there are two distinct periods. Due to aging, E and σr increase in the first period, then they decrease in the second period. ϵr decreases first and then increases. Fatigue tests were performed on unaged and aged samples. It was shown that the fatigue behavior of polyurethane (PU) is improved the same way during the first stage of aging. In the second step, the number of cycles to failure increases due to aging. The results show that aging has an important effect on mechanical properties of PU. The strain at break decreases during the first step of aging due to post-cross-linking and then increases due to chain scission in the network. Based on these results, the effect of cross-linking and chain scission on the mechanical properties of PU was discussed.

Polyurethane Nanocomposite Films by Using Cellulose Nanospheres as Green Nanofillers

To overcome poor mechanical properties of polyurethane, carboxylated cellulose nanospheres were incorporated into polyurethane in an organic polar solvent, dimethylformamide to prepare the nanocomposite films. Morphological, structural, mechanical and thermal characterization of the nanocomposites was done with scanning electron microscopy, Fourier transform infrared spectrometry, micro–control electronic universal testing machine and thermal gravimetric analysis. The critical challenge to achieve high macroscale properties of the bulk nanocomposites is the ability to obtain well–dispersed cellulose nanospheres in polymer matrices.

Poly(ε‐caprolactone) and Pluronic Diol‐Containing Segmented Polyurethanes for Shape Memory Performance

A series of novel segmented linear and crosslinked polyurethanes (PUs) are synthesized from poly(ε‐caprolactone) (PCL) (25 kg mol−1), methylene diphenyl diisocyanate (MDI), and various polyether diols (Pluronic (PLU) and polyethylene glycol (PEG)). The basic structures of the highly deformable PUs are PLU/PEG–MDI–PCL–MDI–PLU/PEG and PLU–MDI–PCL–MDI–PLU, respectively. The linear and crosslinked PUs are characterized. Changes in the tensile behavior are attributed to the effects of compositional variables and alterations in the crosslink density. Additional information on the morphology of the segmented PUs is deduced from differential scanning calorimetry, as well as transmission and scanning electron microscopy investigations. Both the linear and the crosslinked PUs exhibit a broad rubbery plateau above the melting temperature of the crystalline PCL phase, which is highly beneficial for shape memory function. This work highlights that the chemical build‐up of soft segments containing high‐molecular‐weight crystallizable chain units is a proper tool to tailor the morphology and mechanical properties of PUs, and thus also their shape memory properties. image

Singlet oxygen generation properties of Fe-OCAP and its influence on the antibacterial and mechanical properties of Fe-OCAP/PU blends

In this paper, the singlet oxygen generation properties of Fe-octacarboxyl acid phthalocyanine (Fe-OCAP)/polyurethane (PU) blends were investigated by ultraviolet–visible spectra. 1,3-diphenylisobenzofuran was used as the reaction substrate to detect the yields of the singlet oxygen of the samples. It was found that Fe-OCAP showed a high efficiency in generating singlet oxygen when it was dissolved in dimethylacetamide (DMAc), while no singlet oxygen was generated when it was in ethanol. The singlet oxygen generation properties of Fe-OCAP/PU blends were also investigated. It was found that with increasing Fe-OCAP content, Fe-OCAP/PU blends showed increased efficiency in generating singlet oxygen. The influence of wavelength of light on the singlet oxygen generation of Fe-OCAP/PU was studied. Compared with orange light, Fe-OCAP/PU had a higher efficiency in generating singlet oxygen under the illumination of red light. The generated singlet oxygen by Fe-OCAP/PU blends had a high efficiency in cell inactivation. As a result, the percentage bacterial reduction of the samples increased with increasing Fe-OCAP content. The influence of the generated singlet oxygen on the mechanical properties of PU was also investigated. The generated singlet oxygen could initiate the oxidation of PU chain and cause the degradation of PU. Therefore, after illuminated by white light, the tensile strength of the samples containing Fe-OCAP decreased, but still was higher than that of pure PU.

Relationship between free volume and mechanical properties of polyurethane irradiated by gamma rays

Polyurethane was irradiated at various gamma radiation doses up to 1,000 kGy at room temperature in nitrogen. Positron annihilation lifetime spectroscopy, tensile test and dynamic mechanical analysis were used to find the relationship between free volume and mechanical properties. An increase of the free volume fraction in soft segments (SS) and a decrease of the free volume fraction in hard segments (HS) during gamma radiation was observed and analyzed. The results showed that HS in polyurethane had the excellent resistance to gamma radiation, whereas SS had a tendency to degrade. The reason for the decrease of the strain at break and the ultimate tensile strength was analyzed, which showed the changes in the mechanical properties of polyurethane irradiated by gamma rays were mainly determined by the changes of free volume in SS. If the resistance properties of polyurethanes exposed to radiations need to be improved, SS should be paid more attention to.

Characterization of solvent-filled polyurethane/urea–formaldehyde core–shell composites

Encapsulation of liquid phases is a crucial step in many self-healing material systems where a healing agent has to be protected during processing and then released during a damage event. In this work, the mechanical properties of polyurethane (PU) reinforced urea–formaldehyde (UF) shells are characterized. It was found that shell thickness is both a function of PU content in the core phase and of the microcapsule diameter. Furthermore, a saturation thickness was found for high PU contents or high capsule diameters and this phenomenon had direct implications on the bursting force under compression of single microcapsules. With help of an analytical model, the Young's modulus of the hybrid PU/UF was determined and in general, PU-reinforced shells had a lower modulus but higher ductility in terms of elongation at break, leading to more resistant microcapsules overall.

The effect of hard/soft segment composition on radiation stability of poly(ester-urethane)s

In this paper studies on the structures and radiation stability of four poly(ester-urethane)s (PUR)s synthesized from oligo(ethylene-butylene adipate)diol of various molecular weights and isophorone diisocyanate/1,4-butanediol are reported. PURs with 40 and 60wt% soft segments were irradiated at ambient temperature with a high energy electron beam to a dose of 112kGy. The effect of different segmental compositions on thermal and mechanical properties of polyurethanes, both before and after irradiation, were investigated using mechanical testing and dynamic mechanical thermal analysis. ATR-FTIR spectroscopy was used to study the progress of polycondensation, structure of synthesized polymers and extent of phase separation were determined on a basis of the contribution of hydrogen bonding in poly(ester-urethane)s. Correlation between degree of phase separation and mechanical and thermal properties of poly(ester-urethane)s was found.

Effect of the diisocyanate structure and the molecular weight of diols on bio‐based polyurethanes

AbstractBio‐based polyurethanes (PU) containing poly(ε‐caprolactone) diol (PCL) and hydroxyl telechelic natural rubber (HTNR) were synthesized. The effect of the diisocyanate structure and the molecular weights of diols on the mechanical properties of PU were investigated. Three different molecular structures of diisocyanate were employed: an aliphatic diisocyanate (hexamethylene diisocyanate, HDI), an aromatic diisocyanate (toluene‐2,4‐diisocyanate, TDI) and a cycloalkane diisocyanate (isophorone diisocyanate, IPDI). Two molecular weights of each diol were selected. When HDI was employed, a crystalline PU was generated while asymmetrical structures of TDI and IPDI provided an amorphous PU. The presence of crystalline domains was responsible of a change in tensile behavior and physical properties. PU containing TDI and IPDI showed a rubber‐like behavior: low Young's modulus and high elongation at break. The crystalline domains in PU containing HDI acted as physical crosslinks, enhancing the Young's modulus and reducing the elongation at break, and they are responsible of the plastic yielding. The crystallinity increased the tear strength, the hardness and the thermal stability of PU. There was no significant difference between the TDI and IPDI on the mechanical properties and the physical characteristics. Higher molecular weight of PCL diol changed tensile behavior from the rubber‐like materials to the plastic yielding. Thermal and dynamic mechanical properties were determined by using DSC, TGA and DMTA. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

Preparation and characterization of microencapsulated ammonium polyphosphate and its synergistic flame-retarded polyurethane rigid foams with expandable graphite

A facile and effective method for the preparation of microencapsulated ammonium polyphosphate (MAPP) by in situ surface polymerization was introduced. The ‘polyurethane-like’ shell structure on the surface of MAPP was characterized by using Fourier transform infrared spectroscopy. The hydrophobicity and thermal behavior of MAPP were studied by using water contact angle tests and thermogravimetric analysis. The foam density and mechanical properties of polyurethane (PU) rigid foams were investigated. The flame retardancy of PU rigid foams formulated with MAPP was evaluated by using limiting oxygen index and cone calorimetry. The results show that MAPP can greatly increase the flame retardancy of PU materials. Also, there is a synergistic effect between MAPP and expandable graphite in flame retarding PU rigid foams. Moreover, the water resistance property of PU/MAPP composites is better than that of PU/ammonium polyphosphate. The morphology and chemical structure of PU/MAPP rigid foams after burning were systematically investigated. © 2013 Society of Chemical Industry

Synthesis and characterization of biodegradable polyurethanes based on L‐cystine/cysteine and poly(ϵ‐caprolactone)

AbstractTunable biodegradable polyurethanes (PUs) with favorable mechanical properties were synthesized from 1,6‐hexamelthylene diisocyanate (HDI) as the hard segment, poly(ϵ‐caprolactone) (PCL) as the soft segment, and L‐cystine ester as chain extender. The structure of PUs was confirmed by FTIR and 1H‐NMR. The results of differential scanning calorimeter, thermogravimetric analysis, dynamic mechanical analysis, and tensile test revealed that the thermal and mechanical properties of PUs were strongly influenced by the molecular weight of soft segment PCL. In the presence of glutathione, the disulfide group cleaved into thiols, realizing the PUs degraded and the molecular weight decreased. For PU [550], it remained only 50% of the original Mw. Evaluation of cell viability demonstrated the nontoxicity of the PUs, which facilitated their potential in biomedical applications. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013