Tensile Properties Of Polyurethanes Research Articles

Effect of the crosslinking degree on the microstructure and thermomechanical properties of a polymer grouting material

Polymer grouting materials are widely used in the field of trenchless rehabilitation of infrastructure, and their properties are closely related to the crosslinking process and crosslinking degree between components. In this paper, polyurethane (PU) models with different crosslinking degrees were built based on the molecular dynamics (MD) simulations method and Python script. We investigated the crosslinking reaction process of PU grouting materials and the effect of their crosslinking degree on the glass transition temperature (Tg) and tensile properties. Also, the rationality of the model was verified by comparing the Tg obtained in the simulation and experiment. The results showed that the crosslinking reaction is a volume shrinkage process, and the PU model has a good network structure. The non-bonding energy is the main reason for the variation in the Tg, which increased with increasing crosslinking degree. Besides, the tensile properties of PU are greatly affected by the crosslinking degree, and the elastic modulus increased with increasing crosslinking degree. The results are of great significance for understanding the microstructure and thermomechanical properties of PU grouting materials at the molecular level.

Glass Transition and Stress-Strain Curve of Polyaspartic Ester Polyurea at Different Tension Condition

The tensile properties of polyurethane are related to the microstructure due to the change of hydrogen bond and hard segment domains at different temperature and velocity. In this paper, the structure and glass transition before and after tensile breakage of polyaspartate (PAE) based polyurea (PU) coatings were analyzed by Fourier Transform Infrared Spectroscopy (FTIR), Differential Scanning Calorimetry (DSC) and tensile strain energy of stress - strain curve. The PAE-PU has not changed its allophanoyl (C=O in urea) and amino (N-H) hydrogen bond content apparently by the comparison of their IR absorption peak height. The PAE-PU has two glass transition temperatures related to soft and hard segments, which move to greater distance after tension. Moreover, the Enthalpy relaxation accompanied by hard segment glass transition almost disappears after tensile break. The dependency of tensile curve of PAE-PU on tensile rate at the same temperature is different from ordinary polymer materials; i.e.it has greatest yielding, strength and strain energy at medial rate of 100mm/min rather than higher ones.

Biocompatible Polyurethane Scaffolds Prepared from Glycerol Monostearate-Derived Polyester Polyol

Biodegradable polyester polyol was synthesized from oleochemical glycerol monostearate (GMS) and glutaric acid under a non-catalyzed and solvent-free polycondensation method. The chemical structure of GMS-derived polyester polyol (GPP) was elucidated by FTIR, 1H and 13C NMR, and molecular weight of GPP was characterized by GPC. The synthesized GPP with acid value of 3.03 mg KOH/g sample, hydroxyl value of 115.72 mg KOH/g sample and Mn of 1345 g/mol was incorporated with polyethylene glycol (PEG) and polycaprolactone diol (PCL diol) to produce a water-blown porous polyurethane system via one-shot foaming method. The polyurethanes were optimized by evaluating glycerol as a crosslinker, silicone surfactant and water blowing agent on tensile properties of polyurethanes. All polyurethanes underwent structural change, and crystalline hard segments of polyurethanes were shifted to higher temperature suggested that hard segments undergone re-ordering process during enzymatic treatment. In terms of biocompatibility, polyurethane scaffold produced by reacting 100% w/w of GPP with isophorone diisocyanate and additives showed the highest cells viability of 3T3 mouse fibroblast (94%, day 1), and MG63 human osteosarcoma (107%, day 1) and better cell adhesion as compared to reference polyurethane produced by only PEG and PCL diol (3T3 cell viability: 8%; MG63 cell viability: 2%). The current work demonstrated GPP synthesized from renewable and environmental friendly resources produced polyurethanes that allows improvement in physico-chemical, mechanical and biocompatibility properties. By blending with increasing content of GPP, the water-blown porous polyurethane scaffold has shown great potential as biomaterial for soft and hard tissue engineering.

Influence of structure-property relationship on the optical, thermal and mechanical properties of castor oil based transparent polyurethane for catheter applications

ABSTRACTCastor oil based transparent polyurethane elastomers were synthesized, which can be used as an advanced catheter material. The effect of NCO: OH ratio on the structural, optical, thermal and physicomechanical properties of polyurethanes (PU) has been studied. The optical properties of the PU was analysed by studying its percentage transmittance and haze. The results showed a high transparency of 90.7% for the PU with a NCO: OH ratio of 0.9:1. Differential scanning calorimetry (DSC) analysis revealed an increase in the glass transition temperature (Tg) of PU with increasing hard segment content whereas thermogravimetric analysis (TGA) shows an increase in the initial decomposition temperature of PU from 262 to 268°C upon increasing the NCO: OH ratio from 0.9 to 1.5. A similar trend of increment in the tensile properties of PU has been observed as a consequence of increasing the molar ratio of NCO: OH. In vitro cytotoxicity analysis of PU was studied using human embryonic kidney (HEK293) cell line that revealed the nontoxic character of PU.

Rigid phase domain sizes determination for poly(urethane–urea)s by solid-state NMR spectroscopy. Correlation with mechanical properties

The solid-state NMR techniques have been applied to study molecular dynamics and domain sizes in polyurethanes based on oligomeric 4,4′-diisicyanate diphenylmethane and polyols with different length. Measurements of proton spin–lattice times in both laboratory frame (T1) and rotating frame (T1ρ) were done for the soft and the rigid segments of all polyurethanes. To determine the size of heterogeneities and characterize the morphology of the polyurethanes the 1H NMR spin-diffusion experiment was performed. The morphology of the dispersed phase was considered cylindrical for all samples. The size of the rigid phase domains was found to be in the range between 4.4 and 8nm depending on the length of the hard segments. The tensile properties of polyurethane were found to be correlated with molecular mobility in polymer matrix and domain size of rigid phase.

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Grafted isopropyl groups were used to control the molecular interactions between polyurethane (PU) copolymers, and their effect on the tensile properties of PU was investigated. The grafted isopropyl groups were selected to interrupt the molecular interactions and disturb the close contact between PU chains through its branched structure, and thus improve the low-temperature recovery while maintaining the high tensile properties and the shape recovery at ambient temperature. The grafted isopropyl groups made a difference to the phase separation of the hard and soft segments in the PU structure, as determined by IR and DSC. The crosslink density and viscosity experienced an unusual increase with the increase in isopropyl content owing to crosslinking by the grafting reagent. The shape recovery and retention remained high even with the grafted isopropyl groups. Finally, the effect of the isopropyl groups on low-temperature recovery was compared with that of the linear PU, and the reason for the flexibility is discussed.

Characterization of the ion-paired polyurethane copolymers

The polyurethane (PU) copolymer was grafted with either 3-dimethylaminopropanol as a basic pendant group or 4-hydroxylphenylacetic acid as an acidic pendant group. The two types of PU were mixed in solution to form ion-pairing between acidic and basic pendant groups. The structural change after grafting and ion-pairing was followed by acid-base titration, infrared spectra, differential scanning calorimetry, and absolute viscosity. The tensile stress can be raised as much as 70 % by the control of the ion-pairing ratio of acidic and basic PUs. Shape recovery was over 80 % and reproducible for four test cycles. The minor control of tensile properties of PU was possible through the ion-pairing method.

The laterally attached tartaric acid of polyurethane copolymer and its impact on shape memory and low-temperature flexibility

The tartaric acid was laterally attached to polyurethane through the carbamate of polyurethane, and the impact on the shape-memory and tensile properties of polyurethane was investigated. The electrostatic repulsion of the tartarate could reduce the molecular interactions between polyurethanes, a result that was designed to improve low-temperature flexibility while maintaining high and reproducible tensile strength and shape recovery above room temperature. The attachment of the tartaric acid was quantitatively determined by acid–base titration, and the change in the molecular interaction between hard segments was confirmed via infrared spectroscopy. Both cross-linking density and viscosity experienced an unusual increase with increasing tartarate content due to partial cross-linking caused by the grafting reagent. Shape recovery and retention were reproducible over repeated shape-memory tests. Finally, the low-temperature flexibility was determined at −10°C, and the reason for the difference was discussed.

Enhancement of fatigue life of polyurethane composites containing carbon nanotubes

The effects of carbon nanotube (CNT) inclusion on cyclic fatigue behavior and the tensile properties of polyurethane (PU) composites have been studied. Tension–tension cyclic fatigue tests were conducted at various load levels (30–50MPa) to establish the relationship between stress and the number of cycles to failure (S–N curves). The tensile energy to break PU composites was enhanced up to 38% by using a low amount of CNTs. In addition, the incorporation of CNTs increased the fatigue life of PU in the high-stress amplitude, low-cycle regime by up to 248%. Micrographs show highly dispersed CNTs and indicate the key mechanisms for enhancement in fatigue life such as CNT crack-bridging and pull-out. The tensile-tensile fatigue properties obtained in this work show that PU systems can outperform epoxy systems widely used in structural applications.

Low temperature shape recovery effect of polyurethane copolymer grafted with pendant n-butyl group

Effect of the pendant n-butyl group on shape recovery and tensile properties of polyurethane (PU) block copolymer was investigated. The grafted n-butyl group was intended to keep PU chains away and to deter molecular interaction between PU chains by its flexible chains, and thus improve shape recovery at subzero temperature while maintaining high and reproducible tensile properties and shape recovery at ambient temperature. The attachment of n-butyl group did not make any change in the molecular interaction and phase separation of hard and soft segments in PU structure as judged from IR and DSC analysis. Cross-link density and intrinsic viscosity increased with the increase of n-butyl content due to the partial cross-linking by the linking reagent. Shape recovery and shape retention were not diminished after cyclic shape memory tests. Finally, the effect of n-butyl group on low temperature shape recovery was compared with linear ones and the potential application of this finding was discussed.

Bioresorbable poly(ester‐ether urethane)s from L‐lysine diisocyanate and triblock copolymers with different hydrophilic character

Bioresorbable linear poly(ester-ether urethane)s with different hydrophilic character were synthesized from block copolymers of poly(epsilon-caprolactone)-poly(ethylene oxide)-poly(epsilon-caprolactone) (PCL-PEO-PCL) as macrodiols, and L-lysine diisocyanate (LDI). A series of PCL-PEO-PCL triblock copolymers with different PEO and PCL chain length was obtained by reacting PEO with epsilon-caprolactone. Polyurethanes were synthesized by reacting the triblock copolymers with LDI in solution using stannous 2-ethylhexanoate as catalyst. The prepared triblock copolymers and polyurethanes were fully characterized by proton nuclear magnetic resonance spectroscopy, size exclusion chromatography, differential scanning calorimetry, and wide-angle X-ray diffraction. Water uptake, hydrolytic stability, and tensile properties of polyurethanes with different composition were evaluated and discussed in terms of the chain length and molecular weight of the polymers and its block components. Water uptake seems to depend on the ethylene oxide unit content of the polyurethane regardless of the triblock structure. Mechanical properties of the synthesized polymers were strongly affected by the molecular weight achieved during polymerization. The use of triblock macrodiols with different hydrophilicity allowed the preparation of a series of polyurethanes having a broad range of properties.

Study of Chemical and Tensile Properties of PU and PU/PS Coated Bamboo Fibers

ABSTRACT The untreated and alkali-treated bamboo (Bambusa balcooa) fibers were coated with polyethylene glycol–based polyurethane (PU) and its semi-interpenetrating polymer network (SIPN) with polystyrene (PS). The tensile strength and chemical resistance were measured on alkali-treated and untreated fibers with or without polymer coating. The PU and PU/PS (50/50) IPN-coated bamboo fibers showed improvement in tensile behavior and chemical resistance.

Study of Chemical and Tensile Properties of Polyurethane and Polyurethane/Polyacrylonitrile Coated Bamboo Fibers

The polyethylene glycol (PEG) based polyurethane (PU) and polyurethane-polyacrylonitrile (PU/PAN) semi-interpenetrating polymer networks (SIPNs) have been coated on the surface of alkali-treated and untreated bamboo fibers (Bambusa balcooa). The chemical resistance and tensile load at break of bamboo fibers before and after coating with SIPNs have been studied. It is observed that the tensile load at break and chemical resistance of bamboo fibers have increased on coating.

Polyesters containing sulfur. VII. New aliphatic-aromatic polyesters for synthesis of polyester-sulfur compositions and polyurethanes

New linear polyesters containing sulfur in the main chain were obtained by melt polycondensation of diphenylmethane-4,4'-bis(methylthioacetic acid) (DBMTAA) or diphenylmethane-4,4'-bis(methythiopropionic acid) (DBMTPA) and diphenylmethane-4,4'-bis(methylthioethanol) (DBMTE) at equimolar ratio of reagents (polyesters E-A and E-P) as well as at 0.15 molar excess of diol (polyesters E-A OH and E-P OH ). The kinetics of these reactions was studied at 150, 160, and 170°C. Reaction rate constants (k 2 ) and activation parameters (ΔG ¬= , ΔH ¬= , ΔS ¬= ) from carboxyl group loss were determined using classical kinetic methods. E-A and E-P (M n = 4400, 4600) were used for synthesis of new rubber-like polyester-sulfur compositions, by heating with elemental sulfur, whereas oligoesterols E-A OH and E-P OH (M n = 2500, 2900) were converted to thermoplastic polyurethane elastomers by reaction with hexamethylene diisocyanate (HDI) or methylene bis(4-phenyl isocyanate) (MDI). The structure of the polymers was determined by elemental analysis, FT-IR and liquid or solid-state 1 H-, 13 C-NMR spectroscopy, and X-ray diffraction analysis. Thermal properties were measured by DTA, TGA, and DSC. Hardness and tensile properties of polyurethanes and polyester-sulfur compositions were also determined.

Evaluation of Branched Glycidyl Azide Polymer Purified by Solvent Extraction

Dimethyl sulfoxide (DMSO), a polar liquid of low volatility, was used as solvent in the synthesis of branched glycidyl azide polymer (GAP) which is a potential energetic binder for rocket propellants. Branched GAP product was purified by an extraction method using dichloromethane to create an organic phase and a mixture of methanol-brine (50:50 in weight) as the extracting solution. The extraction was carried out in four steps, leaving only less than 1% DMSO in the purified branched GAP. The DMSO concentration remaining in the organic phase was deduced from the {sup 1}H NMR spectra taken after each extraction step. Finally, the physical performance of branched GAP was evaluated through the tensile properties, the glass transition temperature, and the thermal degradation of the energetic polyurethanes obtained after curing branched GAP with different isocyanate compounds. The effect of residual DMSO in branched GAP on the tensile properties of polyurethanes was also investigated.