Mechanical Properties Of Polyurea Research Articles

Strength and durability that last—Mechanical properties of polyurea and polyurethane coated composites

AbstractMaterials scientists are interested in the development of impact‐resistant materials for military and commercial products. Polyurea and polyurethane are utilized for impact absorption in numerous industries, however, hybrid polymers and their features are rarely explored. Due to their distinct chemical structures and cure kinetics, polyurea‐polyurethane hybrid materials are still in their infancy. The versatility of these materials drives the research to address this challenge. Small‐scale composite companies generally use spray guns to apply chemicals, raising costs. The current study focused on the development of coated composites for impact applications. Polyurea, polyurethane, and their hybrid were used as a coating material on the glass/epoxy composites. The flexural, impact (Charpy and Izod), and thermomechanical properties of these coated composites were investigated. It was observed that coating thickness enhanced impact properties of composite materials. The loss and storage modulus decreased with an increase in temperature for polyurea and polyurethane coated composites. The thermo‐mechanical analysis of hybrid coated composite showed the behavior to be dominantly similar to the polyurethane‐coated composite materials. The flexural strength of glass/epoxy composites increases with the coating, while increasing number of coating layers counters this effect.

Experimental study on the tension and puncture behavior of spray polyurea at high strain rates

Polyurea is widely used as a protective coating material for structures subjected to impulsive loads. In this study, the mechanical properties of polyurea were investigated experimentally over a wide range of loading rates. Firstly, quasi-static tests were performed using conventional hydraulic machine at strain rates of 7.7 × 10−4 - 7.3 × 10−3 s−1 for direct tension and at speeds of 1.67 × 10−5 - 1.67 × 10−4 m/s for puncture. Then high-speed tests were carried out using a high-speed servo-hydraulic testing machine (INSTRON VHS 160/100-20) at strain rates of 3.3–500.3 s−1 for direct tension and at speeds of 0.1–10 m/s for puncture. Deformation and failure processes of the polyurea specimens under high-speed tension were recorded with the aid of a high-speed camera. The testing results show that polyurea is a strain rate sensitive material. Under tensile loads, the initial yield stress and the strength increase with the increment of the strain rates while the fracture strain decreases. Under puncture loads, the yield force and the strength of the polyurea sheets also increase with loading rates. However, the strain rate effect on the failure deformation of the polyurea is only observed when the loading rate is less than 2 m/s. Based on the testing data, mechanism that causes the dynamic effect of polyurea material properties was discussed and some empirical relations were derived for engineering applications.

Study on mechanical properties of polyurea coating with various process parameters

ABSTRACT Recently polyurea (PU) is widely used as a surface coating to protect the material under various harsh loads, hazardous chemical reactions and climatic conditions. The high efficient isocyanate-amine reaction kinetics makes it mandatory to use a reactive spray coating technique for the realistic production of PU. However, the efficiency of the PU depends on various process parameters of the plural spray coating system. Herein, the effect of plural spray coating process parameters, namely, mixing ratio, temperature, coating pressure, and stand-off distance was studied by comparing mechanical properties such as hardness, tensile, elongation, young’s modulus, tear and wear index of PU. Besides, the optimal process parameters and corresponding levels have been identified using the Taguchi method and it has been found that each property has a different best process parameter. To circumvent this, grey relational analysis (GRA) was carried out and it has improved overall efficiency by 7.71%.

Mechanical behaviors and equivalent configuration of a polyurea under wide strain rate range

The tension tests are systematically conducted on a polyurea by Instron and split Hopkinson tension bar apparatuses for strain rate ranging from 0.0001 s−1 to–3000 s−1, to investigate its mechanical behaviors. It is found that the polyurea presents a high rate-dependent, and the stress strain curves share a similar mechanical trend and consistent strain hardening coefficient trend under wide loading strain rates. The interrupted experiments are designed, and the results demonstrate that the polyurea is sensitive to temperature, which induces distinct softening influence on flow stress. However, the strain hardening coefficient is sharing the same trends and little influenced by the strain rate and adiabatic heating. The equivalent mechanical configuration is investigated by using the two-dimension unit cell model to simulate the polyurea mechanical characteristics. The systematical simulation results facilitate to outline its equivalent configuration: the soft phase dispersing in the hard network matrix. Furthermore, the matrix play a major role in the overall mechanical properties of polyurea. The configuration is further evidenced by the deduced data from reference. Finally, a simple analytical model is proposed with two components, and well capable of describing the mechanical characteristics including large strain behavior, strain rate effect and induced thermal softening effect.

Investigation on the mechanical properties of polyurea (PU)/melamine formaldehyde (MF) microcapsules prepared with different chain extenders

There is lack of understanding on controlling of mechanical properties of moisture-curing PU/MF microcapsules which limited its further application. PU/MF microcapsules containing a core of isophorone diisocyanate (IPDI) were prepared with different chain extenders, polyetheramine D400, H2O, triethylenetetramine and polyetheramine (PEA) D230 by following a two-step synthesis method in this study. Fourier transform infra-red (FTIR) spectroscopy, Malvern particle sizing, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). And micromanipulation technique was used to identify chemical bonds in the shell, size distributions, structure, thickness, and mechanical properties of microcapsules. The results show that PU/MF microcapsules were successfully prepared. Tr increased from 46.4 ± 13.9 N/m to 75.8 ± 23.3 N/m when extender changed from D400 to D230. And the Tr increased from 51.3 ± 14.1 to 94.8 ± 17.5 N/m when the swelling time increased from 1 to 3h. Morphologies of the shell were utilised to understand the mechanism of reactions in forming the shell materials.

Tuning the properties of segmented polyurea by regulating soft‐segment length

ABSTRACTPolyurea is being widely advocated as a “retrofit” coating on structures, which mandate protection against blast. The physical properties of polyurea can be tuned by judicious choice of reactants, and the processing methodology employed for its preparation. The purpose of this study is to establish the dependence of material properties on the soft segment length in polyurea. Polyurea formulations were prepared by reaction of commercially available isocyanate prepolymer with poly(propylene oxide) based amines of varying molecular weights (230–2000 g/mol). The effect of increasing the soft segment length on the mechanical properties of polyurea under both quasi‐static as well as dynamic conditions was determined. Ductility was found to increase proportionally with increasing soft segment length, with a concomitant decrease in the tensile strength. All the compositions exhibited sub‐ambient glass transition temperature, which was found to reduce with increasing soft‐segment length. Time–temperature superposition principle was used to arrive at master curves for all compositions. The frequency essential to initiate the process of dynamic “rubber to glass” transition was found to be directly proportional to the soft segment length. All the formulations were found to be capable of exhibiting an elastomeric response even under high frequencies typical of blast loadings. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46284.

One-pot surface functionalization and reduction of graphene oxide with long-chain molecules: Preparation and its enhancement on the thermal and mechanical properties of polyurea

Graphene oxide (GO) was simultaneously reduced and functionalized with amine-terminated polyether. The results from FTIR, XPS and XRD showed that amine-terminated polyether was successfully attached onto the surface of FGO and most of FGO was reduced. Subsequently the amine-terminated polyether functionalized GO sheets were covalently incorporated into the polyurea matrix via in situ polymerization. The XRD, TEM, SEM and immersion phenomenon showed that FGO sheets were uniformly dispersed in the polyurea matrix and formed the strong interfacial adhesion with polyurea matrix. The properties reinforcements of the nanocomposites were investigated by thermogravimetric analysis (TGA), dynamic mechanical analysis (DMA) and tensile testing machine. The TGA results indicated that the T50wt.% of the nanocomposites was increased by about 10°C compared to pure polyurea at loading of 1.0wt.% FGO. Meanwhile, the storage modulus of the nanocomposites was enhanced due to incorporation of FGO. Furthermore, the tensile test indicated that the FGO could also improve tensile properties of polyurea. It is believed that the reduction and covalent functionalization of graphene can improve both the dispersion of FGO in the polymer matrix and the interfacial interactions between FGO and polyurea matrix.

Effect of surface modification of graphite oxide on the morphological, thermal, and mechanical properties of polyurea/graphite oxide composites

ABSTRACTThree surface modifiers, namely, aminopolyether (D2000), phenyl isocyanate, and poly(ethylene glycol) (PEG800), which have different affinities to the hard and soft segments in polyurea, were used to synthesize functionalized graphite oxides (GO). The PEG800‐modified (PEG800‐GO) and phenyl isocyanate‐modified (i‐GO) GOs were highly exfoliated and dispersed in DMF, whereas the D2000‐modified GO (D2000‐GO) produced some precipitates. Polyurea/GO composites were prepared using a solution‐blending method, in which functionalized GO platelet suspensions in dimethyl formamide were used. Results show that PEG800‐GO and i‐GO are uniformly dispersed throughout the polymer matrix on a nanoscale, whereas D2000‐GO forms visible aggregates. The well‐dispersed GO platelets improved the thermal stability and mechanical properties of polyurea. PEG800‐GO, which has a strong affinity for the soft segments, shows a more significant reinforcing effect. At 2.0 wt % GO loading, the tensile strength of polyurea was enhanced by ∼75%. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 39775.

Effect of isocyanate content on thermal and mechanical properties of polyurea

Novel polyureas with soft segments based on a difunctional amine, Versalink P-1000, and hard segments based on Isonate 143L, which is a mixture of difunctional and trifunctional isocyanates, were synthesized. The stoichiometric ratio of Isonate 143L to Versalink P-1000 in the polyurea material system was incrementally varied. The properties of the resultant polyurea formulations were characterized using dynamic mechanical analysis (DMA) and modulated differential scanning calorimetry (MDSC). The dynamic mechanical properties measured as storage and loss moduli were significantly altered through the variation of the stoichiometric ratio; however, the glass transition temperatures exhibited in all variations were quite consistent. The experimental results indicate that judicious selection of hard segment content can have a marked effect on the ultimate properties and performance of the polyurea material system.

Silicon nanoparticle decorated graphene composites: preparation and their reinforcement on the fire safety and mechanical properties of polyurea

Reduced graphene oxide (rGO) was decorated with organic/inorganic nanoparticles through an in situ sol–gel process with various thicknesses. The presence of organic/inorganic nanoparticles made the rGO lipophilic, as evidenced by the good dispersion of the nanoparticles–rGO in dimethyl formamide solvent (DMF). The thickness of the nanoparticles–rGO could be varied by adjusting the amount of the silicane additive, as evidenced by the AFM results. The nanoparticles–rGO was then incorporated into polyurea in different ratios via in situ polymerization and the property enhancement of the nanocomposites was investigated. The TEM morphological study showed that, due to the good interfacial interaction between the nanoparticles–rGO and polyurea, nanoparticles–rGO was dispersed well in the polyurea matrix. Compared with the rGO, the nanoparticles could significantly improve the thermal stability and thermal conductivity of polyurea, implying that the good dispersion of rGO and the functional groups on the surface of rGO had a significant effect on the thermal stability and thermal conductivity of polyurea. The peak heat release rate (pHRR) of nanoparticles–rGO/polyurea nanocomposites was significantly reduced, which indicated that the combustible gas releasing rate of polyurea was reduced. Moreover, the storage modulus and tensile strength of the nanocomposites with 0.2 wt% have been enhanced by about 60% and 110% in comparison with those of neat polyurea, respectively. This simple and effective approach, decorating the rGO with organic/inorganic nanoparticles, is believed to offer possibilities for broadening the graphene applications in the polymer materials and make it possible to decorate the graphene with other functional groups and vary the aspect ratio of decorated graphene according to its application.