Polyurea

The polyurea elastomer coating / lining technology has shown some very significant inroads since the introduction of the technology back in the late 1980's. Initially, the polyurea technology had set itself in a different class of coating / lining systems as compared to conventional urethane coating / lining systems. This has been primarily due to the unique characteristics of the technology, both in processing and performance. However; over the years there has been a melding of the various technologies, and many have now classified or implied that polyureas are the same as urethane and/or urethane/urea systems. There is now a new class of polyurea systems that have different processing characteristics and some feel that these are not polyurea systems at all. "They can't be" people say since you don't need the high-pressure plural component processing equipment for application. This has led to some reluctance on the part of engineers and specifiers to confidently specify polyurea systems for projects. As a result, there has been some major confusion as to what classifies a system as a polyurea and, what is not. This paper will take a look at the polyurea technology, formulation basics; and, compare that to what a polyurethane and polyurethane/polyurea system is, along with some performance issues.

We present dynamic mechanical analysis (DMA) and thermomechanical analysis (TMA) measurements of a new type of polyurea elastomer nanocomposites based on inorganic  MoS2 nanotubes and Mo6S2I8 nanowires. The addition of a small amount of nanoparticles (<1 wt-%) leads to an increase of the glass transition temperature Tg as compared to the pure elastomeric matrix. A second peak observed in tan d in the pure and mixed elastomer is attributed to a second glass transition occurring in regions near the hard nanodomains of the microphase separated polyurea system. It is also found that the small amount of nanoparticles leads to an increase in Young's modulus of up  to 15% in the whole measured temperature range from -130 °C to 20 °C). The thermal expansion of doped samples is considerably larger above Tg. Below Tg, this difference vanishes completely. Very similar behaviour was also found in measurements of polyisoprene/multiwall carbon nanotube (MWCNT) composites.

A series of elastomers based on polyurea chemistry is synthesized by crosslinking amino-terminated polyethers with a triisocyanate using an appropriate solvent, which slowed downthe reactivity of the amino groups. Control of the reactivity allows the shaping of the material,and films of defined thickness can be achieved for mechanical testing. The strength of thefinal network can be tuned by the crosslinking density of the network chemical constitution.The resulting materials show a good thermal stability and promising mechanical enhancement.

Polyurea elastomer is known to exhibit advantageous impact-mitigation characteristics and thus can improve the dynamic performance of various components and structures. This study identifies the mechanisms of dynamic response of thin metallic plates, covered by a frontal polyurea layer, using a physically verified, custom material model for two-part polyurea implemented within a finite-element-method framework. A linear increase in the ballistic performance of a target with polymer coating is consistent with experimental work captured for the first time in a numerical study. A reported ballistic-limit improvement of 7.4 m s-1 per millimetre increase of polyurea thickness for frontal-layer thicknesses higher than 4 mm on the thin monolithic plate was established. In contrast, the application of polyurea coating thinner than 4 mm resulted in a diminished ballistic performance of the target. These outcomes are attributed to significant alterations in the energy-absorbing capacity of thin plates with the introduction of the polyurea layer that strongly depend on the impact velocity, polymer thickness, and interfacial interactions.

Novel polyurea was synthesized from lysinyl residue, L-lysine-4-nitroanilide (L-Lys-4-NA) and 1,4-phenylene diisocyanate (1,4-PDI). The polyurea thus prepared gave durable self-standing membranes. The polyurea was converted into molecular recognition materials by using Z-D-Glu or Z-L-Glu as a print molecule. The Z-D-Glu molecularly imprinted membrane adsorbed the D-isomer of Glu in preference to the corresponding L-isomer and vice versa. Even though the polyurea consisted of L-lysinyl residue, both Z-D-Glu and Z-L-Glu worked as print molecules to construct molecular (chiral) recognition sites in the membrane. Those two types of molecularly imprinted membrane show chiral separation abilities, adopting a concentration gradient or an applied potential difference as a driving force for membrane transport.

The temperature dependence of ultrasonic velocity and ultrasonic attenuation were
measured in polyurea elastomer composites with inorganic nanoparticles. The
decrease in the ultrasonic velocity along with an attenuation maximum was observed
above the glass transition temperature, Tg. The shape and position of this peak are
directly proportional to the amount of embedded nanoparticles. In addition, the sharp
anomalies in the ultrasonic velocity and ultrasonic attenuation were observed above
the glass transition temperature in semicrystalline polyurea elastomers. These
anomalies are related to the corresponding first order phase transition of these
crystalline domain-containing networks. The ultrasonic attenuation peak related to
glass transition is considerably smaller in these polyurea networks showing a small
influence of the soft domains below the melting temperature, Tm. The first order phase
transition in the semicrystalline polyurea elastomers shows a large temperature
hysteresis of more than 10 K, which was confirmed by dielectric investigations. The
addition of small amounts of inorganic nanoparticles resulted in a shift of the first
order phase transition temperature in semicrystalline nanocomposites.

The influence of structural constraints on the relaxation dynamics of three polyurea networks with a varying degree of crosslinking, has been studied by means of a thorough analysis of broadband dielectric spectroscopy measurements. Two different relaxation processes are observed, namely, a fast process involving the soft poly(propylene oxide) chains, and a slower and much broader process associated with the immediate surroundings of the hard crosslinkers. Microphase separation in soft and hard domains characterizes the systems in the presence of hydrogen bonding. In this case, different confinement conditions are explored by varying the soft chain length; overall, so called ''adsorption'' effects dominate. With respect to both cooperativity and the rearrangement energy threshold in fast relaxation, it is found that the enhancement of configurational constraints is similar to cooling, but only on qualitative grounds. An upper bound of the hard domains' interface thickness, in which the slow relaxation is believed to take place, is estimated from the analysis of the fast relaxation in the system characterized by the highest degree of confinement, taking into account the results of the structural analysis. Dropping the hydrogen bonding mechanism, phase separation does not occur anymore and the configurational constraints at the ends of the soft chains are reduced, leaving just those imposed by the rigid crosslinkers. This leads to a significant increase in cooperativity on approaching the glass transition, and to a complex behavior that is thoroughly discussed in comparison with those observed in the micro-segregated systems.

We studied the photo-elastic and photo-thermal response of two new nanocomposites base on a polyurea elastomer mixed with inorganic nanotubes (MoS2) or nanowires  (Mo6S2I8). The investigation has been performed using time-resolved laser spectroscopy, transient grating technique (TG), based on short laser pulses. This spectroscopic tool enables the measurement of the thermo-elastic response of the nanocomposites covering a very large time window, from nanoseconds to milliseconds, revealing the different dynamic phenomena present in these materials. On the fast timescale (from 1 to 100 ns) the TG signal shows the propagation of a high-frequency acoustic wave enabling the measure of its sound velocity and damping time. In the slow time window (from 5  to 100 micros) the TG signal presents a slow decay due to the thermal diffusion process. As expected, these features are common for both pure polymeric and nanocomposite samples. Surprisingly, the presence of nanotubes or nanowires in the polymeric matrix produces on the intermediate time scale a new dynamic phenomenon in the experimental data, whose origin is not clear.

We studied the photo-elastic and photo-thermal response of two new nanocomposites base on a polyurea elastomer mixed with inorganic nanotubes (MoS2) or nanowires (Mo6S2I8). The investigation has been performed using time-resolved laser spectroscopy, transient grating technique (TG), based on short laser pulses. This spectroscopic tool enables the measurement of the thermoelastic response of the nanocomposites covering a very large time window, from nanoseconds to milliseconds, revealing the different dynamic phenomena present in these materials. On the fast timescale (from 1 to 100 ns) the TG signal shows the propagation of a high frequency acoustic wave enabling the measure of its sound velocity and damping time. In the slow time window (from 5 to 100 s) the TG signal presents a slow decay due to the thermal diffusion process. As expected, these features are common for both pure polymeric and nanocomposite samples. Surprisingly, the presence of nanotubes or nanowires in the polyme...

Polyurea elastomer exhibits desirable characteristics for impact mitigation, with varying stoichiometric-dependent properties that can be tailored for specific applications and applied to reinforce existing and new structural components. This numerical study aims to investigate the ballistic performance of polyurea-aluminium laminate targets, employing a user-defined material model for polyurea elastomer developed in a finite-element (FE) framework. The model consists of a rigid spherical projectile impacting the considered target plate. A linear increase in the ballistic performance with a growing thickness of polymer coating was observed and is consistent with previously conducted experimental work. The ballistic limit is increased by some 5% per millimetre of polymer coating thickness, when compared to the monolithic metallic plate. The presence of the polymer layer significantly affects the dynamic response mechanisms of the component during bending due to impact. The result is a more localised deformation compared to global bending of the target. Abstract Polyurea elastomer exhibits desirable characteristics for impact mitigation, with varying stoichiometric-dependent properties that can be tailored for specific applications and applied to reinforce existing and new structural components. This numerical study aims to investigate the ballistic performance of polyurea-aluminium laminate targets, employing a user-defined material model for polyurea elastomer developed in a finite-element (FE) framework. The model consists of a rigid spherical projectile impacting the considered target plate. A linear increase in the ballistic performance with a growing thickness of polymer coating was observed and is consistent with previously conducted experimental work. The ballistic limit is increased by some 5% per millimetre of polymer coating thickness, when compared to the monolithic metallic plate. The presence of the polymer layer significantly affects the dynamic response mechanisms of the component during bending due to impact. The result is a more localised deformation compared to global bending of the target.

We report the room temperature synthesis of spherical millimeter-size polyurea (PUA) aerogel beads. Wet-gels of said beads were obtained by dripping a propylene carbonate solution of an aliphatic triisocyanate based on isocyanurate nodes into a mixture of ethylenediamine and heavy mineral oil. Drying the resulting wet spherical gels with supercritical fluid (SCF) CO 2 afforded spherical aerogel beads with a mean diameter of 2.7 mm, and a narrow size distribution (full width at half maximum: 0.4 mm). Spherical PUA aerogel beads had low density (0.166 ± 0.001 g cm-3), high porosity (87% v/v) and high surface area (197 m 2 g-1). IR, 1 H magic angle spinning (MAS) and 13 C cross-polarization magic angle spinning (CPMAS) NMR showed the characteristic peaks of urea and the isocyanurate ring. Scanning electron microscopy (SEM) showed the presence of a thin, yet porous skin on the surface of the beads with a different (denser) morphology than their interior. The synthetic method shown here is simple, cost-efficient and suitable for large-scale production of PUA aerogel beads.

We present dynamic mechanical analysis (DMA) and thermomechanical analysis (TMA) measurements of a new type of polyurea elastomer nanocomposites based on inorganic MoS2 nanotubes and Mo 6 S 2 I 8 nanowires. The addition of a small amount of nanoparticles (&lt;1 wt-%) leads to an increase of the glass transition temperature T g as compared to the pure elastomeric matrix. A second peak observed in tan in the pure and mixed elastomer is attributed to a second glass transition occurring in regions near the hard nanodomains of the microphase separated polyurea system. It is also found that the small amount of nanoparticles leads to an increase in the Young´s modulus of up to 15 % in the whole measured temperature range (from -130 °C to 20 °C). The thermal expansion of doped samples is considerably larger above T g . Below T g , this difference vanishes completely. A very similar behaviour was also found in measurements of polyisoprene/multiwall carbon nanotube (MWCNT) composites.

The elastic properties of new polyurea elastomers have been studied by varying the segmental molecular weight and the chemical nature of the polymer end groups. Three different types of elastomers were synthesized leading to three different types of response. The elastomers with a high degree of polymerisation and primary amines as terminal groups show two plateaus: at high temperature, the common permanent plateau related to the rubber behaviour of elastomeric systems and, at low temperature, a transient plateau associated with the hydrogen bonding of the urea motives occurring in the interfacial zone between the soft polyetheramine and the hard crosslinker domains. The elastomers with a low degree of polymerization and primary amines as terminal groups show that the transient plateau is masked by the glassy plateau because the hydrogen bonds occur in the same temperature range as the glass transition effects, except for very slow heating rates for which the transient network can be resolved. Lastly, the elastomers with no hydrogen bonding just show the common step in the elastic behaviour from the rubbery to the glassy state.

he properties of polymers can be significantly changed by incorporating nanoparticles, which yields great potential for applications. In the present study, we use nanocomposites of new polyurea elastomers filled with 0.1, 0.5, and 1 wt.% MoS2nanotubes. Using dynamic mechanical analysis (DMA) measurements we show, that the glass transition temperatures Tg of the nanocomposites are increased by small amounts of inorganic nanotubes. In line with results from computer simulations of polymer melts with nanoscopic particles, we explain the observed shift ofTgto be due to a gradual slowing down of polymer chain dynamics in the proximity of nanotubes.

We report on the network characterization of a series of hybrid nanocomposites consisting of integrated anisotropic nanoparticles (NPs) within a polyurea elastomeric matrix with low weight fractions ranging from 0.3 to 1.2 wt%. The grafting method employed to incorporate the silica-coated spindle-type he-matite nanoparticles (SCH NPs), promotes the stability of the NPs in dispersion, and further enables theirintegration within the elastomeric polymer matrix, where the NPs are acting as multifunctional chemicalcrosslinkers and reinforcingfillers. The mechanical properties of these nanocomposite materials havesystematically been investigated for both small and large deformations as a function of the particlesconcentration in the matrix. The results indicate that significant reinforcement of the hybrid nano-composite is achieved even at very low NP loading with respect to the pristine elastomeric matrix.

The temperature dependencies of ultrasonic velocity and attenuation were measured in pure polyurea elastomer and doped with inorganic MoS2 nanotubes. Below room temperature, the large ultrasonic relaxational attenuation maxima and velocity dispersion  were observed. It was found that the attenuation peak in elastomer shifted to a lower temperature after doping with nanotubes. The ultrasonic attenuation data were fitted to the relaxation equation with temperature-dependent relaxation time. The thermal activation energy of the relaxation process, which was calculated from ultrasonic data, was found to increase in polyurea elastomer doped with MoS2 nanotubes. The low-temperature ultrasonic velocity increases in polymer with nanotubes and it is determined by the increase of elastic modulus.

The polyurea elastomer coating / lining technology has shown some very significant inroads since the introduction of the technology back in the late 1980’s. Initially, the polyurea technology had set itself in a different class of coating / lining systems as compared to conventional urethane coating / lining systems. This has been primarily due to the unique characteristics of the technology, both in processing and performance. However; over the years there has been a melding of the various technologies, and many have now classified or implied that polyureas are the same as urethane and/or urethane/urea systems. There is now a new class of polyurea systems that have different processing characteristics and some feel that these are not polyurea systems at all. “They can’t be” people say since you don’t need the high-pressure plural component processing equipment for application. This has led to some reluctance on the part of engineers and specifiers to confidently specify polyurea sy...

We present dynamic mechanical analysis (DMA) and thermomechanical analysis (TMA) measurements of a new type of polyurea elastomer nanocomposites based on inorganic MoS2 nanotubes and Mo 6 S 2 I 8 nanowires. The addition of a small amount of nanoparticles (&lt;1 wt-%) leads to an increase of the glass transition temperature T g as compared to the pure elastomeric matrix. A second peak observed in tan in the pure and mixed elastomer is attributed to a second glass transition occurring in regions near the hard nanodomains of the microphase separated polyurea system. It is also found that the small amount of nanoparticles leads to an increase in the Young´s modulus of up to 15 % in the whole measured temperature range (from -130 °C to 20 °C). The thermal expansion of doped samples is considerably larger above T g . Below T g , this difference vanishes completely. A very similar behaviour was also found in measurements of polyisoprene/multiwall carbon nanotube (MWCNT) composites.

Polymer–nanoparticle composites (PNCs) play an increasing role in technology. Inorganic or organic nanoparticles are usually incorporated into a polymer matrix to improve material properties. Polyurea is a spontaneously occurring PNC, exhibiting a phase segregated structure with hard nanodomains embedded in a soft (elastically compliant) matrix. This system shows two glass transitions at Tg1 and Tg2. It has been argued that they are related to the freezing of motion of molecular segments in the soft matrix (usual polymer a-glass transition at Tg1) and to regions of restricted mobility near the hard nanodomains (a0-process) at Tg2, respectively. We present detailed dynamic mechanical analysis (DMA) measurements for polyurea networks with different segmental lengths lc (2.5, 12.1, 24.5 nm) of the polymer chains, i.e. different volume fractions fx (0.39, 0.12, 0.07) of the hard domains. The two glass
transitions show up in two distinct peaks in tan d at Ta and Ta0. Analysing the data using a Havriliak–Negami term for the a- and a0-relaxation, as well as Vogel–Fulcher dependencies for the corresponding relaxation times, it is found that the a-glass transition at Tg1 increases strongly (up to DT ¼ 70 K) with increasing fx, whereas the a0-transition at Tg2 remains unchanged. At fcx z 0.19 the two curves intersect, i.e. Tg1 ¼ Tg2. This value of fcx is very close to the percolation threshold of randomly oriented overlapping ellipsoids of revolution with an aspect ratio of about 1 : 4–1 : 5. We therefore conclude that around 19% of the hard nanodomains polyurea changes from a system of hard nanoparticles embedded in a soft matrix (fx # fcx) to a system of soft domains confined in a network of percolated hard domains at fx $ fcx.

One of the promising methods to increase the resistance of polymer-matrix composite materials to impact damage is the use of protective coatings. In this work, the effect of polyurea coating on impact-performance parameters of a woven glass-fibre-reinforced laminate is studied. The study was performed on a specially developed ballistic experimental test rig employing a pneumatic gun. Eleven polymer composite targets with dimensions 200 mm x 300 mm x 8 mm were impacted orthogonally with a steel projectile with 23.8 mm diameter and weight 54.7 g in the range of the impact speed up to 150 m/s. A comparative assessment of the ballistic limit for targets with a 1.2 mm protective coating on the front and rear faces of the target, as well as for samples without any protective coating, was performed. The impact process was captured using two high-speed cameras for filming the front and top views at 25,000 frames per second. Experimental data on the ballistic limit for uncoated and polyurea coated fiberglass plates on the front and back surfaces were obtained. It was shown that 1.2 mm thick coating on the face surface increases the ballistic limit by 20%. The nature of the damage of the GRP base plate and coating has been analyzed. The obtained data can be used for validation of numerical models of ballistic impacts of polyurea-coated laminates.