Structure Evolution in a Polyurea Segmented Block Copolymer Because of Mechanical Deformation

Favorable Heteroaromatic Thiazole-Based Polyurea Derivatives as Interesting Biologically Active Products

This research sought to synthesize a new set of heteroaromatic thiazole-based polyurea derivatives with sulfur links in the polymers' main chains, which were denoted by the acronyms PU_1-5. Using pyridine as a solvent, a diphenylsulfide-based aminothiazole monomer (M2) was polymerized via solution polycondensation with varied aromatic, aliphatic, and cyclic diisocyanates. Typical characterization methods were used to confirm the structures of the premonomer, monomer, and fully generated polymers. The XRD results revealed that aromatic-based polymers had higher crystallinity than aliphatic and cyclic derivatives. SEM was used to visualize the surfaces of PU₁, PU₄, and PU₅, revealing spongy and porous shapes, shapes resembling wooden planks and sticks, and shapes resembling coral reefs with floral shapes at various magnifications. The polymers demonstrated thermal stability. The numerical results for PDTmax are listed in the following order, ranked from lowest to highest: PU₁ < PU₂ < PU₃ < PU₅ < PU₄. The FDT values for the aliphatic-based derivatives (PU₄ and PU₅) were lower than those for the aromatic-based ones (616, 655, and 665 °C). PU₃ showed the greatest inhibitory impact against the bacteria and fungi under investigation. In addition, PU₄ and PU₅ demonstrated antifungal activities that, in contrast with the other products, were on the lower end of the spectrum. Furthermore, the intended polymers were also tested for the presence of the proteins 1KNZ, 1JIJ, and 1IYL, which are frequently utilized as model organisms for E. coli (Gram-negative bacteria), S. aureus (Gram-positive bacteria), and C. albicans (fungal pathogens). This study's findings are consistent with the outcomes of the subjective screening.

Self- and Cross-Fusing of Furan-Based Polyurea Gels Dynamically Cross-Linked with Maleimides

Bio-based polyureas (PUs) with main-chain furan rings were synthesized by the polyaddition of 2,5-bis(aminomethyl)furan with various diisocyanates, such as methylene diphenyl diisocyanate. Several PU's were soluble in polar organic solvents, and were cast to form thermomechanically stable films with softening temperatures of over 100 °C. The furan rings of the PU main chains underwent a dynamic Diels-Alder (DA) reaction with bismaleimide (BMI) cross-linkers. While the mixed solution of PU and BMI did not show any apparent signs of reaction at room temperature, the DA reaction proceeded to form gels upon heating to 60 °C, which became a solution again by further heating to 80 °C (retro-DA reaction). The solution phase was maintained by rapid quenching from 80 °C to room temperature, while the gel was reformed upon slow cooling. The recovered gels exhibited self-healing properties. A scratch made by a hot knife at temperatures above 80 °C disappeared spontaneously. When two different gels were cut using a knife at room temperature, placed in contact with each other, and heated to 60 °C, they fused. The ability to control the DA/retro-DA reaction allowed gels of varying composition to heal.

Tensile Properties and Fracture Mechanism of Thermal Spraying Polyurea

In this study, polyurea was experimentally tested under various spraying temperatures and pressures. The number of holes and the pore size produced after the tensile fracture of the polyurea were counted to illustrate the effect of the various spraying temperatures and pressures on the performance of the polyurea. The tensile characteristics of polyurea were greatly influenced by the spraying temperatures and pressures, according to the experimental findings and statistical analysis. The polyurea tensile performance was best when the spraying pressure was 17.25 MPa with a spraying temperature of 70 °C. The fracture mechanism was illustrated by the silver streaking phenomenon generated during the tensile stretching process. The fracture energy was absorbed by the fracture holes and pores during silver streaking, thus creating the huge gap in tensile properties.

Tensile Mechanical Properties and Dynamic Constitutive Model of Polyurea Elastomer under Different Strain Rates

In order to clearly explain the large deformation mechanical characteristics of polyurea under impact and to construct a dynamic model that can be used for finite element analysis, two kinds of polyurea materials were prepared by formula design, and their uniaxial tensile properties were tested with strain rates ranging from 10⁻³~10³ s⁻¹ using an electronic universal testing machine and a split Hopkinson tensile bar (SHTB). The tensile stress–strain curves of polyurea were obtained under different strain rates. The difference in tensile mechanical properties of the materials was analyzed under dynamic loading and quasi-static loading. Based on the nonlinear viscoelastic theory and the energy dissipation rate inequality, a dynamic visco-hyperelastic constitutive model of polyurea elastomer was established. The research results showed that the uniaxial tensile stress–strain curves of two kinds of polyurea at different strain rates had obvious nonlinear characteristics and strain rate sensitivity and that their tensile strength increased with increased strain rate. The polyurea gradually changed from exhibiting rubbery mechanical behavior under quasi-static loading to glassy mechanical behavior under dynamic loading. The fitting analysis of experimental data and the results of finite element simulation showed that the dynamic constitutive model can predict the nonlinear mechanical behavior of polyurea elastomers over a wide range of strain rates. The research results could contribute to a deepening of the understanding of the damage and failure behavior of polyurea under impact load and provide a theoretical basis for numerical studies on impact safety design of polyurea-coated protective structures.

Explosion Test and Numerical Simulation of Coated Reinforced Concrete Slab Based on BLAST Mitigation Polyurea Coating Performance

The mechanical strength, thermal stability, thermal performance, and microstructure of Qtech T26 blast mitigation polyurea (T26 polyurea) were studied using quasi-static and dynamic mechanical experiments, thermogravimetric experiments, differential scanning calorimetry (DSC), scanning electron microscopy (SEM) experiments, and contact explosion and non-contact explosion experiments with polyurea-coated reinforced concrete slabs. Additionally, the energy dissipation mechanism of the coating was analyzed. The blast mitigation ability and blast mitigation mechanism of T26 polyurea-coated reinforced concrete slabs were investigated by analyzing the macroscopic morphology of reinforced concrete slabs with or without coatings and the contact explosion simulation of polyurea-coated reinforced concrete slabs. The results showed that T26 polyurea exhibited a certain strain rate effect. Its initial thermal decomposition temperature reached 286 °C, and its thermal stability was good. After carbonization, carbon slag can form and adhere to the structural surface. The glass transition temperature Tgs of the soft segment was −44.9 °C, and the glass transition temperature Tgh of the hard segment was 36.5 °C, showing a certain amount of microphase separation morphology. After the explosion test, there was a small pit on the front surface of the coated reinforced concrete plate, and there was no damage on the back surface. The integrity of the plate was good. The uncoated reinforced concrete slab had a large crater on the front of the explosion surface, and the back of the explosion surface experienced explosion collapse, concrete crushing, and an overall loss of stability. The numerical simulation results showed that the failure mode of the coated plate was consistent with the test. The kinetic energy conversion rate of the uncoated reinforced concrete plate was 87.27%, and the kinetic energy conversion rate of the coated reinforced concrete plate was 95.36%. The T26 coating improved the kinetic energy conversion rate of the structure and improved the blast mitigation ability of the reinforced concrete plate structure.

New sensing platform of poly(ester-urethane)urea doped with gold nanoparticles for rapid detection of mercury ions in fish tissue

A new electrochemical sensor has been fabricated based on the in situ synthesis of poly(ester-urethane) urea (PUU) doped with gold nanoparticles (AuNPs), and the obtained composite materials (PUU/AuNPs) were used as a new sensing platform for highly sensitive and selective detection of mercury(II) ions in fish tissue. PUU was synthesized and fully characterized by XRD, TGA, DSC, and FTIR to analyze the chemical structure, thermal stability, and morphological properties. As a polymeric structure, the PUU consists of urethane and urea groups that possess pronounced binding abilities to Hg2+ ions. SEM-EDX was carried out to confirm this kind of interaction. Using ferricyanide as the redox probe, PUU alone exhibited weak electrochemical signals due to its low electrical conductivity. Therefore, a new series of nanocomposites of PUU with different nanostructured materials were applied, and their electrochemical performances were evaluated. Among these materials, the PUU/AuNP-modified electrode showed high voltammetric signals towards Hg2+. Consequently, the parameters affecting the performance of the assay, such as electrode composition, scan rate, and sensing time, as well as the effect of electrolyte and pH were studied and optimized. The sensor showed a linear range of 5 ng mL-1 to 155 ng mL-1 with the regression coefficient R 2 = 0.986, while the calculated values of the limit of detection (LOD) and limit of quantification (LOQ) were 0.235 ng mL-1 and 0.710 ng mL-1, respectively. In terms of cross reactivity testing, the sensor exhibited a high selectivity against heavy metals which are commonly determined in seafood (Cd2+, Pb2+, As3+, Cr3+, Mg2+, and Cu2+). For real applications, total Hg2+ ions in fish tissue were determined with very high recovery and no prior complicated treatments.

DEFORMATION INDEX APPLIED TO IMPACT

Almost three decades ago, S. Futamura devised the deformation index concept for determining the control parameter for the viscoelastic response of deformed elastomers. We have extended this concept to impact mitigation, wherein material hardness and energy dissipation typically both affect the behavior. Laboratory impact tests were carried out on a series of compounds to deduce the deformation index pertinent to the rubber component. We then analyzed ballistic experiments, wherein material failure is associated with more complex conditions. The utility and limitations of this approach are discussed.

Preparation of crosslinked porous polyurea microspheres in one-step precipitation polymerization and its application for water treatment

Porous polyurea microspheres (PPUMs) were simply prepared in one-step by the precipitation polymerization of isophorone diisocyanate with triethylenetetramine and SiO₂ particles.

Polyurea coatings for enhanced blast-mitigation: a review

Major developments in the area of blast mitigation using polyurea coatings as retrofit or existing structures are discussed.

Two glass transitions of polyurea networks: effect of the segmental molecular weight

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 α-glass transition at Tg1) and to regions of restricted mobility near the hard nanodomains (α'-process) at Tg2, respectively. We present detailed dynamic mechanical analysis (DMA) measurements for polyurea networks with different segmental lengths l(c) (2.5, 12.1, 24.5 nm) of the polymer chains, i.e. different volume fractions ϕ(x) (0.39, 0.12, 0.07) of the hard domains. The two glass transitions show up in two distinct peaks in tan δ at Tα and Tα'. Analysing the data using a Havriliak-Negami term for the α- and α'-relaxation, as well as Vogel-Fulcher dependencies for the corresponding relaxation times, it is found that the α-glass transition at Tg1 increases strongly (up to ΔT = 70 K) with increasing ϕ(x), whereas the α'-transition at Tg2 remains unchanged. At ϕ(x)(c) ≈ 0.19 the two curves intersect, i.e. Tg1 = Tg2. This value of ϕ(x)(c) 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 (ϕ(x) ≤ ϕ(x)(c)) to a system of soft domains confined in a network of percolated hard domains at ϕ(x) ≥ ϕ(x)(c).