Blending In Situ Polyurethane-Urea with Different Kinds of Rubber: Performance and Compatibility Aspects

Spectroscopic probing of ultraviolet-induced degradation in elastomeric polyurea

Aromatic polyurea has garnered assiduous research due to its excellent impact, shock, abrasion, moisture, and chemical resistance properties. Polyurea can be used in protective coating and impact mitigation applications but is inevitably exposed to harsh deployment conditions such as extended ultraviolet (UV) radiation. Fourier Transform Infrared (FTIR) spectroscopy, Terahertz-time domain spectroscopy (THz-TDS), and Excitation-Emission Matrix spectroscopy (EEMS) deciphered the effects of UV radiation on radiated polyurea samples under ambient and nitrogen-rich conditions. Samples were radiated continuously for up to 15 weeks in increments of 3 weeks. Comprehensive FTIR analyses revealed a monotonic increase in disordered hydrogen bonding as a function of exposure duration in an ambient environment. Otherwise, marginal changes were observed in UV-radiated samples under nitrogen. The hydrogen bond length exhibited significant variations in the former compared to their nitrogen atmosphere counterparts. The results infer the nitrogen shielding effect, protecting polyurea from the photodegradation and photo-oxidation observed in samples radiated under the ambient atmosphere. THz-TDS spectra affirmed the FTIR results by probing changes in the complex refractive index. Terahertz spectral peaks associated with torsional vibrations of intermolecular hydrogen bonds in polyurea were notably correlated with increased exposure duration in the ambient atmosphere. Changes in the complex index as a function of exposure duration under nitrogen are minimal. The excitation-emission spectra of polyurea samples reveal a strong fluorescent behavior in 9-week and 12-week ambient-exposed polyurea due to cluster-triggered emission mechanisms. The results synthesized based on three different spectroscopy techniques paint a holistic portrait of the adverse effects of extended ultraviolet radiation of macromolecules deployed in harsh environmental conditions.

Synthesis and Characterization of New Polycarbonate-Based Poly(thiourethane-urethane)s

The new segmented poly(thiourethane-urethane)s (PTURs) based on 1,1′-methanediylbis(4-isocyanatocyclohexane) (HMDI, Desmodur W^®), polycarbonate diol (PCD, Desmophen C2200) and (methanediyldibenzene-4,1-diyl)dimethanethiol were synthesized by one-step melt polyaddition method. The obtained PTURs, with a content of 30–60 wt% of the hard segments (HS), were tested in which the influence of changes in the HS content on their properties was determined. The polymers were characterized by Fourier transform infrared spectroscopy (FTIR), gel permeation chromatography (GPC), thermal analysis (DSC, TGA) and thermomechanical analysis (DMTA). Additionally, tensile strength, optical (refractive index, UV-VIS and color) and surface properties of the obtained polymers (contact angle and surface free energy) and adhesion to copper were examined. FTIR analysis verified the supposed structure of the polymers obtained and showed a complete conversion of the isocyanate groups. TGA analysis confirmed the relatively good thermal stability of the polymers. On the other hand, after performing the DSC analysis, it was possible to state that the obtained materials were partially or completely amorphous, and the microphase separation decreased with increasing HS content in the polymer. Similar observations were made from the DMTA data. In addition, the hardness, tensile strength, modulus of elasticity, storage modulus, adhesion to copper, refractive index and total free surface energy increased with increasing HS content in the polymer.

Mini-Review of Self-Healing Mechanism and Formulation Optimization of Polyurea Coating

Self-healing polymers are categorized as smart materials that are capable of surface protection and prevention of structural failure. Polyurethane/polyurea, as one of the representative coatings, has also attracted attention for industrial applications. Compared with polyurethane, polyurea coating, with a similar formation process, provides higher tensile strength and requires shorter curing time. In this paper, extrinsic and intrinsic mechanisms are reviewed to address the efficiency of the self-healing process. Moreover, formulation optimization and strategic improvement to ensure self-healing within a shorter period of time with acceptable recovery of mechanical strength are also discussed. The choice and ratio of diisocyanates, as well as the choice of chain extender, are believed to have a crucial effect on the acceleration of the self-healing process and enhance self-healing efficiency during the preparation of polyurea coatings.

Effects of ionic liquid on cellulosic nanofiller filled natural rubber bionanocomposites

Cellulosic nanofillers are sustainable replacements of synthetic fillers while the agglomeration limits their potentials in high-performance rubber bionanocomposites. Herein, we investigate the effects of ionic liquid (IL) on cellulose nanocrystal and cellulose nanofibril filled natural rubber (NR) compounds and vulcanizates. The results indicate that IL improves the dispersion of cellulosic nanofillers, crosslinking density of NR matrix and mechanical strength of the vulcanizates. Invesigations of viscoelastic rheological behaviors show amplitude of Payne effect faints in compounds and raises relatively in vulcanizates with the increment of cellulosic nanofillers and IL.