Thermomechanical investigation of hydroxyl-terminated polybutadiene-based linear polyurethane elastomers

Fabrication, Thermo-Mechanical, and Morphological Characterization of Hydroxyapatite-Reinforced Polyurethane Biocomposites as Dye Adsorbent for Effluent

Petrochemical costs, limited fossil fuel reserves, and concerns about greenhouse gas emissions have raised interest in developing renewable approaches for synthesizing biobased polyurethanes. This study aims to solve these problems by making nanocrystalline hydroxyapatite (HA) reinforcement from waste chicken eggshells and adding it to polyurethane synthesis through in situ polymerization. The novelty of the research lies in the utilization of HA as a reinforcement material and renewable resources for polyurethane production. The results confirm that HA was successfully added to the polyurethane backbone. Fourier transform infrared (FTIR) analysis confirmed that the NCO groups were changed to urethane linkages. TGA examination demonstrated that the samples exhibited thermal stability up to 457 °C with a mass loss of 61%, indicating enhanced thermal stability. DMA measurements showed improved mechanical properties of the synthesized polyurethanes, with storage modulus (E'), complex modulus (E*), and compliance complex (D*) values of 0.177, 22.522, and 0.660 MPa-1, respectively. SEM analysis confirmed the homogeneous surface and well-dispersed HA reinforcement. Swelling characteristics revealed an optimum absorption of 30% H2O, 35% CH3OH, and 45% CCl4. Polyurethane composites exhibited significant chemical resistance and hydrolytic stability in acidic and basic media. Additionally, the composites demonstrated efficient adsorption of methyl orange from wastewater, with the PUHCI series achieving a maximum adsorption capacity of 85.50 mg/g under optimal conditions of 0.030 g/mL dose, 45 °C temperature, 2.5 h contact time, and pH 6.0..

The Effect of Single Curing Agents on the Curing Reactions of the HTPB-based Binder System

As the hydroxyl-terminated polybutadiene (HTPB)-based binder system is widely applied in many industries, the curing process plays an important role in the final properties of the resulting product containing such a binder system. This study used a viscometer to measure viscosity buildup in the curing process of the binder system with various curing agents under isothermal conditions. Key parameters such as rheological reaction rate constant (kƞ) and pot life of different were measured and calculated. The rheological reaction rate constants of the HTPB-based binder systems included 0.0423 min−1 (MDI), 0.0049 min−1 (HDI-trimer) and 0.0014 min−1 (HMDI). The pot lives of the HTPB-MDI, HTPB-TDI, and HTPB-HDI-trimer were 0.6 h, 3.6 h and 8.1 h, respectively. One interesting finding is that HTPB-HDI-trimer binder, which had the long pot life, exhibited an accelerated trend in the viscosity buildup in the late phase. This feature is of great significance to improving the final properties of the products generated in propellant manufacturing and other fields. The cause of this phenomenon and the curing process of HTPB-HDI-trimer binder system were analyzed and discussed in the present study.

Role of Macrodiols in the Synthesis and Thermo-Mechanical Behavior of Anti-Tack Water Borne Polyurethane Dispersions

The texture and molecular weight of polymer drastically affect the adhesion or tack strength. Waterborne polyurethane dispersions (WBPU) have been prepared using two different macrodiols of hydroxyl terminated polybutadiene (HTPB; Mn = 2912 g/mol⁻¹) and four compositions of Polypropylene glycol (PPG Mn = 425, 1000, 2000, 2700 g/mol⁻¹). The contents of the macrodiols have been varied using HTPB as 5, 10 and 15 mol%. The prepolymer of HTPB and Poly propylene glycol (PPG) have been developed using 4,4-Methylene bis(cyclohexyl isocyanate) (H₁₂MDI) which is extended using 1, 4 butanediol (BD) followed by the dispersion of polymers in deionized water. Fourier Transform Infra-red spectroscopy (FTIR) is used to confirm the desired PU linkage. The probe tack graphs for tack analysis have not shown any plateau indicating absence of fibrillation. Two different values of glass transition temperature (Tg) have been observed for each dispersion using Differential Scanning Calorimetry(DSC). Storage modulus (E′) up to 3.97 MPa and (tanδ/E′) from 0.01–0.30 MPa⁻¹ has been observed via Dynamic Mechanical Analysis (DMA). Introducing the HTPB has resulted in a decrease in the values of (tanδ/E′). No adhesion favorable parameters have been retrieved, indicating the molar variation a key factor in the development of anti-tack dispersions.

Influence of microstructural variations on morphology and separation properties of polybutadiene-based polyurethanes

Polybutadiene-based polyurethanes with different cis/trans/1,2-vinyl microstructure contents are synthesized. The phase morphology and physical properties of the polymers are investigated using spectroscopic analysis (FTIR and Raman), differential scanning calorimetry (DSC), X-ray scattering (WAXD and SAXS) and atomic force microscopy (AFM). In addition, their gas transport properties are determined for different gases at 4 bar and 25 °C. Thermodynamic incompatibility and steric hindrance of pendant groups are the dominant factors affecting the morphology and properties of the PUs. FTIR spectra, DSC, and SAXS analysis reveal a higher extent of phase mixing in high vinyl-content PUs. Moreover, the SAXS analysis and AFM phase images indicate smaller microdomains by increasing the vinyl content. Smaller permeable soft domains as well as the lower phase separation of the PUs with higher vinyl content create more tortuous pathways for gas molecules and deteriorate the gas permeability of the membranes.

Influence of Graphene Oxide Contents on Mechanical Behavior of Polyurethane Composites Fabricated with Different Diisocyanates

The exceptional behavior of graphene has not yet been entirely implicit in the polymer matrix. To explore this fact in the present work, two series of Polyurethan (PU) composites were synthesized. The structural modification was observed by the use of two different diisocyanate of methylene diisocyanate (MDI) and hexamethylene diisocyanate (HMDI) in hydroxylterminated polybutadiene (HTPB) by using I,4 Butane diol (BD) as the chain extender. The variation in hard segment up to 25 (wt.%) in both series led to significant changes in the mechanical behavior of graphene oxide (GO) induced composites. Both series were prepared by an in situ polymerization process. Fourier transform infrared (FTIR) analysis showed a peak in the region of 1700 cm⁻¹, which confirmed the conversion of the NCO group into urethane linkages. Thermal gravimetric analysis (TGA) revealed a thermal stability up to 450 °C @ 90% weight loss. The swelling behavior showed the optimum uptake of 30% of water and 40% of dimethyl sulfoxide (DMSO) with aliphatic diisocyanate. The values of storage modulus (E′), complex modulus (E*), and compliance complex (D*) were observed up to 7 MPa, 8 Mpa, and 0.7 MPa⁻¹, respectively. The degree of entanglement (N) values were calculated from DMA and were found in the range of 1.7 × 10⁻⁴ (mol/m³). Phase segregation of PU was observed by scanning electron microscopy (SEM), elucidating the morphology of composites.

Fluorescent Metallosupramolecular Elastomers for Fast and Ultrasensitive Humidity Sensing

Fluorescent supramolecular polymers that can respond to subtle external stimuli to generate luminescence signals are promising in a wide range of applications, including probes, anti-counterfeiting materials, and sensors. However, complicated preparative procedures, limited responsive speed, and relatively low sensitivity still limit their practical sensing applications. Herein, we report europium-containing metallosupramolecular (PU-Eu) elastomers for fast and ultrasensitive humidity sensing by employing hygroscopic polyurethane (PU), whose urethane groups can coordinate with europium ions (Eu³⁺), emitting a strong luminescent signal by ligand-to-metal energy transfer. The variant of the coordination bond strength triggered by external humidity imparts the PU-Eu elastomer with a fast (∼1.1 s) and ultrasensitive response to the humid condition, where the external humidity increases by ∼1% and the corresponding fluorescence intensity will drop by ∼421.98 a.u. By a dip-coating process, PU-Eu elastomers can be conveniently coated on a hydrophilic and porous cellulose acetate nanofiber membrane, and the resulting composite membrane can achieve real-time and reversible monitoring of environmental humidity and human respiration. Given the versatility of PU-Eu elastomers, this study provides a low-cost and facile route of obtaining fluorescent metallosupramolecular polymers for fast and ultrasensitive humidity sensing.

Synthesis, characterization, and aging resistance of the polyurethane dimethacrylate layer for dental restorations

In this study, polyurethane dimethacrylate (PUDMA) was synthetized from different components and incorporated into a direct resin composite restoration system with the aim to buffer tooth-resin interfacial stresses and maintain the marginal adaptation. The tensile strength, elongation at fracture (ε), and thermal stability of the PUDMA layer were characterized, showing a tensile strength of 22 MPa, an ε of 112%, and a thermal decomposition temperature of about 282°C. In addition, the degree of conversion, water sorption/solubility, hydrophobicity, microtensile bond strength (μTBS), marginal leakage, and cytotoxicity in vitro were evaluated for the PUDMA layer. The data were analyzed using one-way ANOVA, except for leakage depths (which were analyzed using the Wilcoxon paired-rank test). The level of significance was set at 0.05. Compared with dental adhesives, PUDMA displayed a higher degree of conversion, lower water sorption/solubility, and improved hydrophobicity and biocompatibility in vitro. After thermocycling, the μTBS of the restoration system containing PUDMA had increased compared with the μTBS at 24 h. Restorations containing PUDMA showed lower leakage depths than those which did not contain PUDMA. In conclusion, because of its hydrophobic and elastic nature, the PUDMA layer, when used as an intermediate between tooth and resin restoratives, may buffer interfacial stresses, improve the stability and durability of the bonding interface, and reduce microleakage.

Recent advances in soft functional materials: preparation, functions and applications

Synthetic materials and biomaterials with elastic moduli lower than 10 MPa are generally considered as soft materials. Research studies on soft materials have been boosted due to their intriguing features such as light-weight, low modulus, stretchability, and a diverse range of functions including sensing, actuating, insulating and transporting. They are ideal materials for applications in smart textiles, flexible devices and wearable electronics. On the other hand, benefiting from the advances in materials science and chemistry, novel soft materials with tailored properties and functions could be prepared to fulfil the specific requirements. In this review, the current progress of soft materials, ranging from materials design, preparation and application are critically summarized based on three categories, namely gels, foams and elastomers. The chemical, physical and electrical properties and the applications are elaborated. This review aims to provide a comprehensive overview of soft materials to researchers in different disciplines.