Polyurethane Formation Research Articles

Preparation and properties of biomass castor oil polyurethane films

In order to investigate the optimal conditions for the formation of castor oil-based polyurethane (CO-PU) films and their comprehensive performance, a series of experiments were carried out utilising biomass castor oil (CO) as the main reactant, 4,4-diphenylmethane diisocyanate (MDI) as the other main reactant, benzoyl peroxide (BPO) as the radical initiator, and dibutyltin dilaurate (DBTDL) as the catalyst. The CO-PUs with different R-values (the number ratio of –NCO/–OH substances) were prepared by pre-polymerisation under single-variable control. The effects of different R-values, DBTDL contents and curing temperatures on the mechanical properties and film-forming state of the CO-PUs were then investigated. Finally, the liquid-resistant medium properties and thermo-gravimetric analyses of CO-PU films were investigated. The experimental results demonstrate that when the R value is 2.5, the DBTDL content is 0.1 ‰, and the curing temperature of the film-forming process is 80 °C, the tensile strength and elongation at break of the CO-PU film are 36.4 MPa and 49.05 % respectively, and the hardness of the pencil at this time is 6H. The water absorption rate is 0.01 %, and the contact angle of water is up to 83.5°. CO-PU displays a commendable resistance to sulfuric acid, sodium hydroxide, and ethyl acetate. Additionally, CO-PU exhibits a high thermal decomposition temperature. The comprehensive performance of CO-PU can be enhanced by modifying the film-forming conditions of CO-PU, which paves the way for further expansion of the applications of CO-PU in the future.

The Polyurethane-Polystyrene Composite—Influence of the Blowing Agent Type on the Foaming Process, the Structure and the Properties

In this study, polyurethane-polystyrene composites (RPURF-EPS) were obtained with the co-expansion method. This method consists of utilizing the heat of the exothermic reaction of polyurethane (PUR) formation to expand polystyrene beads (PSBs). The materials were obtained using polyurethane systems based on the selected blowing agents, such as cyclopentane, a mixture of fluorocarbons and water. The analysis of the foaming process was carried out using a special device called FOAMAT. The characteristic start, rise, gelation and curing times were defined. The rise profile, the reaction temperature, the pressure and the dielectric polarization were measured. The influence of selected blowing agents on the cell structure and physical–mechanical properties of reference rigid polyurethane foam (RPURF) and RPURF-EPS, such as apparent density, compressive strength and thermal conductivity, were evaluated. Based on the research, the blowing agents that have the most beneficial influence on the properties and structure of the composites and that provide the most efficient expansion of PSBs in a light porous composite were found.

Study of the Characteristics of Polyurethane as a Sustainable Material used for Buildings, Polymer Composite, Biomedical, and Electronics Application

This research is focused on studying the characteristics of Polyurethane in engineering applications as a sustainable material employed for buildings and as reinforcement for polymer composite, electronics, and biomedical applications. This study discussed and reviewed papers cut across the Polyurethane Formation, Engineering Attributes of Polyurethane, and Polyurethane Applications in various fields such as Buildings, Polymer Composite Materials, Biomedical, and Electronic, which has proven that Polyurethane is a multi-functional material that has been employed in biomedical engineering used for tissue, wound treatment, breast implant, drug delivery systems. Also, it has been applied for sensors, actuators, Flexible electronics, Energy harvesters and storage, and Shape memory applications. Furthermore, its application in buildings, Polyurethane (PU) foam as an insulation material embedded in the aluminium roofing system for sustainable human comfort. This study also identifies the challenges of Polyurethane and provides sustainable solutions. In conclusion, site materials and structural application have shown excellent performance from studying the Polyurethane characteristics as embedded materials for roofing sheets.

The state-of-art polyurethane nanoparticles for drug delivery applications.

Nowadays, polyurethanes (PUs) stand out as a promising option for drug delivery owing to their versatile properties. PUs have garnered significant attention in the biomedical sector and are extensively employed in diverse forms, including bulk devices, coatings, particles, and micelles. PUs are crucial in delivering various therapeutic agents such as antibiotics, anti-cancer medications, dermal treatments, and intravaginal rings. Effective drug release management is essential to ensure the intended therapeutic impact of PUs. Commercially available PU-based drug delivery products exemplify the adaptability of PUs in drug delivery, enabling researchers to tailor the polymer properties for specific drug release patterns. This review primarily focuses on the preparation of PU nanoparticles and their physiochemical properties for drug delivery applications, emphasizing how the formation of PUs affects the efficiency of drug delivery systems. Additionally, cutting-edge applications in drug delivery using PU nanoparticle systems, micelles, targeted, activatable, and fluorescence imaging-guided drug delivery applications are explored. Finally, the role of artificial intelligence and machine learning in drug design and delivery is discussed. The review concludes by addressing the challenges and providing perspectives on the future of PUs in drug delivery, aiming to inspire the design of more innovative solutions in this field.

Impact of Bark-Sourced Building Blocks as Substitutes for Fossil-Derived Polyols on the Structural, Thermal, and Mechanical Properties of Polyurethane Networks.

The hydrophilic extractives isolated from black alder (Alnus glutinosa) bark through hot water extraction were characterized as novel renewable macromonomers capable of forming polyurethane (PU) networks based on a commercial polyisocyanate, with partial or complete replacement of petroleum-derived polyol polyether. The bark-sourced bio-polyol mainly consists of the xyloside form of the diarylheptanoid oregonin, along with oligomeric flavonoids and carbohydrates, resulting in a total OH group content of 15.1 mmol·g-1 and a molecular weight (Mn) of approximately 750 g∙mol-1. The 31P NMR data confirmed a similar proportion of aliphatic OH and phenolic groups. Three-component PU compositions were prepared using polyethylene glycol (Mn = 400 g∙mol-1), bio-polyol (up to 50%), and polymeric diphenylmethane diisocyanate, which were pre-polymerized in tetrahydrofuran (THF) solution with tin organic and tertiary amine catalysts. The resulting mixture was cast and subjected to thermal post-curing. Calculation and experimental data confirmed the crosslinking activity of the bark-sourced bio-polyol in PU, leading to an increase in glass transition temperature (Tg), a decrease in sol fraction yield upon leaching of cured PU networks in THF, a significant increase in Young's modulus and tensile strength. The macromonomers derived from bark promoted char formation under high temperature and oxidative stress conditions, limiting heat release during macromolecular network degradation compared to bio-polyol-free PU. It was observed that amine catalysts, which are active in urethane formation with phenolic groups, promoted the formation of PU with higher Tg and modulus at tensile but with less limitation of heat liberation during PU macromolecular structure degradation. The high functionality of the bark-derived bio-polyol, along with the equal proportion of phenolic and aliphatic OH groups, allows for further optimization of PU characteristics using three variables: increasing the substitution extent of commercial polyethers, decreasing the NCO/OH ratio, and selecting the type of catalyst used.

Synthesis and Characterization of Hydrophobic and Low Surface Tension Polyurethane

Polyurethane is a common polymeric coating, providing abrasion resistance, chemical durability, and flexibility to surfaces in the biomedical, marine, and food processing industries with great promise for future materials due to its tunable chemistry. There exists a large body of research focused on modifying polyurethane with additional functionalities, such as antimicrobial, non-fouling, anticorrosive action, or high heat resistance. However, there remains a need for the characterization and surface analysis of fluoro-modified polyurethanes synthesized with commercially available fluorinated polyol. In this work, we have synthesized traditional solvent-borne polyurethane, conventionally found in food processing facilities, boat hulls, and floor coatings, with polyurethane containing 1%, 2%, and 3% perfluoropolyether (PFPE). Polyurethane formation was confirmed by attenuated total reflectance Fourier-transform infrared (ATR-FTIR) spectroscopy, with the urethane band forming at 1730 cm−1 and the absence of free isocyanate stretching from 2275–2250 cm−1. X-ray photoelectron spectroscopy (XPS) was used to confirm perfluoropolyether polymerization with an increase in the atomic percentage of fluorine. Wettability and hydrophobicity were determined using a dynamic water contact angle with significant differences in advancing the water contact angle with the inclusion of perfluoropolyether blocks (PU–co–1PFPE 131.5° ± 8.0, PU–co–2PFPE 130.9° ± 5.8, and PU–co–3PFPE 128.8° ± 5.2) compared to the control polyurethane (93.6° ± 3.6). The surface orientation of fluorine supported the reduced critical surface tensions of polyurethane modified with PFPE (12.54 mN m−1 for PU–co–3PFPE compared to 17.19 mN m−1 for unmodified polyurethane). This work has demonstrated the tunable chemical qualities of polyurethane by presenting its ability to incorporate fluoropolymer surface characteristics, including low critical surface tension and high hydrophobicity.

Molecular mobility of liquid crystalline polyurethanes modified by polyhedral oligomeric silsesquioxanes

Molecular mobility and liquid crystalline order formation of liquid crystalline polyurethanes (LCPU) modified by trisilanolphenyl-POSS was investigated by using dielectric spectroscopy (DRS), differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA). Hybrid materials with 2, 4 and 6 wt% of POSS load were studied. Small-angle X-ray scattering (SAXS) results suggested that the nanoscale morphology was not significantly altered by the introduction of POSS into the LCPU matrix. The presence of liquid crystal phase transitions was confirmed by both DRS and DSC measurements. Dielectric study showed changes in relaxation steps and conductivity in the LC transitions region due to a shift in phase order. Using partially cross-linked POSS particles, an enhancement of the material's rubber modulus was observed in the DMA measurement. Deterioration in charge transfer was observed for the composites, which was attributed to the crosslinking nature of the silsesquioxane used. Further, dynamic calorimetric studies in different cooling rates were performed for detailed study of liquid crystalline transitions. In summary, it was found that the addition of POSS causes a nucleation effect and does not impair LC phase formation.

Towards Solar-Driven Formation of Robust and Self-Healable Waterborne Polyurethane Containing Disulfide Bonds via in-situ Incorporation of 2D Titanium Carbide MXene

Waterborne polymers are vital for coating industry to reduce carbon emissions. However, formation of robust and self-healable films at ambient temperature remains a challenge owing to high energy cost of film formation process. This work reports a solar-driven film formation of waterborne polyurethanes (WPUs) containing disulfide bonds via in-situ incorporation of 2D titanium carbide (MXene) with ability to convert light to heat. Instead of directly mixed with WPUs, MXene is added to join the reaction with isocyanate-terminated pre-polymer before emulsification process. This approach not only prevents aggregation of MXene in water but stabilizes MXene against thermal degradation which is the key hurdle for mass production of MXene/WPU composites. More importantly, our results show that mechanical performance of WPU films under visible light (100 mW/cm2) is overwhelmingly competitive with that processed in oven. Furthermore, the existence of disulfide bonds in PU chains enables fast self-healing of micro-cracks under natural visible light which could vanish completely within 40 min. The fractured specimens were repaired under natural visible light for 2 h, and the self-healing efficiency of tensile strength and elongation at break reached over 94.00%.

Production of “Green” Thermoplastic Polyurethanes from Decamethylene Sebacate‐co‐Isosorbide Copolymers

AbstractLong‐chain aliphatic copolyesters based on sebacic acid (SA) and isosorbide (IS), of renewable origin, are synthesized by a “green” and sustainable route, without the use of solvents, for the synthesis of polyurethanes (PUs). The polyesters are characterized by size exclusion chromatography (SEC), proton nuclear magnetic resonance (¹H NMR), Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), and thermogravimetry (TG). ¹H NMR and FTIR analyses confirm the production of copolyesters with the incorporation of IS, while SEC indicates that the addition of IS to copolyesters decreases the molecular weights. The results suggest the formation of random copolymers in the presence of IS, which makes the polymer chains more rigid. The formation of PUs by the reaction of copolyesters with 1,8‐diisocyanatooctane is confirmed by FTIR. Thermal behavior is compatible with thermoplastic processing and use in different biomedical applications.

Preparation of laminated safety glass based on high strength polyurethane film by solution annealing

AbstractCompared with the traditional polyvinyl butyral (PVB) laminated glass, the polyurethane (PU) based laminated glass has the advantages of higher impact strength and longer service life. Thus, aromatic polyurethane films have attracted more attentions in recent years due to their high light transmittance, adhesion and functionality. In this paper, the tensile strength of polyurethane films based on bis(4‐isocyanatocyclohexyl)‐methane (HMDI) have been increased from 27 to 51 MPa and their elongation at break have been increased from 330% to 525% after solvent annealing in toluene. It is attributed to molecular segments with high crystallization and hydrogen bond formation of PU, which are confirmed by FT‐IR and XRD characterization. Based on this, laminated glasses with higher impact strength based on the thermoplastic polyurethane films are constructed successfully.

Simple Trivalent Cobalt Complex-Mediated Copolymerization of Epoxides with Isocyanate: Combining High Activity and Selectivity

Controlled ring-opening copolymerization involving epoxides represents a valuable strategy for the synthesis of oxygenated polymers with unique biodegradability and biocompatibility. In this study, simple trivalent metal complexes, salenM(III)X (salen = N,N′-bis(salicylidine) diamine derivatives, M = Al, Cr, and Co), are employed for copolymerizing p-tosyl isocyanate (TSI) with epoxides, generating perfectly alternating polyurethanes with various structures and tunable properties. The trivalent cobalt acetate complex of N,N′-bis(salicylidine)-o-phenylenediamine bearing 3- and 3′-, 5- and 5′-tert-butyl groups exhibited the highest activity of up to 41,400 h–1 under mild conditions. This single-site catalyst also showed excellent activity and selectivity for copolymer formation even at an extremely low loading of 0.002 mol % without any cocatalyst activator and operated efficiently for various terminal epoxides, affording completely alternating polyurethanes with high molecular weights and narrow polydispersities. Also, this catalyst was tolerant of large quantities of chain transfer agents, thereby allowing control of the molecular weight. Notably, the ring opening of terminal epoxides predominantly occurring at the methylene C–O bond resulted in the formation of stereoregular polyurethanes with more than 96% head-to-tail content.

Synthesis and characterization of polyurethane foam based on vegetable oil

This research shows the production and characterization of the polyurethane foam produced from moringa oil with low energy expenditure. Vegetable oil, polyol and the foam were characterized by hydroxyl, acid and Iodine index, Fourier Transform Infrared Spectroscopy (FTIR), 1H RMH spectra, Thermo gravimetric analysis (TG), Scanning Electrical Microscopy (SEM), X-Ray Diffractogram (XRD) and Mass Spectroscopy. The physical-chemical results showed the modified oil potential for the polyurethane formation reaction due to the hydroxyls index of 257.52 mg KOH g-1 and acidity of 2.38 mg KOH g-1. FTIR spectra showed the hydroxylation reactions and urethane groups formation in the oil by bands wich referring to hydroxyl groups and their NH groups superposition. Foam TG showed a degradation profile between 281 °C and 750 °C, losing half of its mass in temperatures higher than 400 °C. Micrographies showed that foam is composed by opened and closed cells, characteristic of semi-flexibility of the foam.

Superhydrophobic coordination polyurethane films based on methylolated-cardanol and hexamethylene diisocyanate: Synthesis, characterization and antibacterial evaluation

A novel in-situ formation of bio-based coordination polyurethane (CPUs) have been demonstrated which could substitute to traditional petroleum-built PUs and was formulated by considering the objectives of green and sustainable development. Present work seeks to synthesize cheap and environment-friendly M(II) [Mn(II), Co(II), Ni(II) and Zn(II)] coordinated PUs [M(II)ColF-AliPU] using cardanol formaldehyde (ColF) and aliphatic diisocyanate. The ambient-cured free-standing film/coatings were developed and their properties were discussed and compared. However, free-standing films of Ni(II)-ColF-AliPU and Zn(II)-ColF-AliPU were not obtained even after subjecting the curing at elevated temperatures. FTIR and UV–Visible analysis helps in confirming the octahedral [Mn(II), Co(II), Ni(II)] and tetrahedral [Zn(II)] coordinated structures. The incorporation of metal ions was confirmed by EDX analysis, and the semi-crystalline behavior observed (XRD) was collaborated to the presence of hexamethylene chains of HMDI with nanostructured framework (spheres and tubes). Metal incorporation increases the thermal stability of M(II)-ColF-AliPU and accredits the applications up to 200–220 °C. Co(II) showed the best thermal stability and flame retardancy among other PUs, however, these films were found to be comparatively less thermally stable than aromatic diisocyanate (TDI) based CPUs. After metal integration, the physicomechanical study indicated significant mechanical strength in terms of scratch resistance (1.8 kg), high impact (1.50 × 102 lb./in.), excellent adhesion, bending (1/8 in.), and improved gloss value, although less than M(II)-ColF-ArPU (CPU with aromatic diisocyanate). Water contact angle of ColF-AliPU (151°), Mn(II)-ColF-AliPU and Co(II)-ColF-AliPU (152° and 153°, respectively) revealed the development of superhydrophobic surfaces. The antibacterial activity results revealed Co(II)-ColF-AliPU to be the best composition for inhibiting the bacterial growth (E. coli, S. aureus, K. pneumoniae, and B. subtilis) and thus can be employed in market as antibacterial thin films and coatings.

Study of Polymer Binders to Develop Low Emissive Paints for Thermal Radiation Management Applications

The management of thermal emittance always possess challenges in both military and civil domains. The low emissive materials in form of paints offers viable solution for minimising thermal emittance of military objects for camouflage and enhancing infrared reflectivity of roof to reduce cooling loads. Binder apart from pigments is one of the critical components of low emissive paint formulation to decide its ultimate performance. For selection of appropriate resin and binder, a comparative study of five prevalent polymers viz. polyurethane (PU), poly vinyl chloride (PVC), polyethylene (PE), polypropylene (PP) and poly methyl methacrylate (PMMA) has been carried out. Polymeric film of thickness 100μm of each of the polymer is prepared by Elcometer 4340 motorized film applicator. Infrared spectra and thermogravimetric profile have been obtained by Bruker make Tensor 27 FTIR in spectral range 4000 – 600 cm-1 and TGA Q 500. Film formation of PU is excellent and transmission in 3-5 μm is almost 100%. Hence, it may be chosen as binder in low emissive paint for MWIR band. PVC and PMMA among the polymers offer excellent transmission 87-99% in both thermal transmission windows 3-5 μm and 8-12 μm. Thermogravimetric (TG) profile of polymer films evident of thermal stability of PVC, PMMA and PU polymers up to 200 °C. Infrared transmission, TG profile and film formability manifest that both binders- PVC and PMMA are suitable for development of low emissive paints applicable up to temperature 200 °C for both IR transmission windows to evade thermal detectors working for detection of military objects and reducing cooling load in buildings by enhancing reflectivity of roof by application of low emissive paint.

Introducing a Sustainable Bio-Based Polyurethane to Enhance the Healing Capacity of Bitumen

This paper introduces the in-situ formation of biomodified polyurethane in bitumen as a novel strategy to enhance the healing capacity and aging resistance of bitumen. Bitumen is a substance that is known to have the capacity for healing. Self-healing bituminous composites can recover their properties. An increase in bitumen’s healing capacity can be facilitated using various modifiers. This study examined the merits of using a biobased polyurethane to both improve the healing capacity of bitumen and to enhance its resistance to aging through in-situ polymerization of polyurethane. The effect of aging on healing capacity was examined by studying specimens before and after aging in the laboratory. To do so, thermomechanical analysis and spectroscopy were used to characterize bitumen containing a biobased polyurethane from castor oil. It was found that the biobased polyurethane was quite compatible with bitumen, and the presence of polyurethane improved the overall thermomechanical properties of the bitumen. To evaluate the extent of healing, a time-sweep rheometry test was used to create samples with specific initial damage degrees. The degree of damage was selected to be a 30%, 45%, or 60% reduction in complex modulus. A healing index was calculated for each of the three damage levels after a 60-min rest period. The study results showed that the introduction of biobased polyurethane not only improved the healing index, it also mitigated the negative effects of aging on bitumen’s healing capacity. Compared to samples of unmodified bitumen, the average healing index of samples containing biomodified polyurethane was 1.3 times higher at 16% in the unaged state and 3.5 times higher at 7% in the aged state. In addition, the samples containing biomodified polyurethane showed better resistance to aging as evidenced by average 72% and 50% lower increases, respectively, in carbonyl and sulfoxide (known products of aging in bitumen) when exposed to the same aging protocol.

Polydimethylsiloxane based polyurethane and its composite with layered double hydroxide: Synthesis and its thermal properties

AbstractThis investigation reports the synthesis of a new class of polyurethane (PU) based on bis(hydroxyalkyl) polydimethylsiloxane (PDMS) as diol and isophorone diisocyanate as diisocyanate followed by the preparation of PU/layered double hydroxide (PU/LDH) nanocomposite via ex‐situ technique. Nuclear magnetic resonance and Fourier‐transform infrared spectroscopy studies confirm the formation of PU and incorporation of PDMS into the PU backbone. Thermogravimetry analysis revealed that thermal stability of the composite improves significantly with incorporation of LDH into the PU matrix. This may be accredited to the barrier effect rendered by the LDH layers. Differential scanning calorimetry study reveals that with the incorporation of LDH, glass transition temperature (Tg) of the composite increases for an optimum level of loading beyond which it remains constant.

Mechanical behavior of carboxylic functionalized graphene reinforced polyurethane nanocomposites under static and dynamic loading

AbstractThe present work reports formation of polyurethane (PUR) and carboxylic functionalized graphene (COOH‐fG) nanocomposites via solution mixing method and static and dynamic mechanical characterization with dynamic mechanical analysis (DMA), nano indentation, and tensile and compressive testing. Magnetic stirring of the solutions of PUR in N,N dimethylformamide (DMF) and COOH‐fG in DMF was performed for different compositions of filler, 1%, 3%, 5%, 7%, and 10%, which were heated to obtain nanocomposite films followed by injection molding to cast into samples. Uniform dispersion and good intercalation were observed upon characterization by field emission scanning electron microscopy and X‐ray diffraction techniques. DMA showed that the storage modulus improved with increasing frequency of loading, and a linear decrement in the damping factor with an increase in the concentration of filler was observed. The maximum depth of indent in nano‐indentation test showed a decreasing trend, indicating improvement in nanohardness and elastic modulus with an optimum obtained at 5 wt% composition. An improvement in tensile modulus, tensile strength, and toughness, which were more substantial at lower compositions of filler, was observed. An optimum compressive modulus was obtained for 10 wt% of filler due to more resistance provided by graphene plates to compression as compared to PUR.

Polyurethane derived from castor oil monoacylglyceride (Ricinus communis) for bone defects reconstruction: characterization and in vivo testing

Biomaterials used in tissue regeneration processes represent a promising option for the versatility of its physical and chemical characteristics, allowing for assisting or speeding up the repair process stages. This research has characterized a polyurethane produced from castor oil monoacylglyceride (Ricinus communis L) and tested its effect on reconstructing bone defects in rat calvaria, comparing it with commercial castor oil polyurethane. The characterizations of the synthesized polyurethane have been performed by spectroscopy in the infrared region with Fourier transform (FTIR); thermogravimetric analysis (TG/DTG); X-ray diffraction (XRD) and Scanning Electron Microscopy (SEM). For the in vivo test, 24 animals have been used, divided into 3 groups: untreated group (UG); control group treated with Poliquil® castor polyurethane (PCP) and another group treated with castor polyurethane from the Federal University of Piauí - UFPI (CPU). Sixteen weeks after surgery, samples of the defects were collected for histological and histomorphometric analysis. FTIR analysis has shown the formation of monoacylglyceride and polyurethane. TG and DTG have indicated thermal stability of around 125 °C. XRD has determined the semi-crystallinity of the material. The polyurethane SEM has shown a smooth morphology with areas of recesses. Histological and histomorphometric analyzes have indicated that neither CPU nor PCP induced a significant inflammatory process, and CPU has shown, statistically, better performance in bone formation. The data obtained shows that CPU can be used in the future for bone reconstruction in the medical field.

Glass‐rigid foam composite for innovative concrete sandwich elements

AbstractIn building envelopes, sandwich elements with facings made of glass currently require either adhesives or mechanical connectors. The avoidance of any connectors seems to be favorable in terms of resource and energy savings both in production and in building envelopes. The present studies are part of the development of a glass‐rigid foam‐concrete sandwich element without additional adhesives and mechanical connectors. This paper reports on the structural bond behavior between polyurethane rigid foam and float glass with different surfaces with or without applying a bonding agent. Tensile bond and shear tests show, that a sandblasted toughened glass surface results in cohesive failure of the insulation layer. The two production‐related surfaces of float glass are defined as atmosphere and tin side. Both surfaces offer an adhesive failure between the insulation layer and glass. Test specimens of glass and insulation layer without bonding agent show no significant differences between the atmosphere and the tin side. Overall, the test specimens with bonding agents achieve higher levels of adhesive tensile bond and shear strength. Light and electron microscopic studies of fractured surfaces show, that the bonding agent has a significant influence on the wetting and pore formation of the liquid polyurethane.

Chemorheology and Kinetics of High‐Performance Polyurethane Binders Based on HMDI

AbstractAliphatic diisocyanates, such as 1,6‐hexamethylene diisocyanate (HMDI), are preferred curing agents for the formation of polyurethanes (PUs) in applications where resistance to abrasion or degradation by ultraviolet light takes precedence. Aside from the final properties, the curing agent plays a key role in the bulk manufacturing of such materials, and it mainly affects the polymerization kinetics and their rheology. The copolymerization of HMDI and a metallo‐prepolymer derivative from hydroxyl‐terminated polybutadiene (HTPB) is studied under isothermal conditions (50–80 °C). This study is carried out by means of an indirect method, using both rotational viscometry and dynamic rheometry. At the beginning of the process, the viscosity growth fit well to a first‐order kinetic model. Afterward, the reactive system passes through gelation, from which only rheology is allowed for the investigation of the entire polymerization process. This transition is analyzed in depth together with predictions from percolation theory. The conversion degree is determined from rheological measurements, and then an autocatalytic kinetic model is applied to describe the overall process. Finally, an isoconversional method allows the evolution of activation energy to be studied. This analysis merits attention for the development of high‐performance binders that are of great interest in aerospace propulsion technology.