Curable Polyurethane Research Articles

Impact of moisture curing conditions on the chemical structure and rheological and ultimate adhesion properties of polyurethane adhesives based on castor oil and cellulose acetate

On account of the heavy reliance of the adhesive industry on petrochemical derivatives, there is a particular interest in the development of bio-sourced polyurethane adhesives. In this context, a moisture-curable polyurethane adhesive has been synthesized from cellulose acetate and castor oil, using 1,6-hexamethylene diisocyanate as a crosslinker. In particular, this research delves into the rheological and adhesion properties achieved by bio-inspired polyurethanes cured at 20 °C and under different relative humidity conditions (11, 33, 64, and 90.4%). Green shear and peeling strengths on wood and stainless steel as well as chemical structure variations were monitored over curing time. Moreover, fully cured polyurethane-urea adhesives were thermally (thermogravimetric and differential scanning calorimetric analyses) and rheologically characterized within the linear viscoelastic region. The results corroborated the noteworthy impact of environmental humidity throughout the curing process of the synthesized bio-sourced adhesives, favoring the formation of urea linkages, while sharply reducing the crystalline/amorphous ratio. All the bio-based polyurethane-urea copolymers showed a predominant elastic behavior and the time-Temperature superposition principle was found to be applicable up to around 120 °C, due to the thermal rearrangement of the hard segment units. The crosslinking density of the resulting supramolecular structure depends on the humidity-driven balance between the urethane and urea linkages production. As a consequence of the balance between the establishment of bidentate hydrogen bonds and the curing rate, moisture curable polyurethane adhesive cured at 33% relative humidity exhibited the most appropriate shear adhesion performance on wood, while the debonding shear strength on stainless steel increased with the relative humidity due to the higher urea:urethane ratio and larger proportions of non-bonded urethane and urea groups, thus enhancing secondary interactions. Therefore, on the basis of the present study results, it might be concluded that the synthesis of bio-inspired moisture-curable polyurethane can be tuned according to its end-use application through the control of the environmental conditions, and thereby optimizing their adhesion performance, while meeting the Green Chemistry tenets.

Effect of Hydrophilic Bentonite as a Filler on Curing Performance of Pigmented UV Curable Polyurethane Acrylate Coating

The effect of hydrophilic bentonite incorporation on the curing performance of pigmented ultra violet (UV) curable polyurethane acrylate (PUA) coating was investigated. To the best of our knowledge, crock fastness and gloss properties of pigmented bentonite incorporated UV curable PUA coating have been examined for the first time. Fourier Transform Infrared (FTIR) spectroscopy analysis of the cured films showed that addition of both bentonite and pigment decreased the conversion of C=C. However a more significant drop was observed with the addition of pigment into the formulation. The drop of conversion with the incorporation of bentonite did not adversely affect the hardness and crock fastness values and hence the UV curing performance of the films. Bentonite particles were efficiently distributed in the film and intercalation was achieved owing to the ball milling process. Hardness of the cured films increased with the increase in energy levels. On the other hand, hardness decreased at higher pigment concentrations however, was not affected adversely by bentonite incorporation. Gloss was found to be enhanced with the addition of bentonite in both pigmented and unpigmented films. Significant improvement in crock fastness could not achieved with the addition of bentonite.

UV curable hyperbranched polyester polyurethane acrylate for hydraulic machinery coating

The content of river cement and sand in our country is relatively high, and the surface of hydraulic machinery in hydropower stations is often subject to fatigue damage and erosion. This topic is mainly used to solve the problem of abrasion and corrosion of hydraulic machinery coatings. UV curable polyurethane acrylate (PUA) can be quickly solidified into film and directly coated on the surface of hydraulic machinery with excellent anti-wear, adhesion properties and low cost. In this work, a hyperbranched polyester synthesized by the stepwise reaction of trimethylolpropane (TMP) and dimethylolpropionic acid (DMPA) was as a ‘nucleus’, and the polyurethane prepolymer was obtained by grafting IPDI and PTMG (C Schüll, H Frey, 2013 Grafting of hyperbranched polymers: from unusual complex polymer topologies to multivalent surface functionalization, Polymer, 54, 5443–5455). The UV-curing hyperbranched polyester polyurethane acrylate (PUA-1) was prepared by capping with HEA (Xu, W, Wang, W, Hao, L, Zhao, W, Liu, H, Wang, X 2020 Effect of generation number on properties of fluoroalkyl‐terminated hyperbranched polyurethane latexs and its films. J. Appl. Polym. Sci., e49215). Another UV-curing hyperbranched polyester polyurethane acrylate (PUA-2) was prepared as comparison by using TDI and PTMG as the main raw materials. Fourier Transform Infrared Spectrometer,1H-nuclear magnetic resonance spectroscopy, Gel Permeation Chromatography, thermogravimetric analysis and dynamic thermomechanical analysis were used to characterize its structure and properties. The wear rate of the two hyperbranched polyesters measured by the underwater steel ball method is below 3%, The swelling rate of PUA-1 is between 250%–300%, and the swelling rate of PUA-2 is around 260%, indicating that PUA-2 has better solvent resistance than PUA-1, and the internal structure of the film is more dense. TG analysis showed that the thermal stability of the two materials was good.

Spray-Coated Organic Light-Emitting Electrochemical Cells Realized on a Standard Woven Polyester Cotton Textile

In this article, organic light-emitting electrochemical cells (OLECs) have been fabricated on a substrate consisting of a standard woven polyester cotton textile. The textile substrate is presmoothed by first screen printing an ultraviolet (UV) curable polyurethane layer, termed the interface layer. Solution-processed spray coating is then utilized to deposit all the functional layers on the textile to achieve fully spray-coated flexible OLECs. OLEC devices were initially fabricated on ITO-coated glass substrates for process optimization. Then, the OLECs were fabricated on flexible textile using the optimized spray coating process. Finally, both OLECs devices on the glass and textile substrates were encapsulated by stencil printing epoxy before testing in an ambient environment. The OLECs on ITO-coated glass exhibit a turn-on voltage of 3 V, a brightness level of 200 cd/m2 and a lifetime of at least 60 min. The OLECs on textile exhibit a turn-on voltage of 4 V, a brightness level of 80 cd/m2 level and a lifetime of at least 30 min.

UV-LED as a New Emerging Tool for Curable Polyurethane Acrylate Hydrophobic Coating.

The elimination of mercury, low energy consumption, and low heat make the ultraviolet light-emitting diode (UV-LED) system emerge as a promising alternative to conventional UV-mercury radiation coating. Hence, a series of hydrophobic coatings based on urethane acrylate oligomer and fluorinated monomer via UV-LED photopolymerisation was designed in this paper. The presence of fluorine component at 1160 cm−1, 1235 cm−1, and 1296 cm−1 was confirmed by Fourier Transform Infra-Red spectroscopy. A considerably high degree C=C conversion (96–98%) and gel fraction (95–93%) verified the application of UV-LED as a new technique in radiation coating. It is well-accepted that fluorinated monomer can change the surface wettability as the water contact angle of the coating evolved from 88.4° to 121.2°, which, in turn, reduced its surface free energy by 70.5%. Hence, the hydrophobicity of the coating was governed by the migration of the fluorine component to the coating surface as validated by scanning electron and atomic force microscopies. However, above 4 phr of fluorinated monomer, the transparency of the cured coating examined by UV-visible spectroscopy experienced approximately a 16% reduction. In summary, the utilisation of UV-LED was a great initiative to develop green aspect in photopolymerisation, particularly in coating technology.

Synthesis and thermal decomposition kinetics of moisture curable polyurethane films as a reinforcing material for cultural relics

In situ consolidation is the most common treatment to conserve cultural relics, but materials for preserving fragile organic cultural relics in humid archaeological excavation sites are scarce. To solve the problem, a moisture-curable polyurethane (MCPU) prepolymer was synthesized by reacting isophorone diisocyanate with polyethylene glycol 600. The standard acetone–dibutylamine method, Fourier transform infrared spectroscopy, gel chromatography and thermogravimetric analysis were utilized to determine the change in isocyanate groups before and after the reaction, the prepolymer molecular weight, the thermal decomposition kinetic parameters and the MCPU film lifetime. The results showed that the number-average molecular weight of the prepolymer was 749, and the weight average molecular weight was 1684. Isophorone groups in the prepolymer react with moisture in the air to form colorless, transparent, flexible films. The thermal decomposition of the MCPU films was a first-order reaction, and the decomposition process consisted of two stages. The Dakin equation was used to obtain the thermal aging equation lg t = 4600.82/T − 8.07, meaning that at 15 °C, the sample has an approximately 150-year lifetime. A new conservation material was developed, and its thermal decomposition kinetics were studied, which are significant for the conservation of fragile organic cultural relics in humid environments.

Hygrothermal aging, fatigue and dynamic mechanical behavior of cellulosic particles reinforced one-component moisture curable polyurethane adhesive joints

Microcrystalline cellulose (MCC) and sawdust (SD) green fillers have great potential to act as moisture reservoirs and reactive fillers. In the present study, a one-component moisture curable polyurethane (PU) adhesive was reinforced with MCC and SD fillers. The durability of aluminum/steel joints produced using unreinforced and reinforced PU adhesives was studied using dynamic mechanical analysis (DMA), fatigue, and hygrothermal aging experiments. Lap-shear tests were conducted to evaluate the effects of aging on joints strength. Fourier-transform infrared spectroscopy (FTIR) experiments were performed on adhesive joints after hygrothermal aging to understand the changes in chemical structure due to aging, and the influence of cellulosic fillers on the aging phenomena. DMA results showed that the glass transition temperature of the reinforced PU was similar to that of the unreinforced PU. Fatigue performance of MCC and SD reinforced PU adhesive joints was found to be better than unreinforced PU joints. Further, MCC reinforced PU adhesive joints were found to be more resistant to hygrothermal aging than SD reinforced and unreinforced PU joints. Overall, MCC reinforced PU adhesive joints exhibited good fatigue and superior long-term properties.

Synthesis and characterization of UV curable polyurethane acrylate derived from α-Ketoglutaric acid and isosorbide

A thermally stable coating of UV curable polyurethane acrylate (PUA) was prepared from bio-based PU and methyl 3-(4-hydroxy-3-methoxyphenyl)acrylate(MHPA). The presence of the aromatic ring in the backbone associated with MHPA imparts thermal stability in the structure. The bio-based PU was prepared through the condensation polymerization of hexamethylene diisocyanate(HDI) and a polyol prepared by the condensation reaction of α-ketoglutaric acid(KA) with isosorbide(IS). Isosorbide and α-ketoglutaric acid represent the replacement of the petroleum-based precursors used in polyol synthesis. Characterization of the new compound has been carried out using Fourier transform infrared spectroscopy(FT-IR) and nuclear magnetic resonance spectroscopy(NMR) and correlated with the quantitative analysis through hydroxyl and acid value. The UV curable PUA was added into the commercial polyurethane acrylate(CPUA) coating system and assessed based on their functional properties. The flexibility of the cured coating was determined by understanding the glass transition temperature through differential scanning calorimetry(DSC). Thermal gravimetric analysis was used to measure the thermal stability of the PUA and CPUA mixture. With an increase in the concentration of PUA, the thermal stability of the mixture improves. The structure of the prepared coating has been assessed using X-ray diffraction methods. The dynamic mechanical properties such as storage and loss modulus of the coating were determined from the rheological behavior. The mechanical properties and chemical/solvent resistance of the mixture were calculated and correlated with the gel content and moisture content. The nature of the fracture of the coating was observed through scanning electron microscopy(SEM).

Preparation and characterization of modified castor oil via photo‐click chemistry forUV‐curable waterborne polyurethane with enhanced water resistance and low conductive percolation threshold

AbstractA castor oil (CO) was modified via thiol‐ene click chemistry reaction between CO and 3‐mercaptopropyl trimethoxysilane, with the conversion of CC bonds of CO over 99% based on1HNMR spectra. The obtained modified castor oil (MCO) was used as a biobased polyol to prepare waterborne polyurethane (WPU) dispersions. The modification of CO exhibited a great effect on the properties of WPU dispersions and coatings, and an obvious change is the improvement of the water resistance of WPU coatings. WPU dispersions with MCO had good storage stability. A WPU coating with 7% MCO had high surface hydrophobicity, and its water absorption was as low as 3.2%. Conductive carbon black filled WPU coatings with MCO were cured by efficient UV radiation, and their conductive percolation threshold could decrease to 0.76%, which could be attributed to the well filler dispersion and strong filler‐polymer interaction. The WPU dispersions are ecofriendly, and can be used to produce biobased WPU coatings with a great application potential in antistatic coating fields.

Research on the Performance of Series Waterborne Polyurethane Acrylate Modified Epoxy Acrylates

In this study, a series of bifunctional-based UV curable waterborne polyurethane acrylate modified epoxy acrylate (UV-WPUA) was prepared by using 2,4-toluene diisocyanate (TDI), Epoxy resin (E51) and polyethylene glycol (PEG) as the main materials. Waterborne resin and UV curing film with content of C-O-C were obtained by using polyethylene glycols with different molecular weights. The infrared spectra (FT-IR) demonstrated the presence of C=C and epoxy bond in the UV curing film chains. In addition, the molecular weight of the oligomer, and glass transition temperature, gelation rate and thermogravimetric analysis of the films were investigated.

High dielectric constant UV curable polyurethane acrylate/indium tin oxide composites for capacitive sensing

Taking into consideration environmental issues and additive manufacturing technologies, the development of advanced UV curable polymers and polymer composites is an area of increasing interest. In this scope, polyurethane acrylate (PUA) composites with Indium Tin Oxide (ITO) were produced in order to tune morphology, optical, thermal, mechanical and dielectric properties. It is shown that ITO particles are well dispersed within the polymer matrix and that the polymerization rate and the UV curing conversion degree are influenced by the ITO content. Moreover, the optical transparency has decrease to 20% for the samples containing 10 wt% ITO content and the elastic modulus increases 10% for same sample. On the other hand, the glass transition temperature of PUA is independent of the ITO amount. ITO/PUA composites with 25 wt% ITO filler content presents high dielectric constant of 33. This composite has been used for developing a capacitive sensor, showing the suitability of the UV curable materials for capacitive sensing applications.

Synthesis of ultraviolet (UV)-curable water-borne polyurethane acrylate binders and comparison of their performance for pigment printing on synthetic leather

PurposeIn this study, it is aimed to synthesize ultraviolet (UV)-curable water-borne polyurethane acrylate (WPUA) binders using different types of polyols (poly (propylene glycol), PPG1000 and PPG2000 and poly (ethylene glycol), PEG1000 and PEG2000) at different molecular weights, DMPA (2,2-bis(hydroxymethyl) propionic acid) at different amounts and isophorone diisocyanate (IPDI) and use for pigment printing on synthetic leather.Design/methodology/approachUV-cured films were characterized by Fourier transform infrared spectroscopy (FTIR) and differential scanning calorimeter (DSC). The effect of binder structure on printing performance was determined with hardness, crock fastness, abrasion resistance and color measurements.FindingsThe highest abrasion resistance (60,000 cycles) and crock fastness values (dry crock and wet crock: 3/4) were obtained with binder PEG-C synthesized with PEG2000 and lower DMPA amount of 4.89 wt%; however, PEG-C binder showed lower hardness values. Due to lower urethane groups in PEG-C binder, more flexible films were obtained which imparted good adhesion property to printing film. Synthesized binders provided lower crock fastness and abrasion resistance properties than commercial WPUA binder.Originality/valuePigmented formulations including UV-curable water-borne synthesized PUA binder were developed and for the first time applied onto synthetic leather using screen printing method. Within this context, a new environmentally friendly printing method was proposed in this study including binder synthesis in the preparation of printing formulations.

Synthesis and characterization of one-component, moisture curing polyurethane adhesive based on Rokopol D2002

One-part, moisture curing polyurethane (PUR) adhesives based on poly(oxypropylene)diol Rokopol® and 4,4’-diphenylmethylene diisocyanate (MDI) modified with di-isononyl phthalate and a number of inorganic fillers and additives such as carbon black, thixotropic agent, dispersants and dibutyltin dilaurate as curing catalyst were developed. Adhesive curing was followed using dynamic oscillation rheometry and effect of some components on viscoelastic properties of curing materials was discussed. The cured materials were characterized by means of differential scanning calorimetry (DSC) and water contact angle measurements. The adhesive performance of obtained materials in bonding aluminum was evaluated by tensile shear bond strength tests.

Removal of Human Leukemic Cells from Peripheral Blood Mononuclear Cells by Cell Recognition Chromatography with Size Matched Particle Imprints.

We report a cell recognition chromatography approach for blood cancer cell separation from healthy peripheral blood mononuclear cells (PBMCs) based on size-matched functionalized particle imprints. Negative imprints were prepared from layers of 15 μm polymeric microbeads closely matching the size of cultured human leukemic cells (HL60). We replicated these imprints on a large scale with UV curable polyurethane resin using nanoimprinting lithography. The imprints were functionalized with branched polyethylene imine (bPEI) and passivated by Poloxamer 407 to promote a weak attraction toward cells. When a matching cell fits into an imprint cavity, its contact area with the imprint is maximized, which amplifies the attraction and the binding selectivity. We tested these imprints specificity for depleting myeloblasts from a mixture with healthy human PBMCs in a cell recognition chromatography setup hosting the imprint. The mixture of fixed HL60/PBMCs ratio was circulated over the imprint and at each step the selectivity toward HL60 was assessed by flow cytometry. The role of the imprint length, flow rate, channel depth, and the bPEI coating concentration were examined. The results show that HL60 cells, closely matching the imprint cavities, get trapped on the imprint, while the smaller PBMCs are carried away by the drag force of the flow. Lower flow rates, longer imprints, and interim channel depth favor HL60 specific retention. The bPEI concentration higher than 1 wt % on the imprint made it less selective toward the HL60 because of indiscriminate attraction with all cells. Particle imprint based cell recognition chromatography was able to achieve selective myeloblast depletion from initial 11.7% HL60 (88.3% PBMC) to less than 1.3% HL60 for 3 h of circulation. The cell recognition chromatography with size-matched microbead imprints can be employed as an efficient cell separation technique and potentially lead to alternative therapies for myeloblasts removal from peripheral blood of patients with acute myeloid leukemia.

Recyclable, remendable and healing polyurethane/acrylic coatings from UV curable waterborne dispersions containing Diels-Alder moieties

The aim of the present work is to increase the sustainability of UV curable waterborne polyurethane dispersions using the Diels-Alder chemistry. In this way, the obtaining of crosslinked polyurethane coatings presenting healing and recycling properties is proposed.Thus, waterborne polyurethanes were obtained by the acetone process replacing the chain extender by a diol containing the Diels Alder adduct and using acrylic chain ends that allowed the UV cross-linking. Photo-DSC results showed that the Diels Alder adduct did not prevent the UV cross-linking of the coating. In addition, FTIR, DSC and rheological experiments confirmed the occurrence of the DA and retro DA reaction (at 60 °C and 120 °C respectively) in the cross-linked polymer. Thanks to this reaction, the materials obtained by this methodology could be healed and reprocessed when increasing the temperature as shown by the maintenance of the mechanical properties and carbon dioxide permeability after repairing. These results can be of great interest towards the development of more sustainable waterborne polyurethane coatings.

Research on synthesis and properties of room temperature curing polyurethane damping materials

Room temperature curing polyurethane (PU) damping materials were synthesized with PU prepolymer and self-made curing agent. The prepolymer was synthesized from poly (neopentyl adipate) with higher side methyl content and toluene diisocyanate. Effects of molecular weight of poly (neopentyl adipate) and curing agent types on mechanical properties and damping properties of PU damping materials were investigated. Results showed that tensile strength of room temperature curing PU damping materials is 22.4MPa and the tan δmax reaches 1.10. The damping temperature range of tanδ>0.3 is more than 60°C, which is a kind of damping material with excellent comprehensive properties.

Enhancing the Flame Retardancy of UV Curable Polyurethane Acrylate Coated Films with Alumina Trihydrate Filling

In this study, the flame retardancy of ultra violet (UV) curable polyurethane acrylate (PU) coated films were enhanced. For this aim, alumina trihydrate (ATH) filling material was mixed with the pastes including a photoinitiator and a UV curable PU. ATH filling ratio was preciously adjusted to obtain a uniform coating. The coated films were cured with a UV curing system equipped with gallium (Ga) and mercury (Hg) lamps. The chemical changes and the curing degree of the UV cured films were examined by a Fourier Transform Infrared Spectrum (FTIR) and a pendulum hardness tester. The thermal properties of the UV cured films were evaluated using a Differential Scanning Calorimeter (DSC). Moreover, vertical flammability and limiting oxygen index (LOI) measurements were conducted in order to determine the burning behavior of the UV cured films. The successful curing of the films was evidenced by means of FTIR results. The addition of ATH slightly increased the hardness values of the films. DSC results showed that ATH addition not only increased the enthalpy values but also enhanced the flame retardant property of the coated films and maximum LOI was achieved as 31.5%.  

Waste Utilization: Insulation Panel from Recycled Polyurethane Particles and Wheat Husks.

This study provides a solution for the utilization of two waste materials, namely the residues of soft polyurethane foam from the production of mattresses and winter wheat husks. Thermal insulation panels with a nominal density of 50–150 kg/m3, bonded one-component moisture curing polyurethane adhesive, were developed, and the effect of the ratio between recycled polyurethane foam and winter wheat husk on internal bond strength, compressive stress at 10% strain, water uptake, coefficient of thermal conductivity, and volumetric heat capacity was observed. The developed composite materials make use of the very good thermal insulation properties of the two input waste materials, and the coefficient of thermal conductivity of the resulting boards achieves excellent values, namely 0.0418–0.0574 W/(m.K). The developed boards can be used as thermal insulation in the structures of environmentally friendly buildings.

Synthesis and characterization of lignin-polyurethane based wood adhesive

The present work aims to evaluate the influence of addition of kraft lignin in moisture curing polyurethane (PU) based wood adhesives. The mechanical, thermal properties and chemical structure of the adhesive were studied. The lignin-PU adhesives were obtained by replacing 1%, 3% and 5% of polypropylene glycol (PPG) by Kraft lignin and further reacted with monomeric diphenylmethanediisocyanate (MDI). The aliphatic hydroxyl level of lignin was not taken into consideration in the stoichiometry, in order to find out effect on % free NCO of the final product. The chemical structure of the synthesized lignin-PU adhesives were analyzed by Fourier transform infrared spectroscopy (FTIR). The lap shear strength of the adhesives was tested by bonding canarium wood substrates. The results illustrated that by increasing the weight % of lignin in such lignin-PU adhesives, a decrease in the free isocyanate content, leading to slower setting time but higher shear strength values, were observed. Similarly, the thermal properties of lignin-PU adhesive were also studied, showing an increase in glass transition temperature (Tg) with increase in lignin content.

Preparation and Properties of UV-Curable Polyurethane-acrylate Coatings Based on Polyhedral Oligomeric Silsesquioxanes (POSS)

In order to develop ultraviolet (UV)-curable coatings applicable to pre-coated metal (PCM), organic-inorganic hybrid UV curable polyurethane (PU)-acrylates were prepared using cage type metacryl-polyhedral oligomeric silsesquioxane (POSS) as a reactive diluent. To investigate the effect of POSS content on the physical properties of organic-inorganic hybrid polyurethane-acrylate coatings for PCM in this study, prepolymer was prepared by using H12MDI in PCL and HPBD, and oligomers capped at the end of 2-HEMA were synthesized. This study investigated the viscosities of the synthesized oligomers and prepared coatings; the thermal properties, mechanical properties, and transmittance of the UV-cured films; and the surface energy, adhesive property, pencil hardness, and MEK rubbing of the UV-curable films coated on the metal plate.