Synthesis and characterization of cardanol based aqueous 2K polyurethane coatings

Silane Effects on Adhesion Enhancement of 2K Polyurethane Adhesives

With excellent properties such as great flexibility, outstanding chemical resistance, and superb mechanical strength, two-part polyurethane (2K PU) adhesives have been widely applied in many applications, including those in transportation and construction. Despite the extensive use, their adhesion to nonpolar polymer substrates still needs to be improved and has been widely studied. The incorporation of silane molecules and the use of plasma treatment on substrate surfaces are two popular methods to increase the adhesion of 2K PU adhesives, but their detailed adhesion enhancement mechanisms are still largely unknown. In this research, sum frequency generation (SFG) vibrational spectroscopy was used to probe the influence of added or coated silanes on the interfacial structure at the buried polypropylene (PP)/2K PU adhesive interface in situ. How plasma treatment on PP could improve adhesion was also investigated. To achieve maximum adhesion, two methods to involve silanes were studied. In the first method, silanes were directly mixed with the 2K PU adhesive before use. In the second method, silane molecules were spin-coated onto the PP substrate before the PU adhesive applied. It was found that the first method could not improve the 2K PU adhesion to PP, while the second method could substantially enhance such adhesion. SFG studies demonstrated that with the second method silane molecules chemically reacted at the interface to connect PP and 2K PU adhesive to improve the adhesion. With the first method, silane molecules could not effectively diffuse to the interface to enhance adhesion. In this research, plasma treatment was also found to be a useful method to improve the adhesion of the 2K PU adhesive to nonpolar polymer materials.

Molecular Behavior of 1K Polyurethane Adhesive at Buried Interfaces: Plasma Treatment, Annealing, and Adhesion

One-part (1K) polyurethane (PU) adhesive has excellent bulk strength and environmental resistance. It is therefore widely used in many fields, such as construction, transportation, and flexible lamination. However, when contacting non-polar polymer materials, the poor adhesion of 1K PU adhesive may not be able to support its outdoor applications. To solve this problem, plasma treatment of the non-polar polymer surface has been utilized to improve adhesion between the polymer and 1K PU adhesive. The detailed mechanisms of adhesion enhancement of the 1K PU adhesive caused by plasma treatment on polymer substrates have not been studied extensively because adhesion is a property of buried interfaces which are difficult to probe. In this study, sum frequency generation (SFG) vibrational spectroscopy was used to investigate the buried PU/polypropylene (PP) interfaces in situ nondestructively. Fourier-transform infrared spectroscopy, the X-ray diffraction technique, and adhesion tests were used as supplemental methods to SFG in the study. The 1K PU adhesive is a moisture-curing adhesive and usually needs several days to be fully cured. Here, time-dependent SFG experiments were conducted to monitor the molecular behaviors at the buried 1K PU adhesive/PP interfaces during the curing process. It was found that the PU adhesives underwent rearrangement during the curing process with functional groups gradually becoming ordered at the interface. Stronger adhesion between the plasma-treated PP substrate and the 1K PU adhesive was observed, which was achieved by the interfacial chemical reactions and a more rigid interface. Annealing the samples increased the reaction speed and enhanced the bulk PU strength with higher crystallinity. In this research, molecular mechanisms of adhesion enhancement of the 1K PU adhesive caused by the plasma treatment on PP and by annealing the PU/PP samples were elucidated.

Bio-Based 2K PU Coating for Durable Textile Applications

Polyurethane (PU) coatings are often applied on high added value technical textiles. To date, most PU textile coatings are solvent based or water based. Recent advances are made in applying high solid and two-component (2K) PU on textiles. Currently, polymers made from renewable raw materials are experiencing a renaissance, owing to the trend to reduce CO2 emissions and switch to CO2-neutral renewable products. There is also the tendency towards the “bio, eco, natural” consciousness-awakening of the end consumer and the market-driven question to implement renewable materials. However, the application of bio-based coatings on textiles is limited. In this regard, the present study is conducted to develop bio-based 2K PU coating specifically designed for waterproof textiles. A 2K PU coating formulation, composed of bio-based polyol and bio-based isocyanate Desmodur Eco N7300, was made and directly applied on a polyester fabric prior to thermal curing in an oven. The coating was characterized via Fourier-transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The coatings were not thermoplastic and had a glass transition temperature of approximately 50 °C. Since a bio-based pentamethylene diisocyanate trimer (PDI-trimer), Desmodur Eco N7300 was used as an isocyanate source and not a diisocyanate derivative, and the resulting bio-based 2K coating was a thermoset instead of a thermoplastic. The effect of the additives and content of isocyanate on the elongation and stress at break was studied by performing tensile tests (ISO 13934-1) on 50 µm 2K PU films and comparing the obtained values. The performance of the coating was studied by evaluating the resistance to hydrostatic pressure initially and after washing, the Q-panel Laboratory UltraViolet (QUV) aging and the hydrolysis test. The developed bio-based 2K PU coating had excellent hydrostatic pressure, QUV aging resistance, hydrolysis resistance and wash fastness at 60 °C.

Nonedible Vegetable Oil-Based Polyols in Anticorrosive and Antimicrobial Polyurethane Coatings

This review describes the preparation of nonedible vegetable oil (NEVO)-based polyols and their application in anticorrosive and antimicrobial polyurethane (PU) coatings. PUs are a class of versatile polymers made up of polyols and isocyanates. Renewable vegetable oils are promising resources for the development of ecofriendly polyols and the corresponding PUs. Researchers are interested in NEVOs because they provide an alternative to critical global food issues. The cultivation of plant resources for NEVOs can also be popularized globally by utilizing marginal land or wastelands. Polyols can be prepared from NEVOs following different conversion routes, including esterification, etherification, amidation, ozonolysis, hydrogenation, hydroformylation, thio-ene, acrylation, and epoxidation. These polyols can be incorporated into the PU network for coating applications. Metal surface corrosion and microbial growth are severe problems that cause enormous economic losses annually. These problems can be overcome by NEVO-based PU coatings, incorporating functional ingredients such as corrosion inhibitors and antimicrobial agents. The preferred coatings have great potential in high performance, smart, and functional applications, including in biomedical fields, to cope with emerging threats such as COVID-19.

Thermal and anticorrosion properties of polyurethane coatings derived from recycled polyethylene terephthalate and palm olein-based polyols

Polyols of palm olein/polyethylene terephthalate (PET) were synthesized by means of incorporating recycled PET from waste drinking bottles in different proportions into palm olein alkyd in the presence of ethylene glycol. The polyols were characterized by FTIR, and theirs hydroxyl value (OHV), acid value (AV) and viscosity were determined. The formulation of the polyurethane coating was carried out by dissolving the polyol in mixed solvent of cyclohexanone/tetrahydrofuran (THF) (4 : 1) followed by reacting 1 hydroxyl equivalent of the polyol with 1.2 equivalents of methylene diphenyldiisocyanate and 0.05% dibutyltin dilaurate (DBTDL) catalyst. The coating cured through the cross-linking reactions between hydroxyl and isocyanate groups. The formation of urethane linkages was established by FTIR spectroscopy. The set films were characterized by thermal analysis. To study their anticorrosion properties, polarization measurements and EIS in 3.5% NaCl solution were determined. The coatings displayed good thermal stability and anticorrosion properties which were supported by XRD analysis. The PU7 coating, with the highest proportion of PET (up to 15% w/w), displayed significantly improved thermal stability and anticorrosion properties. It is evident that the performance of the polyurethane (PU) coatings could be enhanced by the incorporation of PET.

Cardanol based benzoxazine blends and bio-silica reinforced composites: thermal and dielectric properties

In the present work, a novel cardanol based benzoxazine was synthesised by reacting three different amines (aniline (CrAb), N,N-dimethylaminopropylamine (CrDb) and caprolactam modified N,N-dimethylaminopropylamine (CrCb)) with cardanol in the presence of formaldehyde under appropriate experimental conditions.

Design and synthesis of bio-based UV curable PU acrylate resin from itaconic acid for coating applications

UV curable PUA resin was successfully synthesized from polyol based on sustainable resource originated from itaconic acid (IA), isophorone diisocyanate (IPDI) and 2-hydroxyethyl methacrylate (HEMA). A polyol was synthesized by condensation reaction of IA with 16-hexanediol in the presence of p-Toluenesulfonic acid (pTSA). The synthesized PUA resin was characterized for its structural elucidation by using Fourier Transform Infrared Spectrophotometer (FTIR), ¹H and ¹³C NMR spectroscopy. The synthesized UV curable PUA resin was incorporated in varying concentrations in conventional PUA coating system. The effects of varying concentration of synthesized UV curable PUA resin on rheology, crystallinity, thermal and coating properties were evaluated. The rheological behavior of the resins were evaluated at variable stress and result showed decrease in viscosity of resin as concentration of synthesized UV curable PUA resin increases in conventional PUA resin. The cured coatings have been evaluated for glass transition temperature (T_g) and thermal behavior by differential scanning calorimeter and thermogravimetric analysis respectively. The degree of crystallinity of the coatings was determined from X-ray diffraction patterns using the PFM program. It was found that increase in the mass proportion of IA based PUA in coatings, the coating becomes more rigid and crystalline. The synthesized UV curable PUA coatings showed interesting mechanical, chemical, solvent and thermal properties as compared to the conventional PUA. Further, cured coatings were also evaluated for gel content and water absorption.