Tung based reactive diluents for alkyd systems: Film properties (2023)

The evolution towards an increasingly more sustainable development and a more circular economy requires the development of materials based on renewable feedstocks, to replace the still dominant non-renewable resources. Several imitation leather materials produced from renewable feedstocks have recently emerged to replace animal or synthetic leathers used in car interiors, with good performance results. However, few Life Cycle Assessment (LCA) studies are available for evaluating the potential environmental impacts of these new materials. Thus, the present study contributes to fill this gap, carrying out an anticipatory LCA (a-LCA) of a new bio-based material, a vegetable leather, intended for coatings in car interiors, produced from olive pomace, an abundant by-product of olive oil production in Portugal. For the life cycle inventory analysis, information from the literature and industrial practice was used, such as information from similar production processes, correlations, or simplistic approximations, in order to obtain an estimate of energy and materials consumption for the new vegetable leather production. Four environmental impact categories were evaluated: Global Warming Potential (GWP), Acidification Potential (AP), Eutrophication Potential (EP) and Photochemical Oxidation Potential (POP). Six scenarios were compared, defined considering the incorporation of different percentages of alkyd resin and polyurethane into the vegetable leather. The calculations were carried out using the openLCA software and considering a “cradle-to-gate” approach. The results show that the new vegetable leather presents significant environmental impacts, being the production of polyethylene terephthalate (PET) mesh fabric the greatest contributor, followed by energy consumption. A recycled PET mesh fabric was also analyzed. It is concluded that despite the bio-based components used, a high percentage of synthetic materials is still required, which leads to higher environmental impacts of the whole material.

Two cardanol (CO) derivatives, methacrylated cardanol (MACO) and triethoxysilane functionalized cardanol (TSCO) were investigated as the reactive diluents for a zinc phosphate pigmented alkyd coating. It was found that 5 wt% of MACO or TSCO can reduce the dosage of xylene by ∼ 3 wt% while maintaining the viscosity of the alkyd coating system. TSCO presented a negative influence on the drying time and the pull-off adhesion strength of the alkyd coating; however, the addition of 15 wt% MACO decreased the drying time from 12 h to 8 h and increased the pull-off adhesion strength from ∼ 1.73 to ∼ 2.10 MPa, comparing with the neat alkyd coating (without MACO and TSCO). As evidenced by the salt spray test, the addition of TSCO did not show an enhancement of corrosion resistance for the alkyd coating; however, the alkyd coating containing 15 wt% MACO (labelled as M-15) presented superior corrosion resistance to other coating systems. M-15 and the neat alkyd coating were further characterized by electrochemical impedance spectroscopy (EIS). The results of EIS further demonstrated that the corrosion resistance of M-15 is much better than the neat alkyd coating in the 3.5 wt% NaCl solution immersion. Importantly, M-15 can provide an excellent protection of the steel in the corrosive immersion condition for at least 123 days. The improvement of the overall performance was attributed to the homo-polymerization of the methacrylate moiety in MACO. Taken these results together, MACO is an efficient chemical for formulating high solid alkyd coatings with outstanding corrosion resistance.

With the increase in demand for bio-based coatings with lower volatile organic compound (VOC) emissions, methacrylated cardanol (MACO) and triethoxysilane-functionalized cardanol (TSCO) have been investigated as bio-based reactive diluents for formulating alkyd coatings as a substitute for volatile solvents. The viscosity of the representative alkyd resin was significantly reduced through the use of cardanol-based reactive diluents (over 84% diluent efficiency at 30 wt% loading). Both MACO and TSCO were able to participate in the cross-linked network of the alkyd coating as confirmed by the gel content and cross-link density of the cured coating films. Moreover, the cross-link density of the alkyd coating was significantly improved by using TSCO as the reactive diluent, leading to a significant enhancement in mechanical strength and solvent resistance of the alkyd coating. This work will facilitate the adoption of cardanol as a renewable building block in the coating industry in order to produce greener alkyd coatings.

In this work, the urushiol analogues (CAT-ME) carrying the functional groups of double bonds and phenolic hydroxyls were synthesized by Friedel-Crafts alkylation reaction of methyl eleostearate (the main component of tung oil) with catechol via ultraviolet photocatalysis. By comparison of catalytic results of different photoinitiators, it was found that cationic photoinitiators (triarylsulfonium salts) could be used to catalyze this alkylation reaction, which could not only dramatically boost the yield (71%) of the urushiol analogues, but also greatly shorten the reaction time (8 min) at a low UV light (100 W). And the chemical structures of the target compounds were also confirmed by Fourier transform infrared spectroscopy (FTIR), ultraviolet and visible spectroscopy (UV–vis), nuclear magnetic resonance spectroscopy (NMR) and liquid chromatography-mass spectroscopy (LC–MS). In addition, the photoactivity of the urushiol analogues was also discussed and the results showed that the UV-cured polyurethane films mixed with CAT-ME had excellent mechanical property and thermal stability, and the gel fraction of the film mixed with 15% CAT-ME reached 99.5%, and the tensile strength was up to 25.07 MPa while the breaking elongation increased by 4.57%. Thus, this approach of photocatalysis using cationic photoinitiators as catalysts showcases a promising method to direct other chemical reactions and provides a platform to guide the further modification of other unsaturated natural oil, expanding the application of vegetable oil.

With the rapid development of industry and the growing shortage of fossil energy, tung oil has attracted much attention of researchers because of its environment-friendly and renewable advantages. In this work, the curing mechanism of tung oil under UV irradiation is studied by the titration of the peroxide value, Fourier transform infrared spectroscopy and nuclear magnetic resonance spectroscopy. In addition, the effects of different photoinitiators on the UV curing behavior of tung oil are investigated through monitoring the gel fraction of the cured films. Finally, the morphology and the solvent resistance of the films cured with different condition are estimated by scanning electron microscope and solvent resistance testing. The results display that UV curing of tung oil is composed of oxidative polymerization and free radical polymerization. Among the different photoinitiators, the triarylsulfonium salts at amount of 5wt% is one of the most efficient ones for the UV curing of tung oil. A novel UV curable system containing tung oil is constructed to supply a reference to expand the application of drying oils.

As a response to environmental problems caused by plasticisers, the feasibility of replacing a significant proportion of the plasticisers in a synthetic ethylene-propylene-diene monomer copolymer (EPDM) matrix with bio-based materials was studied. In that context, different bio-based commercials plasticisers such as Radia® supplied by Oleon, methyl ester of soybean oil, epoxidized methyl ester of soybean oil, methyl oleate, methyl linoleate and untreated vegetable oils (rapeseed, soybean, linseed and tung) were tested. Diffusion analysis using the bi-layers rheology method and exudation analysis highlighted an important exudation phenomenon at 80°C for all oils tested. To overcome this problem, a second part of this work was focused on the use of a specific highly reactive vegetable tung oil. The in situ polymerisation of this oil by thermal activation without the use of catalysts allowed to totally prevent the exudation phenomenon by increasing the viscosity of the oil. Compared with the use of pure tung oil, the degree of exudation was greatly decreased, from more than 8% to less than 1%.

Progress in Organic Coatings, Volume 95, 2016, pp. 46-53

The effect of the addition of two anticorrosive phosphate pigments, standard zinc phosphate and modified zinc phosphate (zinc molybdenum phosphate modified with a surface treatment) on the corrosion protection of an alkyd coating on steel, has been investigated by means of a traditional accelerated test (salt fog spray test) and an electrochemical technique (accelerated cyclic electrochemical technique). Solvent-based alkyd coatings based on phenolic modified resins were formulated with different anticorrosive pigment concentrations (3%, 4.5% and 6%, expressed as anticorrosive pigment volume concentration in dry film volume, PVC) and finally characterised. An improvement in the anticorrosive properties is obtained with the addition of both pigments, the coatings formulated with modified zinc phosphate having better performance. Both techniques showed results that can be correlated.

Progress in Organic Coatings, Volume 77, Issue 2, 2014, pp. 388-394

A cardanol-based UV-curable vinyl ester (VE) monomer was prepared via simple esterification, and its successful synthesis was demonstrated by FTIR and ¹H-NMR. In order to improve its rigidity, it was mixed with certain proportions of another reactive bio-based VE monomer, maleic anhydride modified dimer fatty acids polymerized glycidyl methacrylate (MA-m-DA-p-GMA) which had rigid and strong polar groups, and then a series of UV-cured copolymers were prepared from the two VE monomers. The UV curing process was monitored by FTIR analysis. The tensile and thermal properties of the cured copolymer films were also investigated. UV curing analysis demonstrated that the double bonds in the mixed VE could be converted to ultimate curing level within 40s. Tensile tests showed the prepared copolymers had a tensile strength of 8.86MPa. Dynamic mechanical analysis (DMA) revealed the copolymers had relatively high glass transition temperature (T_g) from 40 to 60°C. Thermogravimetric analysis (TGA) showed the copolymers containing higher content of CDMA had higher thermal stability, and all copolymers’ main thermal initial decomposition temperatures were above 410°C, indicating the copolymers had certain thermal stability. These copolymer films can be used as eco-friendly materials in coatings and other applications to replace the currently used petroleum-based polymers.

Progress in Organic Coatings, Volume 86, 2015, pp. 59-70

A one pot synthesis of alkyd resins based on the Camelina sativa oil as a new renewable raw material and on polyglycerols as polyols was carried out. The oligomerization of glycerol was conducted in the presence of LiOH (0.1wt%) at 245°C. The total content of diglycerol reached its maximum (about 33.5wt%) after 7h. The oligomerization product with no additional treatment was subjected to the alcoholysis reaction with purified camelina oil. The alkyd resin was obtained after polycondensation of the alcoholysis products with phthalic and maleic anhydrides at 230–250°C. A real possibility was determined for the synthesis of alkyd resins with some properties similar to those which can be found in equivalent products manufactured on the basis of semi drying oil and pentaerythritol like flexibility and drying time.

Progress in Organic Coatings, Volume 122, 2018, pp. 189-198

In near future, bio-based polymer coatings are expected to gradually replace the fossil oil based coating materials. However, extensive application of bio-based polymer is still a challenge because of its several limitations. The use of organic-inorganic hybrid cross linker is one of the interesting strategies used for the processing of highly crosslinked polymer coatings with improved mechanical and anticorrosive performance. Thus present work reports the preparation of organic-inorganic hybrid (OIH) cross linker using melamine formaldehyde (MF) and 3 isocynatopropyl triethoxy silane (IPTES). The structural characterization was carried out using various spectroscopic techniques, which provide ample evidence in favor of MF/IPTES cured alkyd formation. The impact of OIH cross linker on various properties like physico-mechanical, adhesion, thermal stability and anticorrosive properties was investigated systematically. The enhancement in aforementioned properties could be explained in terms of synergistic effect of s-triazine ring of melamine formaldehyde and IPTES.

Progress in Organic Coatings, Volume 77, Issue 11, 2014, pp. 1715-1723

In this work, a modified alkyd resin (basic alkyd resin) was synthesized using maleic anhydride (MAH) to replace part of phthalic anhydride (PA) to achieve the target product acrylate-grafted-alkyd hybrid resin. The resin was then dispersed in water to form water-reducible emulsion. The properties were examined, including the extent of neutralization of final emulsion, ratio of MAH/PA in basic alkyd resin, mole ratio of basic alkyd resin to modified vinyl monomers, mole ratio of vinyl monomers (MMA/St/AA) on water dispersion stability of emulsion, particle size, drying time and mechanical properties. The optimal synthesis conditions produced a final emulsion particle size of 81.1nm with good storage stability, hydrolytic stability and shorter drying time. The optimized synthesis conditions were identified as 80% neutralization, 1:0.8 mole ratio of basic alkyd resin to modified monomers, 4:3:2 modified monomers MMA/St/AA and 0.18 mole ratio of MAH/PA.

Applied Surface Science, Volume 481, 2019, pp. 960-971

The ecofriendly waterborne alkyd coatings generally compromise the coating performance. Incorporation of polyaniline into alkyd to form nanocomposites can improve the corrosion resistance; however, the uniform distribution of polyaniline (PANI) within the alkyd resin remains a challenge. In this work, PANI is grafted onto epoxy functionalized phosphorylated poly (vinyl alcohol) (PPVA) with different side-chain configurations in order to improve compatibility and dispersion stability. These functionalized PPVA are synthesized using epichlorohydrin (ECIP) or γ-glycidyl methacrylate (GMA) as modifying agents, and respectively labeled as E-PPVA and G-PPVA. G-PPVA/PANI dispersion is stable even at a high PANI loading of 50%, while the maximum PANI loading for E-PPVA/PANI is only 30%. With the incorporation of G-PPVA/PANI into waterborne alkyd resins (AR), the coating resistance is increased by 7 orders of magnitude, and the corrosion inhibition efficiency is up to 99.9%. The coating with the incorporation of G-PPVA/PANI also demonstrates superior long-term corrosion resistance in comparison with that AR/E-PPVA/PANI nanocomposite coating.