This review highlights both the various polymers grafted to alkyd resins reported in the literature and the different routes to synthesize these alkyd hybrids. Alkyd resins were discovered in the mid-1920s. Then, they quickly found a prominent place among coatings and paint binders thanks to their numerous advantages such as good heat resistance, excellent gloss, and low cost. Nevertheless, in the 50s, the emergence of new synthetic polymers with better properties (chemical resistance, mechanical and thermal properties) such as epoxy, acrylic or polyurethane, weakened the position of the alkyd resins among coating industry. Nowadays, due to global issues such as health and environmental concerns, research focuses on biobased polymers. Since, alkyd resins are mainly biobased, they have gained increasing attention in the last decade. Nevertheless, the issue of using volatile organic compounds (VOC) and the urge of replacing them, have led to the development of new synthetic routes. Moreover, in order to enhance alkyd properties and bridge the gap with new materials, other polymers such as epoxy, acrylates, polyurethanes or siloxanes were used to form alkyd hybrids. Hence, the different strategies to perform alkyd hybrids are detailed and discussed in this review. Furthermore, composites made with alkyd hybrid matrix are presented. Finally, the perspectives about the future developments of alkyd hybrids and the most promising hybrids are discussed.
This article focuses on the synthesis of polyhydroxyurethane (PHU) materials containing novel phosphorus flame retardants (FR). Four different phosphorus compounds were grafted onto cyclic carbonate: 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO), diethyl phosphite (DEP), diphenyl phosphite (DPP) and dibenzo[d,f][1,3,2]dioxaphosphepine 6-oxide (BPPO). Thus, three novel phosphorus reactive cyclic carbonates which have never been reported so far were synthetized. Phosphorus FR containing PHU materials were characterized by FTIR to evidence the total conversion of the cyclic carbonate. Moreover, the gel contents up to 80% confirmed the formation of the polymer network. Then, the thermal stability and the flame-retardant properties were investigated by thermogravimetric analyses, cone calorimeter and pyrolysis combustion flow calorimeter. The mode of action of phosphorus compounds, depending on the oxidation state, was especially highlighted. Phosphonate (+III) provided better action in a condensed phase than phosphinate thanks to a more efficient char formation. Among phosphonates, differences were observed in terms of char-formation rate and expansion. DEP provided the best flame-retardant properties, with a reduction of 76% of pHRR with 2 wt% of phosphorus in cone calorimeter analysis. Therefore, this article highlighted the different modes of action of phosphorus flame retardants, depending on the oxidation state of phosphorus, in PHU materials.
Novel phosphorylated cardanol molecules based on phosphonate (PO3CR) and phosphate (PO4CR) functions were synthetized. Those molecules have two main actions which are described in this article: the reduction in volatile organic compounds (VOC) and the development of flame retardant (FR) properties conferred on alkyd resins used as coatings for wood specimen. Phosphorylated cardanol compounds have been successfully grafted by covalent bonds to alkyd resins thanks to an auto-oxidative reaction. The impact of the introduction of PO3CR and PO4CR on the film properties such as drying time and flexibility has been studied and the thermal and flame retardant properties through differential scanning calorimeter, thermogravimetric analysis and pyrolysis-combustion flow calorimeter. These studies underscored an increase in the thermal stability and FR properties of the alkyd resins. In the cone calorimeter test, the lowest pHRR was obtained with 3 wt% P of phosphate-cardanol and exhibited a value of 170 KW.m−2, which represented a decrease of almost 46 % compared to the POxCR-free alkyd resins. Moreover, a difference in the mode of action between phosphonate and phosphate compounds has been highlighted. The most effective coating which combined excellent FR properties and good coating properties has been obtained with 2 wt% P of phosphate-cardanol. Indeed, the film properties were closed to the POxCR-free alkyd resin and the pHRR decreased by 41 % compared to the reference alkyd resin.
Over the past decade, with the emergence of environmental and human health concerns, research has focused on developing new solutions to replace fossil resources with more sustainable biobased resources. Furan derivatives can be obtained from plants and their structures provide high resistance to high temperatures. Therefore, these furan derivatives have been functionalized with phosphorus to increase their fire resistance properties. Thus, a new biobased bisfuran containing nitrogen and phosphorus (HMF-MXDA-DEP) was synthesized and used for the first time in polymerization to develop alkyd resins. The flame retardant properties of these resins have been studied. These alkyd resins are generally used as a binder in paint or varnish formulations. The use of a reactive flame retardant during the polycondensation reaction of alkyd resins makes it possible to form covalent bonds and offer better durability over time. The impact of HMF-MXDA-DEP on film properties such as drying time, flexibility, adhesion and color was studied and the thermal and flame retardant properties by differential scanning calorimeter, thermogravimetric analysis and calorimeter pyrolysis-combustion fluxes were evaluated. Increased thermal stability and good flame retardant (FR) properties of alkyd resins have been demonstrated. In the cone calorimeter test, the lowest peak in heat release rate (pHRR) was obtained with a 2 wt % coating of P HMF-MXDA-DEP on wood and a 49 % decrease in pHRR compared to FR-free alkyd resins has been demonstrated.
Cardanol, a waste from the food industry and widely produced (1 Mt/y), has been used as a chain stopper during the polycondensation of short oil alkyd resins in order to replace benzoic acid. Then, phosphorylated cardanol has been added in order to both reduce solvent content and bring flame-retardant (FR) properties to the alkyd resins. The renewable carbon content of the formulations has been increased up to 23%. The impact of the introduction of phosphorylated cardanol molecules on the drying time and flexibility has been studied as well as the thermal and flame-retardant properties by differential scanning calorimeter, thermogravimetric analysis and pyrolysis-combustion flow calorimeter. The most effective flame-retardant coating that was associated with excellent FR properties and excellent coating properties has been obtained with phosphate-cardanol added at 2%wt of P. Indeed, the film properties were closed to the classical alkyd resin, the solvent content was reduced by 50% and the pHRR decreased by 42% compared to the reference alkyd resin.
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