Development of toughened bio‐based epoxy with epoxidized linseed oil as reactive diluent and cured with bio‐renewable crosslinker

Abstract

In the current work, renewable resourced toughened epoxy blend has been developed using epoxidized linseed oil (ELO) and bio-based crosslinker. Epoxidation of linseed oil was confirmed through FTIR and 1 H NMR spectra. The ELO bio-resin was blended at different compositions (10, 20, and 30 phr) with a petroleum-based epoxy (DGEBA) as reactive diluent to reduce the viscosity for better processibility and cured with cardanol-derived phenalkamine to overcome the brittleness. The flow behavior of the neat epoxy and modified bio-epoxy resin blend systems was analyzed by Cross model at low and high shear rates. The tensile and impact behavior studies revealed that the toughened bio-epoxy blend with 20 to 30 phr of ELO showed moderate stiffness with much higher elongation at break 7% to 13%. Incorporation of higher amount of ELO (20 to 30 phr) increases enthalpy of curing without affecting peak temperature of curing. The thermal degradation behavior of the ELO based blends exhibits similar trend as neat epoxy.The higher intensity or broadened loss tangent curve of bio-epoxy blends revealed higher damping ability. FE-SEM analysis showed a rough and rippled surface of bio-based epoxy blends ensuring effective toughening. Reduced viscosity of resin due to maximum possible incorporation of bio-resin and use of phenalkamine as curing agent leads to an eco-friendly toughened epoxy and can be useful for specific coating and structural application. KEYWORDSbio-based epoxy, epoxidized oil, phenalkamine, thermomechanical properties, toughening Functionalized vegetable oils have been reported as renewable resourced toughening diluents for epoxy to overcome its inherent brittleness. [5][6][7][8][9][10][11][12][13][14][15][16] Particularly, epoxidized oils having multiple epoxy groups are more preferable to be used as reactive diluents being eco-friendly and ease synthesis process. Soybean oil due to ease of availability, higher number of reacting sites (4.6 double bonds per triglyceride chain), and low cost has attracted attention of researchers in employing it to enhance toughness of petro-based epoxies in the last decade. However, the tensile and thermal properties of epoxy drastically reduce with increase in ESO content because of its lower reactivity, low oxirane content, and inferior crosslink density. 5-10Further, the wide use of soybean oil in thermoset and thermoplastic has been reported on ELO-based bio-epoxy blends using bio-renewable PKA as curing agent.In the current work, ELO was synthesized through in-situ method, and bio-epoxy blends were prepared with varying ELO content as reactive diluent. The diluent content can be optimized based on rheological, mechanical, and thermo-mechanical specification needed for specific structural application. | Synthesis of epoxidized linseed oilLinseed was epoxidized through in-situ method in the presence of glacial acetic acid and hydrogen peroxide as reported earlier by Kim et al 6 and Sahoo et al. 13 Epoxidation of oil was performed in a 3-necked flask equipped with a magnetic st...

Influence of epoxidized linseed oil and sisal fibers on structure–property relationship of epoxy biocomposite

“…A similar morphology was observed earlier in 20 phr of ESO and epoxidized hemp oil (EHO)‐based epoxy composites with no interfacial gap . In our earlier work, it has been shown that ELO addition reduces the viscosity of epoxy resin and also toughens the epoxy matrix by incorporating the ductility within matrix . It is evident that the fibers are well adhered to the matrix and breakage occurs in fiber only with no cracks in matrix.…”

“…A similar improvement in modulus was found in glassy region for 20% ESO and 20% epoxy methyl soyate modified SF‐reinforced epoxy composite reported earlier by Sahoo et al . However, beyond the respective glass transition that is, in rubbery region, the modulus of EPSF composite is higher than all the ELO‐modified composite system because of higher crosslink density of the epoxy matrix and presence of higher amount of rigid aromatic groups. It is notable that in case of 30 phr of ELO‐modified composite system, modulus is lower than EPSF composite both before and after glass transition because of lower crosslink density and undesirable plasticization caused by surplus of bio‐resin.…”

“…In the current investigation, maximum tensile strength of 84.83 MPa and modulus of 2.3 GPa was observed for EPELO20SF. In our previous work, it was reported that 20 phr ELO adequately reduces the viscosity of the epoxy resin from 11.43 to 4.37 Pa.s . This enables the fibers to get nicely impregnated resulting in their improved packing and stronger matrix‐fiber interface resulting in improvement of the roughness and the rigidity of bio‐resin‐based epoxy composite by them .…”

Development of completely bio‐based epoxy networks derived from epoxidized linseed and castor oil cured with citric acid

“…Most importantly, ELO exhibits a linear shear stress versus shear rate relation. The curve reveals that epoxy resin displays complete shear thinning or pseudoplastic (non‐Newtonian) behavior, whereas ELO displays completely Newtonian behavior and ECO shows moderate pseudoplastic nature or nearly Newtonian behavior, over entire shear rate . This is primarily due to the difference in their backbone structures, branching, and degree of entanglement.…”

“…Its high degree of unsaturation (6.6 double bonds per triglyceride) receives greater importance as a biorenewable raw material to form prepolymers or even polymers. Consequently, there has been a growing interest by researchers from academia as well as industry for adhesive, coating, and composite applications to use epoxidized LO (ELO), acrylated ELO, and epoxidized methyl esters of LO . Similarly, castor oil (CO) is a natural polyol consisting of unsaturated fatty acid, hydroxyl functionalities, usually ricinoleic acid (12‐hydroxy‐9‐ cis ‐octadecenoic acid), which almost covers 90% of the fatty acid content .…”