Comparison of thermoset soy protein resin toughening by natural rubber and epoxidized natural rubber

Abstract

Fully bio-based soy protein isolate (SPI) resins were toughened using natural rubber (NR) and epoxidized natural rubber (ENR). Resin compositions containing up to 30 wt % NR or ENR were prepared and characterized for their physical, chemical and mechanical properties. Crosslinking between SPI and ENR was confirmed using 1 H-NMR and ATR-FTIR. All SPI/NR resins exhibited two distinctive drops in their modulus at glass transition temperature (T g ) and degradation temperature (T d ) at around 250 and 215 8C, corresponding to major segmental motions of NR and SPI, respectively. SPI/ENR resins showed similar T g and T d transitions at slightly higher temperatures. For SPI/ENR specimens the increase in ENR content from 0 to 30 wt % showed major increase in T g from 223 to 13 8C as a result of crosslinking between SPI and ENR. The increase in ENR content from 0 to 30 wt % increased the fracture toughness from 0.13 to 1.02 MPa with minimum loss of tensile properties. The results indicated that ENR was not only more effective in toughening SPI than NR but the tensile properties of SPI/ENR were also significantly higher than the corresponding compositions of SPI/NR. SPI/ENR green resin with higher toughness could be used as fully biodegradable thermoset resin in many applications including green composites.

RETRACTED: Epoxy Resins Toughened with Surface Modified Epoxidized Natural Rubber Fibers by One-Step Electrospinning

“…E-ERF 5 and E-ERF 10 show about 1.2 GPa and 1.1 GPa of modulus, and 52 MPa and 47 MPa of fracture strength, respectively, compared to that of neat epoxy resin having modulus of 1.4 GPa and tensile strength of 58 MPa. Compared to other studies, epoxy resin containing ENR particles (not in fiber form) showed much loss in tensile properties [24,51,52]. For example, epoxy resin with 12% liquid epoxidized natural rubber (particle size 0.48 to 0.67 in diameter) increased 125% impact toughness, but decreased tensile properties by 15 MPa from 65 MPa to 50 MPa, compared to neat epoxy resin [51].…”

“…The broad peak around 1600 cm −1 corresponds to NH 2 bending of excess amine group from the curing agent in the epoxy resin. Neat ERFs transmittance peaks at 751 cm −1 , 852 cm −1 and 1246 cm −1 corresponding to the oxirane groups appeared in the spectra [ 24 ].…”

“…Again, this trend is due to esterification reaction occurring at the interface between the hydroxyl groups of glycerol and the carboxylic groups of PLA [ 22 ]. Eco-friendly natural toughening agents such as epoxidized natural rubber (ENR) and liquid natural rubber have been found to be effective in improving the toughness in brittle resins because of functional groups such as oxirane groups or hydroxyl groups [ 23 , 24 , 25 ]. One explanation is that the oxirane groups of ENR are able to react with carboxyl, amine, glycidyl and hydroxyl groups of matrices, crosslinking with ENR to offer good interfacial bonding in the matrix [ 26 ].…”

Toughening of thermoset green zein resin: A comparison between natural rubber‐based additives and plasticizers

“…Zein protein has been recently used as a sustainable natural material in a wide variety of applications including resins for green composites, bioplastics, air filtration (in fiber form), food packaging (in film form), tissue engineering, and adhesive, due to its fully renewable and biodegradable nature and low cost. 1,2 However, in its pure form it suffers from brittleness and low resistance to crack propagation. In particular, crosslinked thermoset zein resins have been shown to possess poor toughness and resistance to crack propagation.…”

“…as natural rubber (NR) in the polymer resin has been a promising method. 1 Plant derived NR is also a biodegradable and fully sustainable material which possesses moderate tensile strength but good tear resistance, toughness and high resilience. 6 Due to its very low glass transition temperature (T g ) of about -65 °C and flexible backbone structure, NR is highly extensible at room temperature (RT) and makes it a desirable candidate for toughening purposes.…”