Soy protein plastics reinforced and toughened by SiO₂ nanoparticles

Abstract

The nano-SiO 2 particles were compounded into soy protein isolated (SPI) matrix to produce a series of reinforcing nanocomposite sheets by compression-molding. Except for the expected increase of strength and modulus, the elongation was also enhanced when the nano-SiO 2 content was lower than 8 wt %. Moreover, two nanocomposite materials were recommended: the one is a nanocomposite containing 4 wt % nano-SiO 2 with the highest strength and enhanced elongation, the other is a reinforced material with the best elongation filled by 8 wt % nano-SiO 2 . The increase of nano-SiO 2 content produced many kinds of distributions in SPI matrix, such as single nanosphere, $ 100 nm nanocluster, interconnected network structure and great domain. Such structures strongly affected the mechanical performances of nanocomposite materials. The simultaneous enhancement of strength and elongation was related to homogeneous dispersion of nanoclusters while aggregated great domains severely decreased elongation in spite of obvious reinforcing effect. However, the reinforced materials with high loading of inorganic filler should be paid attention and have economic value to some extent in practical application. With the changes of nano-SiO 2 distribution, the structures of SPI matrix changed as well. After adding a mall amount of nano-SiO 2 , the damage of glycerol plasticization to ordered structure of SPI was reduced. But as nano-SiO 2 content increased, the SPI microphase was separated from nano-SiO 2 domains. Furthermore, the condition of simultaneous reinforcing and toughening was put forward: the moderate aggregation of nano-SiO 2 as well as all kinds of strong interfacial interactions.

Effects of layered silicate structure on the mechanical properties and structures of protein‐based bionanocomposites

“…The resultant viscous solution (dark-gray for the REC/PPI blends and light-yellow for the MMT/PPI blends) was freeze-dried for 48 h to obtain the nanocomposites (gray REC/PPI powder or yellow MMT/PPI powder), which preserved the original complex state in solution. According to the REC content in solid powders of 2,4,8,12,16,20, and 24 wt %, the gray nanocomposite powders were coded as RP-2-P, RP-4-P, RP-8-P, RP-12-P, RP-16-P, RP-20-P, and RP-24-P, respectively. Meanwhile, the yellow nanocomposite powders containing 2,4,8,12,16,20, and 24 wt % MMT were coded as MP-2-P, MP-4-P, MP-8-P, MP-12-P, MP-16-P, MP-20-P, and MP-24-P, respectively.…”

“…5 The exfoliated lamella of layered silicates strongly adhered onto the soy protein matrix by electrostatic affiliating as well as hydrogen bonding to produce reinforced materials. 6,7 The nano-clusters of aggregated spherical SiO 2 nanoparticles 8 and flexible carbon nanotubes 9 played a role on reinforcing and toughening soy protein plastics simultaneously. Meanwhile, the biodegradable polysaccharide nanoparticles, such as rod-like cellulose 10 and chitin 11 whiskers, and platelet-like starch nanocrystal, 12 were used to reinforce soy protein as well as enhancing water resistance.…”

Properties of soy protein isolate/nano‐silica films and their applications in the preservation of Flammulina velutipes

“…This could be attributed to chain cross‐linking, which established hydrogen bonds and coordination bonds between the nano‐SiO 2 and SPI. Thus, more compact film structures were formed when the nano‐SiO 2 addition increased so that the diffusion of the water vapor and oxygen were disturbed (Ai, Zheng, Wei, & Huang, ; Bai, Xu, Liao, & Liu, ). Tunç, Duman, and Polat () came to similar conclusions, namely, that the montmorillonite nanocomposite could decrease the WVP in methyl cellulose films.…”

Progress in Bionanocomposite Materials

“…Recently, it has been explored the use of rectorite, a clay mineral consisting of regular interstratification of montmorillonite-type and mica-type layers, as filler, being also observed that the bionanocomposite with a 12 wt% clay loading shows the highest strength [68]. The use of rigid nanoparticles of SiO 2 produces a kind of reinforced and toughened bionanocomposite however the amount of nanofiller must be controlled as separation of SPI microphases and SiO 2 domains has been observed [70]. More interesting seems to be the use of MWCNTs that with just a 0.25 wt% content results in reinforced and thoughened SPI bionanocomposites provided also of higher water resistance.…”

“…Soybean protein isolate (SPI) extracted from soybean contains more than 90% of proteins (mainly glycinin and β-conglycinin) and attracts increasing interest because it can be thermoplastically processed by using plasticizer small molecules, such as glycerol. The incorporation of different type of fillers, including polyphosphates [64], different type of clays [65][66][67][68], talc powders and zeolites [65], carbon nanotubes [69] or SiO 2 nanoparticles [70] have been tested to improve its film properties. The use of clays introduces improvement of the tensile strength decreasing water vapor permeability and water solubility but also elongation at break in the biocomposites [65].…”