The synergistic effects of lignin and cellulose nanofibers on the properties of starch/zein blends

Abstract

The study aimed to develop cornmeal-based thermoplastic composites by using corn starch and zein (the two major components of cornmeal) as the matrix and lignin as the compatibilizer, while cellulose nanofibrils (CNFs) served as the reinforcement. The research examined the individual effects of lignin and CNFs on the mechanical properties of the composites. Two parts of lignin decreased the domain size of the blend and increased the strength and modulus by 31% and 44%, respectively. Six parts of CNFs led to a 137% and 399% increase in strength and modulus, respectively. The addition of two parts of powder lignin and six parts of CNFs resulted in the largest increases in strength (236%) and modulus (510%), suggesting a strong synergy between lignin and CNFs in reinforcing the corn-based thermoplastic. This study differentiates itself from previous research on thermoplastic starch composites by using a starch/zein blend as the matrix instead of pure starch. It demonstrates a novel method for producing cornmeal-based thermoplastics with significantly enhanced mechanical properties by separately controlling the contents of lignin and CNFs and optimizing the formulations to achieve desired composite properties. Furthermore, the research revealed the strong compatibilizing effect of lignin on the starch/zein blend. The results obtained in this research could facilitate the direct use of low-cost cornmeal as a feedstock for producing sustainable materials which could find application in the packaging and household plastic industries, among others.

Thermoplastic starch nanocomposites derived directly from cornmeal

“…As discussed in our previous study, the increases can be attributed to the synergetic reinforcement effect of the lignin and CNFs. 1 Lignin nanoparticles in the starch-zein blend have been shown to refine the phase structure of the blend and increase the compatibility of the two phases, leading to improved mechanical properties. CNFs as a nanofibrous material are known to significantly reinforce biopolymers at low fiber concentrations.…”

“…In our previous study, we increased the mechanical properties of TPS by incorporating zein, lignin, and cellulose nanofibers (CNFs) into the bioplastic through extrusion. 1 We showed that lignin improved the dispersion of zein and reduced its particle size in the TPS matrix by functioning as a compatibilizer, leading to increased strength and modulus of the composites. The addition of CNFs, an effective reinforcement for natural polymers, also significantly improved the composite properties.…”

“…In our previous study, 50 wt% of water and 50 wt% of glycerol (out of the starch/zein mixture weight) were added to the formulations as plasticizers to allow stable extrusion. 1 In this study, only ∼0.5 wt% of CA was used to replace all the added water and part of the glycerol to achieve similar processability. This was made possible because CA-induced acid hydrolysis of starch reduced its molecular weight and therefore lowered the viscosity of TPS during extrusion.…”

“…In this study, SZ-LP6-CNF6 shows the highest strength and modulus (19.7 and 237.1 MPa, respectively) among all the formulations, which are much higher than those of GP-2-CNF6 (14.8 and 83.7 MPa, respectively), the highest properties obtained from our previous study. 1 This early formulation contains two parts of lignin powder and six parts of CNFs as well as water and glycerol as the plasticizers. These comparisons demonstrate the advantages of using CA in producing TPS composites because of the chemical's reactivity.…”

“…4 In our prior study, mixtures of pure starch and zein were used to simulate the main composition of corn. 1 These two materials are extracted from corn kernels and the extraction processes increase the material costs. Especially, zein is an expensive biopolymer and costs dozens of US dollars per kilogram even at the wholesale scale due to its complex separation and purification processes.…”