Use of lignin strengthened with modified wheat gluten in biodegradable composites

Abstract

In this study, composites from alkali lignin and wheat gluten, modified with different percentages of sodium silicate, were prepared and characterized. Moreover, the addition of silica to the aforementioned composites was studied with the aim of improving the thermal and mechanical properties. The effect of wheat gluten percent and the extent of its modification on the blends properties were investigated via diametric tensile strength, thermomechanical analysis (TMA), scanning electron microscope (SEM), thickness swelling and thermogravimetric analysis (TGA). The results showed significant improvement in the diametric tensile strength, thickness swelling, uniformity in the fracture surface, and the shift of glass transition temperature (T g ) toward higher values with increasing wheat gluten percent and its modification extent. These results reflect the enhancement of interaction between alkali lignin and wheat gluten. Alkali lignin/wheat gluten blends filled with silica possessed distinguishable characteristics and improved diametric tensile strength, low thermal expansion, and high T g . Interestingly, TMA results showed that high dimensional stability against heating (thermal expansion percent) could be obtained using 60% wheat gluten modified with 15% sodium silicate and filled with 10% silica. This sample showed the highest T g and the lowest thickness swelling in addition to smooth, uniform, and glossy surface as shown from the SEM images and TMA charts.

Modification of Lignin with Silane Coupling Agent to Improve the Interface of Poly(L-lactic) Acid/Lignin Composites

“…It serves as a continuous matrix component in plant cell walls, providing mechanical strength and structural support (Wang et al 2001;El-Wakil 2009;Yu et al 2010;Ouyang et al 2012). Lignin and derivatives chemistry is applicable for use in composites because they have small particle size, are hydrophobic, and can form chemical connections with other materials.…”

“…It is well known that the mechanical properties of composites are closely related to the interfacial connection between the filler and the matrix (Yu et al 2010) and that interfacial adhesion can be improved by adding a reactive compatibilizer or coupling agent (Wang et al 2001;El-Wakil 2009). Silane coupling agents such as 3-aminopropyltriethoxysilane (KH550), γ-glycidoxypropyltrimethoxysilane (KH560), and g-methacryloxypropyltrimethoxysilane (KH570) have been widely used (Pilla et al 2008;Pilla et al 2009;Chen et al 2010;Wang et al 2011;Zhong et al 2011;Yu et al 2012) and have also been applied in PLA and inorganic composites (Rakmae et al 2012) with natural fillers, such as coconut shell powder (Chun et al 2012), kenaf fiber (Huda et al 2008), cellulose fiber (Frone et al 2011), and wood flour (Pilla et al 2009).…”

Mechanical and Thermal Properties of Toughened Poly(L-lactic) Acid and Lignin Blends

“…It serves as a continuous matrix component in plant cell walls, providing mechanical strength and structural support (Ibrahim et al 2011;Rozman et al 2011;Silva et al 2011;Yue et al 2011Yue et al , 2012. However, almost 99% of lignin is either burned in an energy recovery step in the pulping process or disposed of in waste streams (El-Wakil 2009;Song et al 2011;Yuan et al 2011). This not only produces large amounts of carbon dioxide polluting the environment, but also wastes resources.…”

Improving wheat gluten materials properties by Kraft lignin addition

“…Ali et al (1997)11 used lignin as a main component to fabricate lignin‐based blend with poly(vinyl acetate). Recently, El‐Wakil (2009)12 studied the properties of KL‐based materials, reinforced with both WG and sodium silicate. This reinforcement improved the diametric tensile strength, and increased the T g , but this study did not elucidate the role of each of those compounds taken independently.…”