The next generation of manufactured products must be sustainable and industrially eco-efficient, making materials derived from plants an alternative of particular interest. Wheat gluten (WG) is an ...interesting plant material to be used for production of plastic similar materials due to its film-forming properties. For usage of plastics in a wider range of applications, composite materials with improved mechanical properties are demanded. The present study investigates the possibilities of reinforcing WG plastics with hemp fibers. Samples were manufactured using compression molding (130 °C, 1600 bar, 5 min). Variation in fiber length, content (5, 10, 15 and 20 wt%) and quality (poor, standard, good) were evaluated. Mechanical properties and structure of materials were examined using tensile testing, light and scanning electron microscopy. Hemp fiber reinforcement of gluten plastics significantly influenced the mechanical properties of the material. Short hemp fibers processed in a high speed grinder were more homogenously spread in the material than long unprocessed fibers. Fiber content in the material showed a significant positive correlation with tensile strength and Young's modulus, and a negative correlation with fracture strain and strain at maximum stress. Quality of the hemp fibers did not play any significant role for tensile strength and strain, but the Young's modulus was significantly and positively correlated with hemp fiber quality. Despite the use of short hemp fibers, the reinforced gluten material still showed uneven mechanical properties within the material, a result from clustering of the fibers and too poor bonding between fibers and gluten material. Both these problems have to be resolved before reinforcement of gluten plastics by industrial hemp fibers is applicable on an industrial scale.
Wheat gluten (WG) is a promising base material for production of “green” plastics, although reinforcement is needed in more demanding applications. Hemp fiber is a promising reinforcement source but ...difficulties exist in obtaining desired properties with a WG-based matrix. This study aimed at improving fiber dispersion and fiber–matrix interactions using a high speed blender and a diamine as a cross-linker. Samples were manufactured using compression molding, two types of blenders and addition of diamine. Mechanical properties were assessed with tensile testing. Tensile-fractured surfaces were examined with scanning electron microscopy (SEM). Protein polymerization and fiber–protein matrix interactions were examined using high performance liquid chromatography (HPLC) and confocal laser scanning microscopy (CLSM). The results showed that a higher-speed grinding yielded a more even distribution of fibers and a more polymerized protein structure compared to a lower-speed grinding. However, these improvements did not result in increased strength, stiffness, and extensibility for the higher-speed grinding. The strength was increased when the grinding was combined with addition of a diamine (Jeffamine
®
EDR-176). HPLC, SEM, and CLSM, indicated that diamine added samples showed a more “plastic” appearance together with a stiffer and stronger structure with less cracking compared to samples without diamine. The use of the diamine also led to an increased polymerization of the proteins, although no effect on the fiber–protein matrix interactions was observed using microscopical techniques. Thus, for future successful use of hemp fibers to reinforce gluten materials, an appropriate method to increase the fiber–protein matrix interaction is needed.
The quality of fibres obtained from flax, hemp and reed canary grass is dependent on the moisture characteristics of the crops. In this study, the adsorption equilibrium moisture contents of ...un-retted and dew-retted flax straw, un-retted and frost-retted hemp stalks and spring-harvested reed canary grass were determined using the dynamic gravimetric method at different temperatures (5, 15, 25
°C) for relative humidities in the range 35–95%. Non-linear regression was used to fit five commonly used three-parameter isotherm models the modified Henderson model, the modified Chung–Pfost model, the modified Halsey model, the modified Oswin model and the modified Guggenheim–Anderson–de Boer (GAB) model to the data obtained. The goodness-of-fit of the models was compared using the mean relative percentage deviation, the standard error of estimate and residual plots. The modified Halsey model was considered the best for predicting the equilibrium moisture content of un-retted flax and spring-harvested reed canary grass, and the modified Oswin model for predicting the equilibrium moisture content of dew-retted flax and un-retted hemp, while the Chung-Pfost model was the best for predicting the equilibrium moisture content of frost-retted hemp. For flax and hemp, there were statistically significant differences between un-retted and retted plant materials, whereas the differences between varieties were small.
