Ma Yunhai

Preparation and flexural properties of biomimetic laminated boards made from starch and maize straw fibers

In this study, maize stalk tegument separated from the maize pith was crushed to obtain the fiber. The cross-linking maize starch adhesives considering four main factors (water content, gelatinization temperature, NaOH as gelatinization agent and Na2B4O7·10H2O as cross-linking agent) with three levels were prepared based on an orthogonal test scheme L9(3 ) in order to increase the water-resisting property and the bonding strength of the common maize starch adhesives. The bonding properties of maize starch adhesives were characterized using shearing strength under compression loading. Physical models of fiber reinforced composites were established according to the microstructure analysis of the four species of insects’elytra including Protaetia orentalis, Copris ochus Motschulsky, Anoplophora chinensis and Cytister bengalensis Aube, which will provide the biomimetic models for the biomimetic laminated boards. The maize stalk fiber biomimetic laminated boards were prepared based on the structural models of the elytra material. The flexural strength and flexural elastic modulus of the biomimetic boards were examined. The results showed that the flexural strengths of the single layer jute fiber, -reinforced maize stalk fiber boards and the dual layer jute fiber reinforced maize stalk fiber boards are higher than those of the common maize stalk fiber boards and the other three groups of jute fiber hybrid reinforced stalk fiber boards because of the biomimetic laminated design.

Mechanical properties and microstructure of potato peels

ABSTRACT Potato peel, as the outermost tissue of the fruit, playing a role of protection and fresh keeping on the pulp tissue, is crucial for the design of potato harvesting machines. In this study, two types of potato ‘Yangyu 4’ and ‘Helan 14’ were selected to conduct friction, tensile and tear tests on their peel. Longitudinal and transverse tensile tests were conducted on the peels of two potato cultivars using an electronic universal testing machine, and tear tests were carried out on peels as well. The static friction coefficient for different materials, stress-strain curves and tear force-deformation curves of the peels were obtained and the tensile strength, elastic modulus, failure strain tear strength of the peels were measured. The results showed that the maximum value of the static friction coefficient against metallic materials was and against rubber materials, respectively. The maximum values of the tensile strength, elastic modulus, fracture strain, tear strength were 1.648 MPa, 0.388 MPa, 4.5%, 0.326 kN·m-1, respectively. Scanning electron microscopy images show that many compact and regular polygonal similar-grain grid structures distributed onty the epidermis surface and microcrack basically did not exist on the peel. The spherical micro-convex structures arranged closely and linearly at the boundary of the grid structure. Hierarchical structure surface with spherical micro-convex structures was one of the reasons for its outstanding friction coefficient. The bearing capacity of the peel depended on the number and distribution of grid structures on the surface, and the size and shape of the epidermal cells.