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In this work, the effect of the incorporation of leather wastes from chrome tanning on the mechanical and rheometric properties of natural rubber-based composite was evaluated. Chrome content in leather wastes diminished as a result of a chemical treatment with a sodium bicarbonate solution. The treatment also improved the tensile properties of composites with 0, 20 and 40 parts per hundred rubber of leather wastes with particle size between 590 and 840 µm. In a second stage of the experimental work, 0, 20, 40, 60, 80 and 100 parts per hundred rubber of chemically treated leather wastes with particle size between 297 and 590 µm were incorporated to the same natural rubber compound studied in the first part of this study. All the composites were prepared in a torque rheometer, seeking to determine their rheological behaviour during mixing. Rheometric properties of all the composites during curing were monitored in a moving die rheometer. Tensile properties, tear strength, hardness, compressive modulus, compression-set, abrasive wear resistance and De Mattia flexing fatigue resistance for composites obtained in the second experimental set of this work were evaluated. It was found that leather wastes improved the hardness, stiffness, tear strength and abrasive wear resistance on the composites. However, elongation at break, flexural fatigue and tensile strength diminished when a large quantity of wastes was incorporated.

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The morphological and structural changes of the granule architecture of normal starch during the melt blending in a batch mixer were investigated. Native potato, maize, and chestnut starch with different crystal structures were used as raw materials. Samples obtained at different times of melt blending were characterized by X‐ray diffraction (XRD), scanning electron microscopy (SEM), and polarized light (PL) microscopy techniques. The variation of torque versus time depended on the starch type; the thermo‐plasticization of potato starch (B‐type) occurred in two steps, whereas that of maize (A‐type) and chestnut (C‐type) starches took place in one step. An enhancement of the thermo‐plasticization after 15 min of starch processing was not observed by SEM and PL microscopy. However, the potato starch with longer amylopectin chains and higher phosphorus content presented a higher extent of destructurization when compared with the maize and chestnut starches. The XRD patterns of the plasticized starch samples showed residual and V‐type induced crystallinity, corroborating the partial thermo‐plasticization of starches. The extent of thermo‐plasticization depended on the crystallinity type and phosphorus content of normal starch.