Agglomerated materials based on residual leather from the footwear industry: Study of tensile absorption and shrinkage strength,

Abstract

In the present investigation, leather waste from the footwear manufacturing industry was used to make polymer-bound compounds. The objective of this work was to find the most appropriate leather and polymer mixtures that achieve the best physical-mechanical properties for possible use in applications in the leather-footwear sector. For this purpose, the effect of the type of binder polymer (polyester resin (RP), polyurethane (PU) and urea-formaldehyde (UF)) and the polymer/leather mass ratio (70/30; 80/20 and 90/10) on tensile strength, linear shrinkage and absorption were studied. In addition, the influence of the average leather particle size (0.840mm; 2mm and 4.76mm) and the leather/PU volume ratio (70/30, 80/20 and 90/10) on the tensile strength were studied. For the process of elaboration of study specimens with constant thickness, the manual hydraulic pressing method was used using an open steel mold and 8 tons of force. From the results obtained in the agglomerates with different polymers, it was determined that the PU allows obtaining the highest values of tensile strength, achieving a value of 9.5 MPa at a vol. ratio of 90/10 PU/leather. While the 70/30 UF/leather mix achieved the lowest tensile strength with a value of 1.7 MPa.Regarding moisture absorption, the highest value of 129% was obtained for the 70/30 UF/leather combination, while the minimum absorption of 5% was presented in the 90/10 PU/leather compound. For linear contraction, the lowest levels were obtained in the 70/30 PU/leather compound, while the highest values were identified in 90/10 RP/leather agglomerates.In the case of the agglomerated compounds of leather and PU, it was determined that for the 90/10 leather/PU ratio, the tensile strength tends to increase as the particle size becomes smaller. However, for the 70/30 and 80/20 ratios, the behavior is inverse, but the highest mechanical tensile strength (6.02 MPa) was obtained in test tubes with 70/30 leather/PU and 4.76 mm particle size of recycled leather.