Utilization of collagen protein extracted from chrome leather scraps as a set retarders in gypsum

摘要

Chrome leather scraps have always been difficult to disposal in leather making, the effective use of it to produce valuable products can help to achieve sustainability in leather industry. Inspired by the protein gypsum retarder, the characteristics of collagen protein (CP) extracted from chrome leather scraps and retarding feature of it as gypsum additive were studied in this paper. The results showed that the protein content of CP arrived 85.4% while mineral and salt content kept one low level. Moreover, 13 kinds of amino acid were detected in the extracted CP. The addition of CP efficiently prolonged the setting time of gypsum but caused a decrease in strength. SEM, XRD, TG/DSC and FTIR analysis indicated that less gypsum dihydrate was formed and the hydration reaction of gypsum hemihydrate were inhibited after the addition of CP. Furthermore, the retarding mechanism of gypsum was also investigated by modifying the functional groups (carboxyl groups and amino groups) on the CP chain. The carboxyl groups on the CP chain combined with Ca2+ ions in the gypsum paste inhibited the hydration reaction of gypsum, thereby the setting process of gypsum was prolonged. This study indicates that CP extracted from chrome leather scraps can be used as a gypsum retarder to achieve the recycling and utilization of leather waste. (C) 2019 Elsevier Ltd. All rights reserved.