Exploration of GSK'S solvent selection guide in leather industry: a CSIR-CLRI tool for sustainable leather manufacturing†
For the first time, GSK's solvent selection guide (SSG) has been explored for leather making from the view of sustainable manufacturing. A novel “Solvent Selection Tool” has been developed to identify sustainable non-aqueous media for leather making from the solvents listed in GSK's SSG. The developed solvent selection tool has been structured into four segments and each one has a particular screening criterion. Preliminary screening-I, based on the cumulative score of GSK's SSG, enabled the shortlisting of 41 solvents from 110. Screening-II, based on toxicity (LD50 value >5000 mg kg−1 of rat), has filtered the number of solvents down to 16 from 41. The effect of the selected 16 solvents on the hydrothermal stability of the skin matrix (screening-III) shows that 9 solvents, namely propylene carbonate, 1,2-propane diol, 2-butanol, ethyl lactate, tetraethylene glycol, ethyl acetate, ethanol and dimethyl carbonate, have no negative impact, whereas the other 7, namely glycerol, DMGMBE, diethylene glycol, propyl acetate, 1,3-propane diol, 1,4-butane diol and 2-propanol, have a negative impact on thermal stability. Propylene carbonate, dimethyl carbonate, ethanol and 2-butanol show superior tanning performance (screening-IV) in terms of mass transfer efficiency (>99% w/w), hydrothermal resistance (104 °C) and leather quality compared to the other selected solvents. The internal comparison results show that propylene carbonate is an ideal medium for a sustainable tanning process. The propylene carbonate based tanning process enjoys zero discharge of water/chromium(III), avoids the usage of fungicides in the tanning process and is ecologically acceptable.