Jeremy Kroon Department of Chemistry and Biochemisty South dakota state University

Purpose of Tanning  To bring about irreversible stabilization of the skin substance that is to prevent putrefaction.  stabilize it against enzymatic degrading and increase its resistance to chemicals  raise its shrinking temperature and increase its resistance to hot water  reduce or eliminate its ability to swell  enhance its strength properties  lower its density by isolating the fibers  reduce its deformability  reduce its shrinkage in volume, area and thickness  enhance the porosity of its fiber texture.

Current Tanning processing Wet ProcessesPre-TanneryDry Processes Hide/Skin Curing & Storagae Soaking, brining Tanyard Operations Pickling Degreasing Tanning Beam- House Operations Unhairing & Liming Deliming & Bating Post- Tanning Operations Retanning Fat Liquoring Dying Finishing Operations Mechanical Surface Coating

Beamhouse  Unhairing & Liming pH is raised to 12 to 12.6 Removes the epidermis including the hair calcium hydroxide, sodium hydroxide, sodium sulfide, and enzymes  Deliming & Bating Ammonium salts added Enzymes are added to remove non-collogen proteins

Tanyard  Degreasing (pigs and sheep) Organic Solvents ○ Hexane, trichloroethylene Aqueous Surfactants ○ nonylphenol ethoxylates  Pickling pH lowered to 3 Hydrochloric or Sulphuric acid

Tanyard  Vegetable Tanning 2 to 4 days Tannic acids for tree bark  Chrome Tanning Most common 8 hours Cr +3

Post Tanning Operations  Neutrilizing Brings hides back to neutral pH  Retanning Vegetable tannins, syntans Used to impart specific characteristics  Dyeing Anionic dyes  Fatliquoring Oils added back to leather

Disadvantages  metric ton of salted cattle hides m 3 of wastewater ○ 5-6 kg of chromium ○ 10 kg of sulfide 40 kg of volatile organics (VOC).8 x 10 6 to 4.0 x 10 7 BTU of energy  Capital investment for pollution control purposes can be as high as 50% of the total value of plant

Leather and CO 2  Replacing Water with liquid CO 2 diffusion advantage simple adjustments of temperature and pressure may result in the precipitation of residual leather treatment agents ○ allows subsequent recycling or disposal of these materials cheap and readily accepted

Approach  Dyeing and waterproofing greatest probability of success  Degreasing and Fat liquoring Fats and oils are highly soluble  Tanning and retanning Largest challenge since chrome ions are highly insoluble Focus largely on vegetable tannins and syntans

Waterproofing  fluorocarbons, silicones, waxes, aqueous-based oils, and fluoropolymers Each was loaded onto cotton Extracted using supercritical CO 2 at 2500psi and 50°C All were found to be soluble

Waterproofing  Allowed to soak with leather sample Mass loading showed equal weight to manufactures' method No caking, or discoloration CO2 treatmentManufactures’ CO2 treatment Oil Based AgentSilicone Based Agent

Dyeing  CO 2 dyeing currently commercialized in textile industry ○ Introduced in early 1990’s ○ Even color distribution

Degreasing and Fat Liquoring  Been used in oilseed extraction  Supercritical CO 2 limited use in leather industry  reported degreasing efficiencies up to 94%  With sheep reported no damage to the skin structure

Tanning and Retanning  Tanning agents Metal tanning ○ Not soluble in CO 2 Vegetable tanning ○ Soluble ○ Make hard leather Saddles, belts, etc. Syntans ○ Soluble ○ Mainly for retanning ○ Used to impart specific characteristics

Conclusion  Our goal for this project is to develop a technique that will make leather production: FASTER MORE ECONOMICAL CLEANER

Acknowledgements  Dr. Raynie  Environmental Protection Agency  BASF