Contents
- How to use this guide
- Where it fits
- Why degreasing and retanning matter
- Degreasing fundamentals
- Retanning fundamentals
- Typical wet-end sequence (high-level)
- Monitoring signals (what to trend)
- Troubleshooting: symptom → first checks
- Specification & acceptance checks (COA/SDS)
- RFQ notes (what to include)
How to use this guide
This is a practical decision aid for B2B teams. Use it to align procurement, EHS, and operations on selection criteria, acceptance checks, and monitoring signals. Share site constraints and target article specs (hand, firmness, fullness, color) and we can propose compliant options.
Safety note: Wet-end products may be corrosive (acids), irritating (surfactants), or contain regulated components. Always follow site EHS rules, SDS/labels, and wastewater permit constraints.
Where it fits
- Process goal: define the KPI you are optimizing (shade levelness, softness, fullness, tight grain, yield, or defect reduction).
- Operating window: float ratio, temperature, pH curve, time, drum loading and mechanical action.
- Interfaces: compatibility with dyes, fatliquors, syntans/resins/veg retans, and subsequent finishing.
- Constraints: wastewater (COD/oil & grease), restricted substances (e.g., APEO, formaldehyde), VOC/solvent policies, customer specs.
Why degreasing and retanning matter
| Step | Main purpose | If under-controlled | If over-aggressive |
|---|---|---|---|
| Degreasing | Remove natural fats/greases and processing oils so dye/retan/fatliquor penetrate evenly | Grease spew, patchy dye, sticky grain, milky floats, odor, variable softness | Loose grain, dryness/harsh hand, tensile loss (system-dependent) |
| Retanning | Build fullness/firmness, refine grain, improve dye receptivity, tune hand and physicals | Flat/empty feel, loose grain, poor dye build, weak body, unevenness | Over-tight grain, boardy feel, reduced elongation, poor softness (depends on article) |
Practical rule: If you’re chasing dye levelness or softness problems, check degreasing first.
If you’re chasing body/firmness/grain issues, check retan selection + pH/timing before increasing dosage.
Degreasing fundamentals
Degreasing success depends on both the chemical package and the process window.
| Decision factor | Why it matters | What to specify / ask |
|---|---|---|
| Hide/skin type & fat load | Sheep/goat and some articles have higher natural fat; variable fat distribution affects levelness | Raw material type, average fat content (if known), target residual oil/grease level |
| Degreaser type | Different blends favor penetration, emulsification stability, low foam, or rinseability | Nonionic/anionic character, foam profile, solvent-free requirement, compatibility with electrolytes |
| pH + temperature window | Controls emulsification and fiber swelling; affects removal efficiency and risk of damage | Target pH range and ramping steps; target temperature band; time and mechanical action |
| Wastewater impact | Oil/grease and COD load can constrain dosing and product choice | COD contribution, oil separation behavior, biodegradability statements (as available) |
What “good” looks like: stable emulsification during the step, then good rinsing/float clarity afterward— without persistent foam or oily rings on the drum.
Retanning fundamentals
Retanning is where you “engineer” the leather feel and grain. Selection is article-driven.
| Retan family | Typical contribution | Common watch-outs |
|---|---|---|
| Syntans | Clean shade, dye receptivity, controlled fullness; good leveling in many systems | Overuse can tighten grain or shift shade (system-dependent) |
| Resin retans | Firmness/body; helps certain articles needing structure | Can become boardy if fixed too quickly or overdosed |
| Vegetable extracts | Fullness, character, sometimes warmth in shade | May affect color tone; can increase astringency if not balanced |
| Acrylic/Polymer retans | Fullness and grain tightness; can improve levelness depending on sequence | Compatibility with dyes/fatliquors matters; fixation timing critical |
Sequencing note: Many wet-end issues are sequencing problems (penetration vs fixation), not “bad chemicals.”
Define your pH curve and add-fix timing as part of the specification.
Typical wet-end sequence (high-level)
Exact steps vary by tanning system (wet blue, wet white, veg) and article. This is a generic map.
| Stage | Purpose | Key control points |
|---|---|---|
| Wash / rewet | Uniform hydration and temperature | Temperature, float ratio, time |
| Degrease | Remove fats/oils; stabilize emulsions | pH window, temperature, foam, float appearance |
| Neutralize | Prepare for retan/dye penetration | pH target and stability; avoid sudden jumps |
| Retan | Build fullness/firmness/grain; tune dye receptivity | Addition order, penetration time, fixation timing |
| Dye + fatliquor | Color and softness; lubricate fibers | Levelness, compatibility, emulsification and fixation |
| Fixation | Set retan/dye/fatliquor in the structure | pH ramp rate, final pH, time |
Monitoring signals (what to trend)
| Area | Signals | Early warning pattern |
|---|---|---|
| Degreasing | Float clarity, surface oil rings, foam persistence, odor; (if measured) oil/grease in effluent | Milky float that doesn’t break, sticky drum/grain, recurring grease spew, rising foam |
| Retan/dye | Penetration time, shade levelness, grain tightness, handle/softness | Uneven shade, loose grain on bellies/shoulders, harsh hand after drying |
| Process control | pH curve adherence, temperature stability, float ratio, drum loading | pH overshoot or rapid drops; temperature swings; repeatability issues lot-to-lot |
Troubleshooting: symptom → first checks
| Symptom | First checks | Likely direction |
|---|---|---|
| Grease spew / oily spots after drying | Confirm degreasing pH/temperature/time; check emulsification stability; review fatliquor type and fixation; verify rinse effectiveness | Under-degreasing or poor fixation/compatibility |
| Uneven shade / streaking | Check residual fats; confirm neutralization pH and penetration time; review retan order and dye addition; check drum loading and float ratio | Penetration problem (often linked to fats or pH/timing) |
| Loose grain | Review mechanical action; check over-aggressive degreasing; evaluate retan selection and fixation ramp rate | Process window or retan/fix balance |
| Harsh hand / dryness | Check degreasing severity; verify fatliquor dosage/emulsion; confirm fixation pH/time; review resin retan level | Over-degreasing or over-tight retan/fix |
| Excess foam | Confirm degreaser foam profile; check water hardness/electrolytes; review agitation and additions; consider defoamer compatibility | Foam-prone surfactant or process agitation mismatch |
Specification & acceptance checks (COA/SDS)
When comparing products, ask for data you can verify on receipt:
| Product class | What to request (spec) | COA / receipt checks |
|---|---|---|
| Degreasers | Type (nonionic/anionic blend), solvent/VOC status, foam profile, recommended pH window, compatibility notes | Active content/solids (as applicable), density, appearance, pH (as supplied), batch traceability |
| Retanning agents | Family (syntan/resin/veg/acrylic), ionic character, shade influence notes, recommended fixation profile | Solids/active, density, appearance, pH (as supplied), viscosity (if relevant), batch traceability |
| Fatliquors / auxiliaries | Emulsifiability, oxidation stability, compatibility with dyes/retans, restricted substance statements if required | Solids/active, density, appearance, emulsion stability observation (on receipt, as practical) |
| Compliance & safety | Up-to-date SDS, handling precautions, storage/segregation guidance; statements (e.g., APEO-free/formaldehyde-free) if required | SDS revision date accepted by EHS; labels match PO; packaging intact |
| Logistics | Lead time, Incoterms, shelf life, storage temperature limits | Shelf life acceptable; FEFO workable; packaging fits pumps/hoses and containment |
RFQ notes (what to include)
- Article target: softness, fullness, firmness, grain tightness, dye depth/levelness, and end-use (shoe upper, garment, upholstery, etc.).
- Substrate: hide/skin type (bovine/sheep/goat), thickness range, tanning state (wet blue/wet white/veg), and known fat level if available.
- Current wet-end recipe outline: degrease/neutralize/retan/dye/fatliquor/fix sequence and target pH points.
- Operating conditions: float ratio, temperature, drum load/mechanical action, water hardness/electrolytes.
- Issues observed: grease spew, uneven shade, foam, loose grain, harsh hand (include photos if possible).
- Compliance: wastewater limits (COD, oil & grease), restricted substance requirements, preferred packaging (drum/IBC/bulk), monthly volume, delivery country.
Need a compliant alternative?
Send your constraints and target performance. We’ll propose options with SDS/COA expectations and procurement-ready specs.
Educational content only. Always follow site EHS rules and the supplier SDS for safe use.