Leather Fungicides Compared: PCMC vs TCMTB vs MBT vs Glutaraldehyde

A practical guide for tanneries, leather chemical formulators and exporters — by Syner Chem, supplier of leather biocides and preservation systems.

Introduction: The Cost of Mould in Leather

Leather is a natural, protein-based material — rich in nutrients, and under warm, humid conditions, an ideal breeding ground for mould, bacteria and yeast. The damage is real and expensive: mould spots and stains on wet-blue in storage, bacterial odour and degradation in pickle, rot in raw hides, and container "bloom" on finished leather arriving at the customer's warehouse thousands of kilometres away.

For decades the industry has relied on a handful of proven active ingredients. Four names appear most often: PCMC, TCMTB, MBT and glutaraldehyde. They are not interchangeable. Each has its own chemistry, strengths, weaknesses and regulatory position. This guide compares them head-to-head so you can make an informed choice — or build a rational combination strategy.

1. Quick Comparison Table

2. PCMC (p-Chloro-m-cresol) — The All-Rounder

CAS 59-50-7 · chlorinated phenol · the LANXESS PREVENTOL® CMK active

PCMC is the most versatile of the four. A membrane-active phenolic microbicide with a multi-site mode of action, it kills Gram-positive and Gram-negative bacteria, mould and yeast — with a special reputation against putrefactive bacteria in protein-based systems (leather's collagen is exactly that).

Why leather professionals choose PCMC:

• Alkali-stable (pH \~1–14): survives chrome tanning basification where many biocides die. Added with the basifying alkali, it dissolves freely — no extra process step.

• Oil-soluble: can ride the fatliquor emulsion straight into the drum — a delivery route most other biocides cannot use.

• Broad stage coverage: pickle (0.15–0.25%), chrome tanning (0.10–0.20%), fatliquoring, adhesives (0.05–0.10%), finishing (0.20–0.40%), and finished-leather both-sides treatment (0.2–0.4%).

• Low resistance risk: multi-site mechanism.

• Fully registered for leather: U.S. EPA (registered since 1968) and the first major leather biocide to gain EU BPR registration for leather manufacture (2016) — critical for exporting treated leather to Europe.

Watch-outs: phenolic compounds can sensitize skin and have aquatic toxicity at high concentrations — handle per MSDS, respect effluent limits, use registered concentrations.

3. TCMTB (2-(Thiocyanomethylthio)benzothiazole) — The Classic Pickle-Stage Fungicide

CAS 21564-17-0 · benzothiazole, usually sold as 30% emulsion

TCMTB has been the most widely used fungicide in leather for decades. The U.S. and New Zealand list it as a standard leather additive; it was even specified for American military leather. Its strengths are real: extremely effective mould control on Aspergillus niger, Penicillium and Trichoderma at very low dosages, and outstanding performance in low-pH pickle liquor — which is why it became the industry default for pickled pelts and wet-blue storage.

Why tanneries still love it:

• Powerful, broad-spectrum mould inhibition at low dose (0.05–0.2% on pelt weight at the wet-blue stage).

• Excellent in acid conditions.

• Price-performance is hard to beat.

Why its position is eroding:

• Deactivates above pH 8 — useless in alkaline stages.

• Degrades into 2-mercaptobenzothiazole (CAS 149-30-4 — a different chemical also abbreviated "MBT", not the methylene bisthiocyanate of this guide) on contact with sulfides or sulfites (common in leather processing), reducing efficacy.

• Regulatory cloud: the U.S. EPA classified TCMTB as a possible human carcinogen in 2006, and environmental NGOs have listed it as a carcinogenic pesticide. Leather producers exporting to strict markets are actively seeking alternatives.

• Picks up less in leather, so more is lost to effluent.

Bottom line: still the benchmark for low-pH mould control, but increasingly paired with — or replaced by — PCMC in integrated preservation programs.

4. MBT (Methylene bis(thiocyanate)) — The Pre-Tanning Workhorse

CAS 6317-18-6 · organic thiocyanate · also sold as MTC / methylene dithiocyanate · the Buckman Busan® 110 active

⚠️ Name warning: in the leather industry, "MBT" means methylene bis(thiocyanate) (CAS 6317-18-6), i.e. 二硫氰基甲烷 (methylene dithiocyanate). Do not confuse it with 2-mercaptobenzothiazole (CAS 149-30-4), a rubber-vulcanization accelerator that shares the same abbreviation and also happens to be a degradation product of TCMTB. The two are entirely different molecules.

MBT is a fast-acting, broad-spectrum bactericide and fungicide for the pre-tanning stages — soak, pickle and liming liquors — where raw hides carry the heaviest bacterial and fungal loads of the whole process. Its molecule is simple (SCN–CH₂–SCN) with excellent penetration, so it reaches deep into the hide structure and process liquors, protecting the collagen before bacteria and mould can downgrade the raw material.

Why tanneries use it:

• Rapid, broad-spectrum kill of bacteria, mould, yeast and algae at low dosages (with very low use concentrations effective against sulphate-reducing bacteria).

• Deep penetration into hides and liquors — ideal for heavily contaminated pre-tanning conditions.

• Non-metallic organic-sulfur chemistry — no heavy-metal load on the effluent.

• Long regulatory track record: EPA-registered active ingredient since 1949, still registered today (e.g., Buckman Busan® 110, also registered under PMRA Canada); 49 U.S. registered products span leather, cooling water, paper, wood, adhesives and coatings.

• Who makes it: Buckman Laboratories (USA) is the historic U.S. basic manufacturer; India is the other major production hub (Aquapharm, Hydrochem Chemicals, Benzo Chem, Pax Group and 20+ more); Chinese producers (e.g., Guangdong Xingning Fine Chemicals, Taicang Liyuan) also export worldwide.

Watch-outs:

• Alkali-sensitive: stable near neutral pH but hydrolyses rapidly above \~pH 8 — it cannot serve the alkaline chrome-tanning or basification stages (that is PCMC's territory).

• Toxicity: hazardous by inhalation (dust) and irritating to skin/eyes; aquatic toxicity — handle per MSDS, avoid dusting.

• Not a finished-goods anti-mould agent: for long-term mould protection of wet-blue in storage or finished leather, pair with PCMC/TCMTB-type chemistry.

Bottom line: the right tool for heavy-duty microbial control in soak and pickle — complementary to PCMC, which covers the alkaline, oil-phase and finished-goods stages.

5. Glutaraldehyde — The Tanning Agent That Also Kills

CAS 111-30-8 · dialdehyde, sold as 25% / 50% solution

Glutaraldehyde is the odd one out in this list because its primary job in leather is tanning, not mould prevention. It cross-links collagen fibres, producing leather with excellent sweat, heat and soap resistance. It is the backbone of chrome-free / aldehyde tanning and is widely combined with chrome for garment leather and glove leather.

Why it matters to a biocide buyer:

• Strong bactericide: kills bacteria including spores — the reason it is used to preserve raw hides and to control bacteria in soak and pickle. Its disinfectant credentials (medical-grade sterilant since the 1960s; recommended by WHO for hepatitis B disinfection in 1973) speak to its power.

• Dual role economics: one chemical can serve as tanning agent and process bactericide.

• Regulatory standing: registered as a biocidal active under EU BPR (PT2/3/4) and widely used in industrial water treatment and oilfield applications.

Watch-outs:

• Alkali instability: above pH \~8.5 the monomer polymerizes and biocidal activity is lost — so it cannot serve the same alkali-stage role as PCMC.

• Strong irritant: handling requires care.

• Incompatibility: must not be mixed with vegetable tanning agents or phenolic (synthetic) tanning agents.

• As a mould inhibitor on finished leather it is less commonly the first choice — that role belongs to PCMC/TCMTB-type fungicides.

Bottom line: indispensable for chrome-free tanning and raw-hide bactericidal control; complementary to, rather than a substitute for, PCMC.

6. How to Choose (Decision Guide)

The modern trend: integrated programs that combine PCMC for alkali/oil/protein stages with TCMTB for low-pH pickle — or shift fully to PCMC-based chemistry to simplify compliance and reduce regulatory exposure.

7. Market & Regulatory Context

• Global leather chemical market: roughly USD 6.6 billion (2025); tanning chemicals \~USD 1.9 billion; fatliquors \~USD 1.85 billion; finishing \~USD 1.6 billion.

• Where the leather is made: Asia-Pacific dominates (\~45% of tanning chemicals), led by China, India (\~2 billion sq ft of leather/year) and Vietnam (\~400 tanneries). Brazil is the world's largest commercial hide processor (\~42 million hides/year); Argentina, Turkey, Pakistan and Mexico are significant producers. North America and Europe consume premium leather (automotive, luxury) and set the regulatory agenda.

• Regulatory gravity: the EU Biocidal Products Regulation (BPR) governs treated articles — leather/shoes treated with a biocide can only enter the EU if the active substance is registered for that use. Chlorocresol (PCMC) achieved this for leather in 2016; it is the reference point for compliance-minded tanneries. Practical note for buyers: the BPR active-substance approval was filed by LANXESS, while product authorisations for individual biocidal products are held by EU-based applicants (formulators/importers). Non-EU suppliers of the active substance therefore serve the EU through a registered European partner or an appointed EU "only representative" — when sourcing PCMC for EU-bound production, ask your supplier about their EU compliance pathway and documentation. EPA classification of TCMTB (2006) continues to push brand- and LWG-compliant supply chains toward PCMC-based alternatives.

• Sustainability pressure: Leather Working Group (LWG) ratings, ZDHC MRSL compliance and brand restricted-substance lists all reward formaldehyde-free, fully-registered chemistry — PCMC's home turf.

8. Practical Recommendation for Buyers

1. Map your process stages first — pickle, tanning, fatliquoring, finishing, storage each have different pH, temperature and carrier requirements. No single chemical does everything.
2. Specify PCMC for alkali, oil-phase, protein and finished-goods protection — it is the most versatile and the most regulatory-safe option in this family.
3. Keep TCMTB only where it earns its place (low-pH pickle) and manage its effluent and toxicity obligations.
4. Buy from a supplier with documentation — CoA per batch, TDS, MSDS, registration/regulatory support, and free samples that match bulk quality.
5. Test before switching — accelerated mould-chamber testing (e.g., tropical chamber protocols) will tell you in weeks what a container voyage would tell you in months.

Conclusion

The four workhorses of leather preservation are not rivals but tools — each best in its own stage. PCMC is the versatile all-rounder and the regulatory-safe choice for modern, export-oriented tanneries; TCMTB remains the low-pH classic; MBT (methylene bisthiocyanate) protects hides through the pre-tanning stages; glutaraldehyde tans chrome-free and kills hard-to-beat bacteria. A rational preservation program uses the right tool at the right stage — and increasingly, PCMC at the centre.

Syner Chem supplies PCMC, TCMTB, MBT and glutaraldehyde for the leather industry — with CoA, TDS, MSDS, free samples and export experience across Brazil, Argentina, Chile, India, Vietnam, Russia and North America. Contact us for a tailored recommendation.

Keywords: leather fungicide, leather biocide, leather preservative, PCMC, p-chloro-m-cresol, chlorocresol, TCMTB, 2-thiocyanomethylthiobenzothiazole, MBT, methylene bisthiocyanate, methylene dithiocyanate, MTC, 二硫氰基甲烷, Busan 110, glutaraldehyde, wet-blue mould control, pickle liquor preservative, chrome-free tanning, anti-mold agent for leather, mould prevention in leather, leather chemicals.