Why do some finished leather products from the same batch develop mold after three months of storage, while others survive the entire shipping cycle?
The difficulty of leather anti-mold lies not in a single process step, but in the full-chain control from wet blue tanning to finished product packaging. Our tests reveal that over 70% of leather mold cases can be traced back to three overlooked stages: the pH environment during wet blue storage, oxidation of residual fats in the fatliquoring process, and secondary contamination from packaging materials. Below, we break down each one.
First Control Point: pH and Active Fungicide Addition During Wet Blue Storage
Chrome-tanned leather in its wet blue state typically has a pH between 3.5 and 4.5. This acidic environment naturally inhibits some bacteria but is insufficient against mold. When wet blue leather is stacked in warehouses with high surface moisture and ambient humidity exceeding 75%, Aspergillus niger and Trichoderma viride rapidly proliferate. The organic acids produced by mold metabolism further damage the collagen structure of the leather, leading to grade degradation.
The solution is to add the leather fungicide iHeir-PF after the chrome tanning process and before stacking the wet blue leather. The active ingredient of iHeir-PF is TCMTB (30%), a low-toxicity, broad-spectrum biocide that works by penetrating mold cell walls and disrupting the electron transport chain in respiration. The recommended dosage is 0.05% to 0.2% of the leather weight. In practice, mix iHeir-PF with an appropriate amount of water (note: always add the fungicide to water, never the reverse), then apply it evenly to the wet blue surface via spraying or dipping. pH control is critical—iHeir-PF should not be used in environments with pH > 8, as the active ingredient will decompose and lose efficacy.
Second Control Point: Oxidation of Residual Fats in the Fatliquoring Process and Cutting Off Nutrient Sources
Fatliquoring is essential for achieving softness in leather, but natural oils (e.g., fish oil, neatsfoot oil) or synthetic esters in fatliquoring agents can oxidize during storage, producing short-chain fatty acids and aldehydes. These oxidation products serve as excellent carbon sources for mold. We conducted comparative tests: on the same batch of leather, samples without anti-mold treatment after fatliquoring showed mold spots on day 7 at 35°C and 85% RH, while treated samples remained mold-free for 45 days under the same conditions.
The recommended solution at this stage is to add iHeir-PF to the fatliquoring liquor or finishing paste, still at 0.05% to 0.2% of the leather weight. The emulsifiable concentrate form of iHeir-PF disperses evenly in the fatliquoring liquor, forming a stable mixture with oil molecules. If the factory also uses water-based finishes, iHeir-Spray (a water-based anti-mold and antibacterial agent) can be applied during the finishing process for surface treatment. The active ingredient of iHeir-Spray is a nano-scale cationic polymer that adsorbs onto leather fibers and kills microorganisms by disrupting the permeability of mold cell membranes. Its applicable pH range is 4 to 10, offering good compatibility with leather finishing processes.
Third Control Point: Secondary Contamination from Packaging Materials and Anti-Mold Closure
Finished leather products are most susceptible to mold spore introduction during packaging. Many factories focus solely on the anti-mold treatment of the leather itself, overlooking hidden carriers like wrapping paper, cardboard boxes, and non-woven bags. Wrapping paper may carry mold spores from the papermaking process and easily absorbs moisture during storage and transport. When leather is packed, the paper comes into direct contact with the leather, transferring moisture and spores to the leather surface.
The solution is to use packaging materials treated with anti-mold agents. For wrapping paper, for example, add iHeir-JSTC glue fungicide during the pulp stage or paper coating stage. iHeir-JSTC is a yellow transparent liquid with an active content of ≥20% and a MIC value of only 5 mg/kg against Aspergillus niger. For surface coating, the recommended dosage is 1% to 2% of the paper weight, thoroughly mixed with water-based coatings or adhesives before application. For pre-formed cardboard boxes or shoe boxes, spray iHeir-Spray directly on the inner surface at a rate of 1 L per 20 to 40 square meters.
A detail often overlooked: the anti-mold treatment of the contact surface between wrapping paper and leather must use non-releasing fungicides to prevent migration of the active ingredient to the leather surface, which could cause discoloration or odor. iHeir-JSTC is non-releasing; its active ingredient forms covalent bonds with fibers, ensuring it does not migrate.
Synergy of the Three Stages
iHeir-PF cuts off mold nutrient sources in wet blue and fats during tanning and fatliquoring; iHeir-Spray establishes a long-lasting antibacterial barrier on the leather surface during finishing; and iHeir-JSTC seals the forgotten secondary contamination entry point of packaging paper. If any of these three stages is missing, the entire leather anti-mold system may collapse at its weakest link. We recommend that factories take samples from each stage before production and conduct accelerated mold tests (referencing GB/T1741-2007 method for determining mold resistance of paint films) to validate the effectiveness of the anti-mold plan before mass production.
For specific plan design or free sample testing, contact our technical consultants for customized recommendations tailored to your process parameters.