Industrial Chemical Raw Material Transportation FIBC 1200kg Anti-Caking PE Liner for Hygroscopic Powder Calcium

1. Problem: Caking — When a Free-Flowing Powder Becomes a Solid Block

Calcium chloride (CaCl₂) and magnesium sulfate (MgSO₄) are among the most aggressively hygroscopic industrial chemicals, absorbing moisture from air at relative humidity as low as 15-20%. During sea freight, even minor moisture ingress through FIBC liners causes surface dissolution of salt particles, followed by re-crystallization during cooler night periods. This dissolution-recrystallization cycle creates crystalline bridges between adjacent particles — a process known as "caking" or "lumping." Within 30 days of exposure to cyclic humidity, a 1000kg bag of CaCl₂ can transform from free-flowing prills into a single solid block requiring pneumatic hammer for discharge.

The operational impact is severe: caked product cannot be discharged through standard FIBC spouts (requiring cutting the bag open and manually breaking the block), may damage downstream equipment (crushers, conveyors, dissolution tanks), and often fails customer acceptance criteria for particle size distribution (PSD specification typically requires >90% passing through 5mm sieve — caked product fails this criterion regardless of original PSD). The economic cost includes: 15-30% product loss from bag cutting and manual handling, 3-5 hours additional labor per blocked bag, and potential customer rejection of the entire shipment.

2. Cause: The Caking Mechanism — Crystal Bridge Formation

Caking proceeds through a 4-step mechanism documented in powder technology literature. Step 1 — Moisture sorption: hygroscopic salt particles absorb water vapor, forming a saturated solution film on the particle surface at the deliquescence relative humidity (DRH). For CaCl₂, DRH is approximately 15% at 25°C — one of the lowest among common salts — meaning surface moisture forms even at ambient humidity levels. Step 2 — Capillary condensation: in the contact regions between adjacent particles, the Kelvin effect lowers the equilibrium vapor pressure, causing preferential condensation in particle-particle contact zones.

Step 3 — Liquid bridge formation and dissolution: the condensed moisture dissolves salt at the contact point, creating a liquid bridge with high salt concentration (typically 40-50% w/w for CaCl₂ solutions). Step 4 — Recrystallization: when the ambient humidity drops (night cooling), the liquid bridge evaporates, depositing dissolved salt as a solid crystalline bridge at the particle-particle interface. Each humidity cycle (typically one per day during sea freight) deposits additional crystalline material, progressively strengthening the inter-particle bonds. After 30-40 humidity cycles, the bulk crushing strength can exceed 500 kPa — sufficient to resist gravity discharge from a FIBC spout.

3. Solution: Anti-Caking Liner with Enhanced Moisture Barrier

Our CRM-FIBC-1200-AC employs a dual-action anti-caking strategy. First, the liner provides enhanced moisture barrier: the multi-layer PE construction (120μm total) with metallocene-catalyzed PE (mPE) core layer reduces WVTR to below 0.5 g/m²/24h — a 6-12* improvement over standard LDPE liners. The mPE layer's higher crystallinity (55-60% vs 40-45% for LDPE) and narrower molecular weight distribution (PDI 2.5 vs 4-6 for LDPE) create a denser, less permeable polymer matrix through which water molecules must diffuse.

Second, the liner's inner food-contact surface incorporates a silica anti-block treatment (synthetic amorphous silica, 1500ppm, particle size 3-5μm) that creates a micro-rough surface topography. This micro-roughness prevents the formation of continuous solution films on the liner surface during inevitable minor moisture events by providing nucleation sites where moisture forms discrete droplets rather than continuous films — the "lotus leaf effect" at the microscopic scale.

Each bag includes a humidity indicator card (cobalt-free, 10-60% RH range) visible through a transparent window in the closure area. This provides a simple visual check — if the 30% indicator spot has changed color, the bag has been exposed to humidity above specification and should be investigated before customer delivery.

4. Application: Hygroscopic Chemical Export Supply Chains

4.1 Calcium Chloride Prills to Middle East Oilfield Services

Oilfield completion fluids require free-flowing CaCl₂ prills (94-97% purity, <1% moisture) for brine preparation. Shipments from China to UAE and Saudi Arabia transit through high-humidity Persian Gulf routes where container humidity reaches 90%+ RH. Our anti-caking FIBCs maintain product flowability verified by customer receiving inspection at destination.

4.2 Magnesium Sulfate Heptahydrate for Agricultural Fertilizer

MgSO₄·7H₂O is both hygroscopic and efflorescent — absorbing moisture in high humidity and releasing water of crystallization in low humidity. Our bags maintain the critical 7-hydrate stoichiometry throughout 45-day transit to agricultural distributors in Brazil and Southeast Asia.

5. How to Choose: Anti-Caking Protection Level

6. FAQ