Baby Diaper
Baby Pull Up Pants
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How Does “Clumping” Occur in Diaper Cores? How to Prevent It Through Formulation and Process
How Does Clumping Occur? The Core Structure Falls Apart
The core of a diaper is made of wood pulp fibers mixed with super absorbent polymer (SAP), then bonded into a thin sheet using hot melt adhesive or pressure. When the core gets wet, the SAP absorbs liquid and swells into gel particles. If the wood pulp fibers do not have enough strength to hold those swollen particles together, the core breaks, shifts, and shrinks into lumps under gravity or the baby’s movement. Simply put, clumping happens because the “skeleton” of the core is not strong enough.
✅ Four Main Causes of Clumping
Too much wood pulp, too little SAP: An all wood pulp core easily falls apart when wet, and wood pulp itself has no liquid locking ability – once wet, it loses its supporting strength. Too few SAP particles cannot form a stable gel network, so the core is like sand without cement.
Wood pulp fibers are too short: Short fibers do not entangle well and cannot hold the SAP particles in place. Some suppliers use recycled pulp or low grade pulp to cut costs, resulting in short fiber length and greatly increased risk of clumping.
Uneven spraying of hot melt adhesive: The core layers need to be bonded with hot melt adhesive or powder. If the amount of adhesive is insufficient, the spray points are too far apart, or the powder does not fully melt, the interlayer bond strength is weak. When urine comes, the layers separate and the core falls apart.
Insufficient compaction pressure during production: After the core is formed, it passes through a pair of compaction rollers to press the fibers and SAP into a thin sheet. If the pressure is too low, the core is loose and naturally tends to clump when soaked.
💬How to Prevent Clumping Through Formulation and Process
Wood pulp to SAP ratio: control between 6:4 and 5:5. Too little SAP causes clumping; too much SAP reduces absorption speed. The mainstream ratio for baby diapers is about 50% wood pulp : 50% SAP. For Adult Pull Up Pants, adults urinate a larger volume at once, so SAP content can be increased to about 55%, with a corresponding increase in hot melt adhesive amount.
Use long fiber wood pulp. For example, southern pine or North American softwood pulp – fiber length is more than 30% longer than hardwood pulp, making entanglement easier.
Increase the spray density of the hot melt adhesive in the core. Denser and more uniform adhesive points make the core less likely to delaminate. We use intermittent spray application to ensure bonding strength without affecting absorption speed.
Control compaction roller pressure and temperature. Too much pressure can crush the core and impair absorption. The correct pressure compacts the core while keeping enough loft and liquid penetration speed. Our process parameters were established after hundreds of tests.
🏭How Our Factory Does It
We produce baby diapers and adult pull up pants. Our cores use a composite core process with long fiber wood pulp and high quality SAP, combined with precision hot melt adhesive spraying and compaction. Even after soaking, the core does not break or clump, even with vigorous shaking.