Absorbent core layer is the key structural part of diapers, and its absorption directly affects the quality of diaper absorption. It is composed of fluffy pulp and absorbent resin (SAP), which absorbs a large amount of liquid; the back layer is mainly polypropylene (PP) breathable microporous film or hot rolled non-woven material polyethylene (PE) composite film, which prevents urine from seeping out and plays a role in isolation.
SAP is a special functional polymer material, which can absorb hundreds to thousands of times of water, or tens to hundreds of times of salt water. Under the appropriate pressure, the inhaled water will not be squeezed out. SAP has a large absorption capacity, can effectively reduce the amount of fluff pulp, greatly reduce the thickness of the product, and is widely used in absorbent products. The following is a qualitative and quantitative analysis of the water absorption mechanism of SPA.
SAP is a polymer with a three-dimensional spatial network whose hydrophilic and hydrophobic groups interact with water molecules. When encountering water molecules, the hydrophilic ions on the dense polymer chains are rapidly ionized and hydrolyzed, and the electrostatic repulsion on the polymer chains increases as the same charge accumulates. It is this electrostatic repulsion that gradually expands the three-dimensional network and guides water molecules into the resin. At the same time, in order to maintain electrical neutrality, another charge that competes with the charge accumulated on the polymer chain will not diffuse to the outside, and will be bound inside and outside the resin network to form a large concentration difference, resulting in a large osmotic pressure and further absorbing water. Molecules enter a three-dimensional network. As the network expands, the elastic shrinkage force of the 3D network will gradually increase, and as a competitive force, it will gradually counteract the electrostatic repulsion, and finally make the SAP reach the equilibrium of water absorption.
Fluff pulp is an advanced water-absorbing pulp, which is torn into fluff tufts by the bleached drum drying board in the pulverizer. Absorbency is an important quality indicator of fluff pulp, which mainly depends on the capillary effect between the transverse fibers of the paper. The fluff pulp acts like a transport conduit in the absorbent core. In the raw material properties of fluff pulp, the linear density of fibers and the thickness of fiber cell walls directly affect the properties of fluff pulp, and the content and composition of organic solvent extracts will have different effects on the properties of fluff pulp. diaper The liquid absorption performance is not only related to the SAP content and the mixing state of SAP and pulp, but also to the linear density, fiber gap and surface material of the fibers in the pulp.
The basic function of diapers is to absorb liquid, which is the function of absorbent core. Therefore, the screening of SAP and fluff pulp should be strictly controlled so as not to affect the normal use of the product.