Properties, Functions, Structure, Raw Materials and Manufacturing of Sanitary Pads

Last Updated on 30/10/2021

What is Sanitary Napkin / Sanitary Pads?
Puberty comes with all kinds of changes in a woman’s body – including the way the body looks and smells. Once women begin menstruating, they need to use something to soak up the menstrual fluid – either a pad or a tampon. Sanitary napkin is a hygiene absorbent product used by women during menstrual periods. It is a product of technical textiles. A sanitary napkin, sanitary towel, sanitary pad, menstrual pad, maxi pad, or pad is an absorbent item worn by a woman while she is menstruating, recovering from vaginal surgery, for lochia (post birth bleeding), abortion, or any other situation where it is necessary to absorb a flow of blood from a woman’s vagina. They also give girls and women the discretion, comfort and feminine design that has been sought after for generations.

The menstrual cycle stars for young women between the ages 11-17, frequently around 12-13 years. On average a woman experiences a period every 28th day, 12-13 times in a year. A menstrual period normally lasts 3-7 days. The loss of fluid in a period is on average half a cup or 65-80 ml. The menstrual pattern is influenced by giving birth and contraceptive methods. Menstruation lasts until menopause at the age 45-55. The feminine hygiene products market has evolved over more than 100 years.

Important Properties of Sanitary Napkin:

  1. No Leakage,
  2. No unaesthetic appearance or color,
  3. No odor,
  4. No noise,
  5. Stay in place,
  6. Comfortable to wear,
  7. Hygienic

Types of Sanitary Napkins:
There are 3 major types of sanitary pads,

  1. Thick sanitary napkins;
  2. Ultra thin sanitary napkins and
  3. Panty liners being used in the market.

The size of each and their content vary from market to market.

Now there are two types of sanitary napkin widely used; panty system sanitary napkin and belt system sanitary napkin.

belt system sanitary pad
Figure 1: belt system sanitary pad
panty system sanitary pad
Figure 2: Panty system sanitary pad

How does Sanitary Napkin Work?
A feminine sanitary napkin is another important disposable absorbent hygiene product. It’s functions are to (a) absorb menstrual liquid discharge, (b) isolate wetness from the skin, (c) retain menstrual liquid discharge, and (d) isolate menstrual liquid from the female’s environment. These functions should be accompanied by providing a feel of maximum comfort, having an aesthetic appearance, preventing odor, and staying in place.

Sanitary napkins are usually composed of three layers. Their inner surface layer that contacts the skin is made of nonwoven. The performance items required are (1) the quick transfer of menstrual blood from the inner surface to the central layer and the stop of counter blood flow to the inner surface, (2) to give feeling of comfortable softness and pliability, and (3) wet mechanical sustainability. Its central layer composed of super absorbent polymer absorbs the transferred blood. Its outer surface layer is usually made of polyethylene (PE) film to guard the leakage of the blood.

The nonwoven is usually made by spun-laying or SMS combined with thermal bonding or with water jet entanglement. Some nonwovens have pore size gradient for better efficiency of blood transfer by the enhancement of capillary effect.

Structure and Components of Sanitary Napkin:
The feminine sanitary pad is constantly being innovated. Although the ultrathin products have begun to garner a higher market share, there is still a need for a thick product as it is believed to be a sign to most people of a good product with superior protection. Like baby diapers, this product is also a multi- layered complex structure where each layer has a specifically allocated task. Figure 3 shows that a disposable sanitary pad that typically consists of coverstock, acquisition and distribution layer, absorbent core, back sheet, tissue, elastic wing, and siliconized paper. Of them, coverstock, acquisition and distribution layer, absorbent core, and back sheet are made up of nonwovens. The function and composition of each of these four materials are discussed below.

sanitary napkin structure
Figure 3: Schematic diagram of the sanitary napkin structure

Coverstock:
In general, the coverstock of a sanitary pad is lighter than that of a baby diaper. Nevertheless, in common with baby diapers, the nonwoven coverstock in sanitary napkin was earlier thought to be as absorbent as possible. As a result, we observed that viscose rayon was extensively used to prepare the coverstock. It was then thought that the coverstock should be hydrophobic to offer better skin care; hence synthetic fibers such as polypropylene and polyester were found in the coverstock of sanitary pads. Later, it was understood that the hydrophobicity in sanitary pads was necessary but not sufficient for optimum performance. The coverstock must also quickly pass the liquid through to the core of the pad (rapid strike- through) and at the same time it must restrict the passage of the liquid back through in the reverse direction (wet- back) so as to maintain a dry surface to the skin. This tricky problem was solved by applying a small amount of an effective rewetting agent on the surface of the coverstock. Today, the coverstock is generally made up of polypropylene spunbond nonwoven, treated by a small amount of rewetting agent.

Besides this material, perforated films were found limited usage as a coverstock in sanitary napkins.

Acquisition and distribution layer:
The acquisition and distribution layer of a sanitary pad is expected to perform the same functions as the acquisition and distribution layer of a baby diaper does. As the absorbent core cannot absorp the localized discharge instantaneously, this layer imbibes the liquid away from the point of discharge, distributes it laterally, and holds it for the core to absorb it. This layer is generally made up of thermally bonded or through- air bonded composite nonwoven material. As known, most of the structures can do an adequate job of acquisition and transporting a relatively small amount of liquid, such as that needed to be managed during menstruation.

However, when large amounts of liquid need to acquired and distributed, none of the structures seems to function well enough to justify the incremental cost.

Absorbent core:
The absorbent core of a sanitary pad was earlier made up of wood pulp. But there has been continued interest to replace this by air- laid pulp in combination with super absorbent polymers at the desired position in the structure. There is a significant use of super absorbent polymer in many brands of sanitary pads. In many cases, the solid polymer in powder form is lightly affixed to a tissue. This composite layer is then inserted between the back sheet and the absorbent pulp pad or in a lower layer of the pad. The position of the superabsorbent polymer is very important in a sense that it must absorb and hold liquid, but must not retard the flow-in of the subsequent additional liquid by blocking the pores of the structure due to swelling.

Back sheet:
The back sheet is an impermeable thin film or barrier fabric that prevents leakage. It is a breathable but liquid impervious film and generally made up of polyethylene.

Raw Material of Sanitary Napkin / Pads:
Materials used in absorbent hygiene products:

  • Nonwoven
  • Pulp
  • Super absorbent
  • Plastic film
  • Elastic materials
  • Fastening devices
  • Packaging

Specification of the Raw Material of the Sanitary Napkins:

  • Pulp: Fluff pulp, thickness 1-2mm, width 280-410mm (500gmm2 up)
  • Tissue: So called tissue 18gm/square meter standard width 180mm
  • P.E. Film: The thickness 0.0015mm, width 85-105mm
  • Non-woven fabric: Good thermo-bonding 16-18gm/square meter, standard width: 175-180mm
  • Hot melt gum: It is pressure sensitive and endurance ,good stickiness, white solid adhesive.
  • Release paper: Good release, width 19-50mm (standard)

Production Process Flow Chart of Sanitary Napkin:

Pulp

Grinding

Mat formation

Tissue spread (up layer, lower layer)

Mat section

Wrap P.E.Film

Hot-melt seal embossing

Applying hot melt adhesive

Release belt

Finished products section

Finished products arranged in parallel (sanitary napkin)

Manufacturing Method of Sanitary Napkin:
The absorbent cores of sanitary napkin were prepared from multilayered carded webs to have required mass per unit area. The carded webs of viscose and SAF blend were prepared with varying SAF percentages and mass per unit area. The webs were carded a second time to achieve better fiber opening, better fiber alignment and homogenous blending. The card webs were then sandwiched between two layers of same nonwoven fabric to integrate the web and encapsulate it to get the absorbent core.

sanitary napkin manufacturing
Figure 4: Sanitary napkin manufacturing

The absorbent pad is the most important component of napkin. Absorbant pad is made of wood pulp mixed with super absorbent polymer (SAP). Absorbent pad is prepared first. The absorbent pad is first created by using shredded wood pulp and vacuum laid to required shape and size, the weight is automatically controlled. By pressing it is formed to required thickness. Before forming the pad the pulp is mixed with super absorbent polymers (SAP) for enhancing fluid holding capacity.

The super absorbent polymer is basically acrylic based polymer that forms gel after absorbing liquid. By this it can hold water up to 30 times its weight. Sodium acrylate, potassium acrylate, alkyl acrylate. This absorbent pad is attached to permeable top sheet made of nonwoven, mainly spunlace fabric. Then the same is attached to non-permeable bottom sheet made of polyethylene. The three layers/components are glued and sealed to prevent leakage by using heat or ultrasonic vibrations. The content of absorbing pad composite will vary for different types napkins.

The application of accessories like tapes, sealing, etc for comfort of fit to the undergarments is required in some cases. This multi-step manufacturing and folding and packaging is carried out automatically. Precise control on SAP mixing with pulp, pulp weight, size and thickness, quality of seal to ensure leakage prevention, wastage control, etc is an important step in the manufacturing. However, the counting and packaging can be made non-automatic to reduce machine cost. But it may increase recurring cost and wastage.

References:

  1. Composite Nonwoven Materials: Structure, Properties and Applications Edited by Dipayan Das and Behnam Pourdeyhimi
  2. Advanced Technical Textile Products By T. Matsuo
  3. Medical and Healthcare Textiles Edited by S. C. hand, J. F. Kennedy, M. Miraftab and S. Rajendran

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  1. Applications of Nonwoven Hygiene Materials
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