We live in a world that is constantly changing with a population that is rapidly expanding. Currently, the world population exceeds 7.1 billion people, and is projected to grow to 9.2 billion by 2050, with an estimated one birth every 8 seconds in the U.S. alone. As medical advances allow people to live longer, it is estimated that the senior citizen population in the U.S., those age 65 and older, will more than double from 43.1 million to 92 million between 2012 and 2060. What do these numbers mean to hygiene nonwoven producers? The staggering growth rate of the world population coupled with the dynamic nature of age distribution promises continued growth in the hygiene nonwovens market, as population statistics place over 50% of the world population into the category of consumers who will need nonwovens, including diapers, adult incontinence, or feminine hygiene products, for years to come.

In a market that will continue to expand with the population and is expected to grow to $78.9 billion by 2018, manufacturers must find ways to differentiate their products from the competition by addressing specific customer demands. Product differentiation must be achieved not only through functional design and use of quality materials, but also with careful selection of the finishing touch—the fiber finish.

Fiber finishes offer a variety of advantages to the final product, including absorbency, softness, antistatic or antimicrobial benefits, and much more. While fiber finishes enhance many nonwoven properties, a review of leading fiber finishes and consultation with nonwovens producers revealed a specific market need for finishes giving improved strike-through and rewet performance. These contrary characteristics require a delicate balance, as a fast strike-through time requires a reduction in surface tension, while low rewet limits that reduction in surface tension. Croda has responded to this need with the development of the new Cirrasol 900 Series, a trio of fiber finishes that will help manufacturers deliver added benefits to their nonwoven products, whether they require fast strike-through time, low rewet, or a balanced combination of the two.

Hygiene nonwoven manufacturers must not only strive to meet new demands to stay competitive in the market, but must also ensure that critical elements of their products are not forgotten. These key benefits include leakage prevention, which can be achieved with a finish that ensures high eluate surface tension, as well as skin sensitivity, which can be attained with a low cytotoxicity profile. The Cirrasol 900 Series delivers these crucial benefits with the added advantage of fast strike-through and low rewet properties.

The design of every hygiene nonwoven product presents the challenge of balancing all of the intended benefits from performance to skin sensitivity. The manufacturer’s task of balancing these benefits can be made easier by completing the nonwoven with a fiber finish that is designed and proven to deliver a distinct advantage.

Testing Fiber Finishes

The International Organization for Standardization (ISO) is the world’s largest developer of international standards, providing quality specifications for products and services. The following test methods generated by ISO are recommended for the validation of claims for hygiene nonwoven fiber finishes.

Improving Strike-through and Repeat Strike-through
Strike-through time (ISO-9073-8:1995) is measured as the time necessary for a known volume of liquid (stimulated urine) to pass through a treated nonwoven into an absorbent medium. Low strike-through time is desired in hygiene nonwoven applications to transfer liquid away from the skin quickly for maximum comfort. This benefit is achieved by a finish that lowers the surface tension of the liquid, allowing for quick passage to the absorbent layer. The repeat strike-through test (ISO-9073-13:2006) demonstrates the resilience of the fiber finish by measuring the strike-through time for multiple doses of stimulated urine applied to the treated nonwoven. The strike-through and repeat strike-through test methods are depicted in Figure 1.

Two of the three Cirrasol 900 Series fiber finishes offer excellent strike-through time advantage. Cirrasol 900XP offers a balance between fast strike-through time and low rewet, while Cirrasol 910XS is designed specifically for applications where a fast initial strike-through is required.

Lowering Rewet
While a fast initial strike-through is achieved by lowering the surface tension of the liquid, an excessively low surface tension can have a negative effect on the ability of the finished product to retain the liquid, resulting in leakage to untreated areas of the finished product. The finish must, therefore, lower the surface tension enough to achieve a fast strike-through time, but not so much as to cause high rewet. The rewet test (ISO-9073-14:2006) measures the ability of the treated nonwoven to resist the transport of liquid back onto the skin after the liquid has penetrated the nonwoven. Low rewet is desired for the prevention of leakage and irritation to the skin. The rewet test method is depicted in Figure 2.



Again, the Cirrasol 900XP fiber finish offers a balance between rewet and strike-through time, while the Cirrasol 920XR delivers extremely low rewet, helping to keep the skin dry and prevent irritation and leakage. An example of the rewet test using filter paper is shown in Figure 3.



Eluate Surface Tension
The quality of a fiber finish can also be gauged using the eluate surface tension test, which measures the loss in surface tension caused by the finish. While the finish must lower the surface tension of the liquid for fast transfer from the topsheet to the absorbent layer, an excessively low surface tension will result in wetting of untreated, hydrophobic areas of the finished product, such as the leg or waist cuffs, causing leakage and chaffing.

The eluate surface tension test depicted in Figure 4 measures the maximum force necessary to separate a plate in contact with the surface of a test liquid. First, the surface tension of brine at room temperature is measured. The treated nonwoven is then placed into the vessel and the vessel is agitated. Finally, the nonwoven is removed, and the surface tension is measured a second time.



The importance of a high eluate surface tension is sometimes difficult to envision, but it can be demonstrated using an Optical Contact Angle (OCA) instrument. Figure 5 compares two eluate droplets deposited onto an untreated, hydrophobic nonwoven. The high surface tension of the eluate droplet from the Cirrasol 900XP finish prevents the absorption of the eluate onto the untreated nonwoven. The competitive finish has excessively decreased the surface tension of the eluate, allowing the eluate to be absorbed onto the untreated, hydrophobic nonwoven. A high eluate surface tension is essential to ensuring that integral parts of the product remain dry. 



Cytotoxicity
Skin sensitivity is an essential property of hygiene nonwovens, as these products will come in direct contact with skin. The skin sensitivity profile is demonstrated by measuring the cytotoxicity profile using the in vitro cytotoxicity test method (ISO-10993-5:2009), which determines the biological response of mammalian cells to the fiber finish through the incubation of cultured cells that have been in direct contact with the fiber finish product. The product is given a cytotoxicity rating from 0-4, defined below:

0: no cells damaged
1: < 20% cells damaged
2: 20 – 50% cells damaged
3: 50 – 70% cells damaged
4: > 70% cells damaged

The low cytotoxicity profile of the Cirrasol 900 Series is essential to ensuring a skin-sensitive finish. The results of the cytotoxicity test are listed in Table 1, where in-use concentrations are highlighted in blue.



Conclusion

With the continued growth of the world population, increasing global demand for hygiene nonwoven products is inevitable. This rapid growth places high pressure on nonwoven producers to not only meet demands for a high quantity of products, but to maintain standards of quality and performance while increasing production. These challenges can be met through the use of quality materials, precise product design, and careful selection of superior fiber finishes. A fiber finish should be tailored to the manufacturer’s needs, delivering advantages that will enhance the material and design properties, ultimately winning over the consumer.

For more information on the Cirrasol 900 Series, please visit Croda’s website at www.crodahomecare.com, or email [email protected].