Nonwovens is a relatively new industry that is replacing and improving conventional materials ranging from diapers to airplane parts.
Causey Engineering Associates have expertise in much of the raw material science and processes, (including polypropylene-base spun-bound and melt-blown fabrics, both rigid or elastic) as well as in the equipment used to manufacture what has been absorbed into an industry called nonwovens. Even though the textile industry claims the nonwovens industry, the petrochemical and paper industries have also advanced nonwovens. (Naming an industry a “non” something-or-other leaves its scope rather undefined!)
During the last 50 years many international participants in this composite industry have developed the science and application of specialized fibers. These new, advanced engineering fibers enable manufacturers to produce web structures and improved new products that compete with traditional materials. Causey’s knowledge and experience in the Nonwovens industry and Forensic Engineering is available now for your case. See Dr. Armenag Dekmezian and Gerald Hietpas P.E. CV’s on the website.
Nonwovens encompass products with vastly different properties for a wide spectrum of applications. They include new as well as improved products. Nonwovens include use of engineered fiber and polymer based products. In addition to the few examples below for personal care and construction, nonwovens are used for medical, leisure & travel, school & office, as well as industrial applications. A book titled “Introduction to Nonwovens Technology” by Subhash K. Batra and Behnam Pourdeyhimi is an excellent reference.
Tyvek is a non woven product. It is used extensively in construction as shown because of its durability as a long lasting moisture and air barrier, performing the function better than tar paper.
What we see around construction sites for sedimentation and erosion control appears to be ordinary tar paper but it is actually a strong sheet of a nonwoven product.
Several national manufacturing firms offer about a dozen personal care and hygiene products from nonwovens. I recall a Kimberly Clark VP mentioning “We have this new fabric-like product that will pass water in one direction, but not the other direction. What applications can you suggest for such a product?” The rest is history.
Nowadays the inner liner in diapers and continence care products pass the urine away from the skin into a pocket of super absorbent material, and the skin stays dry.
The manufacturing technology produced many US Patents, a few of which are described here:
The Dan-Web web former is one of several methods to airlay staple fibers into a web. Here, pulverized pulp from a fiberizer is blown into a drum having special features that allow fibers to be strategically sifted out slots onto a moving screen below and form a web or fabric. With additional fiberizer and drum systems to deposit additional layers onto the web, a different length or type fiber can create a layer with different properties, and together they become a composite fabric. There are numerous combinations that serve different applications. Fabrics from an airlay system often do not have the anisotropy that fabrics made from carded webs have.
The Spunbond process is a nonwoven invention. Chips of thermoplastic polymer resin are formed into a plastic fabric. It integrates preparation, web formation, bonding and sometimes finishing into a single one-step process. One iteration shown here is from the Appel-Mormon patent. It combines the quenching and filament draw operation in a full-width slot attenuator and by using the same air supply at low pressure the process costs were reduced. These subsequent systems were called closed systems. Reifenhauser’s Reicofil system modified the full-width slot concept, and other modifications followed. It is a rich story of development, albeit it borrows from other industries. Likely there are other proprietary systems in use.
The Meltblowing process was developed in parallel with the Spunbond process. It also starts with a polymer resin on the feed end and produces a web or fabric. Exxon engineers improved the process to market its new commercial polypropylene-fiber resin. The process attracted the attention of others due to the short fiber it produces, as well as interest in using other thermoplastic polymers. The first step involves special ways to dry the granules or pellets. A special helical screw then conveys, heats and compresses the pellets into a high pressure liquid that is forced through a filter pack, then with a gear metering pump into orifices, called a die. Then it goes into the distribution reservoir where hot and high pressure air is directed into slots to pick up fibers of the melt to form fine fibers as it cools. The resulting dust is collected onto a suction drum or screen, thus forming a web or fabric. The figure shown here is from a patented modification to the Exxon system. Again, likely there are other proprietary improvements in industry.
US Patent 7,998,579
The softness of Polypropylene spunbond nonwoven fabrics can be controlled by blending various types of polyaphaolefin (PAO) plasticizers along with slip agents. These two components not only enhance the soft-touch feel of the fabric, but also its drapability (or foldability). The design of Polypropylene-based compositions intended for nonwoven applications requires the judicious balancing act: one must choose the appropriate ingredients not only to control the rheological (or flow) properties of the compound during the fiber-forming stage but also the optimization of the mechanical and tactile properties of the resulting nowoven fabric.